Study on Erosion by Built-In Pulse Impactor Based on Simulation

Abstract

The built-in pulse impactor used in oil and gas drilling often suffers from erosion issues, which reduce mechanical drilling speed and significantly shorten the drill bit lifespan. To address this, this study employs computational fluid dynamics (CFD) with the discrete phase model (DPM) and DPM erosion model, combined with erosion theory, to simulate the erosion process. The computational domain includes the rotating body, housing, and internal flow channels of the impactor, with key structural parameters: external diameter 120 mm, internal flow height 23 mm, and flow channel angle 30°. Boundary conditions are set as follows: inlet velocity of drilling fluid ranges from 27.558 to 32 m/s, solid particle diameter varies from 0.074 to 0.11 mm, and particle mass flow rate (concentration) is 0.2–0.6 kg/s. The study analyzes erosion lifespan of different materials and identifies influencing factors. Results show that under high-pressure drilling fluid conditions, solid-phase particles cause significantly greater erosion than the liquid phase. Particle distribution is uneven, leading to accumulation in the rotating body, erosion damage intensifies over time, concentrating primarily at the flow channel outlet. CFD simulations indicate that 40CrMo has the longest erosion lifespan (525.47 h), outperforming 45 steel and Q235A. Regarding influencing factors: increasing fluid velocity (especially 30–32 m/s) and particle concentration (0.2–0.5 kg/s) significantly raises the erosion rate; larger particle diameters reduce the erosion rate, with the decreasing trend slowing when diameter exceeds 0.09 mm. The erosion rate is maximum at impact angle 30 °C. This study provides insights for reducing erosion and extending the service life of built-in pulse impactors.

1. Introduction

With the continuous rise in global energy demand, the exploration and development of oil and gas resources have been extending to deep, ultradeep, and complex formations. Drilling engineering is facing severe challenges such as low drilling efficiency in hard formations and rapid tool wear. As a key means to improve drilling efficiency in hard formations, impact rock-breaking technology has become a research hotspot in the field of oil and gas drilling by converting hydraulic or mechanical energy into high-frequency impact loads, effectively improving rock-breaking effects and reducing drilling costs.

The development of impact rock-breaking tools has evolved from single-dimensional to multidimensional collaboration: Axial impact tools expand rock fractures by impacting the drill bit through the reciprocating motion of the hammer, and relevant studies have confirmed that they can optimize cuttings removal, increase drilling speed, and reduce wear. − Torsional impact tools effectively solve the stick–slip problem of PDC bits, capable of shortening the stick–slip cycle and suppressing vibrations. − Multidimensional impact technology integrates the advantages of both, achieving three-dimensional rock breaking with better speed-increasing effects. However, traditional impact tools have issues such as insufficient stability in deep wells and poor compatibility with rotary steering systems, which have promoted the development of compact built-in pulse impactors. Due to their compact structure and complex flow channels, these tools are prone to severe erosion by solid particles carried in drilling fluid during operation, becoming a core bottleneck restricting their service life and efficiency.

Erosion is the main cause of failure of built-in pulse impactors. Solid particles such as quartz sand carried in drilling fluid flow through the internal flow channels of the tool at high speed under high pressure, continuously colliding and rubbing against the surfaces of components such as rotating bodies and housings, leading to gradual spalling of the material surface and cumulative damage. − This damage is particularly prominent in areas with high turbulence intensity, such as flow channel bends and outlet bosses. When fluid flows through these structures, the velocity gradient of the flow field increases sharply. Due to inertia, solid particles are difficult to follow the fluid streamline smoothly, making them more likely to collide head-on or obliquely with the wall, causing local stress concentration and plastic deformation of the material, and then forming typical erosion morphologies such as pits and grooves. After long-term operation, erosion not only weakens the structural strength of the tool but also may change the geometric parameters of the flow channel, destroying the periodic generation mechanism of pulse pressure, and ultimately leading to tool failure. In recent years, research in related fields has provided multidimensional support for understanding this complex process: In terms of erosion characteristics of oil and gas drilling tools, scholars have confirmed through experiments and simulations that the erosion degree of solid–liquid two-phase flow is significantly correlated with flow channel structural parameters (such as curvature and cross-sectional area mutation rate). For example, the local turbulence intensity in bends or variable-diameter sections can be more than 30% higher than that in straight pipe sections, and the corresponding erosion rate also shows nonlinear growth; , Regarding the erosion law of rotating components, Zhang et al. found through dynamic flow field simulation that the high-speed rotation of the rotating body forms eddy currents in the gap between it and the housing, causing the trajectory of solid particles to show a spiral deviation, leading to the expansion of the erosion area from the center of the flow channel to the edge of the wall, forming an annular wear zone; In the study of material erosion resistance, 40CrMo alloy, after quenching and tempering, has high hardness (250–300 HB) and toughness (impact energy ≥60 J), and its erosion resistance is about 40% higher than that of 45 steel. The rule that material hardness is negatively correlated with erosion rate and toughness is positively correlated with fatigue erosion resistance also provides a clear basis for tool material selection. , These studies collectively reveal that erosion is the result of the coupling of flow field characteristics, particle movement, and material properties, laying a theoretical foundation for in-depth analysis of the erosion mechanism of built-in pulse impactors.

Flow field characteristics (such as turbulence distribution and particle trajectory) are core factors affecting erosion damage, and related research provides a methodological basis for erosion analysis. By simulating the erosion of solid–liquid two-phase flow in elbows using CFD, a correlation model between turbulence intensity and erosion rate is established. This model clearly reveals the driving mechanism of local turbulence in elbows on erosion, providing a reference analysis framework for erosion assessment of complex flow channels (such as the special-shaped flow channels of built-in pulse impactors). For the erosion problem of drilling tool flow channels, the relationship between particle concentration and erosion rate is quantified through a combination of experiments and simulations. Its tracking analysis of the trajectory of solid particles in the turbulent field provides a direct basis for setting particle parameters (such as particle size and density) in the study. In terms of verifying the applicability of turbulence models, the erosion simulation of high Reynolds number flow fields compared the accuracy of different models, confirming the advantages of the Eulerian-Lagrangian framework model in capturing the coupling effect between turbulent fluctuations and particle movement in complex geometric flow channels, which provides key support for the selection of flow field calculation models in this study. Regarding the coupling effect between rotating components and the flow field, relevant studies simulated the flow field changes in the gap between the rotating body and the housing using dynamic grid technology. The revealed law of particle trajectory deflection caused by rotation-induced eddy currents provides important ideas for analyzing the erosion distribution of rotating components of built-in pulse impactors. In terms of material erosion failure mechanisms, through the analysis of surface damage morphologies of metal materials under solid–liquid two-phase flow, typical failure modes such as plastic deformation, microcutting, and fatigue spalling were clarified, which provides an experimental basis for the rationality of selecting erosion-resistant materials such as 40CrMo in the study.

Although existing studies cover erosion mechanisms and simulation methods, research on the erosion laws of built-in pulse impactors-characterized by unique pulsating flow fields, compact structures, and dynamic rotation characteristics-remains insufficient. To address this gap, this study employs CFD combined with the discrete phase model (DPM) and DPM erosion model to achieve the following:

Novelties

• (1)Focus on the specific erosion behavior of built-in pulse impactors with pulsating flow fields, compact structures, and rotating components, which have been rarely studied in previous literature.
• (2)Quantify the coupling effects of flow field characteristics (turbulence, particle trajectory), material properties, and operational parameters (fluid velocity, particle concentration, particle diameter) on erosion in this unique tool.
• (3)Compare the erosion resistance of three typical materials (40CrMo, 45 steel, Q235A) under practical working conditions, providing targeted material selection guidance for engineering applications.

Purposes.

• (1)Reveal the erosion mechanism of built-in pulse impactors, particularly the distribution and evolution of erosion damage in key components (e.g., flow channel outlets).
• (2)Identify critical factors influencing erosion rates (fluid velocity, particle concentration, particle diameter) and their quantitative relationships.
• (3)Provide theoretical support and practical guidance for reducing erosion wear and extending the service life of built-in pulse impactors.

2. Working Principle of Built-In Drill Bit Pulse Impactor

2.1. Structural Composition of the Built-In Drill Bit Pulse Impactor

The structural diagram of the internal pulse impactor for drill bits is shown in Figure . It primarily includes the rotary power mechanism, sealing device, bearings, and housing. The rotary power mechanism, composed of the connector and the rotating body, is the core component of the self-rotating internal drill bit impactor, responsible for energy conversion and generating pulse pressure.

1.

Structure diagram of built-in drill bit pulse impactor: 1 connector, 2 bearing, 3 rotating body, 4 housing, 5 sealing ring.

2.2. Operating Principle of the Built-In Drill Bit Pulse Impactor

The built-in drill bit pulse impactor is an effective auxiliary tool for drilling that enhances mechanical drilling speed without compromising the build rate. Its power source, driven by hydraulic pressure and the flow of drilling fluid, effectively addresses the issue of downhole power supply and demonstrates significant development potential.

This design harnesses the kinetic energy of the drilling fluid to activate the rotary power mechanism. As the drilling fluid traverses the channels of the built-in drill bit pulse impactor, it impacts the outer shell at high speed. The angled orientation between the channels and the shell allows the jet reaction force of the high-speed drilling fluid to drive the rotary power mechanism, causing the rotating body to spin. The shell is equipped with blocking components that fully obstruct the channels of the rotating body. During the rotation, intermittent contact between the channels and the blocking components alters the flow area of the drilling fluid. By minimizing the size of the power-generating mechanism, this design significantly reduces the overall volume of the device, addressing the issue of increased distance between the bit and the stabilizer in existing impactors, and enabling combined use with rotary steerable systems in build sections.

As illustrated in Figure , the arrows indicate the flow direction of the drilling fluid, with green representing the shell surface and red indicating the channels. Under the jet reaction force of the drilling fluid, the channels of the rotating body rotate, resulting in periodic changes in the area between the channels and the shell surface. These variations in the flow area produce fluctuations in pulse pressure.

2.

Schematic of self-rotation.

2.3. Built-In Drill Bit Pulse Impactor Structure

The structural parameters of the built-in drill bit pulse impactor are shown in Table .

1. Primary Parameters of Built-In Drill Bit Pulse Impactor.

parameter	value
cabinet minister (mm)	120
external diameter (mm)	120
internal flow height (mm)	23
internal flow channel angle (°)	30
working displacement (L/s)	40
theoretical pressure drop (MPa)	3
rated frequency (Hz)	10–15
shock load (kN)	20–30
average frictional torque (N·m)	22
connected buckle type	NC50
tool materials	40CrMo
maximum operating temperature of (°C)	200
life length (h)	200

2.4. Built-In Drill Impulse Impulse Analysis

2.4.1. The Etching Theory

When the self-rotating built-in drill bit impactor operates, solid particles carried by the drilling fluid move at high velocities. These particles, propelled by high-speed jets, collide with the impactor walls, causing significant erosion. This paper investigates the erosion characteristics of the built-in drill bit pulse impactor within its operational environment. The study reveals that various erosion mechanisms are active in different working conditions. Consequently, appropriate erosion mechanisms are selected based on the unique structure of the built-in drill bit pulse impactor to analyze its erosion behavior.

The deformation wear theory, proposed by Bitter in 1963, − is pertinent to scenarios where materials experience deformation wear due to erosion. This theory can be categorized into three scenarios:

Plastic deformation: when particles impact the material surface with a force that reaches the material’s yield strength, the material undergoes plastic deformation.

Elastic deformation: when particles impact the material surface with a force that does not reach the material’s yield strength, the material experiences elastic deformation.

Erosion failure: prior to erosion failure, work hardening occurs due to repeated particle impacts on the material surface, which increases the material’s elastic limit. When the particle impact force again exceeds the material’s yield strength, the material fails, leading to crack formation and subsequent erosion failure.

The deformation wear theory provides a robust framework for understanding the wear and deformation of materials caused by solid particle impacts. Therefore, this theory is employed to study the erosion phenomena of the impactor.

2.4.2. Discrete Phase Models

In this study, the FLUENT discrete phase model is used for erosion simulation. This model primarily separates the continuous flow of fluid from discrete impurities for individual analysis. The continuous fluid flow is solved using the Eulerian coordinate system, while the discrete impurities are solved using the Lagrangian coordinate system.

Based on the discrete phase model, the following assumptions are made.

• 1The interaction between the continuous fluid flow and the discrete impurities is ignored.
• 2The interactions between discrete impurities are neglected.
• 3The discrete impurities are considered to be in nonrotational motion.
• 4The particle volume fraction of the discrete impurities does not exceed 10%.

2.4.3. The DPM Erosion Model

2.4.3.1. Equation of Motion

For the particle motion trajectory of the discrete phase, it is solved using Lagrangian coordinates. Therefore, for single particles, the eq of motion is established ,

$$\frac{\mathrm{d}{u}_p}{\mathrm{d}t}=f_{\mathrm{D}}(u-u_{\mathrm{p}})+\frac{g_x({\rho }_{\mathrm{p}}-\rho )}{{\rho }_{\mathrm{p}}}+f_x$$ 1

where f _x is acceleration extra term, $\frac{g_x(r_p-r)}{r_p}$ is combined forces subjected by individual DPM particles, f _D(u–u _p ) is resistance imposed by individual DPM particles, u is fluid phase speed, r is density of liquid phase, u _p is the particle speed, r _p is particle density.

2.4.3.2. DPM Erosion Theory

The erosion/accretion method within the FLUENT DPM model is used. This method studies the relationship between fluid velocity, impact angle, and particle shape function with the erosion rate, and provides the calculation Formula as follows

$$R_{\mathrm{e}\mathrm{r}\mathrm{o}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}}=\sum _{n=1}^{N_{\mathrm{p}}}\frac{m_{\mathrm{p}n}C({\mathrm{d}}_{\mathrm{p}n})f(\alpha )v_{\mathrm{p}n}^{b(v_{pn})}}{A_{\mathrm{f}}}$$ 2

where m _pn is mass of the DPM particles per unit time into the flow field, C­(d_pn) is the DPM particle diameter function, α is angle of DPM particle and boundary interface (impact angle), f(α) is impact–angle correlation function­(0, 1), v_pn is relative speed of particles, b(v_pn) is functions related to the relative velocity of the particles, A _f is boundary cell surface area in contact with particles.

• 3Impact Angle Function

Currently, the impact angle function used for simulating wall erosion is commonly based on the impact angle function studied by Huser and Kvemvold. The corresponding relationships are shown in the Table .

2. Impact Angle Table.

	α	f(α)
1	0°	0
2	20°	0.8
3	30°	1
4	45°	0.5
5	90°	0.4
6	135°	0.5
7	150°	1
8	160°	0.8
9	180°	0

The correlation between impact angles and their associated functions established in Table serves as the core parameter basis for analyzing the impact angle effects in subsequent sections. In the following analysis, erosion rates at different impact angles are calculated by referencing the values f(α) in Table and applying the DPM erosion model Formula , which then yields the erosion rate distribution and its variation patterns.

• 4The Boundary Conditions

For the DPM model in FLUENT, three boundary conditions are set: escape, trap, and reflect. Different boundary conditions can be selected based on the model. In this study, the boundary condition used for the impactor model is Escape. This model assumes that particles do not collide with the wall surface but instead directly escape upon encountering it, with no collision contact occurring.

2.4.4. Key Parameter Settings

The impactor flow channel model is imported into FLUENT to accurately simulate the erosion effects of solid particles on the impactor. Specifically, the numerical simulations (including mesh setup, turbulence model configuration, and flow field calculations) are performed using ANSYS Fluent 2023 R1. Subsequent postprocessing of results (such as extracting pressure data, generating flow field contours, and analyzing erosion rates) is conducted in CFD-Post 2023 R1. In this model, water is designated as the continuous phase, while solid particles are treated as the discrete phase. The specific simulation settings are as follows.

• 1General Settings

Gravitational acceleration is set to −9.81 m/s² along the Y-axis, reflecting the model’s operating conditions. Since the model operates under hydraulic drive, the simulation is configured as transient.

2Model Settings

The Realizable k-epsilon turbulence model with the standard wall function is selected. The Discrete Phase Model (DPM) is enabled, with interactions with the continuous phase and updates to the DPM source occurring every iteration. The DPM iteration interval is set to 10, with a maximum of 10,000 steps and a step length factor of 5. The Savart lift and Erosion/Accretion models are also selected. A new injection source is created in the spray source settings, using surface injection from the inlet. The solid particle diameter distribution is uniform with a diameter of 0.074 mm, a velocity of 27.558 m/s, and a total mass flow rate of 0.2 kg/s. The drag force criterion is set to Stokes-Cunningham. For turbulence diffusion, the discrete random trajectory model with 10 trial attempts and a time scale constant of 0.15 is selected.

• 3Material Settings

The density of the continuous phase (liquid water) is set to 1.7 g/mm³, and the density of the solid particles is set to 2.65 g/mm³.

• 4Cell Zone Settings

During mesh generation, due to the complex structure of the flow channel, unstructured meshing is adopted. The global mesh size, global volume mesh size, and global prism mesh parameters are set respectively, and three layers of wall mesh parameters are used for the flow channel wall surface. The specifically divided mesh is shown in Figure .

• 5Solver Settings

3.

Grid diagram.

After importing the file into FLUENT, it is necessary to first check the size of the divided mesh to see if there are negative meshes. After confirming that the mesh size is correct, we will proceed to a crucial step in the simulation calculation–the setting of the solver.

For the flow channel simulation of the self-rotating built-in drill bit impactor, various parameters need to be defined to achieve the ideal simulation effect, and the most important thing is the selection of the solver. Since the liquid flow is an incompressible liquid with a density of 1700 kg/m³, after analysis, the pressure based solver and Transient solver are finally selected, and the gravitational acceleration downward along the Y-axis is set. All other settings are the default options of the software.

Based on the actual operating environment of the built-in drill pulse impactor, this study selected the realizable k-epsilon turbulence model, the reasons for the choice are as follows:

The selection of the realizable k-ε turbulence model is primarily based on its adaptability and computational accuracy for complex flow scenarios, making it particularly suitable for simulating turbulence inside the built-in drill bit pulse impactor. The specific reasons are as follows:

Better alignment with actual turbulent physical properties: the realizable k-ε model addresses the inaccuracies of the standard k-ε model in predicting rotating flows, strong adverse pressure gradient flows, and other scenarios by modifying the turbulent viscosity coefficient and the production term in the ε equation. The flow channel of the built-in drill bit pulse impactor contains complex structures such as curved sections, variable-diameter regions, and gaps between rotating components, where the flow field exhibits intense shear, vortices, backflow, and other complex phenomena. The realizable k-ε model can more accurately capture these turbulent characteristics, avoiding errors caused by the standard model’s assumption of turbulent isotropy.

Accurate prediction of near-wall flows: when combined with standard wall functions, this model can better simulate the behavior of turbulent boundary layers near walls. The flow channel walls of the built-in drill bit pulse impactor (e.g., gaps between the rotating body and housing, outlet bosses) are regions with sharp changes in pressure and velocity gradients. The realizable k-ε model can more precisely calculate wall shear stress and turbulent energy dissipation, which is crucial for analyzing key performance parameters such as erosion and pressure drop.

Balance between computational efficiency and accuracy: compared to high-precision but computationally expensive models like large eddy simulation (LES), the realizable k-ε model belongs to the reynolds-averaged Navier–Stokes (RANS) family. It has moderate computational requirements and can perform transient or steady-state simulations of complex flow channels while ensuring engineering accuracy. This efficiency is particularly important for studies involving repeated optimization of structural parameters (e.g., flow channel angle, height) of the built-in drill bit pulse impactor.

Validation through extensive engineering applicability: This model has been validated by numerous experiments and engineering cases in scenarios such as pipe flow, rotating machinery, and jet flows. It is especially suitable for simulating flows with high turbulence intensity and complex geometric boundaries. The operation of the built-in drill bit pulse impactor relies on the jet reaction force of drilling fluid to drive the rotating body, and the flow field contains high-frequency pulsed pressure fluctuations. The Realizable k-ε model can stably predict the pressure and velocity distributions of such unsteady flows, providing a reliable basis for structural optimization.

In summary, the accuracy, stability, and computational efficiency of the Realizable k-ε turbulence model in simulating complex flow fields make it a reasonable choice for analyzing the flow field of the built-in drill bit pulse impactor.

The inlet is set as a pressure inlet, with a flow rate of 40 L/s and an inlet diameter of 43 mm. The inlet velocity is calculated using the Formula

$$v=\frac{Q}{A}$$ 3

The calculated velocity v = 27.558 m/s.

To simulate fluid flow, the sliding mesh technique is used to establish the flow channel interface between the rotating body flow channel and the housing baffle. The outlet of the rotating body flow channel is set as interface1, and the housing flow channel is set as interface2 to establish the contact surface. Since the power source of the rotating body is the reaction force of the liquid jet, the DOF dynamic mesh technology is used to simulate the passive rotation of the rotating body under the reaction force of the liquid flow.

The mesh method is set to use the smoothing and mesh reconstruction method for local mesh reconstruction, with a minimum length scale of 0.951 mm, a maximum length scale of 5.125 mm, and a size reconstruction interval of 1.

• 6Boundary Conditions

The inlet is configured as a velocity inlet with a speed of 27.558 m/s, a turbulence intensity of 5%, and a hydraulic diameter of 32 mm. The discrete phase type at the inlet is set to escape. The outlet is configured as a free outlet with the discrete phase type also set to escape. The wall surface is set as a rotating wall with the rotation axis along the Y-axis. The discrete phase boundary condition is set to reflect, using a polynomial function for the normal reflection coefficient with four angle function coefficients: 0.993, −0.0307, 0.000475, and −2.61 × 10^–6; and for the tangential reflection coefficient with four angle function coefficients: 0.988, −0.029, 0.000643, and −3.56 × 10^–6. The impact angle function in the erosion model is piecewise-linear.

2.4.5. Grid-Independent Validation

Grid quality significantly impacts the accuracy of simulation results, so it is crucial for the simulation model. To shorten calculation time while ensuring computational accuracy, we opted to use appropriately sized grids. Specifically, we tested grid sizes of 10 mm, 8 mm, 6 mm, 4 mm, 2 mm, and 1 mm by refining the grid step by step, and extracted the pressure data corresponding to each grid size. The quantity and distribution of grids at different levels are shown in Table , and the details are presented in Figure .

3. Grid Distribution.

grid size (mm)	rotator	shell wall	total
10	5283	9717	15,000
8	8962	12,053	21,015
6	16,387	23,651	40,038
4	34,129	41,893	76,022
2	112,568	147,832	260,400
1	387,521	492,679	880,200

4.

Verification diagram of grid independence.

As can be seen from the figure, as the mesh size gradually decreases, the maximum pressure increases gradually, and the increasing amplitude slows down. When the mesh size reaches 4 mm, the maximum pressure remains almost unchanged with further reduction of the mesh size. Therefore, considering both the computational time cost and the reliability of the results, this paper selects a mesh size of 4 mm for further research, with a total mesh count of 76,022.

The final grid parameters are as follows:

Number of mesh elements: A total of 76,022 elements, all of which are prism meshes.

Number of mesh nodes: A total of 142,893 nodes. The node distribution matches the unit topology structure. Node refinement has been implemented in complex structures of the flow channel (e.g., bends, sudden cross-sectional changes) to ensure the accuracy of geometric shape fitting.

Orthogonal quality: the overall average value is 0.72, and the minimum value is 0.48 (located in the local complex area of the flow channel corner). This result is far higher than the general qualification standard of “orthogonal quality ≥0.3” in numerical simulations, which can effectively reduce calculation errors caused by insufficient mesh orthogonality.

Aspect ratio: The average value is 2.8, and the maximum value is 7.3 (concentrated in the prism meshes near the wall). The stretching of meshes along the normal direction near the wall is to meet the y ⁺ requirement (ensuring accurate capture of flow characteristics in the boundary layer). The overall aspect ratio does not exceed the critical threshold of 10, avoiding the impact of excessive unit stretching on calculation convergence.

Skewness: the average value is 0.21, and the maximum value is 0.38, which is much lower than the risk threshold of 0.8 (industry consensus: skewness >0.8 is prone to mesh element distortion, leading to calculation divergence or result deviation). This indicator shows that the overall shape of the mesh is regular, which can ensure the interpolation accuracy of flow field variables.

Y ⁺ distribution: To verify the compatibility with the turbulence model, we measured y ⁺ values across key wall regions of the flow channel. The y ⁺ range is 32–48, with an average of approximately 40-specifically, 32 at straight wall segments and 48 at bend regions. This distribution is compatible with the standard wall function of the Realizable k-ε turbulence model, as it falls within the optimal application interval (30–60) of the standard wall function for wall-bounded flows. This ensures accurate capture of near-wall turbulent boundary layer characteristics (e.g., viscous sublayer and log layer) while balancing computational efficiency and precision. Excessive mesh refinement (e.g., grid size ≤2 mm) would reduce y⁺ to below 30 but only increase computational cost without significant improvement in simulation accuracy, which is unnecessary for the engineering-oriented research objectives of this study.

2.4.6. Verification of Simulation Model

To validate the simulation model, we conducted experiments using a prototype of the metal-built-in drill bit pulse impactor, focusing on analyzing its pressure drop and frequency. The fabricated prototype is installed, and pressure pulses are monitored using a pressure sensor, with the experimental process illustrated in Figure .

5.

Test flow.

The experimental setup comprises four core systems. The drilling fluid circulation system consists of a high-pressure plunger pump, a 500 L liquid storage tank, a 5 μm filter, a flow control valve, and a pressure stabilizer, forming a closed-loop circulation to provide stable flow and adjustable pressure while removing impurities and suppressing fluid pulsation. The impactor test fixture includes a rigid mounting frame, centering fixture, torque sensor, and rotational speed sensor to stably install the impactor and real-time measure torque and rotational speed. The pressure detection system is composed of high-frequency pressure sensors, a data acquisition card, and a computer with LabVIEW 2021 software, collecting pressure signals at 10 kHz to obtain pulse pressure fluctuation parameters. The Auxiliary System includes a 200 L cooling water tank and circulating water pump to control drilling fluid temperature at 25 ± 2 °C, along with a pressure relief valve, emergency stop button, and protective cover for safety.

It should be noted that the experimental conditions and structural parameters are kept consistent with those in the simulation: the average pressure drop of the built-in drill bit pulse impactor is set to 3 MPa, the flow rate is 25 L/s, the channel height is 20 mm, and the channel angle is 20°.

A finite element simulation analysis is performed based on the structural parameters of the built-in drill bit pulse impactor, and the corresponding results are presented in Figure . As depicted in Figure , the tool is capable of generating an average pressure drop of 3.02 MPa with a frequency of 8.33 Hz. The error between the simulation results and the predicted values is less than 3%, which confirms the effectiveness of the simulation model.

6.

Pressure fluctuation diagram.

3. Results and Discussion

3.1. Analysis of Erosion Results

3.1.1. Distribution of Particle Concentrations

From the working mechanism of the built-in drill bit pulse impactor, it is evident that under high-pressure drilling fluid conditions, the erosion damage caused by solid particles in the drilling fluid is significantly greater than that caused by the liquid phase. Therefore, under the same operating conditions, the more solid particles that flow out of the rotating body’s flow channel along with the liquid phase, the fewer solid particles remain inside the rotating body. As the operational time of the built-in drill bit pulse impactor increases, the particles remaining inside the rotating body will be further eroded by the liquid phase, leading to increased erosion damage and affecting the tool’s service life and shell wall strength.

Figure a shows the concentration distribution of solid particles within the rotating body. From the distribution map, it can be observed that during the process of high-volume drilling fluid passing through the rotating body, the distribution of solid particles retained inside the rotating body is quite uneven. Due to the combined effects of the liquid phase flow and the gravity of the solid particles, varying degrees of particle deposition occur inside the rotating body. , As the operational time of the built-in drill bit pulse impactor increases, these deposited particles will repeatedly erode the shell wall surface under the action of the liquid phase, leading to a certain degree of erosion damage on the shell wall. This impacts the normal use of the shell wall and the drilling efficiency of the drill bit. Figure b shows the particle tracking of the built-in drill pulse impactor. Through particle tracking, it is easier to understand the erosion process and damage law of the built-in impactor.

7.

Particle distribution results: (a) cloud plot of particle concentration distribution; (b) particle tracking diagram.

3.1.2. The Erosion Rate

From the erosion rate distribution map in Figure , it is evident that when high-volume drilling fluid drives the built-in drill bit pulse impactor, erosion wear is primarily concentrated around the protruding areas of the shell wall surface that obstruct the flow. This erosion phenomenon is particularly pronounced in these regions.

8.

Cloud plot of the erosion rate.

The erosion simulation results indicate that severe erosion wear occurs at the protruding positions of the shell wall surface, specifically at the flow channel exit of the rotating body. This is attributed to the sudden change in fluid dynamics as the solid particles in the high-volume drilling fluid approach the flow channel exit in the upstream laminar section. Under the influence of pressure differentials and the particles’ own gravity, the velocity of the solid particles gradually increases, along with their kinetic energy. This escalation leads to direct impacts with the shell wall surface, resulting in significant erosion wear.

3.1.3. Life Prediction

The erosion rate obtained from CFD is defined as the mass loss of metal material per unit time and unit area. Therefore, mass loss is used as the failure criterion. The average erosion rate of the outer and inner surfaces of the built-in drill bit pulse impactor is used as the basis for calculation to estimate its erosion life. The Formula for predicting erosion life is

$$t=\frac{\mathrm{\Delta }{G}_{\max }}{R^{\prime }A}$$ 4

where t is time of erosion destruction, R is average erosion rate of the housing inner wall surface, △G _max is maximum mass loss amount.

Although erosion is concentrated on the protruding areas, the average erosion rate of the shell wall surface is calculated by integrating the local erosion rate over the entire wall area, which comprehensively reflects the overall erosion level of the impactor. For engineering applications, predicting service life based on average erosion rate is a mature and widely used method, , which balances calculation accuracy and practical operability. We have verified through comparative analysis that the service life predicted by the average erosion rate is consistent with the failure cycle of the prototype in field tests, further confirming its rationality.

Based on the above life calculation formula, the erosion life of the built-in drill bit pulse impactor is predicted. The average erosion rate of the inner surface of the shell is extracted, as shown in the table. The predicted life of the built-in drill bit pulse impactor is 525.47 h, which meets the design requirements (As show in Table ).

4. Life-Span Prediction Results.

initial inlet fluid velocity (m/s)	average erosion velocity of the shell inner wall surface (kg/(m2·s))	forecast life (h)
27.558	3.14 × 10–5	525.47

3.2. Analysis of the Erosion Life of Different Materials

Based on the analysis, it is evident that the tool exhibits significant erosion, with the extent of erosion influenced by the choice of material. Consequently, a comparative analysis of erosion effects for different materials is necessary to provide theoretical guidance for material selection. This study examines three materials: 45 steel, Q235A, and 40CrMo.

Using the same flow rate, density, and structural parameters, erosion simulations are conducted for each material, following the procedures previously described. The erosion rates and lifespans for these materials are presented in Figure .

9.

Erosion comparison of different materials.

From Figure , it is evident that the erosion rate and erosion life differ significantly among the materials tested. Of the three materials, 45 steel demonstrates the highest erosion rate at 6.27 × 10^–5 kg/(m²·s). Q235A follows, while 40CrMo exhibits the lowest erosion rate. , Regarding erosion life, 40CrMo has the longest duration at 525.47 h, followed by Q235A, with 45 steel showing the shortest erosion life. In practical drilling operations, selecting 40CrMo as the manufacturing material of built-in pulse impactors can extend the tool’s service life by more than 30% compared to traditional 45 steel and Q235A, reducing downtime for tool replacement and lowering overall drilling costs. This provides clear material selection guidance for engineering applications.

3.3. Analysis of Impact Impact Factors

The severity of erosion wear on the built-in drill bit pulse impactor can be assessed through overall mass loss and maximum erosion rate. However, the maximum erosion rate is more significant in practical conditions and plays a crucial role in ensuring safety during production. Therefore, it is used as the primary measurement indicator when analyzing the factors affecting erosion in the central pipe.

Given the operational characteristics of the built-in drill bit pulse impactor, it is observed that when a high-volume drilling fluid containing solid particles drives the impactor, the erosion wear on the shell surface is influenced by several factors. These factors include design structural parameters, material properties, fluid velocity of the drilling fluid, characteristics of the solid particles, and the quantity of solid particles. In this analysis of erosion wear impact factors, material properties and design structural parameters are kept constant. The solid particles in the drilling fluid are quartz sand particles. Consequently, the study primarily focuses on analyzing the effects of drilling fluid velocity, solid particle concentration, and particle diameter.

3.3.1. Particle Entrance Velocity

Based on the geometric structure of the rotating body, variations in fluid velocity within the rotating body evidently induce changes in the velocity of solid particles, which subsequently affect the erosion of the shell surface. Additionally, differing entrance velocities of the drilling fluid impact the performance requirements of the built-in drill bit pulse impactor. To analyze the effect of drilling fluid velocity in the straight section of the rotating body flow path on the erosion wear of the central pipe wall, discrete phase modeling is employed. Simulations are conducted for entrance velocities of 27.88, 29, 30, 31, and 32 m/s, while other parameters are held constant. The simulation results are as follows.

From Figure , it is evident that, during the erosion simulation process, the erosion rate on the shell surface increases progressively with the rise in drilling fluid velocity, while other flow field parameters remain constant. The erosion predominantly occurs at the protruding area of the shell surface that obstructs the outlet of the rotating body flow path. Additionally, the rate of increase in the maximum erosion rate varies with different drilling fluid entrance velocities. Specifically, when the fluid velocity is between 28 and 30 m/s, the increase in the maximum erosion rate is relatively small. In contrast, when the drilling fluid velocity is between 30 and 32 m/s, the increase in the maximum erosion rate becomes significantly more pronounced as the entrance velocity rises.

10.

Effect of entrance velocity on the maximum impact rate.

From the erosion rate distribution cloud maps under different entrance velocities (Figure ), it is evident that increasing the entrance velocity of the drilling fluid exacerbates erosion at the protruding areas of the shell surface obstructing the outlet of the rotating body flow path. − This phenomenon can be attributed to the following factors.

11.

Cloud plot of erosion rate distribution at different entrance velocity.

Increased inertia of solid particles: As the entrance velocity of the drilling fluid rises, the inertia of the solid particles also increases. Consequently, when these particles collide with the shell surface, their relative velocity is higher, resulting in greater kinetic energy and increased contact pressure between the particles and the wall.

Higher contact frequency: elevated entrance velocities lead to a higher frequency of contact between the solid particles and the pipe wall. The high-speed fluid continuously drives the solid particles to impinge on the wall, thereby intensifying the erosion rate as the entrance velocity increases.

Furthermore, the erosion cloud maps indicate that the location of erosion on the shell surface remains relatively constant, primarily occurring at the protruding areas that obstruct the outlet of the rotating body flow path.

3.3.2. Particle Diameter

During the motion of solid particles within a flow field, the particle diameter significantly influences erosion damage on the pipe wall. When the particle diameter is too small, both the particle mass and contact area decrease, resulting in lower kinetic energy and consequently reduced erosion damage. In contrast, larger particle diameters lead to increased kinetic energy and more severe erosion damage, assuming a constant mass flow rate. However, beyond a certain critical diameter, the impact area of the particles on the wall increases, leading to a relatively minor change in impact force per unit area. Additionally, larger particles may exhibit reduced hardness and a higher propensity for breakage, which can diminish the efficacy of their impact collisions on the wall.

To further investigate the effect of varying particle diameters on erosion damage under practical conditions, simulations are conducted while keeping other parameters constant. Particle diameters are set at 0.074 mm, 0.08 mm, 0.09 mm, 0.10 mm, and 0.11 mm. The results of these simulations are presented below.

As illustrated in Figure , the maximum erosion rate on the central pipe wall generally decreases with increasing particle diameter. However, the rate of decline varies across different diameter intervals. Specifically, for particle diameters less than 0.09 mm, the maximum erosion rate on the central pipe wall decreases significantly, exhibiting a substantial drop. In the range of 0.09 mm–0.11 mm, the maximum erosion rate continues to decline, albeit at a slower pace, due to the influence of the particle diameter.

12.

Effect of solid phase particle diameter on the maximum impact rate.

Figure illustrates the erosion rate distribution under varying solid particle diameters. The primary erosion area remains at the protruding position at the outlet of the rotating body flow channel, obstructed by the outer shell wall, with minimal changes in the erosion area.

13.

Cloud distribution of erosion rate under different solid particle diameters.

The reduction in maximum erosion rate with increasing particle diameter is mainly attributable to the following factors: when other influencing factors remain constant, smaller particle diameters lead to a higher number of particles, resulting in increased impact frequency on the outer shell wall and, consequently, a higher erosion rate. However, given a constant mass flow rate of solid particles, an increase in particle diameter beyond a critical value reduces the number of particles, thereby decreasing the total number of impacts on the outer shell wall and lowering the erosion rate. Although larger particle diameters increase the energy of individual particles, the macroscopic cumulative projected area of all particles colliding with the wall per unit time increases significantly. This is because the projected area of a single spherical particle on the wall is proportional to the square of its diameter, and the total cumulative effect of all particles changes the force distribution on the outer shell wall, resulting in a reduction in the force per unit area. ,

Combining the above analysis and simulation results, it is evident that the erosion effect inside the built-in drill bit pulse impactor decreases as particle diameter increases, with a corresponding reduction in erosion on the outer shell wall. The overall trend of erosion reduction is primarily due to the balance between the effects of particle diameter and particle number on erosion. , If the mass flow rate (concentration) of particles is appropriately increased while particle diameter continues to increase-ensuring an increase in the number of particles and maintaining the energy of individual particles-the erosion rate on the outer shell wall would increase with particle diameter. However, once the particle diameter reaches a certain limit, the erosion rate will stabilize, primarily due to the “size effect”.

3.3.3. Particle Mass Flow Rate

Under constant conditions, an increase in the concentration of solid particles in the drilling fluid leads to a higher frequency of particle-wall collisions per unit time, thereby increasing the impact force on the wall. However, when the concentration exceeds a critical threshold, several effects occur. First, the fluidity of the drilling fluid decreases, which increases its resistance to movement and consequently reduces the relative velocity of the solid particles. Second, as the concentration of solid particles rises, particle–particle interactions intensify, diminishing the number of particles that effectively impact the pipe wall. This interaction mitigates the erosion damage to the wall.

In the discrete phase model, solid particle concentration is often represented by the mass flow rate, defined as the mass of solid particles passing through the pipe interface per unit time. When the inlet displacement of the central pipe remains constant, higher solid particle concentrations result in greater mass flow rates.

To investigate the relationship between particle concentration and erosion, mass flow rates of solid particles are set to 0.2 kg/s, 0.3 kg/s, 0.4 kg/s, 0.5 kg/s, and 0.6 kg/s. The simulation results are presented as follows.

From Figure , it is evident that, with other flow field parameters held constant, the maximum erosion rate on the shell wall surface increases as the mass flow rate (concentration) of solid particles rises. Notably, when the mass flow rate of solid particles ranges from 0.2 kg/s to 0.5 kg/s, the increase in the maximum erosion rate is substantially greater compared to the range between 0.5 kg/s and 0.6 kg/s.

14.

Effect of solid-phase particle mass flow rate on the maximum impact rate.

This phenomenon can be attributed to two primary factors: First, when the mass flow rate of solid particles surpasses a certain critical threshold, the fluidity of the liquid phase decreases, resulting in increased resistance to movement and a mitigated scouring effect on the solid particles. Second, as the concentration of solid particles increases, the interference among them intensifies, reducing the number of particles effectively impacting the pipe wall and thereby diminishing the growth rate of the maximum erosion rate. Overall, the maximum erosion rate escalates with the increase in the mass flow rate (concentration) of solid particles. The primary driver of this trend is that a higher mass flow rate (concentration) of solid particles leads to a greater number of impacts on the wall surface, thereby increasing the frequency of impacts per unit area and consequently elevating the erosion rate.

Based on the erosion diagram in Figure , it is evident that the erosion sites on the shell wall remain largely unchanged. The primary erosion occurs at the protruding areas of the shell wall that obstruct the flow path at the outlet of the rotating body.

15.

Cloud plot of erosion rate distribution at different mass flow rates.

3.3.4. Particle Impact Angle

Figure is the erosion rate distribution at different impact angle.

16.

Cloud plot of erosion rate distribution at different impact angle.

It can be seen from the curve in the figure that as the impact angle increases, the erosion rate first rises rapidly and then drops sharply, reaching a peak at around 30°. In the small–angle interval (10°–20°), the particle impact is dominated by tangential action, and the tangential component of the particle kinetic energy accounts for a high proportion. Although the normal impact is weak, due to the large contact area with the wall surface and the long sliding distance, the continuous scratching gradually expands the erosion area. Moreover, as the angle increases from 10° to 20°, the proportion of the normal component increases, and the synergistic effect of “scratching + light impact” is enhanced, so the erosion rate rises gradually.

When the impact angle reaches the critical angle of about 30°, the erosion rate is the highest. At this time, the normal and tangential components of the particle kinetic energy are “optimally synergistic”. , The normal component provides sufficient impact force to make the particles embed/break the wall surface, and the tangential component maintains the scratching action to expand the damage range. In the cloud diagram, the local red area at 30° is more concentrated, indicating that the energy density in the area with a high erosion rate is the largest, and the composite damage of “impact + scratching” is the most significant.

When the impact angle is ≥45° and enters the large–angle interval (45°–90°), the erosion rate decreases rapidly as the angle increases (reaching the minimum at 90°). The reason is that the larger the angle, the higher the proportion of the normal component (close to “normal impact” at 90°), but the tangential scratching action weakens sharply. In addition, under a large angle, the contact area between the particles and the wall surface increases (similar to “pressing”), the impact force per unit area decreases, and at the same time, the rebound probability of the particles increases, and the number of effective impacts decreases (the area with a high erosion rate in the cloud diagram is significantly reduced). Taking 90° as an example, although the normal component of the kinetic energy of a single particle is the largest, the “normal impact” causes the energy to be concentrated in a very small area, and the synergistic damage of tangential scratching is lacking, so the erosion efficiency is instead the lowest.

The quantified influence laws of fluid velocity, particle concentration, and diameter provide specific operational guidelines for field engineers. For example, controlling the drilling fluid velocity below 30 m/s and the particle mass flow rate within 0.5 kg/s can effectively reduce erosion. Additionally, the revealed erosion concentration at the flow channel outlet offers a basis for structural optimization-measures such as increasing the thickness of protruding areas or applying WC-Co wear-resistant coatings can further improve the tool’s erosion resistance.

4. Conclusions

The study investigated the erosion characteristics of a built-in drill bit pulse impactor. Utilizing erosion theory, the discrete phase model, and the DPM erosion model, the research examined the effects of entrance velocity, particle diameter, and mass flow rate on the erosion rate. The main findings are as follows.

• (1)Under the influence of high-pressure drilling fluid, the erosion caused by solid particles is significantly greater than that caused by the liquid phase. The uneven distribution of solid particles leads to their accumulation in the rotor, which, over time, exacerbates erosion damage to the tool. This damage affects both the tool’s service life and the strength of the shell wall. When large volumes of drilling fluid pass through the rotor, the concentration distribution of solid particles becomes uneven. Due to the combined effects of liquid phase flow and particle gravity, varying degrees of particle deposition occur in the rotor, intensifying erosion damage. Erosion wear is primarily concentrated in the protruding areas of the shell wall that obstruct the rotor flow channel outlet. The sudden changes in fluid motion and the increased speed of solid particles make erosion in this area particularly significant.
• (2)CFD simulations estimated the erosion life of the built-in drill bit pulse impactor to be 525.47 h, meeting design requirements. Among the materials tested-45 steel, Q235A, and 40CrMo–40CrMo exhibited the longest erosion life, at 525.47 h. Significant differences are observed in erosion rates and lifespans among the materials, with 40CrMo demonstrating the lowest erosion rate and the longest lifespan, making it the most suitable for extending the tool’s service life.
• (3)As the entrance velocity of the drilling fluid increases, the maximum erosion rate of the shell wall surface also increases. Within the velocity range of 28–30 m/s, the erosion rate grows slowly; however, between 30 and 32 m/s, the growth rate increases significantly. As particle diameter increases, the erosion rate generally decreases. When the particle diameter is small, the erosion rate drops significantly; beyond a diameter of 0.09 mm, the rate of decrease slows. As the mass flow rate of solid particles increases, the maximum erosion rate of the shell wall surface also rises. Within the mass flow rate range of 0.2 kg/s–0.5 kg/s, the erosion rate increases significantly; beyond 0.5 kg/s, the growth rate diminishes. Additionally, With the increase of impact Angle, the erosion rate first rises rapidly and then drops sharply, and reaches the peak around 30°.

In conclusion, the erosion wear of the built-in drill bit pulse impactor is jointly influenced by fluid velocity, particle concentration, and particle diameter: increasing the drilling fluid velocity and particle concentration elevates the erosion rate, while increasing particle diameter reduces it, and the erosion rate stabilizes when these factors reach a dynamic balance. These findings hold significant practical implications for drilling operations and related engineering applications: first, the identification of 40CrMo as the optimal material provides a direct basis for the manufacturing of built-in pulse impactors, effectively extending the tool’s service life in practical engineering; second, the quantified operational parameter range (fluid velocity <30 m/s, particle concentration <0.5 kg/s) offers clear guidance for field teams to optimize drilling fluid circulation systems and strengthen solid control measures, thereby reducing erosion-related tool failures; third, the predicted erosion life (525.47 h) serves as a scientific reference for formulating reasonable tool maintenance schedules, helping to avoid sudden downtime and ensure the safety and continuity of drilling operations; fourth, the revealed erosion concentration areas (primarily at the flow channel outlet and protruding regions of the shell wall) provide targeted directions for the structural optimization of impactors, facilitating the development of more durable and reliable products. Overall, these results bridge the gap between numerical simulation and engineering application, providing valuable technical support for improving drilling efficiency and reducing operational costs in deep, ultradeep, and complex formations.

All data are available in the manuscript.

The authors declare no competing financial interest.