Table 2.

Effect of whisker undulations on VIVs.

Hanke et al. [32]
techniques:	Head-mounted video recordings, force measurement at the base of excised whiskers using piezoelectric transducer, micro-PIV, CFD simulations.
findings:	Undulations reduced the primary vortex separation region, displaced the first vortices further downstream and made the pressure field more symmetric about the whisker (figure 4a), resulting in a reduction in VIVs by a factor of 6×.
Miersch et al. [42]
techniques:	Piezoelectric transducer to measure forces during interaction of isolated harbour seal and sea lion whiskers with upstream vortex generator.
findings:	Harbour seal whisker displayed a much higher SNR than sea lion whisker owing to a 10× reduction in VIVs, indicating superior wake detection.
Murphy et al. [33]
techniques:	Laser Doppler vibrometer (LDV) to measure the velocity of the midpoint of harbour seal and sea lion whiskers.
findings:	Similar VIV response for both whiskers, i.e. no effect of undulations.
Bunjevac et al. [43]
techniques:	Snapshot and time-resolved PIV for elephant seal and sea lion whiskers (full length).
findings:	Undulations promoted better mixing within the wake and reduced the turbulence intensity and reversed-flow region compared with the smoother whisker.