Fig. 8. Normalized dye concentration in the outlet stream of the PAA190 viscoelastic fluid as a function of time for Wi = 30.6 and AR = 1.1 (a) and Wi = 35.6 and AR = 1.8 (b). Only a part of the measured signal is shown. Power spectral density, P, of the normalized dye concentration as a function of the frequency for AR = 1.1 (c) and AR = 1.8 (d). The red lines represent the fit to a power-law decay with exponent α. The dye intensity was measured at (x,y) = (0,w), except for the highest Wi (Wi = 153 for AR = 1.1 and Wi = 178 for AR = 1.8), for which the concentration was measured at (x,y) = (0,w/2). For clarity, the power spectral density of curves B and C in plot (c) and curve C in plot (d) were multiplied by a constant k to shift vertically the curves.
