Measurements of steady axial streaming at a rotating disc with torsional oscillations

Electrochemical measurements of steady axial streaming induced by a rotating disc with angular velocity waveform Ω = Ω0[1 + α cos (σt)] and α < 1 are compared to asymptotic and numerical theory. A simple theory is developed to describe the contribution of steady axial streaming to the mean component of mass flux at the reactive disc surface when the mass transfer oscillation frequency (σ/Ω0)Sc⅓ is large. The experiments use a high Schmidt number (Sc ≈ 3 × 106) glycerine-based (80:20 glycerine : water, w/o) electrolyte designed to satisfy the theoretical constraint (σ/Ω0)Sc⅓ ≫ 1 while simultaneously allowing a wide range of flow oscillation frequencies σ/Ω0to be probed. Our measurements verify that the magnitude of steady axial streaming at a rotating disc with torsional osillations is O(α2) when α < 1 and we show that the frequency dispersion of the phenomenon is a complicated function that reaches a maximum intensity at σ ≈ 2Ω0, confirming asymptotic and numerical predictions.