PIV Investigation of Couette-Taylor Flows With Axial Flows

The Couette Taylor flows CTF strongly depend on geometrical characteristics of CT systems radio and aspect ratios. The superposition of axial flow may accentuate this dependence. Previous studies carried with relatively small radial and/or aspect ratios [1–3] or relatively low Taylor numbers (or rotational Reynolds number Re_Ω) and/or low axial flux rates (exp. [4]: Re_Ω < 50 and Re_ax < 400; [1] : Re_ax < 4), or limited to analytical approaches or numerical simulations adopting simplified hypothesis and assumptions. In order to complete information obtained for vortices characterization for relatively “high” Taylor numbers (303 ≤Ta≤ 1212) and relatively “high” axial Reynolds numbers (Re_ax ≤107), for relatively “big” CTS with a radial ratio η = R_int/R_out = 0.855 and an aspect ratio Γ= H/d = 31.03 (where H is the CTS height and d = (R_out – R_int) is the gap thickness), we realized a quantitative experimental study using standard and speed Velocimetry per Image of Particles (PIV) technique. The vortex structures for CTF with and without an “ascending” axial flow, according to the “direct protocol” i.e. The axial flow is superposed to an initial fully developed rotational flow were studied [5]. The vortex direction strongly depends on protocol history. The cartographies of velocity components are illustrated. The results mainly concern axial and radial velocity components. The cartographies of the vorticity ω, and the detection criteria Q and Γ₂ are presented and discussed. The alternating between positive and negative values of axial velocity component characterizes the presence of contrarotating vortices. This allows determining the axial wavelengths (λ) for WTVF and MWTVF with and without axial flows. A same axial flow can have a stabilizing effect for a regime flow and a destabilizing effect for another. It enhanced the overlapping, the stretching, the folding or the breaking of vortices. From WTVF to MWTVF to TN, we illustrated that the vortices mixing is enhanced when the Taylor number increases due to vortices stretching and folding.