PIV Investigation of Couette-Taylor Flows With Axial Flows

Emna Berrich,Jack Legrand,Fethi Aloui

doi:10.1115/ajkfluids2015-14086

Abstract

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 ReΩ) and/or low axial flux rates (exp. [4]: ReΩ < 50 and Reax < 400; [1] : Reax < 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 (Reax ≤107), for relatively “big” CTS with a radial ratio η = Rint/Rout = 0.855 and an aspect ratio Γ= H/d = 31.03 (where H is the CTS height and d = (Rout – Rint) 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.

Highlights

Taylor-Couette CT flow is a rich fluid with series of clearly distinguishable flow regimes, depending on several operating parameters, from laminar Couette Flow CF via Wavy Taylor vortices flow WTVF [3], Modulated Wavy Taylor Vortex Flow MWTVF and chaotic flows to full turbulence
We propose a quantitative study of CouetteTaylor-Poiseuille flows for relatively "high" Taylor numbers and axial Reynolds numbers, using PIV to characterize WTVF, MWTVF and TN flows with and without relatively high axial flows according to the "direct" protocol
The cartography of the iso-lines values of the axial and radial velocities at a Taylor number equals to torsional flow (Ta) = 303, without and with an axial upflow corresponding to Reax = 73.17 are shown in Figures 2 and 3

Summary

INTRODUCTION

Taylor-Couette CT flow is a rich fluid with series of clearly distinguishable flow regimes, depending on several operating parameters, from laminar Couette Flow CF via Wavy Taylor vortices flow WTVF [3], Modulated Wavy Taylor Vortex Flow MWTVF and chaotic flows to full turbulence. In our previous experimental work using PIV [11], spatial distribution of the flow without and with a "low" axial flow were illustrated via the cartographies of vorticity as a swirling structures detection criterion, the criterion Q, and the instantaneous fields of 2 criterion [13] obtained after the post-processing of the PIV data on a surface 7 layers. It shown that the axial flow superposed to WVF can have a stabilizing effect. The Velocimetry per Image of Particles (PIV) laser technique was used to determine the instantaneous velocity field

Effect of axial flow on velocity

Effect of high axial flow on Velocity components

CONCLUSION