Comparisons between flow tagging measurements and computations in a complex rotating flow

Abstract

The phenomena of vortex breakdown has been the subject of much attention because of its practical importance in many different situations, as well as its attraction as a fundamental problem in fluid mechanics. Experiments by Vogel [15, 16] showed that the flow produced by a rotating end wall inside a closed cylindrical container can undergo vortex breakdown under certain conditions. Only two non dimensional parameters, the aspect ratio 6 = ^ and the Reynolds number Re = TM-, completely determine the flow in this geometry. Escudier [4] extended the work of Vogel and examined this system using laser sheet fluorescence dye visualizations over the range 1000 < Re < 4000 and 1.0 < 6 < 3.5 and found that in this parameter range, the flow could undergo up to three breakdowns as well as become unsteady. Because of its simple geometry and completely specified boundary conditions, this flow is an excellent system, both computationally and experimentally, in which to study fundamental issues related to vortex breakdown. Using the PHANTOMM flow tagging technique we obtain quantitative measurements of velocity as well as visualizations similar to those obtained with stan•Graduate Student. Member AIAA t Professor. Associate Fellow AIAA ' Senior Research Scientist. Member AIAA This paper is a declared a work of the U.S. Government and is not subject to copyright protection in the United States. dard laser sheet fluorescence techniques. In addition, the axisymmetric Navier-Stokes equations are solved using a vorticity-stream function formulation. The computed flow is compared to measurements in order to evaluate and validate the PHANTOMM technique so that one can be confident of measurements in flow regimes where accurate computations are not available.