THE LEVICH INSTITUTE ANNOUNCES THE FOLLOWING SEMINAR:

Tuesday, 9/15/98
4:00 PM
Steinman Hall, Room #1M-22
Professor Zvi Rusak
Rensselaer Polytechnic Institute
Department of Mechanical Engineering, Aeronautical Engineering and Mechanics
"Axisymmetric Vortex Breakdown in a Pipe - Theoretical, Numerical and Experimental Studies"


ABSTRACT

A recent study of the nearly axisymmetric vortex breakdown in a pipe is presented. The study is built of a theoretical phase, a numerical phase and special experiments that were guided by the theory. I will first present the recent theoretical investigation of the motion of an axisymmetric and inviscid swirling flow in a pipe with certain boundary conditions that may reflect the physical situation. The theory is composed of global analysis of solutions of the Squire-Long equation and linear stability analysis of these solutions. It will be demonstrated that the theory unifies the major previous theoretical approaches and provides for the first time a consistent explanation of the physical mechanism leading to the vortex breakdown phenomenon as well as the conditions for its occurrence.

In the second part of the talk I will describe numerical computations of the axisymmetric vortex breakdown. These unique simulations are guided by the rigorous theory. It has been established that the fundamental characteristics which lead to vortex instability and breakdown in high Reynolds number flows may be calculated from considerations of a single nonlinear ordinary differential equation, representing a columnar flow problem. Necessary and sufficient criteria for the onset of vortex breakdown in a Burgers' vortex or in a Q-vortex will be presented.

In the third part, recent experiments will be discussed. These experiments are also guided by the rigorous theory. The existence of two stable states in a certain range of incoming swirl and a hysteresis loop, that is predicted by the theory, is demonstrated in the experiments. In addition, it is experimentally shown that even a very large perturbation to the flow just below the threshold for breakdown would not permanently change the flow from being almost columnar as predicted by the theory.

BRIEF ACADEMIC/EMPLOYMENT HISTORY:

*Ph.D., Aerospace Eng., Techion-IIT, Israel 1989
*Associate Prof., MEAEM, RPI, 1995-present
*Technical chair of the AIAA 2nd theoretical Fluid Mechanics conference June 1998.

RESEARCH INTERESTS:

Theoretical fluid dynamics and aerodynamics, vortex stability and breakdown, transonic flows.


Return to Fall, 1998 Seminar Schedule