University of Minnesota
Aerospace Engineering and Mechanics
Fall 1997 Seminar Series



Vortex-dominated Wake Interactions Behind Bluff-Bodies


Professor Hiroshi Higuchi

Department of Mechanical, Aerospace and Manufacturing Engineering

Syracuse University

Abstract

Results from the experimental investigation on bluff-body wakes will be presented. Effects of flow accelerations and decelerations, model three-dimensionality and porosity were examined systematically. The study was motivated by needs for better physical understanding of parachute aerodynamics. The wake development behind a disk started from rest and subsequently decelerated showed strong flow-structure interactions. A high initial drag peak after near-impulsive start was followed by a negative peak drag at the onset of the deceleration as the wake vortex overtook the model under certain deceleration patterns. (Such a flow interaction is associated with accidental parachute canopy collapse shortly after its inflation.) While the simple added mass concept and so-called Morrison's equation were inadequate in predicting the drag time histories, a discrete vortex method simulation resulted in a good agreement. The time-dependent flow field will be discussed together with the circulation measurement with the PIV technique. It is to be noted that the disk wake remains axisymmetric only within a short period after the start-up prior to three-dimensional vortex sheddings. The three dimensional vortex dynamics was further investigated using a family of polygonal plates. Subsequently, the effect of porosity (slots) on the wake was studied and the multiply-stable wake patterns and the corresponding velocity time histories were analyzed. The talk will conclude with a brief discussion on assessment of prediction capability and future direction of work.

Friday, October 3, 1997
209 Akerman Hall
2:30-3:30 p.m.


Refreshments served after the seminar in 227 Akerman Hall.
Disability accomodations provided upon request.
Contact Audrey Stark-Evers, Senior Secretary, 625-8000.