University of Minnesota
Aerospace Engineering and Mechanics
Fall 1997 Seminar Series
Vortex-dominated Wake Interactions Behind Bluff-Bodies
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
Refreshments served after the seminar in
227 Akerman Hall.
Disability accomodations provided upon request.
Audrey Stark-Evers, Senior Secretary,