Date of Award

Spring 1993

Document Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical & Aerospace Engineering


Mechanical Engineering

Committee Director

Robert L. Ash

Committee Member

Colin P. Britcher

Committee Member

John Heinbockel

Committee Member

George C. Greem

Committee Member

Osama A. Kandil


Aircraft wakes represent potential hazards which can control aircraft spacing and thus limit airport capacity. Wake vortex trajectories and strengths are altered radically by interactions with the ground plane and by atmospheric conditions. This work has been concerned with developing more accurate numerical predictions. A two-dimensional, unsteady numerical-theoretical study is presented which has included viscous effects, the influence of stratification, crosswind and turbulence on vortex behavior near the ground plane, using a vorticity-streamfunction formulation.

A two-parameter perturbation procedure has been developed which uses analytic solutions for the initial flow field to accommodate the ground effect region in the numerical simulation. Using an order of magnitude analysis, it was possible to justify the Boussinesq approximations for turbulent wake vortex predictions, including ground effects and atmospheric stratification. It has been shown that the eddy-viscosity turbulence models were not effective in predicting wake vortex flows and a Reynolds stress transport model was implemented.

The numerical solutions to the Navier-Stokes equations have been compared with experimental results for the laminar, unstratified cases and good agreement has been obtained. The computational simulations show that the vortex rebound near the ground plane is caused by ground boundary-layer separation. High stratification levels can confine the motion of the vortex system and alleviate the primary vortex strength. Vortex turbulence influences vortex trajectories more strongly than it influences the rate of change in vortex strength. Weak crosswinds cause the upstream primary vortex to rebound less strongly than the downstream vortex. Finally, suggestions are made for future research.