A study of compressibility effects on laminar, unsteady flow past a two-dimensional bluff body
Cope, William Kevin
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https://hdl.handle.net/2142/20673
Description
Title
A study of compressibility effects on laminar, unsteady flow past a two-dimensional bluff body
Author(s)
Cope, William Kevin
Issue Date
1996
Doctoral Committee Chair(s)
Vanka, Surya Pratap
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
A study has been conducted of the effects of compressibility on the laminar, unsteady flow past a two-dimensional bluff body. The study was performed by solving the governing equations of fluid motion. The set of integral-differential equations which govern the fluid motion were approximated by a finite volume discretization. A fifth order upwind biased interpolation was developed which satisfies the convective boundedness criteria (CBC) of Gaskell and Lau, 1988. This was seen to be essential in avoiding the calculation of unphysical Riemann states used in the approximation of inviscid flux vectors. An analysis was performed of the numerical method. The method was found to be conservative, consistent, linearly stable, and second order accurate. An initial study has been performed of inlet boundary condition effects on the flow over a two-dimensional bluff body. It was concluded that specification of velocity and static temperature at an inlet boundary can lead to a physically unrealistic problem when used for internal flow simulations. The study of compressibility effects on the flow past a bluff body considered five Mach numbers ranging from low subsonic to supersonic. It has been observed that embedded shock waves form in the vortex formation region even when the inflow is subsonic. The presence of normal shock waves which bound the near wake has also been observed. At supersonic speeds, the wake structure changed significantly. The vortex roll up observed at low Mach number was seen to be replaced by an elongated and gradual evolution of the vorticity field. Finally, at a large enough Mach number (Ma = 1.7 in this study), the flow was observed to be steady. No vortex shedding or unsteady forcing of the plate was observed. The results of this study suggest that for laminar, unsteady flow past a two-dimensional bluff body, compressibility acts to damp flow field disturbances which at low subsonic values lead to quasi-periodic unsteady flow.
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