Date of Award

9-1994

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Supervisor

M. Shoukri

Co-Supervisor

P. Wood

Abstract

The cooling of a hot surface by fluid motion has many applications in engineering. For
these mixed convective problems, the forced component of fluid motion may be in the direction
of the buoyancy vector or it may oppose the buoyancy force. In the present study, the opposing
mode is used to study the interaction of inertia and buoyancy forces in a fluid. Both numerical
and experimental techniques are used to study the flow in a rectangular cavity of aspect ratio 2.

The inlet Reynolds number is varied between 800 and 1300 and the Grasbof number
based on the height of the enclosure is varied between 0 and 2.4 X 10¹⁰. The cases considered
correspond to Archimedes numbers of approximately 0, 1, 10 and 20.

The flow field is observed qualitatively using laser induced fluorescence and a detailed
flow field is generated using a laser doppler anemometer. Temperature profiles are found using
fine wire thermocouple probes. These detailed measurements may provide a data base for the
verification of computer programs used to predict mixed convection as there are no such detailed
chita bases in the present literature.

Numerical modelling is based on the SIMPLER algorithm with QUICK differencing. The
observed flow field indicated that some regions in the cavity were turbulent while other regions
were laminar. This observation suggests the necessity of a low Reynolds number turbulence
model. In this study, two forms of the low Reynolds number k-ε model are used. In addition,
the commercial computational fluid dynamics program, FLUENT, is used to predict the flow.

Comparison of the experimental and computational results suggest that for isothermal and buoyancy dominated flow cases the computational modelling is adequate. Difficulties arise in the prediction of the intermediate Archimedes number cases as the predicted flow is dominated by
buoyancy while the experiments show more of a balance. Sources for this discrepancy are
discussed.


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