Turbulent Transport
Characteristics in a Low-Speed Boundary Layer Subjected to
Adverse Pressure
Alberto Ayala
Department
of Mechanical and Aerospace Engineering
West Virginia University
Bruce R. White and Dae-Seong Kim
Department
of Mechanical and Aeronautical Engineering
University
of California, Davis
Nader Bagheri
Department
of Mechanical Engineering
California Maritime Academy, California State University
Abstract
Thermal
anemometry measurements were performed to evaluate the heat and momentum
transport characteristics of wall turbulence over a slightly heated, smooth
flat plate with a step-change in wall temperature. Single-wire, X-probe and
triple-wire sensors were employed to measure mean and fluctuating velocity and
temperature as well as Reynolds stress and heat flux productions. “Equilibrium”
boundary layers were considered for mild and moderate adverse-pressure-gradient
(APG) conditions for a wall-to-free-stream temperature difference of
approximately 12oC. The base case for zero-pressure-gradient (ZPG)
conditions was also investigated. The origins of the momentum and thermal
boundary layers did not coincide, resulting in a layer development of
approximately 0.8, 1.2 and 1.5 for ZPG, mild and moderate APG, respectively. Findings
suggest that the mean flow field and the fluctuating streamwise and normal flow
fields responded proportionally to the magnitude of the adverse-pressure
gradient present. The failure of the law-of-the-wall for velocity for the APG
conditions considered was not severe. And the equilibrium condition of the flow
was maintained through a balance of adverse pressure and turbulent stress
production. The Reynolds analogy was confirmed for ZPG conditions while, in
adverse pressure, the turbulent stress production scaled with the streamwise
heat flux. The heat flux production was found to be self-similar for the
pressure gradient cases investigated.
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