Experimental investigation of a sheared thermally unstable boundary layer

by Giuseppe Gabriele Nunnari
Doctoral thesis
Date of Examination:2021-06-14
Date of issue:2021-07-02
Advisor:Dr. Stephan Weiss
Referee:Prof. Dr. Andreas Tilgner
Referee:PD Dr. Olga Shishkina
Referee:Dr. Michael Wilczek
Referee:Prof. Dr. Andreas Dillmann
Referee:Prof. Dr. Jens Niemeyer
Persistent Address: http://dx.doi.org/10.53846/goediss-8698

 

 

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Abstract

English

In many natural and industrial systems, heat is transported by mixed convection, where an externally driven flow causes advection of the temperature field in addition to the fluid motion due to buoyancy of differentially heated areas. We investigate experimentally the heat flux across a thermally unstable boundary layer subject to a shear flow. In the experiment, we use a two meter long aluminium plate that is subject to a shear flow above its heated surface. For varying Richardson, Reynolds and Grashof numbers, we measure the heat flux from the plate, as well as the vertical velocity and temperature profiles above it by using hot-wire anemometry and thermistors arrays. The fluid is air at atmospheric pressure, resulting in a Prandtl number of Pr = 0.75. The goal of this research is not only to investigate the transition from fully forced to dominantly free convection, but we also hope to better understand the difference between a shear driven turbulent boundary layer and a laminar boundary layer which is perturbed by thermal plumes.
Keywords: Mixed convection; Boundary layer; Boundary layer transition; Turbulence K-1 energy scaling
 
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