A study of the thermal law of the wall for separated flow caused by a backward facing step

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Title: A study of the thermal law of the wall for separated flow caused by a backward facing step
Author: Pak, Jongyoun
Abstract: A thermal law of the wall provides important information to predict the surface temperature of an object in turbulent flow . Surface temperature predictions for an Radial Jet Reattachment (RJR )nozzle were overpredicted particularly inside the reattachment dome using the conventional thermal law of the wall . As a result , the convective heat transfer coefficient was underpredicted in that region . The present research was motivated to more accurately predict the surface temperature of a heated surface subject to turbulent recirculating flow caused by a sudden geometry change using a new thermal law of the wall . To determine a new thermal law of the wall , thermal and hydrodynamic characteristics of turbulent airflow inside the recirculation region caused by a sudden change in geometry with no external pressure gradient were investigated experimentally . A backward facing step was utilized to predict the recirculation region over a heated flat surface . Temperature and velocity data were measured inside the recirculation region using a thermocouple and an X hot -film probe respectively for step heights of 0 .043 , 0 .057 , and 0 .072 m and Reynolds numbers of 4452 , 6678 , and 8904 . The turbulent Prandtl number was calculated inside the recirculation region and was found to be 0 .25 . Using the maximum backflow velocity inside the recirculation region as the reference velocity and the measured experimental data , a new thermal law of the wall for separated flows caused by sudden geometry changes was obtained by using the mixing length theory . The new thermal law of the wall was utilized in a Computational Fluid Dynamics (CFD ) code to predict surface temperature distribution and air temperature distribution within the recirculation region of a backward facing step geometry . The average error from the wall temperature predictions using the new thermal law of the wall decreased by 77 .4 % when compared to predictions that used the conventional thermal law of the wall .
URI: http : / /hdl .handle .net /2346 /15560
Date: 1999-08

Citation

A study of the thermal law of the wall for separated flow caused by a backward facing step. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /15560 .

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