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Proceedings of CHT-15. 6th International Symposium on ADVANCES IN COMPUTATIONAL HEAT TRANSFER
May, 25-29, 2015, Rutgers University, New Brunswick, NJ, USA

DOI: 10.1615/ICHMT.2015.IntSympAdvComputHeatTransf


ISBN Print: 978-1-56700-429-8

ISSN: 2578-5486

Computing Turbulent Flow and Heat Transfer past a Wall-Mounted Cube in a Channel

page 1471
DOI: 10.1615/ICHMT.2015.IntSympAdvComputHeatTransf.1430
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RESUMO

Turbulent flow and heat transfer past a cube (L × L × L) mounted on one wall of a channel of height 2L have served as a benchmark problem to validate computational methods and turbulence models because of the richness in the flow features induced by an unassumingly simple geometry. These include an unstable bi-modal horse-shoe vertical structure upstream of the cube, vortex shedding from the two sides of the cube that extend to the aft of the cube, and periodic separation from the top of the cube. In this study, simulations based on steady and unsteady Reynolds-Averaged Navier-Stokes (RANS and URANS) and large-eddy simulations (LES) were performed to understand the nature of the flow and how that flow affects pressure, drag, and surface heat transfer distributions. For RANS and URANS, the following turbulence models were assessed: the realizable k−ε model, the shear-stress transport (SST) model with and without corrections for curvature, the Reynolds stress model with linear pressure strain (RSM-LPS), and the stress-omega Reynolds stress model. In this study, the RANS and URANS results were generated by using the ANYSYS Fluent code, and the LES results were generated by using the PowerFlow code.
Results obtained show RANS to be unacceptable in predicting the reattachment of the separation bubble downstream of the cube. URANS by being able to resolve the oscillatory shedding from the two sides of the cube was able to predict the reattachment with reasonable accuracy. URANS with the SST model that has the curvature correction gave the best results for the reattachment length downstream of the cube (relative error within 5% of the experimental data). Also, this model was able to capture all details of the flow features revealed in the experimental oil-flow study with considerable accuracy. However even with this model, the predicted pressure just downstream of the cube is incorrect by up to 50%. This is because URANS was unable to predict the unstable bi-modal, horse-shoe vortex system upstream of the cube induced by interactions between the spanwise vortices in the turbulent boundary layer and the horsehoe vortex system. This interaction was found to cause the separation bubble on top of the cube to shed periodically. By being able to capture this interaction, LES was able to better predict the pressure just downstream of the cube. This shows why LES is needed and why RANS and URANS are inadequate unless those models can be modified to account for these unsteady interactions.
Steady and unsteady RANS based on the SST model were also employed to study the heat transfer about the surface of the cube. Reasonably good results were obtained for the leading and trailing faces of the cube but not for the top and the two side faces. A parametric study on the effects of the turbulent Prandtl number show the connection between the turbulent eddy viscosity and the turbulent thermal conductivity cannot be represented by a simple algebraic equation, the Prandtl number. Thus, better RANS models are needed to capture the physics embedded in the correlations between the fluctuating velocities and temperatures.
A paper on this work is being prepared. The order of authorship will be X. Chi, K, Adeel Ahmad, Surya Muthukannan Chinnamani, and T. I-P. Shih. The author of this abstract thanks his students who worked on the different parts of this problem.

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