Large-Eddy Simulations of heated flows in ribbed channels with spanwise rotation

Abstract

We report on the outcome of a computational study of heat and momentum transport in a heated ribbed straight channel rotated about a spanwise axis. The flow is of both practical and fundamental interest, the latter due to the simultaneous presence in this flow of a number of complicating effects. These include system rotation, mean-flow unsteadiness, large-scale flow separation, and subsequent reattachment; their interactions severely distort the turbulence structure and thus pose this flow as a challenge to engineering prediction methods. In this study, the predictions were obtained using Large-Eddy Simulations with the objectives of assessing the performance of this approach in this flow, and gaining better understanding of the factors that influence the quality of the solutions. Thus, the numerical accuracy of the simulations was determined using Grid Convergence Index (GCI) method, and additionally by comparing results obtained using discretization schemes of different orders of accuracy. The dependence of the computed results on the models for the sub-grid scale correlations in both the momentum and thermal energy equations was checked by performing computations with alternative closure assumptions. These included the Smagorinsky and the dynamic models for momentum, and both linear and non-linear models for the thermal energy fluxes. The computations, which were performed with OpenFOAM, were compared with benchmark experimental data from both heated and isothermal flows. The correspondence between predictions and measurements was generally satisfactory but some important differences remain. It is argued that these are in part due to ambiguities in the way in which temporal and spatial averages are obtained in the computations and in the measurements.