Contrasting zonal LES and non-linear zonal URANS models when predicting a complex electronics system flow

Zonal non-linear URANS (unsteady Reynolds-averaged Navier–Stokes) and hybrid RANS/LES (large eddy simulation) model variants are presented. Performances of these models are compared for an unsteady, relatively high Reynolds number, complex electronics-related geometry, non-isothermal flow. Comparison is made with heat transfer, velocity and turbulence intensity data. The URANS models investigated involve zonal k–l/EASM (explicit algebraic stress model) and k–l/HCubic (high Reynolds number cubic model) variants. A k–l-based hybrid RANS/LES (zonal LES) method is also applied and four RANS–LES switching criteria considered. Results are found to be relatively insensitive to this. To aid comparisons, the Smagorinsky, Yoshizawa, non-linear Kosovic and mixed Leray subgrid scale LES models are considered. All models give similar mean velocity predictions. However, for turbulence intensities, the hybrid RANS/LES and LES give considerably more accurate predictions than the URANS. For heat transfer, none of the models performs well. The local Nusselt number is largely overpredicted by the URANS and underpredicted by the hybrid RANS/LES. However, the worst hybrid RANS/LES model Nusselt number error is around 30% less than the best URANS model error. Also, the most accurate URANS heat transfer is for the crudest model. On average, the hybrid RANS/LES model heat transfer results are marginally more accurate than the LES. Copyright q 2006 John Wiley & Sons, Ltd