This paper presents results of a computational study conducted to assess the multiscale resolution capabilities and limitations of different Detached Eddy Simulation (DES) multiscale turbulence models in unsteady flow predictions for internal axial flow in a single rod channel configuration. Two different DES models are compared in the present analysis. The DES models are based on the Spalart-Allmaras (S-A) one-equation model and the two-equation realizable k-ε model. A detailed assessment of the DES turbulence model coefficient for the S-A based DES model is presented. The predicted time-averaged mean velocity and turbulent stresses are compared with the available experimental results. Flow unsteadiness, which is important for determining heat, momentum, and mass transfer in the gap region, is presented through time histories and spectra of flow quantities. The unsteady spectra for the velocity fluctuations are also compared with the experimental observations. The results demonstrate that the DES turbulence model coefficient significantly influence the predicted solution. The realizable k-ε-model-based DES model is found to be numerically more stable than the one-equation S-A-based DES model. Predicted results demonstrate that the modifications need to be incorporated in the current DES model formulations for proper prediction of wall bounded internal turbulent flows.

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