Large-eddy simulation of the flow in a low-speed centrifugal compressor

The results of a series of numerical simulations for the NASA low-speed centrifugal compressor are presented. Large-eddy simulation (LES) is carried out together with the most commonly used Reynoldsaveraged Navier–Stokes (RANS) models, including the mixing length, k– and k– models. Predictions are compared with the available experimental data. It is seen that quantitative predictions of LES are better than those of RANS models for the tip jet and wake regions. LES, unlike these RANS models and the past computational fluid dynamics predictions, shows separation near the casing starting around the halfway of the impeller and reveals a vortex bubble close the impeller exit/casing corner. The tip leakage flow, which is the main characteristic of an unshrouded compressor, is investigated using the probability density function (PDF) and the power spectral density (PSD) of the instantaneous velocity values. The skewness and flatness calculated from the PDF profiles show that the unsteady flow in the tip wake region is less-intermittent compared with the flow in the tip jet region. The PSD analysis shows that the turbulent energy transfer rate from the larger scales to the smaller scales and the frequency range where the inertial region is valid increase in the tip wake region. Copyright q 2008 John Wiley & Sons, Ltd.