Effect of wall temperature in supersonic turbulent boundary layers: A numerical study

The present work is dedicated to the numerical study of statistical characteristics of spatially-evolving supersonic turbulent boundary layers (STBL) with cooled walls. Large-Eddy Simulations (LESs) are performed to gain further insight into the role of wall temperature on the mean and fluctuating-flow properties of STBL. The velocity fluctuations, which are scaled according to the Morkovin's hypothesis, have shown acceptable agreement with available experimental and DNS results of literature. However, the van Driest transformed skin friction C-fInc lies below the incompressible theoretical curves as a function of Re-theta Inc for cold STBL, whereas compressible skin friction is found to be relatively higher for cold wall boundary layers than adiabatic boundary layers. The variation of total shear stress remains unaffected throughout the boundary layer for 0.5 <= T-w/T-r <= 1. The total temperature fluctuations are non-negligible for cold cases and surface cooling changes the near-wall turbulent structures. Additionally, the stream-wise velocity and temperature fluctuations for the coldest isothermal STBL case are strongly correlated compared to the anti-correlation behavior of the adiabatic STBL in the near-wall region (y(+) approximate to 9). Furthermore, the pressure fluctuations are found to be non-negligible for cooled boundary layers and a positive correlation between pressure and density fluctuations are observed in the log-layer. These tendencies have also been verified through a detailed statistical analysis of the unsteady flow-field. (C) 2014 Elsevier Ltd. All rights reserved.