Compressible flow over a heated cylinder with constant and temperature-dependent transport coefficients

A flow over a heated cylinder is a strongly coupled heat transfer and fluid dynamics problem that arises in various engineering applications, such as hypersonic flight conditions, particle-fluid interactions, and re-entry problems. Due to the high-temperature variations observed in these flows, the constant fluid transport property assumptions may not be sufficient to capture the actual physics. This study compares constant and temperature-dependent (using a power-law with a power of 0.75) transport coefficient models where thermal conductivity and shear viscosity depend on the temperature for compressible flows over a two-dimensional cylinder using direct numerical simulations (DNS). For such comparison, we have performed DNS at different temperature ratios where the cylinder surface temperature is 1.2, 1.5, and 3.0 times larger than the free-stream flow temperature. In addition, we compare two Mach numbers with Reynolds numbers ranging from 20 to 150. It is observed that both models provide similar aerodynamic characteristics at the low-temperature ratio (1.2); however, the aerodynamic characteristics calculated for the two different models start to show significant differences when the temperature ratio is higher than 1.5. For example, the mean drag coefficient and separation angle are considerably larger for the cases where we account for temperature-dependent fluid transport properties compared to their counterparts with constant fluid transport properties. We also found that the heat transfer parameters, such as Nusselt number and total convective heat flux, of the problem become highly sensitive to the choice of the transport coefficient model even with low-temperature ratios, and the differences become more prominent with increasing temperature ratios. A detailed comparison of the effects of transport coefficient models on aerodynamics, heat transfer, and vortex dynamics will be presented.