Heat Transfer Effects in Turbulent, Dense Gas Flow Over a Cylinder

Supercritical carbon dioxide (sCO2) has the potential to greatly improve the efficiency and sustainability of modern power cycles. However, many components of sCO2 power cycles are yet to be optimized. External flows, such as flows over turbine and compressor blades and heat exchangers, play an important role in determining the efficiency of the cycle and optimizing the components. One canonical external flow configuration that can be extended to the blade configurations is flow over a cylinder. Currently, very few studies of heat transfer effects in compressible, dense gas flow over a cylinder exist in the literature. This canonical configuration provides not only a foundation for future studies of dense gas aerodynamics and heat-transfer but also a high-resolution database that will contribute to the literature. The goal of this study is to analyze heat transfer effects in compressible, turbulent dense gas flow over a cylinder. Large-eddy simulations (LES) of calorically perfect and dense gas cylinder flows with the same density ratio are run, and mean profiles, turbulence statistics, and heat-transfer-related quantities are compared side-by-side. The results show a slower recovery of mean properties and greater property variations in the upper and lower outer regions of the wake for the critical-point/Widom-straddling dense gas cylinder case as compared to the completely supercritical and perfect gas cases. In addition, the location of peaks in the density defect and variance profiles at the x-stations within the separation bubble agrees well with the location of the Widom line at the edges of the shear layer region. The Stanton and Nusselt numbers are both higher for the perfect gas case highlighting a difference in the mechanisms of heat transfer near the cylinder wall.