Numerical Predictions of Turbulent Mixed Convection Heat Transfer to Supercritical Fluids Using Various Low Reynolds Number k-ε Turbulence Models

There are a number of systems in which supercritical cryogenic fluids are used as coolants or propellant fluids. In some modern military aircraft, the fuel is pressurized above its critical point and used as a coolant to remove heat from the aircraft engine. Accurate prediction of heat transfer coefficients to turbulent flows of supercritical fluids is essential in design of such systems. One of the most challenging parts in mathematical modeling of this phenomenon is the turbulence modeling. The turbulence modeling, like other aspects of the supercritical fluid flows, seems to be highly affected by the large variations of the fluid properties. A two dimensional CFD code has been developed in this study and a number of the Low Reynolds Number (LRN) k-ε turbulence models have been examined. Both flow conditions corresponding to the heat transfer enhancement and deterioration have been studied. The results appear to be quite sensitive to the choice of the turbulence model, especially in the deteriorated regime of heat transfer. The turbulence model assisting the two-dimensional numerical model of the present study to best fit the experiments has been determined for both cases of the enhanced and deteriorated heat transfer. That is while the jump in the wall temperature occurring in the deteriorated regime of heat transfer is over- predicted by the present numerical code regardless of the turbulence model used.