Discussion on improved method of turbulence mode for supercritical water flow and heat transfer

Abstract

The turbulence model fails in supercritical fluid-flow and heat transfer simula-tion, owing to the drastic change of thermal properties. The inappropriate buoy-ancy effect model and the improper turbulent Prandtl number model are several of these factors lead to the original low-Reynolds number turbulence model una-ble to predict the wall temperature for vertically heated tubes under the deterio-rate heat transfer conditions. This paper proposed a simplified improved method to modify the turbulence model, using the generalized gradient diffusion hypothe-sis approximation model for the production term of the turbulent kinetic energy due to the buoyancy effect, using a turbulence Prandtl number model for the tur-bulent thermal diffusivity instead of the constant number. A better agreement was accomplished by the improved turbulence model compared with the experimental data. The main reason for the over-predicted wall temperature by the original turbulence model is the misuse of the buoyancy effect model. In the improved model, the production term of the turbulent kinetic energy is much higher than the results calculated by the original turbulence model, especially in the bounda-ry-layer. A more accurate model for the production term of the turbulent kinetic energy is the main direction of further modification for the low Reynolds number turbulence model.