Computation of upward pipe flows at supercritical pressures with blended turbulence model

Abstract

A flow field at supercritical pressure may undergo a strong mixed convection at a certain combination of mass and heat flux, and there are more than one flow (or heat transfer) mode in such a flow field. Therefore, it is unlikely to be able to simulate such a complicated flow field with a single turbulence model. It is known that the flow (or heat transfer) modes are effectively distinguished through the degree of buoyancy parameter. In order to computationally reproduce the flow including various flow modes, two turbulence models that well reproduce the flow with weak and strong buoyancy were blended with buoyancy as a parameter. The algebraic heat flux model (AHFM) was also adopted to model the turbulence production by buoyancy. The temperature variance used in the AHFM was calculated by solving the transport equation for temperature variance. The coefficient of temperature variance used in the AHFM was treated as a function of dimensionless enthalpy. The turbulent Prandtl number was treated as a function of flow variables and physical properties. The proposed computational model was successfully validated against the DNS and experimental data for upward flow in vertical tubes, in which the wall temperatures were satisfactorily reproduced.