PREDICTION OF TURBULENT HEAT TRANSFER IN STATIONARY AND ROTATING U-DUCTS WITH RIB ROUGHENED WALLS

摘要

Numerical simulations of a stationary and rotating rib-roughened U-bend at high Reynolds number, Re_D = 95 000, are presented. Using a recently developed k―ω turbulence model, the predicted velocity and heat transfer in the two legs of the U-bend are in excellent agreement with measured data. In the bend, the streamline curvature makes any unmodified eddy-viscosity models inadequate and hence larger discrepancies are found. Similarly to the measurements the model predicts increased heat transfer downstream the bend, due to the higher levels of turbulence. Under rotating conditions, Ro = 0.2, the model faithfully alters the predicted Nusselt number, to as high as 30% above those for the non-rotating case. To reduce computational demands a newly developed wall treatment is applied to the baseline model, enabling a relatively coarse mesh, with a first interior node location at y~+ ≈ 5, to be used. The wall treatment which is based on the near-wall variation of flow variables, reduces the mesh dependency, and improves numerical stability.