Heat Transfer Predictions for Rotating U-Shaped Coolant Channels With Skewed Ribs and With Smooth Walls

Abstract

A computational study was performed for the flow and heat transfer in rotating coolant passages with two legs connected with a U-bend. The dimensionless flow conditions and the rotational speed were typical of those in the internal cooling passages of turbine blades. The calculations were performed for two geometries and flow conditions for which experimental heat transfer data were obtained under the NASA HOST project. The first model had smooth surfaces on all walls. The second model had opposing ribs staggered and angled at 45 deg. to the main flow direction on two walls of the legs, corresponding to the coolant passage surfaces adjacent to the pressure and suction surfaces of a turbine airfoil. Results from these calculations were compared with the previous measurements as well as with previous calculations for the nonrotating models at a Reynolds number of 25,000 and a rotation number of 0.24. At these conditions, the predicted heat transfer is known to be strongly influenced by the turbulence and wall models. The differential Reynolds-stress model (RSM) was used for the calculation. Local heat transfer results are presented as well as results averaged over wall segments. The averaged heat transfer predictions were close to the experimental results in the first leg of the channel, while the heat transfer in the second leg was overestimated by RSM. The flow field results showed a large amount of secondary flow in the channels with rotational velocities as large as 90 percent of the mean value. These secondary flows were attributed to the buoyancy effects, the Coriolis forces, the curvature of the bend and the orientation of the skewed ribs. Details of the flow field are discussed. Both the magnitude and the change of the heat transfer were captured well with the calculations for the rotating cases.