Computations were performed to study the three-dimensional flow and heat transfer in a ribbed U-shaped duct of square cross section under operating conditions that are typical of industrial gas turbines. Basically, all walls were maintained at a temperature of 800 K, and the coolant air at the duct inlet had a temperature of 550 K and a pressure of 10 atm. Both rotating and non-rotating cases were investigated. When rotating, the angular speed was 3,600 rpm. The Reynolds number based on the duct hydraulic diameter was set at 350,000, which represents an upper limit in coolant flow. The results obtained in this study were compared with those from previous numerical studies with a lower Reynolds number, namely 25,000, which represents a lower limit in coolant flow.
This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy. Turbulence is modelled by two low-Reynolds number k-ω models: an SST version with isotropic eddy diffusivity and a nonlinear version with anisotropic eddy diffusivity from an explicit algebraic Reynolds stress model. Solutions were generated by using a cell-centered finite-volume method, that is based on flux-difference splitting and a diagonalized alternating-direction implicit scheme with local time-stepping and V-cycle multigrid.