Large Eddy Simulation of Flow and Heat Transfer in a Channel Roughened by Square or Semicircle Ribs

The internal cooling passage of a gas turbine blade has been modeled as a ribbed channel. In the present study, we consider two different rib geometries, i.e., square and semicircle ribs, in order to investigate their thermal and aerodynamic performance. Large eddy simulations (LESs) of turbulent flow in a ribbed channel with a dynamic subgrid-scale model are performed. In our simulation, the no-slip and no-jump conditions on the rib surface are satisfied in the Cartesian coordinates using an immersed boundary method. In order to validate the simulation results, an experimental study is also conducted, where the velocity and temperature fields are measured using a hot wire and a thermocouple, respectively, and the surface heat transfer is measured using the thermochromic liquid crystal. LES predicts the detailed flow and thermal features, such as the turbulence intensity around the ribs and the local heat transfer distribution between the ribs, which have not been captured by simulations using turbulence models. By investigating the instantaneous flow and thermal fields, we propose the mechanisms responsible for the local heat transfer distribution between the ribs, i.e., the entrainment of the cold fluid by vortical motions and the impingement of the entrained cold fluid on the ribs. We also discuss the local variation of the heat transfer with respect to the rib geometry in connection with flow separation and turbulent kinetic energy. The total drag and heat transfer are calculated and compared between the square and semicircle ribs, showing that two ribs produce nearly the same heat transfer, but the semicircle one yields lower drag than the square one.