The effects of the inflow turbulence on the fluid flow and heat transfer of a gas turbine passage flow have been investigated using wall... Show moreThe effects of the inflow turbulence on the fluid flow and heat transfer of a gas turbine passage flow have been investigated using wall-resolved large eddy simulations. Numerical simulations are conducted in a linear vane cascade at different levels of inflow turbulence up to 12.4% at nominal exit chord Reynolds number of 500,000. At this Reynolds number and without any inflow turbulence, the boundary layer remains laminar on both sides of the vane. The presence of the velocity disturbances at the inlet augments the heat transfer on the leading edge and pressure side, triggers transition to turbulence over the suction side and alters the structure of the secondary flow in the turbine passage.The detailed analysis of the flow field indicates formation of large scale leading edge structures that wrap around the large leading edge and extend into both suction and pressure sides of the vane. These structures disturb the boundary layer and form streaky structures which augment the heat transfer on the pressure side. The perturbed boundary layer on the suction side eventually breaks up to turbulence due to the inner mode secondary instability which was reported earlier in a handful of studies.The vane and endwall heat transfer in regions affected by the secondary flows in the turbine passage are also studied in detail. A new representation on the origin and evolution of the passage vortex is presented. The passage vortex in the current geometry is originated from the pressure side passage circulation and not the pressure leg of the horseshoe vortex at the leading edge. Furthermore, it is observed that the distribution of the heat transfer coefficient on the endwall is significantly altered by the change in the level of the freestream turbulence and the approach boundary layer thickness. Finally, the effect of the freestream turbulence on the effectiveness of a slot cooling system in a symmetrical airfoil is studied. The large eddy simulations are conducted for a Reynolds number of 250,000 (based on the approach velocity and the leading edge diameter) and freestream turbulence levels of up to 13.7%. Current predictions capture the decay of the film cooling effectiveness at higher turbulence levels due to the higher mixing of the incoming hot gases and the coolant. It is been shown that the presence of arrays of pin fins in the preconditioning section of the slot cooling system plays a major role in the near field film cooling effectiveness and surface temperature distribution. Show less
