Effect of Mach number on secondary flow characteristics

Endwall secondary flows in gas turbines are complicated by highly non-uniform combustor exit profiles. Most experimental endwall studies do match turbine Reynolds numbers, but not Mach numbers, and assume constant temperature conditions with a simple turbulent boundary layer. This paper presents results for benchmarking of a CFD code with experimental data and the effects of inlet profiles at both low and high Mach number conditions under matched Reynolds number conditions. Detailed flowfield measurements were obtained in a large scale, linear turbine vane cascade and were used for CFD benchmarking. Analysis of the results for spanwise varying inlet profiles indicate that the stagnation pressure gradient is the key parameter in determining the character of the secondary flows in the first stator vane passage. Temperature gradients applied at the inlet were distorted in relation to the secondary flows influencing heat transfer to the vane and the inlet thermal field for the next rotor stage. Comparisons of CFD simulations at engine operating Mach number and Reynolds number conditions to the low-speed wind tunnel simulations indicate that the secondary flow pattern develops similarly up to the location of the shock.