An Aerothermal Investigation of Purge Flow Behaviour in a Linear Turbine Cascade with Upstream Wakes

摘要

Background: Over all efficiency of a turbofan engine can be improved by increasing turbineinlet temperature. To withstand the high turbine inlet temperatures advanced cooling techniques androbust materials are required. Air supplied from compressor can be used to purge turbine componentsand disk cavities from the incoming hot gas.Objective: In the present study, an attempt is made to understand the aerodynamic and thermal effectscaused by the purge flow in the presence of stationary upstream wakes.Methods: Reynolds Averaged Navier Stokes Equation coupled with SST turbulence model is used forcomputational study. Base case experimental data conducted on a 5 blade linear cascade is used fornumerical validation. The coolant to mainstream blowing ratio is varied from 0.2 to 1.2 with a step sizeof 0.2.Results: It is observed that with an increase in the blowing ratio, the mass averaged total pressure lossesalso increase. Purge flow shifts the passage vortex away from the endwall and causes significant overturningup to a span of 30-40mm, before they exhibit underturning up to midspan. In an effort to reducethe losses, purge ejection angle is reduced to 45° from 90°. Significant loss reduction and improvedendwall protection are observed at 45° ejection angle. This ejection angle provides enough accelerationand momentum to the fluid inside the endwall boundary layer. But the upstream secondary wakes andsecondary flows enhanced the mixing losses within the blade passage.Conclusion: The turbulent mixing generated by upstream wakes reduced the film cooling effectivenessover the endwall. The numerical results show that film cooling effectiveness can be improved by reducingthe purge ejection angle. Various patents have been discussed in this article.