Experimental Study of the Endwall Heat Transfer of a Transonic Nozzle Guide Vane With Upstream Jet Purge Cooling: Part 1 — Effect of Density Ratio

Abstract

Nozzle guide vane platforms often employ complex cooling schemes to mitigate ever-increasing thermal loads on endwall. Understanding the impact of advanced cooling schemes amid the highly complex three-dimensional secondary flow is vital to engine efficiency and durability. This study analyzes and describes the effect of coolant to mainstream blowing ratio, momentum ratio and density ratio for a typical axisymmetric converging nozzle guide vane platform with an upstream doublet staggered, steep-injection, cylindrical hole jet purge cooling scheme. Nominal flow conditions were engine representative and as follows: Maexit = 0.85, Reexit/Cax = 1.5 × 106 and an inlet large-scale freestream turbulence intensity of 16%. Two blowing ratios were investigated, each corresponding to upper and lower engine extrema at M = 3.5 and 2.5, respectively. For each blowing ratio, the coolant to mainstream density ratio was varied between DR = 1.2, representing typical experimental neglect of coolant density, and DR = 1.95, representative of typical engine conditions. An optimal coolant momentum ratio between = 6.3 and 10.2 is identified for in-passage film effectiveness and net heat flux reduction, at which the coolant suppresses and overcomes secondary flows but imparts minimal turbulence and remains attached to endwall. Progression beyond this point leads to cooling effectiveness degradation and increased endwall heat flux. Endwall heat transfer does not scale well with one single parameter; increasing with increasing mass flux for the low density case but decreasing with increasing mass flux of high density coolant. From the results gathered, both coolant to mainstream density ratio and blowing ratio should be considered for accurate testing, analysis and prediction of purge jet cooling scheme performance.