First stage nozzle guide vane platforms often employ complex cooling schemes to mitigate the ever-increasing thermal load on endwall. Understanding the impact of advanced cooling schemes amid the highly complex three-dimensional secondary flows is vital to engine efficiency and durability. The study presented herein analyzes and describes the effect of coolant to mainstream density ratio on endwall thermal performance at varying blowing rates for a typical nozzle guide vane platform jet purge cooling scheme. An axisymmetric converging endwall with an upstream doublet staggered steep injection cylindrical hole jet purge cooling scheme was investigated. Nominal flow conditions were engine representative and as follows: Ma_Exit = 0.85, Re_Exit,C_ax  = 1.5 × 10\^6, and an inlet large-scale freestream Tu = 16%. Two blowing ratios were investigated corresponding to the upper and lower engine extrema, M = 2.5 and 3.5 respectively. Each blowing ratio was investigated amid two density ratios; one representing typical experimental neglect of density ratio, at DR = 1.2, and another engine representative density ratio achieved by mixing foreign gases, DR = 1.95. All tests were conducted on a scaled linear cascade in the Virginia Tech Transonic Blowdown Wind Tunnel using IR thermography and transient data reduction techniques. Oil paint flow visualization techniques were used to gather qualitative information regarding the alteration of endwall flow physics due to two different blowing rates of high-density coolant. High resolution endwall adiabatic film cooling effectiveness, Nusselt number, and Net Heat Flux Reduction contour plots were used to analyze the thermal effects of both parameters.

The effect of coolant density varies greatly with coolant to mainstream blowing ratio. At low coolant blowing rates, increased coolant density results in more favorable thermal performance near-hole, but lack of coolant momentum results in increased endwall exposure near pressure and suction sides, leading to potential hot spots. Conversely, density ratio had minimal effects at the high blowing condition due to increasingly dominant momentum effects. Increased coolant blowing rate at engine representative density ratio increased coolant effectiveness in high secondary flow regions near pressure and suction sides due to increased coolant momentum. However, augmented local freestream turbulence as a result of jet detachment decreased thermal performance at passage onset. From these results, both non-dimensional coolant flow parameters should be matched for accurate analysis and prediction of cooling scheme performance.


Experimental Study of the Endwall Heat Transfer of a Transonic Nozzle Guide Vane With Upstream Jet Purge Cooling: Part 1 \u2014 Effect of Density Ratio

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

Turbo Expo - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.