The internal cooling passages of an advanced gas turbine blade are typically designed with varying aspect ratios from one passage to another due to the nature of the blade design. This study investigates the flow and heat transfer in a two-pass rectangular channel, with an aspect ratio (AR) of 4:1 in the first passage, and 2:1 in the second pass, that follows a 180-deg tip turn. A transient liquid crystal measurement technique (TLC) is used to obtain detailed heat transfer coefficients (HTC) on all surfaces within the flow passages, including the top surface, inner walls, outer walls, and tip wall. The experiments are performed for a range of Reynolds numbers (Re) from 15,000 to 45,000, based on the first pass geometry with pressure drop measurements using pressure taps at channel inlet and outlet. The results show high heat transfer on the first pass tip wall due to flow impingement. Relatively low heat transfer is measured on the second pass tip wall, due to the turning of the flow away from the tip into the second pass. Also, the smooth surface results show heat transfer magnitudes in the second pass are higher than the first pass due to flow acceleration. Moreover, the results show that the corner vortex in the second channel, which can normally be observed in a typical two-pass square duct, is relatively diminished due to the reduction of the cross-sectional area after the turn.   

 

The integration of turning vanes in the 180-degree sharp bend is believed to reduce pressure losses while keeping the heat transfer levels high. Therefore, this study investigates the influence of different turning vane configurations on both pressure loss and local heat transfer distributions. The first vane configuration is one solid-vane with a half-circle cross-section connecting the two flow passages. The second configuration has three broken-vanes with a quarter-circle cross-section; two broken vanes are located downstream in the first passage (entering the turn), and one broken vane is upstream in the second passage (exiting the turn). In addition to the turning vanes, round edges are placed at the sharp corners of the 180-degree turning region in order to further reduce pressure losses through the channel. Detailed heat transfer coefficients are obtained on all of the multi-pass surfaces as well as the turning vane’s inner and outer surfaces. Also, the pressure drop is measured for each of the turning vane configurations and compared to the reference, smooth case.  

      

*Key Words: Transient Liquid Crystal Technique, Internal flow, Turning Vanes, Pressure loss, Heat Transfer Enhancement.*

 


Heat Transfer and Pressure Loss in a Two-Pass, Rectangular Channel Featuring a Reduced Cross-Sectional Area After the 180-Degree Tip Turn With Different Turning Vane Configurations

Division / Sponsor:
International Gas Turbine Institute (IGTI)

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

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