A frequency domain analysis of surface heat transfer/free-stream turbulence interactions in a transonic turbine cascade
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Results are presented for both mean and fluctuating velocity and heat flux. Mean heat transfer is highest for the smaller length scale grid, but inlet integral length scale appears of limited use in predicting surface heat flux interactions with the observed complex passage flow. While free-stream rms velocity, u', and surface rms heat flux, q', show some correlation with mean heat transfer in the laminar region near the leading edge, no such correlation is seen on the pressure side. Instead, u' decreases along the pressure side while low frequency transitional activity causes q' to increase. Application of laminar heat transfer correlations to the near leading edge region shows some success. However, application of laminar and turbulent heat transfer correlations along the pressure side gives poor results which are likely due to the transitional state of the boundary layer and complex flow.
Frequency domain analysis allowed estimation of scales, frequency, and time lag across the boundary layer of passing flow structures. Coherence between free-stream velocity and surface heat flux was found useful for determining the scale and frequency range of free-stream turbulent structures interacting with the surface heat flux, but did not correlate with mean heat transfer. Suction side coherence was low relative to the pressure side and isolated to a narrow frequency band. Pressure side coherence was broadband with significant low frequency energy near the leading edge. This low frequency energy (larger structures) decayed along the pressure side whilehigher frequency coherent structures were seen to grow.
- Doctoral Dissertations