The relationship of time-resolved surface heat flux to the turbulent free-stream flow over
a turbine blade is investigated. Measurements are made in a transonic linear cascade with a
modem high pressure turbine blade profile. Time-resolved direct heat transfer measurements are
made with Heat Flux Microsensor (HFM) inserts along the pressure side, and with one HFM
directly deposited on the suction surface near the leading edge. Simultaneous velocity
measurements are made above the heat flux sensors using miniature hot-wire probes. Grids are
used to produce two turbulence fields of constant inlet turbulence intensity, Tu = 5%, but
significantly different integral length scales (Ax). Results are compared with a low free-stream
turbulence baseline condition. Special emphasis is given to frequency domain analysis of the
data via coherence function magnitude and phase, energy spectra, and time auto- arid crosscorrelations.
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.
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