The interactions of boundary layer flow temperature fluctuations (t′) and velocity fluctuations (u′, v′) together with surface heat flux fluctuations (q′) have been investigated experimentally in a flat plate turbulent boundary layer in order to better understand time-resolved interactions between flow unsteadiness and surface heat flux. A Heat Flux Microsensor (HFM) was placed on a heated flat plate beneath a turbulent wall jet, and a split-film boundary layer probe was traversed above it together with a cold-wire temperature probe. The recorded simultaneous time-resolved u′v′t′q′ data can be correlated across the boundary layer. Results indicate that wall heat transfer (both mean and fluctuating components) is controlled by the u′ fluctuating velocity field. In the presence of high free-stream turbulence (FST), the heat flux is largely controlled by free stream eddies of large size and energy reaching deep into the boundary layer, such that heat flux spectra can be determined from the free-stream velocity field. This is evidenced by uq coherence present across the boundary layer, as well as by similarity in heat flux and u velocity spectra, and by the presence of large velocity scales down to the nearest wall measuring location just above the laminar sublayer.
Two color double pulsed Particle Image Velocimetry (PIV) measurements of simulated turbine film cooling flows have been made for blowing ratios of 0.5, 0.7, and 1.0 in the near field of the film cooling hole, x/d≤2.5. The effect of the vane wake on the rotor film cooling flow is simulated by periodically forcing the film cooling flows at the nnn dimensional reduced frequency. Phase locked measurements at 45 deg. increments of the periodic film forcing (0, 45, 90, 135, 180, 225, 270, and 315 deg.) for free stream turbulence levels of 1 and 17% have been made. The effects of reduced frequencies of 20 and 80, at free stream turbulence levels of 1 and 17% on the spreading of the film cooling jet are investigated. Increases in the jet spread with forcing and free stream turbulence are > 2 times those in the unforced 1% free stream turbulence case.
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