SPECTRAL-ANALYSIS OF BOUNDARY-LAYER-TRANSITION ON A HEATED FLAT-PLATE

A spectral analysis was made for a boundary layer undergoing laminar-t urbulent transition over a heated flat plate with free-stream turbulen ce intensities of 0.5% and 6.4%. Detailed boundary-layer measurements were made with a three-wire probe that simultaneously measured two vel ocity components and the temperature. The power spectra of u', v', and t', as well as their co-spectra, were analyzed. The spectral analogy and the differences between the momentum and thermal transports were i nvestigated. The results showed that the location of maximum turbulenc e production (y/d approximate to 0.1) coincided with the peak location of u'; whereas, the region of high turbulent shear (y/d approximate t o 0.35) produced little turbulence energy. The power spectrum of t' wa s mostly correlated with u' in the early to middle transitional flow, but it was significantly correlated with v' in the late transitional a nd early turbulent flow regions. The dissipation power spectra for bot h u' and v' evolved faster than their turbulence power spectra. vt see ms to be transported by smaller eddies than ut A hypothetical energy t ransfer process during laminar-turbulent transition was then proposed.