Abstract
A spectral analysis was made for a boundary layer undergoing laminar-turbulent transition over a heated flat plate with free-stream turbulence intensities of 0.5% and 6.4%. Detailed boundary-layer measurements were made with a three-wire probe that simultaneously measured two velocity 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 investigated. The results showed that the location of maximum turbulence production (y/d ∼ 0.1) coincided with the peak location of u′; whereas, the region of high turbulent shear (y/d ∼ 0.35) produced little turbulence energy. The power spectrum of t$́was mostly correlated with u′ in the early to middle transitional flow, but it was significantly correlated with v′ in the late transitional and early turbulent flow regions. The dissipation power spectra for both u′ and v′ evolved faster than their turbulence power spectra. vt seems to be transported by smaller eddies than ut. A hypothetical energy transfer process during laminar-turbulent transition was then proposed.
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