Combined Influence of Free-Stream Turbulence and Favorable Pressure Gradients on Boundary Layer Transition and Heat Transfer

摘要

Experimental research was conducted to examine the combined effects of free-stream turbulence and streamwise acceleration on transitional boundary layer flows. During this period convective heat transfer coefficients, boundary layer mean velocity and temperature profile data, and wall static pressure distribution data were obtained for four combinations of streamwise acceleration and free-stream turbulence intensity. Free-stream multicomponent turbulence intensity, longitudinal integral length scale, and spectral distribution data were obtained for the four test cases. The profile results indicate that the data are accurate and consistent and that the experimental boundary layers were highly two-dimensional. The freestream turbulence distributions generated for these tests have been shown to be both homogeneous and nearly isotropic. It is anticipated that these results will provide a needed set of fundamental, well documented experimental test cases to which analytical predictions can be compared. Examinations of the transitional profile shape factors and wall heat transfer distribution data indicate that fully turbulent mean velocity profiles are achieved upstream of fully turbulent wall heat transfer rates. The present data suggest that the turbulent mean velocity profile is established in a shorter length than is required for the development of the equilibrium turbulence distribution. Transition location data obtained in the present program agree very well with data from other flat wall studies. Suggested correlation curves are given for predicting flat wall transition locations with the combined effects of free-stream turbulence and streamwise acceleration.