ENHANCED HEAT-TRANSFER AND SHEER STRESS DUE TO HIGH FREE-STREAM TURBULENCE

Surface heat transfer and skin friction enhancements, as a result of f ree-stream turbulence levels between 10 percent < Tu < 20 percent, hav e been measured and compared in terms of correlations given throughout the literature. The results indicate that for this range of turbulenc e levels, the skin friction and heat transfer enhancements scale best using parameters that are a function of turbulence level and dissipati on length scale. However, as turbulence levels approach Tu = 20 percen t, the St' parameter becomes more applicable and simpler to apply. As indicated by the measured rms velocity profiles the maximum streamwise rms value in the near-wall region, which is needed for St', is the sa me as that measured in the free stream at Tu = 20 percent. Analogous t o St', a new parameter, Cf', was found to scale the skin friction data . Independent of all the correlations evaluated the available data sho w that the heat transfer enhancement is greater than the enhancement o f skin friction with increasing turbulence levels. At turbulence level s above Tu = 10 percent, the free-stream turbulence starts to penetrat e the boundary layer and inactive motions begin replacing shear-stress producing motions that are associated with the fluid/wall interaction . Although inactive motions do not contribute to the shear stress, the se motions are still active in removing heat.