Effect of free-stream turbulence on heat transfer in the turbulent boundary layer. I - Heat transfer and skin friction

The effect of free-stream turbulence on heat transfer and skin friction in developed turbulent boundary layers on a plate is investigated experimentally for Re(x) between 10 to the 4th and 5 x 10 to the 6th, Pr from 0.7 to 100, turbulence levels between 0.1 and 15 percent, and L/delta from 0.2 to 0.5. It is found that for liquids with Pr = 1, the increment of the heat transfer coefficient in the turbulent boundary layer is greater than that of skin fricion. With increasing Pr, the effect of free-stream turbulence on the heat transfer coefficient decreases. The increase in skin friction and heat transfer with turbulence level is asymptotic, the effect being strongest at turbulent levels below 4-5 percent.