Effect of free stream turbulence on the turbulent boundary layer

Abstract It is pointed out in the present study that by allowing the entrainment of free stream turbulence into the turbulent boundary layer and performing an overall turbulent energy balance, very satisfactory quantitative predictions of the effect of free stream turbulence upon the turbulent boundary layer behavior can be made. Furthermore, both theory and experiment indicate a 30 per cent increase in wall friction arising from a free stream turbulence level of only 5 per cent. Since it is felt that some sort of Reynolds analogy would hold, it is suggested that the frequently quoted result of little direct effect of free stream turbulence level on the heat transfer other than a movement of the transition point may be valid only at low Reynolds numbers.