Effect of Free-stream Turbulence Properties on Boundary Layer Laminar-Turbulent Transition: A New Approach

The effect of length scale on flat-plate by-pass transitional boundary layers subject to free stream turbulence intensities ranging from 1.3 to 6.0 percent has been investigated. The analysis is based on the recent experimental and numerical observations into non-equilibrium flows that considering the effect of turbulence properties at the plate leading edge on the transition onset. According to this analysis, physical correlation is developed and incorporated in a conventional boundary layer computer scheme for prediction of transitional flows. The scheme was proposed to calculate the characteristics of the boundary layers under the effect of moderate free-stream turbulence levels by enhancing established integral techniques in conjunction with intermittency weighted model of the transitional boundary layer. To support the results validation, the experimental ERCOFTAC Test Cases T3A, T3B and T3AM for transitional integral parameters have been represented. The results show that the transition location for turbulence level higher than 4% is only a function of turbulence intensity (Tu) and unaffected by significant changes in the length scale (L-x). Whereas for low level of the incoming turbulent flows the transition onset is extremely dependent on FST characteristics, turbulence intensity and integral length scale.