An Improved Empirical Correlation for Boundary Layer Transition Considering the Effects of Both the Streamwise Pressure Gradient and Freestream Turbulence Intensity

the empirical correlation for prediction of the onset of boundary layer transition, presented previously by Taghavi et al., was extended by taking into account both the effects of the streamwise pressure gradients and the freestream turbulence intensity. The correlation was derived based on experimental data of transitional boundary layers subjected to different freestream turbulence intensities and streamwise pressure gradients, obtained by authors and other researchers. The author’s experiments were carried out in two different free stream turbulence levels and four different pressure gradients. A single hot-wire probe was used for measurements of instantaneous flow velocities within the boundary layer. Experiments were conducted in an open circuit wind tunnel of suction type. For each pressure gradient in a distinct free stream turbulence level, the mean longitudinal velocity and root mean square, RMS, of the velocity fluctuations were obtained at several streamwise locations. Experimental results were used to determine variations of streamwise skin friction coefficient and boundary layer shape factor versus the local Reynolds number. Based on the available measurements and mathematical models, an improved empirical correlation was developed. Comparisons with other existing empirical correlations show that the new correlation was more consistent with experimental data.