On the applicability of the boundary layer independence principle to free and bounded turbulent flows in absence of pressure gradient

Recent observations in a turbulent mixing layer emanating from a skewed trailing edge indicated that within the context of the boundary layer approximation the “Independence Principle” applies to yawed turbulent mixing layers of infinite aspect ratio. The observations were carried out at two different velocity ratios to ensure that the wake generated by a splitter plate did not affect these observations. The analysis suggests that turbulent boundary layers over yawed flat plates should obey the same principle; although this idea was debunked some sixty years ago. Reexamination of existing results confirmed that the mean velocity profiles normal to the leading edge are proportional to the velocity profiles parallel to it. This is the necessary and sufficient condition to make the wall stress components normal and parallel to the leading edge also proportional to one another. This has been proven in the integral sense for turbulent and laminar flows alike.