Hanin Prize Seminar - A Fluidic Fence Resulting from the Applicability of the Boundary Layer Independence Principle to Turbulent Flows

Prof. Israel Wygnanski
The 2014 Meir Hanin International Prize Laureate
University of Arizona and Emeritus from Tel Aviv University

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 such flows. Further analysis suggested that turbulent boundary layers over yawed airfoils should obey the same principle; although this idea was debunked for some sixty years. Reexamination of existing experimental results confirmed that mean velocity profiles normal to the leading edge are proportional to the velocity profiles parallel to it. This is a necessary and sufficient condition to make the respective wall stress components also proportional to one another. The result has been proven in the integral sense for turbulent and laminar flows alike and it suggested that there was an error in the interpretation of the old measurements. Based on this precept various older experiments on sweptback wings of finite aspect ratio were reexamined and the result led to the conclusion that in the absence of separation the surface streamlines near the trailing edge of a lifting wing are almost tangential to it. It implied that in practice one has to eliminate or at least reduce the spanwise component of the boundary layer flow before attempting to control the flow separation on such wings. This led to the construction of fluidic fences consisting of sparsely placed small jets emanating periodically along the span of such wings. The results indicated that collective momentum coefficients of the order of 0.1% were able to substantially increase the lift and inhibit the typical wing–tip stall that is so problematic at large angles of sweep back.

The talk will be given in English

Wed, 12-03-2014, 16:30 (Gathering at 16:00)

Classroom, ground floor, Library, Aerospace Eng.

Light refreshments will be served before the lecture


Hanin Prize Seminar – A Fluidic Fence Resulting from the Applicability of the Boundary Layer Independence Principle to Turbulent Flows