Figure 2. Instantaneous turbulent kinetic energy deficit for a turbulent boundary layer with a turbulent free-stream (u’/U = 0.12)

Boundary layers with Free-stream Turbulence


Turbulent boundary layers are one of the primary areas of research and theory advancement in modern fluid mechanics.  These flows are often studied with an approximately laminar free-stream, however, in many applications the free-stream is in fact turbulent. 

The present investigation studies the effect of free-stream turbulence on the phenomenology of a turbulent boundary layer.  An active grid is used to generate the free-stream turbulence (Figure 1).  The active grid provides a wide range of variability to both the length scales in the turbulence as well as the turbulence intensity. 

It is found that the boundary layer under the influence of free-stream turbulence consists of similar mean structure when compared at constant shear levels to a canonical turbulent boundary layer.  However, several other phenomena, such as the appearance of a distinct interface where the energy from the boundary layer no longer penetrates into the mean flow, or the existence of uniform momentum zones, appears to be destroyed by the free-stream turbulence.

Project leader : Eda Dogan,

Secondary investigator: Dr R. Jason Hearst

Main supervisor(s): Prof. Ganapathisubramani,