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

Abstract


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,