Free stream turbulence induced disturbances in a uniform suction boundary layer

Författare: Fransson, J. H. M., Alfredsson, P.H.
Dokumenttyp: Konferens
Tillstånd: Publicerad
Tidskrift: 53rd Meeting of the APS Division of Fluid Dynamics, Nov. 19-21, Washington (D.C.), USA. Abstract in Bull. Am. Phys. Soc.
Volym: 45  
År: 2000


An experimental set-up has been developed to establish the asymptotic suction profile boundary layer in the MTL-wind tunnel. A flat plate with an insert (2.25 m long and 1 m wide) of smooth porous material is used and at a free stream speed of 5 m/s a suction speed of 1.4 cm/s gives a boundary layer of 5 mm thickness. The experiments show good agreement of the decay rate for 2D waves as compared with linear stability calculations. Free stream turbulence gives rise to regions of high and low velocity (streaky structures) and in a Blasius boundary layer the streamwise disturbance energy grows in linear proportion to the downstream distance. In the case with suction the growth seems to be eliminated and the disturbance level saturates, the saturation level depends on the level of FST. The streamwise velocity disturbance profile has in both cases a maximum close to 1.5 times the displacement thickness. Two-point correlation show that the spanwise scale of the streaky structures is only slightly decreased by suction, despite a twofold reduction in boundary layer thickness, indicating the importance of the scale of the FST.