Combined influence of the Reynolds number and localised wall suction on a turbulent boundary layer

This paper considers the effect the Reynolds number has on a turbulent boundary layer that is subjected to concentrated suction, applied through a short porous wall strip. The response of the skin friction coefficient to suction is strongly modulated by the momentum thickness Reynolds number R (theta 0). The magnitude and wavelength of the variation of the skin friction decrease as R (theta 0) increases. Measurements clearly show that it is the combination of R (theta 0) and the suction rate sigma that controls the boundary layer response. Relaminarisation of the near-wall flow, which occurs just downstream of the suction strip when sigma =5.5 and R (theta 0)=660, could not be achieved at higher Reynolds numbers. It is suggested that the ratio R (theta 0)/ sigma should not exceed a (as yet undetermined) critical value if pseudo-relaminarisation is to occur. The mean velocity profiles differ from the undisturbed profile for all the values of R (theta 0) and sigma considered here. Although the redistribution of the turbulent kinetic energy among the normal Reynolds stresses is affected by sigma, a variation in R (theta 0) does not appear to alter the effect of sigma on this redistribution.