Examination of anisotropy of the small-scale motion in a perturbed low Reynolds number turbulent boundary layer

Hot wire measurements have been made in a turbulent boundary layer subjected to concentrated suction applied through a porous wall strip in order, to examine the influence of suction on the anisotropy of the small-scale motion. Compensated energy spectra and normalised turbulent energy structure function for Kolmogorov normalised wavenumber k1∗<0.2 and Kolmogorov normalised radius r∗ > 20 depart from those for suction rate σ = 0, reflecting a modification in the energy level. This change is a result of the alteration in the large-scale motion. The effect is increased as the suction rate is increased. The degree of anisotropy as measured by the ratio of calculated second-order structure function to the measured second-order structure function (〈(δvc)2〉/〈(δvm)2〉) is increased as σ is increased albeit marginally as distance from the wall normalised by boundary layer thickness (y/δ) is increased. The overall result suggests that suction alter the pseudo-equilibrium and the anisotropy of the small-scale motion.