H. Wengle et al., The manipulated transitional backward-facing step flow: an experimental and direct numerical simulation investigation, EUR J MEC B, 20(1), 2001, pp. 25-46
Results from a joint experimental and direct numerical simulation (DNS) inv
estigation are presented for the flow over a backward-facing step manipulat
ed by low-amplitude time-periodic (harmonic) blowing/suction excitation thr
ough a narrow slot at the edge of the step. For a Reynolds number of Re-h =
3000 (based on step height, h, and inflow velocity, U-o) and for laminar i
nflow, a 33% reduction of the mean recirculation length (in comparison to t
he non-manipulated reference case) could be obtained with a forcing amplitu
de of the order of one per cent of U-o. Based on the momentum thickness, th
eta, of the incoming laminar boundary layer (at the edge of the step), the
corresponding optimum Strouhal number is St(theta) = f(opt)theta /U-o = 0.0
12. From the experimental data it can be concluded that, in our how case, t
he optimum frequency, f(opt) = 50 Hz, was the most amplified frequency in t
he transition-to-turbulence process of the separated laminar shear layer. D
etailed comparison of the experimental data with data from the numerical si
mulation shows that DNS and experimental data agree up to second-order stat
istics. The joint experimental and numerical investigations exhibit a compl
ementary nature in the sense that, on the one hand, the main advantage of t
he experiment was the relative ease with which a wide range of forcing para
meters could be tested and, on the other hand, DNS could provide spatio-tem
poral details of the how which could not be so easily obtained in the exper
iment. (C) 2001 Editions scientifiques et medicales Elsevier SAS.