THE STRUCTURE OF AVERAGED FLOW BEHIND A BACKWARD-FACING STEP IN A SLOTTED CHANNEL

The results are given of an experimental investigation of the structur e of averaged Row behind a backward-facing step flown about by a turbu lent flow of air in a slotted channel. The fields of two components of averaged velocity of Row are measured by a laser Doppler anemometer, manufactured by Dantec Electronic A/C (Denmark), in the subsonic range of forward flow velocity, corresponding to the range of Reynolds numb ers of 2600-11200 calculated by the step height, An analysis of the re sultant velocity fields enables one to reveal that the position of the boundaries and longitudinal and transverse axes of the main and secon dary recirculation vortices is independent of the velocity of forward flow in the investigated range, as well as to propose simple approxima tion formulas for their description. The results of a special investig ation of the distribution of the tangential derivative of the averaged component W demonstrate that the averaged held of velocity behind a s tep may be treated as two-dimensional. The approximation of the measur ed profiles of longitudinal velocity to the Falkner-Skan profile (m = 0.7) in the wall region of the main recirculation vortex points to lam inarization of flow in this zone.