Fluid dynamics of flat plates and rectangular prisms in the presence of moving surface boundary-layer control

Fluid dynamics of a family of two-dimensional hat plates and rectangular pr isms (aspect ratio of 0.27, 0.5 and 1.0) with moving surface boundary-layer control (MSBC) was carried out employing three complementary approaches: ( i) extensive wind tunnel test program; (ii) finite element-based numerical integration of the complete Navier-Stokes equations; and (iii) flow visuali zation. A comparison between the drag of rectangular prisms of varying aspe ct ratios with sharp and rounded corners reveal substantial drag reduction, even in absence of the MSBC. It suggests fundamentally different fluid mec hanical processes involved. The surface pressure distribution, resultant fo rces, streamline patterns and wake characteristics suggest significant incr ease in the wake pressure, with associated decrease in the drag, in presenc e of the MSBC, Results show increase in the Strouhal number indicating effe ctive decrease in the bluffness. Both the numerical and flow visualization results show narrowing of the wake with increasing momentum injection and e ventual suppression of the vortex shedding. In case of the flat plate, clas sical quasi-steady analysis suggests significant improvement against gallop ing type of instability. Implications of the present study to alleviate flo w-induced instabilities such as vortex resonance and galloping are apparent . (C) 1999 Elsevier Science Ltd. All rights reserved.