Effects of freestream turbulence on streamwise pressure measured on a square-section cylinder

Fluid dynamics of a family of two-dimensional flat plates and rectangular prisms (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 visualization. A comparison between the drag of rectangular prisms of varying aspect ratios with sharp and rounded corners reveal substantial drag reduction, even in absence of the MSBC. It suggests fundamentally different fluid mechanical processes involved. The surface pressure distribution, resultant forces, streamline patterns and wake characteristics suggest significant increase in the wake pressure, with associated decrease in the drag, in presence of the MSBC. Results show increase in the Strouhal number indicating effective decrease in the bluffness. Both the numerical and flow visualization results show narrowing of the wake with increasing momentum injection and eventual suppression of the vortex shedding. In case of the flat plate, classical quasi-steady analysis suggests significant improvement against galloping type of instability. Implications of the present study to alleviate flow-induced instabilities such as vortex resonance and galloping arc apparent, (c) 1999 Elsevier Science Ltd. All rights reserved.