Experimental investigation on the aerodynamic loads and wake flow features of low aspect-ratio triangular prisms at different wind directions

The results are described of measurements of the mean and fluctuating forces acting on low aspect-ratio triangular prisms placed vertically on a plane, having isosceles triangular cross-section with 60∘ or 90∘ apex angles and aspect ratios ranging from 1.0 to 3.0. The tests are carried out in a wind-tunnel by varying the wind direction, θ, between 0∘ and 180∘, at a Reynolds number Re ≃1.2×105. Furthermore, for the model with apex angle of 60∘ and aspect ratio 3.0, flow visualizations with tufts and hot-wire measurements are performed, which permit to characterize the wake morphology as a function of wind direction and to assess that an alternate vortex shedding always exists, with a frequency that is roughly inversely proportional to the wake width. The force measurements show that large variations in the mean values of the drag and cross-flow forces occur by varying θ, in strict correspondence with changes in wake flow features. The intensity of the fluctuating cross-flow forces, directly connected with vortex shedding, is found to vary significantly with flow orientation and aspect ratio, and to be approximately proportional to the streamwise projection of the body surface immersed in the separated wake. Finally, an increase in vortex shedding frequency is generally found with decreasing aspect ratio.

[1]  Tetsuya Kitagawa,et al.  An experimental study on vortex-induced vibration of a circular cylinder tower at a high wind speed , 1997 .

[2]  W. F. Lindsey,et al.  Drag of Cylinders of Simple Shapes , 1937 .

[3]  T. Fox,et al.  The aerodynamic disturbance caused by the free-ends of a circular cylinder immersed in a uniform flow , 1993 .

[4]  Cheol Woo Park,et al.  Free end effects on the near wake flow structure behind a finite circular cylinder , 2000 .

[5]  Yozo Fujino,et al.  Wind pressures measurement on end-cell-induced vibration of a cantilevered circular cylinder , 2002 .

[6]  Dominique Laurence,et al.  Large Eddy Simulation of Turbulent Flow for Wall Mounted Cantilever Cylinders of Aspect Ratio 6 and 10 , 2007 .

[8]  S. C. Luo,et al.  Effects of incidence and afterbody shape on flow past bluff cylinders , 1994 .

[9]  Yukisada Sunabashiri,et al.  Vortex Shedding From a Circular Cylinder of Finite Length Placed on a Ground Plane , 1992 .

[10]  K. Karamcheti,et al.  An experiment on the flow past a finite circular cylinder at high subcritical and supercritical Reynolds numbers , 1982, Journal of Fluid Mechanics.

[11]  M. Adaramola,et al.  Turbulent wake of a finite circular cylinder of small aspect ratio , 2006 .

[12]  D. .. Farivar,et al.  Turbulent uniform flow around cylinders of finite length , 1981 .

[13]  Seung-O Park,et al.  Vortical flow over the free end surface of a finite circular cylinder mounted on a flat plate , 2003 .

[14]  S. Srigrarom,et al.  Flow field of self-excited rotationally oscillating equilateral triangular cylinder , 2008 .

[15]  Stephen R. Turnock,et al.  Measurements of the flow over a low-aspect-ratio cylinder mounted on a ground plane , 2005 .

[17]  Guido Buresti,et al.  Large-eddy simulation of the flow around a triangular prism with moderate aspect ratio , 2006 .

[18]  D. Sumner,et al.  Wake structure of a finite circular cylinder of small aspect ratio , 2004 .

[19]  Hiroshi Sakamoto,et al.  Flow Around a Normal Plate of Finite Width Immersed in a Turbulent Boundary Layer , 1983 .

[20]  S. El-Sherbiny.  Flow separation and reattachment over the sides of a 90° triangular prism , 1983 .

[21]  Yang Liu,et al.  A finite cantilevered cylinder in a cross-flow , 2005 .

[22]  Guido Buresti,et al.  On the analysis of fluctuating velocity signals through methods based on the wavelet and Hilbert transforms , 2004 .

[23]  Jochen Fröhlich,et al.  LES of the flow around a circular cylinder of finite height , 2004 .

[24]  M. Budair,et al.  Frequency measurements in a finite cylinder wake at a subcritical Reynolds number , 1991 .

[25]  Hiroshi Sakamoto,et al.  Vortex shedding from a rectangular prism and a circular cylinder placed vertically in a turbulent boundary layer , 1983, Journal of Fluid Mechanics.