Experimental Determination of Organized Fluctuating Fluid Forces acting on the Finite Circular Cylinders with Different Aspect Ratios

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The organized fluctuating fluid forces acting on finite circular cylinders with aspect ratios of 1 to 12 located on the ground plate in a uniform flow have been determined experimentally. The fluctuating pressures on the cylinder surface were processed using the conditional sampling technique, for which the filtered fluctuating velocity signals with well defined frequencies at which the clear organized behaviors can be confirmed in the analysis with FFT.The local and global organized fluctuating fluid forces have been obtained from these results, and the influences of aspect ratios on the details of the organized fluctuating fluid forces have been discussed. The results obtained from the present research project can be summarized as follows :(1) The aerodynamic characteristics of the finite circular cylinders are severely affected by the aspect ratios, but the general characteristics can be classified in two cases. The first is the case for the cylinders with large aspect ratios as high as more than 7 or 8, which can be called "high aspect ratio cylinder", and the other is the case for the cylinders with low aspect ratios smaller than 7 or 8, which can be called "low aspect ratio cylinder".(2) In the case of high aspect ratio cylinders, many noticeable organized fluctuating fluid forces have been confirmed. The three organized fluctuations with different frequencies and different natures on the side wall appears as well as two organized fluctuations on the top.(3) In the case of low aspect ratio cylinders, only a single noticeable organized fluctuating fluid force have been detected on the side wall and the top. On the side wall of the cylinders a fluctuation corresponding to the Karman's vortex street appears with Strouhal numbers from 0.15 to 0.21. For the cylinders with aspect ratios of 2 or 3, a organized fluctuation corresponding to the Karman's vortex street can be also detected on the top surfaces.