The Experimental study of the bluff body aerodynamics and vortex-shedding behaviour

SUMMARY THE EXPERIMENTAL STUDY OF THE BLUFF BODY AERODYNAMICS AND VORTEX SHEDDING BEHAVIOUR Flow parameters around bluff-bodies are too complex. In spite of many investigation on this subject nave been made, relatively little is known about them. The subject of bluff-body flows has recently been receiving a great of attention, because of its importance for energy conservation. Large structures must be designed so as to avoid wind-induced large-amplitude oscillations. Wind flowing around bluff bodies and structures results in a distribution of pressure to produce mean and local forces which may damage or uncomfortably vibrate the body. Engineers began to incorporate the influence of the wind in their designs during nineteenth century. Flow parameters around bluff-bodies, turbulence intensity and vortex-shedding create dynamic forces on the system. Vortex-shedding is an important phenomenon which occurs around circular or rectangular cylinders and airfoils or plates inclined at high angles of attack. Fluctuating forces which are produced from vortex shedding, may vibrate structures in their nature frequencies. For these reasons, the investigation of vortex shedding around bluffbodies is important for aerodynamic forces, structural vibration and turbulent mixing. In this study, flow parameters and pressure distrubition around circular cylinders which the separation points change with Reynolds number and rectangular section cylinders with different aspect ratios in the range 0.5^w/h^2, which the separation points are almost fixed, are experimentally investigated in the Reynolds number ranging from lxl 04 to 1.5x1 05 (in the subcritical region). Furthermore, to determine parameters which influence on the turbulence instability, spectral measurements have been made in the wake of the circular cylinder and the rectangular cylinder with different angles of attack. From these measurements, the distributions of spectral density, power spectrum, auto-correlation and cross-correlation in the wake of models were determined. Vortex shedding behaviour depending on the models and flow parameters were obtained. Key- Words : Bluff Body, Vortex-Shedding, Bluff Body Aerodynamic, Wake, Wake Flow, Seperation VI