Drag Measurement On 2-Dimensional Bodies Using Wake Survey Method

Abstract

Wide research has been done in the field of flow around a circular cylinder to understand the flow physics around it. When fluid flows around a cylinder, the flow separation may takes place and the flow becomes unsteady which may results in increase in the drag force and may also induce vibration. The wake induced drag around the cylinder can be evaluated by determining the momentum deficit created in the wake region due to presence of the cylinder. In the present study, the Numerical as well as Experimental investigations were carried out to analyse the wake region of the cylinder. Initially, numerical analysis of flow around the cylinder was carried out in the transient state condition in FLUENT software at five different wind velocities i.e. 6, 12, 18, 23 and 27 m/s. For the experimental work 1” diameter (D) stainless steel cylinder was selected. The experiments were carried out in the subsonic wind tunnel available at Nirma University. The wind tunnel was calibrated using pitot-tube and micro-manometer. In order to measure the pressure on the surface of the cylinder, eight pressure tapings were provided at an angle of 45° in the central plane of the cylinder. The wake measurement setup was comprised of hollow NACA 0020 profile airfoil (chord length of 135 mm) shaped container installed at a distance of 3 x D (downstream of cylinder) in the test section of the wind tunnel. On the leading edge of the airfoil, twelve numbers of pressure tapings were provided which were connected with multi-tube manometer for the pressure measurement. Based on the pressure readings, pressure drag acting on the cylinder was determined. The experiments were carried out on flow over cylinder at five different wind velocities. Fluid flow visualization was carried out near the cylinder surface using tufts. The pressure coefficient and drag coefficient were evaluated from the experimental readings. From the analysis it was found that the drag coefficient decreased with increase in the Reynolds number. The CFD analysis results were validated with the experimental results and the error was found less than 10%.