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Unformatted text preview: Drag and Momentum Balance Aerodynamic drag is exerted on an object when fluid flow passes through it. This force is due to a combination of the shear and pressure forces acting on the surface of the object. The determination of these forces is difficult since it involves the measurement of both velocity and pressure fields near the surface of the object. However, based on the momentum balance concept, this force can also be determined as carrying out the momentum balance around the object. Drag force on a circular cylinder (unit width 1m) will be given here as an example. As shown below, velocity profiles before and after the cylinder are measured. Determine the drag force acting on the cylinder by assuming uniform pressure at the measuring stations. 1 m V in =50 m/s u(y)=50 (m/s), |y|>1 =20+30|y| (m/s), |y| 1 x y (1) (2) (3) (4) (5) Control Volume and Control Surfaces 1 m x y (5) (1) (2) (3) (4) Consider a control volume surrounding the cylinder as shown in the previous slide. Assume the flow around the cylinder is symmetric, therefore, only half of...
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