Question

Which one the below is not true for the given figure? the downstream and upstream part of this object. between the downstream and upstream part of this object and 12. (4p) a. The drag force consist of only the frietional drag for this object. b. The drag force is formed due to the pressure difference between c. The drag force is formed both due to the pressure difference the frictional forces d. It is possible to obtain a lift force by using an angle of attack with respect to the incoming flow for this flat plate Good luck Dr. Bureu Erba

Answer 1

Force in the direction of flow exerted by the fluid on the solid is called drag.

a stationary smooth sphere of diameter D_P situated in a stream, whose velocity far away from the sphere is uµ to the right. Except at very low velocities, when the flow is entirely laminar, the wake immediately downstream from the sphere is unstable, and turbulent vortices will constantly be shed from various locations round the sphere. Because of turbulence, the pressure on the downstream side of the sphere will never fully recovered to that on the upstream side, and there will be a form drag to the right of the sphere. (For purely laminar flow, the pressure recovery is complete, and the form drag is zero.)

In addition, because of the velocity gradients that exist near the sphere, there will also be a net viscous drag (also called as wall drag) to the right (In potential flow there is no wall drag). The sum of these two effects is known as the (total) drag force, F_D. A similar drag occurs for spheres and other objects moving through an otherwise stationary fluid - it is the relative velocity that counts.

The Bernoulli principle says that for an inviscid fluid, an increase in fluid velocity causes a decrease in pressure. For lift producing shapes, the fluid must travel faster over the shape than under which mean the pressure below is higher than above

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