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Published on:2015-1-8 9:41:54 Hits:

1. And phenomena produced Karman vortex street

To illustrate generate Karman vortex street, we consider viscous fluid flow around a cylinder flows. When the fluid velocity is very low, the forward stagnation point flow velocity is zero, current flow along the sides of the cylinder to about the first half of the cylinder speed is gradually increased, the pressure drop, the second half of the speed drop, the pressure rise, after resident rate to zero again. Then the flow of ideal fluid flow system the same cylinder, no vortices, as shown in Figure 3-7a.

With increasing flow velocity, the pressure gradient increases the latter part of the cylinder, causing separation of the fluid boundary layer, as shown in Fig. 3-7b. When the Reynolds number Re to flow and then increase to around 40, because after half a cylinder boundary layer of fluid micelles by larger block, produces a pair of S at the separation point of the boundary layer Instead rotationally symmetric vortex. As shown in Figure 3-7c.

Stay within a certain range of Reynolds numbers Re, stable Karman vortex street and vortex shedding frequency is proportional to the flow rate of fluid.

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