New features of swirling jets
نویسندگان
چکیده
Important new features are found for a family of swirling jets with velocity v;z, where z is the distance from the jet origin. First, there is a sharp minimum of the pressure coefficient at a certain value of the swirl number Sw which is nearly n independent; this feature can be utilized in technological devices. Second, as Sw increases, a separation zone develops, where the fluid is not at rest in the inviscid limit ~contrary to the claims of recent vortex breakdown theories!. These results are obtained under the boundary layer approximation for incompressible jets characterized by n and Sw5vfm /vzm , where vfm and vzm are the maximal values of the swirl and longitudinal velocities at z5const. Unlike prior results viewed in terms of parameter L ~which is the vf /vz ratio at the outer edge of the jet!, the solution dependence on Sw is found similar for both n,1 and n.1. For any n, ~a! the pressure coefficient is minimum at Sw'0.65; ~b! two solutions exist for Sw ,Sw f ~fold value!, none for Sw.Sw f ; ~c! as Sw decreases, the jets either consolidate near the axis or separate from it, depending on the solution branch; and ~d! the flow in the separation zone tends to become swirl-free and potential. © 2000 American Institute of Physics. @S1070-6631~00!01311-8#
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