Vortex Whistle in Radial Intake
PRATT AND WHITNEY CANADA CORP LONGUEUIL (QUEBEC)
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In a radial-to-axial intake with inlet guide vanes IGV at the entry, a strong flow circulation Gamma can be generated from the tangential flow components created by the IGVs when their setting exceed about halfclosing approx. 45 deg.. The circulation is convected downstream in the gaspath. As the flow area of the gaspath is reduced towards the axial-exit, the initial circulation is stretched. This increases the vorticity intensity as a result of conservation of circulation, leading to a strong audible vortex whistle tone, together with flow energy separation with up to 20 deg. F difference between the hub and the shroud surfaces. A solution of suppressing the vortex whistle was found experimentally. This was achieved by installing 5 fences equally distributed at mid gaspath around the hub surface. Test results indicate that the vortex whistle 100-700Hz can be suppressed by the fences, but at the expense of generating higher broadband noise at higher frequencies. Experimental results demonstrate that the vortex whistle fundamental frequency fo is equal to the swirling flow frequency fs evaluated at the viscous core of a Rankine-vortex model for the tangential flow velocity. It is concluded that a vortex whistle can generally be suppressed by preventing the buildup of vorticity intensity.
- Fluid Mechanics
- Numerical Mathematics
- Hydraulic and Pneumatic Equipment