<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">Future jet engines&nbsp;are&nbsp;moving towards&nbsp;shorter&nbsp;and thinner&nbsp;intakes&nbsp;to reduce fuel consumption.&nbsp;These intakes&nbsp;present&nbsp;a greater risk of&nbsp;flow separation when operating at high angle of attack or&nbsp;in&nbsp;extreme crosswind. Any separation&nbsp;leads&nbsp;to&nbsp;a&nbsp;complex tip-low total pressure distortion&nbsp;pattern of varying circumferential extent. The aim of this&nbsp;paper&nbsp;is&nbsp;to&nbsp;determine the impact&nbsp;of&nbsp;such distortion patterns on the&nbsp;operating range and&nbsp;stalling behaviour&nbsp;of a&nbsp;low-speed&nbsp;fan.&nbsp;<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">&nbsp;<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">An experimental study of a low-speed&nbsp;rig fan operating in radial tip-low total pressure distortions&nbsp;of varying&nbsp;circumferential extents&nbsp;was completed.&nbsp;Three&nbsp;inflows&nbsp;were considered&nbsp;in detail:&nbsp;clean, axisymmetric tip-low&nbsp;distortion, and half-annulus tip-low&nbsp;distortion&nbsp;(a continuous&nbsp;180°&nbsp;sector of tip-low distorted inflow&nbsp;and&nbsp;clean inflow elsewhere).&nbsp;The performance&nbsp;was measured&nbsp;for each inflow&nbsp;and at&nbsp;the last stable operating point, detailed&nbsp;area&nbsp;traverse&nbsp;measurements were&nbsp;performed at&nbsp;the fan face and&nbsp;the&nbsp;rotor outlet using a five-hole probe.&nbsp;Unsteady casing pressure measurements were&nbsp;also&nbsp;taken&nbsp;at&nbsp;18&nbsp;circumferential&nbsp;locations&nbsp;upstream of the fan during&nbsp;stall events.&nbsp;&nbsp;<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">&nbsp;<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">Axisymmetric&nbsp;tip-low distortion was found to reduce&nbsp;the stability margin by 3.4%&nbsp;of flow&nbsp;coefficient.&nbsp;However, it&nbsp;was found to not change the stalling mechanism&nbsp;relative to clean flow.&nbsp;In both&nbsp;cases, stall&nbsp;was driven by a combination of high incidence onto the rotor&nbsp;tip&nbsp;and the separation of the casing boundary layer.&nbsp;Half annulus tip-low distortion was found to reduce the stability margin by 3.5% of flow coefficient.&nbsp;For this case, the&nbsp;amplitudes&nbsp;of&nbsp;casing&nbsp;pressure&nbsp;disturbances&nbsp;were&nbsp;found to grow in regions of&nbsp;high incidence and&nbsp;to&nbsp;decay rapidly in the undistorted sector.&nbsp;Stall&nbsp;was found to&nbsp;only&nbsp;occur&nbsp;when&nbsp;these&nbsp;disturbances&nbsp;became sufficiently large that they did not&nbsp;fully&nbsp;decay&nbsp;in the undistorted sector.&nbsp;The&nbsp;half-annulus distortion was&nbsp;therefore&nbsp;found to change the stall mechanism.&nbsp;&nbsp;<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">&nbsp;<p class="Paragraph SCXW190332211 BCX9" style="margin: 0px; padding: 0px; font-weight: normal; font-style: normal; vertical-align: baseline; background-color: transparent; color: windowtext; text-align: left; text-indent: 0px">Further unsteady measurements were then taken during stall events in 8&nbsp;different&nbsp;circumferential extents of tip-low distortion.&nbsp;The&nbsp;variation of&nbsp;the&nbsp;maximum amplitude of disturbances at the last stable operating point&nbsp;with circumferential extent of distortion was&nbsp;found to be&nbsp;driven&nbsp;by two factors.&nbsp;When&nbsp;the&nbsp;extent&nbsp;was&nbsp;less than&nbsp;120°,&nbsp;the&nbsp;amplitude of&nbsp;disturbances&nbsp;that&nbsp;were observed to&nbsp;grow&nbsp;was limited.&nbsp;When it was&nbsp;greater than 300°, the small&nbsp;extent&nbsp;of the clean sector limited the&nbsp;distance available for&nbsp;disturbances&nbsp;to&nbsp;decay, such that&nbsp;instability&nbsp;was found to occur&nbsp;almost&nbsp;instantaneously.&nbsp;

An Experimental Investigation Into the Impacts of Varying the Circumferential Extent of Tip-Low Total Pressure Distortion on Fan Stability

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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An Experimental Investigation Into the Impacts of Varying the Circumferential Extent of Tip-Low Total Pressure Distortion on Fan Stability

An Experimental Investigation Into the Impacts of Varying the Circumferential Extent of Tip-Low Total Pressure Distortion on Fan Stability