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Inlet-Air Distortion Effects on Stall Surge, and Acceleration Margin of a Turbojet Engine Equipped With Variable Compressor Inlet Guide Vanes


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The turbojet engine was investigated in an altitude test chamber at the NACA Lewis laboratory to determine the effects of a wide range ofuneven inlet-air pressure distributions on transient characteristics and stall phenomenon. Circumferential, radial, and mixed pressure variations were run at simulated altitudes of 15,000, 35,000, and 50,000 feet at a simulated flight Mach number of 0.80. In the range investigated, circumferential distortions did not change the span-wise blade loading or seriously impair operation. Surge occurredwhen any segment of the compressor reached the undistorted surge pressure ratio. Radial distortions with low pressure at the rotor blade tip increased the loading in a region that was normally heavily loaded. Serious reductions in acceleration margin resulted; slightly larger distortions than those investigated may completely prevent acceleration. Inverse radial (low pressure at the hub) distortions increased acceleration margin at lower speeds, though some reductions occurred at high speeds. Mixed (combination circumferential and radial or inverse radial) distortions produced changes similar to the corresponding radial distortion alone.



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