Investigation of Microjet Engine Inlet Pressure Distortions at Angled Inflow Velocity Conditions

The Armfield CM14 microjet axial flow turbine engine has been tested in open space at ambient conditions with engine inlet pressure at the aerodynamic interface plane (AIP) measured by a built-in pressure sensor for validating computational fluid dynamics (CFD) studies. A three-dimensional computational domain of the test engine intake duct configuration is defined, followed by mesh convergence studies. The latter results in a fine mesh of 5.7 million cells on which CFD-predicted engine inlet pressures are in good agreement with the experimental measurements at the AIP face for 20–100% throttles. CFD studies are continued to investigate the engine inlet pressure distortions at two inflow velocities of 35 m/s and 70 m/s, and various inflow angles ranging from 0° to 30° with a step of 5°, to evaluate their impacts on engine inlet pressure distortions. It is found that pressure distortions increase with the inflow angle, with severe pressure distortions occurring at higher inflow angles above 15°. At the same flow conditions of inflow angle and velocity, pressure distortions from an intake with a flat lip are overall higher than those of a bell-mouth round lip. This is primarily due to a rapid geometry change at the intake entrance causing large vortical flow motions, accompanied by local flow separations at higher inflow angles, therefore impacting the downstream flow field towards the engine inlet.