Study And Optimization On Aerodynamic Performance Of APU Intake System Containing Perforated Plate

The aerodynamic performance of APU (Auxiliary Power Units) intake system is advancing withthe development of aircraft. APU intake system is different from the main propulsion engine inlet dueto its special configuration, it is usually naming exterior inlet duct that from intake flap to anti-foreignobject damage and interior inlet duct that from anti-foreign object damage to compressor inlet. Inorder to provide a reference for the design and optimization of the APU intake system, theaerodynamic performance of a typical APU interior inlet duct with dual compressors and perforatedplates was studied and optimized using CFD (computational fluid dynamics) and experimentalmethod.The use of3D CFD and experimental methods for the basis of APU intake system model (thebasis of inlet duct and perforated plates, its orifice ratio of0.479) and other orifice ratios model, twoflow allocation cases were researched: the fixed proportion(1.67) and the total mass fluxes(0.6kg/s).The result shows: the total pressure loss of APU intake system consists of several factors: throttle,mixing near the perforated plates; collision, turning in duct and boundary layer. The total pressurerecovery coefficient of two outlet with increasing mass fluxes decrease slightly in given total massfluxes and linearity in fixed proportion. Total pressure distortion is mainly affected by the perforatedplates area without holes in circumferential direction and by duct curvature in radial direction,distortion index value is minimizing (DC60<7‰).With the increase of orifice ratio, the total pressurerecovery coefficient increase accordingly. The total pressure distortion of power section is mainlyinfluenced by radial in different orifice ratios; but load section is mainly influenced by around insmall orifice ratio and by radial in large orifice ratio.The aerodynamic performance optimization of APU intake system was conducted. Theoreticalanalysis found that perforated plates losses mainly depend on the orifice ratio, inlet duct loss dependon the geometric parameters. The inlet profiles of Meridian cross-section and perforated plates wereoptimized using CFD, inlet duct was enlarged throat area and turning radius, perforated plates wereamplified orifice rate to0.544.At the same time3D CFD and experimental investigation into optimization model (optimizationof inlet duct and perforated plates) were presented. The results show: its aerodynamic performance isbetter than the basis model, the total pressure loss of both outlet respectively reduced by2.42%and3.04%and the distortion (DC60) also improve slightly in design condition, the perforated plates optimization more obvious impact on load section. The computational and experimental resultsdemonstrated the coupling of inlet duct and the perforated plates results in the loss of APU intakesystem.3D unsteady CFD for orifice plate and APU intake system with perforated plates model by largeeddy simulation (LES) method were performed. The result show: the orifice plate flow characteristicsis similar to the around obstructions stream (such as flow around a cylinder) at middle Re number, butthe wake vortices are sheared and squeezed by the mainstream. With perforated plates APU intakesystem show: in APU inlet duct, the eddy is mainly originated from perforated plates; with the orificeratio increasing, the eddies (either wall-end eddy or vortex) after perforated plates tend to weaker, butwake zone tend to widen by mainstream shear suppression.