Computational Simulations of a Three-Dimensional High-Lift Wing

Mehdi R. Khorrami 1NASA Langley Research CenterMS 128, Hampton VAMert E. Berkman 2andFei Li 3High Technology Corporation28 Research Drive, Hampton VABart A. Singer 4NASA Langley Research CenterMS 128, Hampton VAAbstractHighly resolved computational simulations of a three-dimensional high-lift wing are presented. The steadyReynolds Averaged Navier-Stokes computations aregeared towards understanding the flow intricaciesassociated with inboard and outboard flap side edges.Both moderate and high flap deflections are simulated.Computed surface pressure fields accurately capture thefootprint of vortices at flap side edges and are inexcellent agreement with pressure sensitive paintmeasurements. The computations reveal that theoutboard vortex possesses higher rotational velocitiesand lower core pressure than the inboard vortex andtherefore is susceptible to severe vortex breakdown.IntroductionProjected future growth in air travel and significantquieting of modern jet engines has brought renewedattention to the non-propulsive (airframe) component ofaircraft noise. Past studies that focused on airframenoise have identified high-lift devices along with thelanding gears as dominant noise producingcomponents. 1'2 Those studies have established flap-side-edges as a potent noise source that deservesfocused attention. The present paper continues oureffort towards uncovering prominent flow structures ata flap side edge in high-lift settings. These efforts aremotivated by our lack of understanding of noise1 Research Scientist, Computational Modeling andSimulation Branch, Associate Fellow AIAA.2 Research Scientist: currently with ArvinMeritorExhaust Systems.3 Senior Scientist, Member AIAA.4 Assistant Branch Head, Computational Modelingand Simulation Branch, Senior Member AIAA.producing fluid dynamical processes at a flap side edge.The deeper insight gained through this work will guidethe development of simplified physics-based modelsthat mimic flow unsteadiness (and thus noise generationmechanisms) at the edge. Ultimately, such physics-based models will allow efficient design of quietairplanes.In a parallel effort to several companion experiments,our previous research focused on steady ReynoldsAveraged Navier-Stokes (RANS) simulations ofunswept and untapered high-lift configurations. 3-6 Theconfigurations were generic two-or three-element high-lift models that consisted of a two-dimensional (2D)main element with or without a 2D slat and a part spanflap. These early studies captured the complex natureof the flap side-edge flow field and revealed theintricacies of shear layer roll-up, multiple vortexformation, vortex merging, and vortex breakdownprocesses. Two important aspects of a high-liftconfiguration left for future exploration were the effectsof sweep and taper on a flap side-edge flow field.These aspects were addressed in a series of testsconducted at NASA Langley Research Center (LaRC)in the 14x22 foot wind tunnel during 1998-1999. Thetested model is a trapezoidal (trap) wing design thatprovides a 3D high-lift flow environment. Extensiveacoustic and limited aerodynamic measurements wereobtained. Using a microphone array technique,acoustic measurements were obtained by a team fromthe Boeing Company. Sample ground-ward flapacoustic spectra at moderate and high flap deflectionsare shown in Fig. 1. At a flap deflection angle of 20degrees, the emitted noise from the inboard andoutboard side-edges are nearly similar both in