CONTROL OF DYNAMIC STALL THROUGH DIFFERENT PASSIVE DEVICE CONFIGURATIONS

Abstract

Rotorcraft performance, structural integrity and acoustics have been a major research area in the aerospace industry and this credit goes to the phenomenon of dynamic stall. This unsteady aerodynamic phenomenon occurs on the retreating side of the rotor blade, which for a stable flight has to produce enough lift to balance the normal forces created by the advancing blade. However, the maximum dynamic pressure on the retreating side is significantly less than that present on the advancing blade. As helicopter speed increases, the imbalance of maximum dynamic pressure also tends to increase, leading to high frequency oscillatory motion, where in some cases the airfoil goes beyond the static stall angle. This results in negative damping and flutter phenomenon and the onset of high torsional loads and aero-elastic instabilities limiting the rotorcraft structural life span and performance. For the past two decades a number of active and passive techniques have been implemented to control the dynamic stall aerodynamic parameters. Most of the control studies which have been carried out have focused on either one or two passive devices integrated on the airfoil test section. In the present study, three passive devices have been introduced namely; Gurney Flap, Fixed Droop Leading Edge and Vortex Generators. Numerical simulations have been carried out and cases include; Single Passive Device (SPD) Configurations, Dual Passive Device (DPD) Configurations and Triple Passive Device (TPD) Configurations and comparative analysis was carried out. Unsteady compressible Navier Stokes equations were solved using S-A model for turbulence closure. O-type mesh topology has been used to discretize the computational domain with highly resolved structured mesh. Simulations were performed using commercial CFD code ANSYS FLUENT at xx Re of 3.45 × 106 . Out of all the computational cases carried out, the 20o droop case gave the best results. It considerably reduced the hysteresis effects and improved the moment coefficient values by about 85.4% and reduced the drag coefficient by 84.3%.