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%.
