COMPUTATIONAL INVESTIGATION OF BLADE SAILING PHENOMENON BY FLUID STRUCTURE INTERACTION APPROACH
Enormous application of rotary wing aircraft at diverse scenario has pervasive interest in the subject of vertical take-off and landing (VTOL) flight aerodynamics. Maneuvering of rotary aircrafts has always been considered as a challenging process due to variety of flight aerodynamics complications. Foremost, the most complex problem is blade sailing; an aero-elastic phenomenon affecting helicopter rotors when rotating at low speeds in high wind conditions. Inception of such scenario frequently appears in nature when a helicopter operates under the condition of reverse flow or its own wake. Initial effect is on blades which start to deform with high vibration leading towards the stall condition (operating condition when aircraft exceeds the critical angle of attack and start losing the required lift for normal flight) and deteriorates the helicopter flight aerodynamics.
In order to understand this phenomenon, turbulent flow characteristics of the helicopter rotor wakes have been computationally investigated by Reynolds averaged Navier-Stokes (RANS) method. A full-scale CAD model using ONERA OA209 airfoil, having four blades has been chosen for this study. To get better insight of the critical parameters and their effect on flow phenomena; 3D flow analysis has been carried out using Moving Reference Frame (MRF) method. Along with Fluid Structure Interaction (FSI) approach has been used in order to calculate structure deformation due to the aerodynamic pressure loading on blades. The effect of angle of attack and blade twist at different rotor speeds are investigated in detail. For each case, blade deflection has been calculated under the consideration of one-way FSI coupling. Finally, a comparative study has been done to analyze the conjoint effects of parameters in order to get the favorable operating conditions with respect to minimum blade deflection.