Applications of Zero-Net-Mass Jets for Enhanced Rotorcraft Aerodynamic Performance

Numerical studies were conducted to investigate the benee cial effects of using arrays of zero-net-mass (ZNM) “ synthetic” jets on the aerodynamic characteristics of the NACA-0012 airfoil. Flowe eld predictions were made using modie ed versions of the NASA Ames ARC2D, U.S. Army 2DBVI unsteady, two-dimensional, compressible thin-layer Navier ‐Stokes e ow solvers. An unsteady surface transpiration boundary condition was enforced over a user-specie ed portion of the airfoil’ s upper, or lower, surface to emulate the time variation of the mass e ux out from and into the airfoil’ s surface. Special emphasis is placed on two-dimensional model problems that are representativeofthemorecomplexthree-dimensionalhelicopterrotore owe eldenvironment.Thenumericalresults have indicated that ZNM jets can be used to enhance the lift characteristics of airfoils (helicopter rotor blades ) and alleviate the impulsive aerodynamic response of a helicopter blade during encounters with the tip vortex wake. The effectiveness of ZNM jets for aerodynamic control is shown to increase with the increase in freestream Mach number and, more importantly, with the decrease in the ratio between the peak jet Mach number to the freestream Mach number. The striking similarities with the aerodynamics of an airfoil having an array of surface protuberances are presented.