The objective of this work is to numerically simulate the effect of blade loading on the noise generated by rotor-rotor interactions in counter-rotating cascades. A moving-body immersed boundary method is used to directly compute the noise generated by rotor-rotor interactions of counter-rotating cascades. The time-dependent and compressible Euler equations are numerically solved using a finite volume discretization where the fluxes are computed with fourth-order precision in space, while the time marching process is achieved using a third-order Runge-Kutta scheme. This method is based on a discrete forcing approach where the boundary conditions are directly imposed in the control volumes that contain the immersed boundary points, resulting in a sharp representation of the moving solid boundaries of the counter-rotating cascades. For all simulated cases, those boundaries correspond to the near-tip geometry of the counter-rotating rotor blades of a generic public domain open-rotor geometry. The rotors blades loading is lowered by increasing the axial free-flow velocity while keeping the circumferential velocity of the blades constant, with a Mach number equal to 0.65. Seven cases were simulated, with decreasing blade loading and corresponding increasing Mach numbers of the free-flow equal to 0.15, 0.20,0.22, 0.25, 0.27,0.29, and 0.30. The numerical results show that the OASPL is minimum for a free-flow Mach number of 0.22, that corresponds approximately to the design condition of the cascade, with a maximum OASPL corresponding to a Mach number of 0.30, i.e., for a minimum blade loading.
展开▼
