Computational Investigation of Microscale Coaxial-Rotor Aerodynamics in Hover

摘要

In this work, a compressible Reynolds-averaged Navier–Stokes solver is used to investigate the aerodynamics of anmicroscale coaxial-rotor configuration in hover, to evaluate the predictive capability of the computational approachnand to characterize the unsteadiness in the aerodynamic flowfield of the microscale coaxial systems. The overallnperformance is well-predicted for a range of rpm and rotor spacing. As the rotor spacing increases, the top-rotornthrust increases and the bottom-rotor thrust decreases, while the total thrust remains fairly constant. The thrustsnapproach a constant value at very large rotor spacing. Top rotor contributes about 55%of the total thrust at smallernrotor spacing, which increases to about 58% at the largest rotor separation. The interaction between the rotornsystems is seen to generate significant impulses in the instantaneous thrust and power.Unsteadiness ismainly causedndue to blade loading and wake effect. Additional high-frequency unsteadiness was also seen due to shedding near thentrailing edge. The phasing of the top vortex impingement upon the bottomrotor plays a significant role in the amountnof unsteadiness for the bottom rotor. Interaction of the top-rotor tip vortex and inboard sheet with the bottom rotornresults in a highly three-dimensional shedding on the upper surface of the blade in the outboard region and a two-ndimensional shedding on the lower surface at the inboard portion of the blade. The wake of the top rotor contractsnfaster compared with that of the bottom rotor because of the vortex–vortex interaction. Further, the top-rotor wakenconvects vertically down at a faster rate due to increased inflow.