Numerical study on flow separation control is conducted for a stalled airfoil with steady-blowing jet. Stall conditions relevant to a rotorcraft are of interest here. Both static and dynamic stalls are simulated with solving compressible Reynolds-averaged Navier-Stokes equations. It is expected that a jet flow, if it is applied properly, provides additional momentum in the boundary layer which is susceptible to flow separation at high angles of attack. The jet angle can influence on the augmentation of the flow momentum in the boundary layer which helps to delay or suppress the stall. Two distinct jet angles are selected to investigate the impact of the jet angle on the control authority. A tangential jet with a shallow jet angle to the surface is able to provide the additional momentum to the flow, whereas a chord-normal jet with a large jet angle simply averts the external flow. The tangential jet reduces the shape factor of the boundary layer, lowering the susceptibility to the flow separation and delaying both the static and dynamic stalls.

A rotorcraft main-rotor blade experiences a broad range of the Mach number in high-speed forward flights or rapid maneuvering conditions. Near the boundary of the flight envelope, the rotor blade often encounters severe dynamic stall which limits the overall aerodynamic performance. Of interest here is effects of the Mach number on the dynamic stall. A rotor airfoil, VR-12, is computationally investigated for both static and dynamic stall conditions with varying the Mach number from 0.2 to 0.4. For the small enough Mach number 0.2, both static and dynamic stall are significantly influenced by flow separation due to adverse pressure gradient. For the highest Mach number 0.4, compressibility near the leading edge is no longer negligible, forming a shock there. The shock-induced separation occurs near the leading edge, which dominates both the static and dynamic stall at the high Mach number. At the intermediate Mach number 0.3, it is observed that both adverse pressure gradient and the shock affect the stall. Current computations are conducted with the unsteady Reynolds-averaged Navier Stokes approach with the Spalart-Allmaras model. Numerical results are compared to relevant wind-tunnel test data.

View Video Presentation: https://doi.org/10.2514/6.2022-1069.vid Multicopter aerodynamics is numerically investigated in this study. The main objective is to understand unsteady aerodynamic loads and major unsteady flow structures for a multicopter. The open-source CFD solver OpenFOAM with the overset mesh method is used to resolve rotors with the stationary fuselage simultaneously. Tip vortices from multicopter rotors are influenced by adjacent rotors and the fuselage. Tip vortices from two counter-rotating rotors are merged to a vortex tube, and tip vortices are broken down to smaller structures when the tip vortex collides with the fuselage. This complex vortical structures induce the local inflow on the rotor blades. In addition, the rotor blade encounters the ground effect from the fuselage, when the rotor blade is passing above it. With these rotor-rotor and rotor-fuselage interactions, unsteady airloads on the rotor blade occur in every revolutions, and a multicopter experiences a 6/rev fluctuation of the aerodynamic forces.