Performance and Physics of a S-76 Rotor in Hover With Non-Contiguous Hybrid Methodologies

Modifications to allow non-contiguous, moving grids have been made to a hybrid computational fluid dynamics free-wake (CFD-FW) solver for aeroelastic rotors. In the CFD-FW approach, a CFD code resolves the unsteady Reynolds-Averaged Navier-Stokes equations in the near field, and a vortex free-wake analysis models the wake beyond the near-field CFD grids. Blade loading from the CFD solver is utilized to calculate circulation and advance the free-wake solver. The outer boundaries of the CFD domain have boundary conditions that are modified based on the induced velocities from the free-wake code. Previous studies have demonstrated that the application of the free-wake code in the far-field allows the computational domain to be smaller than in a traditional CFD analysis which saves computational cost and memory while maintaining the accuracy of the solution. Before the current modifications, the hybrid solver was limited to CFD domains that included off-body grids with outer boundaries that were stationary in an inertial frame. By allowing grid systems with moving outer boundaries, the inertial grids can be removed, further reducing the computational cost and memory required by the hybrid solver. The resulting meshes consist of only near-body grids that can be non-contiguous, i.e., not requiring overlap of the meshes. In this work, hover performance predictions of a scaled S-76 rotor are performed using the hybrid CFD non-contiguous grid approach and compared to those of the hybrid solver with the inertial background grids and full CFD simulations. The noncontiguous grid approach predicts comparable thrust coefficients, torque coefficients, and figures of merit, within 2.0 counts of the experimental data, at 7.6% of the computational cost of full CFD simulations. A preliminary study of sensitivity to different model inputs is performed.