Validation of a Transient 3-D CFD Mars Rotorcraft Performance Simulation Using Experimental Data

Given the success of NASA/JPL’s Ingenuity helicopter, the study of Martian flight vehicles and their aerodynamic characteristics has become a rapidly growing field of research. At NASA Ames, the "Rotor Optimization for the Advancement of Mars eXploration" (ROAMX) team and their partners have published designs for an advanced, second generation Mars helicopter - the "Mars Science Helicopter" (MSH) - which possesses a novel rotor geometry. This paper presents the independent development and validation of a numerical model for assessing Mars rotorcraft performance, which uses an MSH-inspired rotor as the primary research artifact. Performing Mars-analogous or exact recreations of Mars environmental conditions on Earth is both a costly and difficult technical challenge. Therefore, a transient, 3-D unsteady Reynolds-Averaged Navier Stokes (RANS) CFD model is proposed to estimate the performance of an MSH-inspired rotor in Earth atmospheric conditions. The experimental data presented in this paper corresponds to a sweep of collectives for a 75% span rotor Reynolds numbers of 2.87*10^5. The numerical simulations use the results of the experimental campaign to validate the accuracy and fidelity of the model. Delayed Detached Eddy Simulations (DDES) and a computationally cheaper steady-state RANS approach were validated using experimental data at low thrust conditions. Then, the RANS approach was used to sweep different collective pitch angles for both nominal and modified twist geometries that attempt to account for aeroelastic deformations using low-fidelity modeling. The blades with a modified twist show an improved agreement with the experimental data, with errors of about 5% in the thrust and torque coefficients for low collectives. For large collective angles, beyond which the figure of merit peaks, the RANS simulations predict premature stall compared to the experimental data. The methods and results presented in this paper are the first phase of an effort to independently estimate both the aerodynamics and dynamics of such a unique rotor geometry.