Optimizing Rotor Blades for Heavier-Than-Air Flight on Mars : Using the Discrete Adjoint Method in the Open-SourceFramework DAFoam

The Martian atmosphere differs dramatically from Earth’s. It has ultra-low density, very low Reynolds numbers and much lower speed of sound, all of which make rotorcraft aerodynamics unusually challenging. Yet the success of the Mars helicopter Ingenuity has opened the door for a next generation of Mars helicopters. These future Mars helicopters will be designed to have higher payload, be able to take samples from the ground, fly farther and operate at higher tip speeds. To achieve this, the rotor blades need to be optimized for the Martian atmosphere. This thesis evaluates how DAFoam - an open-source, gradient based optimizer which uses the discrete-adjoint method can be used to minimize drag for rotor blades in the Martian environment. A seven-level grid study first identifies a deformation robust mesh that remains stable during large shape changes. Single point optimizations are then performed at three different Mach numbers (0.13, 0.325, 0.65) for both Earth and Mars, plus a transonic tip case at Mach = 0.8 for Marsonly. Relative drag reduction on Mars match the values for the Earth simulations (25-30%), even though the absolute drag remains up to 95% higher on Mars due to the flow conditions. Modification of the thickness constraint to minimum 25% of the initial thickness and volume constraint to minimum 60% of the initial volume, allows the solver to resemble a ”knife-edged” leading edgedesign previously only obtained with genetic algorithms, this gave additional 3% drag reduction in the single point case. A three-point angle of attack multipoint simulation confirms the trade-off between peak performance and robustness. The study shows that, given a suitable mesh and constraint modification, DAFoam can deliver both conventional and non-intuitive low drag geometries for Martian rotorcraft. All with a workflowthat can be produced with publicly available software. Further work should extend the multipoint set with more angles of attack, refine the free-form-deformation (FFD) control box, explore additional constraint optimization and, ultimately, extend the workflow to three-dimensional blades to achieve a fully operational rotor blade design.