A High-Efficiency Damped Delta Trim Method Tightly Coupling Lagrangian and Hybrid Lagrangian-Eulerian Methods

This paper introduces a novel delta trim method for helicopter rotor aerodynamics, featuring a tightly coupled mid-fidelity Lagrangian solver (DUST) and a high-fidelity hybrid Lagrangian-Eulerian solver. The primary objective is to enhance the efficiency of computationally intensive rotor trimming procedures. The method also integrates a damping factor into the Newton iteration process to accelerate convergence in both main and sub-loops of the delta scheme. Benchmark cases, including the hovering Caradonna-Tung rotor, the AH-1/OLS rotor in forward flight, and the HART II rotor in descending flight, are used to evaluate the method's performance. Results demonstrate significant reductions in computational cost, achieving over 70% CPU time savings compared to traditional methods, while maintaining comparable accuracy in predicting aerodynamic loads and control settings. The study also investigates the conditional effectiveness of the damping factor and the impact of solver initialization strategies on overall efficiency and solution fidelity.