Abstract:

Based on the nonlinear numerical model of flight dynamics developed for a helicopter, a new trim method is proposed by coupling the model with the computational fluid dynamics (CFD) method in forward flight. In order to enhance the calculation precision of aerodynamic forces on aerodynamic components, such as rotor, fuselage, tail-rotor, etc., and reduce dependency on test data, a CFD model based on Navier-Stokes equations is established which includes rotor and tail-rotor momentum sources. Grids around the helicopter are generated by using unstructured grids technology. Jameson central-difference scheme is adopted in spatial discretization and the five-step Runge-Kutta method is used for temporal discretization. Artificial viscosity is added to overcome numerical oscillation of solutions. Local time step method and variable coefficient implicit residual smoothing method are used to accelerate the convergence for the helicopter flowfield. A high-efficient coupling strategy for trimming calculation coupled with CFD method is put forward by coupling the aerodynamic force from the CFD model with that from the flight dynamics model. Then the trim calculations are conducted by taking UH-60A helicopter as a numerical example on the basis of the flight dynamics model and CFD method validations. Special analysis on the precision and convergence rate of the present trim method is performed. It is demonstrated that the trim method can effectively improve trim analysis precision and meet engineering analysis requirements.

Key words: helicopter, rotor, flight dynamics, trimming analysis, momentum source method, computational fluid dynamics