Acceleration techniques for an aeroelastic Euler method for a hovering rotor

Abstract

Computational fluid dynamics (CFD) methodologies for rotors usually do not permit the rotor to deflect during analysis. However, these deflections do occur in the physical domain and can affect the performance of the rotor. By coupling a Euler code and a structural beam model, these deflections have been incorporated into a CFD simulation. The implementation of the structural beam model is straightforward and can be applied to existing CFD methodologies without extensive effort. However, the cost of the tightly coupled simulation is prohibitive. Techniques to accelerate the convergence of these methods for the quasisteady hover condition are explored. The methods include application of a loosely coupled aeroelastic methodology (vs a tightly coupled methodology), implementation of the full structural deflections using larger update intervals for methodology stability, application of relaxation factors to the full structural deflections, and application of blade deflections predicted by lower-order aerodynamic methods for initial deflections. All of these methods showed some merit, as discussed fully in this article. Aeroelastic analyses with surface deflection updates every 20 iterations provide results that are within 90% of the more expensive tightly coupled analysis results. These methods, while applied to rotors, are also pertinent for fixed-wing applications.