A Hybrid Non-Linear Unsteady Vortex Lattice-Vortex Particle Method for Rotor Blades Aerodynamic Simulations

Vincent Proulx-Cabana,Guilhem Michon,Minh Tuan Nguyen,Eric Laurendeau,Sebastien Prothin

doi:10.3390/fluids7020081

Abstract

This study presents a hybrid non-linear unsteady vortex lattice method-vortex particle method (NL UVLM-VPM) to investigate the aerodynamics of rotor blades hovering in and out of ground effect. The method is of interest for the fast aerodynamic prediction of helicopter and smaller rotor blades. UVLM models the vorticity along the rotor blades and near field wakes with panels that are then converted into their equivalent vortex particle representations. The standard Vreman subgrid scale model is incorporated in the context of a large eddy simulation for mesh-free VPM to stabilize the wake development via particle strength exchange (PSE). The computation of the pairwise interactions in the VPM are accelerated using the fast-multipole method. Non-linear UVLM is achieved with a low computational cost viscous-inviscid alpha coupling algorithm through a stripwise 2D Reynolds-averaged Navier–Stokes (RANS) or empirical database. The aerodynamics of the scaled S76 rotor blades in and out of ground effect from the hover prediction workshop is investigated with the proposed algorithm. The results are validated with experimental data and various high-fidelity codes.

Highlights

Computational rotary wing aerodynamics is challenging because of the intrinsic three dimensional and unsteady nature of the complex rotor-wake interactions in most flight conditions
This article details a new method towards rotor aerodynamics analysis that is the combination of the non-linear Unsteady Vortex Lattice Method (UVLM) (NL UVLM) via the alpha coupling and the vortex particle method (VPM) with an added Large-eddy simulations (LES) viscosity diffusion term
The added eddy viscous term is able to stabilize the simulations of a hovering rotor for both in and out of ground effects

Summary

Introduction

Computational rotary wing aerodynamics is challenging because of the intrinsic three dimensional and unsteady nature of the complex rotor-wake interactions in most flight conditions. Because of this complexity, the balance between fidelity and computational cost is hard to achieve, especially in the early design phases where a high number of configurations must be analyzed. Hovering rotor free of any azimuthal asymmetries is a special case where the aerodynamic forces can reach a steady state [2]. The complex wake forming around the rotor can be hard to predict for special cases, like in the proximity of the ground or with the presence of obstacles. Most rotorcraft aerodynamics are investigated using a free wake approach where no assumptions for the wake shape are needed, unlike fixed wing simulations where many studies have been conducted with fixed wake to avoid the numerical complexity of wake evolution [3,4]

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Results

Conclusion