Abstract
This paper concerns a new coupled free wake-CFD method for proper calculation of aerodynamic loads on a two bladed helicopter rotor in hovering flight. Loading is computed by solving the three dimensional Euler equations in a rotating coordinate system. However, since direct simulation of the tip vortices and wake requires a very fine grid, the rotor’s wake effects are modeled by a free wake approach and included into the CFD calculation by a transpiration boundary condition at the rotor surface. An influence coefficient solution method is used to find the rotor’s wake shape, being steady in a rotating frame. Euler equations are also considered in the form of absolute flow variables and solved by a multi grid Jameson’s finite-volume method. The accuracy of the proposed method is illustrated by comparing numerical results to the available experimental results for the pressure distribution on a blade of a model helicopter rotor at different tip Mach numbers.
Highlights
The flow field around rotors is inherently complex
A proper evaluation of the rotor aerodynamic loading has an important role in the analysis and design of helicopter rotor blades
The inviscid or viscous set of governing equations is solved by a proper Computational Fluid Dynamic (CFD) method (Roberts and Murman, 1985; Chen and McCroskey, 1988; Kramer et al, 1988)
Summary
The flow field around rotors is inherently complex. In the vicinity of the blade tip, it is highly three dimensional and vortical and it is characterized by non-uniform inflow with blade-vortex interactions and transonic conditions. The inviscid or viscous set of governing equations is solved by a proper Computational Fluid Dynamic (CFD) method (Roberts and Murman, 1985; Chen and McCroskey, 1988; Kramer et al, 1988). In this approach, the vortex system near the blade tips and the wake region below the rotor disk must be captured accurately for realistic pressure and load estimations. The tip vortices and the helical wake system are not solved by the CFD calculation and instead, the influence of strong tip vortices and the geometry of the wake are included by a vortex-wake model
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