A Lagrangian Vortex Method for Desktop Simulation of Rotor-blade Flows

Start: 04/25/2018 - 4:15pm
End  : 04/25/2018 - 5:15pm


Adrin Gharakhani


There has been significant interest and research activity in the past decade to develop robust methods for simulation of unsteady vortex dominated flow about and due to rotor-blades, not only in the context of traditional helicopters, but more recently for the purpose of design and optimization of wind turbines, as well as multi-copter drones and advanced VTOL (Vertical Take-Off and Landing) aircraft. To this end, flow simulation via traditional low-order grid-based Computational Fluid Dynamics (CFD) methods has proven to be very challenging and highly inefficient, because (1) they suffer from high numerical diffusion, which rapidly dissipates the turbulent vorticity generated by the rotating blades (often within just 2~3 blade rotations); and (2) meshing is often complicated and/or very time consuming, especially due to the relative motion of the blades with respect to each other and stationary objects. To address these challenges, high-order solvers with adaptive mesh refinement are being developed by many researchers.  An alternative approach is to use the Lagrangian vortex particle method (LVPM) – a solution-adaptive meshless method which discretizes the vorticity transport equivalent of the Navier-Stokes equations. In this approach, the Lagrangian evaluation of convection eliminates numerical diffusion and, hence, maintains the compact nature of the blade-induced wake vortices for long distances and times. Further, LVPMs are meshless and obviate the need for volumetric meshing altogether, requiring the meshing of only the boundaries of the objects (and the boundary layer if ultra-high-accuracy simulation is desired). Finally, since LVPMs discretize the vorticity field, the computational domain is compact, often reducing the problem size by 1~2 orders of magnitude compared to traditional CFD.

This presentation will provide a brief, yet comprehensive, introduction to the various computational aspects of developing a robust, high-fidelity LVPM for simulation of unsteady laminar and turbulent vortex dominated flows. Discussion will then focus on our group’s recent activity in modeling and simulation of rotor-blade flows. Validation benchmark data using isolated rotors in hover and forward-flight conditions, as well as preliminary simulation results for a new complex VTOL aircraft design will be presented.

Kravis 62, CMC

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