An innovative dual-mesh CFD paradigm is developed and validated for hovering rotor computations. An unstructured RANS solver is applied to a near-body mesh in order to capture complex geometry and wall-bounded viscous effects, while a structured adaptive Cartesian Euler solver is applied to the off-body to resolve the rotor wake. The motivation for approach is to create a CFD solution methodology which exercises the best features of both solvers i.e., body-conforming unstructured grids to capture the geometry and boundary layer effects, and efficient adaptive Cartesian grids with a high-order flow solver to resolve the wake. The code that employs this strategy is called 'Helios'. In comparison to calculations with a fully unstructured mesh, the dual-mesh approach in Helios is able to achieve significantly better aerodynamic performance predictions for about the same cost. The cost savings arise because of the inherent efficiency of the Cartesian off-body solver, which means that significantly larger grids can be solved with only nominal increases in CPU time. Moreover, high- order solutions in the Cartesian off-body solver incurs negligible cost; e.g. the 5th-order algorithm is only about 6% more expensive than the standard 2nd-order scheme. Further savings arise because of the use of adaptive mesh refinement in the off-body, which is able to resolve the wake with one-fifth the number of grid points as a fixed-refined case with the same resolution. Calculations with the steady hover assumption - fixed grid with rotational source terms applied to the equations solved on the grid - gives nearly identical results to a moving-grid (inertial) hover calculations, in which the near- body grid rotates while the background Cartesian grid remains fixed. Further, we have shown that the adaptive scheme was found to be robust for the moving-grid calculations and also gives comparable results. Using a fine 8.3M point near-body mesh, the dual-mesh scheme provides figure of merit predictions to within 1 % - 3 % of experimental data for a range of collective angles. It is noteworthy that these results were obtained on a relatively modest cluster employing 64 cores.


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    Title :

    A coupled unstructured-adaptive cartesian CFD approach for hover prediction


    Additional title:

    Ein gekoppelter, unstrukturiert-adaptiver, kartesischer CFD-Ansatz zur Simulation des Schwebeverhaltens von Hubschraubern



    Published in:

    Publication date :

    2010


    Size :

    18 Seiten, 12 Bilder, 8 Tabellen, 44 Quellen


    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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