SBIR-STTR Award

The incorporation of viscous analysis in design is vital for a complete understanding of aerodynamic problems. This proposal offers to develop and integrate with RotCFD a method for semi-automatically generating grids suitable for viscous analysis on complex configurations as well as parallelize the solver in RotCFD to take advantage of today's multi-core machines. The principle idea behind the semi-automation of the grid generation is to divide the geometry surface into patches and generate body-conforming grids from these patches. This partitioning allows for automatic generation of grids with aspect ratios suitable for viscous flows. Convection dominates the outer region, so unstructured Cartesian meshes can be generated quickly and easily here. The outer grid will be conformed to the inner grid so the entire grid can be treated as one unstructured grid with an unstructured solver, or as a hybrid grid with multiple zones and solvers. In the hybrid approach, viscous solvers can be used for the inner zone while the faster inviscid solvers can be used in the far-field. In Phase I a proof-of-concept grid generator, and a conceptual methodology for solver parallelization will be developed and demonstrated to work with RotCFD the rotor aerodynamic design tool. In Phase II, the features of the grid generator and solver will be fully developed and expanded.

During initial design studies, parametric variation of vehicle geometry is routine. In addition, rotorcraft engineers traditionally use the wind tunnel to evaluate and finalize designs. Correlation between wind tunnel results and flight tests, when not good, have been often attributed in part to uncertainty in blockage corrections. Estimation of rotor blockage is significantly more complex than bluff body corrections as the correction depends on operational characteristics such as rotor RPM and thrust produced. This proposal offers to develop an Integrated Design Environment (IDE) which can simulate a complete rotorcraft with or without wind tunnel walls including all the facility effects. At the heart of the innovation are: 1. An automated hybrid grid generator. (viscous grids near the bodies and unstructured Cartesian grid everywhere else) 2. A robust and economical incompressible flow solver for the entire system of grids. 3. Momentum source based rotor model that is suitable and economical for simulating configurations with multiple rotors. In Phase I, the proof-of-concept developed used unstructured Cartesian grid for the model and wind tunnel. In phase II, the tool will be extended to hybrid grid with viscous grid near solid surfaces and will include several tools including a simple CAD like geometry manipulation tool and pre- and post-processing tools all integrated in one environment to facilitate ease of use.