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Generation of Advanced Helicopter Experimental Aerodynamic Database for CFD code validation

Final Report Summary - GOAHEAD (Generation of advanced helicopter experimental aerodynamic database for CFD code validation)

During the last ten years, considerable progress has been made in developing aerodynamic prediction capabilities for isolated helicopter components such as an isolated main rotor or an isolated fuselage. Today leading edge Computational fluid dynamics (CFD) software systems are available, and others are being developed, which are capable of predicting the viscous flow around main rotor-fuselage configurations or even complete helicopters. The greatest shortcoming for qualifying these methods as design tools in the industrial design process is the lack of detailed experimental validation data for the aerodynamics of complete helicopters. To overcome these shortcomings, the project GOAHEAD was carried out with the following main objectives:
- to enhance the aerodynamic prediction capability of Europe's helicopter industry with respect to complete helicopter configurations;
- to create an experimental database for the validation of three-dimensional (3D) CFD and comprehensive aeromechanics methods for the prediction of unsteady viscous flows including rotor dynamics for complete helicopter configurations, i.e. main rotor - fuselage - tail rotor configurations with emphasis on viscous phenomena like flow separation and transition from laminar to turbulent flow;
- to evaluate and validate Europe's most advanced solvers of the unsteady Reynolds-averaged Navier-Stokes (URANS) equations for the prediction of viscous flow around complete helicopters including fluid-structure-coupling;
- to establish best practice guidelines for the numerical simulation of the viscous flow around helicopter configurations.

The wind tunnel experiment planned within GOAHEAD concerned itself with the Mach scaled model of a modern transport helicopter consisting of the main rotor, the fuselage (including all control surfaces) and the tail rotor. In order to keep the costs of the experimental campaign as low as possible, existing components were reused, i.e. the fuselage, the instrumented main rotor and the instrumented tail rotor. The test configuration was therefore not a scaled model for an existing helicopter.

After the wind tunnel experiment, the partners started the post test computations. The grids and the computational set-up were improved based on the experiences of the blind test phase. In the meantime, several partners have implemented new advanced techniques in their solvers (paid from resources outside GOAHEAD) which were also applied in the post test exercise. Conclusions were drawn out of the CFD and the experimental data and best practice guidelines for the URANS simulation of complete helicopter configurations will be established.

Due delays in the preparation of the wind tunnel model (underestimation of work and broken gear some days before installation in wind tunnel), it was necessary to postpone the wind tunnel entry by half a year. Consequently, the duration of the GOAHEAD project has been extended by half a year.

The specific results were exploited as the programme proceeded. Since all European helicopter manufacturers apply CFD methods that have been and are being developed by one of the research centres or universities of the GOAHEAD consortium the validation of these URANS methods directly improved the industrial design processes because of improved accuracy and reliability.

In detail, the GOAHEAD RTD work produced the following economic benefits:
- cost reduction for single partners in developing and validating new CFD methods;
- increase of competitiveness of helicopters produced in Europe through increased aerodynamic performance and efficiency;
- reduction of development costs, by shorter design cycles for main, tail rotors and fuselages leading to higher aerodynamic performance (e.g. by improved mast fairing, control surfaces, etc.). Less uncertainty, especially when assessing novel vertical takeoff configurations in the early design phase, fewer delays in development;
- improved experimental and theoretical knowledge will also reduce development risks and ease certification.

Overall this will improve the competitiveness and economic prospects of the European helicopter manufacturers especially in the face of strong competition from the United States. Higher aerodynamic performance will reduce the specific fuel consumption and so reduce pollution, this is a benefit for the community in its quest for a clean and healthy environment.

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