Overview
During the last ten years, considerable progress has been made in developing aerodynamic prediction capabilities for isolated helicopter components. This progress has been made possible due to co-operations that were partly funded by European research projects. Today, cutting-edge CFD codes are available that are capable of predicting the viscous flow around main rotor-fuselage configurations. The greatest shortcoming for qualifying these methods as design tools in the industrial design process is the lack of detailed experimental validation data for complete helicopters.
The main objectives of GOAHEAD are:
- To enhance the aerodynamic prediction capabilities of Europe's helicopter industry with regard to complete helicopter configurations.
- To create an experimental database for validation of 3D unsteady Reynolds-averaged Navier-Stokes (URANS) CFD methods for unsteady viscous flows, including rotor dynamics for complete helicopter configurations (main rotor-fuselage-tail rotor), with emphasis on viscous phenomena like flow separation and transition from laminar to turbulent flow.
- To evaluate and validate Europe's most elaborate URANS solvers for the prediction of viscous flow around a complete helicopter, including fluid-structure coupling.
- To establish best practice guidelines for the numerical simulation of the viscous flow around helicopter configurations.
The project had a four-year duration and consisted of five Work Packages:
- In Work Package 1 the detailed specifications of the test matrix for the wind tunnel experiment and the CFD evaluation and validation task were elaborated.
- Work Package 2 is the CFD Work Package in which existing CFD codes were applied to complete helicopter configurations in a blind-test and a post-test exercise.
- The wind tunnel experiments was carried out in Work Package 3. The configuration investigated in the DNW LLF was a Mach-scaled model of a modern transport helicopter consisting of the main rotor (R=2.1m), 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. This means that the test configuration is not a scaled model for an existing helicopter, but this is not important because the aim of the project was to produce data for CFD validation for any realistic configuration. The experimental set-up was tailored to serve the needs of the aerodynamic validation for methods based on the unsteady Reynolds-averaged Navier-Stokes equations. The 6m x 8m closed test section was used. Velocity profiles and the turbulent kinetic energy were measured at the inflow plane in order to define accurate boundary conditions in the CFD simulations. The measurement comprised global forces of the main rotor and the fuselage, steady and unsteady pressures, transition positions, stream lines, position of flow separation, velocity fields in the wake, vortex trajectories and elastic deformations of the main and tail rotor blades. The data was used in Work Package 4 for the validation of the CFD methods.
- Work Package 4 established best practice guidelines for the URANS simulation of complete helicopter configurations.
- Work Package 5 concerned itself with project management and will be responsible for the project exploitation.
Funding
Results
The main project results are:
- Within the GOAHEAD project a comprehensive data base with high quality data and documentation for complete helicopters has been generated.
- All CFD-solvers are capable to simulate the unsteady flow about complete helicopters with good accuracy for certain features. Interaction phenomena are partly captured. This is a big step forward having in mind that the first successful RANS helicopter simulations in Europe have been published in 2002.
- The European helicopter industry took advantage from the improvements and validation of their URANS-CFD tools. By working jointly with research centers industry extended the range of applications for in-house simulations.
The experimental database in combination with the validated CFD models will allow new helicopter designs to be assessed in a considerably reduced time span without the need for large corrections after flight testing.
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 will directly improve the industrial design processes.
Technical Implications
Main project conclusions:
- A full understanding of the data base will require many more years of research and data analysis like for any other experimental database.
- Due to the complexity and instationarity of the flow the solution accuracy has not reached the same level like for fixed wing applications. Further CFD developments and validation is required in order to further improve the CFD software, for example coupling of CFD methods to structural mechanics and flight mechanics, turbulence and transition modelling, and CPU time reduction.
- CFD-simulations for complete helicopters are still a challenge.
- Access to modern supercomputers is crucial.
- However, due to the large computational effort complete helicopter simulations will not be routinely run in near future in industry.
Policy implications
The specific results were exploited as the programme proceded. 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 will directly improve the industrial design processes because of improved accuracy and reliability.
In detail the GOAHEAD RTD work will produce 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 (for example by improved mast fairing, control surfaces, etc.).
- Less uncertainty, especially when assessing novel vertical take off 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 US. Higher aerodynamic performance will reduce specific fuel consumption and so reduce pollution, this is a benefit for the community in its quest for a clean and healthy environment.
Many partners in the consortium educate and train scientists and engineers (all the universities and also the research establishments). The GOAHEAD findings, basic and fundamental aerodynamic phenomena and algorithmic approaches and RTD progress will thus directly be translated into the respective technical community and into higher education.