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Wind Tunnel Test of a Double Blade Swept Propeller and Analysis of Real Geometry effects

Sandra Busch ; Isak Jonsson
Göteborg : Chalmers tekniska högskola, 2015.
[Examensarbete på avancerad nivå]

This Master Thesis has been carried out at Chalmers University of Technology in Göteborg and GKN Aerospace in Trollhättan during the spring of 2015. The aim was to identify the effects of as-manufactured geometry and mechanical deformation on the aerodynamic performance of a double blade swept propeller, also called "Boxprop". The Boxprop is a new high speed propeller concept that was developed by Richard Avellan and Anders Lundbladh at Volvo Aero Corporation in Trollhättan, now GKN Aerospace Sweden. In the past, research has been focused mainly on jet engines, since propeller driven aircraft only form a small part of the commercial air traffic. Nevertheless, propellers have high propulsive efficiencies due to low operating pressure ratios, which is of interest in terms of a reduction of emissions and noise. The blades of conventional high speed propellers are swept rearwards whereas the Boxprop comprises forward swept blades that are joined at the tip. The forward sweep is supposed to have a positive influence at the tip flow but the drawbacks are usually aerodynamic instabilities and flutter. These disadvantages may be eliminated by the joined blade tips which make the Boxblade geometry stiffer and improves the stability. Chalmers University of Technology in Göteborg and GKN Aerospace collaborate in the NFFP iFram project to develop the Boxprop concept further. Previous master theses' showed discrepancies between CFD simulation results and experimental testing. By realising further CFD simulations and static as well as dynamic experimental tests, these differences could be identified and thus be considered in further research. The CFD simulations yielded that roughness of the propeller blades may reduce the turbo efficiency up to 15%, and causes an increase in propeller torque as well as a decrease in propeller thrust. Those values change in function of the employed advance ratio of the propeller. Another contributing factor that could be identified was the geometry of the nacelle, which causes a light increase in performance due to lower local wind speed in front of the propeller. Last but not least, also the deformation of the blade causes an increase in performance, due to a larger diameter when deformed. The performance is also influenced by the change of the angle of the leading edge, resulting in slightly twisted blade. The effect on the flow field of the deformed GPX-313 can only be estimated, since it would involve an extended analysis of various blade sections in CFD that could not be realised in the time available. Experiments with Boxprops made out of rigid opaque material with a diameter of 0:15m and 0:3m have been realised statically and in the Chalmers L2 wind tunnel at speeds up to 40 m=s and a rotational tip speed up to 210 m=s, corresponding to up to 26000 rpm rotational speed, to further study the performance of the Boxprop. An analysis of the flow field in the propeller swirl of the propeller was carried out with a stereo PIV, studying a plane along the wind tunnel flow field. Surface roughness measurements and 3D scans have been conducted on Boxprop blades to identify manufactured defects that can have impact on aerodynamic performance. FE simulations were done to calculate deformation of a Boxprop due to rotational load during testing. Polished and non-polished blades have been compared experimentally to test the impact of decreased roughness. The ability to conduct experiments in the Chalmers wind tunnel gave comparable experimental results for various advance ratios to verify the performance of the propeller. Considering roughness effects and disturbances in material deformation and flow field, the experimental results are on the same level as the results from the CFD simulations.

Publikationen registrerades 2015-09-29. Den ändrades senast 2016-01-12

CPL ID: 223369

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