Reduction of Noise Emission of Suboptimal Operating Propellers
A. Hirner, Th. Lutz and E. Krämer
Paper Nr: 71183, 7th International Airship Convention 2008, Friedrichshafen 9-11 October 2008
Propellers designed for cruising flight often suffer from an increased noise radiation if they are operating under off-design conditions such as take-off and approach as well as reverse thrust where partially high flow velocities and separations on the propeller blades can occur. This is especially true for the airship Zeppelin NT where the propellers have to cover a very large pitch angle range when used for manoeuvering on the ground. In cooperation with the project partners Zeppelin Luftschifftechnik GmbH and Steinbeis Transferzentrum a combined theoretical and ex- perimental design approach is established which comprises modified vortex lattice methods for preliminary design as well as CFD calculations for the analysis of the aerodynamic and aeroacou- stic behaviour of the propeller designs. To validate the theoretical results additional aerodynamic and aeroacoustic tests with a propeller test bench are conducted. Besides load measurements the detection of characteristic noise sources on a propeller blade is done by scanning the propeller blade with an acoustic mirror. The project aims at the development of a time-efficient process chain to reduce turn-around times in the design phase of new propellers. This comprises prelimi- nary design codes, subsequent highly automated propeller CAD design and grid generation for the CFD calculations as well as structural analysis and milling of selected propeller designs.