Funding granted for collaborative research project on aeroacoustics
SNSF and DFG have granted us funding for the collaborative research project Combined aeroacoustic and flow diagnostic analysis of the motion induced sound generation by an oscillating airfoil with active flap proposed by us in collabortation with Arne Henning from DLR in Göttingen.
This bilateral project focusses on the sound generation and emission from a two dimensional wind turbine blade with a trailing edge flap. The motivation is guided by ongoing efforts to increase the efficiency and life span of modern wind turbines by smart individual blade pitch control mechanisms combined with active trailing edge flaps that are supposed to alleviate unsteady loads. The pitching motion, that compensates for the variable flow conditions within a single rotation of the wind turbine rotor, is a large amplitude motion whereas the trailing edge flap motion will lead to smaller excursions of the trailing edge but with higher frequencies. The different kinematics associated with the airfoil and flap pitching motions will give rise to the generation of flow structures of different scales that will affect the aerodynamic and aeroelastic performance of the blade but also the aero-acoustic properties in terms of trailing edge sound generation and emission in different ways. The research question underlying this proposal is how the individual blade pitch and trailing edge flapping motions affect the location and strength of sound sources and the directivity of the sound emission. To answer this question, a fundamental understanding of the development and interaction of multi-scale coherent structures in the near-field of an unsteadily pitching blade or flap is desirable and needs to be tied to the acoustic footprint in the far-field. The objectives of the proposed research are two-fold. The first objective is to further develop an acoustic causality correlation method based on turbulent fluctuations in the flow field near the airfoil's trailing edge, measured by means of particle image velocimetry (PIV), and pressure fluctuations in the acoustic far- field, measured by a microphone array, into a robust strategy that allows for unambiguous identification of sound source regions and characterisation of sound emission in flows past unsteadily moving objects. The second objective is to characterise the full causal chain from airfoil kinematics via vortex dynamics to the acoustic signature as well as the blade loads.