Aeroacoustic Optimization of Wind Turbine Airfoils by combining thermographic and acoustic measurements Christoph Dollinger M.Sc., Dipl.-Ing. Michael Sorg, Phillip Thiemann M.Sc. Introduction On this poster first results of a combined measuring method for the acoustic aerodynamic optimization of rotor blades for wind turbines are presented. The method combines thermographic data for turbulence boundary layer analysis with the measurement data of an acoustic camera. Thus, the amplitudes and frequencies of the three-dimensional acoustic emission field can be associated with the geometry of the rotor blade and the inflow-conditions. The flow tests were conducted at the Deutsche WindGuard Aeroacoustic Wind Tunnel in Bremerhaven. Laminar air flows at speeds of up to 360 km/h and chord-Reynolds numbers of up to 6 million can be generated in this acoustically optimized wind tunnel. Fig. 4: Measurements data of the research wind turbine Repower 3.4M104 of the University of Bremen Aeroacoustic Measurements Thermographic Measurements The thermographic measurements were accomplished with two different thermographic imaging systems. On the suction side of the airfoil a 640 x 480 pixel microbolometer-focal-plane-array with a wavelength range from 7.5 to 14 µm and a temperature resolution of at least 0.03 K is used. The thermographic sensor on the pressure side is a 640 x 512 pixel InSbfocal-plane-array. An acoustic array with 40 MEMS (micro-electro-mechanical system) Microphones was used to measure the noise emitted by the airfoils. The microphone array is mounted in the wind tunnel wall (in flow) on the suction side of the airfoil in a random geometrical arrangement. Fig. 1: Based on the geometric arrangement of the thermographic cameras in the wind tunnel and the geometry of the airfoil, the thermographic data is aligned to the shape of the airfoil. Fig. 5: Geometrical arrangement of the microphone array in the wind tunnel wall on the suction side. Fig. 6: Results of an acoustic. Airfoil a) untreated and b) with badly applied serration (sawtooth geometry) at the trailing edge. Fig. 2: Thermographic images aligned to the geometry of the airfoil with turbulent boundary layer transition on a) the suction side and b) on the pressure side of the airfoil. Conclusions and future investigations Thermographic and aeroacoustic measurements on airfoils in a wind tunnel provide additional information concerning turbulent boundary transition and trailing edge noise. The thermographic method for turbulence boundary layer analysis can be used to validate XFOIL and CFD simulations in a wind tunnel test. The position of the transition can be detected without preparing the airfoil for surface pressure measurements. Current results show the suitability of the microphone array. Due to structure-borne noise and flow noise, the measurement of trailing edge noise is not satisfactory possible yet. The acoustic shielding between wind tunnel wall and microphones one the next tasks in the project. Fig. 3: Position of the calculated transition over the angle of attack (α) compared to an XFOIL-Simulation a) on the suction side (Top Xtr) and b) on the pressure side (Bot Xtr) an airfoil. High precision parallel kinematic for positioning samples with freeform surfaces BIMAQ Bremer Institut für Messtechnik, Automatisierung und Qualitätswissenschaft Telefon Fax E-Mail www 0421 / 218-646 01 0421 / 218-646 70 [email protected] www.bimaq.de The research project is funded by the State of Bremen within the Applied Environmental Research Program (AUF) and the European Regional Development Fund EFRE 2007-2013. Kontakt: Telefon Fax E-Mail Christoph Dollinger M.Sc. 0421 / 218-646 28 0421 / 218-646 70 [email protected]