New Acoustic Test Section Launched in Large Scale Wind Tunnel

New procedure allows for simultaneous acoustic and aerodynamic measurements

Bremerhaven, 2015-03-18 Deutsche WindGuard launches their new acoustic test section at the large scale wind tunnel in Bremerhaven. The new equipment permits measuring the precise location of noise sources on rotor blade profiles and thus give clues to their origin. A special feature of the wind tunnel is that it allows for simultaneous aerodynamic and acoustic measurements on rotor blade profiles with realistic Reynolds-numbers. This way, all necessary measurements can be performed in one wind tunnel with the same model in an integrated measurement campaign, saving the customer’s precious time and money.

“For the new acoustic test section we doubled the number of microphones in the acoustical camera to a total of 80”, says Nicholas Balaresque, manager of the wind tunnel, “The more microphones, the higher the resolution of the measurement. This means, we are able to clearly differentiate between the noise coming from the model and background wind tunnel noise.”

The acoustical sensors are individually incorporated in a casing specifically designed for this purpose. A significant amount of development work was put into the task of finding the best layout of the sensors. The complex system is completed by special sound absorbers which increase the signal-to-noise-ratio between the model and the wind tunnel.

The system allows locating and measuring the noise sources on the rotor blade profile created by aerodynamic effects. As the better part of wind turbine noises is caused by aerodynamic effects, more and more attention in rotor blade development is paid to this phenomenon. The main focus is on the trailing edge of the rotor blade. This non-invasive system requires no modifications to the model, and is especially appropriate for testing add-ons such as trailing edge serrations.  

A high-speed thermographic camera is supporting the acoustical measurement system by visualizing the transition line. It represents the transition point between laminar and turbulent flow zones. “The position of the transition line affects the noise generation at the trailing edge significantly”, explains Nicholas Balaresque, “We are now able to test different configurations under realistic conditions in a short period of time. Especially around the rotor blade tip, measurements with full-scale profiles are possible”, he continues, “Acoustic measurements can now be conducted at speeds of up to 100m/s. This responds to the trend of increasing tip speeds and gives us a solid market position for the years to come.”

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