Wind noise generated by façade elements
The surrounding buildings are reflected by them, sometimes plants wind their way up to the top of them, sometimes their movable elements create waves at high walls, thus visualizing the wind: We are talking about high-rise building façades. They are the architect’s business card and a visible expression of his design. Building façades meet multiple functions: They protect the interior of the building from weather conditions, they insulate the building and help to increase its energy efficiency. Beyond these elementary functions, they also help to meet comfort requirements, for example by controlling the light incidence and shading, and by implementing acoustic aspects such as sound insulation.
However, façades may also entail undesirable aspects: In high-rise buildings for example, people can hear flow noise caused by the wind. Due to the large size of the façade areas, the flow noise can partly reach such a high sound level that the well-being of the people inside the building and in its immediate vicinity can be affected. This does not necessarily require medium or high wind velocities. Notably a gentle breeze can lead to a distinctive noise that may be much more annoying, as it contrasts distinctly with the background noise.
How the design of the façade and the produced noise correlate and interact can be investigated both computationally by CFD (Computational Fluid Dynamics) or CAA (Computational Aeroacoustics), or by tests carried out in the wind channel. Scientists of the Fraunhofer IBP install façade sections into the wind channel at the Fraunhofer Institute, using them as test specimen to analyze their acoustic characteristics. If the size of the façade section is small enough, it can be placed into the closed measurement section of the wind channel. Larger objects are investigated by the scientists, with the measuring section opened, both in the reverberation room and at the opening of the wind channel. A beamforming microphone array helps to visualize and localize the noise sources resulting from the air flow around the test specimen. Larger façade sections are placed and analyzed by the scientists right behind the outlet nozzle of the wind channel having a size of about five square meters. They examined for example a wave shape façade and optimized its material and suspension. Based on the gained results no additional noise source was to be expected and the planned façade design could be maintained.