Case Study - Siemens Industrial Turbomachinery AB

Problem

Two large gas turbines (approximately 25m x 12m x 10m) were installed in an industrial area nearby an office building. The gas turbines generate a tonal noise component at around 2700Hz caused by the inlet channel blades pass frequency. This tone imposes a more stringent noise requirement on the supplier, forcing noise reducing actions being made on the turbine.

Measurements and noise source identification with traditional methods (i.e. Sound Intensity with probe) is impossible, partly because of the gas turbine size but also because of the interference tone is represented over a larger area around the turbine, with only small dynamic noise level difference, where it´s very difficult to determine direction of the sound.

Measurement

The acoustic camera was placed at several points around the gas turbine, partly to see if the tone was leaked from multiple sources. But also to see if detected leakages are repeated and not an effect of reflections or measurement artifacts.

The measurement system’s Virtual microphone feature was also extremely useful, with this function you can (even in real time!) scan and listen to the desired spots in the image, and also filter the listening function to desired frequency range. This way you can listen only to the pure tone leakages.

Result

With the acoustic camera it was possible to detect the tonal sound of the most crucial parts of the turbine. This meant that they could focus on and implement noise reduction actions in the right places. Instead of the traditional and difficult, step by step action method, which in the end could have been very expensive for the supplier.

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