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HomeVisit by Dr. Till Biedermann, Hochschule Düsseldorf

Visit by Dr. Till Biedermann, Hochschule Düsseldorf

The department of Mechanical and Mechatronic Engineering at Stellenbosch University has been privileged to have Dr. Till Biedermann who is a lecturer at the Institute of Sound and Vibration Engineering (ISAVE) at Hochschule Düsseldorf, University of Applied Sciences, Germany, visit us. During his stay he conducted research alongside Prof. Johan van der Spuy. Dr. Biedermann is also the vice chair for the Fans and Blowers Committee of the American Society of Mechanical Engineers (ASME).

Accompanied by Mr. Coenraad Swanepoel, our PhD candidate in Solar Thermal Energy Research, he spent the last three months conducting noise and performance experiments on an industrial cooling fan. They investigated the aerodynamic noise impact and how to reduce the noise of these fans.

Experimental testing was done at the ISO5801, Type A Fan Test facility of the Mechanical and Mechatronic Engineering Department. For the tests, two microphones were used to carry out noise coherence studies by Dr. Biedermann. One microphone was placed outside the plenum and one inside the plenum. Dr. Biedermann found that the microphone placed inside the plenum chamber gave clearer results than the microphone placed outside the plenum chamber. Noise sources from the motor was reduced through insulation.

Experiments were carried out on eight- and four bladed, 1.542 meter diameter, fan configurations, with the same solidity. The impact on noise and fan performance were investigated by reducing the blade tip clearance near the shroud from 4 mm (0.26% fan diameter) to 2 mm (0.13% fan diameter), to 0 mm, for both fan configurations. The noise profile of each fan configuration at the same blade tip clearance and volumetric flow rate was then compared to each other. The results were clear and conclusive. The largest blade tip clearance was used as the baseline to measure the nett increase or decrease in sound levels. Dr. Biedermann and Mr. Swanepoel found that reducing the blade tip clearance in both fan configurations increased the fan performance along with a significant reduction in noise emissions from both fans at design flow rate. It was also discovered that the four bladed fan configuration had lower noise emissions than the eight bladed fan configuration at all blade tip clearances due to its lower blade passing frequency and longer chord length at design flow rate. It is concluded that reducing the blade tip clearance and number of blades, at constant solidity, reduces sound emissions. The 0 mm blade tip clearance for the four bladed fan produced the greatest reduction in noise emissions. An increase in fan total-to-static performance with reduction on blade tip clearance was also observed for both fan configurations.

We thank Dr. Biedermann for his valuable contribution at Stellenbosch University, for sharing his insights and skills with us at the Department. We also want to acknowledge the Institute of Sound and Vibration Engineering (ISAVE) at Hochschule Düsseldorf, University of Applied Sciences, for permitting this exchange of expertise. We appreciate the visit immensely and look forward to future cooperation.

 

In the foto below, from left to right: Coenraad Swanepoel, Dr. Till Biedermann and Prof Johan van der Spuy at the ISO5801, Type A Fan test facility.