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The acoustic characteristics of barriers with a T-shaped profile are studied by finite element simulation. It has been found that the sound reduction efficiency of this barrier is related not only to diffraction, but also to sound interference at the leading and trailing edges of the barrier. It is shown that the sound interference at the trailing...
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... In recent studies [1,3,2], a circular micro-perforated panel (MPP) arrangement using the principle of λ/4 reflection damping, has been applied adjacent to a lowpressure axial fan. The MPP in combination with an airtight back volume of length L c forms a micro-perforated absorber (MPA). ...
... These offer the advantage that they do not generate any additional pressure loss and can be designed for corresponding frequency-specific absorption levels. These sound absorbers have already been integrated, for example, in the direct proximity of axial fans in ducts, in HVAC systems or in rooms [9][10][11][12][13][14][15][16]. In addition, MPAs offer the properties that they are non-flammable, do not concentrate toxic substances, and do not pose a risk to humans from accumulated viruses or smallest fibers. ...
In air conditioning systems heat exchangers are frequently installed upstream of ventilators. These modules are part of the daily life of humans and should therefore create an environment that is as quiet as possible. The heat exchanger generates increased turbulence, which leads to increased sound emissions of the ventilator. Due to installation space limitations, it is not possible to connect silencers to the heat exchanger module. A novel concept is presented, which allows to reduce the sound emissions of heat exchanger due to plate absor-bers without the need of additional installation room. The plates contain sub-millimeter openings. They are integrated into the heat exchanger housing together with back volumes. This arrangement guarantees compact-ness and generates no additional flow resistance. The emitted sound could be reduced by up to 2.9 dB in the partial load range. The main advantages of the concept presented are individual adjustment, cost-effective design and simple installation.
... Also the experimental setup and a selection of MPA investigated structures are described (cf. [17,18]). In Section 3 the simulation results of the MPA configurations are compared to measured data. ...
The reduction of fan noise in ducts is a challenging task for acoustic engineers. Usually, the confined space where an absorber can be integrated is small. In addition, one has to consider the influence of the absorber on the flow field and the attenuation of noise should be as great as possible. In this contribution, we investigate the application of a micro-perforated absorber (MPA) in the direct vicinity of a low-pressure axial fan operating at low Mach number conditions. The micro-perforated plates (MPP) are modeled using the Johnson-Champoux-Allard-Lafarge (JCAL) model for porous materials. The entire geometrical setup of duct, fan and MPA is then simulated with the Finite Element (FE) method; the pre-processing effort is reduced by using non-conforming grids to discretize the different regions. The influence of the cavity length and the positioning of the fan are analyzed. The results are then applied to the construction of a full-sized MPA duct component that takes the limited space into consideration. Simulation results and overall functionality are compared to experimental results obtained in an axial-fan test rig. The Finite Element framework proved to be robust in predicting overall sound pressure level reduction in the higher volume flow rates. It is also shown that the MPP increases sound reduction in the low-frequency regime and at two resonant frequencies of the MPA setup. However, its main benefit lies in maintaining the efficiency of the fan. The location of the fan downstream or within the MPA has a significant effect on both the simulated and measured sound reduction.
... Mit den Verwendungen von mikroperforierten Absorbern (MPA) in HVAC-Systemen [1] und als Rohrauskleidung in Axialventilator-Rohrsystemen [2] konnte gezeigt werden, dass die von der Turbomaschine abgestrahlte Schallleistung mittels der mikroperforierten Absorber deutlich reduziert werden kann. Dabei werden die MPAs flach an die Oberfläche montiert während sich hinter diesen ein mit Luft gefülltes Rückvolumen befindet. ...
Axialventilatoren werden in einer großen Anzahl von Systemen für die Bereitstellung eines hohen Volumenstroms verwendet. So kommen diese Turbomaschinen beispielsweise in der Kühlungs- und Klimatisierungstechnik zum Einsatz. Da sich diese Anlagen oftmals in der Nähe von Personen befinden, werden vor allem die akustischen Emissionen mit einzuhaltenden Grenzwerten belegt. Dies soll vermeiden, dass umgebende Menschen von zu hohen Geräuschkulissen belästigt oder gestört werden. Neben den Schallreduktionsmaßnahmen am Axialventilator, wie zum Beispiel Ventilatorsichelung oder Schaufelblattmodifikationen, können Belüftungsanlagen auch mit passiven Schallabsorbern ausgestattet werden, welche zu einer Verringerung des emittierten Schalldruckpegels führen. Eine solche Maßnahme ist die Verwendung von mikroperforierten Absorbern, welche in das Rohrsystem des Ventilators intrigiert werden. In diesem Anwendungsfall werden die Absorber von dem Fördermedium direkt überströmt. Die Funktionsweise solcher überströmten Absorber in direkter Nähe zu den Ventilatorschaufeln ist noch nicht verstanden und wurde bislang nicht untersucht. Im Zuge dieser experimentellen Studie wurde die Schallreduktion von kommerziell erwerblichen mikroperforierten Absorber auf den Anwendungsfall von Axialventilatoren optimiert. Dabei wurden verschiedene Parameter wie axiale Position der Absorber, Art des Rückvolumens und Unterteilung des Rückvolumens berücksichtigt. Zudem war eine Variation der Zuströmbedingungen zum Axialventilator Teil der Untersuchungen.
