{"title":"On the impact of operating condition and testing environment on the noise sources in an industrial engine cooling fan","authors":"","doi":"10.1016/j.apacoust.2024.110252","DOIUrl":null,"url":null,"abstract":"<div><p>Engine cooling fan noise is a relevant issue for manufacturers. It is well known that both the operating point and testing environment can affect the noise generation mechanisms and, consequently, the measured noise may change. Therefore, these aspects are investigated on a reference industrial fan, for which experimental data exists, using high-fidelity numerical simulations based on the lattice-Boltzmann method. Two operating conditions, namely the free blowing and the maximum efficiency ones, and three testing environments are analyzed: (i) a conventional semi-anechoic room, (ii) an ideal free field environment, and (iii) a testing environment resembling an anechoic aeraulic facility. For cases (i) and (ii) no pressure difference across the fan is imposed, while, for case (iii), a pressure difference across the fan can be imposed. For the latter, the impact of a fully reflective and fully absorbing wall separating the two regions upstream and downstream of the fan is analyzed. At free blowing conditions, the flow over the blades is largely separated. When the blade passes through a blockage region, because of the presence of a honeycomb-like structure needed for structural purposes, it experiences a prominent loading hump. The far-field noise, at a listener located along the axis of rotation, is therefore highly tonal, with a clear peak at the blade passing frequency tone. When the same fan is tested in a free field environment, it is found that there is a difference in the acoustic pressure at higher harmonics of the blade passing frequency due to the presence of flow recirculations in the anechoic room. Placing a thin wall across the fan increases the mass flow rate, for a given rotational speed, which results in a more severe flow separation over the blades and, therefore a higher tone prominence at the blade passing frequency. If the thin wall is modeled as a sound-absorbing wall, there is a drop of the overall sound pressure level of about 2 dBA. When the fan is tested at its maximum efficiency, i.e., nonzero pressure difference across the fan, it is found that the blockage effect is less relevant. The main noise generation mechanism is the back-flow vortex induced by the pressure difference across the fan interacting with the blade tip leading edge.</p></div>","PeriodicalId":55506,"journal":{"name":"Applied Acoustics","volume":null,"pages":null},"PeriodicalIF":3.4000,"publicationDate":"2024-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0003682X24004031/pdfft?md5=e4074919b461e832c05c642105db4428&pid=1-s2.0-S0003682X24004031-main.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Applied Acoustics","FirstCategoryId":"101","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0003682X24004031","RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ACOUSTICS","Score":null,"Total":0}
引用次数: 0
Abstract
Engine cooling fan noise is a relevant issue for manufacturers. It is well known that both the operating point and testing environment can affect the noise generation mechanisms and, consequently, the measured noise may change. Therefore, these aspects are investigated on a reference industrial fan, for which experimental data exists, using high-fidelity numerical simulations based on the lattice-Boltzmann method. Two operating conditions, namely the free blowing and the maximum efficiency ones, and three testing environments are analyzed: (i) a conventional semi-anechoic room, (ii) an ideal free field environment, and (iii) a testing environment resembling an anechoic aeraulic facility. For cases (i) and (ii) no pressure difference across the fan is imposed, while, for case (iii), a pressure difference across the fan can be imposed. For the latter, the impact of a fully reflective and fully absorbing wall separating the two regions upstream and downstream of the fan is analyzed. At free blowing conditions, the flow over the blades is largely separated. When the blade passes through a blockage region, because of the presence of a honeycomb-like structure needed for structural purposes, it experiences a prominent loading hump. The far-field noise, at a listener located along the axis of rotation, is therefore highly tonal, with a clear peak at the blade passing frequency tone. When the same fan is tested in a free field environment, it is found that there is a difference in the acoustic pressure at higher harmonics of the blade passing frequency due to the presence of flow recirculations in the anechoic room. Placing a thin wall across the fan increases the mass flow rate, for a given rotational speed, which results in a more severe flow separation over the blades and, therefore a higher tone prominence at the blade passing frequency. If the thin wall is modeled as a sound-absorbing wall, there is a drop of the overall sound pressure level of about 2 dBA. When the fan is tested at its maximum efficiency, i.e., nonzero pressure difference across the fan, it is found that the blockage effect is less relevant. The main noise generation mechanism is the back-flow vortex induced by the pressure difference across the fan interacting with the blade tip leading edge.
期刊介绍:
Since its launch in 1968, Applied Acoustics has been publishing high quality research papers providing state-of-the-art coverage of research findings for engineers and scientists involved in applications of acoustics in the widest sense.
Applied Acoustics looks not only at recent developments in the understanding of acoustics but also at ways of exploiting that understanding. The Journal aims to encourage the exchange of practical experience through publication and in so doing creates a fund of technological information that can be used for solving related problems. The presentation of information in graphical or tabular form is especially encouraged. If a report of a mathematical development is a necessary part of a paper it is important to ensure that it is there only as an integral part of a practical solution to a problem and is supported by data. Applied Acoustics encourages the exchange of practical experience in the following ways: • Complete Papers • Short Technical Notes • Review Articles; and thereby provides a wealth of technological information that can be used to solve related problems.
Manuscripts that address all fields of applications of acoustics ranging from medicine and NDT to the environment and buildings are welcome.