著者

金子 友暁 横山 博史 佐藤 充 西川原 理仁 柳田 秀記

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

pp.22-00044, (Released:2022-05-25)

参考文献数

16

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For a small axial fan in a duct, the effects of acoustic resonance occurring in the duct on the flow around the fan are focused on. To clarify the condition for the intense acoustic resonance, the effects of the rotational speed and duct width on the flow and acoustic fields around the fan were investigated by compressible flow simulations with a volume penalization method. The computational methods were validated by comparing the predicted static pressure rise and aerodynamic sound by the fan with those measured. The sound pressure level became most intense for a specific rotational speed, where the acoustic resonance occurs at the blade passing frequency in the upstream duct. Although the overall tendency of the increase in the static pressure coefficient was found for a higher rotational speed with the thinner momentum thickness around the blade surface, the static pressure coefficient drops at the rotational speed for the acoustic resonance. Moreover, the acoustic resonance became more intense for a narrower duct width. In this condition, flow disturbances occur near the wall of the bell-mouthed inlet of upstream duct due to the acoustic resonance, which prompts the inflow turbulence to the fan. To clarify the effects of the acoustic resonance on the flow around the fan, the computation with the artificially suppressed acoustic resonance was also performed and the predicted flow fields were compared with those with intense acoustic resonance for the same rotational speed and duct width. The incoming flow to the fan is confirmed to become more turbulent when the acoustic resonance occurs, which promotes the spreading of the tip vortices between rotor blades. As a result, the blade loading decreases and the turbulence in the blade wake leading to mixing loss becomes intense, causing the static pressure rise by the fan to decrease.

著者

飯田 明由 小久保 あゆみ 塚本 裕一 本田 拓 横山 博史 貴島 敬 加藤 千幸

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 B編 (ISSN:03875016)

巻号頁・発行日

vol.73, no.732, pp.1637-1646, 2007-08-25 (Released:2011-03-03)

参考文献数

10

被引用文献数

4 1 7

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The aim of this investigation is to understand the generation mechanism of aero-acoustic feedback noise radiated from rear-view mirrors. In order to clarify the relationship between the velocity fluctuation and radiated noise, correlation in terms of aerodynamic noise and velocity fluctuations were measured in a low-noise wind tunnel. The experimental results showed that noise level of the tonal-noise depended on the ratio of the height of the bump to the thickness of the boundary layer. Strong tonal-noise was generated when the height of the bump was almost equal to 40% of the height of the boundary layer. The tonal-noise level also depended on the length between the trailing-edge of the bump and the edge of rear-view mirror. The frequency of the tonal noise can be calculated by modified Rossiter equation. The tonal-noise was disappeared in the case of the bump was placed at separated boundary layer. It revealed that the seed of the tonal noise was small disturbances generated by the bump on the surface of the rear-view mirror.

著者

吉永 司 横山 博史

出版者

一般社団法人 日本フルードパワーシステム学会

雑誌

フルードパワーシステム (ISSN:13467719)

巻号頁・発行日

vol.53, no.4, pp.170-174, 2022 (Released:2023-11-02)

参考文献数

13

著者

横山 博史 北宮 克哉 飯田 明由

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:18848346)

巻号頁・発行日

vol.79, no.804, pp.1419-1433, 2013 (Released:2013-08-25)

参考文献数

16

被引用文献数

1 1

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To clarify the mechanism of acoustic radiation in flows around a cascade of flat plates, fluid structures and acoustic fields were elucidated by direct simulations. The simulations were mainly performed for flows around 5 parallel plates and the separation-to-thickness ratio s/d was 6.0. The freestream velocity was changed from 30 m/sec to 60 m/sec, and the acoustic resonance occurs between plates at the freestream velocity of 44 m/sec. At that velocity, the Reynolds number based on the chord length and the freestream velocity was 8.7×104 and that based on the plate thickness was 5.8×103. Computational results were validated by the experimental results performed in the present research. The computational results showed that large-scale vortices composed of fine-scale vortices are shed in the wakes of the plates independently of the acoustic resonance. When the large-scale vortex is shed from the upper or lower face, an expansion wave is radiated around the downstream edge of the upper or lower face, respectively. The compression wave is radiated around the downstream edge of the opposite face. The simulation for the flow around a single plate was also performed, and the results confirmed the above-mentioned acoustic radiation mechanism. For the flows around a cascade of flat plates, the sheddings of the vortices from neighboring plates are synchronized when the acoustic resonance occurs. It was also clarified that the mode of the synchronization is an anti-phase mode and the standing waves generated between plates are reinforced.

著者

山崎 貴史 松岡 常吉 横山 博史 中村 祐二

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.86, no.889, pp.20-00210, 2020 (Released:2020-09-25)

参考文献数

25

被引用文献数

1 1

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The effects of the traveling sound wave generated by the speaker on diffusion flame were investigated experimentally. The sound frequency was varied from 50 to 1000 Hz using two sizes of loudspeakers, whose peak frequency showing the maximum sound pressure amplitude is nearly identical. A spirit lamp was used as the reference (diffusion) flame. Having irradiation of sound, the flame was inclined and stretched toward the traveling direction under specific range of the exposed frequencies and importantly, the effective range of the frequency was found to be quite different in two speakers used in this study. Precisely speaking, the deformed flame length reached its maximum value under the condition of 200 to 400 Hz for small speaker and 50 to 200 Hz for large speaker, respectively. In addition, the velocity distribution around the speaker was measured to reveal that the variation of flame length with respect to frequency, and it was found that the response against the applied frequency was rather close to that of flow velocity, not that of the acoustic pressure amplitude. Further investigation of flow field nearby the speaker clearly showed that the pump-like flow acceleration was induced by the periodic motion of the membrane of the speaker. From the above results obtained, it was confirmed that the effect of acoustic sound on the flame shall be come not only from pure acoustic wave feature but also from the factors depending on the hardware. Without the eliminating the latter effect, nature of acoustic-flame interaction behavior by using acoustic characters (e.g., frequency or acoustic pressure) is not readily available.

著者

田所 真樹 横山 博史 水野 雅隆 飯田 明由 若松 幹生 Phan Vinh Long 田中 博

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.84, no.863, pp.18-00199, 2018 (Released:2018-07-25)

参考文献数

19

被引用文献数

2

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Aerodynamic noise generated around a step such as front pillars of automobiles, which is transmitted into the cabin through the window glass, can negatively affect the comfort of the passengers. For the reduction of this noise, it is necessary to clarify the acoustic source and process of the propagation of the acoustic waves from the step. To do this, direct aeroacoustic simulations were performed along with wind tunnel experiments for flows around a forward step in a turbulent boundary layer, where the freestream Mach number was 0.1 and the Reynolds number based on the incoming boundary layer thickness, δ, and the freestream velocity was 2.73×104. The computations were performed for the height of h/δ = 0.9 and 3.4, where the effects of the step height on the radiated sound were investigated. The radiated sound becomes more intense for the higher step of h/δ = 3.4 particularly in a low frequency range of St ≤ 1.5, where St is the non-dimensional frequency based on the step height and freestream velocity, due to the occurrence of the large-scale vortices in the separated flow. To elucidate the radiation of the acoustic waves, the pressure fluctuations were decomposed into non-radiating convective and radiating acoustic components by usage of two methods. One is utilizing wavenumber-frequency spectra and the other one is spatial Gaussian filtering for the fluctuations at each frequency, which is proposed in this paper. The results by the former method present that the level of convective components is larger than the acoustic components by 20 - 40 dB. Moreover, the radiating components by the proposed spatial filtering method show that the radiation occurs around the step edge and the reattachment point. It is indicated that the proposed method is effective for the investigation of the acoustic radiation for the pressure fluctuations composed of convective and acoustic components.

著者

宮本 孟宜 横山 博史 飯田 明由

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.84, no.861, pp.18-00121-18-00121, 2018 (Released:2018-05-25)

参考文献数

19

被引用文献数

1

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Intense sound is radiated due to aeroacoustic feedback loop from a flow around the trailing edge of a curved plate with a kink shape such as a bonnet of an automobile. For the reduction of this noise, the control by a plasma actuator (PA) was investigated. The aim of this investigation is to clarify the effects of flow control by the PA on noise reduction and the noise reduction mechanism. To do this, wind tunnel experiments with a half-scale bonnet model and direct numerical simulations of flow and sound fields were performed. The investigation of the effects of the position for the installation of the PA on the control presents that the control at the position close to the flow separation point around the kink is effective for the noise reduction. Also, the control effects were compared between co-flow and counter-flow configurations regarding the direction of the mean induced flow by the actuator to the freestream. The mean velocity profiles showed that the flow separation was suppressed by the control with both configurations, while this control effect is more effective for the counter-flow configuration. The measured velocity fluctuations present that the power in broadband frequency range in the downstream of the actuator becomes larger by the control with both configurations. The predicted results show that small-scale vortices are shed near the wall around the actuator due to the large counter-flow induced flow. This introduction of the vortices and the intensification of the broadband velocity fluctuations lead to the suppression of the flow separation. Also, the development of the power of the velocity fluctuations at the fundamental frequency of the baseline tonal sound is weakened by the suppression of the flow separation. This supports the predicted results of the suppression of the two-dimensional vortices contributing to the acoustic radiation around the re-attachment point by the control. Consequently, the control can lead to the suppression of the feedback loop of the radiating mechanism of tonal sound.

著者

飯田 明由 小久保 あゆみ 塚本 裕一 本田 拓 横山 博史 貴島 敬 加藤 千幸

出版者

一般社団法人日本機械学会

雑誌

日本機械学會論文集. B編 (ISSN:03875016)

巻号頁・発行日

vol.73, no.732, pp.1637-1646, 2007-08-25

被引用文献数

6

---

The aim of this investigation is to understand the generation mechanism of aero-acoustic feedback noise radiated from rear-view mirrors. In order to clarify the relationship between the velocity fluctuation and radiated noise, correlation in terms of aerodynamic noise and velocity fluctuations were measured in a low-noise wind tunnel. The experimental results showed that noise level of the tonal-noise depended on the ratio of the height of the bump to the thickness of the boundary layer. Strong tonal-noise was generated when the height of the bump was almost equal to 40% of the height of the boundary layer. The tonal-noise level also depended on the length between the trailing-edge of the bump and the edge of rear-view mirror. The frequency of the tonal noise can be calculated by modified Rossiter equation. The tonal-noise was disappeared in the case of the bump was placed at separated boundary layer. It revealed that the seed of the tonal noise was small disturbances generated by the bump on the surface of the rear-view mirror.