日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
27 巻 , 8 号
選択された号の論文の9件中1~9を表示しています
  • 早坂 寿雄
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 361-362
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
  • 奥田 襄介
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 363-372
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
    In the proceeding paper(this Journal 25(3)1969, p. 122), it was shown that the noise reducing effect of a muffler is deduced by means of the four-terminal constants of the equivalent electrical network of the whole muffler system, and for expansion chamber type mufflers, approximate equations are very simple and the noise reducing curve is easily obtained by a graphical method. In this paper, a similar method is applied to the resonator type mufflers, and equations are shown in Eq. (11), (12), (13) and (16), and a graphical method in Table 1 and Fig. 8. Practically, as shown in Fig. 7(a), the resonator type muffler is efficient only in the region near the first resonant frequency, and furthermore the loss at the mouth of resonator is not negligible. But the calculation of the loss is very difficult, so the loss is estimated as convenient to the graphical process as shown id Fig. 9. By this estimation, the noise reducing curve is very easily obtained by a graphical method, and as shown in Fig. 7(b), the resulted curve is useful for practical purposes. When the connecting points of the cavity of a resonator and the pipe are in two locations or are distributed as Fig. 11, the four-terminal constants are shown in Eq. (28) and (31). In a practical case, when the distance between the two connecting points or the distributing length of connecting points and the total connecting area are very large, the muffler is approximately equivalent to an expansion chamber type muffler as illustrated in Fig. 13.
  • 今市 憲作, 徳島 耕次
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 373-386
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー

    The heat exchangers with tube banks have been widely used for steam power plants and other purposes. In such heat exchangers, violent acoustical oscillations have often been experienced and they have yielded extraordinarily heavy noises and such intensive vibrations that the duct wall breaks sometimes. It has been revealed by many authors that those phenomena resulted from fluctuating pressure due to periodic generation of Karman vortices from the tube bank. In this study, the model tube banks of an in-line arrangement or a staggered one, such as shown in Fig. 2 and Table 1, were used and the fluctuating pressure occurring in the tube banks was elaborately measured and the associated phenomena were observed. The notations to express the tube arrangements were defined as follows. For example, S8-4(-10) shows the staggered arrangement, P_L=L/D=8, P_T=T/D=4 (and that the number of rows of tubes in the flow direction is 10), or P4-2(-5) does in-line arrangement, P_L=4, P_T=2 (and the number of rows of tubes in the flow direction is 5). The used apparatus, measuring devices and instrumentation were such as shown in Fig. 1 to Fig. 5. Since the working section was the duct with the rectangular section which had one side shorter than the other, it was able to be regarded as a two-dimensional field. As the representive value of fluctuating pressure in the tube bank, the measured one on the upper wall at the section immediately upstream form the tube bank was taken. Fig. 6 is typical example of the overall level of fluctuating pressure, L_0, shedding frequency of Karman vortices, f_k and intensity of the component of f_k, L_k plotted against mean flow velocity in the duct, U_0. In this example, L_0 took two extreme values at f_k=375Hz and f_k=705Hz. These values were nearly equal to the natural acoustic frequencies of the duct, f_b(1/2)=355Hz for 1/2 wave mode and f_b(1)=710Hz for 1 wave mode. These and following facts proved acoustical resonance. Such extremities were observed in the relations of L_0 or L_k over U_0 for all arrangements of 2<P_L<10 and 2<P_T<4. While, Fig. 9 shows the same relations in the case of P2-4. In this case, though the fluctuating pressure component of f_k could be clearly identified, no resonant state was observed, that is no extreme point was found on its L_0-U_0 or L_k-U_0 relation. Therefore, it was clear that, even if Karman vortices may generate from tubes, resonance does not always occur but needs the condition that the tube arrangement must be confined with in a certain range. In each case, f_k was accurately proportional to U_0 and , then, the Strouhal number became a certain constant depending only on the pattern of tube arrangement, regardless of the total number of tubes. The Strouhal numbers gained in this study are shown in Table 3. From these results, it was deduced that a slight variation of tube arrangement gave a considerable change to the value of the Strouhal number. It seems that the relation of St with P_L and P_T is not very simple but quite complicated and perhaps discontinuous. Fig. 7 shows the distribution of L_0 along Y-axis at the duct section immediately upstream of tube bank in the case of S8-4 with U_0/U_r as parameter. Where, U_r is the flow velocity at resonance. Fig. 8(b) is an example of the distribution of equal L_0 lines over X-Y plane at resonance. As evidently shown in both the figures, on the resonant state, an obvious standing wave was found in within in the tube bank or its close vicinity. In Fig. 10, the resonance level of 1/2 wave mode standing wave, L_b(1/2) is plotted against the total number of tubes, N, for different types of tube arrangement. It followed from these results, that, as the number of tubes increased, resonance became stronger. Further, by comparing the level of 1/2 wave mode for S4-4-10 with that of 1 wave mode for the same arrangement which is shown in Fig. 10, it is known that the

    (View PDF for the rest of the abstract.)

  • 広瀬 達三, 木本 日出夫
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 387-393
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
    One of the reasons, why the intense first subharmonic component is contained in the cavitation noise produced in the relatively weak acoustic field, is often explained to be caused by the re-radiation sound pressure of the parametricly excited bubbles, whose radius is approximately twice the resonance bubble size for the acoustic frequency. However, the reason why such bubbles are produced in the acoustic field has not yet been clarified. In this paper, according to the consideration of the gas diffusion through the wall of the cavitation bubble, we have theoretically verified the fact that the bubbles, with radius approximately twice the resonance bubble size, can stationarily exist in the acoustic field. Considering on the rectified diffusion model of the cavitation bubble, we assumed the followings;(1) There is a spherical diffusion boundary layer of thickness a surrounding the bubble wall. (2) Gas concentration in the boundary layer changes from C_(SR) on the bubble wall(r=R) to C_(S∞) on the outside of the layer(r=R+a). (see Fig. 1)(3) The velocity of diffusion of the gas through the bubble wall is faster than the oscillating velocity of the bubble wall, and the diffusion of gas is always in the static equilibrium state. Under the above assumptions we determined the distribution of gas concentration in the diffusion boundary layer surrounding the bubble wall. (see Eq. (3))Thus the increase of gas content in the bubble at time t, after begining of the pulsating motion of the bubble, is given by the following equation. ΔM=(4πC_<s0>D)/a∫^^t__0((C_<S∞>)/(C_<S0>)R^2-(R^3_0)/R)dt (8)On the other hand, according to the cavitation bubble model, the time change of the bubble radius is governed by the following equation. (d^2R)/(dt^2)+(2R)/3((dR)/(dt))^2=1/(ρR)(P_g-(2σ)/R-P_a+P_0cosωt) (9)According to the increase or decrease of the gas content in the bubble, that is, if ΔM is positive or negative, we decide that the bubble will become to grow or not. If ΔM is equal to zero during the pulsating motion for several cycles of acoustic field, we decide that the bubble is in the equilibrium state. In Fig. 2, one of our calculated results, the domain bounded by the dotted lines gives the equilibrium state of cavitation bubbles. The domain of the stable equilibrium state gives that of the stationarily pulsating cavitation, and the value of the acoustic pressure of the domain of the unstable equilibrium state gives the so-called cavitation threshold value. Comparing the recently published results with out result in Figs. 5 to 7, we can confirm that they have very good agreement with each other. Attending to the bubble radius of the stationarily pulsating cavitation bubble in Figs. 2 and 7, we can confirm that its size is approximately twice the resonance bubble size. Expanding ΔM in power series of β, we obtain the approximate expression of ΔM in the Eq. (17). Moreover, the condition of the stable equilibrium of the bubble is given in Eq. (19), and from this equation we can confirm that the bubbles which have the approximately twice the radius of the resonance bubble can stationarily be exist in the acoustic field. Thus we can make it clear that the first subharmonic component contained in the cavitation noise caused by the re-radiation of sound by the parametricly excited bubbles in the acoustic fields.
  • 牧野 敏博, 橋本 清
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 394-395
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
  • 藤崎 博也, 須藤 寛
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 396-397
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
  • 中島 平太郎
    原稿種別: 本文
    1971 年 27 巻 8 号 p. 398-406
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
  • 原稿種別: 本文
    1971 年 27 巻 8 号 p. 409-410
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
  • 原稿種別: 付録等
    1971 年 27 巻 8 号 p. 419-
    発行日: 1971/08/10
    公開日: 2017/06/02
    ジャーナル フリー
feedback
Top