• 제목/요약/키워드: Wall pressure spectrum

검색결과 32건 처리시간 0.025초

Time domain broadband noise predictions for non-cavitating marine propellers with wall pressure spectrum models

  • Choi, Woen-Sug;Hong, Suk-Yoon;Song, Jee-Hun;Kwon, Hyun-Wung;Park, Il-Ryong;Seol, Han-Shin;Kim, Min-Jae
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제13권1호
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    • pp.75-85
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    • 2021
  • The broadband noise can be dominant or important for total characteristics for marine propeller noise representing the minimum base of self-noise. Accurate prediction of such noise is crucial for survivability of underwater military vessels. While the FW-H Formulation 1B can be used to predict broadband trailing edge noise, the method required experiment measurements of surface pressure correlations, showing its limitations in generality. Therefore, in this study, the methods are developed to utilize wall pressure spectrum models to overcome those limitations. Chase model is adopted to represent surface pressure along with the developed formulations to reproduce pressure statistics. Newly developed method is validated with the experiments of airfoils at different velocities. Thereafter, with its feasibility and generality, the procedure incorporating computational fluid dynamics is established and performed for a propeller behind submarine hull. The results are compared with the experiments conducted at Large Cavitation Tunnel, thus showing its usability and robustness.

Active Control of Flow Noise Sources in Turbulent Boundary Layer on a Flat-Plate Using Piezoelectric Bimorph Film

  • Song, Woo-Seog;Lee, Seung-Bae;Shin, Dong-Shin;Na, Yang
    • Journal of Mechanical Science and Technology
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    • 제20권11호
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    • pp.1993-2001
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    • 2006
  • The piezoelectric bimorph film, which, as an actuator, can generate more effective displacement than the usual PVDF film, is used to control the turbulent boundary-layer flow. The change of wall pressures inside the turbulent boundary layer is observed by using the multi-channel microphone array flush-mounted on the surface when actuation at the non-dimensional frequency $f_b^+$:=0.008 and 0.028 is applied to the turbulent boundary layer. The wall pressure characteristics by the actuation to produce local displacement are more dominantly influenced by the size of the actuator module than the actuation frequency. The movement of large-scale turbulent structures to the upper layer is found to be the main mechanism of the reduction in the wall- pressure energy spectrum when the 700$700{\nu}/u_{\tau}$-long bimorph film is periodically actuated at the non- dimensional frequency $f_b^+$:=0.008 and 0.028. The biomorph actuator is triggered with the time delay for the active forcing at a single frequency when a 1/8' pressure-type, pin-holed microphone sensor detects the large-amplitude pressure event by the turbulent spot. The wall-pressure energy in the late-transitional boundary layer is partially reduced near the convection wavenumber by the open-loop control based on the large amplitude event.

후향계단 주위의 난류 박리재부착유동에서의 벽압력변동의 통계적 특징 (Cross-Spectral Characteristics of Wall Pressure Fluctuations in Flows over a Backward-Facing Step)

  • 이인원;성형진
    • 대한기계학회논문집B
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    • 제24권2호
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    • pp.280-287
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    • 2000
  • Laboratory measurements were made of wall pressure fluctuations in a separated and reattaching flow over a backward-facing step. An array of 32 microphones along the streamwise direction was utilized. Various statistical properties of pressure fluctuations were scrutinized. The main emphasis was placed on the flow inhomogeneity along the streamwise direction. One point statistics such as the streamwise distribution of rms pressure and autospectra were shown to be generally consistent with other studies. The coherences and wavenumber spectra in the streamwise directions were indicative of the presence of dual modes in pressure; one is the large-scale vortical structure in low frequency and the other is the boundary-layer-like decaying mode in high frequency.

축대칭 3차원 물체의 유동 소음 스펙트럼 측정 (A measurement of flow noise spectrum of an axisymmetric body)

  • 박연규;김양한
    • 대한기계학회논문집B
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    • 제22권6호
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    • pp.725-733
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    • 1998
  • The pressure fluctuation on the surface of a submerged body has been recognized as a dominant noise source. There have been many studies concerning the flow induced noise on a flat plate. However, the noise over an axisymmetric body has not been well reported. This paper addresses the way in which we have investigated the mechanism of noise generation due to an axisymmetric body. The associated experiments and signal processing methods are introduced. A 3-dimensional axisymmetric body whose length and diameter were 2 m and 10.4 cm, was prepared as a test specimen. The wall pressure on the surface of the body was measured in a large scale low noise wind tunnel at KIMM(Korea Institute of Machinery and Metals). To measure the wall pressure, we used two microphone arrays which were tangential and normal to the flow. Based on the measured signal, frequency-wavenumber spectrum which explains the structure of turbulence noise, was estimated. Tangential to the flow, there exists convective ridge at a relatively higher wavenumber region; this can cause spatial aliasing. To circumvent this problem, the cross spectrum was interpolated. The interpolation has been performed by unwrapping the phase and smoothing the cross spectrum. The phase unwrapping was done based on the Corcos model; the phase of cross spectrum decreases linearly with the distance between microphones. Aforementioned signal processings are possible by employing the experimental results that the estimated wavenumber spectrum quite resembles the Corcos model. We try to modify the Corcos model which is applicable to the flat plate, by altering the magnitude of cross spectrum to fit the experimental data more accurately. We proposed that this wavenumber spectrum model is suitable for the 3-dimensional axisymmetric body. Normal to the flow, there exists a little correlation between signals of different microphones. The circumferential wavenumber spectrum contains uniform power along the wavenumbers.

난류 경계층에서 컴플라이언트 코팅된 벽면과 점탄성 벽면의 방사 소음에 관한 실험적 연구 (Radiated Sound from Compliant and Viscoelastic Plates in a Turbulent Boundary Layer)

  • 이창준;이승배;권오섭;전우평
    • 대한기계학회논문집B
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    • 제27권3호
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    • pp.294-301
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    • 2003
  • We examine a problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick. open-cell foam with fabric covering and a viscoelastic-painted plate of 1mm thick over an acoustic board of 4mm thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber (k$_{c}$h) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

평판 난류경계층에서의 벽 압력섭동에 대한 실험적 연구 (Experimental Study on Wall Pressure Fluctuations in the Turbulent Boundary Layer on a Flat-Plate)

  • 이승배;김휘중
    • 대한기계학회논문집B
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    • 제23권6호
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    • pp.722-733
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    • 1999
  • The wall pressure fluctuations of a turbulent boundary layer over a flat plate have been investigated in an anechoic wind tunnel facility. The anechoic wind tunnel consists of acoustically-lined duct, muffler, and splitter-type silencer for noise suppression and vanes for reducing head losses involved. To improve spectra characteristics in high frequency range, a 1/8" pressure-type microphone sensor, which has a pin-holed cap of various diameters, was employed in this experiment. It was shown that the pin-holed microphone sensor with a dimensionless diameter $d^+$ of 7.1 resolved the high frequency pressure fluctuations most effectively among ones with various pin-hole diameters. The measured wall pressure spectra in terms of three types of scaling parameters were in good agreement with other experimental and numerical results. The pressure events of high amplitude were found to contribute to total fluctuating pressure energies in the turbulent boundary layer significantly and supposed to radiate to the far-field effectively.

침투성 코팅 처리된 벽면 주위의 벽 압력 특성 (Characteristics of Wall Pressure over Wall with Permeable Coating)

  • 송우석;신승열;이승배
    • 대한기계학회논문집B
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    • 제36권11호
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    • pp.1055-1063
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    • 2012
  • 16채널 어레이 마이크로폰을 이용하여 난류 유동장 내 벽면 압력섭동에 대한 측정을 수행하였다. 본 실험에 사용된 코팅재질은 약 50 ppi (pores per inch)의 다공성 구조로 이루어진 우레탄 물질로 이루어져 있다. 코팅의 주된 목적은 난류 유동장 내 최소한의 공간을 유지하면서 대류속도로 진행하는 난류 와들을 필터링하는 역할을 하는 것이다. 평판 위 경계층의 측정은 열선 유속계를 이용하였으며 표면 마찰계수 값을 얻기위해 CPM법을 사용하였다. 벽압력 스펙트럼과 파수-주파수 스펙트럼 측정은 코팅에 의해 얼마나 에너지가 저감되는 지를 비교하기 위해 사용되었다. 벽면 코팅은 대류하는 무차원 벽면섭동압력에너지를 저감시켰지만, 컴플라이언트 코팅된 벽면 거칠기로 인해 일반 강체 평판에 비해 상대적으로 발달된 경계층을 형성하였으며 벽면 평균전단응력과 저주파수 압력스펙트럼 레벨도 함께 증가하였다.

축대칭 물체의 경계층 유동소음에 대한 실험적 연구 ( I ) - 축대칭 물체 전두부 및 실린더 벽면 섭동압력 - (Experimental Study on Flow Noise Generated by Axisymmetric Boundary Layer ( I ) - Wall Pressure Fluctuations on Axisymmetric Noses and on a Cylinder in an Axial Flow -)

  • 이승배;김휘중;권오섭;이상권
    • 대한기계학회논문집B
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    • 제24권7호
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    • pp.945-956
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    • 2000
  • The axisymmetric bodies considered in this study have hemispherical and ellipsoidal noses. The near-field pressure fluctuations over each nose model at $Re_D=2.43{\times}10^5$ were investigated in the laminar separation region and developing turbulent boundary layers using a 1/8' pin-holed microphone sensor. The wall pressure fluctuations were also measured in an axisymmetric boundary layer on a cylinder parallel to mean flow at a momentum thickness Reynolds number of 850 and a boundary layer thickness to cylinder radius ratio of 1.88.

난류 경계층에서 컴플라이언트 코팅과 점탄성 벽면의 방사 소음에 관한 실험적 연구 (Radiated Sound from Compliant and Viscoelastic Plates in a Turbulent Boundary Layer)

  • 이승배;이창준;권오섭;전우평
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2002년도 학술대회지
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    • pp.779-782
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    • 2002
  • We examine the problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick, open-cell foam with fabric covering and a viscoelastic painted plate of 1mm thick over an acoustic board of 4m thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber ($k_{ch}$) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

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난류경계층에 의한 다층재질 원통형 실린더의 유체소음 해석 연구 (A Study of Flow Induced Noise for Multilayered Cylinder due to Turbulent Boundary Layer)

  • 신구균;홍진숙;이헌곤
    • 소음진동
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    • 제6권5호
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    • pp.671-677
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    • 1996
  • This paper presents the analytical method for predicting turbulence- induced noise in the multilayered cylinder composed of an outer hose, an inner fluid and an internal core. It is assumed that an infinite axisymmetric cylinder is located horizontally in water with free stream velocity and the turbulent boundary layer (TBL) surrounding the outer hose is fully developed and homogeneous. The transfer function at the core surface due to the propagation of the pressure fluctuation within the TBL is formulated using the linearized Navier-Stockes equation for solid and fluid. In the estimation of the energy spectrum of wall pressure fluctuation, the empirical formula proposed by Strawderman based on the Corcos model is used. A general algorithm for the calculation of the pressure level at the surface of a core, that is, turbulence- induced noise, is presented. Through the detailed numerical simulation, it is found that the major noise mechanism is the propagation of the bulge wave along hose.

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