• Title/Summary/Keyword: Transverse Acoustic Modes

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Theoretical Study on Acoustic Instability in Liquid Rocket Engine (액체 로켓 엔진의 음향 불안정 예측에 관한 이론적 연구)

  • Sohn, Chae-Hoon
    • 한국연소학회:학술대회논문집
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    • 2000.12a
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    • pp.92-100
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    • 2000
  • One method to analyse acoustic modes is proposed to predict the characteristics of acoustic instability in liquid rocket engine. It is based on the similarity between transverse acoustic modes and adopts two-dimensional axisymmetric geometry. Using this method, the first tangential mode in the prototype combustor can be analysed through the analysis of the first radial mode in the model combustor with doubled chamber diameter. Sample numerical calculation is demonstrated applying this method to sample rocket engine and thereby acoustic instabilities of the engine are investigated. The present results show a good agreement with the previous findings. The numerical analysis based on the proposed method is cost-effective and serves as the first approximation to the true solution.

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Acoustic Coupling between Longitudinal and Transverse Modes in an Annular Gas Turbine Combustor (환형 가스터빈 연소기에서 종방향 및 횡방향 음향모드 커플링)

  • Kim, Jihwan;Kim, Daesik
    • Journal of the Korean Society of Combustion
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    • v.23 no.1
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    • pp.13-20
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    • 2018
  • Transverse acoustic mode in annular combustion chambers affects air-fuel mixing characteristics in the nozzle and can result in heat release fluctuations in the combustor. In addition, the acoustic mode coupling between the nozzle and the combustion chamber is one of the key parameters determining combustion instability phenomenon in the annular combustor. In this study, acoustic coupling between the nozzle and annular combustor was numerically analyzed using 3D-based in house FEM code. As a result, it was found that the acoustic mode inside the combustion chamber at anti-node locations of the transverse mode was strongly influenced by the nozzle inlet boundary conditions.

Acoustic Analysis of KSR-III Combustion Chamber with Various 5-Blade Baffles under Non-Reacting Condition (5-블레이드 배플이 설치된 로켓엔진 연소실에서의 상온음향 해석)

  • Kim, Hong-Jip;Kim, Seong-Ku;Sohn, Chae-Hoon
    • 한국연소학회:학술대회논문집
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    • 2003.05a
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    • pp.167-171
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    • 2003
  • Acoustic characteristics of baffled combustion chamber to elucidate suppressing effect of baffle on combustion instability are numerically investigated by linear acoustic analysis. A hub-blade baffle of 5 blades is selected as a candidate one and five variants of baffles with various configuration are designed. Resonant-frequency shift and damping factor are analyzed quantitatively as damping parameters. When the hub is located radially at the pressure node, the decrease of resonant frequency and increase of damping factor in 1R mode are dominant. But sub-1T mode is formed within hub, therefore, there would be a possibility of initiating 1T mode in unbaffled region, which would occur another problem. For smaller hub size, four kinds of axial baffle length is selected. As the axial baffle length increases, resonant frequency shift and increase of damping factor of transverse acoustic modes is obtained. Especially, two close acoustic modes such as 1L and 1T could be overlapped for a certain axial length, resulting in extreme increase of damping factor. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

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A Numerical Analysis on Acoustic Radiation Efficiency of One Side-Wetted Rectangular Mindlin Plate with Simply Supported Boundaries (Mindlin 판 이론을 적용한 단순지지 단면 접수평판의 음향방사효율 수치해석)

  • Lee, Jong-Ho;Cho, Dae-Seung
    • Journal of the Society of Naval Architects of Korea
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    • v.55 no.4
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    • pp.281-288
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    • 2018
  • Acoustic radiation efficiency is a crucial factor to estimate Underwater Radiated Noise (URN) of ships accurately. This paper describes a numerical method to analyse acoustic radiation efficiency of one side-wetted rectangular Mindlin plate with simply supported boundaries excited by a harmonic point force. Transverse displacements of plate and acoustic radiation pressures are evaluated by the mode superposition method. The acoustic radiation efficiencies analyzed by both Mindlin and thin plate theories show little differences at monopole and corner modes of low frequency regions but relatively large differences at edge and critical modes of high frequency regions. Especially, the critical frequency with the highest acoustic radiation efficiency evaluated by the Mindlin plate theory is higher than that of thin plate theory. In addition, the acoustic loading effect of fluid also increases bending wave-number of plate and its critical frequency. Finally, the acoustic radiation characteristics of plates with different aspect ratios and thicknesses through numerical analyses are investigated and discussed.

Acoustic Analysis for Design Optimization of Hub-Blade Baffle in Liquid Rocket Engine (액체로켓엔진에서 음향해석을 통한 허브-블레이드 배플 형상의 최적화)

  • Kim, Hong-Jip;Kim, Seong-Ku;Seol, Woo-Seok
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.8 s.227
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    • pp.945-952
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    • 2004
  • Acoustic characteristics of combustion chamber having various baffle configurations are numerically investigated by linear acoustic analysis to suggest reliable baffle specifications in first stage of KSLV-I. To determine the configuration of baffles, an acoustic modal analysis as well as the macroscopic analysis has been done. Hub has another effect of suppressing transverse acoustic mode by confining flow in baffled compartment over general effect of increase in acoustic damping of radial acoustic modes. So, a sufficient number of hub needs to be installed to obtain acoustic damping capacity. 3-blade configuration designed to suppress the first tangential mode has relatively low damping capacity, compared to 5 or 6-blade one. Optimum value of axial baffle length has been determined by comparing acoustic characteristics of combustion chamber having various baffle lengths.

A New Code for Relativistic Hydrodynamics

  • Seo, Jeongbhin;Kang, Hyesung;Ryu, Dongsu
    • The Bulletin of The Korean Astronomical Society
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    • v.45 no.1
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    • pp.55.1-55.1
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    • 2020
  • In an attempt to investigate the nonlinear dynamics such as shock, shear, and turbulence associated with ultra-relativistic jets, we develop a new relativistic hydrodynamics (RHD) code based on the weighted essentially non-oscillatory (WENO) scheme. It is a 5th-order accurate, finite-difference scheme, which has been widely used for solving hyperbolic systems of conservation equations. The code is parallelized with MPI and OpenMP. Through an extensive set of tests, the accuracy and efficiency of different WENO reconstructions, and different time discretizations are assessed. Different implementations of the equation of state (EOS) for relativistic fluid are incorporated, As the fiducial setup for simulations of ultra-relativistic jets, we adopt the EOS in Ryu et al. (2006) to treat arbitrary adiabatic index of relativistic fluid, the WENO-Z reconstructions to minimize numerical dissipation without loss of stability, and the strong stability preserving Runge-Kutta (SSPRK) method to achieve stable time stepping with large CFL numbers. In addition, the code includes a high-order flux averaging along the transverse directions for multi-dimensional problems, and the modified eigenvalues for the acoustic modes to effectively control the carbuncle instability. We find that the new code performs satisfactorily simulations of ultra-relativistic jets.

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Characterization of [011] Poled Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals by Resonance Method (공진법 기반의 [011] 분극 Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 압전단결정 물성규명)

  • Je, Yub;Sim, Min Seop;Cho, Yohan;Lee, Wonok;Lee, Sanggoo;Lee, Jeong Min;Seo, Hee Seon
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.34 no.6
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    • pp.466-474
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    • 2021
  • [011] poled ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals have been investigated for active materials for acoustic transducers because of their high piezoelectric properties in both shear and transverse modes. In order to use [011] poled PIN-PMN-PT single crystals for acoustic transducers, the characterization of full-matrix material properties is required. In this study, full sets of compliance, dielectric, and piezoelectric constants of [011] poled rhombohedral PIN-PMN-PT were measured by a resonance method. Dimensions and geometries of 12 samples were proposed for measuring 17 independent material constants of [011] poled rhombohedral PIN-PMN-PT single crystals. Two sets of samples with different PT concentrations, 0.24PIN-0.49PMN-0.27PT and 0.24PIN-0.46PMN-0.30PT, were fabricated and their material properties were measured. Measured impedance spectra and simulated impedance spectra of the samples were compared to check the accuracy of the measurements.

New Design and Application of PVDF Ultrasonic Transducer for Measurement of Material Properties (재료물성 측정을 위한 직선집속 PVDF 초음파 트랜스듀서의 새로운 설계 및 응용)

  • Hong Soung-Wook;Kim Jung-Soon;Kim Sang-Yoon;Kim Moo-Joon;Ha Kang-Lyeol
    • The Journal of the Acoustical Society of Korea
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    • v.25 no.4
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    • pp.164-171
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    • 2006
  • If the velocities of longitudinal, transverse and leaky surface acoustic waves in an isotropic material are given, the elastic constants and density of the material can be deduced analytically. Those velocities have been measured using three ultrasonic transducers with different vibrational modes so far. In this paper a line-focusing PVDF transducer with divided electrodes was newly proposed and designed for measuring approximate velocities of the three waves. The measurement method established in this study for each waves using the transducer was applied to several isotropic materials including fused quartz. The elastic stiffness constants and densities of the materials were calculated using the measured velocities, and the accuracies were discussed. It was shown that the obtained results are in good accord with the reference values.