• Title/Summary/Keyword: pulsating flow

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Experimental study on the transfer in pulse tube (맥동관 내부의 열전달에 관한 실험적 연구)

  • 김민규;남관우;정상권;장호일;정은수
    • Progress in Superconductivity and Cryogenics
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    • v.2 no.1
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    • pp.45-50
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    • 2000
  • The present study has been conducted to observe the heat transfer under pulsating pressure and oscillating flow. The experimental apparatus was fabricated to measure the gas temperature, the wall temperature. the pressure and the instantaneous heat flux inside the pulse tube. The measured gas temperature and heat flux must be calibarated to compensate their finite time constant in the oscillating flow conditious. The experiment was performed from 1 Hz to 5 Hz. The phase difference between the instantaneous heat flux and the gas-wall temperature difference was clearly observed. The experimental heat fluxes were compared to the theroretical correlations such as Complex Nusselt Number Model(CNNM) and Variable Coefficient Model(CVM). The heat flux predisted by CNNM was always greater than that of VCM. The experiment confirmed the valisity of the VCM for the instantaneous heat flux under the pulsating pressure and oscillating flow in the warm end of the pulse tube.

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An Experimental Study on the Flame Localization Characteristics and Pulsating Instability in a Radial Multi-channel (반경방향 다중 채널 내 예혼합 화염의 안정화 특성과 맥동 불안정성에 관한 실험적 연구)

  • Lee, Dae Keun;Ko, Chang-Bog
    • 한국연소학회:학술대회논문집
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    • 2013.06a
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    • pp.41-43
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    • 2013
  • In order to simulate and visually observe combustion phenomena in cylindrical radial-flow porous inert media, a radial multi-channel burner, made of transparent quartz plates, was fabricated. Flame stabilization characteristics and its pulsating instability in the burner were experimentally investigated with respect to various mixture flow rates and equivalence ratio. As a result, five different flame behaviors, such as stable flame, pulsating instability, sudden extinction, blowout and unstable extinction, were observed. Mean radial position of circularly arranged multi-flame and its averaged burning velocity were measured and then compared to the freely propagating flame. The multi-flame pulsation frequency is about several tens of Hz and it is supposed to be generated by the heat diffusion enhancement to cold pre-mixture by the intensive gas-solid interaction.

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A study of the transfer characteristics of pressure waves using two-port network analysis in exhaust system of engine (양단자 회로망 분석을 이용한 기관배기계의 압력파 전달특성에 관한 연구)

  • 이준서;유병구;차경옥
    • Journal of Advanced Marine Engineering and Technology
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    • v.22 no.1
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    • pp.77-84
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    • 1998
  • Based on experimental analysis, the characteristics of pulsating pressure wave propagation is clarified by testing of 4-stroke gasoline engine. The pulsating pressure wave in exhaust system is generated by pulsating gas flow due to working of exhaust valve. The pulsating pressure wave is closely concerned to the loss of engine power according to back pressure and exhaust noise. It is difficult to exactly calculate pulsating pressure wave propagation in exhaust system because of nonlinear effect. Therefore, in the first step for solving these problems, this paper contains experimental model and analysis method which are applied two-port network analysis. Also, it shows coherence function, frequency response function, back pressure, and gradient of temperature in exhaust system.

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A Study on the Characteristics of Pressure Wave Propagation in Automotive Exhaust System (자동차 배기계의 압력파 전파특성에 관한 연구)

  • 차경옥;이준서;김형섭
    • Transactions of the Korean Society of Automotive Engineers
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    • v.4 no.4
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    • pp.18-26
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    • 1996
  • Based on experimental analysis, the characteristics of pulsating pressure wave propagation is clarified by testing of 4-stroke gasoline engine. The pulsating pressure wave in exhaust system is generated by pulsating gas flow due to working of exhaust valve. The pulsating pressure wave is closely concerned to the loss of engine power according to back pressure and exhaust noise. It is difficult to exactly calculate pulsating pressure wave propagation in exhaust system because of nonlinear effect. Therefore, in the first step for solving these problems, this paper contains experimental model and analysis method which are applied two-port network analysis. Also, it shows coherence function, frequency response function, back pressure, and gradient of temperature in exhaust system.

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A PIV Study of Flow Patterns Over Stationary and Pitch-Oscillating Airfoils with Blowing Jet

  • Lee, Ki-Young;Chung, Hyoung-Seog;Cho, Dong-Hyun
    • International Journal of Aeronautical and Space Sciences
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    • v.9 no.1
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    • pp.111-120
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    • 2008
  • A particle image velocimetry (PIV) technique was employed to investigate the effects of blowing jet on the flow characteristics over stationary and pitch-oscillating airfoils. The Reynolds number was $7.84{\times}10^5$ based on the chord length. It was found that for stationary airfoil cases, continuous and pulsating blowing jets successfully reduced separated wake region at high angles of attack. A comparison study of two different types of jet blowing indicated that pulsating jet is more effective than continuous jet for flow separation control. Pulsating leading-edge blowing postpones flow separation and increased stall angle of attack by $2^{\circ}{\sim}3^{\circ}$. For pitch-oscillating airfoil cases, the PIV results showed that blowing jet efficiently delays the separation onset point during pitch-up stroke, whereas it does not prevent flow separation during pitch-down stroke, even at angles of attack smaller than static ones.

A Study on Turbulent Characteristics of Turbulent Pulsating Flows in a Square Duct (4각 덕트내에서 난류 맥동유동의 난류특성에 관한 연구)

  • Park, G.M.;Go, Y.H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.2 no.3
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    • pp.188-198
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    • 1990
  • Turbulent characteristics of turbulent pulsating flows were studied experimentally in a square duct. Velocity waveforms, velocity profiles, and turbulent intensity of turbulent pulsating flow were investigated by using a hot-wire anemometer with data acquisition and a processing system in a square duct with a ratio of 1 ($40mm{\times}40mm$) to 4,000mm long. Turbulent components were shown to be larger in decelerating than in accelerating regions and also larger for a large phase of velocity and U'rms distribution of turbulent flow. The effect of velocity amplitude ratio does not exist for specified time [${\theta}(z^{\prime})$], amplitude ratio (${\mid}U^{\prime}_{rms.os.1}{\mid}/{\mid}U_{m.os.1}{\mid}$), and phase difference (${\Delta}U^{\prime}_{rms.os.1}-{\Delta}U_{m.os.1}$) in either turbulent oscillating or cross-sectional mean velocity components. The effect of dimensionless angular frequency for specified time [${\theta}(z^{\prime})$] can be disregarded because the dimensionless angular frequency does not affect the specified time. The velocity distributions of turbulent pulsating flows for various time-averaged Reynolds numbers are in approximate agreement with the velocity distributions for equivalent Reynolds numbers and 1/7th power law of steady flow.

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Numerical Analysis of Heat Transfer in Pulsating Turbulent Pipe Flow (원관내 맥동난류유동에서의 열전달 수치해석)

  • 박희용;이관수;김창기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1282-1289
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    • 1990
  • A numerical solution for heat transfer of pulsating turbulent pipe flow was presented under the condition of fully developed dynamic regime and uniform well heat flux. The k-.epsilon. turbulent model was adopted to describe turbulent characteristics. The results were given at following conditions ; Time-averaged Reynolds number equal to 10000 ; Strouhal number ranged from 0.0005 to 0.05 ; The peak velocity fluctuation varied from 20 to 80 percent of the mean velocity. It was found that the effect of pulsation on local heat transfer rate is greater at downstream than upstream and the heat transfer was increased or decreased according to the pulsating conditions.

A study on the pulsating combustion of coal in a Rijke type combustor (Rijke형 연소기에서 석탄의 맥동연소에 관한 연구)

  • 권영필;이동훈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.3
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    • pp.508-516
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    • 1989
  • The objective of this study is to investigate on the pulsating combustion of a granular coal in a Rijke type pulse combustor. The combustor is made of a 120cm long pipe with a honeycomb as a fire grate in the lower half. A fixed amount of coal is laid on the honeycomb and burned downward after ignition by using propane gas. Then the combustion driven acoustic oscillation occurs and makes the combustion pulsate with a very high amplitude. The effect of the pulsation and the air flow rate on the combustion characteristics is examined in comparison with the normal combustion. The non-pulsating combustion is made possible by placing absorbing material under the honeycomb. The combustion phenomena are observed visually, the burning time is measured in order to evaluate the combustion rate, and the variation of the gas temperatures is recorded. It is found that the fuel particle is greatly agitated like boiling by the flow pulsation and the burning-down velocity is so fast that the fuel is burned almost simultaneously. The combustion rate can be increased as twice as that of non-pulsating combustion with increase of the air flow rate. And the combustion becomes clean with less soot deposit and emission.

Effects of Pulsating Jet Blowing on Stall Control of Two Dimensional Elliptic Airfoil (이차원 타원형 날개꼴의 실속제어에서 간헐제트 브로잉의 효과)

  • Lee, Ki-Young;Sohn, Myong-Hwan;Jeong, Hung-Seok
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.33 no.9
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    • pp.1-8
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    • 2005
  • This paper explored the effects of separation control through the use of pulsating jet blowing on a two dimensional elliptical airfoil. To develop an active control technique of flow separation, a flow control actuator utilizing continuous/pulsed jet of pressurized air was designed and installed in a wind tunnel testing model of elliptic wing. PIV measurement and flow visualization of the wing near field were conducted to access the feasibility and effectiveness of the pulsed jet blowing on controlling the stall of the elliptical wing in subsonic flow. PIV experimental results show that separation control can provide significant reduction in turbulent flow wake and separation bubbles by jet blowing. The pulsating jet blowing is more effective on the separation control than continuous one. Increased jet frequency suppressed the turbulent separated flow wake effectively at even higher AOAs.

Dynamic Characteristics of Pressure Propagation According to Boundary Condition Changes in a Transmission Line (경계조건변화에 따른 동력전달관로의 동특성)

  • 나기대;유영태;김지환
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.11 no.6
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    • pp.75-82
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    • 2002
  • Design for a quiet operation of fluid power system requires the understanding of noise and vibration characteristics of the system. It's not easy to analyze noise problem in hydraulic cylinder used in typical actuator Because they've got complex fluid dynamics. One of the fundamental problems associated with the hydraulic system is the pulsating flow in pipe lines, which can be tackled by the analysis under simplifying assumptions. The present study focuses on theoretic analysis and experimental study on the dynamics of laminar pulsating flow in a circular pipe. We analyze the propagation characteristics of the pressure pulse within a hydraulic pipe line taking into account the pulsating flow frequency variation. We also measure instantaneous pressure pulses within pipe line to identify the transfer functions. We conduct series of experiments to investigate the propagation characteristics of pressure pulse for various pressure of pulsating flow. The working fluid of the present study is ISO VG46 and the temperature ranges from 20 to $60^{\circ}$ with normal pressure at 4000kPa. The flow rate is measured by using an ultrasonic flow meter. Pressures at fixed upstream and downstream positions are measured concurrently. The electric signals of the pressure sensor are stored and analyzed using a system analyzer(PKE 983 series). The frequency is varied in the range of 10~500Hz. The Reynolds number is kept below 2,000. In the present study, boundary condition was varied by installing a surge tank and an orifice at the end of pipe. Experimental and theoretical results were compared each other under various boundary conditions.