• Title/Summary/Keyword: Lift Fluctuation

Search Result 39, Processing Time 0.024 seconds

The Power Spectral Density Characteristics of Lift and Drag Fluctuation of Fin Tube in a Heat Recovery Steam Generator (배열회수 보일러 단일 휜튜브의 양력과 항력 변동에 따른 PSD 특성 연구)

  • Ha, Ji Soo;Lee, Boo Youn
    • Journal of the Korean Institute of Gas
    • /
    • v.20 no.2
    • /
    • pp.23-29
    • /
    • 2016
  • Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift and drag fluctuation over the fin tube was investigated. The derived nondimensional lift PSD was compared with the results of the previous experimental studies and the characteristics of lift and drag PSD over a single fin tube was established from the present CFD study.

Linear Proportional Control of Flow Over a Sphere (구 주위 유동의 선형비례제어)

  • Jeon, Seung;Choi, Hae-Cheon
    • Proceedings of the KSME Conference
    • /
    • 2007.05b
    • /
    • pp.2753-2756
    • /
    • 2007
  • In the present study, we reduce the drag and lift fluctuations of the sphere by providing a linear proportional control. For this purpose, we measure the radial velocity along the centerline in the wake and provide blowing and suction at a part of sphere surface based on the measured velocity. Zero-net mass flow rate is satisfied during the control. This control is applied to the flow over a sphere at Re=300 and 425. We vary the sensing location at $0.8d{\leq}X_s{\leq}1.3d$ and find that the most effective sensing region coincides with the location at which minimum correlation between the lift and sensing-velocity directions occurs. As a result, the lift and drag fluctuations are significantly reduced.

  • PDF

The Power Spectral Density Characteristics of Lift and Drag Fluctuation on a Heat Exchanger Circular Tube (열교환 단일 원관의 양력과 항력 변동에 따른 PSD 특성 연구)

  • Ha, Ji Soo
    • Journal of the Korean Institute of Gas
    • /
    • v.19 no.4
    • /
    • pp.35-40
    • /
    • 2015
  • Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift and drag fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift and drag PSD over a single circular cylinder was established from the present CFD study.

A Study on the Characteristics of Lift and Drag Fluctuation Power Spectral Density in a Heat Exchanger Tube Array (전열관군에서 양력과 항력 변동의 PSD 특성 연구)

  • Ha, Ji-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
    • /
    • v.17 no.2
    • /
    • pp.712-718
    • /
    • 2016
  • A heat exchanger tube array in a heat recovery steam generator is exposed to hot exhaust gas flow that can cause flow induced vibrations, which could damage the heat exchanger tube array. The characteristics of flow induced vibration in the tube array need to be established for the structural safe operation of a heat exchanger. Several studies of the flow induced vibrations of typical heat exchangers have been conducted and the nondimensional PSD (Power Spectral Density) function with the Strouhal number, fD/U, had been derived using an experimental method. The present study examined the results of the previous experimental research on the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array was determined from the present CFD analysis. The present CFD analysis introduced circular cylinder tube array and calculated using unsteady laminar flow for the tube array. The characteristics of lift and drag fluctuations over the cylinder tube array was investigated. The derived nondimensional lift and drag PSD was compared with the results of the previous experimental research and the characteristics of lift and drag PSD for a circular cylinder tube array was established from the present CFD study.

Optimal Shape of Blunt Device for High Speed Vehicle

  • Rho, Joo-Hyun;Jeong, Seongmin;Kim, Kyuhong
    • International Journal of Aeronautical and Space Sciences
    • /
    • v.17 no.3
    • /
    • pp.285-295
    • /
    • 2016
  • A contact strip shape of a high speed train pantograph system was optimized with CFD to increase the aerodynamic performance and stability of contact force, and the results were validated by a wind tunnel test. For design of the optimal contact strip shape, a Kriging model and genetic algorithm were used to ensure the global search of the optimal point and reduce the computational cost. To enhance the performance and robustness of the contact strip for high speed pantograph, the drag coefficient and the fluctuation of the lift coefficient along the angle of attack were selected as design objectives. Aerodynamic forces were measured by a load cell and HWA (Hot Wire Anemometer) was used to measure the Strouhal number of wake flow. PIV (Particle Image Velocimetry) was adopted to visualize the flow fields. The optimized contact strip shape was shown a lower drag with smaller fluctuation of vertical lift force than the general shaped contact strip. And the acoustic noise source strength of the optimized contact strip was also reduced. Finally, the reduction amount of drag and noise was assessed when the optimized contact strip was applied to three dimensional pantograph system.

Decrease of Gate Leakage Current by Employing Al Sacrificial Layer Deposited on a Tilted and Rotated Substrate in the DLC-coated Si-tip FEA Fabrication (DLC-coated Si-tip FEA 제조에 있어서 기판 상에 경사-회전 증착된 Al 희생층을 이용한 Gate누설 전류의 감소)

  • 주병권;김영조
    • Journal of the Microelectronics and Packaging Society
    • /
    • v.7 no.3
    • /
    • pp.27-29
    • /
    • 2000
  • For the DLC-coaled Si-tip FEA, the modified lift off-process, by which DLC coated on both gate electrode surface and gate insulator in the gate aperture could be removed, was proposed. In the process, the Al sacrificial layer was deposited on a tilted and rotated substrate by an e-beam evaporation, and DLC film was coated on the substrate by PA-CVD method. Afterward the DLC was perfectly removed except the DLC films coated on emitter tips by etch-out of Al sacrificial layer. Current-voltage curves and current fluctuation of the DLC-coated Si-tip FEA showed that the proposed lift-off process played an important role in decreasing gate leakage current and stabilizing omission current.

  • PDF

Effects of the Lift Valve Opening Area on Water Hammer Pump Performance and Flow Behavior in the Valve Chamber

  • Saito, Sumio;Dejima, Keita;Takahashi, Masaaki;Hijikata, Gaku;Iwamura, Takuya
    • International Journal of Fluid Machinery and Systems
    • /
    • v.5 no.3
    • /
    • pp.109-116
    • /
    • 2012
  • Water hammer pumps can effectively use the water hammer phenomenon for water pumping. They are capable of providing an effective fluid transport method in regions without a well-developed social infrastructure. The results of experiments examining the effect of the geometric form of water hammer pumps by considering their major dimensions have been reported. However, these conventional studies have not fully evaluated pump performance in terms of pump head and flow rate, common measures of pump performance. The authors have focused on the effects on the pump performance of various geometric form factors in water hammer pumps. The previous study examined how the hydrodynamic characteristics was affected by the inner diameter ratio of the drive and lift pipes and the angle of the drive pipe, basic form factors of water hammer pumps. The previous papers also showed that the behavior of water hammer pump operation could be divided into four characteristic phases. The behavior of temporal changes in valve chamber and air chamber pressures according to the air volume in the air chamber located downstream of the lift valve was also clarified in connection with changes in water hammer pump performance. In addition, the effects on water hammer pump performance of the length of the spring attached to the drain valve and the drain pipe angle, form factors around the drain valve, were examined experimentally. This study focuses on the form of the lift valve, a major component of water hammer pumps, and examines the effects of the size of the lift valve opening area on water hammer pump performance. It also clarifies the behavior of flow in the valve chamber during water hammer pump operation.

Fabrication and Characterization of Si-tip Field Emitter Array (실리콘 팁 전계 방출 소자의 제조 및 동작 특성 평가)

  • 주병권;이상조;박재석;이윤희;전동렬;오명환
    • Journal of the Microelectronics and Packaging Society
    • /
    • v.6 no.1
    • /
    • pp.65-73
    • /
    • 1999
  • Si-tip FEAs were fabricated by a lift-off based process and their operating properties were evaluated. The dependence of emission current on applied gate and anode voltages, maximum emission current, hysteresis phenomena, MOSFET-type curves, current fluctuation, light emission from the emitted electrons, and failure mechanism of the device were widely discussed based on the experimental results.

  • PDF

Numerical Study on the Active Control of Aerodynamic Properties of 2 - D Square Prism (2차원 각주의 공력특성 능동제어에 관한 수치해석 연구)

  • 이영호;김춘식;조대환
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.17 no.1
    • /
    • pp.33-44
    • /
    • 1993
  • Active control of a flow field is essential to design efficient parts or elements relating to fluid machineries. The present study is aimed to suggest a new discretization technique of the convection term by renewing the non-conservative equation found in SOLA-VOF into a conservative one. And, as an application, flow characteristics are investigated by adjusting the backward ejecting velocity of 2-D square prism to control the aerodynamic properties. Strouhal number, drag and lift coefficient are compared in terms of various ejecting velocity. Among the results, the transient weak fluctuation of the lift and drag coefficient when the ejecting velocity equals channel inlet velocity is remarkably noticed.

  • PDF

The Effects of Yaw on the Vortex-Shedding Sound from a Circular Cylinder (원형실린더 와류발생 소음에 대한 경사각 효과)

  • 홍훈빈;최종수
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
    • /
    • 1997.10a
    • /
    • pp.263-270
    • /
    • 1997
  • For a cylinder in a uniform flow stream, sound is generated by the fluctuating pressure on the cylinder surface due to the vortex shedding behind the cylinder. It is known that the major parameters to predict the sound pressure are the characteristic length of the flow along the cylinder axis and the fluctuating lift coefficient. These parameters strongly depend on the Reynolds number and the yaw angle of the cylinder to the free stream. In this experimental study the effects of yaw on the flow parameters, and consequently on the generated sound are investigated. The surface pressure and the radiated sound are measured simultaneously for different yaw angles and showed that the reduced normal velocity component to the cylinder axis reduces the unsteady lift fluctuation which results in lowered sound press-are level, However, experimental result shows that "the cosine law" which uses the normal velocity component as a characteristic velocity for noise Generation from a yawed cylinder needs to be carefully reviewed. reviewed.

  • PDF