• Title/Summary/Keyword: Unsteady Fluid Flow

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Numerical Analysis of Unsteady Viscous Flow Through a Weis-Fogh Type Ship Propulsion Mechanism Using the Advanced Vortex Method

  • Ro Ki-Deok;Kang Myeong-Hun;Kong Tae-Hee
    • Journal of Advanced Marine Engineering and Technology
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    • v.29 no.7
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    • pp.769-778
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    • 2005
  • The velocity and pressure fields of a ship's Weis-Fogh type propulsion mechanism are studied in this paper using an advanced vortex method. The wing (NACA0010 airfoil) and channel are approximated by source and vortex panels. and free vortices are introduced away from the body surfaces. The viscous diffusion of fluid is represented using the core-spreading model to the discrete vortices. The velocity is calculated on the basis of the generalized Biot-Savart law and the pressure field is calculated from an integral, based on the instantaneous velocity and vorticity distributions in the flow field. Two-dimensional unsteady viscous flow calculations of this propulsion mechanism are shown. and the calculated results agree qualitatively with the measured thrust and drag due to un-modeled large fluctuations in the measured data.

Numerical Evaluation of Dynamic Transfer Matrix and Unsteady Cavitation Characteristics of an Inducer

  • Yonezawa, Koichi;Aono, Jun;Kang, Donghyuk;Horiguchi, Hironori;Kawata, Yutaka;Tsujimoto, Yoshinobu
    • International Journal of Fluid Machinery and Systems
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    • v.5 no.3
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    • pp.126-133
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    • 2012
  • The transfer matrix and unsteady cavitation characteristics, cavitation compliance and mass flow gain factor, of cavitating inducer were evaluated by CFD using commercial software. Quasi-steady values of cavitation compliance and mass flow gain factor were obtained first by using steady calculations at various flow rate and inlet cavitation number. Then unsteady calculations were made to determine the transfer matrix and the cavitation characteristics. The results are compared with experiments to show the validity of calculations.

Unsteadiness of Tip Leakage Flow in an Axial Compressor (축류 압축기 팁 누설 유동의 비정상 특성에 관한 연구)

  • Hwang, Yoo-Jun;Kang, Shin-Hyoung
    • The KSFM Journal of Fluid Machinery
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    • v.15 no.1
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    • pp.58-63
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    • 2012
  • Three dimensional unsteady numerical calculations were performed to investigate unsteadiness of the tip leakage flow in an axial compressor. The first stage of the four-stage low-speed research axial compressor was examined. Since this compressor has a relatively large tip clearance, the unsteadiness of the tip leakage flow is induced. Through the results from the unsteady calculations, the process of the induced unsteady tip leakage flow was investigated. It was shown that the leakage flow that occurred at a rotor blade tip clearance affected the pressure distribution on the pressure side near the tip of the adjacent blade, thus caused the fluctuation of the pressure difference between the pressure side and suction side. Consequently, the unsteady tip leakage flow was induced at the adjacent rotor blade. The unsteady feature of the tip leakage flow was changed as the operating point was moved. The interface between the tip leakage flow and the main flow only affected the trailing edge region at the design point whereas the interface influenced up to the leading edge at the low flow rate point. As the flow rate decreased, additionally, it was seen that the vortex size of the tip leakage flow increased and the relatively large length scale disturbance occurred. On the other hand, using frequency analysis, it was shown that the unsteadiness was not associated with the rotor speed and was about 40% of the blade passing frequency. This feature was explained in the rotor relative frame of reference, and the frequency decreased as the flow rate decreased.

UNSTEADY FLUID FIELD ANALYSIS OF STAGING SYSTEM (단분리 비정상 유동장의 수치적 해석)

  • Yoon Y. H.;Kwon K. B.;Hong S. K.
    • 한국전산유체공학회:학술대회논문집
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    • 2005.10a
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    • pp.261-267
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    • 2005
  • The unsteady flow analysis of staging system is conducted. This study focuses on comparing the results of two different governing equations between Euler equations and Navier-Stokes equations. The Chimera grid scheme is applied to moving simulations for unsteady flow analysis with dynamic simulation. As a result, it is certified that inviscid simulation have capabilities enough to analyze the present staging problem.

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Spectral Element Analysis of the Pipeline Conveying Internal Unsteady Fluid (내부 비정상 유동을 갖는 파이프계의 스펙트럼요소해석)

  • Park, Jong-Hwan;Lee, U-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.12 s.243
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    • pp.1574-1585
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    • 2005
  • In this paper, a spectral element model is developed for the uniform straight pipelines conveying internal unsteady fluid. Four coupled pipe-dynamics equations are derived first by using the Hamilton's principle and the principles of fluid mechanics. The transverse displacement, the axial displacement, the fluid pressure and the fluid velocity are all considered as the dependent variables. The coupled pipe-dynamics equations are then linearized about the steady state values of the fluid pressure and velocity. As the final step, the spectral element model represented by the exact dynamic stiffness matrix, which is often called spectral element matrix, is formulated by using the frequency-domain solutions of the linearized pipe-dynamics equations. The FFT-based spectral dynamic analyses are conducted to evaluate the accuracy of the present spectral element model and also to investigate the structural dynamic characteristics and the internal fluid transients of an example pipeline system.

Steady and unsteady flow computation in an elbow draft tube with experimental validation

  • Vu, Thi C.;Devals, Christophe;Zhang, Ying;Nennemann, Bernd;Guibault, Francois
    • International Journal of Fluid Machinery and Systems
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    • v.4 no.1
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    • pp.85-96
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    • 2011
  • Steady state computations are routinely used by design engineers to evaluate and compare losses in hydraulic components. In the case of the draft tube diffuser, however, experiments have shown that while a significant number of operating conditions can adequately be evaluated using steady state computations, a few operating conditions require unsteady simulations to accurately evaluate losses. This paper presents a study that assesses the predictive capacity of a combination of steady and unsteady RANS numerical computations to predict draft tube losses over the complete range of operation of a Francis turbine. For the prediction of the draft tube performance using k-${\varepsilon}$ turbulence model, a methodology has been proposed to average global performance indicators of steady flow computations such as the pressure recovery factor over an adequate number of periods to obtain correct results. The methodology will be validated using two distinct flow solvers, CFX and OpenFOAM, and through a systematic comparison with experimental results obtained on the FLINDT model draft tube.

Hall Effect on Unsteady Hartmann Flow with Heat Transfer Under Exponential Decaying Pressure Gradient

  • Attia Hazem A.
    • Journal of Mechanical Science and Technology
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    • v.20 no.8
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    • pp.1302-1308
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    • 2006
  • The unsteady Hartmann flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity and temperature distributions is examined.

Variable Geometry Mixed Flow Turbine for Turbochargers: An Experimental Study

  • Rajoo, Srithar;Martinez-Botas, Ricardo
    • International Journal of Fluid Machinery and Systems
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    • v.1 no.1
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    • pp.155-168
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    • 2008
  • This paper investigates a variable geometry (VG) mixed flow turbine with a novel, purposely designed pivoting nozzle vane ring. The nozzle vane ring was matched to the 3-dimensional aspect of the mixed flow rotor leading edge with lean stacking. It was found that for a nozzle vane ring in a volute, the vane surface pressure is highly affected by the flow in the volute rather than the adjacent vane surface interactions, especially at closer nozzle positions. The performance of the VG mixed flow turbine has been evaluated experimentally in steady and unsteady flow conditions. The VG mixed flow turbine shows higher peak efficiency and swallowing capacity at various vane angle settings compared to an equivalent nozzleless turbine. Comparison with an equivalent straight vane arrangement shows a higher swallowing capacity but similar efficiencies. The VG turbine unsteady performance was found to deviate substantially from the quasi-steady assumption compared to a nozzleless turbine. This is more evident in the higher vane angle settings (smaller nozzle passage), where there are high possibility of choking during a pulse cycle. The presented steady and unsteady results are expected to be beneficial in the design of variable geometry turbochargers, especially the ones with a mixed flow turbine.

Hall Effect on Unsteady Couette Flow. with Heat Transfer Under Exponential Decaying Pressure Gradient

  • Attia HazemAIi
    • Journal of Mechanical Science and Technology
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    • v.19 no.11
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    • pp.2053-2060
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    • 2005
  • The unsteady Couette flow of an electrically conducting, V1SCOUS, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer taking the Hall effect into consideration. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to an exponential decaying pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the ion slip and the uniform suction and injection on both the velocity and temperature distributions is examined.

Unsteady Pressure Distributions in a Channel Diffuser of Centrifugal Compressor (원심압축기 채널디퓨저 내부의 비정상 압력분포)

  • Kang, Jeong-Seek;Cho, Sung-Kook;Kang, Shin-Hyoung
    • The KSFM Journal of Fluid Machinery
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    • v.3 no.2 s.7
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    • pp.57-65
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    • 2000
  • The aim of this paper is to understand the unsteady flow phenomena in a high speed centrifugal compressor channel diffuser. Instantaneous pressures aye measured at six locations in the diffuser using fast-response pressure transducers. Instantaneous pressure ratio decomposition was applied to analyze the pressure signal. In vaneless space where impeller-vaned diffuser interaction is strong, aperiodic unsteadiness is high and periodic pressure waveforms by blade passing are not clear at low flow rates, especially near vane suction side. High aperiodic unsteadiness decreases downstream of diffuser. The blade-to-blade pressure wave does not disappear in surge flow condition. In surge there exist not only large scale periodic surge wave but also blade-to-blade pressure wave.

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