• Title/Summary/Keyword: turbulent flow control

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Suboptimal Control for Drag Reduction in Turbulent Pipe Flow (환형관내 유동에서의 항력감소를 위한 준최적 제어)

  • Choi, Jung-Il;Xu, Chun-Xiao;Sung, Hyung-Jin
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.377-382
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    • 2001
  • A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables ${\partial}p/{\partial}{\theta}\;|_w\;and\;{\partial}{\upsilon}_{\theta}/{\partial}r\;|_w$ are applied with two actuations ${\phi}_{\theta}$ and ${\phi}_r$. To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at $Re_r=150$ are performed. When the control law is applied, a $13{\sim}23%$ drag reduction is achieved. The most effective drag reduction is made at the pair of ${\partial}{\upsilon}_{\theta}/{\partial}r\;|_w$ and ${\theta}_r$. An impenetrable virtual wall concept is useful for analyzing the near-wall suction and blowing. The virtual wall concept is useful for analyzing the near-wall behavior of the controlled flow. Comparison of the present suboptimal control with that of turbulent channel flow reveals that the curvature effect is insignificant.

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Assessment of Suboptimal Control in Turbulent Pipe Flow (원관내 유동에서의 준최적 제어의 평가)

  • Choe, Jeong-Il;Xu, C.X.;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.2
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    • pp.345-352
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    • 2002
  • A suboptimal control law in turbulent pipe flow is derived and tested. Two sensing variables ∂p/∂$\theta$$\_$w/ and ∂v$\_$$\theta$/∂γ│$\_$w/ are applied with two actuations ø$\_$$\theta$/ and ø$\_$γ/. To test the suboptimal control law, direct numerical simulations of turbulent pipe flow at Re$\_$$\tau$/=150 are performed. When the control law is applied, a 13∼23% drag reduction is achieved. The most effective drag reduction is made at the pair of ∂v$\_$$\theta$/∂γ│$\_$w/ and ø$\_$γ/. An impenetrable virtual wall concept is useful for analyzing the near-wall suction and blowing. The virtual wall concept is useful for analyzing the near-wall behavior of the controlled flow. Comparison of the present suboptimal control with that of turbulent channel flow reveals that the curvature effect is insignificant.

A study on the Characteristics of In-Cylinder Intake Flow in Spark Ignition Engine Using the PIV

  • Lee Suk-Young;Jeong Ku-Seob;Jeon Chung-Hwan;Chang Young-June
    • Journal of Mechanical Science and Technology
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    • v.19 no.2
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    • pp.704-715
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    • 2005
  • In this study, to investigate in-cylinder tumble or swirl intake flow of a gasoline engine, the flow characteristics were examined with opening control valve (OCV) and several swirl control valves (SCV) which intensify intake flow through steady flow experiment, and also turbulent characteristics of in-cylinder flow field were investigated by 2-frame cross-correlation particle image velocimetry (PIV) method. In the investigation of intake turbulent characteristics using PIV method, the different flow characteristics were showed according to OCV or SCV figures. The OCV or SCV installed engine had higher vorticity and turbulent kinetic energy than a baseline engine, especially around the wall and lower part of the cylinder. Above all, SCV B type was superior to the others. About energy dissipation and reynolds shear stress distribution, a baseline engine had larger loss than OCV or SCV installed one because flow impinged on the cylinder wall. It should be concluded, from what has been said above, as swirl component was added to existing tumble flow adequately, it was confirmed that turbulent intensity was enlarged, flow energy was conserved effectively through the experiment. In other words, there is a suggestion that flow characteristics as these affected to in-cylinder combustion positively.

Effect of a Turbulent Wake on Two-Dimensional Subsonic Jet (노즐내 물체의 후류가 아음속 이차원 제트구조에 미치는 영향에 관한 연구)

  • Kim, Tae-Ho;Lee, Sang-Chan;Yoon, Bok-Hyun;Oh, Dae-Geun;Kim, Heuy-Dong
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.986-991
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    • 2003
  • A turbulent wake generated by a cylinder in nozzle contraction affects to the jet flow characteristics. In this study, a computational work to investigate the effect of the turbulent wake on two-dimensional subsonic jet was carried out with three different kinds of nozzle. Computations are applied to the two-dimensional unsteady, Navier-Stokes equations. Several kinds of turbulent models and wall functions are employed to validate the computational predictions. It was known that the wake flow enhanced the spread of the jet flow, compared with no wake flow condition. It was also found that the jet core is shortened by the wake flow developed from a control cylinder.

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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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    • v.20 no.11
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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.

Research on Turbulent Skin Friction Reduction with the aid of Direct Numerical Simulation

  • Fukagata, Koji
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03a
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    • pp.347-354
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    • 2008
  • We introduce a series of studies on turbulent skin friction drag reduction in wall-turbulence. First, an identity equation relating the skin friction drag and the Reynolds shear stress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.

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Research on Turbulent Skin Friction Reduction with the aid of Direct Numerical Simulation

  • Fukagata, Koji
    • 한국전산유체공학회:학술대회논문집
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    • 2008.10a
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    • pp.347-354
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    • 2008
  • We introduce a series of studies on turbulent skin friction drag reduction in wall-turbulence. First, an identity equation relating the skin friction drag and the Reynolds shear stress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.

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Evaluation of Suboptimal Control in Turbulent Channel Flow (난류채널유동에서의 준최적제어 평가)

  • Seong, Hyeong-Jin;Choe, Jeong-Il
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.9
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    • pp.1227-1236
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    • 2001
  • A systematic analysis is made of suboptimal control for drag reduction. The influence of the amplitude of actuation (A) and the time scale of actuation ($\Delta$t(sub)a(sup)+) is evaluated. Two wall sensing variables are employed (∂w/∂y│(sub)w and ∂p/∂z│(sub)w) with two wall actuations (${\Phi}$$_2$and ${\Phi}$$_3$). To test the suboptimal control, direct numerical simulations of turbulent channel flow at Re(sub)$\tau$=100 are performed in a spectral domain. It is found that the effect of A and $\Delta$t(sub)a(sup)+∼1. The near-wall behaviors of flow structure are analyzed to characterize the drag reduction. The size effect of the sensor/actuator is examined.

Turbulent natural convective heat transfer charateristics in a square enclosure with control plates attached at the horifontal partition (제어판이 부착된 수평격판에 의해 분리되는 밀폐공간내의 난류 자연대류 열전달 특성)

  • 김점수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.12 no.2
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    • pp.150-160
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    • 2000
  • Turbulent natural convective flow and heat transfer in a square enclosure with horizontal partition are investigated numerically. The enclosure is composed of a lower hot and a upper cold horizontal walls and adiabatic vertical walls. Partitions carried with the upward, downward, and both control plates are attached perpendicularly to the one of the vertical insulated walls, respectively. The low Reynolds number $k-\varepsilon$ model is adopted to calculate the turbulent thermal convection. The governing equations are solved by using the finite element method with Galerkin method. The computations have been carried out by varying the length of partition, the position of control plates, and the Rayleigh number based on the temperature difference between two horizontal walls and the enclosure height for water(Pr=4.95). When the control plates are attached at the edge of partition, the stability of oscillating flow grows wrose with the increase of Rayleigh number and the partition length. The heat transfer rate has been reducer than that of no control plate due to the restraint of control plates with the increase of Rayleigh number.

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STUDY ON THE IN-CYLINDER FLOW CHARACTERISTICS OF AN SI ENGINE USING PIV

  • LEE S.-Y.;JEONG K.-S.;JEON C.-H.;CHANG Y.-J.
    • International Journal of Automotive Technology
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    • v.6 no.5
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    • pp.453-460
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    • 2005
  • The tumble or swirl flow is used to promote mixing of air and fuel in the cylinder and to enlarge turbulent intensity in the end of the compression stroke. Since the in-cylinder flow is a kind of transient state with rapid flow variation, which is non-steady state flow, the tumble or swirl flow has not been analyzed sufficiently whether they are applicable to combustion theoretically. In the investigation of intake turbulent characteristics using PIV method, typical flow characteristics were figured out by SCV configurations. An engine installed SCV had higher vorticity and turbulent strength by fluctuation and turbulent kinetic energy than a baseline engine, especially near the cylinder wall and lower part of the cylinder. Above all, the engine with SCV 8 was superior to the others in aspect of vorticity and turbulent strength. For energy dissipation, a baseline engine had much higher energy loss than the engine installed SCV because flow impinged on the cylinder wall. Consequently, as swirl flow was added to existing tumble flow, it was found that fluctuation increased and flow energy was conserved effectively through the experiment.