• Title/Summary/Keyword: Linear Cascade

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INVERSE ENERGY CASCADE AND MAGNETIC HELICITY IN 3-DIMENSIONAL DRIVEN ELECTRON MAGNETOHYDRODYNAMIC TURBULENCE

  • Kim, Hoon-Kyu;Cho, Jun-Hyeon
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.2
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    • pp.112.1-112.1
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    • 2011
  • We present numerical simulations of inverse energy cascade and in driven three-dimensional (3D) electron magnetohydrodynamic (EMHD) turbulence. It has been known that inverse energy cascade only occurs in two-dimensional (2D) turbulence. However, we demonstrate that inverse energy cascade occurs in 3D driven EMHD turbulence. When magnetic helicity is injected on a small-scale, magnetic energy goes up to larger scales. The energy spectrum clearly shows inverse energy cascade. At the same time, magetic helicity spectrum also shows that the helicity goes up to larger scales. We obviously confirm inverse energy cascade. Net magnetic helicity for scales larger than the driving scale shows linear growth, and magnetic energy shows non-linear growth. On the other hand, when we drived turbulence without magnetic helicity, we do not observe inverse energy cascade.

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Time-domain Computation of Broadband Noise due to Turbulence - cascade Interaction (난류-캐스케이드 상호 작용에 의한 광대역 소음장의 시간영역 계산)

  • Jung, Sung-Soo;Cheung, Wan-Sup;Lee, Soo-Gab;Cheong, Cheol-Ung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.16 no.3 s.108
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    • pp.263-269
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    • 2006
  • The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

Time-domain Computation of Broadband Noise due to Turbulence-Cascade Interaction (난류-캐스케이드 상호 작용에 의한 광대역 소음장의 시간영역 계산)

  • Cheong, Cheol-Ung;Jeong, Sung-Su;Cheung, Wan-Sup;Lee, Soo-Gab
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11a
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    • pp.812-817
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    • 2005
  • The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

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On-line process identification for cascade control system (Cascade 제어를 위한 실시간 공정 식별법)

  • 박흥일;성수환;이인범
    • 제어로봇시스템학회:학술대회논문집
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    • 1996.10b
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    • pp.1412-1415
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    • 1996
  • In this paper, a new identification method of the cascade control system is proposed which can overcome the weak points of Krishnaswamy and Rangaiah(1987)'s method. This new method consists of two steps. One is on-line process identification using the numerical integration to approximate the two process dynamics with a high order linear transfer function. The other is a model reduction technique to derive out low order transfer function(FOPTD or SOPTD) from the obtained high order linear transfer function to tune the controller using usual tuning rules. While the proposed method preserves the advantages of the Krishnaswamy and Rangaiah(1987)'s method, it has such a simplicity that it requires only measured input and output data and simple least-squares technique. Simulation results show that the proposed method can be a promising alternative in the identification of cascade control systems.

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Endwall Heat (Mass) Transfer Characteristics of a Linear Turbine Cascade at Off-Design Conditions (탈설계점에서의 선형 터빈 익열 끝벽 열(물질)전달 특성)

  • Lee, Sang-Woo;Park, Jin-Jae
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.1092-1097
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    • 2004
  • The heat (mass) transfer characteristics on the endwall surface of a first-stage linear turbine rotor cascade at off-design conditions has been investigated by employing the naphthalene sublimation technique. The experiments are carried out at the Reynolds number of $2.78{\times}10^{5}$ for two incidence angles of -5% and +5%. The positive incidence angle results in intensification of the pressure-side leg of a leading-edge horseshoe vortex, which delivers higher heat transfer along its trace. On the other hand, the negative incidence angle show an opposite tendency.

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Numerical simulation of tip clearance flows through linear turbine cascades (선형터빈 익렬의 익단간극유동에 대한 수치해석적 연구)

  • Lee, Hun-Gu;Yu, Jeong-Yeol
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.6
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    • pp.813-821
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    • 1997
  • Three-dimensional turbulent incompressible flow through the tip clearance of a linear turbine rotor cascade with high turning angle has been analyzed numerically. As a preliminary study to predict the tip clearance loss realistically, a generalized k-.epsilon. model derived by RNG (renormalized group) method is used for the modeling of Reynolds stresses to account for the strain rate of turbulent flow. The effects of the tip clearance flow on the passage vortex, the total pressure loss are considered qualitatively. The existences of vena contract and tip clearance vortex have been confirmed and it has been shown that as the size of the tip clearance increases, the accumulated flow through the tip clearance and the total pressure loss downstream of the cascade increase.

The Flow Analysis of Supercavitating Cascade by Nonlinear Theory (비선형이론에 의한 Supercavitation 익렬의 유동해석)

  • Pak, Ee-Tong;Hwang, Yoon
    • Solar Energy
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    • v.17 no.1
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    • pp.35-46
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    • 1997
  • In this study comparison of experiment results with the computed results of linear theory and nonlinear theory using singularity method was obtainable. Specially singularity points like sources and vortexes on hydrofoil and freestreamline were distributed to analyze two dimensional flow field of supercavitating cascade using nonlinear theory, and governing equations of flow field were derived and hydraulic characteristics of cascade were calculated by numerical analysis of the governing equations. The results compared linear theory and nonlinear theory with the experiment results of the study are as follows: The tolerances of nonlinear theory were larger than those of linear theory in case of ${\alpha}<10^{\circ}$. Moreover the computational range of attack angles could be expanded from ${\alpha}=10^{\circ}$ to ${\alpha}=25^{\circ}$, the flow field of supercavitating cascade could be analyzed in the condition which the wake thickness and the length of cavity are a variable. The shapes of cavity were changed sensitively according to various variable such as attack angles, pitches and wake thickness, and the pressure distribution of hydrofoil surface was identical almost disregarding wake thickness but changed largely according to attack angle and the length of cavity. Lift coefficient and drag coefficient were reduced according to increasing of wake thickness but the influences of wake thickness were very little in the situation of small pitch and long cavity.

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The Flow Analysis of Supercavitating Cascade by Linear Theory (선형이론에 의한 Supercavitation 익렬의 유동해석)

  • Pak, Ee-Tong;Hwang, Yoon
    • Solar Energy
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    • v.16 no.2
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    • pp.79-86
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    • 1996
  • In order to reduce damages due to cavitation effects and to improve performance of fluid machinery, supercavitation around the cascade and the hydraulic characteristics of supercavitating cascade must be analyzed accurately. And the study on the effects of cavitation on fluid machinery and analysis on the performances of supercavitating hydrofoil through various elements governing flow field are critically important. In this study comparison of experiment results with the computed results of linear theory using singularity method was obtainable. Specially singularity points like sources and vortexes on hydrofoil and freestreamline were distributed to analyze two dimensional flow field of supercavitating cascade, and governing equations of flow field were derived and hydraulic characteristics of cascade were calculated by numerical analysis of the governing equations.

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Influence of Unsteady Wake on Flow Characteristics and Heat Transfer from Linear Turbine Cascade (비정상후류가 선형터빈익렬의 유동 특성 및 익형의 열전달에 미치는 영향에 관한 연구)

  • Yoon, Soon-Hyun;Sim, Jae-Kyung;Lee, Dae-Hee
    • Proceedings of the KIEE Conference
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    • 1998.11c
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    • pp.1061-1064
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    • 1998
  • To examine the influence of unsteady wake on the flow and heat transfer characteristics, an experiment has been conducted in a four-vane linear cascade. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress were measured using hot wire anemometer, and to measure the convective heat transfer coefficients on the blade surfaces liquid crystal/gold film Intrex technique was used. The disturbance by the unsteady wake is characterized by the unresolved unsteadiness. The unsteady wake enhances the turbulent motion of flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the suction surface increase with increasing unresolved unsteadiness.

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Measurement of Heat Transfer and Pressure Distributions on a Gas Turbine Vane Endwall (가스터빈 베인 끝벽의 열전달 특성 및 정압분포 측정)

  • Lee, Yong-Jin;Shin, So-Min;Kwak, Jae-Su
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.14 no.2
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    • pp.33-38
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    • 2006
  • Heat transfer coefficients and static pressure distributions on a gas turbine vane endwall were experimentally investigated in a 5 bladed linear cascade. The Reynolds number based on an axial chord length and the cascade exit velocity was 500,000. Both heat transfer and pressure measurements on the vane endwall were made at the two different turbulence intensity levels of 6.8% and 10.8%. Detailed heat transfer coefficient distributions on the vane endwall region were measured using a hue detection based transient liquid crystals technique. Results show various regions of high and low heat transfer coefficients on the vane endwall surface due to several types of secondary flows and vortices. Heat transfer coefficient and endwall static pressure distributions showed similar trends for both turbulence intensity, however, the averaged heat transfer coefficients for higher turbulence intensity case was higher than the lower turbulence intensity case by 15%.

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