• Title/Summary/Keyword: 박리기포

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Analysis of the Transitional Separation Bubble Using Partially Parabolized Navier-Stokes Equations (천이 박리기포의 포물형 방정식을 이용한 수치적 해석)

  • 강동진;최도형
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.6
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    • pp.1257-1268
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    • 1989
  • 본 연구에서는 이에 천이와 난류모델을 첨가하여 층류 경계층이 천이를 거쳐 난류 경계층으로 발달해가는 전과정을 해석하려고 한다. 또, 이러한 부분 면파의 특성을 needle contact법에 의하여 측정 포물형이나 완전 Navier-Stokes 방정식을 사용함에 있어서 표면곡률항의 중요성을 보이며, 익형의 선단등 표면곡률이 중요한 영역에서도 적용가능한 수치적 방법을 제시한다.

Calculation of two-dimensional incompressible separated flow using parabolized navier-stokes equations (부분 포물형 Navier-Stokes 방정식을 이용한 비압축성 이차원 박리유동 계산)

  • 강동진;최도형
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.5
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    • pp.755-761
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    • 1987
  • Two-Dimensional incompressible laminar boundary layer with the reversed flow region is computed using the parially parabolized Navier-Stokes equations in primitive variables. The velocities and the pressure are explicity coupled in the difference equation and the resulting penta-diagonal matrix equations are solved by a streamwise marching technique. The test calculations for the trailing edge region of a finite flat plate and Howarth's linearly retarding flows demonstrate that the method is accurate, efficient and capable of predicting the reversed flow region.

Optimization Study of Pulsating Jet to Reduce the Separation Bubble behind the Fence (후방 박리기포 감소를 위한 맥동제트의 최적화 연구)

  • Choi, Young-Ho;Kang, In-Su;Kim, Hyoung-Bum
    • Journal of the Korean Society of Visualization
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    • v.6 no.1
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    • pp.53-58
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    • 2008
  • We carried out the experiments which controled the periodic jet in front of the fence to alter the fence wake. The experiments were performed in circulating water channel and the vertical fence was submerged in the boundary layer. The frequency, jet nozzle distance and speed of jet passing the slit were investigated. Each case divided into 20 phases and phase-averaged results were compared with uncontrolled fence flow. From the results, we found the specific frequency and nozzle distance which were good for reducing the reattachment length. In this case, the reattachment length was decreased 35% compared with the uncontrolled fence flow.

The Study for the Air Bubble Deterioration of Combined High Flowing Self-Compacting Concrete (병용계 고유동 자기충전콘크리트의 기포저감을 위한 연구)

  • Choi, Yun-Wang;Kim, Kyung-Hwan;Ruy, Deug-Hyun;Jeong, Jae-Gwon;Kang, Hyun-Jin;Lee, Jae-Nam
    • Proceedings of the Korea Concrete Institute Conference
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    • 2008.04a
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    • pp.449-452
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    • 2008
  • This study is to manufacture HSCC (High flowing Self-Compacting Concrete) be able to construction without vibration & hardening, and it is stable according to the change of the surface number of aggregate and to examine the factor of reduction occurred before after hardening through the indoor experiment. It is essential to use of the thickener to increase the viscosity in the combined HSCC. In this result, it make more bubbles than HSCC of pulverulent body. The result of study has shown, through the surface air bubble by not passed air bubbles within concrete after hardening, It has bad effect in not only appearance of structures but strength & duration. It is the experiment for air bubble of concrete according to the types of aggregate (fine aggregate), mixing time of concrete, exfoliation, material of model form and so that reduce the air bubble of combined HSCC. Experiments have shown, the effect of exfoliation was bigger than the effect of form for the performance of surface finishing of combined HSCC after hardening according to the exfoliation or material of model form and the opaque guris has good condition of finishing.

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Influence of unsteady wake on a turbulent separation bubble (난류박리기포에 대한 비정상 후류의 영향)

  • Chun, Se-Jong;Sung, Hyung-Jin
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.294-299
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    • 2001
  • An experimental study was made of turbulent separated and reattaching flow over a blunt body, where unsteady wake was generated by a spoke wheel-type wake generator with cylindrical rods. The influence of unsteady wake was scrutinized by altering the rotating direction (CW and CCW) and the normalized passing frequency $(0{\leq}St_H{\leq}0.20)$. The Reynolds number based on the cylindrical rod was $Re_d=375$. A phase-averaging technique was employed to characterize the unsteady wake. The effect of different rotating directions was examined in detail, which gave a significant reduction of $X_R$. The wall pressure fluctuations on the blunt body were analyzed in terms of the spectrum and the coherence.

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Influence of Unsteady Wake on a Turbulent Separation Bubble (난류박리기포에 대한 비정상 후류의 영향)

  • Jeon, Se-Jong;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.353-361
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    • 2002
  • An experimental study was made of turbulent separated and reattaching flow over a blunt body, where unsteady wake was generated by a spoke wheel-type wake generator with cylindrical rods. The influence of unsteady wake was scrutinized by altering the rotating direction (CW and CCW) and the normalized passing frequency (0 St$\_$H/ 0.20). The Reynolds number based on the cylindrical rod was Re$\_$d/=375. A phase-averaging technique was employed to characterize the unsteady wake. The effect of different rotating directions was examined in detail, which gave a significant reduction of x$\_$R/. The wall pressure fluctuations on the blunt body were analysed in terms of the spectrum and the coherence.

Large-Scale Vortical Structure of Turbulent Separation Bubble Affected by Unsteady Wake (비정상 후류가 난류박리기포의 응집구조에 미치는 영향)

  • Jeon, Se-Jong;Seong, Hyeong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.9
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    • pp.1218-1225
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    • 2002
  • Large-scale vortical structure of a turbulent separation bubble affected by unsteady wake is essential to understand flow mechanisms in various fluid devices. A spoked-wheel type of wake generator provides unsteady wake, which modifies the turbulent separation bubble significantly by changing rotation directions and passing frequencies. A detailed mechanism of vortex shedding from the separation bubble with unsteady wake is analyzed by taking a conditional average with spatial box filtering, which spatially integrates measured signals at pre-determined wavelength. A convecting nature of the large-scale vortical structure is analyzed carefully. Spatial evolution of the large-scale vortical structure with frequency variance is also exemplified.

Discrete-vortex Simulation of Turbulent Separation Bubble Excited by Acoustic Perturbatioons (음향교란을 받는 난류박리기포의 이산와류 수치해석)

  • 임재욱;성형진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.4
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    • pp.775-786
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    • 1992
  • Studies are made of the turbulent separation bubble in a two-dimensional semi-infinite blunt plate aligned to a uniform free stream when the oncoming free stream contains a pulsating component. The discrete-vortex method is applied to simulate this flow situations because this approach is effective to represent the unsteady motions of turbulent shear layer and the effect of viscosity near the solid surface. The two key external paramenters in the free stream, i.e., the amplitude of pulsation, A, and the frequency parameter St[=fH/ $U_{1}$], are dealt with in the present numerical computations, A particular frequency gives a minimum reattachment which is related to the drag reduction and the most effective frequency is dependent on the most amplified shedding frequency. The turbulent flow structure is scrutinized. A comparison between the unperturbed flow and the perturbed at the particular frequency of the minimum reattachment length of the separation bubble suggests that the large-scale structure is associated with the shedding frequency and the flow instabilities.

A New Steady Approach to Predict the Transonic Buffet Onset (천음속 버펫 발단 예측을 위한 새로운 정상 접근 방법)

  • Jeong, In-Jae
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.34 no.5
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    • pp.12-18
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    • 2006
  • A new steady approach has been developed to predict the transonic buffet onset of a high speed aircraft. In this paper, the flow is assumed to be steady for the buffet onset. The present study involves the analysis of a distinct change in the variation of various static aerodynamic parameters. These distinct changes indicates the onset of transonic buffet. Among the various aerodynamic parameters considered in this study, the variation in the center of pressure has shown to provide a clearest indicator of transonic buffet onset. This new steady approach can be applied to predict the transonic buffet onset for airfoils with shock induced separation bubble and for large swept wings with small aspect ratios. Good agreements have been obtained compared with unsteady wind tunnel buffet test data. Based on the results obtained the new steady approach, it can be newly suggested that the distinct slope changes of the center of pressure curve can be used as an indicator of buffet onset for the steady experimental method on a full aircraft configuration.