• Title, Summary, Keyword: Reynolds Equation(레이놀즈 방정식)

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Prediction of Polymer Drag-Reduction Turbulent Channel Flow with a Reynolds Stress Transport Equation Model (레이놀즈응력 수송방정식 모형에 의한 폴리머 항력감소 난류 채널유동의 예측)

  • Shin, Jong-Keun;Byun, Sun-Joon
    • Journal of the Korean Society of Mechanical Technology
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    • v.20 no.5
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    • pp.549-555
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    • 2018
  • An elliptic blending Reynolds stress transport equation model for Newtonian fluids has been extended to predict polymer-induced drag reduction FENE-P fluids. The conformation tensor equation which is related to the polymer stress is adopted from the model form of Resende et al., and the models of redistribution and dissipation rate terms for the Reynolds stress transport equation are considered by the elliptic blending equation. Also, the new model terms for viscoelastic turbulent transport and viscoelastic dissipation in the Reynolds stress transport equation are introduced to consider the polymer additives effect. The prediction results are directly compared to the DNS data to assess the performance of the present model predictions.

Prediction of Turbulent Boundary Layers on Convex Surfaces with Reynolds Stress Closure Model (레이놀즈응력모델을 사용한 곡면상의 난류경계층에 대한 수치해석)

  • 김광용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1717-1726
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    • 1991
  • 본 연구에서는 낮은 레이놀즈수 영역에도 적용될 수 있는 레이놀즈응력모델의 개발을 위해, 우선 벽근처 영역에서 사용되는 실험식(벽법칙)을 Hassid와 Poreh에 의 해 개발된 1-방정식모델로 대체하고 이를 레이놀즈응력모델과 접속시키는 방식을 사용 하였다. Hassid-Poreh의 1-방정식모델은 이미 Gibson등에 의해 그 성능이 평가되어 압력구배가 크지 않은 경계층유동의 낮은 레이놀즈수 영역에서 매우 좋은 결과를 보여 줌이 밝혀졌다. 본 연구에서는 곡면위의 난류경계층에 대해 위에서 설명한 바 있는 난류모델을 적용함에 있어 Gillis등과 Gibson등에 의해 실험된, 각각 곡률이 큰 경우 와 작은 경우의 대표적인 유동을 선택하여 모델의 성능을 시험하였다. 1-방정식모델 내에 포함된 길이차원(length scale)에 대해서는 곡률을 고려한 수정이 이루어졌다.

Computation of supersonic turbulent base flow using two-equation and Reynolds stress models (2-방정식 및 레이놀즈 응력 모형을 이용한 초음속 난류 기저유동의 수치적 계산)

  • Kim M. H.;Park S. O.
    • Journal of computational fluids engineering
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    • v.2 no.2
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    • pp.9-17
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    • 1997
  • The performance of several turbulence models in computing an axisymmetric supersonic base flow is investigated. A compressible Navier-Stokes code, which incorporates k-ε, k-ω model and Reynolds stress closure with three kinds of pressure-strain correlation model, has been developed using implicit LU-SGS algorithm with second-order upwind TVD scheme. Numerical computations have been carried out for Herrin and Dutton's base flow. It is observed that the two-equation models give large backward axial velocity approaching to the base and somewhat larger variation of base pressure distribution than the Reynolds stress model. It is also found that the Reynolds stress model with third order pressure-strain model in the anisotropy tensor predicts most accurate mean flow field.

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A Reynolds Stress Model for Low-Reynolds-Number Turbulence (저레이놀즈수 난류에 대한 레이놀즈 응력모델)

  • 김광용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.6
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    • pp.1541-1546
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    • 1993
  • To extend the widely used Gibson and Launder's second order closure model to the low-Reynolds-number region near a wall, modifications have been made for velocity pressure-gradient interaction and dissipation terms in the stress equations, and also for the dissipation rate equation. From the computation of fully developed plane channel flow, it is found that the results with present model agree well with the data of direct numerical simulation in the predictions of stress components. And, the computed mean velocity profile coincides with the universal velocity law.

A Comparative Study of the Navier-Stokes Equation & the Reynolds Equation in Spool Valve Analysis (스풀밸브 해석에서 Navier-Stokes 방정식과 Reynolds 방정식에 의한 비교 연구)

  • Hong, Sung-Ho;Son, Sang-Ik;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.28 no.5
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    • pp.218-232
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    • 2012
  • In a spool valve analysis, the Reynolds equation is commonly used to investigate the lubrication characteristics. However, the validity of the Reynolds equation is questionable in a spool valve analysis because cavitation often occurs in the groove and the depth of the groove is much higher than the clearance in most cases. Therefore, the validity of the Reynolds equation in a spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and the Navier-Stokes equation. Dimensionless parameters are determined from a nondimensional form of the governing equations. The differences between the lateral force, friction force, and volume flow rate (leakage) obtained by the Reynolds equation and those obtained by the Navier-Stokes equation are discussed. It is shown that there is little difference (less than 10%), except in the case of a spool valve with many grooves where no cavitation occurs in the grooves. In most cases, the Reynolds equation is effective for a spool valve analysis under a no cavitation condition.

Critical Reynolds Number for the Occurrence of Nonlinear Flow in a Rough-walled Rock Fracture (암반단열에서 비선형유동이 발생하는 임계 레이놀즈수)

  • Kim, Dahye;Yeo, In Wook
    • Economic and Environmental Geology
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    • v.52 no.4
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    • pp.291-297
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    • 2019
  • Fluid flow through rock fractures has been quantified using equations such as Stokes equations, Reynolds equation (or local cubic law), cubic law, etc. derived from the Navier-Stokes equations under the assumption that linear flow prevails. Therefore, these simplified equations are limited to linear flow regime, and cause errors in nonlinear flow regime. In this study, causal mechanism of nonlinear flow and critical Reynolds number were presented by carrying out fluid flow modeling with both the Navier-Stokes equations and the Stokes equations for a three-dimensional rough-walled rock fracture. This study showed that flow regimes changed from linear to nonlinear at the Reynolds number greater than 10. This is because the inertial forces, proportional to the square of the fluid velocity, increased enough to overwhelm the viscous forces. This tendency was also shown for the unmated (slightly sheared) rock fracture. It was found that nonlinear flow was caused by the rapid increase in the inertial forces with increasing fluid velocity, not by the growing eddies that have been ascribed to nonlinear flow.

Comparative Study of the Navier-Stokes Equation & the Reynolds Equation in Spool Valve Analysis Considering Cavitation (캐비테이션을 고려한 스풀밸브 해석에서 Navier-Stokes 방정식과 Reynolds 방정식에 의한 비교 연구)

  • Hong, Sung-Ho;Son, Sang-Ik;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.29 no.5
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    • pp.275-285
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    • 2013
  • The Reynolds equation is commonly used to investigate the lubrication characteristics of a spool valve. However, the applicability of the Reynolds equation is questionable for analyzing a spool valve because cavitation often occurs in the grooves of the valve and the depth of a groove is much higher than the clearance in most cases. In this study, the validity of the Reynolds equation in the spool valve analysis is investigated by comparing the results obtained from the Reynolds equation and those obtained from the Navier-Stokes equation. The results are compared in terms of the lateral forces, friction forces, and volume flow rates (leakages). A significant difference of more than 20% is found in the lateral forces in cases where cavitation occurs and there are many grooves. Therefore, the Navier-Stokes equation should be used to investigate the lubrication characteristics of a spool valve when cavitation occurs and when the spool valve contains many grooves.

Coupled Analysis of the Fluid Dynamic Bearings with the Recirculation Channel by Solving the Reynolds and Hagen-Poiseuille Equations (Reynolds 방정식과 Hagen-Poiseuille 방정식의 연성해석을 통한 재순환홀을 갖는 유체동압베어링의 해석)

  • Kang, Chiho;Jang, Gunhee;Jung, Yeonha
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.760-767
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    • 2014
  • This paper proposes a method to calculate pressure and flow of the fluid dynamic bearings (FDBs) with a recirculation channel (RC) by solving the Reynolds and the Hagen-Poiseuille equations at the same time. The Hagen-Poiseuille equation is one-dimensional equation which describes the flow in a circular pipe such as the RC. This research developed a finite element program to solve the Reynolds and the Hagen-Poiseuille equation together. The proposed method was applied to calculate the pressure and flow of the FDBs which are composed of grooved or plain journal and thrust bearings, and RC. To verify the proposed method, it also developed a finite volume model of the FDBs, and pressure and flow were calculated by the commercial CFD solver. They agree well with the pressure and flow calculated by the proposed method. Finally, this research investigated the characteristics of the FDBs due to the radius change of the RC.

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Study on Flexible Airfoil in Low Reynolds Number Flow Field (저 레이놀즈 수 유동장에서의 유연 익형에 대한 연구)

  • Gwon, Gi Beom
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.3
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    • pp.1-7
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    • 2003
  • In the study, aeroelastic behaviors and aerodynamic performances of flexible airfoil in low Reynolds number environment are evaluated. To facilitate the present study, flexible airfoil in modeled through attaching massless membrane in portion of the upper CLARK-Y airfoil surface, which is often proposed low Reynolds number airfoil. The behavior of membrane in governed by aerodynamic forces and membrane equilibrium equation. Nondimensional parameter deducted by nondimensionalizing the membrane equilibrium equation, which represents the interaction between fluid and membrane has a great influence on membrane aeroelastic behavior. Changing the starting point of the membrane is conducted on aerodynamic performances. As a result, the value of nondimensional parameter should almost linearly increase according to moving the starting point of the membrane surface toward the trailing edge.

Accelerating Numerical Analysis of Reynolds Equation Using Graphic Processing Units (그래픽처리장치를 이용한 레이놀즈 방정식의 수치 해석 가속화)

  • Myung, Hun-Joo;Kang, Ji-Hoon;Oh, Kwang-Jin
    • Tribology and Lubricants
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    • v.28 no.4
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    • pp.160-166
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    • 2012
  • This paper presents a Reynolds equation solver for hydrostatic gas bearings, implemented to run on graphics processing units (GPUs). The original analysis code for the central processing unit (CPU) was modified for the GPU by using the compute unified device architecture (CUDA). The red-black Gauss-Seidel (RBGS) algorithm was employed instead of the original Gauss-Seidel algorithm for the iterative pressure solver, because the latter has data dependency between neighboring nodes. The implemented GPU program was tested on the nVidia GTX580 system and compared to the original CPU program on the AMD Llano system. In the iterative pressure calculation, the implemented GPU program showed 20-100 times faster performance than the original CPU codes. Comparison of the wall-clock times including all of pre/post processing codes showed that the GPU codes still delivered 4-12 times faster performance than the CPU code for our target problem.