• Title/Summary/Keyword: Spalart-Allmaras Turbulence Model

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Assessment and Validation of Turbulence Models for the Optimal Computation of Supersonic Nozzle Flow (초음속 노즐 유동의 최적해석을 위한 난류모델의 평가와 선정)

  • Kam, Ho Dong;Kim, Jeong Soo
    • Journal of the Korean Society of Propulsion Engineers
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    • v.17 no.1
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    • pp.18-25
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    • 2013
  • Assessment and validation of RANS turbulence models are conducted for the optimal analysis of supersonic converging-diverging nozzle through the comparison between computational results and experimental data. One/two equation turbulence closures such as Spalart-Allmaras, RNG k-${\varepsilon}$, and k-${\omega}$ SST are employed to simulate the two-dimensional nozzle flow. Computational results with the turbulence models mentioned fairly well predict shock structure of the nozzle-inside and pressure distribution along the wall. Especially, SST model among the employed ones shows the best agreement to experimental results.

Effects of Underexpanded Plume in Transonic Region on Longitudinal Stability (천음속 영역에서 과소 팽창 화염이 종안정성에 미치는 영향에 관한 연구)

  • Jung, Suk-Young;Yoon, Sung-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.32 no.8
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    • pp.118-128
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    • 2004
  • Exhaust plume effects on longitudinal aerodynamics of missile were investigated by wind tunnel tests using a solid plume simulator and CFD analyses with both the solid plume and air jet plumes. Approximate plume boundary prediction technique was used to produce the outer shape of the solid plumer and chamber conditions and nozzle shapes of the air jet plumes were determined through plume modeling technique to compensate the difference in thermodynamic properties between air and real plume. From comparisons among turbulence models in case of external flow interaction with the air jet plume, Spalart-Allmaras model turned out to give accurate result and to be less grid-dependent. Effects induced by the plume were evaluated through the computations with Spalart-Allmaras turbulence model and the air jet plume to account for various ratios of chamber and ambient pressure and Reynolds number under the flight test condition.

Numerical Analysis on Screech Tone in a Supersonic Jet (숯계산에 의한 초음속 제트의 스크리티 톤 소음 해석)

  • Kim, Yong-Seok;Lee, Duck-Joo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.2
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    • pp.94-100
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    • 2007
  • An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with a modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures and large-scale instability waves.

Numerical Simulation of the Screech Phenomenon in a Supersonic Jet (수치계산에 의한 초음속 제트에서의 스크리치 현상 해석)

  • Kim, Yong-Seok;Kim, Sung-Cho;Kim, Jeong-Soo
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2007.04a
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    • pp.329-334
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    • 2007
  • An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures, unsteady shock motions and large-scale instability waves.

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Turbulent Flow Calculations Using an Unstructured Hybrid Meshes (2차원 혼합격자를 이용한 난류유동 계산)

  • Kim J. S.;Oh W. S.;Kwon O. J.
    • 한국전산유체공학회:학술대회논문집
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    • 1999.05a
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    • pp.90-97
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    • 1999
  • An implicit turbulent flow solver is developed for 2-D unstructured hybrid meshes. Spatial discretization is accomplished by a cell-centered finite volume formulation using an upwind flux differencing. Time is advanced by an implicit backward Euler time stepping scheme. Flow turbulence effects are modeled by the Spalart-Allmaras one equation model, which is coupled with wall function. The numerical method is applied for flows on a flat plate, the NACA 0012 airfoil, and the Douglas 3 element airfoil. The results are compared with experimental data.

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A Study on the Accuracy of CFD Prediction for Small Scaled 4 Nozzle Clustered Engine Using Air (공기를 이용한 축소형 4노즐 클러스터드 엔진 저부 유동의 CFD 해석 검증)

  • Kim, Seong-Lyong;Kim, In-Sun
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.11a
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    • pp.78-84
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    • 2011
  • CFD simulation has been conducted on a small scaled 4 nozzle clustered engine operating with air. In the present paper, the effects of grid size, turbulence models, flux difference methods have been compared. The results show that the base flows are somewhat different as the turbulence models, while Roe and AUSM flux differences produced almost the same results. Spalart-Allmaras turbulence model produces more accurate results rather than famous SST k-w model. The calculated Mach number and pressure profile in the engine base reveal the complex base flow structure, which is somewhat different from the generally estimated flow fields.

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EFFECT OF BASE FLOW AND TURBULENCE ON THE SEPARATION MOTION OF STRAP-ON ROCKET BOOSTERS (기저부 유동 및 난류가 다단 로켓의 단 분리 운동에 미치는 영향)

  • Ko, S.H.;Kim, J.K.;Han, S.H.;Kim, J.H.;Kim, C.
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.83-86
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    • 2007
  • Turbulent flow analysis is conducted around the multi-stage launch vehicle including base region and detachment motion of strap-on boosters due to resultant aerodynamic forces and gravity is simulated. Aerodynamic solution procedure is coupled with rigid body dynamics for the prediction of separation behavior. An overset mesh technique is adopted to achieve maximum efficiency in simulating relative motion of bodies and various turbulence models are implemented on the flow solver to predict the aerodynamic forces accurately. At first, some preliminary studies are conducted to show the importance of base flow for the exact prediction of detachment motion and to find the most suitable turbulence model for the simulation of launch vehicle configurations. And then, developed solver is applied to the simulation of KSR-III, a three-stage sounding rocket researched in Korea. From the analyses, after-body flow field strongly affects the separation motions of strap-on boosters. Negative pitching moment at initial stage is gradually recovered and a strap-on finally results in a safe separation, while fore-body analysis shows collision phenomena between core rocket and booster. And a slight variation of motion is observed from the comparison between inviscid and turbulent analyses. Change of separation trajectory based on viscous effects is just a few percent and therefore, inviscid analysis is sufficient for the simulation of separation motion if the study is focused only on the movement of strap-ons.

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Analysis of a Rim-Seal with a Semicircular Rib or Groove (반원형 리브 혹은 그루브가 부착된 림실에 대한 연구)

  • Lee, Chung-Suk;Moon, Mi-Ae;Kim, Kwang-Yong
    • The KSFM Journal of Fluid Machinery
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    • v.16 no.3
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    • pp.39-47
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    • 2013
  • Effect of semicircular rib or groove on the performance of a rim-seal was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations. The turbulence was modeled using the one-equation Spalart-Allmaras turbulence closure model. Reynolds number based on the axial chord of the turbine blade was 500,000 at the mainstream outlet. The numerical results for a sealing effectiveness was validated in comparison with experimental data. To examine the effect of the semicircular rib or groove on sealing effectiveness of the rim-seal, location and diameter of the rib or groove were selected as the parameters to be performed. The rim-seals with the semicircular groove showed a higher sealing effectiveness than that with the semicircular rib. The semicircular groove installed on the stator side showed best sealing effectiveness among the numerical simulation results.

Numerical study of CEDS scheme for turbulent flow (난류 유동장에 대한 CFDS 기법의 수치적 연구)

  • Moon Seong Mok;Kim Chongam;Rho Oh Hyun;Hong Seung Kyu
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.23-26
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    • 2002
  • An evaluation of one algebraic and two one-equation eddy viscosity-transport turbulence closure models as implemented to the CFDS(Characteristic Flux Difference Splitting) scheme is presented for the efficient computation of the turbulent flow. Comparisons of Baldwin-Lomax model as algebraic turbulence model and Baldwin-Barth and Spalart-Allmaras model as one-equation turbulence model are presented for three test cases for 3-dimensional flow. The numerical result of the CFDS schem is examined through comparison with the experimental data.

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Numerical Simulation for Transonic Wing-Body Configuration using CFD (CFD를 이용한 천음속 날개-동체 형상 해석)

  • Kim, Younghwa;Kang, Eunji;Ahn, Hyokeun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.3
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    • pp.233-240
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    • 2017
  • The flowfield around transonic wing-body configuration was simulated using in-house CFD code and compared with the experimental data to understand the influence of several features of CFD(Computational Fluid Dynamics) ; grid dependency, turbulence models, spatial discretization, and viscosity. The wing-body configuration consists of a simple planform RAE Wing 'A' with an RAE 101 airfoil section and an axisymmetric body. The in-house CFD code is a compressible Euler/Navier-Stokes solver based on unstructured grid. For the turbulence model, the $k-{\omega}$ model, the Spalart-Allmaras model, and the $k-{\omega}$ SST model were applied. For the spatial discretization method, the central differencing scheme with Jameson's artificial viscosity and Roe's upwind differencing scheme were applied. The results calculated were generally in good agreement with experimental data. However, it was shown that the pressure distribution and shock-wave position were slightly affected by the turbulence models and the spatial discretization methods. It was known that the turbulent viscous effect should be considered in order to predict the accurate shock wave position.