• Title, Summary, Keyword: 혼합 RANS/LES

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Numerical Investigation of Nonpremixed Turbulent Flame of Cracked Kerosene in a Model Scramjet Combustor using Zonal Hybrid RANS/LES Method (Zonal Hybrid RANS/LES를 이용한 크랙된 케로신 스크램제트 연소기의 비예혼합 난류 연소 연구)

  • Shin, Junsu;Sung, Hong-Gye
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.304-309
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    • 2017
  • This paper studies a nonpremixed turbulent flame in a model scramjet combustor using zonal hybrid RANS/LES method. The numerical domain is divided into two region, RANS and LES region. The interface between the two regions is treated with synthetic eddy method. A model scramjet combustor experimented at German aerospace center is selected for the comparative study. The fuel injection of cracked kerosene surrogate which is composed of ethylene and methane is considered. Turbulent combustion of cracked kerosene surrogate is achieved using flamelet approach.

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Computation of Serrated Trailing Edge Flow and Noise Using a Hybrid Zonal RANS-LES (혼합 영역 RANS-LES를 이용한 톱니 뒷전 유동 및 소음장의 계산)

  • Kim, Tae-Hyung;Lee, Seung-Hoon;Lee, Soo-Gab
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.22 no.5
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    • pp.444-450
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    • 2012
  • The evaluation of a zonal RANS-LES approach is documented for the prediction of broadband noise generated by the flow past unmodified and serrated airfoil trailing edges at a high Reynolds number. A multi-domain decomposition is considered, where the acoustic sources are resolved with a LES sub-domain embedded in the RANS domain. A stochastic vortex method is used to generate synthetic turbulent perturbations at the RANS-LES interface. The simulations are performed with a general-purpose unstructured control-volume code FLUENT. The far-field noise is calculated using the aeroacoustic analogy of Ffowcs Williams-Hawkings. The results of the simulation are validated through the full-scaled wind turbine acoustic measurements. It is found that the present approach is adequate for predicting noise radiation of serrated trailing edge flow for low noise rotor system.

Computation of serrated trailing edge flow and noise using a hybrid zonal RANS-LES

  • Kim, Tae-Hyung;Lee, Seung-Hoon;Lee, Soo-Gab
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.414-419
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    • 2012
  • The evaluation of a zonal RANS-LES approach is documented for the prediction of broadband noise generated by the flow past unmodified and serrated airfoil trailing edges at a high Reynolds number. A multi-domain decomposition is considered, where the acoustic sources are resolved with a LES sub-domain embedded in the RANS domain. A stochastic vortex method is used to generate synthetic turbulent perturbations at the RANS-LES interface. The simulations are performed with a general-purpose unstructured control-volume code FLUENT. The far-field noise is calculated using the aeroacoustic analogy of Ffowcs Williams-Hawkings. The results of the simulation are validated through the full-scaled wind turbine acoustic measurements. It is found that the present approach is adequate for predicting noise radiation of serrated trailing edge flow for low noise rotor system.

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Hybrid RANS/LES Simulation of Subsonic Cavity Flow (Hybrid RANS/LES 방법을 이용한 이음속 공동 유동의 수치적 모사)

  • Chang K. S.;Park S. O.;Choi S. K.
    • Journal of computational fluids engineering
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    • v.9 no.2
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    • pp.23-29
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    • 2004
  • A numerical simulation of an incompressible cavity flow is conducted using the hybrid turbulence model. The model adopted is a modified type of DES using k- ε two-equation model. Cavity geometry and flow condition are based on Cattafesta's experiment. Computational results are compared with the results of Cattafesta's experiment. The simulation successfully predicts the oscillatory features and the Strouhal number of the oscillation compares very favorably with that of the dominant mode of experimental data. Vorticity contours obtained from the simulation data are consistent with the smoke visualization of the Cattafesta's experiment. The coherent structures of cavity flow are also investigated using Q criterion.

RANS-LES Simulations of Scalar Mixing in Recessed Coaxial Injectors (RANS 및 LES를 이용한 리세스가 있는 동축분사기의 유동혼합에 대한 수치해석)

  • Park, Tae-Seon
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.1
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    • pp.55-63
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    • 2012
  • The turbulent flow characteristics in a coaxial injector were investigated by the nonlinear $k-{\varepsilon}-f_{\mu}$ model of Park et al.[1] and large eddy simulation (LES). In order to analyze the geometric effects on the scalar mixing for nonreacting variable-density flows, several recessed lengths and momentum flux ratios are selected at a constant Reynolds number. The nonlinear $k-{\varepsilon}-f_{\mu}$�� model proposed the meaningful characteristics for various momentum flux ratios and recess lengths. The LES results showed the changes of small-scale structures by the recess. When the inner jet was recessed, the development of turbulent kinetic energy became faster than that of non-recessed case. Also, the mixing characteristics were mainly influenced by the variation of shear rates, but the local mixing was changed by the adoption of recess.

Large Eddy Simulation for the Analysis of Practical Combustion Field (실용 연소장 해석을 위한 대 와동 모사)

  • Hwang, Cheol-Hong;Lee, Chang-Eon
    • 한국연소학회:학술대회논문집
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    • pp.181-188
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    • 2005
  • Large eddy simulation(LES) methodology used to model the isothermal swirling flows in a dump combustor and the turbulent premixed flame in a model gas turbine combustor. The LES solver was implemented on parallel computer consisting 16 processors. In isothermal flow simulation, the results was compared with that of ${\kappa}-{\varepsilon}$ model as well as experimental data, in order to verify the capability of LES code. To model the turbulent premixed flame in a gas turbine, the G-equation flamelet model was used. The results showd that LES and RANS well predicted the mean velocity field of a non-swirling flow. However, in swirling flow, LES showed a better performance in predicting the mean axial and azimuthal velocities, and the central recirculation zone than those of RANS. In a model gas turbine combustor, the operation condition of high pressure and temperature induced the different phenomena, such as flame length and flow-field information, comparing with the condition of ambient pressure and temperature. Finally, it was identified that the flame and heat release oscillations are related to the vortex shedding generated by swirl flow and pressure wave propagation.

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Turbulent mixing of suspended sediments in the Kelvin-Helmholtz instability using Large-eddy Simulation (켈빈-헬름홀츠 불안정성 내에서의 부유사 혼합 거동 모사)

  • Ku, Hyeyun;Hwan, Jin Hwan
    • Proceedings of the Korea Water Resources Association Conference
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    • pp.386-386
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    • 2015
  • 담수가 해수에서 흘러드는 하구에서는 성층이 관측되며 이것은 난류의 미세구조를 변화시키는 주요 원인으로 작용한다. 이러한 성층화 현상은 하구 내 부유사의 군집인 하구 최대혼탁수(Estuarine Turbidity Maximum, ETM)의 형성에 영향을 주게 된다. 본 연구는 성층의 하구 최대 혼탁수 생성 메커니즘에 관심을 두고 수치모델링을 활용한 미세 난류의 부유사 거동 분석에 초점을 두었다. 성층과 전단응력 사이의 난류 혼합을 대표하는 유동인 켈빈-헬름홀츠 불안정성(Kelvin-Helmholtz Instability)을 도입하고 성층 경계면 근처에서 부유사의 이송을 높은 레이놀즈수(Reynolds number) 유동에서 RANS(Reynolds-averaged Navier-Stokes Simulation)보다 다양한 규모의 에너지 획득이 가능하여 미세 난류 구조 재현에 장점을 갖는 Large-eddy Simulation(LES)를 활용하여 모사하였다. 여기에서, 부유사는 주위 유동의 물리적 특성 변화에 영향을 미치지 않는 Passive scalar로 가정하였으며 $6^{th}$-order Lagrangian 다항식 보간법을 적용하여 입자의 이동 속도를 계산하고 이를 시간에 대해 적분함으로써 이동 궤적을 추적하였다. 수치 모델 결과 Lock-exchange 유동 내에서 켈빈-헬름홀츠 불안정성이 발생함에 따라 경계면 주위에 위치한 부유사가 billow 내에서 트랩핑(trapping)되는 것을 보여주어 KH-billow 혹은 braids 내의 미세 난류에 의한 영향이 확인되었다. 본 연구에서는 LES를 활용하여 성층류 및 성층류 내의 부유사 혼합을 모사하여 난류의 정도에 따른 이동 궤적의 차이에 대해서 분석함으로써 성층의 난류 강도 저하에 따른 부유사의 군집으로의 영향에 대해 서술한다.

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Numerical Study on the Flow and Combustion Characteristics in Swirl-Premix Burners (스월 예혼합 버너의 유동 및 연소특성에 관한 수치적 연구)

  • Lim, Jun-Seok;Lee, Jong-Hyeok;Baek, Gwang-Min;Cho, Ju-Hyeong;Kim, Han-Seok;Sohn, Chae-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.1
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    • pp.103-110
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    • 2012
  • The flow field, fuel-air mixing, and behaviors of turbulent flames have been investigated using the large eddy simulation (LES) numerical technique in a premixed swirl combustor equipped with EV double cone burners. Recirculation zones are generated by the swirl burner, and lean premixed flames are formed within a distance of 0.2 m from the tip of the burner. NOx emission of 0.46 ppm is predicted at 1 atm and an air/fuel ratio of 38.7. However, most of the CO generated in a flame front continues to be oxidized as it moves toward the exit, and CO emission of 5.45 ppm is predicted at the exit. The NOx emission can be reduced by decreasing the pressure and air/fuel ratio. The characteristics of NOx emission have been investigated through RANS simulations for various fuel injection types, and it is found thereby that five-lance-hole injection produces the lowest NOx emission rate.

Analysis of Hydraulic effects on Piers and Transverse Overflow Type Structures in Urban Stream (도시하천의 교각 및 횡단 월류형 구조물에 의한 수리영향 분석)

  • Yoon, Sun-Kwon;Chun, Si-Young;Kim, Jong-Suk;Moon, Young-Il
    • Journal of Korea Water Resources Association
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    • v.41 no.2
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    • pp.197-212
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    • 2008
  • Recently, stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many condition limits. In this study, FLOW-3D using CFD (Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS (Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behaviors and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as ${\kappa}-{\varepsilon}$, RNG (Renormalized Group) ${\kappa}-{\varepsilon}$ and LES (Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the piers and transverse overflow type structures. These results will be able to used by basis data that catch hold of effects on long-term bed elevation changes, sediment accumulations, scours and water aggravations by removal of obsolete transverse over flow type structures in urban stream.