• Title/Summary/Keyword: CFD and unsteady RANS

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Unsteady RANS Analysis of the Hydrodynamic Response for a Ship with Forward Speed in Regular Wave (규칙파중 전진하는 선박의 유체역학적 응답에 대한 비정상 수치해석)

  • Park, Il-Ryong;Kim, Kwang-Soo;Kim, Jin;Van, Suak-Ho
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.1
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    • pp.29-41
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    • 2008
  • The present paper provides a CFD analysis of diffraction problem for a ship with forward speed using an unsteady RANS simulation method, a WAVIS code. The WAVIS viscous solver adopting a finite volume method has second order accuracy in time and field discretizaions for the RANS equations. A two phase level-set method and a realizable ${\kappa}-{\varepsilon}$ turbulence model are adopted to compute the free surface and to meet the turbulence closure, respectively. To validate the capability of the present numerical methods for the simulation of an unsteady progressive regular wave, computations are performed for three grid sets with refinement ratio of ${\sqrt{2}}$. The main simulation is performed for a DTMB5512 model with a forward speed in a regular head sea condition. Validation of the present numerical method is carried out by comparing the present CFD results with available unsteady experimental data published in the 2005 Tokyo CFD Workshop: resistance, heave force, pitch moment, unsteady free surface elevations and velocity fields.

Unsteady Flow Analysis Around a HAWT System Using Sliding Mesh Technique (미끄럼 격자를 이용한 HAWT 시스템 주위의 비정상 유동장 해석)

  • Lee, Chi-Hoon;Kim, Sang-Gon;Joh, Chang-Yeol
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.3
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    • pp.201-209
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    • 2011
  • An unsteady RANS analysis study of the 3-D flow around the NREL Phase VI horizontal axis wind turbine(HAWT) was performed using sliding mesh approach. Two different analysis models such as rotor-only and rotor with tower/nacelle were constructed to investigate the blade/tower interaction. Analysis results for the rotor with tower/nacelle were compared with the corresponding NREL's experimental data which produced fairly good validation of the present CFD model. Comparison of flows around those two models also clearly showed the blade/tower interaction even it was small for upwind configuration. Other visualization results and integrated aerodynamic loads including torque of the blade demonstrated the effective unsteady flow simulation capability of the present CFD model.

Numerical Analysis of Ship Motions in Beam Sea Using Unsteady RANS and Overset Grid Methods (비정상 RANS 법과 중첩격자계를 이용한 횡파중 선박운동 수치해석)

  • Park, Il-Ryong;Hosseini, Seyed Hamid Sadat;Stern, Frederick
    • Journal of the Society of Naval Architects of Korea
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    • v.45 no.2
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    • pp.109-123
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    • 2008
  • The present paper presents the CFD result for a beam wave test case. An ONR tumblehome ship model with bilge keels is used. The beam wave test is for zero forward speed and roll and heave 2DOF with wave slope $a_k=0.156$ and wavelength ${\lambda}=1.12L_{PP}$, with $L_{PP}$ the ship length. The problems is solved numerically with an unsteady Reynolds averaged Navier-Stokes approach. The free surface flow is computed using a single-phase level-set method and the motions in each time step are integrated using a predictor-corrector iteration approach which uses dynamic overset grids moving with relative ship motion. The predicted CFD results for motions and forces are compared with experimental data, showing a reasonable agreement.

Investigation of Turbulent Analysis Methods for CFD of Gas Dispersion Around a Building (건물주위의 가스 확산사고에 대한 CFD 난류 해석기법 검토)

  • Ko, Min Wook;Oh, Chang Bo;Han, Youn Shik;Do, Kyu Hyung
    • Fire Science and Engineering
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    • v.29 no.5
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    • pp.42-50
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    • 2015
  • Three simulation approaches for turbulence were applied for the computation of propane dispersion in a simplified real-scale urban area with one building:, Large Eddy Simulation (LES), Detached Eddy Simulation (DES), and Unsteady Reynolds Averaged Navier-Stokes (RANS). The computations were performed using FLUENT 14, and the grid system was made with ICEM-CFD. The propane distribution depended on the prediction performance of the three simulation approaches for the eddy structure around the building. LES and DES showed relatively similar results for the eddy structure and propane distribution, while the RANS prediction of the propane distribution was unrealistic. RANS was found to be inappropriate for computation of the gas dispersion process due to poor prediction performance for the unsteady turbulence. Considering the computational results and cost, DES is believed to be the optimal choice for computation of the gas dispersion in a real-scale space.

Numerical investigation of the unsteady flow of a hybrid CRP pod propulsion system at behind-hull condition

  • Zhang, Yuxin;Cheng, Xuankai;Feng, Liang
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.12 no.1
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    • pp.918-927
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    • 2020
  • Flows induced by hybrid CRP pod propulsion systems (CRP-POD) are fundamentally characterized by unsteadiness. This work presents a numerical study on the unsteady flow of a CRP-POD at behind-hull condition based on CFD (Computational Fluid Dynamics). Unsteady RANS method is adopted, coupled with SST k-u turbulence model and sliding mesh method. The propeller thrusts and torques obtained by CFD is validated by model tests and acceptable agreements are obtained. The time histories of shingle-blade loads and pressures near the hull surface are recorded for the analysis of unsteady flow features. The cases of forward propeller alone and aft propeller alone are also computed to distinguish the hull-propeller interaction and propeller-propeller interaction. The results show the blade loads of both forward and aft propellers strongly fluctuate with phase angles. For the forward propeller, the blade load fluctuation is mainly governed by the hull-propeller interaction, while the aft blade load is remarkably affected by the propeller-propeller interaction in terms of the load average and fluctuation pattern. The fields of pressure, vorticity and velocity are also analyzed to reveal the unsteady flow features.

Comparison of CFD simulations with experimental data for a tanker model advancing in waves

  • Orihara, Hideo
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.3 no.1
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    • pp.1-8
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    • 2011
  • In this paper, CFD simulation results for a tanker model are compared with experimental data over a range of wave conditions to verify a capability to predict the sea-keeping performance of practical hull forms. CFD simulations are conducted using WISDAM-X code which is capable of unsteady RANS calculations in arbitrary wave conditions. Comparisons are made of unsteady surface pressures, added resistance and ship motions in regular waves for cases of fully-loaded and ballast conditions of a large tanker model. It is shown that the simulation results agree fairly well with the experimental data, and that WISDAM-X code can predict sea-keeping performance of practical hull forms.

Extreme Design Load Case Analyses of a 5 MW Offshore Wind Turbine Using Unsteady Computational Fluid Dynamics (비정상 CFD 해석기법을 활용한 5 MW 해상풍력터빈 극한 설계하중조건 해석)

  • Kim, Dong-Hyun;Lee, Jang-Ho;Tran, Thanh-Toan;Kwak, Young-Seob;Song, Jin-Seop
    • Journal of Wind Energy
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    • v.5 no.1
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    • pp.22-32
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    • 2014
  • The structural design of a wind turbine must show the verification of the structural integrity of all load-carrying components. Also, design load calculations shall be performed using appropriate and accurate methods. In this study, advanced numerical approach for the calculation of design loads based on unsteady computational fluid dynamics (CFD) is presented considering extreme design load conditions such as the extreme coherent gust (ECG) and the 50 year extreme operating gust (EOG). Unsteady aerodynamic loads are calculated based on Reynolds average Navier-Stokes (RANS) equations with shear-stress transport k-ω(SST k-ω) turbulent model. A full three-dimensional 5 MW offshore wind-turbine model with rotating blades, hub, nacelle, and tower configuration is practically considered and its aerodynamic interference effect among blades, nacelle, and tower is also accurately considered herein. Calculated blade loads based on unsteady CFD method with respect to blade azimuth angle are compared with those by NREL FAST code and physically investigated in detail.

Influence of geometric configuration on aerodynamics of streamlined bridge deck by unsteady RANS

  • Haque, Md. N.;Katsuchi, Hiroshi;Yamada, Hitoshi;Kim, Haeyoung
    • Wind and Structures
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    • v.28 no.5
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    • pp.331-345
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    • 2019
  • Long-span bridge decks are often shaped as streamlined to improve the aerodynamic performance of the deck. There are a number of important shaping parameters for a streamlined bridge deck. Their effects on aerodynamics should be well understood for shaping the bridge deck efficiently and for facilitating the bridge deck design procedure. This study examined the effect of various shaping parameters such as the bottom plate slope, width ratio and side ratio on aerodynamic responses of single box streamlined bridge decks by employing unsteady RANS simulation. Steady state responses and flow field were analyzed in detail for wide range of bottom plate slopes, width and side ratios. Then for a particular deck shape Reynolds number effect was investigated by varying its value from $1.65{\times}10^4$ to $25{\times}10^4$. The aerodynamic response showed very high sensitivity to the considered shaping parameters and exhibited high aerodynamic performance for a particular combination of shaping parameters.

A BEM/RANS interactive method for predicting contra-rotating propeller performance

  • Su, Yiran;Kinnas, Spyros A.
    • Ocean Systems Engineering
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    • v.7 no.4
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    • pp.329-344
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    • 2017
  • This paper introduces a BEM/RANS interactive scheme to predict the contra-rotating propeller (CRP) performance. In this scheme, the forward propeller and the aft propeller are handled by two separate BEM models while the interactions between them are achieved by coupling them with a RANS solver. By using the body force field and mass source field to represent the propeller in the RANS model, the number of RANS cells and the number of required RANS iterations reduce significantly. The method provides an efficient way to predict the effective wake, the steady/unsteady propeller forces, etc. The BEM/RANS interactive scheme is first applied to a CRP in both an axisymmetric manner and a non-axisymmetric manner. Results are shown in good agreement with the experimental data in moderate to high advance ratios. It is proved that the difference between the axisymmetric scheme and the non-axisymmetric scheme mainly comes from the non-axisymmetric bodies. It is also found that the error is larger at lower advance ratios. Possible explanations are given. Finally, some additional cases are tested which justifies that the non-axisymmetric BEM/RANS scheme is able to handle a podded CRP working at given inclination angles.

Efficient Prediction of Broadband Noise of a Centrifugal Fan Using U-FRPM Technique (U-FRPM 기법을 이용한 원심팬 광대역소음의 효율적 예측)

  • Heo, Seung;Cheong, Chulung
    • The Journal of the Acoustical Society of Korea
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    • v.34 no.1
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    • pp.36-45
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    • 2015
  • Recently, a lot of studies have been made about the methods used to generate turbulent velocity fields stochastically in order to effectively predict broadband flow noise. Among them, the FRPM (Fast Random Particle Mesh) method which generates turbulence with specific statistical properties using turbulence kinetic energy and dissipation obtained from the steady solution of the RANS (Reynolds Averaged Navier-Stokes) equations has been successfully applied. However, the FRPM method cannot be applied to the flow noise problems involving intrinsic unsteady characteristics such as centrifugal fan. In this paper, to effectively predict the broadband noise generated by centrifugal fan, U-FRPM (unsteady FRPM) method is developed by extending the FRPM method to be combined with the unsteady numerical solutions of the unsteady RANS equations to generate the turbulence considered as broadband noise sources. Firstly, an unsteady flow field is obtained from the unsteady RANS equations through CFD (Computational Fluid Dynamics). Then, noise sources are generated using the U-FRPM method combined with acoustic analogy. Finally, the linear propagation model which is realized through BEM (Boundary Element Method) is combined with the generated sources to predict broadband noise at the listeners' position. The proposed technique is validated to compare its prediction result with the measured data.