• Title, Summary, Keyword: URANS

Search Result 53, Processing Time 0.05 seconds

NUMERICAL ANALYSIS OF UNSTEADY FLOW FIELD AND AEROACOUSTIC NOISE OF AN AXIAL FLOW FAN (축류팬의 비정상 유동장 및 유동소음의 수치 해석)

  • Kim, Wook;Hur, Nahm-Keon;Jeon, Wan-Ho
    • Journal of computational fluids engineering
    • /
    • v.15 no.4
    • /
    • pp.60-66
    • /
    • 2010
  • Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

Numerical Comparisons Between URANS and Hybrid RANS/LES at a High Reynolds Number Flow Using Unstructured Meshes

  • You, Ju-Yeol;Kwon, Oh-Joon
    • International Journal of Aeronautical and Space Sciences
    • /
    • v.11 no.1
    • /
    • pp.41-48
    • /
    • 2010
  • In the present study, the turbulent flow fields around a circular cylinder at $Re=3.6{\times}10^6$ were investigated based on an unstructured mesh technique, and the comparisons between URANS(S-A, SST) and hybrid RANS/LES(DES, SAS) methods for the simulation of high Reynolds number flow have been conducted. For this purpose, unsteady characteristics of vortex shedding and time-averaged quantities were compared. A quasi-steady solution-adaptive mesh refinement was also made for the URANS and hybrid RANS/LES approaches. The results showed that the simple changes in the turbulent length scale or source term of turbulent models made the flow fields less dissipative and more realistic in hybrid RANS/LES methods than the URANS approaches.

ASSESSMENT OF URANS AND DES SIMULATIONS FOR TWO-DIMENSIONAL BACKWARD FACING STEP FLOW (2차원 후항계단유동에 대한 URANS와 DES의 수치해석 평가)

  • Song C.S.;Park S.O.
    • Journal of computational fluids engineering
    • /
    • v.11 no.2
    • /
    • pp.25-31
    • /
    • 2006
  • A two-dimensional backward facing step flow is simulated by using URANS and Detached Eddy Simulations(DES) approaches. Turbulence models adopted for URANS and DES simulations are Spalart-Allmaras(S-A) model and Shear Stress Transport(SST) model. The target flow with ER=1.125, $Re_H=37,500$ is experimentally studied by Driver & Seegmiller. Various versions of DES have been tested in this paper. Results of the simulations are compared with the experimental data available to evaluate the merits and demerits of URANS and several versions of DES. URANS simulation converges to a steady state and hence unsteady characteristics are not featured. DES simulations in general successfully mimic large scale structures and oscillation characteristics of the flow.

Mean pressure prediction for the case of 3D unsteady turbulent flow past isolated prismatic cylinder

  • Ramesh, V.;Vengadesan, S.;Narasimhan, J.L.
    • Wind and Structures
    • /
    • v.9 no.5
    • /
    • pp.357-367
    • /
    • 2006
  • Unsteady 3D Reynolds Averaged Navier-Stokes (URANS) solver is used to simulate the turbulent flow past an isolated prismatic cylinder at Re=37,400. The aspect ratio of height to base width of the body is 5. The turbulence closure is achieved through a non-linear $k-{\varepsilon}$ model. The applicability of this model to predict unsteady forces associated with this flow is examined. The study shows that the present URANS solver with standard wall functions predicts all the major unsteady phenomena showing closer agreement with experiment. This investigation concludes that URANS simulations with the non-linear $k-{\varepsilon}$ model as a turbulence closure provides a promising alternative to LES with view to study flows having complex features.

TOWARD AN ACCURATE APPROACH FOR THE PREDICTION OF THE FLOW IN A T-JUNCTION: URANS

  • Merzari, E.;Khakim, A.;Ninokata, H.;Baglietto, E.
    • Nuclear Engineering and Technology
    • /
    • v.41 no.9
    • /
    • pp.1191-1204
    • /
    • 2009
  • In this study, a CFD methodology is employed to address the problem of the prediction of the flow in a T-junction. An Unsteady Reynolds Averaged Navier-Stokes (URANS) approach has been selected for its low computational cost. Moreover, Unsteady Reynolds Navier-Stokes methodologies do not need complex boundary formulations for the inlet and the outlet such as those required when using Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS). The results are compared with experimental data and an LES calculation. In the past, URANS has been tried on T-junctions with mixed results. The biggest limit observed was the underestimation of the oscillatory behavior of the temperature. In the present work, we propose a comprehensive approach able to correctly reproduce the root mean square (RMS) of the temperature directly downstream of the T-junction for cases where buoyancy is not present.

Analysis of added resistance and seakeeping responses in head sea conditions for low-speed full ships using URANS approach

  • Kim, Yoo-Chul;Kim, Kwang-Soo;Kim, Jin;Kim, Yoonsik;Park, Il-Ryong;Jang, Young-Hun
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • v.9 no.6
    • /
    • pp.641-654
    • /
    • 2017
  • The KVLCC2 and its modified hull form were investigated in regular head waves using Unsteady Reynolds Averaged Navier-Stokes (URANS) methods. The modified KVLCC2 (named KWP-bow KVLCC2) is designed for reducing wave reflection from the bow. Firstly, the original KVLCC2 is studied for verification of the present code and methodology and the computed time history of total resistance and 2DOF motions (heave and pitch) for the selected two wave length conditions are directly compared with the results obtained from KRISO towing tank experiment under the identical condition. The predicted added resistance, heave and pitch motion RAOs show relatively good agreement with the experimental results. Secondly, the comparison of performance in waves between KVLCC2 and KWP-bow KVLCC2 is carried out. We confirmed that newly designed hull form shows better performances in all the range of wave length conditions through both the computation and the experiment. The present URANS method can capture the difference of performance in waves of the two hull forms without any special treatment for short wave length conditions. It can be identified that KWP-bow KVLCC2 gives about 8% of energy saving in sea state 5 condition.

Numerical Simulations of Gravity Currents Using Unsteady Statistical Turbulence Models (비정상 통계적 난류모형을 이용한 중력류의 수치모의)

  • Paik, Joong-Cheol
    • Proceedings of the Korea Water Resources Association Conference
    • /
    • /
    • pp.570-574
    • /
    • 2009
  • 벽 근처에서의 흐름(near wall flow)을 해석하기 위한 낮은 레이놀즈수 수정(low-Reynolds number modification)을 포함하는 통계학적 난류모형을 이용한 3차원 비정상 레이놀즈-평균 나비어-스톡스 (URANS) 계산을 실시하여 사각형 수로에서의 중력류를 모의하였다. 3차원 계산 결과를 2차원 URANS 모의에 의한 계산 결과 그리고 실험결과와 비교하였다. 이 연구 결과는 적정 시 공간적 수치해상도를 가지고 벽 근처에서의 흐름을 주의 깊게 직접 해석하는 3차원 URANS 수치모의는 2차원 계산으로는 해석할 수 없는 대규모 Kelvin-Helmholtz 와구조 (vortical structure)의 붕괴(breakdown) 그리고 중력류 선단부에서 발달하는 Lobe-and-Cleft 흐름 불안정 등을 포함하는 중력류의 동적 특성을 높은 정확도로 재현할 수 있음을 보여준다.

  • PDF

PREDICTION OF THERMAL STRATIFICATION IN A U-BENT PIPE: A URANS VALIDATION

  • Pellegrini, M.;Endo, H.;Ninokata, H.
    • Nuclear Engineering and Technology
    • /
    • v.44 no.1
    • /
    • pp.33-42
    • /
    • 2012
  • In the present study, CFD is employed to investigate phenomena occurring during a process of thermal stratification in U-bent pipes at transitional Reynolds number. URANS evaluation had been chosen for its low computational costs during transient analysis and for the evaluation of modeling performance in these conditions. Application of CFD at transitional Reynolds number and buoyancy driven flows indeed contains deeper uncertainties in relation to the range of applicability for hydrodynamic and thermal models. The methodology applied in the work points out, through validations with the basic problems constituting the complex stratified phenomenon, the applicability of the current turbulence modeling. Accurate predictions have been found in relation to transitional Reynolds number in bent pipes and region of stability induced by the gravitational field. On the other hand the defects introduced in the unstable region of the U bent pipe, are discussed in relation to the adopted modeling.

Evaluation of URANS Turbulence Models through the Prediction of the Flow around a Circular Cylinder (원형 실린더 주위의 유동해석을 통한 URANS 난류 모델 성능 비교)

  • Kim, Minjae;Shin, Jihwan;Kwon, Laeun;Lee, Kurnchul
    • Journal of the Korea Institute of Military Science and Technology
    • /
    • v.17 no.6
    • /
    • pp.861-867
    • /
    • 2014
  • In the present study, the flow around a circular cylinder at $Re=3.6{\time}10^6$ is numerically simulated using URANS approach. The objective of this study is to evaluate the turbulence models(Realizable k-${\varepsilon}$, RNG k-${\varepsilon}$) through the prediction of the unsteady flow characteristics around the cylinder. The time-averaged drag coefficients and vortex shedding phenomenon in the wake region are compared to available experimental data and other numerical results. The simulation with Realizable k-${\varepsilon}$ model is found to be more dissipative due to large eddy viscosity predicted in the wake region while the simulation with RNG k-${\varepsilon}$ model predicts a complex vortex shedding phenomenon with more coherent structures realistically.

Two-way fluid-structure interaction simulation for steady-state vibration of a slender rod using URANS and LES turbulence models

  • Nazari, Tooraj;Rabiee, Ataollah;Kazeminejad, Hossein
    • Nuclear Engineering and Technology
    • /
    • v.51 no.2
    • /
    • pp.573-578
    • /
    • 2019
  • Anisotropic distribution of the turbulent kinetic energy and the near-field excitations are the main causes of the steady state Flow-Induced Vibration (FIV) which could lead to fretting wear damage in vertically arranged supported slender rods. In this article, a combined Computational Fluid Dynamics (CFD) and Computational Structural Mechanic (CSM) approach named two-way Fluid-Structure Interaction (FSI) is used to investigate the modal characteristics of a typical rod's vibration. Performance of an Unsteady Reynolds-Average Navier-Stokes (URANS) and Large Eddy Simulation (LES) turbulence models on asymmetric fluctuations of the flow field are investigated. Using the LES turbulence model, any large deformation damps into a weak oscillation which remains in the system. However, it is challenging to use LES in two-way FSI problems from fluid domain discretization point of view which is investigated in this article as the innovation. It is concluded that the near-wall meshes whiten the viscous sub-layer is of great importance to estimate the Root Mean Square (RMS) of FIV amplitude correctly as a significant fretting wear parameter otherwise it merely computes the frequency of FIV.