• 제목/요약/키워드: turbulence and fluid dynamics

검색결과 376건 처리시간 0.032초

Relationship between Cavitation Incipient and NPSH Characteristic for Inverter Drive Centrifugal Pumps

  • Rakibuzzaman, Md;Suh, Sang-Ho;Kim, Hyoung-Ho;Jung, Young-Hoon
    • 한국유체기계학회 논문집
    • /
    • 제18권6호
    • /
    • pp.76-80
    • /
    • 2015
  • The purpose of this study is to understand the cavitation phenomena in centrifugal pumps through computational fluid dynamics method. NPSH characteristic curve is measured from different flow operating conditions. Steady state, liquid-vapor homogeneous method with two equations transport turbulence model is employed to estimate the NPSH curve in centrifugal pumps. The Rayleigh-Plesset cavitation model is adapted as source term for inter-phase mass transfer in order to understand cavitation phenomena in centrifugal pumps. The cavitation incipient curve is clearly estimated at different flows operating conditions. A relationship is made between cavitation incipient and NPSH curve. Also the effects on water vapor volume fraction and pressure load distributions on the impeller blade are also described.

EFFECT OF TURBULENCE AT INLET BOUNDARY ON AIR MOVEMENT IN A ROOM

  • Lee, Heekwan;Hazim B. Awbi
    • 한국대기환경학회:학술대회논문집
    • /
    • 한국대기환경학회 2000년도 춘계학술대회 논문집
    • /
    • pp.162-164
    • /
    • 2000
  • The numerical simulation of air movement in a room using CFD (Computational Fluid Dynamics) requires a complicated set of input data, This includes physical data, such as space geometry, characteristics of supply air flow and contaminant source, etc. as well as computational domain. Among the input data, the boundary conditions related to the inlet are particularly crucial in order to achieve accurate computation results, although there are many other parameters which may also affect the results. (omitted)

  • PDF

원형 노즐의 직경 변화 및 표면으로 부터의 거리변화에 따른 오목한 표면에 충돌하는 제트의 온도장 측정 및 CFD해석 (Temperature field measurement and CFD analysis of a jet impinging on a concave surface depending on changes in nozzle to surface distance and the diameter of a circular nozzle)

  • 조영민;임유진;염은섭
    • 한국가시화정보학회지
    • /
    • 제21권2호
    • /
    • pp.55-62
    • /
    • 2023
  • The characteristic of jet impinging on the concave surface were analyzed through thermographic phosphor thermometry (TPT) and numerical investigation. Under a jet Reynolds number of 6600, nozzle diameters and nozzle-to-surface distances (H/d) were changed 5mm and 10mm and H/d=2 and 5. The RNG k-ε turbulence model can accurately predict the distribution of Nusselt number, compared to other models (SST k-ω, realizable k-ε). Heat transfer characteristics varied with the nozzle diameter and H/d, with a secondary peak noted at H/d =2, due to vortex-induced flow detachment and reattachment. An increase in nozzle diameter enhanced jet momentum, turbulence strength, and heat transfer.

PIV 기법을 이용한 마하 2.0 초음속 노즐의 과대팽창 충격파구조에 대한 연구

  • 김정훈;안규복;김지호;윤영빈
    • 한국추진공학회:학술대회논문집
    • /
    • 한국추진공학회 2002년도 제18회 학술발표대회 논문초록집
    • /
    • pp.64-64
    • /
    • 2002
  • Two dimensional velocity distributions outside a Mach 2.0 supersonic nozzle have been investigated using digital particle image velocimetry (PIV). Mean velocities, turbulence intensities, vorticity field and volume dilatation field are obtained from 300 instantaneous PIV images using 0.33 $\mu\textrm{m}$ $TiO_2$ particle. The seeding particle of larger size, 1.4 $\mu\textrm{m}$ $TiO_2$, is also used for the experimental measurements of velocity lag downstream of shock waves according to particle sizes. The results have been compared and analyzed with schlieren photographs and computational fluid dynamics (CFD) results for the velocity distribution, the locations of shock waves and over-expanded shock structure. It was shown that the locations of normal shock and shock waves can be resolved by the axial or radial velocities, and the velocity lag is more significantly increased due to particle inertia as a particle size increases. And it was also found that over-expanded shock structures call be predicted by volume dilatation fields, and streamwise turbulence intensities are influenced significantly by normal shock waves.

  • PDF

An investigation on the effect of the wall treatments in RANS simulations of model and full-scale marine propeller flows

  • Choi, Jung-Kyu;Kim, Hyoung-Tae
    • International Journal of Naval Architecture and Ocean Engineering
    • /
    • 제12권1호
    • /
    • pp.967-987
    • /
    • 2020
  • A numerical analysis is carried out for the marine propellers in open water conditions to investigate the effect of the wall treatments in model and full scale. The standard wall function to apply the low of the wall and the two layer zonal model to calculate the whole boundary layer for a transition phenomenon are used with one turbulence model. To determine an appropriate distance of the first grid point from the wall when using the wall function, a formula based on Reynolds number is suggested, which can estimate the maximum y+ satisfying the logarithmic law. In the model scale, it is confirmed that a transition calculation is required for a model scale propeller with low Reynolds number that the transient region appears widely. While in the full scale, the wall function calculation is recommended for efficient calculations due to the turbulence dominant flow for large Reynolds number.

CFD investigation of a JAEA 7-pin fuel assembly experiment with local blockage for SFR

  • Jeong, Jae-Ho;Song, Min-Seop
    • Nuclear Engineering and Technology
    • /
    • 제53권10호
    • /
    • pp.3207-3216
    • /
    • 2021
  • Three-dimensional structures of a vortical flow field and heat transfer characteristics in a partially blocked 7-pin fuel assembly mock-up of sodium-cooled fast reactor have been investigated through a numerical analysis using a commercial computational fluid dynamics code, ANSYS CFX. The simulation with the SST turbulence model agrees well with the experimental data of outlet and cladding wall temperatures. From the analysis on the limiting streamline at the wall, multi-scale vortexes developed in axial direction were found around the blockage. The vortex core has a high cladding wall temperature, and the attachment line has a low cladding wall temperature. The small-scale vortex structures significantly enhance the convective heat transfer because it increases the turbulent mixing and the turbulence kinetic energy. The large-scale vortex structures supply thermal energy near the heated cladding wall surface. It is expected that control of the vortex structures in the fuel assembly plays a significant role in the convective heat transfer enhancement. Furthermore, the blockage plate and grid spacer increase the pressure drop to about 36% compared to the bare case.

KARI 중형 아음속 풍동용 돌풍 발생기의 수치해석 (NUMERICAL ANALYSIS OF THE GUST GENERATOR FOR KARI LOW SPEED WIND TUNNEL)

  • 박영민;권기정;이상욱;김태욱
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2005년도 추계 학술대회논문집
    • /
    • pp.275-279
    • /
    • 2005
  • The vortex convection and induced flow field behind the KARI 3m x 4m LSWT gust generator was computed by using Computational Fluid Dynamics. For the accurate simulation of vortex convection, inviscid, laminar, Spalart-Allmars k-e and k-w turbulence models were tested with the NAL gust generator configuration and Spalart-Allmaras turbulence model was selected for the prediction of induced flow field behind the KARI LSWT gust generator. The wind tunnel test was also carried out at KARI LSWT and the results were compared with CFD prediction.

  • PDF

난류모델에 따른 건물주위의 유동 예측 (A Prediction of the Flow Characteristics around Buildings with the Turbulent Models)

  • 이승호;여재현;허남건;최창근
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2008년도 춘계학술대회논문집
    • /
    • pp.168-171
    • /
    • 2008
  • In the present study, turbulent flows around cubic and L-shape buildings were simulated numerically. Standard ${\kappa}$-$\varepsilon$, RNG ${\kappa}$-$\varepsilon$, LES turbulence models were adopted for the present simulation. The wind pressure coefficients from these results were compared with the available experimental data. The result of RNG ${\kappa}$-$\varepsilon$ and LES turbulent models gave better prediction than that of standard ${\kappa}$-$\varepsilon$ turbulent model which is widely used in the turbulent flow simulation.

  • PDF

A 3D CFD analysis of flow past a hipped roof with comparison to industrial building standards

  • Khalil, Khalid;Khan, Huzafa;Chahar, Divyansh;Townsend, Jamie F.;Rana, Zeeshan A.
    • Wind and Structures
    • /
    • 제34권6호
    • /
    • pp.483-497
    • /
    • 2022
  • Three-dimensional (3D) computational fluid dynamics (CFD) analysis of flow around a hipped-roof building representative of UK inland conditions are conducted. Unsteady simulations are performed using three variations of the k-ϵ RANS turbulence model namely, the Standard, Realizable, and RNG models, and their predictive capability is measured against current European building standards. External pressure coefficients and wind loading are found through the BS 6399-2:1997 standard (obsolete) and the current European standards (BS EN 1991-1-4:2005 and A1:20101). The current European standard provides a more conservative wind loading estimate compared to its predecessor and the k-ϵ RNG model falls within 15% of the value predicted by the current standard. Surface shear stream-traces and Q-criterion were used to analyze the flow physics for each model. The RNG model predicts immediate flow separation leading to the creation of vortical structures on the hipped-roof along with a larger separation region. It is observed that the Realizable model predicts the side vortex to be a result of both the horseshoe vortex and the flow deflected off it. These model-specific aerodynamic features present the most disparity between building standards at leeward roof locations. Finally, pedestrian comfort and safety criteria are studied where the k-ϵ Standard model predicts the most ideal pedestrian conditions and the Realizable model yields the most conservative levels.

전산유체역학을 이용한 풍력터빈 축소효과 수치해석 (Numerical Analysis of Wind Turbine Scale Effect by Using Computational Fluid Dynamics)

  • 박영민;장병희
    • 신재생에너지
    • /
    • 제2권2호
    • /
    • pp.28-36
    • /
    • 2006
  • Numerical analysis of wind turbine scale effect was performed by using commercial CFD code, Fluent. For the numerical analysis of wind turbine, the three dimensional Navier-Stokes solver with various turbulence models was tested. As a turbulence mode, the realizable k-e turbulence model was selected for the simulation of wind turbines. To validate the present method, performance of NREL (National Renewable Energy Laboratory) Phase VI wind turbine model was analyzed and compared with its wind tunnel test and blind test data. Using the present method, numerical simulations for various size of wind tunnel models were carried out and characteristics were analyzed in detail. For wind tunnel test model, the size of nacelle may not be scaled down precisely because of available motor. The effect of nacelle size was also computed and analyzed though CFD simulation. The present results showed the good correlations in pre-stall region but much to be improved in post-stall region. In 2006 and 2007, the performance and the scale effect of standard wind turbine model will be tested in KARI(Korea Aerospace Research Institute) LSWT(Low Speed Wind Tunnel) and the present results will be validated with the wind tunnel data.

  • PDF