• Title/Summary/Keyword: Turbulent Kinetic Energy

Search Result 336, Processing Time 0.026 seconds

Numerical Analysis on the Turbulent Mixing Flow Field of $45^{\circ}$ Impinging Round Jet ($45^{\circ}$ 원형충돌분류의 난류혼합유동장에 대한 수치해석)

  • Kim, J.K.;Oh, S.H.
    • Journal of Power System Engineering
    • /
    • v.15 no.3
    • /
    • pp.38-45
    • /
    • 2011
  • The computational flow numerical analysis was introduced to predict thc turbulent characteristics in the mixing flow structure of $45^{\circ}$ impinging round jet. This analysis has been carried out through the commercial fluent software. Realizable(RLZ) k-${\varepsilon}$ was used as a turbulent model. It can be known that mean velocities analysed through RLZ k-${\varepsilon}$ turbulent model comparatively predict well the experiments and show well the elliptic shape of mixing flow structure in the Y-Z plane, but analysed turbulent kinetic energies show somewhat differently from the experiments in certain regions.

PIV measurement of roof corner vortices

  • Kim, Kyung Chun;Ji, Ho Seong;Seong, Seung Hak
    • Wind and Structures
    • /
    • v.4 no.5
    • /
    • pp.441-454
    • /
    • 2001
  • Conical vortices on roof corners of a prismatic low-rise building have been investigated by using the PIV(Particle Image Velocimetry) technique. The Reynolds number based on the free stream velocity and model height was $5.3{\times}10^3$. Mean and instantaneous vector fields for velocity, vorticity, and turbulent kinetic energy were measured at two vertical planes and for two different flow angles of $30^{\circ}$ and $45^{\circ}$. The measurements provided a clear view of the complex flow structures on roof corners such as a pair of counter rotating conical vortices, secondary vortices, and tertiary vortices. They also enabled accurate and easy measurement of the size of vortices. Additionally, we could easily locate the centers of the vortices from the ensemble averaged velocity fields. It was observed that the flow angle of a $30^{\circ}$ produces a higher level of vorticity and turbulent kinetic energy in one of the pair of vortices than does the $45^{\circ}$ flow angle.

Computational modeling of the atmospheric boundary layer using various two-equation turbulence models

  • Juretic, Franjo;Kozmar, Hrvoje
    • Wind and Structures
    • /
    • v.19 no.6
    • /
    • pp.687-708
    • /
    • 2014
  • The performance of the $k-{\varepsilon}$ and $k-{\omega}$ two-equation turbulence models was investigated in computational simulations of the neutrally stratified atmospheric boundary layer developing above various terrain types. This was achieved by using a proposed methodology that mimics the experimental setup in the boundary layer wind tunnel and accounts for a decrease in turbulence parameters with height, as observed in the atmosphere. An important feature of this approach is pressure regulation along the computational domain that is additionally supported by the nearly constant turbulent kinetic energy to Reynolds shear stress ratio at all heights. In addition to the mean velocity and turbulent kinetic energy commonly simulated in previous relevant studies, this approach focuses on the appropriate prediction of Reynolds shear stress as well. The computational results agree very well with experimental results. In particular, the difference between the calculated and measured mean velocity, turbulent kinetic energy and Reynolds shear stress profiles is less than ${\pm}10%$ in most parts of the computational domain.

Numerical Study of Periodic Turbulent Flow for a Pipe with an Orifice Ring (오리피스 링이 부착된 원관내 주기적인 난류운동에 대한 수치해석)

  • 맹주성;양시영;서현철
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.17 no.9
    • /
    • pp.2294-2303
    • /
    • 1993
  • This paper investigated the characteristics of the turbulent incompressible flow past the orifice ring in an axi-symmetric pipe. The flow field was the turbulent pulsatile flow for Reynolds number of $2{\times}10^{5}$ which was defined based on the maximum velocity and the pipe diameter at the inlet, with oscillating frequence $(f_{os})=1/4{\pi}$ which was considered as quasi-steady state frequence. In the present investigation, finite analytic method was used to solve the governing equations in Navier Stokes and turbulent transport formulations. Particularly at high Reynolds number and low oscillation frequency, the effects of orifice ring on the flow were numerically investigated. The separation zone behind the orifice ring during the acceleration phase was found to be decreased. However, during the deceleration phase, the separation behind the orifice ring for pulsatile flow continuously grow to a size even larger than that in steady flow. The pressure drop in steady flow was found to be constant and always positive while for pulsatile flow the pressure drop change with time. And large turbulent kinetic energy, dissipation rate were found to be located in the region where the flow passes through the orifics ring. The maximum turbulent kinetic energy, generally occurs along the shear layer where the velocity gradient is large.

Numerical Simulation of Turbulent Wake Behind SUBOFF Model (SUBOFF 모형 후방 난류항적의 수치 시뮬레이션)

  • Nah, Young-In;Bang, Hyung-Do;Park, Jong-Chun
    • Journal of the Society of Naval Architects of Korea
    • /
    • v.47 no.4
    • /
    • pp.517-524
    • /
    • 2010
  • This paper covers the numerical studies performed to investigate the characteristics of turbulent wake generated by a submarine, SUBOFF model. A SUBOFF model assumed as an axial-symmetric body was used to generate wake. The numerical simulation was performed by using a commercial S/W, FLUENT, with the same condition as the experiments by Shin et al.(2009). Mainly the cross-sectional distribution of the time-averaged mean wake and turbulent kinetic energy was compared with the experiments. Both results are agreed well with each other in the propeller wake section, but the agreement between both is not so satisfied in the far wake field. It means that more numerous number of grid points and their concentration should be required in that field.

An Experimental Study on Turbulent Characteristics of an Impinging Split-Triplet Injector

  • Kang, Shin-Jae;Ryu, Ki-Wahn;Kwon, Ki-Chul;Song, Bhum-Keun
    • Journal of Mechanical Science and Technology
    • /
    • v.15 no.1
    • /
    • pp.117-124
    • /
    • 2001
  • This paper presents turbulent characteristics of an impinging F-O-O-F type injector in which fuel ad oxidizer impinge on each other to atomize under the different momentum ratio. Water was used as an inert simulant liquid instead of fuel and oxidizer. The droplet size and velocity in the impinging spray flow field were measured using a PDPA. The gradient of the spray half-width(b$_2$) along the long-axis direction declined throughout the entire spray flow field with increasing the momentum ratio from 1.19 to 6.48. However, the gradient of the half-width(b$_1$) along the short-axis direction decreased with increasing the momentum ratio. The turbulence intensity and turbulent kinetic energy were converged into the center of the center of the initial region with increasing the momentum ratio. As the momentum ratio increased from MR=1.19 to MR=6.48, the turbulent shear stress decreased. The results of this study can be used for the design of an impinging type injector for liquid rackets.

  • PDF

Redeveloping Turbelent Boundary Layer after Separation-Reattachment(II) -A Consideration on Turbulence Models- (박리-재부착 이후의 재발달 난류경계층 II -난류 모델들에 관한 고찰-)

  • 백세진;유정열
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.13 no.5
    • /
    • pp.999-1011
    • /
    • 1989
  • A consideration on the trubulence models for describing the redeveloping turbulent boundary layer beyond separation-reattachment in the flow over a backward-facing step is given through experimental and numerical studies. By considering the blance among the measured values of respective terms in the transport equations for the turbulent kinetic energy and the turbulent shear stress, the recovering process of the redeveloping boundary layer from non-equilibrium to equilibrium has been investigated, which takes place slowly over a substantial distance in the downstream direction. In the numerical study, the standard K-.epsilon. model and the Reynolds stress model have been applied to two kinds of flow regions, one for the entire downstream region after the backward-facing step and another for the downstream region after reattachment. Then the results are compared to a meaningful extent, with the experimental values of the turbulent kinetic energy k, the turbulent energy production term P, the dissipation term K-.epsilon. model, a necessity for a new modelling has been brought forward, which can be also applied to the case of the nonequlibrium turbulent flow.

Direct Numerical Simulation of Turbulent new Around a Rotating Circular Cylinder at Low Reynolds Number (회전하는 원형단면 실린더 주위의 저 레이놀즈수 난류유동에 대한 직접수치모사)

  • Hwang Jong-Yeon;Yang Kyung-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.29 no.10 s.241
    • /
    • pp.1083-1091
    • /
    • 2005
  • Turbulent flow around a rotating circular cylinder is investigated by Direct Numerical Simulation. The calculation is performed at three cases of low Reynolds number, Re=161, 348 and 623, based on the cylinder radius and friction velocity. Statistically strong similarities with fully developed channel flow are observed. Instantaneous flow visualization reveals that the turbulence length scale typically decreases as Reynolds number increases. Some insight into the spacial characteristics in conjunction with wave number is provided by wavelet analysis. The budget of dissipation rate as well as turbulent kinetic energy is computed and particular attention is given to the comparison with plane channel flow.

Characteristics of the Internal Flow in the Scaled-Up Fuel Nozzle (연료 노즐을 확대한 모형노즐에서의 내부유동 특성)

  • 박장혁;홍성태;구자예
    • Transactions of the Korean Society of Automotive Engineers
    • /
    • v.4 no.3
    • /
    • pp.199-210
    • /
    • 1996
  • The measurements of velocities of internal flow in a scaled-up nozzle were made by laser Doppler velocimetry in order to clarify the effect of internal flow on the characteristics of fuel spray. The investigated length to diameter ratio(L/d) of the orifice were 1, 3, 4, 5 and 8, and inlet radius to diameter ratio(r0/d) were 0 and 0.5. Mean and fluctuating velocities and discharge coefficients were obtained at various Reynolds number ranging between 15,000 and 28,000, and L/d ranging between 1 and 8 in sharp and round inlet nozzle. The turbulent intensity and turbulent kinetic energy at exit in a sharp inlet nozzle were higher than that in a round inlet nozzle. For sharp inlet nozzle, fluctuating velocities near exit were decreased with increasing L/d.

  • PDF

An Experiment on the Effects of Free Stream Turbulence Intensity on the Backward-Facing Step Flow (자유흐름 난류강도가 후향계단유동에 미치는 영향에 대한 실험)

  • 김사량;유정열
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.19 no.9
    • /
    • pp.2297-2307
    • /
    • 1995
  • An experimental study on the structure of a separated shear layer downstream of the backward-facing step has been performed by examining mean flow and turbulent quantities in terms of free stream turbulence. When free stream turbulence exists, the entrainment rate of the separated shear layer and the flow rate in the recirculation region are enhanced, resulting in shorter reattachment length. The production and diffusion terms in the turbulent kinetic energy balance are shown to increase more than the dissipation term does. Rapid decrease of the pressure-strain term in the shear stress balance implies the enhancement of the three-dimensional motion by free stream turbulence.