The Analysis of Direct Numerical Simulation and Experiment in Critical Point of Transitional Flow

2014 ◽  
Vol 1046 ◽  
pp. 196-199
Author(s):  
Jun Wang ◽  
Guang Sheng Du ◽  
Yong Hui Liu
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Critical Point ◽  
Transitional Flow ◽  
Viscous Force ◽  
Wall Region ◽  
Flow State ◽  
Transitional Area ◽  
Simulation And Experiment

In order to study the lower critical point in transitional area of pipe, we used the method of direct numerical simulation to simulate fluid flow and contrasted it with experiment. The result showed that the flow state is close to laminar. Along the pipe axis, the change of pressure is not obviously. The changing rate of axial velocity U near wall region was significantly greater than in the mainstream area, it proved the important role of viscous force.

Direct Numerical Simulation of Drops in Three Dimensional Viscoelastic Simple Shear Flows

2001 ◽  
Author(s):  
Shriram B. Pillapakkam ◽  
Pushpendra Singh
Keyword(s):  
Numerical Simulation ◽  
Shear Flow ◽  
Direct Numerical Simulation ◽  
Viscoelastic Fluid ◽  
Simple Shear ◽  
Polymer Concentration ◽  
Three Dimensional ◽  
Simple Shear Flow ◽  
Splitting Technique

Abstract A three dimensional finite element scheme for Direct Numerical Simulation (DNS) of viscoelastic two phase flows is implemented. The scheme uses the Level Set Method to track the interface and the Marchuk-Yanenko operator splitting technique to decouple the difficulties associated with the governing equations. Using this numerical scheme, the shape of Newtonian drops in a simple shear flow of viscoelastic fluid and vice versa are analyzed as a function of Capillary number, Deborah number and polymer concentration. The viscoelastic fluid is modeled via the Oldroyd-B model. The role of viscoelastic stresses in deformation of a drop subjected to simple shear flow and its effect on the steady state shape is analyzed. Our results compare favorably with existing experimental data and also help in understanding the role of viscoelastic stresses in drop deformation.

The influence of entropy fluctuations on the interaction of turbulence with a shock wave

1997 ◽  
Vol 334 ◽  
pp. 353-379 ◽  
Author(s):  
KRISHNAN MAHESH ◽  
SANJIVA K. LELE ◽  
PARVIZ MOIN
Keyword(s):  
Numerical Simulation ◽  
Shock Wave ◽  
Kinetic Energy ◽  
Direct Numerical Simulation ◽  
Scaling Law ◽  
Linear Analysis ◽  
Turbulent Field ◽  
Bulk Compression ◽  
Baroclinic Torque

Direct numerical simulation and inviscid linear analysis are used to study the interaction of a normal shock wave with an isotropic turbulent field of vorticity and entropy fluctuations. The role of the upstream entropy fluctuations is emphasized. The upstream correlation between the vorticity and entropy fluctuations is shown to strongly influence the evolution of the turbulence across the shock. Negative upstream correlation between u′ and T′ is seen to enhance the amplification of the turbulence kinetic energy, vorticity and thermodynamic fluctuations across the shock wave. Positive upstream correlation has a suppressing effect. An explanation based on the relative effects of bulk compression and baroclinic torque is proposed, and a scaling law is derived for the evolution of vorticity fluctuations across the shock. The validity of Morkovin's hypothesis across a shock wave is examined. Linear analysis is used to suggest that shock-front oscillation would invalidate the relation between urms and Trms, as expressed by the hypothesis.

Direct Numerical Simulation of Passive Scalar Field in a Turbulent Channel Flow

1992 ◽  
Vol 114 (3) ◽  
pp. 598-606 ◽  
Author(s):  
N. Kasagi ◽  
Y. Tomita ◽  
A. Kuroda
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Passive Scalar ◽  
Streamwise Velocity ◽  
Heat Fluxes ◽  
Wall Region ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes

A direct numerical simulation (DNS) of the fully developed thermal field in a two-dimensional turbulent channel flow of air was carried out. The isoflux condition was imposed on the two walls so that the local mean temperature increased linearly in the streamwise direction. With any buoyancy effect neglected, temperature was considered as a passive scalar. The computation was executed on 1,589,248 grid points by using a spectral method. The statistics obtained were root-mean-square temperature fluctuations, turbulent heat fluxes, turbulent Prandtl number, and dissipation time scales. They agreed fairly well with existing experimental and numerical simulation data. Each term in the budget equations of temperature variance, its dissipation rate, and turbulent heat fluxes was also calculated. It was found that the temperature fluctuation θ′ was closely correlated with the streamwise velocity fluctuation u′, particularly in the near-wall region. Hence, the distribution of budget terms for the streamwise and wall-normal heat fluxes, u′θ′ and v′θ′, were very similar to those for the two Reynolds stress components, u′u′ and u′v′.

Direct numerical simulation of transitional flow in the nasal cavity during a sniff

2020 ◽  
Vol 2020.31 (0) ◽  
pp. 1C13
Author(s):  
Keiichiro YOSHIOKA ◽  
Shuta MIURA ◽  
Shinya KIMURA ◽  
Toshihiro SERA ◽  
Kenji Ono ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Nasal Cavity ◽  
Transitional Flow

Direct numerical simulation of the turbulent boundary layer over a cube-roughened wall

2011 ◽  
Vol 669 ◽  
pp. 397-431 ◽  
Author(s):  
JAE HWA LEE ◽  
HYUNG JIN SUNG ◽  
PER-ÅGE KROGSTAD
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Outer Layer ◽  
Large Scale ◽  
Roughness Height ◽  
Wall Region ◽  
Momentum Thickness ◽  
Reynolds Stresses

Direct numerical simulation (DNS) of a spatially developing turbulent boundary layer (TBL) over a wall roughened with regularly arrayed cubes was performed to investigate the effects of three-dimensional (3-D) surface elements on the properties of the TBL. The cubes were staggered in the downstream direction and periodically arranged in the streamwise and spanwise directions with pitches of px/k = 8 and pz/k = 2, where px and pz are the streamwise and spanwise spacings of the cubes and k is the roughness height. The Reynolds number based on the momentum thickness was varied in the range Reθ = 300−1300, and the roughness height was k = 1.5θin, where θin is the momentum thickness at the inlet, which corresponds to k/δ = 0.052–0.174 from the inlet to the outlet; δ is the boundary layer thickness. The characteristics of the TBL over the 3-D cube-roughened wall were compared with the results from a DNS of the TBL over a two-dimensional (2-D) rod-roughened wall. The introduction of cube roughness affected the turbulent Reynolds stresses not only in the roughness sublayer but also in the outer layer. The present instantaneous flow field and linear stochastic estimations of the conditional averaging showed that the streaky structures in the near-wall region and the low-momentum regions and hairpin packets in the outer layer are dominant features in the TBLs over the 2-D and 3-D rough walls and that these features are significantly affected by the surface roughness throughout the entire boundary layer. In the outer layer, however, it was shown that the large-scale structures over the 2-D and 3-D roughened walls have similar characteristics, which indicates that the dimensional difference between the surfaces with 2-D and 3-D roughness has a negligible effect on the turbulence statistics and coherent structures of the TBLs.

Direct numerical simulation of a turbulent channel flow by an improved vortex in cell method

2013 ◽  
Vol 24 (1) ◽  
pp. 103-123 ◽  
Author(s):  
Tomomi Uchiyama ◽  
Yutaro Yoshii ◽  
Hirotaka Hamada
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Channel Flow ◽  
Reynolds Shear Stress ◽  
Turbulent Channel Flow ◽  
Staggered Grid ◽  
Wall Region ◽  
Content Type ◽  
The Mean

Purpose – This study is concerned with the direct numerical simulation (DNS) of a turbulent channel flow by an improved vortex in cell (VIC) method. The paper aims to discuss these issues. Design/methodology/approach – First, two improvements for VIC method are proposed to heighten the numerical accuracy and efficiency. A discretization method employing a staggered grid is presented to ensure the consistency among the discretized equations as well as to prevent the numerical oscillation of the solution. A correction method for vorticity is also proposed to compute the vorticity field satisfying the solenoidal condition. Second, the DNS for a turbulent channel flow is conducted by the improved VIC method. The Reynolds number based on the friction velocity and the channel half width is 180. Findings – It is highlighted that the simulated turbulence statistics, such as the mean velocity, the Reynolds shear stress and the budget of the mean enstrophy, agree well with the existing DNS results. It is also shown that the organized flow structures in the near-wall region, such as the streaks and the streamwise vortices, are favourably captured. These demonstrate the high applicability of the improved VIC method to the DNS for wall turbulent flows. Originality/value – This study enables the VIC method to perform the DNS for wall turbulent flows.

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