scholarly journals Numerical Calculation of Three-Dimensional Turbulent Flow in a Turbine-Stator Passage

1996 ◽  
Author(s):  
B. Song ◽  
R. S. Amano
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Numerical Study ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Turbulence Kinetic Energy ◽  
Wall Region ◽  
Staggered Grids ◽  
Turbine Stator ◽  
Near Wall

A numerical study on three-dimensional turbulent flow in a turbine-stator passage is presented in this paper. The standard κ–ε model with the one equation, near-wall model (SKE) and the Launder-Sharma model (L-S) are used for turbulence computations. The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillation of pressure and velocity due to non-staggered grids is eliminated by using the interpolation method suggested by Rhie and Chow (1983). The predicted midspan pressure coefficients using SKE and L-S models are compared with experimental data. It was shown that the present results obtained by using both models are satisfactory. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that two turbulence models predict similar results for the pressure and velocity but these predict different results in the turbulence kinetic energy.

Predictions of Turbulent Flow in a Turbine Stator/Rotor Passage

1998 ◽  
Author(s):  
R. S. Amano ◽  
B. Song ◽  
S. Sitarama ◽  
B. Lin
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Isotropic Turbulence ◽  
Numerical Study ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Turbulence Kinetic Energy ◽  
Wall Region ◽  
Staggered Grids ◽  
Turbine Stator

Numerical study on a three-dimensional turbulent flow in a turbine stator/rotor passage is presented in this paper. The standard k-ε model was used for the first phase of the turbulence computations. The computations were further extended by employing the full Reynolds-stress closure model (RSM). The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillations in pressure and velocity due to non-staggered grids are eliminated by using a special interpolation method. The predicted midspan pressure coefficients using the k-ε model and the RSM are compared with the experimental data. It was shown that the present results obtained by using either model are fairly reasonable. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that the two turbulence models predict different results for the turbulence kinetic energy. This variation was identified as being related to some non-isotropic turbulence occurring near the blade surface due to the severe acceleration of the flow. It was thus proven that the models based on the RSM give more realistic predictions for highly turbulent cascade flow computations than a Boussinesq viscosity model.

Three-Dimensional Computations of Turbulent Flow in a Turbine-Rotor Passage

1997 ◽  
Author(s):  
B. Song ◽  
R. S. Amano ◽  
S. Sitarama ◽  
B. Lin
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Isotropic Turbulence ◽  
Numerical Study ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Turbulence Kinetic Energy ◽  
Wall Region ◽  
Staggered Grids

Numerical study on a three-dimensional turbulent flow in a turbine-rotor passage is presented in this paper. The standard k-ε model was used for the first phase of the turbulence computations. The computations were further extended by employing the full Reynolds-stress closure model (RSM). The computational results obtained using these models were compared in order to investigate the turbulence effect in the near-wall region. The governing equations in a generalized curvilinear coordinate system are discretized by using the SIMPLEC method with non-staggered grids. The oscillations in pressure and velocity due to non-staggered grids are eliminated by using a special interpolation method. The predicted midspan pressure coefficients using the k-ε model and the RSM are compared with the experimental data. It was shown that the present results obtained by using either model are fairly reasonable. Computations were then extended to cover the entire blade-to-blade flow passage, and the three-dimensional effects on pressure and turbulence kinetic energy were evaluated. It was observed that the two turbulence models predict different results for the turbulence kinetic energy. This variation was identified as being related to some non-isotropic turbulence occurring near the blade surface due to the severe acceleration of the flow. It was thus proven that the models based on the RSM give more realistic predictions for highly turbulent cascade flow computations than a Boussinesq viscosity model.

The structure of the near-wall region of two-dimensional turbulent separated flow

1991 ◽  
Vol 336 (1640) ◽  
pp. 5-17 ◽  
Keyword(s):  
Kinetic Energy ◽  
Shear Layer ◽  
Large Scale ◽  
Outer Region ◽  
Turbulence Kinetic Energy ◽  
Shear Stresses ◽  
Wall Region ◽  
Freestream Velocity ◽  
Outer Flow ◽  
Near Wall

The time-dependent structure of the wall region of separating, separated, and reattaching flows is considerably different than that of attached turbulent boundary layers. Large-scale structures, whose frequency of passage scales on the freestream velocity and shear layer thickness, produce large Reynolds shearing stresses and most of the turbulence kinetic energy in the outer region of the shear layer and transport it into the low velocity reversed flow next to the wall. This outer flow impresses a near wall streamwise streaky structure of spanwise spacing λ z simultaneously across the wall over a distance of the order of several λ z . The near wall structures produce negligible Reynolds shear stresses and turbulence kinetic energy.

scholarly journals Secondary Flow in Smooth and Rough Turbulent Circular Pipes: Turbulence Kinetic Energy Budgets

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 448
Author(s):  
Paolo Orlandi ◽  
Sergio Pirozzoli
Keyword(s):  
Kinetic Energy ◽  
Flow Direction ◽  
Turbulence Kinetic Energy ◽  
Energy Budgets ◽  
Immersed Boundary ◽  
Wall Region ◽  
Turbulent Structures ◽  
Circular Pipes ◽  
Turbulence Kinetic Energy Budget ◽  
Near Wall

Direct Numerical Simulations have been performed for turbulent flow in circular pipes with smooth and corrugated walls. The numerical method, based on second-order finite discretization together with the immersed boundary technique, was validated and applied to various types of flows. The analysis is focused on the turbulence kinetic energy and its budget. Large differences have been found in the near-wall region at low Reynolds number. The change in the near-wall turbulent structures is responsible for increase of drag and turbulence kinetic energy. To investigatselinae the effects of wall corrugations, the velocity fields have been decomposed so as to isolate coherent and incoherent motions. For corrugated walls, we find that coherent motions are strongest for walls covered with square bars aligned with the flow direction. In particular, the coherent contribution is substantial when the bars are spaced apart by a distance larger than their height. Detailed analysis of the turbulence kinetic energy budget shows for this set-up a very different behavior than for the other types of corrugations.

scholarly journals The Impact of Three-Dimensional Effects on the Simulation of Turbulence Kinetic Energy in a Major Alpine Valley

2018 ◽  
Vol 168 (1) ◽  
pp. 1-27 ◽  
Author(s):  
Brigitta Goger ◽  
Mathias W. Rotach ◽  
Alexander Gohm ◽  
Oliver Fuhrer ◽  
Ivana Stiperski ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Three Dimensional ◽  
Turbulence Kinetic Energy ◽  
Alpine Valley ◽  
Dimensional Effects ◽  
The Impact

A revisit of the equilibrium assumption for predicting near-wall turbulence

2014 ◽  
Vol 760 ◽  
pp. 304-312 ◽  
Author(s):  
Farid Karimpour ◽  
Subhas K. Venayagamoorthy
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Stress ◽  
Turbulent Viscosity ◽  
Wall Turbulence ◽  
Wall Region ◽  
Turbulence Decay ◽  
Prime 2 ◽  
Near Wall Turbulence ◽  
Near Wall

AbstractIn this study, we revisit the consequence of assuming equilibrium between the rates of production ($P$) and dissipation $({\it\epsilon})$ of the turbulent kinetic energy $(k)$ in the highly anisotropic and inhomogeneous near-wall region. Analytical and dimensional arguments are made to determine the relevant scales inherent in the turbulent viscosity (${\it\nu}_{t}$) formulation of the standard $k{-}{\it\epsilon}$ model, which is one of the most widely used turbulence closure schemes. This turbulent viscosity formulation is developed by assuming equilibrium and use of the turbulent kinetic energy $(k)$ to infer the relevant velocity scale. We show that such turbulent viscosity formulations are not suitable for modelling near-wall turbulence. Furthermore, we use the turbulent viscosity $({\it\nu}_{t})$ formulation suggested by Durbin (Theor. Comput. Fluid Dyn., vol. 3, 1991, pp. 1–13) to highlight the appropriate scales that correctly capture the characteristic scales and behaviour of $P/{\it\epsilon}$ in the near-wall region. We also show that the anisotropic Reynolds stress ($\overline{u^{\prime }v^{\prime }}$) is correlated with the wall-normal, isotropic Reynolds stress ($\overline{v^{\prime 2}}$) as $-\overline{u^{\prime }v^{\prime }}=c_{{\it\mu}}^{\prime }(ST_{L})(\overline{v^{\prime 2}})$, where $S$ is the mean shear rate, $T_{L}=k/{\it\epsilon}$ is the turbulence (decay) time scale and $c_{{\it\mu}}^{\prime }$ is a universal constant. ‘A priori’ tests are performed to assess the validity of the propositions using the direct numerical simulation (DNS) data of unstratified channel flow of Hoyas & Jiménez (Phys. Fluids, vol. 18, 2006, 011702). The comparisons with the data are excellent and confirm our findings.

Numerical Study on Near-Wall Natural Convection Over a Microscale Heating Wire

2012 ◽  
Author(s):  
Leping Zhou ◽  
Yunfang Zhang ◽  
Lijun Yang ◽  
Xiaoze Du ◽  
Minami Yoda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Heat Transfer Process ◽  
Brownian Diffusion ◽  
Wall Region ◽  
Two Phase ◽  
Heating Wire ◽  
Transfer Problems ◽  
Near Wall

The study of the natural convection over a very small heat sources is important in the analysis of heat transfer problems in the electronics industry. However, the characteristics of the spatial distribution of the velocity in the near wall region, which is crucial to the mechanisms of heat transfer process in natural convection around a microscale object, is not well understood. In this investigation, the microscale natural convection in the near wall region of a platinum micro heat source was investigated numerically, using FLUENT, a commercially available computational fluid dynamics (CFD) software, and compared with corresponding experimental results. The influence of the nanoparticles on the natural convection was observed using the single-phase or two-phase models available in FLUENT. The temperature and velocity fields were obtained, with which the Brownian diffusion coefficient was deduced. The results indicate that the temperature gradient induced Brownian diffusion and thermophoresis in the near wall region plays an important role in the microscale natural convection in the water/nanoparticle mixture investigated and are in good agreement with the results from a corresponding experimental investigation.

Sign in / Sign up

Export Citation Format

Share Document