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.

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.

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.

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

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.

Computational Modeling of Three-Dimensional Endwall Flow Through a Turbine Rotor Cascade With Strong Secondary Flows

1994 ◽  
Author(s):  
Y.-H. Ho ◽  
B. Lakshminarayana
Keyword(s):  
Kinetic Energy ◽  
Turbulence Intensity ◽  
Pressure Loss ◽  
Total Pressure ◽  
Three Dimensional ◽  
Turbulence Kinetic Energy ◽  
Length Scale ◽  
Turbine Cascade ◽  
Turbulence Length ◽  
Turbulence Length Scale

A steady, three-dimensional Navier-Stokes solver which utilizes a pressure-based technique for incompressible flows is used to simulate the three-dimensional flow field in a turbine cascade. A new feature of the numerical scheme is the implementation of a second-order plus fourth-order artificial dissipation formulation, which provides a precise control of the numerical dissipation. A low-Reynolds-number form of a two-equation turbulence model is used to account for the turbulence effects. Comparison between the numerical predictions and the experimental data indicates that the numerical model is able to capture most of the complex flow phenomena in the endwall region of a turbine cascade, except the high gradient region in the secondary vortex core. The effects of inlet turbulence intensity and turbulence length scale on secondary vortices, total pressure loss, and turbulence kinetic energy inside the passage are presented and interpreted. It is found that higher turbulence intensity energizes the vortical motions and tends to move the passage vortex away from the endwall. With a larger turbulence length scale the secondary flow inside the passage is reduced. However, the total pressure loss increases due to higher turbulence kinetic energy production.

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.

A Numerical Study of Turbulent Flow in Helical Static Mixers

2006 ◽  
Author(s):  
Ramin K. Rahmani ◽  
Anahita Ayasoufi ◽  
Theo G. Keith
Keyword(s):  
Turbulent Flow ◽  
Molecular Diffusion ◽  
Stokes Equations ◽  
Numerical Study ◽  
Critical Role ◽  
Three Dimensional ◽  
Turbulent Dispersion ◽  
Working Fluid ◽  
Static Mixer ◽  
Static Mixers

Many processing applications call for the addition of small quantities of chemicals to working fluid. Hence, fluid mixing plays a critical role in the success or failure of these processes. An optimal combination of turbulent dispersion down to eddies of the Kolmogoroff scale and molecular diffusion would yield fast mixing on a molecular scale which in turn favors the desired reactions. Helical static mixers can be used for those applications. The range of practical flow Reynolds numbers for these mixers in industry is usually from very small (Re ∼ 0) to moderate values (Re ∼ 5000). In this study, a helical static mixer is investigated numerically using Lagrangian methods to characterize mixer performance under turbulent flow regime conditions. A numerical simulation of turbulent flows in helical static mixers is employed. The model solves the three-dimensional, Reynolds-averaged Navier-Stokes equations, closed with the Spalart-Allmaras turbulence model, using a second-order-accurate finite-volume numerical method. Numerical simulations are carried out for a six-element mixer, and the computed results are analyzed to elucidate the complex, three-dimensional features of the flow. Using a variety of predictive tools, mixing results are obtained and the performance of static mixer under turbulent flow condition is studied.

scholarly journals Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 199 ◽  
Author(s):  
Daniela Sanagiotto ◽  
Júlia Rossi ◽  
Juan Bravo
Keyword(s):  
Kinetic Energy ◽  
Fish Species ◽  
Three Dimensional ◽  
Maximum Velocity ◽  
Flow Patterns ◽  
Turbulence Kinetic Energy ◽  
Fish Diversity ◽  
Future Design ◽  
Vertical Slot ◽  
Reference Design

Vertical slot fishways are increasingly common structures for the passage of a wide variety of migratory fish and contribute to the maintenance of fish diversity in fragmented rivers. These structures are designed with several geometric arrangements and, consequently, flow patterns through them can be shaped to present suitable characteristics for the fish species. To aid in the design of vertical slot fishways, a three-dimensional numerical model was used to simulate the flow for different geometric configurations. An existing vertical slot fishway with nonstandard dimensions was initially modeled and validated. This geometry was used as a reference design. Modifications to the reference design, such as the insertion of cylinders, changes in the baffle shape and position of the vertical slots, as possible rehabilitation measures, were proposed and tested. In summary, five different designs were evaluated with several slopes, totaling 17 geometries. Hydraulic parameters, flow patterns, maximum velocities, velocity fields and turbulence kinetic energy in the pools were analyzed. The results indicate that the maximum velocity values were between 9% and 68% higher than those obtained by the theoretical equation. This indicates that maximum velocities can be underestimated for nonstandard vertical slot fishways if a simplified evaluation is conducted. The insertion of cylinders in the region close to the slot reduces the maximum velocity up to 8.2%. The positioning of the vertical slots on alternating sides increases the maximum values of turbulence kinetic energy and the regions subjected to higher values. However, this configuration provided greater energy dissipation and reduction of velocities by up to 27%. Thus, modifications in nonstandard vertical slot fishways can be useful in future design or rehabilitation of existing structures in order to provide velocities and turbulence more friendly for a higher number of fish species.

Numerical study on three-dimensional CJ detonation waves interacting with isotropic turbulence

2016 ◽  
Vol 61 (22) ◽  
pp. 1756-1765 ◽  
Author(s):  
Tai Jin ◽  
Kun Luo ◽  
Qi Dai ◽  
Jianren Fan
Keyword(s):  
Isotropic Turbulence ◽  
Numerical Study ◽  
Three Dimensional ◽  
Detonation Waves

Numerical Analysis of Blockage Ratio Effect on a Portable Hydrokinetic Turbine

2016 ◽  
Author(s):  
Cosan Daskiran ◽  
Jacob Riglin ◽  
Alparslan Oztekin
Keyword(s):  
Free Stream ◽  
Numerical Study ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Power Coefficient ◽  
Stream Velocity ◽  
Blockage Ratio ◽  
Ratio Effect ◽  
Turbine Performance ◽  
Hydrokinetic Turbine

Three-dimensional steady state Computational Fluid Dynamics (CFD) analyses were performed for a pre-designed micro-hydrokinetic turbine to investigate the blockage ratio effect on turbine performance. Simulations were conducted using a physical turbine rotor geometry rather than low fidelity, simplified actuator disk or actuator lines. The two-equation k-ω Shear Stress Transport (SST) turbulence model was employed to predict turbulence in the flow field. The turbine performance at the best efficiency point was studied for blockage ratios of 0.49, 0.70 and 0.98 for three different free stream velocities of 2.0 m/s, 2.25 m/s and 2.5 m/s. Distinct blockage ratio results at a free stream velocity of 2.25 were compared to a previous numerical study incorporating the same rotor geometry within an infinite flowing medium. The pressure gradient between turbine upstream and turbine downstream for blocked channel flows elevated the turbine performance. The increment in blockage ratio from 0.03 to 0.98 enhanced power coefficient from 0.437 to 2.254 and increased power generation from 0.56 kW to 2.86 kW for the present study.

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