A Deterministic Stress Model for Rotor-Stator Interactions in Simulations of Average-Passage Flow

2002 ◽  
Vol 124 (2) ◽  
pp. 550-554 ◽  
Author(s):  
Charles Meneveau and ◽  
Joseph Katz
Keyword(s):  
Turbulence Models ◽  
Navier Stokes ◽  
Stress Model ◽  
Direct Measurements ◽  
Blade Row ◽  
Model Predictions ◽  
Stator Vane ◽  
Inflow Condition ◽  
Flow Phenomena ◽  
Inflow Conditions

A procedure for modeling deterministic stresses for average-passage simulations of flow in multiple blade-row turbomachines is proposed and tested. This method uses the results of several (two or more) steady Reynolds-averaged Navier-Stokes (RANS) simulations with boundary conditions that are representative of different inflow conditions encountered during the passage of a neighboring blade-row. The deterministic stresses are calculated by averaging the steady results while weighting them with the approximate duration of each inflow condition. This approach incorporates important rotor-stator interactions that are neglected in models based on a swept-wake approximation. The model is tested successfully by computing the deterministic stresses in the stator vane passage of a centrifugal pump, and comparing them with direct measurements using PIV data. Remaining discrepancies between model predictions and experimental data are probably linked to the inability of the turbulence models to account for flow phenomena at each phase, such as mid-vane separation.

Computations of bladerow stall inception in transonic flows

1999 ◽  
Vol 103 (1025) ◽  
pp. 317-324 ◽  
Author(s):  
L. He ◽  
J. O. Ismael
Keyword(s):  
Three Dimensional ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Stall Inception ◽  
Tip Leakage ◽  
Blade Row ◽  
Inflow Condition ◽  
Shock Oscillation ◽  
Transonic Fan

Abstract A three-dimensional unsteady Navier-Stokes solver has been used to simulate stall inception in a single row ten passage segment of a transonic fan, the NASA rotor-67. At subsonic flow conditions, the 3D results illustrate a rotating stall inception with short scale part-span cells rotating at around 80% rotor speed, similar to that observed in some low speed experiments. However, at a supersonic relative inflow condition, the results show that an isolated blade row tends to stall in a one-dimensional breakdown pattern without first experiencing rotating stall. At near-stall conditions, significant self-excited unsteadiness is generated by the interaction between the tip-leakage vortex and the passage shock wave. Further computations for two-dimensional configurations indicate that it is possible to have a rotating pattern of instability in transonic blade rows associated with circumferential synchronised shock oscillation.

scholarly journals Numerical simulation of different turbulence models aiming at perdicting the flow and temperature separation in a Ranque-Hilsch vortex tube

2014 ◽  
Vol 18 (4) ◽  
pp. 1159-1171
Author(s):  
Hossein Azizi ◽  
Reza Saleh ◽  
Mohsen Kahrom ◽  
Reza Andalibi
Keyword(s):  
Vortex Tube ◽  
Turbulence Models ◽  
Swirl Flow ◽  
Experimental Results ◽  
Navier Stokes ◽  
Temperature Separation ◽  
Experiment Validation ◽  
Performance Curves ◽  
Mass Fractions ◽  
Flow Phenomena

A computational fluid dynamics (CFD) model is used to compare the effect of different Reynolds Averaged Navier-Stokes (RANS) based turbulence models in predicting the temperature separation and power separation in a Ranque-Hilsch vortex tube. Three first order turbulence models (standard k-?, Renormalized group RNG and shear stress transport (SST) K-? model) together with a second order numerical scheme are surveyed in the present work. The simulations are done in 2D steady, axisymetric with high swirl flow model. The performance curves (hot and cold outlet temperatures and power separation versus hot outlet mass fraction) obtained by using these turbulence models are compared with the experimental results in different cold mass fractions. The aim is to select an appropriate turbulence model for the simulation of the flow phenomena. Because of large discrepancy between 2D and experiment, validation in 3D model is also considered. The performance analysis shows that among all the turbulence models investigated in this study, temperature separation predicted by the Renormalized group RNG model is closer to the experimental results.

scholarly journals Effects of the Duct Angle and Propeller Location on the Hydrodynamic Characteristics of the Ducted Propeller

2018 ◽  
Vol 11 (22) ◽  
pp. 41
Author(s):  
Mehdi Chamanara ◽  
Hassan Ghassemi ◽  
Manouchehr Fadavie ◽  
Mohammad Aref Ghassemi
Keyword(s):  
Experimental Data ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Numerical Results ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Stress Model ◽  
Ducted Propeller ◽  
Rans Method

In the present study, the effect of the duct angle and propeller location on the hydrodynamic characteristics of the ducted propeller using Reynolds-Averaged Navier Stokes (RANS) method is reported. A Kaplan type propeller is selected with a 19A duct. The ducted propeller is analyzed by three turbulence models including the k-ε standard, k-ω SST and Reynolds stress model (RSM). The numerical results are compared with experimental data. The effects of the duct angle and the location of the propeller inside the propeller are presented and discussed.

scholarly journals RANS and Hybrid RANS-LES Simulations of an H-Type Darrieus Vertical Axis Water Turbine

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2348 ◽  
Author(s):  
Omar Mejia ◽  
Jhon Quiñones ◽  
Santiago Laín
Keyword(s):  
Turbulence Models ◽  
Vertical Axis ◽  
Navier Stokes ◽  
Speed Ratio ◽  
Small Scale ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Phenomena ◽  
Water Turbine

Nowadays, the global energy crisis has encouraged the use of alternative sources like the energy available in the water currents of seas and rivers. The vertical axis water turbine (VAWT) is an interesting option to harness this energy due to its advantages of facile installation, maintenance and operation. However, it is known that its efficiency is lower than that of other types of turbines due to the unsteady effects present in its flow physics. This work aims to analyse through Computational Fluid Dynamics (CFD) the turbulent flow dynamics around a small scale VAWT confined in a hydrodynamic tunnel. The simulations were developed using the Unsteady Reynolds Averaged Navier Stokes (URANS), Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES) turbulence models, all of them based on k-ω Shear Stress Transport (SST). The results and analysis of the simulations are presented, illustrating the influence of the tip speed ratio. The numerical results of the URANS model show a similar behaviour with respect to the experimental power curve of the turbine using a lower number of elements than those used in the DES and DDES models. Finally, with the help of both the Q-criterion and field contours it is observed that the refinements made in the mesh adaptation process for the DES and DDES models improve the identification of the scales of the vorticity structures and the flow phenomena present on the near and far wake of the turbine.

Numerical Investigation on a Stator Vane Bypass Transition Over a Separation Bubble Using v′2-f and LCL-Models

2006 ◽  
Author(s):  
Axel Heidecke ◽  
Bernd Stoffel
Keyword(s):  
Numerical Investigation ◽  
Turbulence Model ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Suction Side ◽  
Navier Stokes ◽  
Stream Line ◽  
Bypass Transition ◽  
Mean Flow ◽  
Stator Vane

With this paper, results of a numerical investigation of the influence of the inlet condition variation on a stator vane suction side boundary layer and its separation tendencies are presented. The profile used for the examination is a so called high-lift-profile and designed for a laminar-turbulent transition over a steady separation bubble in a 1.5-stage low pressure turbine. Hence, the turbulence model must be capable for these effects. Especially, the stream line curvature has to be kept properly which leads to higher level turbulence models. The calculations were conducted with a two-dimensional Navier-Stokes solver using a finite volume discretisation scheme. The turbulence models used are the v′2-f and the LCL turbulence model which are both of higher order. In the first part of the paper, wake free averaged inflow conditions were used. Through this, the influence of the mean flow on the bubble could be examined.

scholarly journals Three-Dimensional Navier-Stokes Computation of Turbine Nozzle Flow With Advanced Turbulence Models

1995 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Reynolds Stress ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Nozzle Flow ◽  
Stress Model ◽  
Mean Flow ◽  
The Mean ◽  
Algebraic Reynolds Stress Model

A three-dimensional Navier-Stokes procedure has been used to compute the three-dimensional viscous flow through the turbine nozzle passage of a single stage turbine. A low Reynolds number k-ε model and a zonal k-ε/ARSM (algebraic Reynolds stress model) are utilized for turbulence closure. The algebraic Reynolds stress model is used only in the endwall region to represent the anisotropy of turbulence. A four-stage Runge-Kutta scheme is used for time-integration of both the mean-flow and the turbulence transport equations. For the turbine nozzle flow, comprehensive comparisons between the predictions and the experimental data obtained at Penn State show that most features of the vortex-dominated endwall flow, as well as nozzle wake structure, have been captured well by the numerical procedure. An assessment of the performance of the turbulence models has been carried out The two models are found to provide similar predictions for the mean flow parameters, although slight improvement in the prediction of some secondary flow quantities has been obtained by the ARSM model.

SRANS and URANS CFD Simulations of Turbulent VHTR Lower Plenum Flow

2007 ◽  
Author(s):  
A. Ridluan ◽  
A. Tokuhiro
Keyword(s):  
Nuclear Reactor ◽  
Tube Bundle ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Cfd Simulations ◽  
Eddy Simulation ◽  
Flow Phenomena ◽  
Flow Through ◽  
Reynolds Averaged Navier Stokes

Time-dependent and time-independent CFD simulations of the flow through a staggered tube bundle were performed. This flow configuration partially simulates the anticipated flow in the lower plenum of a Very High Temperature Reactor (VHTR) design. To design a nuclear reactor with confidence, one needs strict benchmarking as part of a validation and verification exercise for any and all commercial CFD codes. Thus CFD simulations (FLUENT) of isothermal (at present), periodic flow through a tube bundle using both Steady Reynolds Averaged Navier-Stokes (SRANS) and Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were investigated. Selected turbulence models for a single tube diameter and inlet velocity based Re-number, Re ∼ 1.8 × 104, were investigated. The first-order turbulence models were: a standard k-ε turbulence model, a Renormalized Group (RNG) k-ε model, and lastly, a Shear Stress Transport (SST) k-ε model; the second-order model was a Reynolds Stress Model (RSM). Comparison of CFD simulations against experimental results of Simonin and Barcouda was undertaken at five stations (x, y) locations. Under the SRANS, we found the ability of the models to predict the turbulence stresses (u′u′, v′v′, u′v′) generally marginal to poor. However, upon adapting a concept from Large Eddy Simulation (LES), our URANS simulation with RSM revealed a spatiotemporal, oscillating flow structures in the wake. In contrast, it appears that the URANS with (even a) RNG k-ε model is unable to simulate this flow phenomena. In fact, the data suggests that the RNG k-ε model is too spatiotemporally dissipative. Some aspects of the SRANS versus URANS and using the aforementioned turbulence models will be presented.

CFD Study of Ejector Efficiencies

2014 ◽  
Author(s):  
Giorgio Besagni ◽  
Riccardo Mereu ◽  
Emanuela Colombo
Keyword(s):  
Thermal Field ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Validation Process ◽  
Local Flow ◽  
Convergent Nozzle ◽  
Flow Parameters ◽  
Rans Turbulence Models ◽  
Flow Phenomena ◽  
Computational Fluid Dynamics Cfd

This paper presents a method to evaluate ejector efficiency in function of local flow parameters. The paper is divided into two parts. In the first part, a Computational Fluid-Dynamics (CFD) approach for convergent nozzle ejectors is presented and computational results are validated using experimental velocity and temperature profiles at different sections. The validation process includes the evaluation of seven Reynolds-Averaged Navier–Stokes (RANS) turbulence models: the Spalart-Allmaras and the k–omega SST models show better performance in terms of convergence capability and flow and thermal field prediction. In the second part, local flow phenomena and their influence on ejector component efficiencies are investigated. The validated CFD approach is used to determine the efficiencies of the ejector primary nozzle, suction chamber, and mixing zone. Efficiency maps, regressing equation linking efficiencies, and local flow quantities are proposed and discussed. Finally, global ejector performance is mapped and considerations are outlined.

Three-Dimensional Navier–Stokes Computation of Turbine Nozzle Flow With Advanced Turbulence Models

1997 ◽  
Vol 119 (3) ◽  
pp. 516-530 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Reynolds Stress ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Nozzle Flow ◽  
Stress Model ◽  
Mean Flow ◽  
The Mean ◽  
Algebraic Reynolds Stress Model

A three-dimensional Navier–Stokes procedure has been used to compute the three-dimensional viscous flow through the turbine nozzle passage of a single-stage turbine. A low-Reynolds-number k–ε model and a zonal k-ε/ARSM (algebraic Reynolds stress model) are utilized for turbulence closure. The algebraic Reynolds stress model is used only in the endwall region to represent the anisotropy of turbulence. A four-stage Runge–Kutta scheme is used for time integration of both the mean-flow and the turbulence transport equations. For the turbine nozzle flow, comprehensive comparisons between the predictions and the experimental data obtained at Penn State show that most features of the vortex-dominated endwall flow, as well as nozzle wake structure, have been captured well by the numerical procedure. An assessment of the performance of the turbulence models has been carried out. The two models are found to provide similar predictions for the mean flow parameters, although slight improvement in the prediction of some secondary flow quantities has been obtained by the ARSM model.

scholarly journals Assessment of Numerical Methods for Plunging Breaking Wave Predictions

2021 ◽  
Vol 9 (3) ◽  
pp. 264
Author(s):  
Shanti Bhushan ◽  
Oumnia El Fajri ◽  
Graham Hubbard ◽  
Bradley Chambers ◽  
Christopher Kees
Keyword(s):  
Solitary Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Wave Crest ◽  
Breaking Wave ◽  
Rans Turbulence Models ◽  
Run Up ◽  
Better Than

This study evaluates the capability of Navier–Stokes solvers in predicting forward and backward plunging breaking, including assessment of the effect of grid resolution, turbulence model, and VoF, CLSVoF interface models on predictions. For this purpose, 2D simulations are performed for four test cases: dam break, solitary wave run up on a slope, flow over a submerged bump, and solitary wave over a submerged rectangular obstacle. Plunging wave breaking involves high wave crest, plunger formation, and splash up, followed by second plunger, and chaotic water motions. Coarser grids reasonably predict the wave breaking features, but finer grids are required for accurate prediction of the splash up events. However, instabilities are triggered at the air–water interface (primarily for the air flow) on very fine grids, which induces surface peel-off or kinks and roll-up of the plunger tips. Reynolds averaged Navier–Stokes (RANS) turbulence models result in high eddy-viscosity in the air–water region which decays the fluid momentum and adversely affects the predictions. Both VoF and CLSVoF methods predict the large-scale plunging breaking characteristics well; however, they vary in the prediction of the finer details. The CLSVoF solver predicts the splash-up event and secondary plunger better than the VoF solver; however, the latter predicts the plunger shape better than the former for the solitary wave run-up on a slope case.

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