A Numerical Sensitivity Study of Modeling Parameters in the Combustion of a Swirler

Abstract In this study, a sensitivity analysis based on Reynolds Averaged Navier-Stokes (RANS) equations has been conducted to model the reacting turbulent flow in a swirler used in a (Disk-Oriented) gas-turbine using propane-air mixture. Several popular turbulence models and combustion models have been compared at different equivalence ratios. The effects of simulation parameters such as turbulence intensity, TKE Prandtl number, Schmidt number, and gravity direction have been studied. The contour plots of the species mass fraction (H2, OH) and temperature distributions from the CFD results are compared against the experimental visual results. The results showed that the realizable k-ε model and the steady diffusion flamelet model (SDF) are more suitable to model the turbulence combustion in the swirl domain. The computations further showed that the TKE Prandtl number and gravity are sensitive parameters to model the combustion from the swirler, while the Schmidt number and turbulence intensity showed less sensitivity.

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Numerical Simulation of Flame Propagation in a Staged Combustor

Volume 1: Turbo Expo 2002 ◽

10.1115/gt2002-30097 ◽

2002 ◽

Author(s):

Tomoko Tsuru ◽

Akira Imamura ◽

Yasuhiro Kinoshita ◽

Yoshiharu Nonaka ◽

Yuichi Itoh ◽

...

Keyword(s):

Numerical Simulation ◽

Flame Propagation ◽

Turbulence Intensity ◽

Turbulence Models ◽

Numerical Code ◽

Velocity Fluctuations ◽

Flamelet Model ◽

Eddy Simulation ◽

Large Eddy ◽

Conventional Numerical Method

Highly unsteady flow fields are generated in recent low-emissions gas turbine combustors. Numerical simulation of such flows using conventional numerical code using a time-averaged turbulence model is difficult and time-accurate LES (Large Eddy Simulation) is expected to predict them. Calculation of turbulent combusting and non-combusting flow field in a staged combustor were conducted using LES. To validate the LES calculation, a prediction of time-averaged velocity field is compared with those by an experiment and a conventional numerical method based on RANS model. Turbulence intensity affects flame speed so much that velocity fluctuations were measured to obtain turbulence intensity in the non-combustion test. Strongly turbulent regions between the pilot and main stages, which are important for the flame propagation, were simulated. The combustion was calculated using a laminar flamelet model and the flame propagating phenomenon was simulated properly, which is impractical by the conventional simulations using time-averaged turbulence models. The feasibility of the LES calculation is discussed.

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Sensitivity Study on Turbulence Models for the Prediction of the Reactor Internal Flow

Volume 2B: Thermal Hydraulics ◽

10.1115/icone22-31255 ◽

2014 ◽

Cited By ~ 2

Author(s):

Gong Hee Lee ◽

Young Seok Bang ◽

Sweng Woong Woo ◽

Ae Ju Cheong

Keyword(s):

Power Reactor ◽

Turbulence Models ◽

Flow Distribution ◽

Internal Flow ◽

Sensitivity Study ◽

Measured Data ◽

Prediction Performance ◽

Navier Stokes ◽

Ansys Cfx ◽

Inlet Flow Rate

In this study, in order to assess the prediction performance of Reynolds-averaged Navier-Stokes (RANS)-based turbulence models for the analysis of flow distribution inside the 1/5 scaled-down APR+ (Advanced Power Reactor Plus), the simulation was conducted with the commercial computational fluid dynamics software, ANSYS CFX R.13. The results predicted were then compared with the measured data. It was concluded that reactor internal-flow pattern differed locally; depending on the turbulence models used. In particular, the prediction performance of turbulence models showed the largest difference in the regions from the flow skirt to fuel assembly inlet. The prediction performance of the k-ε model was superior to other turbulence models. This model also predicted the relatively uniform distribution of core-inlet flow-rate.

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Assessment of Numerical Methods for Plunging Breaking Wave Predictions

Journal of Marine Science and Engineering ◽

10.3390/jmse9030264 ◽

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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Comparative Study of Different Turbulence Models for Cavitational Flows around NACA0012 Hydrofoil

Journal of Marine Science and Engineering ◽

10.3390/jmse9070742 ◽

2021 ◽

Vol 9 (7) ◽

pp. 742

Author(s):

Minsheng Zhao ◽

Decheng Wan ◽

Yangyang Gao

Keyword(s):

Angle Of Attack ◽

Large Angle ◽

Turbulence Models ◽

Navier Stokes ◽

Specific Information ◽

Cloud Cavitation ◽

Eddy Simulation ◽

Large Eddy ◽

Shedding Frequency ◽

Reynolds Average

The present work focuses on the comparison of the numerical simulation of sheet/cloud cavitation with the Reynolds Average Navier-Stokes and Large Eddy Simulation(RANS and LES) methods around NACA0012 hydrofoil in water flow. Three kinds of turbulence models—SST k-ω, modified SST k-ω, and Smagorinsky’s model—were used in this paper. The unstable sheet cavity and periodic shedding of the sheet/cloud cavitation were predicted, and the simulation results, namelycavitation shape, shedding frequency, and the lift and the drag coefficients of those three turbulence models, were analyzed and compared with each other. The numerical results above were basically in accordance with experimental ones. It was found that the modified SST k-ω and Smagorinsky turbulence models performed better in the aspects of cavitation shape, shedding frequency, and capturing the unsteady cavitation vortex cluster in the developing and shedding period of the cavitation at the cavitation number σ = 0.8. At a small angle of attack, the modified SST k-ω model was more accurate and practical than the other two models. However, at a large angle of attack, the Smagorinsky model of the LES method was able to give specific information in the cavitation flow field, which RANS method could not give. Further study showed that the vortex structure of the wing is the main cause of cavitation shedding.

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Multiscale Partially Averaged Navier Stokes Approach for the Prediction of Flow in Linear Compressor Cascade With Moving Casing

Volume 7: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2011-45875 ◽

2011 ◽

Author(s):

Domenico Borello ◽

Giovanni Delibra ◽

Franco Rispoli

Keyword(s):

Turbulence Models ◽

Navier Stokes ◽

Test Case ◽

Compressor Cascade ◽

Preliminary Assessment ◽

Linear Compressor ◽

Tip Leakage ◽

Experimental Campaign ◽

Elliptic Relaxation ◽

Linear Compressor Cascade

In this paper we present an innovative Partially Averaged Navier Stokes (PANS) approach for the simulation of turbomachinery flows. The elliptic relaxation k-ε-ζ-f model was used as baseline Unsteady Reynolds Averaged Navier Stokes (URANS) model for the derivation of the PANS formulation. The well established T-FlowS unstructured finite volume in-house code was used for the computations. A preliminary assessment of the developed formulation was carried out on a 2D hill flow that represents a very demanding test case for turbulence models. The turbomachinery flow here investigated reproduces the experimental campaign carried out at Virginia Tech on a linear compressor cascade with tip leakage. Their measurements were used for comparisons with numerical results. The predictive capabilities of the model were assessed through the analysis of the flow field. Then an investigation of the blade passage, where experiments were not available, was carried out to detect the main loss sources.

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Comparison of LES of Steady Transitional Flow in an Idealized Stenosed Axisymmetric Artery Model With a RANS Transitional Model

Journal of Biomechanical Engineering ◽

10.1115/1.4003782 ◽

2011 ◽

Vol 133 (5) ◽

Cited By ~ 26

Author(s):

F. P. P. Tan ◽

N. B. Wood ◽

G. Tabor ◽

X. Y. Xu

Keyword(s):

Experimental Data ◽

Turbulence Intensity ◽

Eddy Viscosity ◽

Flow Analysis ◽

Wall Turbulence ◽

Transitional Flow ◽

Navier Stokes ◽

Turbulence Structures ◽

Eddy Simulation ◽

Accurate Treatment

In this study, two different turbulence methodologies are investigated to predict transitional flow in a 75% stenosed axisymmetric experimental arterial model and in a slightly modified version of the model with an eccentric stenosis. Large eddy simulation (LES) and Reynolds-averaged Navier–Stokes (RANS) methods were applied; in the LES simulations eddy viscosity subgrid-scale models were employed (basic and dynamic Smagorinsky) while the RANS method involved the correlation-based transitional version of the hybrid k-ε/k-ω flow model. The RANS simulations used 410,000 and 820,000 element meshes for the axisymmetric and eccentric stenoses, respectively, with y+ less than 2 viscous wall units for the boundary elements, while the LES used 1,200,000 elements with y+ less than 1. Implicit filtering was used for LES, giving an overlap between the resolved and modeled eddies, ensuring accurate treatment of near wall turbulence structures. Flow analysis was carried out in terms of vorticity and eddy viscosity magnitudes, velocity, and turbulence intensity profiles and the results were compared both with established experimental data and with available direct numerical simulations (DNSs) from the literature. The simulation results demonstrated that the dynamic Smagorinsky LES and RANS transitional model predicted fairly comparable velocity and turbulence intensity profiles with the experimental data, although the dynamic Smagorinsky model gave the best overall agreement. The present study demonstrated the power of LES methods, although they were computationally more costly, and added further evidence of the promise of the RANS transition model used here, previously tested in pulsatile flow on a similar model. Both dynamic Smagorinsky LES and the RANS model captured the complex transition phenomena under physiological Reynolds numbers in steady flow, including separation and reattachment. In this respect, LES with dynamic Smagorinsky appeared more successful than DNS in replicating the axisymmetric experimental results, although inflow conditions, which are subject to caveats, may have differed. For the eccentric stenosis, LES with Smagorinsky coefficient of 0.13 gave the closest agreement with DNS despite the known shortcomings of fixed coefficients. The relaminarization as the flow escaped the influence of the stenosis was amply demonstrated in the simulations, graphically so in the case of LES.

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Numerical Simulation of Turbine Blade Boundary Layer and Heat Transfer and Assessment of Turbulence Models

Journal of Turbomachinery ◽

10.1115/1.2841190 ◽

1997 ◽

Vol 119 (4) ◽

pp. 794-801 ◽

Cited By ~ 7

Author(s):

J. Luo ◽

B. Lakshminarayana

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Reynolds Number ◽

Low Reynolds Number ◽

Turbulence Models ◽

Navier Stokes ◽

Bypass Transition ◽

Boundary Layer Development ◽

Low Reynolds ◽

Layer Development

The boundary layer development and convective heat transfer on transonic turbine nozzle vanes are investigated using a compressible Navier–Stokes code with three low-Reynolds-number k–ε models. The mean-flow and turbulence transport equations are integrated by a four-stage Runge–Kutta scheme. Numerical predictions are compared with the experimental data acquired at Allison Engine Company. An assessment of the performance of various turbulence models is carried out. The two modes of transition, bypass transition and separation-induced transition, are studied comparatively. Effects of blade surface pressure gradients, free-stream turbulence level, and Reynolds number on the blade boundary layer development, particularly transition onset, are examined. Predictions from a parabolic boundary layer code are included for comparison with those from the elliptic Navier–Stokes code. The present study indicates that the turbine external heat transfer, under real engine conditions, can be predicted well by the Navier–Stokes procedure with the low-Reynolds-number k–ε models employed.

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Effects of Ambient Turbulence on Interleaving at a Baroclinic Front

Journal of Physical Oceanography ◽

10.1175/2009jpo4297.1 ◽

2010 ◽

Vol 40 (4) ◽

pp. 685-712 ◽

Cited By ~ 14

Author(s):

William D. Smyth ◽

Barry Ruddick

Keyword(s):

Schmidt Number ◽

Turbulence Models ◽

Underlying Mechanism ◽

Vertical Scale ◽

Salt Fingers ◽

Calculation Results ◽

Frontal Zones ◽

Turbulent Momentum ◽

Salt Fingering ◽

Ambient Turbulence

Abstract In this paper the authors investigate the action of ambient turbulence on thermohaline interleaving using both theory and numerical calculations in combination with observations from Meddy Sharon and the Faroe Front. The highly simplified models of ambient turbulence used previously are improved upon by allowing turbulent diffusivities of momentum, heat, and salt to depend on background gradients and to evolve as the instability grows. Previous studies have shown that ambient turbulence, at typical ocean levels, can quench the thermohaline interleaving instability on baroclinic fronts. These findings conflict with the observation that interleaving is common in baroclinic frontal zones despite ambient turbulence. Another challenge to the existing theory comes from numerical experiments showing that the Schmidt number for sheared salt fingers is much smaller than previously assumed. Use of the revised value in an interleaving calculation results in interleaving layers that are both weaker and thinner than those observed. This study aims to resolve those paradoxes. The authors show that, when turbulence has a Prandtl number greater than unity, turbulent momentum fluxes can compensate for the reduced Schmidt number of salt fingering. Thus, ambient turbulence determines the vertical scale of interleaving. In typical oceanic interleaving structures, the observed property gradients are insufficient to predict interleaving growth at an observable level, even when improved turbulence models are used. The deficiency is small, though: gradients sharper by a few tens of percent are sufficient to support instability. The authors suggest that this is due to the efficiency of interleaving in erasing those property gradients. A new class of mechanisms for interleaving, driven by flow-dependent fluctuations in turbulent diffusivities, is identified. The underlying mechanism is similar to the well-known Phillips layering instability; however, because of Coriolis effects, it has a well-defined vertical scale and also a tilt angle opposite to that of finger-driven interleaving.

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An Investigation of Turbulence Modelling in Transonic Fans Including a Novel Implementation of an Implicit κ–ϵ Turbulence Model

Volume 1: Turbomachinery ◽

10.1115/92-gt-308 ◽

1992 ◽

Cited By ~ 1

Author(s):

Mark G. Turner ◽

Ian K. Jennions

Keyword(s):

Turbulence Models ◽

Algebraic Model ◽

Turbulence Modelling ◽

Experimental Results ◽

Navier Stokes ◽

Multiple Time Scales ◽

Multiple Time ◽

Wall Functions ◽

Solution Methods ◽

Explicit Solver

An explicit Navier-Stokes solver has been written with the option of using one of two types of turbulence models. One is the Baldwin-Lomax algebraic model and the other is an implicit k-ϵ model which has been coupled with the explicit Navier-Stokes solver in a novel way. This type of coupling, which uses two different solution methods, is unique and combines the overall robustness of the implicit k-ϵ solver with the simplicity of the explicit solver. The resulting code has been applied to the solution of the flow in a transonic fan rotor which has been experimentally investigated by Wennerstrom. Five separate solutions, each identical except for the turbulence modelling details, have been obtained and compared with the experimental results. The five different turbulence models run were: the standard Baldwin-Lomax model both with and without wall functions, the Baldwin-Lomax model with modified constants and wall functions, a standard k-ϵ model and an extended k-ϵ model which accounts for multiple time scales by adding an extra term to the dissipation equation. In general, as the model includes more of the physics, the computed shock position becomes closer to the experimental results.

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