Statistical Evaluation of CFD Predictions of Measured Mixing Properties of Hydrogen and Methane for Lean Premixed Combustion

2011 ◽  
Author(s):  
Amin Akbari ◽  
Scott Hill ◽  
Vincent McDonell ◽  
Scott Samuelsen
Keyword(s):  
Fuel Injection ◽  
Turbulence Models ◽  
Numerical Results ◽  
Community Research ◽  
Systematic Evaluation ◽  
Design Matrix ◽  
Injection Point ◽  
Mixing Properties ◽  
Lean Combustion ◽  
Turbulent Schmidt Number

Hydrogen is a fuel of interest to the combustion community research as a promising sustainable alternative fuel to replace fossil fuels. The combustion of hydrogen produces only emission of water vapor and NOx. To alleviate the NOx emission, lean combustion has been proposed and utilized in last three decades for natural gas. Therefore, evaluation of mixing properties of both methane and hydrogen in lean combustion technology such as premixers is crucial for design purposes. Increased capability of computational systems has allowed tools such as computational fluid dynamics to be regularly used for purpose of design screening. In the present work, systematic evaluation of different CFD approaches is accomplished for axial injection of fuel into non swirling air. The study has been undertaken for both methane and hydrogen. Different Reynolds Averaged Navier Stokes (RANS) turbulence models including k–ε and RSM, which are relatively attractive as being computationally efficient, are evaluated. Further, the sensitivity of RANS models to different turbulent Schmidt number (Sct), as an important parameter in mass transport analysis, has been investigated. To evaluate the numerical results, fuel concentration is measured in different locations downstream of the injection point. This is accomplished by means of flame ionization detector (FID). Finally, a comprehensive comparison has been made between numerical and experimental results to identify the best numerical approach. To provide quantitative assessment, the simulations follow a statistically design matrix which allows analysis of variance to be used to identify the preferred simulation strategies. The results suggest high sensitivity of numerical results to different Sct and relatively low sensitivity to turbulence models. However, this general trend is the opposite for radial fuel injection.

Experimental and Computational Analyses of Methane and Hydrogen Mixing in a Model Premixer

2010 ◽  
Author(s):  
Amin Akbari ◽  
Scott Hill ◽  
Vincent McDonell ◽  
Scott Samuelsen
Keyword(s):  
Schmidt Number ◽  
Fuel Injection ◽  
Agricultural Waste ◽  
Cross Flow ◽  
Flux Ratio ◽  
Turbulence Models ◽  
Systematic Evaluation ◽  
Efficient Design ◽  
Efficient Manner ◽  
Turbulent Schmidt Number

The mixing of fuel and air in combustion systems plays a key role in overall operability and emissions performance. Such systems are also being looked to for operation on a wide array of potential fuel types, including those derived from renewable sources such as biomass or agricultural waste. The optimization of premixers for such systems is greatly enhanced if efficient design tools can be utilized. The increased capability of computational systems has allowed tools such as computational fluid dynamics to be regularly used for such purpose. However, to be applied with confidence, validation is required. In the present work, a systematic evaluation of fuel mixing in a specific geometry which entails cross flow fuel injection into axial non-swirling air streams has been carried out for methane and hydrogen. Fuel concentration is measured at different planes downstream of the point of injection. In parallel, different CFD approaches are used to predict the concentration fields resulting from the mixing of fuel and air. Different steady turbulence models including variants of Reynolds Averaged Navier Stokes (RANS) have been applied. In addition, unsteady RANS and Large Eddy Simulation (LES) are used. To accomplish mass transport with any of the RANS approaches, the concept of the turbulent Schmidt number is generally used. As a result, the sensitivity of the RANS simulations to different turbulent Schmidt number values is also examined. In general, the results show that the Reynolds Stress Model, with use of an appropriate turbulent Schmidt number for the fuel used, provides the best agreement with the measured values of the variation in fuel distribution over a given plane in a relatively time efficient manner. It is also found that, for a fixed momentum flux ratio, both hydrogen and methane penetrate and disperse in a similar manner for the flowfield studied despite their significant differences in density and diffusivity.

Experimental and Computational Analyses of Methane and Hydrogen Mixing in a Model Premixer

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Amin Akbari ◽  
Scott Hill ◽  
Vincent McDonell ◽  
Scott Samuelsen
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Schmidt Number ◽  
Fuel Injection ◽  
Agricultural Waste ◽  
Flux Ratio ◽  
Systematic Evaluation ◽  
Efficient Design ◽  
Efficient Manner ◽  
Turbulent Schmidt Number

The mixing of fuel and air in combustion systems plays a key role in overall operability and emissions performance. Such systems are also being looked to for operation on a wide array of potential fuel types, including those derived from renewable sources such as biomass or agricultural waste. The optimization of premixers for such systems is greatly enhanced if efficient design tools can be utilized. The increased capability of computational systems has allowed tools such as computational fluid dynamics to be regularly used for such purpose. However, to be applied with confidence, validation is required. In the present work, a systematic evaluation of fuel mixing in a specific geometry, which entails cross flow fuel injection into axial nonswirling air streams has been carried out for methane and hydrogen. Fuel concentration is measured at different planes downstream of the point of injection. In parallel, different computational fluid dynamics approaches are used to predict the concentration fields resulting from the mixing of fuel and air. Different steady turbulence models including variants of Reynolds averaged Navier–Stokes (RANS) have been applied. In addition, unsteady RANS and large eddy simulation are used. To accomplish mass transport with any of the RANS approaches, the concept of the turbulent Schmidt number is generally used. As a result, the sensitivity of the RANS simulations to different turbulent Schmidt number values is also examined. In general, the results show that the Reynolds stress model, with use of an appropriate turbulent Schmidt number for the fuel used, provides the best agreement with the measured values of the variation in fuel distribution over a given plane in a relatively time efficient manner. It is also found that, for a fixed momentum flux ratio, both hydrogen and methane penetrate and disperse in a similar manner for the flow field studied despite their significant differences in density and diffusivity.

CFD Predictions of Isothermal Fuel-Air Mixing in a Radial Swirl Low NOx Combustor Using Various RANS Turbulence Models

2012 ◽  
Author(s):  
Phil T. King ◽  
Gordon E. Andrews ◽  
Mohamed M. Pourkashanian ◽  
Andy C. McIntosh
Keyword(s):  
Fuel Injection ◽  
Turbulence Models ◽  
Problem Area ◽  
Combustion Modeling ◽  
Fuel Jet ◽  
Turbulent Schmidt Number ◽  
Air Mixing ◽  
Rans Turbulence Models ◽  
Reasonable Prediction ◽  
Future Work

A radial swirl DLE combustion system was investigated for its gaseous fuel-air mixing performance using various different RANS turbulence models. Two different configurations were investigated; vane passage fuel injection and fuel injection from the wall of an outlet throat directly into the shear layer. The results showed that for vane passage fuel injection, only the standard k-ε and standard Spalart-Allmaras models were able to provide a reasonable prediction for the combustor fuel-air distribution, out of all the RANS models and their variants available in Fluent v6.3, although both models predicted that the fuel and air were better mixed than in the measurements. For outlet throat wall fuel injection no models were able to provide a reasonable prediction. This same issue is also reported by several other researchers and represents a serious problem area in combustion modeling for low NOx applications. Improved fuel jet penetration was achieved by using an extremely low value of 0.1 for the turbulent Schmidt number, therefore future work will concentrate on using a localized value of Sc in the vicinity of the fuel injection hole.

scholarly journals Numerical Modeling of Flow Over a Rectangular Broad-Crested Weir with a Sloped Upstream Face

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1663 ◽  
Author(s):  
Lei Jiang ◽  
Mingjun Diao ◽  
Haomiao Sun ◽  
Yu Ren
Keyword(s):  
Numerical Simulations ◽  
Discharge Coefficient ◽  
Separation Zone ◽  
Turbulence Models ◽  
Numerical Results ◽  
Upstream Face ◽  
Flow Conditions ◽  
Flow Features ◽  
The Mean ◽  
Absolute Percent Error

The objective of this study was to evaluate the effect of the upstream angle on flow over a trapezoidal broad-crested weir based on numerical simulations using the open-source toolbox OpenFOAM. Eight trapezoidal broad-crested weir configurations with different upstream face angles (θ = 10°, 15°, 22.5°, 30°, 45°, 60°, 75°, 90°) were investigated under free-flow conditions. The volume-of-fluid (VOF) method and two turbulence models (the standard k-ε model and the SST k-w model) were employed in the numerical simulations. The numerical results were compared with the experimental results obtained from published papers. The root mean square error (RMSE) and the mean absolute percent error (MAPE) were used to evaluate the accuracy of the numerical results. The statistical results show that RMSE and MAPE values of the standard k-ε model are 0.35–0.67% and 0.50–1.48%, respectively; the RMSE and MAPE values of the SST k-w model are 0.25–0.66% and 0.55–1.41%, respectively. Additionally, the effects of the upstream face angle on the flow features, including the discharge coefficient and the flow separation zone, were also discussed in the present study.

Computational Study of Fuel Injection in a Large-Bore Gas Engine

2003 ◽  
Author(s):  
Snehaunshu Chowdhury ◽  
Razi Nalim ◽  
Thomas M. Sine
Keyword(s):  
High Pressure ◽  
Fuel Injection ◽  
Computational Study ◽  
Turbulence Models ◽  
Fuel Flow ◽  
Air Mixing ◽  
Instantaneous Pressure ◽  
Combustion Processes ◽  
High Pressure Injection ◽  
Piston Position

Emission controls in stationary gas engines have required significant modifications to the fuel injection and combustion processes. One approach has been the use of high-pressure fuel injection to improve fuel-air mixing. The objective of this study is to simulate numerically the injection of gaseous fuel at high pressure in a large-bore two-stroke engine. Existing combustion chamber geometry is modeled together with proposed valve geometry. The StarCD® fluid dynamics code is used for the simulations, using appropriate turbulence models. High-pressure injection of up to 500 psig methane into cylinder air initially at 25 psig is simulated with the valve opened instantaneously and piston position frozen at the 60 degrees ABDC position. Fuel flow rate across the valve throat varies with the instantaneous pressure but attains a steady state in approximately 22 ms. As expected with the throat shape and pressures, the flow becomes supersonic past the choked valve gap, but returns to a subsonic state upon deflection by a shroud that successfully directs the flow more centrally. This indicates the need for careful shroud design to direct the flow without significant deceleration. Pressures below 300 psig were not effective with the proposed valve geometry. A persistent re-circulation zone is observed immediately below the valve, where it does not help promote mixing.

An Assessment of Five Turbulence Models in Predicting Turbulent Separation

2004 ◽  
Author(s):  
Robert E. Spall ◽  
Warren F. Phillips ◽  
Nick Alley
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Mach Number ◽  
Turbulence Models ◽  
Streamwise Velocity ◽  
Numerical Results ◽  
Flow Conditions ◽  
Turbulent Separation ◽  
Controlled Flow ◽  
Flow Case

Four different turbulence models were employed to predict the flow over a wall-mounted Glauert-Goldschmied body. The models evaluated include: 1) two-layer k–ε, 2) shear stress transport, 3) low-Reynolds number k–ω, 4) Spalart-Allmaras, and 5) v2−f. Calculations were performed for both an uncontrolled case, and a controlled-flow case which used steady suction through a slot located at the 65% chord station. The flow conditions include a freestream Mach number of approximately 0.1, and a chord Reynolds number of just under 1 million. For each model, the numerical results over predicted the experimentally determined re-attachment length. An examination of streamwise velocity profiles at several stations downstream of the trailing edge revealed considerable variation in the predictions of the five turbulence models.

Experimental and theoretical analyses of two-dimensional flows upstream of broad-crested weirs

2008 ◽  
Vol 35 (9) ◽  
pp. 975-986 ◽  
Author(s):  
M. Salih Kirkgoz ◽  
M. Sami Akoz ◽  
A. Alper Oner
Keyword(s):  
Cfd Simulation ◽  
Turbulence Models ◽  
Free Surface Flows ◽  
Velocity Fields ◽  
Numerical Results ◽  
Cfd Modeling ◽  
Two Dimensional ◽  
The Finite Element Method ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd

Using the particle image velocimetry (PIV) technique, the laboratory experiments are conducted to measure the velocity fields of two-dimensional turbulent free surface flows upstream of rectangular and triangular broad-crested weirs. The experimental flow cases are analyzed theoretically by a computational fluid dynamics (CFD) modeling in which the finite element method is used to solve the governing equations. In the CFD simulation, the volume of fluid (VOF) method is used to compute the free surfaces of the flows. Using the standard k–ε and standard k–ω turbulence models, the numerical results for the velocity fields and flow profiles are compared with the experimental results for validation purposes. The computed results using k–ω turbulence model on compressed mesh systems are found in good agreement with measured data. The flow cases are also analyzed theoretically using the potential flow (PF) approach, and the numerical results for the velocity fields are compared with measurements.

scholarly journals Numerical Analysis of the Aerodynamic Characteristics of NACA-4312 Airfoil

2020 ◽  
Vol 01 (02) ◽  
pp. 29-36
Author(s):  
Md Rhyhanul Islam Pranto ◽  
Mohammad Ilias Inam
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Turbulence Models ◽  
Aerodynamic Characteristics ◽  
Numerical Results ◽  
Ansys Fluent ◽  
Coefficient Increase ◽  
Lift And Drag ◽  
Lift And Drag Coefficient

The aim of the work is to investigate the aerodynamic characteristics such as lift coefficient, drag coefficient, pressure distribution over a surface of an airfoil of NACA-4312. A commercial software ANSYS Fluent was used for these numerical simulations to calculate the aerodynamic characteristics of 2-D NACA-4312 airfoil at different angles of attack (α) at fixed Reynolds number (Re), equal to 5×10^5 . These simulations were solved using two different turbulence models, one was the Standard k-ε model with enhanced wall treatment and other was the SST k-ω model. Numerical results demonstrate that both models can produce similar results with little deviations. It was observed that both lift and drag coefficient increase at higher angles of attack, however lift coefficient starts to reduce at α =13° which is known as stalling condition. Numerical results also show that flow separations start at rare edge when the angle of attack is higher than 13° due to the reduction of lift coefficient.

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