Sensitivity of turbulent Schmidt number and turbulence model to simulations of jets in crossflow

2016 ◽  
Vol 82 ◽  
pp. 218-228 ◽  
Author(s):  
Daniel Valero ◽  
Daniel B. Bung
Keyword(s):  
Turbulence Model ◽  
Schmidt Number ◽  
Turbulent Schmidt Number

scholarly journals ПОВЫШЕНИЕ ТОЧНОСТИ РАСЧЕТА ПОЛЯ ТЕМПЕРАТУР ГАЗА НА ВЫХОДЕ ИЗ КАМЕРЫ СГОРАНИЯ ГТД МЕТОДОМ ТРЕХМЕРНОГО КОМПЬЮТЕРНОГО МОДЕЛИРОВАНИЯ

2020 ◽  
pp. 74-82
Author(s):  
Сергей Анатольевич Евсеев ◽  
Дмитрий Викторович Козел ◽  
Игорь Федорович Кравченко
Keyword(s):  
Numerical Experiment ◽  
Combustion Chamber ◽  
Turbulence Model ◽  
Schmidt Number ◽  
Temperature Pattern ◽  
Gas Temperature ◽  
Ansys Fluent ◽  
Maximum Value ◽  
Turbulent Schmidt Number ◽  
Initial Settings

The problem of numerical simulation of the gas flow with the combustion of atomized liquid fuel was solved (the equilibrium combustion model pdf was used along with the partially mixed mixture model) in the annular combustion chamber of a gas turbine engine. Numerical modeling was performed in Ansys Fluent calculation complex. The purpose of the calculations was to simulate the radial and circumferential unevenness of the gas temperature pattern at the outlet of the combustion chamber. As a result of the calculations, it was found that the accuracy of modeling the radial and circumferential unevenness of the gas temperature pattern at the outlet of the combustion chamber is unsatisfactory when using the k–e turbulence model with the initial settings for the Ansys Fluent calculation complex. Moreover, the maximum value of the radial non-uniformity of the gas temperature pattern at the outlet of the combustion chamber exceeded the value obtained in the experiment by 12.61 %, and the maximum value of the circumferential non-uniformity by 12.69 %. To improve the accuracy of modeling the temperature pattern non-uniformity at the outlet of the combustion chamber, a numerical experiment was conducted to study the effect of the degree of turbulent diffusion of gas components on the value of temperature pattern non-uniformity. To reduce the non-uniformity of the temperature pattern at the outlet of the combustion chamber, the degree of turbulent diffusion of gas components was increased with respect to the initial version of the calculation, performed using the k–e model of turbulence with the initial settings for the Ansys Fluent calculation complex, by reducing the turbulent Schmidt number Sc in the turbulence model. For the initial settings of the k–e turbulence model in the Ansys Fluent calculation complex, the turbulent Schmidt number Sc = 0.85. A numerical experiment was performed for the values of Sc = 0.6, Sc = 0.4, and Sc = 0.2. The results of a numerical experiment confirmed the influence of the turbulent Schmidt number Sc on the result of calculating the gas temperature pattern at the outlet of the combustion chamber; as the value of Sc decreases, the level of the circumferential and radial non-uniformities of the gas temperature pattern decreases. However, the degree of reduction of radial and circumferential irregularities with a decrease in Sc is different. Therefore, to ensure high accuracy in calculating both the circumferential and radial non-uniformities of the gas temperature pattern, it was proposed to use a variable value of the turbulent Schmidt number Sc depending on the gas temperature instead of a constant value. The functional dependence of the turbulent Schmidt number Sc on the gas temperature was implemented in the Ansys Fluent calculation complex using the user function (UDF). The results of modeling the gas temperature pattern using the proposed UDF function for the turbulent Schmidt number Sc are in satisfactory agreement with the experimental data for both radial and circumferential non-uniformities of the gas temperature pattern at the outlet of the combustion chamber.

Analysis of the Mixing and Emission Characteristics in a Model Combustor

2018 ◽  
Author(s):  
Shan Li ◽  
Shanshan Zhang ◽  
Lingyun Hou ◽  
Zhuyin Ren
Keyword(s):  
Gas Turbines ◽  
Schmidt Number ◽  
Numerical Study ◽  
Flame Temperature ◽  
Scalar Dissipation ◽  
Mixing Process ◽  
Nox Formation ◽  
Turbulent Schmidt Number ◽  
Wide Range ◽  
Air Mixing

Modern gas turbines in power systems employ lean premixed combustion to lower flame temperature and thus achieve low NOx emissions. The fuel/air mixing process and its impacts on emissions are of paramount importance to combustor performance. In this study, the mixing process in a methane-fired model combustor was studied through an integrated experimental and numerical study. The experimental results show that at the dump location, the time-averaged fuel/air unmixedness is less than 10% over a wide range of testing conditions, demonstrating the good mixing performance of the specific premixer on the time-averaged level. A study of the effects of turbulent Schmidt number on the unmixedness prediction shows that for the complex flow field involved, it is challenging for Reynolds-Averaged Navier-Stokes (RANS) simulations with constant turbulent Schmidt number to accurately predict the mixing process throughout the combustor. Further analysis reveals that the production and scalar dissipation are the key physical processes controlling the fuel/air mixing. Finally, the NOx formation in this model combustor was analyzed and modelled through a flamelet-based approach, in which NOx formation is characterized through flame-front NOx and its post-flame formation rate obtained from one-dimensional laminar premixed flames. The effect of fuel/air unmixedness on NOx formation is accounted for through the presumed probability density functions (PDF) of mixture fraction. Results show that the measured NOx in the model combustor are bounded by the model predictions with the fuel/air unmixedness being 3% and 5% of the maximum unmixedness. In the context of RANS, the accuracy in NOx prediction depends on the unmixedness prediction which is sensitive to turbulent Schmidt number.

scholarly journals Gas-solid and gas-liquid mass transfer: Effect of turbulent Schmidt number

2007 ◽  
Vol 13 (3) ◽  
pp. 167-168 ◽  
Author(s):  
Aleksandar Dudukovic ◽  
Rada Pjanovic
Keyword(s):  
Mass Transfer ◽  
Eddy Viscosity ◽  
Schmidt Number ◽  
Mass Transfer Rate ◽  
Transfer Effect ◽  
Transfer Coefficients ◽  
Mass Transfer Effect ◽  
Liquid Mass ◽  
Turbulent Schmidt Number ◽  
Liquid Mass Transfer

The scope of this paper is to explain effect of eddy viscosity and turbulent Schmidt number on mass transfer rate. New, theoretically based correlation for gas-liquid mass transfer coefficients are proposed.

Free Turbulent Shear Layers on Plug Nozzles

1977 ◽  
Vol 99 (2) ◽  
pp. 301-308
Author(s):  
C. J. Scott ◽  
D. R. Rask
Keyword(s):  
Turbulent Mixing ◽  
Schmidt Number ◽  
Error Function ◽  
Mixing Layer ◽  
Shear Layers ◽  
Turbulent Shear ◽  
Gas Chromatograph ◽  
Plug Nozzle ◽  
Turbulent Schmidt Number ◽  
Plug Nozzles

Two-dimensional, free, turbulent mixing between a uniform stream and a cavity flow is investigated experimentally in a plug nozzle, a geometry that generates idealized mixing layer conditions. Upstream viscous layer effects are minimized through the use of a sharp-expansion plug nozzle. Experimental velocity profiles exhibit close agreement with both similarity analyses and with error function predictions. Refrigerant-12 was injected into the cavity and concentration profiles were obtained using a gas chromatograph. Spreading factors for momentum and mass were determined. Two methods are presented to determine the average turbulent Schmidt number. The relation Sct = Sc is suggested by the data for Sc < 2.0.

scholarly journals On the Values for the Turbulent Schmidt Number in Environmental Flows

Fluids ◽  
2017 ◽  
Vol 2 (2) ◽  
pp. 17 ◽  
Author(s):  
Carlo Gualtieri ◽  
Athanasios Angeloudis ◽  
Fabian Bombardelli ◽  
Sanjeev Jha ◽  
Thorsten Stoesser
Keyword(s):  
Schmidt Number ◽  
Environmental Flows ◽  
Turbulent Schmidt Number

Turbulent Schmidt number from a tracer experiment

2002 ◽  
Vol 111 (4) ◽  
pp. 299-307 ◽  
Author(s):  
Thomas K. Flesch ◽  
John H. Prueger ◽  
Jerry L. Hatfield
Keyword(s):  
Schmidt Number ◽  
Tracer Experiment ◽  
Turbulent Schmidt Number

S053035 Eddy Diffusivity and Turbulent Schmidt Number in a Reactive Planar Jet in Liquid Phase

2012 ◽  
Vol 2012 (0) ◽  
pp. _S053035-1-_S053035-3
Author(s):  
Tomoaki WATANABE ◽  
Yasuhiko SAKAI ◽  
Kouji NAGATA ◽  
Osamu TERASHIMA ◽  
Yasumasa ITO
Keyword(s):  
Liquid Phase ◽  
Schmidt Number ◽  
Eddy Diffusivity ◽  
Planar Jet ◽  
Turbulent Schmidt Number
Sign in / Sign up

Export Citation Format

Share Document