Numerical study on turbulent mixing process in cross-flow type T-junction

The present work focusses on the numerical study of Vortex-Induced Vibrations (VIV) of an elastically mounted cylinder in a cross flow at moderate Reynolds numbers. Low mass-damping experimental studies show that the dynamic behavior of the cylinder exhibits a three-branch response model, depending on the range of the reduced velocity. However, few numerical simulations deal with accurate computations of the VIV amplitudes at the lock-in upper branch of the bifurcation diagram. In this work, the dynamic response of the cylinder is investigated by means of three-dimensional Large Eddy Simulation (LES). An Arbitrary Lagrangian Eulerian framework is employed to account for fluid solid interface boundary motion and grid deformation. Numerous numerical simulations are performed at a Reynolds number of 3900 for both no damping and low-mass damping ratio and various reduced velocities. A detailed physical analysis is conducted to show how the present methodology is able to capture the different VIV responses.

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Experimental and Numerical Study on the Effects of the Relative Position of Film Hole and Orientation Ribs on the Film Cooling With Ribbed Cross-Flow Coolant Channel

Volume 7B: Heat Transfer ◽

10.1115/gt2020-14389 ◽

2020 ◽

Author(s):

Bingran Li ◽

Cunliang Liu ◽

Lin Ye ◽

Huiren Zhu ◽

Fan Zhang

Keyword(s):

Heat Transfer ◽

Relative Position ◽

Film Cooling ◽

Numerical Study ◽

Cross Flow ◽

Internal Cooling ◽

Transfer Coefficients ◽

Cooling Performance ◽

Heat Transfer Coefficients ◽

Numerical Studies

Abstract To investigate the application of ribbed cross-flow coolant channels with film hole effusion and the effects of the internal cooling configuration on film cooling, experimental and numerical studies are conducted on the effect of the relative position of the film holes and different orientation ribs on the film cooling performance. Three cases of the relative position of the film holes and different orientation ribs (post-rib, centered, and pre-rib) in two ribbed cross-flow channels (135° and 45° orientation ribs) are investigated. The film cooling performances are measured under three blowing ratios by the transient liquid crystal measurement technique. A RANS simulation with the realizable k-ε turbulence model and enhanced wall treatment is performed. The results show that the cooling effectiveness and the downstream heat transfer coefficient for the 135° rib are basically the same in the three position cases, and the differences between the local effectiveness average values for the three are no more than 0.04. The differences between the heat transfer coefficients are no more than 0.1. The “pre-rib” and “centered” cases are studied for the 45° rib, and the position of the structures has little effect on the film cooling performance. In the different position cases, the outlet velocity distribution of the film holes, the jet pattern and the discharge coefficient are consistent with the variation in the cross flow. The related research previously published by the authors showed that the inclination of the ribs with respect to the holes affects the film cooling performance. This study reveals that the relative positions of the ribs and holes have little effect on the film cooling performance. This paper expands and improves the study of the effect of the internal cooling configuration on film cooling and makes a significant contribution to the design and industrial application of the internal cooling channel of a turbine blade.

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Analysis of the Mixing and Emission Characteristics in a Model Combustor

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2018-76272 ◽

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.

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Numerical Simulations of Turbulent Mixing and Autoignition of Hydrogen Fuel at Reheat Combustor Operating Conditions

Volume 2: Combustion, Fuels and Emissions, Parts A and B ◽

10.1115/gt2011-46264 ◽

2011 ◽

Cited By ~ 1

Author(s):

Elizaveta Ivanova ◽

Berthold Noll ◽

Peter Griebel ◽

Manfred Aigner ◽

Khawar Syed

Keyword(s):

Natural Gas ◽

Numerical Simulations ◽

Flue Gas ◽

Turbulent Mixing ◽

Turbulence Modeling ◽

Numerical Study ◽

Operating Conditions ◽

Fuel Blend ◽

Flow Configuration ◽

Modeling Methods

Turbulent mixing and autoignition of H2-rich fuels at relevant reheat combustor operating conditions are investigated in the present numerical study. The flow configuration under consideration is a fuel jet perpendicularly injected into a crossflow of hot flue gas (T > 1000K, p = 15bar). Based on the results of the experimental study for the same flow configuration and operating conditions two different fuel blends are chosen for the numerical simulations. The first fuel blend is a H2/natural gas/N2 mixture at which no autoignition events were observed in the experiments. The second fuel blend is a H2/N2 mixture at which autoignition in the mixing section occurred. First, the non-reacting flow simulations are performed for the H2/natural gas/N2 mixture in order to compare the accuracy of different turbulence modeling methods. Here the steady-state Reynolds-averaged Navier-Stokes (RANS) as well as the unsteady scale-adaptive simulation (SAS) turbulence modeling methods are applied. The velocity fields obtained in both simulations are directly validated against experimental data. The SAS method shows better agreement with the experimental results. In the second part of the present work the autoignition of the H2/N2 mixture is numerically studied using the 9-species 21-steps reaction mechanism of O’Conaire et al. [1]. As in the reference experiments, autoignition can be observed in the simulations. Influences of the turbulence modeling as well as of the hot flue gas temperature are investigated. The onset and the propagation of the ignition kernels are studied based on the SAS modeling results. The obtained numerical results are discussed and compared with data from experimental autoignition studies.

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Large Eddy Simulation of Cross Flow in Pipe Junction

Volume 2: CFD and FSI ◽

10.1115/omae2018-77751 ◽

2018 ◽

Author(s):

Jiajun Chen ◽

Yue Sun ◽

Hang Zhang ◽

Dakui Feng ◽

Zhiguo Zhang

Keyword(s):

Large Eddy Simulation ◽

Stokes Equations ◽

Numerical Study ◽

Three Dimensional ◽

Cross Flow ◽

Exciting Force ◽

Navier Stokes ◽

Pipe Network ◽

Eddy Simulation ◽

Large Eddy

Mixing in pipe junctions can play an important role in exciting force and distribution of flow in pipe network. This paper investigated the cross pipe junction and proposed an improved plan, Y-shaped pipe junction. The numerical study of a three-dimensional pipe junction was performed for calculation and improved understanding of flow feature in pipe. The filtered Navier–Stokes equations were used to perform the large-eddy simulation of the unsteady incompressible flow in pipe. From the analysis of these results, it clearly appears that the vortex strength and velocity non-uniformity of centerline, can be reduced by Y-shaped junction. The Y-shaped junction not only has better flow characteristic, but also reduces head loss and exciting force. The results of the three-dimensional improvement analysis of junction can be used in the design of pipe network for industry.

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