A numerical study of the effect of radial confinement on the characteristics of laminar co-flow methane–oxygen diffusion flames

2011 ◽  
Vol 225 (5) ◽  
pp. 1213-1228 ◽  
Author(s):  
K Bhadraiah ◽  
V Raghavan
Keyword(s):  
Numerical Model ◽  
Oxygen Diffusion ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Air Entrainment ◽  
Maximum Temperature ◽  
Low Oxygen ◽  
Numerical Predictions ◽  
Effect Of Oxygen ◽  
Different Diameters

A numerical investigation of the characteristics of laminar co-flow methane–oxygen diffusion flames has been carried out. The temperature and nitric oxide (NO) distributions in unconfined and partly confined flames are studied in detail. Radial confinements of different diameters and with a length of 150 times the fuel jet diameter have been considered to allow atmospheric nitrogen entry only from the top. A numerical model with a 43-step chemical kinetics mechanism and an optically thin radiation sub-model is employed to carry out simulations. The numerical model has been validated using the experimental data available in the literature. The effect of oxygen flowrate on temperature distributions is studied thoroughly. Confined flame extents are compared with the corresponding unconfined flame extents with the help of OH contours. The effect of confinement diameter on temperature and NO distributions is analysed in detail. At low oxygen flowrates, the extents of confined flames are higher than those of an unconfined flame. At a higher oxygen flowrate, the extent of unconfined flame becomes higher. The confined flames are in general hotter than the unconfined flames. However, at the highest oxygen flowrate and for an intermediate confinement diameter, the flame has the lowest maximum temperature. The amount of NO produced in confined flames is higher than the unconfined flames, due to air entrainment from the top of the confining tube, which increases the residence time for nitrogen transport and its oxidation. At the highest oxygen flowrate considered, numerical predictions show that for a given confinement length, there is an optimum confinement diameter which results in a minimum net production of NO among all the flames.

Experimental and Numerical Study of Ballistic Impact Performance on UHMWPE Composites

2013 ◽  
Vol 818 ◽  
pp. 30-36 ◽  
Author(s):  
Yao Ke Wen ◽  
Cheng Xu ◽  
Ai Jun Chen ◽  
Shu Wang
Keyword(s):  
Numerical Model ◽  
Composite Plate ◽  
Numerical Study ◽  
Von Mises Stress ◽  
High Speed Photography ◽  
Numerical Predictions ◽  
Back Face ◽  
Uhmwpe Composites ◽  
The Impact ◽  
Bulge Height

A series of ballistic tests were performed to investigate the bulletproof performance of UHMWPE composites. The temporal evolution of the UHMWPE composite plate back-face bulge height and diameter were captured by high-speed photography. The experiments show the composite plate were perforated when the impact velocity greater than 880m/s. The maximum bulge height and diameter can reach to 3.63-8.23mm and 37-64.5mm at the experimental velocity range , respectively. After that, the numerical model was built with composite material model MAT59 in LS-DYNA and stress based contact failure between plies were adopted to model the delamination mechanism. The number of plies of numerical model shows a strong dependency on the numerical results. Comparisons between numerical predictions and experimental results in terms of bulge height and diameter are presented and discussed. The maximum bulge diameter is good agreement with experiment, but the computational results under predict the maximum bulge height. The computational analysis show the damage development of the plate penetration by the projectile is shearing dominated at first, then the plate undergoes delamination and stretching in the later part of the impact process. The von mises stress at front and back face of the plate were also studied.

scholarly journals Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 367
Author(s):  
Valentin Ageorges ◽  
Jorge Peixinho ◽  
Gaële Perret ◽  
Ghislain Lartigue ◽  
Vincent Moureau
Keyword(s):  
Free Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Free Surface Flow ◽  
Air Entrainment ◽  
Surface Flow ◽  
Finite Height ◽  
Wave Patterns ◽  
Different Diameters

We present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 <Re< 200,000 and 0.2<Fr<2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments.

Computation of Nitric Oxide and Soot Emissions From Turbulent Diffusion Flames

1985 ◽  
Vol 107 (1) ◽  
pp. 48-53 ◽  
Author(s):  
T. Ahmad ◽  
S. L. Plee ◽  
J. P. Myers
Keyword(s):  
Diffusion Flames ◽  
Soot Oxidation ◽  
Air Entrainment ◽  
Reaction Rates ◽  
Gas Jet ◽  
Maximum Temperature ◽  
Injection Velocity ◽  
Soot Emission ◽  
No Emission ◽  
Jet Flame

An existing steady-state, locally homogeneous flow model of turbulent spray combustion was modified to predict NO emission from a spray flame and soot emission from a gas-jet flame. The effect of turbulent fluctuations on the reaction rates was accounted for. The predicted NO emission from an n-pentane spray with a changing injection velocity could be correlated with the convective time scale of the flow. Calculation of soot emission from a burning turbulent gas jet indicated that the centerline soot concentration reaches a peak upstream of the maximum temperature location and then decreases due to soot oxidation and dilution by air entrainment.

Buried Pipelines Subjected to Transverse Ground Movement: Comparison Between Full-Scale Testing and Numerical Modeling

2006 ◽  
Author(s):  
Hamid Karimian ◽  
Dharma Wijewickreme ◽  
Doug Honegger
Keyword(s):  
Numerical Model ◽  
Constitutive Models ◽  
Full Scale ◽  
Ground Movement ◽  
Soil Response ◽  
University Of British Columbia ◽  
Numerical Predictions ◽  
Pullout Tests ◽  
Soil Constitutive Models ◽  
Different Diameters

A research program has been undertaken to study the behaviour of buried steel pipelines subject to lateral horizontal ground movements, and to provide appropriate data to calibrate and validate numerical model(s). A large sand chamber (2.5 m W × 3.8 m L × 2.5 m H) available at the University of British Columbia was employed to conduct full-scale lateral pullout tests on steel pipelines, with different diameters and buried in sand simulating different overburden ratios. Numerical analyses were performed using finite-difference-method-based software with the soil response simulated using Mohr-Coulomb and hyperbolic elastic constitutive models. The input parameters for the initial computer modeling were based only on element testing results. The numerical predictions, using the two soil constitutive models, are compared with the results of lateral pullout tests. The numerical model, after validation with full-scale test results can be used to predict soil loads on pipe for different overburden ratios, pipe sizes and soil properties.

Non-buoyant diffusion flames with oscillatory air entrainment

1997 ◽  
Author(s):  
U. Hegde ◽  
D. Stocker ◽  
M. Bahadori ◽  
D. Stocker ◽  
M. Bahadori ◽  
...  
Keyword(s):  
Diffusion Flames ◽  
Air Entrainment ◽  
Buoyant Diffusion Flames

scholarly journals Pool Boiling of Nanofluids on Biphilic Surfaces: An Experimental and Numerical Study

Nanomaterials ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 125
Author(s):  
Eduardo Freitas ◽  
Pedro Pontes ◽  
Ricardo Cautela ◽  
Vaibhav Bahadur ◽  
João Miranda ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Heat Dissipation ◽  
Numerical Study ◽  
Pool Boiling ◽  
Temperature Drop ◽  
Surface Cooling ◽  
Average Temperature ◽  
Gold Silver

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool-boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions were developed and used as surface interfaces with different nanofluids (water with gold, silver, aluminum and alumina nanoparticles), in order to evaluate the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. To study the nucleation of a single bubble in pool boiling condition, a numerical model was also implemented. The results show an evident benefit of using biphilic patterns with well-established distances between the superhydrophobic regions. This can be observed in the resulting plot of the dissipated heat flux for a biphilic pattern with seven superhydrophobic spots, δ = 1/d and an imposed heat flux of 2132 w/m2. In this case, the dissipated heat flux is almost constant (except in the instant t* ≈ 0.9 when it reaches a peak of 2400 W/m2), whilst when using only a single superhydrophobic spot, where the heat flux dissipation reaches the maximum shortly after the detachment of the bubble, dropping continuously until a new necking phase starts. The biphilic patterns also allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic spacing between the superhydrophobic regions, which clearly contributes to cool down the surface. This effect is noticeable in the case of employing the Ag 1 wt% nanofluid, with an imposed heat flux of 2132 W/m2, where the coalescence of the drops promotes a surface cooling, identified by a temperature drop of 0.7 °C in the hydrophilic areas. Those areas have an average temperature of 101.8 °C, whilst the average temperature of the superhydrophobic spots at coalescence time is of 102.9 °C. For low concentrations as the ones used in this work, the effect of the nanofluids was observed to play a minor role. This can be observed on the slight discrepancy of the heat dissipation decay that occurred in the necking stage of the bubbles for nanofluids with the same kind of nanoparticles and different concentration. For the Au 0.1 wt% nanofluid, a heat dissipation decay of 350 W/m2 was reported, whilst for the Au 0.5 wt% nanofluid, the same decay was only of 280 W/m2. The results of the numerical model concerning velocity fields indicated a sudden acceleration at the bubble detachment, as can be qualitatively analyzed in the thermographic images obtained in this work. Additionally, the temperature fields of the analyzed region present the same tendency as the experimental results.

scholarly journals Experimental and Numerical Study on Water Filling and Air Expelling Process in a Pipe with Multiple Air Valves under Water Slow Filling Condition

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2511
Author(s):  
Jintao Liu ◽  
Di Xu ◽  
Shaohui Zhang ◽  
Meijian Bai
Keyword(s):  
Numerical Model ◽  
Stokes Equations ◽  
Numerical Study ◽  
Practical Method ◽  
Navier Stokes ◽  
Physical Processes ◽  
Two Phase ◽  
Saint Venant Equations ◽  
Water Filling ◽  
Air Valve

This paper investigates the physical processes involved in the water filling and air expelling process of a pipe with multiple air valves under water slow filling condition, and develops a fully coupledwater–air two-phase stratified numerical model for simulating the process. In this model, the Saint-Venant equations and the Vertical Average Navier–Stokes equations (VANS) are respectively applied to describe the water and air in pipe, and the air valve model is introduced into the VANS equations of air as the source term. The finite-volume method and implicit dual time-stepping method (IDTS) with two-order accuracy are simultaneously used to solve this numerical model to realize the full coupling between water and air movement. Then, the model is validated by using the experimental data of the pressure evolution in pipe and the air velocity evolution of air valves, which respectively characterize the water filling and air expelling process. The results show that the model performs well in capturing the physical processes, and a reasonable agreement is obtained between numerical and experimental results. This agreement demonstrates that the proposed model in this paper offers a practical method for simulating water filling and air expelling process in a pipe with multiple air valves under water slow filling condition.

Experimental and Numerical Study of Methanol-Water Mixture Single-Phase Heat Transfer in a Micro-Channel Heat Sink

2012 ◽  
Author(s):  
Chun K. Kwok ◽  
Matthew M. Asada ◽  
Jonathan R. Mita ◽  
Weilin Qu
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Sink ◽  
Single Phase ◽  
Numerical Study ◽  
Pure Water ◽  
Molar Fraction ◽  
Water Mixture ◽  
Micro Channel ◽  
Numerical Predictions

This paper presents an experimental study of single-phase heat transfer characteristics of binary methanol-water mixtures in a micro-channel heat sink containing an array of 22 microchannels with 240μm × 630μm cross-section. Pure water, pure methanol, and five methanol-water mixtures with methanol molar fraction of 16%, 36%, 50%, 63% and 82% were tested. Key parametric trends were identified and discussed. The experimental study was complemented by a three-dimensional numerical simulation. Numerical predictions and experimental data are in good agreement with a mean absolute error (MAE) of 0.87%.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

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