Effects of Near Wall Flow and Non-equilibrium Reaction Coupling on Heat Flux Prediction Inside a 7-elements GOX/GCH4 Combustion Chamber

2021 ◽  
pp. 118021
Author(s):  
Jianfei Wei ◽  
Silong Zhang ◽  
Xingyu Zhou ◽  
Cheng Cheng ◽  
Jiang Qin ◽  
...  
Keyword(s):  
Heat Flux ◽  
Combustion Chamber ◽  
Equilibrium Reaction ◽  
Wall Flow ◽  
Reaction Coupling ◽  
Near Wall ◽  
Non Equilibrium

Wall heat transfer of unsteady near-wall flow in internal combustion engines

2019 ◽  
Vol 20 (7) ◽  
pp. 817-833 ◽  
Author(s):  
Yuji Harada ◽  
Kenji Uchida ◽  
Tatsuya Tanaka ◽  
Kiyotaka Sato ◽  
Qianjin Zhu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Combustion Chamber ◽  
Wall Turbulence ◽  
Wall Heat Transfer ◽  
Proposed Model ◽  
Engine Combustion ◽  
Wall Flow ◽  
Near Wall Turbulence ◽  
Near Wall

Although the near-wall turbulence is not fully developed in the engine combustion chamber, wall heat transfer models based on flow characteristics in fully developed near-wall turbulence are typically employed in engine simulations to predict heat transfer. Only few studies reported the wall heat transfer mechanism in near-wall flow where the near-wall turbulence was not fully developed as expected in the engine combustion chamber. In this study, the velocity distribution and wall heat flux in such a near-wall flow were evaluated using a rapid compression and expansion machine. In addition to the experimental approach, a numerical simulation with highly resolved calculation mesh was applied in various flow fields expected in the engine combustion chamber. As a result, the turbulent Reynolds number that represents the relationship between turbulent production and dissipation varied in the wall boundary layer according to the near-wall flow condition. This behavior affects the wall heat transfer. Considering this finding, a new model was formulated by introducing a ratio of turbulent Reynolds number in an intended near-wall flow to that in fully developed near-wall turbulence. It was confirmed that the proposed model could improve the prediction accuracy of wall heat flux even in near-wall flow where the near-wall turbulence was not fully developed. By applying the proposed model in engine computational fluid dynamics, it was found that the proposed model could predict the wall heat flux in a homogeneous charge compression ignition gasoline engine with acceptable accuracy.

Comparison of Near-Wall Flow and Heat Transfer of an Internal Combustion Engine Using Particle Image Velocimetry and Computational Fluid Dynamics

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Angela Wu ◽  
Seunghwan Keum ◽  
Mark Greene ◽  
David Reuss ◽  
Volker Sick
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Heat Flux ◽  
Computational Fluid Dynamics ◽  
Velocity Profile ◽  
Law Of The Wall ◽  
Experimental Heat ◽  
Flow And Heat Transfer ◽  
Wall Flow ◽  
Near Wall

In this study, computational fluid dynamics (CFD) modeling capability of near-wall flow and heat transfer was evaluated against experimental data. Industry-standard wall models for RANS and large-eddy simulation (LES) (law of the wall) were examined against the near-wall flow and heat flux measurements from the transparent combustion chamber (TCC-III) engine. The study shows that the measured, normalized velocity profile does not follow the law of the wall. This wall model, which provides boundary conditions for the simulations, failed to predict the measured velocity profiles away from the wall. LES showed a reasonable prediction in peak heat flux and peak in-cylinder pressure to the experiment, while RANS-heat flux was closer to experimental heat flux but lower in peak pressure. The measurement resolution is higher than that of the simulations, indicating that higher spatial resolution for CFD is needed near the wall to accurately represent the flow and heat transfer. Near-wall mesh refinement was then performed in LES. The wall-normal velocity from the refined mesh case matches better with measurements compared with the wall-parallel velocity. Mesh refinement leads to a normalized velocity profile that matches with measurement in trend only. In addition, the heat flux and its peak value matches well with the experimental heat flux compared with the base mesh.

Comparison of Near-Wall Flow and Heat Transfer of an Internal Combustion Engine Using Particle Image Velocimetry and Computational Fluid Dynamics

2018 ◽  
Author(s):  
Angela Wu ◽  
Seunghwan Keum ◽  
Mark Greene ◽  
David Reuss ◽  
Volker Sick
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Velocity Profile ◽  
Mesh Refinement ◽  
Measured Velocity ◽  
Law Of The Wall ◽  
Experimental Heat ◽  
Flow And Heat Transfer ◽  
Wall Flow ◽  
Near Wall

In this study, CFD modeling capability of near-wall flow and heat transfer was evaluated against experimental data. Industry-standard wall models for RANS and LES (law of the wall) were examined against near-wall flow and heat flux measurements from the transparent combustion chamber (TCC-III) engine. The study shows that the measured, normalized velocity profile does not follow law of the wall. This wall model, which provides boundary conditions for the simulations, failed to predict the measured velocity profiles away from the wall. LES showed reasonable prediction in peak heat flux and peak in-cylinder pressure to the experiment, while RANS-heat flux was closer to experimental heat flux but lower in peak pressure. The measurement resolution is higher than that of the simulations, indicating that higher spatial resolution for CFD is needed near the wall to accurately represent the flow and heat transfer. Near-wall mesh refinement was then performed in LES. The wall-normal velocity from the refined mesh case matches better with measurements compared to the wall-parallel velocity. Mesh refinement leads to a normalized velocity profile that matches with measurement in trend only. In addition, the heat flux and its peak value matches well with the experimental heat flux compared to the base mesh.

Statistical Mechanics of Thermotransport of a Heavy Impurity in an Insulating Solid

1971 ◽  
Vol 26 (1) ◽  
pp. 10-17 ◽  
Author(s):  
A. R. Allnatt
Keyword(s):  
Heat Flux ◽  
Time Correlation ◽  
Three Dimensions ◽  
Time Correlation Functions ◽  
Single Vacancy ◽  
One Dimensional ◽  
Enthalpy Of Activation ◽  
Heavy Impurity ◽  
The One ◽  
Non Equilibrium

AbstractA kinetic equation is derived for the singlet distribution function for a heavy impurity in a lattice of lighter atoms in a temperature gradient. In the one dimensional case the equation can be solved to find formal expressions for the jump probability and hence the heat of transport, q*. for a single vacancy jump of the impurity, q* is the sum of the enthalpy of activation, a term involving only averaging in an equilibrium ensemble, and two non-equilibrium terms in­volving time correlation functions. The most important non-equilibrium term concerns the cor­relation between the force on the impurity and a microscopic heat flux. A plausible extension to three dimensions is suggested and the relation to earlier isothermal and non-isothermal theories is indicated

Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

scholarly journals Performance of Turbulence Models and Near-Wall Treatments in Discrete Jet Film Cooling Simulations

1998 ◽  
Author(s):  
Jeffrey D. Ferguson ◽  
Dibbon K. Walters ◽  
James H. Leylek
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Turbulence Models ◽  
Viscous Sublayer ◽  
Reynolds Stress Model ◽  
Quality Data ◽  
Wall Functions ◽  
First Time ◽  
Near Wall ◽  
Non Equilibrium

For the first time in the open literature, code validation quality data and a well-tested, highly reliable computational methodology are employed to isolate the true performance of seven turbulence treatments in discrete jet film cooling. The present research examines both computational and high quality experimental data for two length-to-diameter ratios of a row of streamwise injected, cylindrical film holes. These two cases are used to document the performance of the following turbulence treatments: 1) standard k-ε model with generalized wall functions; 2) standard k-ε model with non-equilibrium wall functions: 3) Renormalization Group k-ε (RNG) model with generalized wall functions; 4) RNG model with non-equilibrium wall functions: 51 standard k-ε model with two-layer turbulence wall treatment; 6) Reynolds Stress Model (RSM) with generalized wall functions; and 7) RSM with non-equilibrium wall functions. Overall, the standard k-ε turbulence model with the two-layer near-wall treatment, which resolves the viscous sublayer, produces results that are more consistent with experimental data.

scholarly journals Investigation of the Turbulent Near Wall Flame Behavior for a Sidewall Quenching Burner by Means of a Large Eddy Simulation and Tabulated Chemistry

Fluids ◽  
2018 ◽  
Vol 3 (3) ◽  
pp. 65 ◽  
Author(s):  
Arne Heinrich ◽  
Guido Kuenne ◽  
Sebastian Ganter ◽  
Christian Hasse ◽  
Johannes Janicka
Keyword(s):  
Heat Flux ◽  
Large Eddy Simulation ◽  
Gas Turbines ◽  
Internal Combustion Engines ◽  
Heat Fluxes ◽  
Maximum Heat ◽  
Eddy Simulation ◽  
Tabulated Chemistry ◽  
Large Eddy ◽  
Near Wall

Combustion will play a major part in fulfilling the world’s energy demand in the next 20 years. Therefore, it is necessary to understand the fundamentals of the flame–wall interaction (FWI), which takes place in internal combustion engines or gas turbines. The FWI can increase heat losses, increase pollutant formations and lowers efficiencies. In this work, a Large Eddy Simulation combined with a tabulated chemistry approach is used to investigate the transient near wall behavior of a turbulent premixed stoichiometric methane flame. This sidewall quenching configuration is based on an experimental burner with non-homogeneous turbulence and an actively cooled wall. The burner was used in a previous study for validation purposes. The transient behavior of the movement of the flame tip is analyzed by categorizing it into three different scenarios: an upstream, a downstream and a jump-like upstream movement. The distributions of the wall heat flux, the quenching distance or the detachment of the maximum heat flux and the quenching point are strongly dependent on this movement. The highest heat fluxes appear mostly at the jump-like movement because the flame behaves locally like a head-on quenching flame.

scholarly journals In Vitro Study of Near-Wall Flow in a Cerebral Aneurysm Model with and without Coils

2010 ◽  
Vol 31 (8) ◽  
pp. 1521-1528 ◽  
Author(s):  
L. Goubergrits ◽  
B. Thamsen ◽  
A. Berthe ◽  
J. Poethke ◽  
U. Kertzscher ◽  
...  
Keyword(s):  
Cerebral Aneurysm ◽  
In Vitro Study ◽  
Vitro Study ◽  
Wall Flow ◽  
Aneurysm Model ◽  
Near Wall
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