NEAR-WALL CHARACTERISTICS OF AN IMPINGING GASOLINE SPRAY AT INCREASED AMBIENT PRESSURE AND WALL TEMPERATURE

2009 ◽  
Vol 19 (11) ◽  
pp. 997-1012 ◽  
Author(s):  
Jochen Stratmann ◽  
D. Martin ◽  
P. Unterlechner ◽  
R. Kneer
Keyword(s):  
Wall Temperature ◽  
Ambient Pressure ◽  
Near Wall

Development of a turbulent near-wall temperature model and its application to channel flow

1986 ◽  
Vol 20 (3) ◽  
pp. 189-201 ◽  
Author(s):  
H. Akbari ◽  
A. Mertol ◽  
A. Gadgil ◽  
R. Kammerud ◽  
F. Bauman
Keyword(s):  
Channel Flow ◽  
Wall Temperature ◽  
Temperature Model ◽  
Near Wall

Effects of tertiary air damper opening on flow, combustion and hopper near-wall temperature of a 600 MWe down-fired boiler with improved multiple-injection multiple-staging technology

2018 ◽  
Vol 91 (4) ◽  
pp. 573-583 ◽  
Author(s):  
Minhang Song ◽  
Lingyan Zeng ◽  
Xiaoguang Li ◽  
Yibo Liu ◽  
Zhichao Chen ◽  
...  
Keyword(s):  
Wall Temperature ◽  
Multiple Injection ◽  
Near Wall

Heat Transfer Modeling and the Assumption of Zero Wall Temperature Fluctuations

1994 ◽  
Vol 116 (4) ◽  
pp. 855-863 ◽  
Author(s):  
T. P. Sommer ◽  
R. M. C. So ◽  
H. S. Zhang
Keyword(s):  
Heat Transfer ◽  
Wall Temperature ◽  
Transfer Problem ◽  
Solid Wall ◽  
Temperature Fluctuations ◽  
Wall Turbulence ◽  
Turbulent Heat ◽  
Fluctuating Temperature ◽  
Temperature Variance ◽  
Near Wall

At present, it is not clear how the fluctuating temperature at the wall can be properly specified for near-wall turbulent heat-flux models. The conventional approach is to assume zero fluctuating temperature or zero gradient for the temperature variance at the wall. These are idealized specifications and the latter condition could lead to an ill-posed problem for fully developed pipe and channel flows. In this paper, the validity and extent of the zero fluctuating wall temperature condition for heat transfer calculations are examined. The approach taken is to assume Taylor series expansions in the wall normal coordinate for the fluctuating quantities that are general enough to account for both zero and nonzero temperature fluctuations at the wall and to develop a near-wall turbulence model allowing finite values of the wall temperature variance. As for the wall temperature variance boundary condition, it is estimated by solving the coupled heat transfer problem between the fluid and the solid wall. The eddy thermal conductivity is calculated from the temperature variance and its dissipation rate. Heat transfer calculations assuming both zero and nonzero fluctuating wall temperature reveal that the zero fluctuating wall temperature assumption is quite valid for the mean field and the associated integral heat transfer properties. The effects of nonzero fluctuating wall temperature on the fluctuating field are limited only to a small region near the wall for most fluid/solid combinations considered.

Characterizing the thermal sensitivity of a gasoline homogeneous charge compression ignition engine with measurements of instantaneous wall temperature and heat flux

2005 ◽  
Vol 6 (4) ◽  
pp. 289-310 ◽  
Author(s):  
J Chang ◽  
Z Filipi ◽  
D Assanis ◽  
T-W Kuo ◽  
P Najt ◽  
...  
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Homogeneous Charge Compression Ignition ◽  
Combustion Stability ◽  
Emission Measurement ◽  
Compression Ignition ◽  
Hcci Engine ◽  
Charge Temperature ◽  
Near Wall ◽  
Homogeneous Charge

An experimental study was performed to provide qualitative and quantitative insight into the thermal effects on a gasoline-fuelled homogeneous charge compression ignition (HCCI) engine combustion. The single-cylinder engine utilized exhaust gas rebreathing to obtain large amounts of hot residual gas needed to promote ignition. In-cylinder pressure, heat release analysis, and exhaust emission measurement were employed for combustion diagnostics. Fast response thermocouples were embedded in the piston top and cylinder head surface to measure instantaneous wall temperature and heat flux, thus providing critical information about the thermal boundary conditions and a thorough understanding of the heat transfer process. Two parameters determining thermal conditions in the cylinder, i.e. intake charge temperature and wall temperature, were considered and their effect on ignition and burning rate in an HCCI engine was investigated through systematic experimentation. The approach allowed quantitative analysis, and separating qualitatively different effects on the core gas temperature from the effects of near-wall temperature stratification. The results show great sensitivity to changes in wall temperature and such like, but a somewhat weaker effect of intake charge temperature on HCCI combustion. Variations of combustion phasing and peak burn rates due to wall temperature changes can be compensated if the intake charge temperature is varied in the opposite direction and with a factor of 1.11. The combustion stability limit of the HCCI engine depends more on wall temperature than on intake charge temperature. Analysis of a large number of individual cycles indicates that decreasing intake temperature retards timing, and the burn rates change primarily as a function of ignition timing. In contrast, lowering the wall temperature led to greater reduction in the bulk burn rate and greater increase in cyclic variability than expected simply as a result of retarded ignition, thus indicating significance of the thermal stratification in the near-wall boundary layer.

Effect of wall cooling on boundary-layer-induced pressure fluctuations at Mach 6

2017 ◽  
Vol 822 ◽  
pp. 5-30 ◽  
Author(s):  
Chao Zhang ◽  
Lian Duan ◽  
Meelan M. Choudhari
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Wall Temperature ◽  
Pressure Fluctuation ◽  
Free Stream ◽  
Pressure Fluctuations ◽  
Turbulent Boundary Layers ◽  
Wall Pressure ◽  
Wall Region ◽  
Near Wall

Direct numerical simulations of turbulent boundary layers with a nominal free-stream Mach number of $6$ and a Reynolds number of $Re_{\unicode[STIX]{x1D70F}}\approx 450$ are conducted at a wall-to-recovery temperature ratio of $T_{w}/T_{r}=0.25$ and compared with a previous database for $T_{w}/T_{r}=0.76$ in order to investigate pressure fluctuations and their dependence on wall temperature. The wall-temperature dependence of widely used velocity and temperature scaling laws for high-speed turbulent boundary layers is consistent with previous studies. The near-wall pressure-fluctuation intensities are dramatically modified by wall-temperature conditions. At different wall temperatures, the variation of pressure-fluctuation intensities as a function of wall-normal distance is dramatically modified in the near-wall region but remains almost intact away from the wall. Wall cooling also has a strong effect on the frequency spectrum of wall-pressure fluctuations, resulting in a higher dominant frequency and a sharper spectrum peak with a faster roll-off at both the high- and low-frequency ends. The effect of wall cooling on the free-stream noise spectrum can be largely accounted for by the associated changes in boundary-layer velocity and length scales. The pressure structures within the boundary layer and in the free stream evolve less rapidly as the wall temperature decreases, resulting in an increase in the decorrelation length of coherent pressure structures for the colder-wall case. The pressure structures propagate with similar speeds for both wall temperatures. Due to wall cooling, the generated pressure disturbances undergo less refraction before they are radiated to the free stream, resulting in a slightly steeper radiation wave front in the free stream. Acoustic sources are largely concentrated in the near-wall region; wall cooling most significantly influences the nonlinear (slow) component of the acoustic source term by enhancing dilatational fluctuations in the viscous sublayer while damping vortical fluctuations in the buffer and log layers.

Bubble Size and Group Influence for CFD Simulation in Vertical Tube Upward Flow

2010 ◽  
Author(s):  
Songwei Li ◽  
Hong Zhang
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Void Fraction ◽  
Wall Temperature ◽  
Cfd Simulation ◽  
Vertical Tube ◽  
Size Group ◽  
Upward Flow ◽  
Wall Area ◽  
Near Wall

The near-wall bubble congregating in vertical tube upward flow exerts an influence on fluid heat transfer. A 0.5m test section is simulated using CFX10.0 to research the bubble influence on the heat transfer. The vapor-water two-phase CFD calculation is done. The bubbles are added at near wall area, taking no account of the mass transfer between water and vapor. The different bubble max diameter and the different MUSIG model size group get different calculation results, these results are compared, include the distribution of vapor void fraction, the wall temperature distribution and near-wall water temperature distribution, the bubble mean diameter. A guide setting is advised. The calculation result shows that the max bubble diameter and the MUSIG size group on the vapor void fraction distribution is large. The near-wall void fraction gets down to the least (nearly zero, while at the inlet, near wall vapor fraction is 0.95) at 0.1m∼0.14m axis height, then rises. The wall temperature gets highest at the same height, and then appears a flat, keeping this temperature about 0.1m long, after that the temperature gets down, then rises along the axis.

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