Mushy zone equilibrium solidification of a semitransparent layer subject to radiative and convective cooling

2002 ◽  
Vol 45 (11) ◽  
pp. 2397-2405 ◽  
Author(s):  
Chengcai Yao ◽  
B.T.F Chung ◽  
G.-X Wang
Keyword(s):  
Mushy Zone ◽  
Convective Cooling ◽  
Equilibrium Solidification ◽  
Semitransparent Layer

Fundamental Issues and Recent Advancements in Analysis of Aircraft Brake Natural Convective Cooling

1998 ◽  
Vol 120 (4) ◽  
pp. 840-857 ◽  
Author(s):  
M. P. Dyko ◽  
K. Vafai
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Three Dimensional ◽  
Convective Cooling ◽  
Cooling Flow ◽  
Physical Mechanisms ◽  
Braking System ◽  
Flow And Heat Transfer ◽  
Convection Cooling

A heightened awareness of the importance of natural convective cooling as a driving factor in design and thermal management of aircraft braking systems has emerged in recent years. As a result, increased attention is being devoted to understanding the buoyancy-driven flow and heat transfer occurring within the complex air passageways formed by the wheel and brake components, including the interaction of the internal and external flow fields. Through application of contemporary computational methods in conjunction with thorough experimentation, robust numerical simulations of these three-dimensional processes have been developed and validated. This has provided insight into the fundamental physical mechanisms underlying the flow and yielded the tools necessary for efficient optimization of the cooling process to improve overall thermal performance. In the present work, a brief overview of aircraft brake thermal considerations and formulation of the convection cooling problem are provided. This is followed by a review of studies of natural convection within closed and open-ended annuli and the closely related investigation of inboard and outboard subdomains of the braking system. Relevant studies of natural convection in open rectangular cavities are also discussed. Both experimental and numerical results obtained to date are addressed, with emphasis given to the characteristics of the flow field and the effects of changes in geometric parameters on flow and heat transfer. Findings of a concurrent numerical and experimental investigation of natural convection within the wheel and brake assembly are presented. These results provide, for the first time, a description of the three-dimensional aircraft braking system cooling flow field.

Overall Effectiveness for a Film Cooled Turbine Blade Leading Edge With Varying Hole Pitch

2010 ◽  
Author(s):  
Thomas E. Dyson ◽  
Dave G. Bogard ◽  
Justin D. Piggush ◽  
Atul Kohli
Keyword(s):  
Turbine Blade ◽  
Hot Spots ◽  
Leading Edge ◽  
Stagnation Line ◽  
Convective Cooling ◽  
Impingement Cooling ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
Overall Effectiveness ◽  
Blade Leading Edge

Overall effectiveness, φ, for a simulated turbine blade leading edge was experimentally measured using a model constructed with a relatively high conductivity material selected so that the Biot number of the model matched engine conditions. The model incorporated three rows of cylindrical holes with the center row positioned on the stagnation line. Internally the model used an impingement cooling configuration. Overall effectiveness was measured for pitch variation from 7.6d to 9.6d for blowing ratios ranging from 0.5 to 3.0, and angle of attack from −7.7° to +7.7°. Performance was evaluated for operation with a constant overall mass flow rate of coolant. Consequently when increasing the pitch, the blowing ratio was increased proportionally. The increased blowing ratio resulted in increased impingement cooling internally and increased convective cooling through the holes. The increased internal and convective cooling compensated, to a degree, for the decreased coolant coverage with increased pitch. Performance was evaluated in terms of laterally averaged φ, but also in terms of the minimum φ. The minimum φ evaluation revealed localized hot spots which are arguably more critical to turbine blade durability than the laterally averaged results. For small increases in pitch there was negligible decrease in performance.

Modeling of a mushy zone during quasi-stationary solidification of TiAl alloy

2020 ◽  
Author(s):  
Olga M. Zhukova ◽  
Irina G. Nizovtseva ◽  
Eugeny V. Pavlyuk ◽  
Ilya O. Starodumov ◽  
Alexander A. Ivanov
Keyword(s):  
Mushy Zone ◽  
Tial Alloy

scholarly journals Homogenisation Efficiency Assessed with Microstructure Analysis and Hardness Measurements in the EN AW 2011 Aluminium Alloy

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1211
Author(s):  
Maja Vončina ◽  
Aleš Nagode ◽  
Jožef Medved ◽  
Irena Paulin ◽  
Borut Žužek ◽  
...  
Keyword(s):  
Experimental Data ◽  
Image Analysis ◽  
Phase Equilibrium ◽  
Aluminium Alloy ◽  
Phase Formation ◽  
Aluminium Alloys ◽  
Eutectic Phase ◽  
The Matrix ◽  
Equilibrium Solidification ◽  
Homogenisation Process

When extruding the casted rods from EN AW 2011 aluminium alloys, not only their homogenized structure, but also their extrudable properties were significantly influenced by the hardness of the alloy. In this study, the object of investigations was the EN AW 2011 aluminium alloy, and the effect of homogenisation time on hardness was investigated. First, homogenisation was carried out at 520 °C for different times, imitating industrial conditions. After homogenisation, the samples were analysed by hardness measurements and further characterised by microscopy and image analysis to verify the influence of homogenisation on the resulting microstructural constituents. In addition, non-equilibrium solidification was simulated using the program Thermo-Calc and phase formation during solidification was investigated. The homogenisation process enabled more rounded shape of the Al2Cu eutectic phase, equilibrium formation of the phases, and the precipitation in the matrix, leading to a significant increase in the hardness of the EN AW 2011 aluminium alloy. The experimental data revealed a suitable homogenisation time of 4–6 h at a temperature of 520 °C, enabling optimal extrusion properties.

Comparison of cracking sensitivity between high-permeability 1.5 wt% Si steel and 6.5 wt% Si steel in mushy zone

2020 ◽  
Vol 510 ◽  
pp. 166927
Author(s):  
W.L. Hu ◽  
Y.X. Zhang ◽  
G. Yuan ◽  
X.M. Zhang ◽  
J.H. Zhao ◽  
...  
Keyword(s):  
Mushy Zone ◽  
High Permeability ◽  
Cracking Sensitivity

Permeability in the Mushy Zone

2010 ◽  
Vol 649 ◽  
pp. 399-408 ◽  
Author(s):  
R.G. Erdmann ◽  
D.R. Poirier ◽  
A.G. Hendrick
Keyword(s):  
Mushy Zone ◽  
Volume Fraction ◽  
Primary Dendrite ◽  
Fluid Velocity ◽  
Interdendritic Liquid ◽  
Creeping Flow ◽  
Liquid Region ◽  
Local Volume ◽  
Local Volume Fraction ◽  
Deterministic Function

When modeled at macroscopic length scales, the complex dendritic network in the solid-plus-liquid region of a solidifying alloy (the “mushy zone”) has been modeled as a continuum based on the theory of porous media. The most important property of a porous medium is its permeability, which relates the macroscopic pressure gradient to the throughput of fluid flow. Knowledge of the permeability of the mushy zone as a function of the local volume-fraction of liquid and other morphological parameters is thus essential to successfully modeling the flow of interdendritic liquid during alloy solidification. In current continuum models, the permeability of the mushy zone is given as a deterministic function of (1) the local volume fraction of liquid and (2) a characteristic length scale such as the primary dendrite arm spacing or the reciprocal of the specific surface area of the solid-liquid interface. Here we first provide a broad overview of the experimental data, mesoscale numerical flow simulations, and resulting correlations for the deterministic permeability of both equiaxed and columnar mushy zones. A extended view of permeability in mushy zones which includes the stochastic nature of permeability is discussed. This viewpoint is the result of performing extensive numerical simulations of creeping flow through random microstructures. The permeabilities obtained from these simulations are random functions with spatial autocorrelation structures, and variations in the local permeability are shown to have dramatic effects on the flow patterns observed in such microstructures. Specifically, it is found that “lightning-like” patterns emerge in the fluid velocity and that the flows in such geometries are strongly sensitive to small variations in the solid structure. We conclude with a comparison of deterministic and stochastic permeabilities which suggests the importance of incorporating stochastic descriptions of the permeability of the mushy zone in solidification modeling.

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