Meso-scale simulations of aluminum-enriched high-speed multi-material reactive flows

The filtered mass density function (FMDF) model has been employed for large-eddy simulations (LES) of compressible high-speed turbulent mixing and reacting flows. However, the mixing model remains a pressing challenge for FMDF methods, especially for compressible reactive flows. In this work, a temporal development mixing layer with two different convective Mach numbers, and , is used to investigate the mixing models. A simplified one-step reaction and a real hydrogen/air reaction are employed to study the mixing and turbulence-chemistry interaction. Two widely used mixing models, interaction by exchange with the mean (IEM) and Euclidean minimum spanning tree (EMST), are studied. Numerical results indicate that no difference is observed between the IEM and EMST models in simple reaction flows. However, for hydrogen/air reactions, the EMST model can predict the reaction more accurately in high-speed flow. For mixing models in compressible reactive flows, the requirement of localness preservation tends to be more essential as the convective Mach number increases. With the increase of compressibility, the sensitivity of the mixing model coefficient is reduced significantly. Therefore, the appropriate mixing model coefficient has a wider range. Results also indicate that a large error may result when using a fixed mixing model coefficient in compressible flows.

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Development of Micro Milling Machine and Experimental Study on Meso Scale Milling

First International Conference on Integration and Commercialization of Micro and Nanosystems, Parts A and B ◽

10.1115/mnc2007-21391 ◽

2007 ◽

Author(s):

Chengfeng Li ◽

Xinmin Lai ◽

Hongtao Li ◽

Linfa Peng ◽

Jun Ni

Keyword(s):

Chip Formation ◽

Cutting Forces ◽

High Speed ◽

End Milling ◽

Three Dimensional ◽

Chip Thickness ◽

Cutting Edge ◽

Micro Milling ◽

Milling Machine ◽

Meso Scale

This paper develops a three-axis micro milling machine for manufacturing meso-scale components and products. This machine utilizes high-speed miniature spindle to obtain appropriate cutting velocities, and three precision linear stages with 50 nm feed resolution to supply the relative motion. The PMAC2 controller is used to control three axes simultaneously, and a piezoelectric dynamometer is mounted on the X-Y stages to measure three-dimensional cutting forces for the real-time measurement and feedback. More than 200 cutting experiments of end milling operations are performed on the developed machine. When the machined feature ranges at meso scale, the characteristics and phenomena in milling process will heavily differ from those of conventional scale milling due to the size effects. The critical differences at meso scale arise from the breakdown of the assumptions of negligible edge radius effects. The roundness of cutting edge and the runout of spindle have a crucial impact on the chip formation process and the characteristics of cutting forces. The roundness of cutting edge also induces the existence of the minimum chip thickness and the intermittency of the chip formation at a low feed per tooth.

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Visualization and Parametric Study of Reaction Propagation in Meso-Scale Tubes

Volume 3: Combustion Science and Engineering ◽

10.1115/imece2009-12516 ◽

2009 ◽

Author(s):

Chan-Yu Wang ◽

Jun-Kai Wang ◽

Ming-Hsun Wu

Keyword(s):

High Speed ◽

Initial Pressure ◽

Transition Process ◽

Ambient Condition ◽

Oxygen Mixture ◽

Reaction Fronts ◽

Detonation Limits ◽

High Speed Cinematography ◽

Deflagration Wave ◽

Meso Scale

Reaction propagation of ethylene/oxygen and methane/oxygen mixtures in capillary tubes of 1 and 2 mm in diameters with initial pressure and temperature at ambient condition were experimentally visualized and analysed using high speed cinematography. Deflagrative flame was initiated in middle of the smooth tube, and the reaction fronts accelerated as they propagated towards the exits in the opposite directions. Lengths of the tubes investigated ranged from 0.4 to 1 m (one side), and deflagration-to-detonation transitions were observed for equivalence ratios between 0.5 and 3. The visible reaction front propagates at speeds approach Chapman-Jouguet speed for ethylene/oxygen mixture in the 1 mm and 2 mm tubes. An overshoot in propagation velocity was found during transition process. For leaner and richer mixtures beyond the detonation limits, steady deflagration wave propagation was observed. Reaction propagation in methane/oxygen mixture was also investigated. Several near-limit propagation modes were found.

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