Aerodynamic characteristics of an element of surface washed by a high-speed free-molecular flow

1976 ◽  
Vol 10 (4) ◽  
pp. 697-700 ◽  
Author(s):  
G. K. Varakin ◽  
V. G. Farafonov
Keyword(s):  
High Speed ◽  
Aerodynamic Characteristics ◽  
Molecular Flow ◽  
Free Molecular Flow

Heat flux correlation for high-speed flow in the transitional regime

2016 ◽  
Vol 792 ◽  
pp. 981-996 ◽  
Author(s):  
Narendra Singh ◽  
Thomas E. Schwartzentruber
Keyword(s):  
Heat Flux ◽  
Flow Regime ◽  
Stagnation Point ◽  
High Speed ◽  
Higher Order ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Burnett Equations ◽  
Transition Flow ◽  
Stagnation Point Heat Flux

An analytical correlation is developed for stagnation-point heat flux on spherical objects travelling at high velocity which is accurate for conditions ranging from the continuum to the free-molecular flow regime. Theoretical analysis of the Burnett and super-Burnett equations is performed using simplifications from shock-wave and boundary-layer theory to determine the relative contribution of higher-order heat flux terms compared with the Fourier heat flux (assumed in the Navier–Stokes equations). A rarefaction parameter ($W_{r}\equiv M_{\infty }^{2{\it\omega}}/Re_{\infty }$), based on the free-stream Mach number ($M_{\infty }$), the Reynolds number ($Re_{\infty }$) and the viscosity–temperature index (${\it\omega}$), is identified as a better correlating parameter than the Knudsen number in the transition regime. By studying both the Burnett and super-Burnett equations, a general form for the entire series of higher-order heat flux contributions is obtained. The resulting heat flux expression includes terms with dependence on gas properties, stagnation to wall-temperature ratio and a main dependence on powers of the rarefaction parameter $W_{r}$. The expression is applied as a correction to the Fourier heat flux and therefore can be combined with any continuum-based correlation of choice. In the free-molecular limit, a bridging function is used to ensure consistency with well-established free-molecular flow theory. The correlation is then fitted to direct simulation Monte Carlo (DSMC) solutions for stagnation-point heat flux in high-speed nitrogen flows. The correlation is shown to accurately capture the variation in heat flux predicted by the DSMC method in the transition flow regime, while limiting to both continuum and free-molecular values.

THE INFLUENCE OF SURFACE ROUGHNESS ON SCATTERING OF FREE-MOLECULAR FLOW BY SOLID BODIES

2016 ◽  
Vol 47 (4) ◽  
pp. 367-388 ◽  
Author(s):  
Alexander Ivanovich Erofeev ◽  
Alexander Petrovich Nikiforov ◽  
Sergei Borisovich Nesterov ◽  
Ramul'ya Amirovna Nezhmetdinova
Keyword(s):  
Surface Roughness ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Solid Bodies

Study of drag molecular dynamics in the range of free-molecular flow.

Shinku ◽  
1990 ◽  
Vol 33 (3) ◽  
pp. 98-100
Author(s):  
N. LIU ◽  
S. J. PANG
Keyword(s):  
Molecular Dynamics ◽  
Molecular Flow ◽  
Free Molecular Flow

scholarly journals Gas Damping in Capacitive MEMS Transducers in the Free Molecular Flow Regime

Sensors ◽  
2021 ◽  
Vol 21 (7) ◽  
pp. 2566
Author(s):  
Boris A. Boom ◽  
Alessandro Bertolini ◽  
Eric Hennes ◽  
Johannes F. J. van den Brand
Keyword(s):  
Flow Regime ◽  
Gas Diffusion ◽  
Diffusion Time ◽  
Molecular Flow ◽  
Free Molecular Flow ◽  
Simple Analytical Model ◽  
Gas Damping ◽  
Wide Range ◽  
Capacitive Mems ◽  
Insight Into

We present a novel analysis of gas damping in capacitive MEMS transducers that is based on a simple analytical model, assisted by Monte-Carlo simulations performed in Molflow+ to obtain an estimate for the geometry dependent gas diffusion time. This combination provides results with minimal computational expense and through freely available software, as well as insight into how the gas damping depends on the transducer geometry in the molecular flow regime. The results can be used to predict damping for arbitrary gas mixtures. The analysis was verified by experimental results for both air and helium atmospheres and matches these data to within 15% over a wide range of pressures.

scholarly journals Research on aerodynamic characteristics of two-stage axial micro air turbine spindle for small parts machining

2020 ◽  
Vol 12 (12) ◽  
pp. 168781402098437
Author(s):  
Liu Jiang ◽  
Guo Zhiping ◽  
Miao Shujing ◽  
He Xiangxin ◽  
Zhu Xinyu
Keyword(s):  
High Speed ◽  
Aerodynamic Characteristics ◽  
Maximum Efficiency ◽  
Two Stage ◽  
Output Torque ◽  
Air Turbine ◽  
Solid Foundation ◽  
Computational Fluid Dynamics Cfd ◽  
Micro Machine ◽  
Small Parts

In order to meet the requirements of output torque, efficiency and compact shape of micro-spindles for small parts machining, a two-stage axial micro air turbine spindle with an axial inlet and outlet is proposed. Based on the k-ω turbulence model of SST, the flow field and operation characteristics of the two-stage axial micro air turbine spindle were studied using computational fluid dynamics (CFD) combined with an experimental study. We obtained the air turbine spindle under different working conditions of the loss and torque characteristics. When the inlet pressure was 300 KPa, the output speed of the two-stage turbine was 100,000 rpm, 9% higher than that of a single-stage turbine output torque. The total torque reached 6.39 N·mm, and the maximum efficiency of the turbine and the spindle were 42.2% and 32.3%, respectively. Through the research on the innovative structure of the two-stage axial micro air turbine spindle, the overall performance of the principle prototype has been significantly improved and the problems of insufficient output torque and low working efficiency in high-speed micro-machining can be solved practically, which laid a solid foundation for improving the machining efficiency of small parts and reducing the size of micro machine tool.

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