Optimal Expansion Angle for Viscous Supersonic Flow in 2-D Micro-Nozzles

Louisos, William; Hitt, Darren L.

doi:10.2514/6.2005-5032

Cited by 17 publications

(8 citation statements)

References 9 publications

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“…Our investigations show that the past references (Alexeenko et al 2002(Alexeenko et al , 2006Louisos and Hitt 2005;Liu et al 2006;Xie 2007) have not investigated the physics of high Knudsen number flows in nanonozzles. In this section, we study the effects of inlet Knudsen number on the nanonozzle flow field, cases 6 and 7.…”

Section: Flow In Nanonozzlesmentioning

confidence: 82%

“…However, the encountered obstacles promote the researchers to choose the kinetic-based approaches, such as the direct simulation Monte Carlo (DSMC) (Bird 1994), to simulate flow in such small scales with a wide range of rarefaction regimes. Literature shows that DSMC has been largely used to predict the flow field inside micro/nanoscale devices such as micro/nanoscale channels (Xue et al 2003;Wang and Li 2004;Yang et al 2009) and nozzles (Alexeenko et al 2002(Alexeenko et al , 2006Louisos and Hitt 2005;Liu et al 2006;Xie 2007). We mainly focus on the activities performed in the latter ones.…”

Section: Introductionmentioning

confidence: 99%

“…They investigated the effect of tangential momentum accommodation coefficient on the flow behavior and showed that the flow would depend on this coefficient weakly if it increases from 0.8 to 1. Louisos and Hitt (2005) solved the NS equations and studied the effects of micronozzle geometry on its performance. They reported a remarkable reduction in the nozzle thrust as the divergent angle exceeded over 60°.…”

Section: Introductionmentioning

confidence: 99%

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Study of subsonic–supersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver

Darbandi

Roohi

2010

Microfluid Nanofluid

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We use an extended direct simulation Monte Carlo (DSMC) method, applicable to unstructured meshes, to numerically simulate a wide range of rarefaction regimes from subsonic to supersonic flows through micro/nanoscale converging-diverging nozzles. Our unstructured DSMC method considers a uniform distribution of particles, employs proper subcell geometry, and follows an appropriate particle tracking algorithm. Using the unstructured DSMC, we study the effects of back pressure, gas/surface interactions (diffuse/specular reflections), and Knudsen number on the flow field in micro/nanoscale nozzles. If we apply the back pressure at the nozzle outlet, a boundary layer separation occurs before the outlet and a region with reverse flow appears inside the boundary layer. Meanwhile, the core region of inviscid flow experiences multiple shock-expansion waves. In order to accurately simulate the outflow, we extend a buffer zone at the nozzle outlet. We show that a high viscous force creation in the wall boundary layer prevents any supersonic flow formation in the divergent part of the nozzle if the Knudsen number exceeds a moderate magnitude. We also show that the wall boundary layer prevents forming any normal shock in the divergent part. In reality, Mach cores would appear at the nozzle center followed by bow shocks and expansion region. We compare the current DSMC results with the solution of the NavierStokes equations subject to the velocity slip and temperature jump boundary conditions. We use OpenFOAM as a compressible flow solver to treat the Navier-Stokes equations.

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Section: Flow In Nanonozzlesmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Study of subsonic–supersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver

Darbandi

Roohi

2010

Microfluid Nanofluid

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“…There have been a number of numerical studies on the thrust performance of microthruster nozzles, but most of the works focused on the steady performance [2,3], and the effect of distortions in the nozzle geometry has not been analyzed. If the duration of the ignition or distinction period is not negligible, thrust during the unsteady propulsion periods may have a substantial effect on the thrust performance of a microthruster.…”

Section: Introductionmentioning

confidence: 99%

Effect of Unsteadiness and Nozzle Asymmetry on Thrust of a Microthruster

Kim

Kwon

Lee

2012

Nanoscale and Microscale Thermophysical Engineering

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Due to the small size and short propulsion pulses of solid propellant microthrusters, unsteady characteristics and/or fabrication errors may cause appreciable effects on the total thrust. The present work simulates a 2D planar and conical nozzle of 200 µm throat diameter using the traditional momentum equations and turbulence closure model. Unsteady characteristics were found to be insensitive to the inlet mass flux but sensitive to the chamber size. The characteristic time of transient momentum variations in the nozzle was found to be on the order of 0.1 ms, and that for decay was smaller than that for development by about 25%. This work confirmed that the magnitude of thrust was not sensitive to distortions in the nozzle geometry. A mismatch of the nozzle throat changed the position of sonic plane, but its effect on thrust was almost negligible.

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“…They investigated the effect of tangential momentum accommodation coefficient magnitude on the flow behavior and showed that the flow would weakly depend on this coefficient when it was increased from 0.8 to 1. Louisos and Hitt [ 13] used the NS equations and studied the geometrical effects on the micronozzle performance. They reported a remarkable reduction in nozzle thrust as the angle of micronozzle divergent parts was increased over 30 degrees.…”

Section: Introductionmentioning

confidence: 99%

Physical Aspects of Rarefied Gas Flow in Micro to Nano Scale Geometries Using DSMC

Roohi

Darbandi

Mirjalili

et al. 2009

39th AIAA Fluid Dynamics Conference

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Rarefied gas flow in micro/nano electro mechanical systems (MEMS/NEMS) does not perform exactly as that in macro-scale devices. The main goal in this study is to investigate mixed subsonic-supersonic flows in micro/nano channels and nozzles and to provide physical descriptions on their behaviors. We use DSMC method as a reliable numerical tool to extend our simulation. It is because the DSMC provides accurate solution for the Boltzmann equations over the entire range of rarefied flow regime or Knudsen numbers. As is known, the appearance of oblique/normal shocks at the inlet of a channel or a nozzle adds to the complexity of internal flow field analyses. We found some very unique physical aspects of micro/nano flows including mixed supersonic-subsonic flow regimes in constant area ducts and the attenuation of emitted shocks, which are attributed to the strong viscous forces and dominant rarefaction effects in micro/nano scales. We simulated nozzle flow under different flow conditions including different Knudsen and Reynolds numbers and inlet-outlet pressure ratios. It was observed that as the Knudsen number increases, the viscous dissipation forces increase and the flow in nozzle would not be choked at its throat and no supersonic flow is observed in the divergent part. Contrary to the classical gas dynamics, no shock stands in the divergent part despite specifying a back pressure at the outlet. Alternatively, we observed that multiple expansion-compression waves would be generated and amplified as the back pressure was decreased.

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Optimal Expansion Angle for Viscous Supersonic Flow in 2-D Micro-Nozzles

Cited by 17 publications

References 9 publications

Study of subsonic–supersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver

Study of subsonic–supersonic gas flow through micro/nanoscale nozzles using unstructured DSMC solver

Effect of Unsteadiness and Nozzle Asymmetry on Thrust of a Microthruster

Physical Aspects of Rarefied Gas Flow in Micro to Nano Scale Geometries Using DSMC

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