Nonlinear Electrohydrodynamic Kelvin-Helmholtz Instability through Two Porous Layers with Suction / Injection : Viscous Potential Theory

2014 ◽  
Vol 7 (2) ◽  
pp. 129-154
Author(s):  
Galal M. Moatimid ◽  
Mohamed A. Hassan ◽  
Bassem E. M. Tantawy
Keyword(s):  
Potential Theory ◽  
Helmholtz Instability ◽  
Porous Layers

Three-Dimensional Viscous Potential Electrohydrodynamic Kelvin–Helmholtz Instability Through Vertical Cylindrical Porous Inclusions With Permeable Boundaries

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Galal M. Moatimid ◽  
Mohamed A. Hassan
Keyword(s):  
Dispersion Relation ◽  
Three Dimensional ◽  
Wave Number ◽  
Helmholtz Instability ◽  
Large Wave ◽  
Porous Layers ◽  
Azimuthal Wave ◽  
Azimuthal Wave Number ◽  
Streaming Velocity ◽  
The Stability

In this paper, the electrohydrodynamic three-dimensional Kelvin–Helmholtz instability of a cylindrical interface with heat and mass transfer between liquid and vapor phases is studied. The liquid and the vapor are saturated, two coaxial cylindrical porous layers, and the suction/injection velocities for the fluids at the permeable boundaries are also taken into account. The dispersion relation is derived and the stability analysis is discussed for various parameters. It is found that the streaming velocity has a destabilizing effect, while the axial electric field has a stabilizing one. The suction for both the liquid and the steam has a destabilizing effect in contrast with the injection at both boundaries. The flow through porous structure is more stable than the pure flow. The case of the axisymmetric (for zero value of the azimuthal wave number m) and asymmetric (for nonzero value of the azimuthal wave number m) disturbances at large wavelength (at the wave number k→0) are always stable. Meanwhile, it is the same dispersion relation for the plane geometry at large wave number. Finally, our results are corroborated by comparing them with the previous published results.

Numerical Simulation and Control of the Flow Around One or Two Ahmed Bodies

2012 ◽  
Author(s):  
Charles-Henri Bruneau ◽  
Emmanuel Creusé ◽  
Delphine Depeyras ◽  
Patrick Gilliéron ◽  
Iraj Mortazavi
Keyword(s):  
Short Distance ◽  
Bluff Body ◽  
Passive Control ◽  
The Body ◽  
Pressure Force ◽  
Helmholtz Instability ◽  
Porous Layers ◽  
Simulation And Control ◽  
And Control ◽  
Two Bodies

The aim of this work is to show that the drag coefficient of a bluff body is mainly linked to the circulation and the distance of the vortices in the close wake of the body. Thus an active control can be used to push away the vortices to decrease the pressure forces at the back. For the size of the vortices a passive control by means of porous layers is used taking benefit of the Kelvin-Helmholtz instability to change the vortex shedding. For two bodies with a short distance between them, the presence of strong vortices in the wake of the first body changes significantly the pressure force in front that governs the drag of the second body. The results of the control processes are illustrated on a single Ahmed body and on two Ahmed bodies following each other on top of a road.

In Situ microscopy of the anodic etching of silicon

1995 ◽  
Vol 53 ◽  
pp. 232-233
Author(s):  
Frances M. Ross ◽  
Peter C. Searson
Keyword(s):  
Composite Structures ◽  
High Surface ◽  
High Surface Area ◽  
Chemical Properties ◽  
Selective Etching ◽  
Silicon On Insulator ◽  
Second Phase ◽  
Porous Layers ◽  
New Class ◽  
Porous Semiconductors

Porous semiconductors represent a relatively new class of materials formed by the selective etching of a single or polycrystalline substrate. Although porous silicon has received considerable attention due to its novel optical properties1, porous layers can be formed in other semiconductors such as GaAs and GaP. These materials are characterised by very high surface area and by electrical, optical and chemical properties that may differ considerably from bulk. The properties depend on the pore morphology, which can be controlled by adjusting the processing conditions and the dopant concentration. A number of novel structures can be fabricated using selective etching. For example, self-supporting membranes can be made by growing pores through a wafer, films with modulated pore structure can be fabricated by varying the applied potential during growth, composite structures can be prepared by depositing a second phase into the pores and silicon-on-insulator structures can be formed by oxidising a buried porous layer. In all these applications the ability to grow nanostructures controllably is critical.

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