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'''Hele-Shaw flow''' (named after [[Henry Selby Hele-Shaw]]) is defined as [[Stokes flow]] between two parallel flat plates separated by an infinitesimally small gap. Various problems in fluid mechanics can be approximated to Hele-Shaw flows and thus the research of these flows is of importance. Approximation to Hele-Shaw flow is specifically important to micro-flows. This is due to manufacturing techniques, which creates shallow planar configurations, and the typically low [[Reynolds number]]s of micro-flows. | |||
The governing equation of Hele-Shaw flows is identical to that of the inviscid [[potential flow]] and to the flow of fluid through a porous medium ([[Darcy's law]]). It thus permits visualization of this kind of flow in two dimensions. | |||
==Mathematical formulation of Hele-Shaw flows== | |||
[[File:Hele Shaw Geometry.jpg|thumb|right|300px|A schematic description of a Hele-Shaw configuration.]] | |||
Let <math>x</math>, <math>y</math> be the directions parallel to the flat plates, and <math>z</math> the perpendicular direction, with <math>2H</math> being the gap between the plates (at <math>z=\pm H</math>). | |||
When the gap between plates is asymptotically small | |||
: <math>H \rightarrow 0, \, </math> | |||
the velocity profile in the <math>z</math> direction is parabolic (i.e. is a quadratic function of the coordinate in this direction). The equation relating the pressure gradient to the velocity is, | |||
: <math> {\mathbf u}={\mathbf \nabla} p \frac{z^2-H^2 }{2\mu} \, </math> | |||
where <math>{u}</math> is the velocity , <math>p(x,y,t)</math> is the local pressure, <math>\mu</math> is the fluid viscosity. | |||
This relation and the uniformity of the pressure in the narrow direction <math>z</math> permits us to integrate the velocity with regard to <math>z</math> and thus to consider an effective velocity field in only the two dimensions <math>x</math> and <math>y</math>. When substituting this equation into the continuity equation and integrating over <math>z</math> we obtain the governing equation of Hele-Shaw flows, | |||
: <math> \frac{\partial^2 p}{\partial x^2}+\frac{\partial^2 p}{\partial y^2}=0.</math> | |||
This equation is supplemented by the no-penetration boundary conditions on the side walls of the geometry, | |||
: <math> {\mathbf \nabla} p \cdot \hat n= 0 \, </math> | |||
where <math>\hat n</math> is a unit vector perpendicular to the side wall. | |||
==Hele-Shaw cell== | |||
The term Hele-Shaw cell is commonly used for cases in which a fluid is injected into the shallow geometry from above or below the geometry, and when the fluid is bounded by another liquid or gas. For such flows the boundary conditions are defined by pressures and surface tensions. | |||
== See also == | |||
* [[Lubrication theory]] | |||
* [[Stokes flow]] | |||
* [[Hele-Shaw clutch]] | |||
: A mechanical transmission clutch invented by Prof. Hele-Shaw, using the principles of a Hele-Shaw flow | |||
==References== | |||
*{{cite book | last = Lamb | first = Horace | authorlink =Horace Lamb| title = Hydrodynamics | publisher = Cambridge University Press | location = Cambridge | year = 1993 | isbn = 978-0-521-45868-9 }} | |||
* [http://www.cambridge.org/uk/series/sSeries.asp?code=CML&srt=T ''An Introduction to Fluid Dynamics'' by G. K. Batchelor] at Cambridge Mathematical Library. | |||
* [[Hermann Schlichting]], Klaus Gersten, ''Boundary Layer Theory'', 8th ed. Springer-Verlag 2004, ISBN 81-8128-121-7 <!-- 7th ed. New York: McGraw-Hill, 1979--> | |||
* [[L. M. Milne-Thomson]] (1996). ''Theoretical Hydrodynamics''. Dover Publications, Inc. | |||
[[Category:Fluid dynamics]] |
Latest revision as of 16:47, 6 February 2013
Hele-Shaw flow (named after Henry Selby Hele-Shaw) is defined as Stokes flow between two parallel flat plates separated by an infinitesimally small gap. Various problems in fluid mechanics can be approximated to Hele-Shaw flows and thus the research of these flows is of importance. Approximation to Hele-Shaw flow is specifically important to micro-flows. This is due to manufacturing techniques, which creates shallow planar configurations, and the typically low Reynolds numbers of micro-flows.
The governing equation of Hele-Shaw flows is identical to that of the inviscid potential flow and to the flow of fluid through a porous medium (Darcy's law). It thus permits visualization of this kind of flow in two dimensions.
Mathematical formulation of Hele-Shaw flows
Let , be the directions parallel to the flat plates, and the perpendicular direction, with being the gap between the plates (at ). When the gap between plates is asymptotically small
the velocity profile in the direction is parabolic (i.e. is a quadratic function of the coordinate in this direction). The equation relating the pressure gradient to the velocity is,
where is the velocity , is the local pressure, is the fluid viscosity.
This relation and the uniformity of the pressure in the narrow direction permits us to integrate the velocity with regard to and thus to consider an effective velocity field in only the two dimensions and . When substituting this equation into the continuity equation and integrating over we obtain the governing equation of Hele-Shaw flows,
This equation is supplemented by the no-penetration boundary conditions on the side walls of the geometry,
where is a unit vector perpendicular to the side wall.
Hele-Shaw cell
The term Hele-Shaw cell is commonly used for cases in which a fluid is injected into the shallow geometry from above or below the geometry, and when the fluid is bounded by another liquid or gas. For such flows the boundary conditions are defined by pressures and surface tensions.
See also
- A mechanical transmission clutch invented by Prof. Hele-Shaw, using the principles of a Hele-Shaw flow
References
- 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - An Introduction to Fluid Dynamics by G. K. Batchelor at Cambridge Mathematical Library.
- Hermann Schlichting, Klaus Gersten, Boundary Layer Theory, 8th ed. Springer-Verlag 2004, ISBN 81-8128-121-7
- L. M. Milne-Thomson (1996). Theoretical Hydrodynamics. Dover Publications, Inc.