No-slip condition

No-slip condition

In fluid dynamics, the no-slip condition for viscous fluids states that at a solid boundary, the fluid will have zero velocity relative to the boundary.

The fluid velocity at all fluid–solid boundaries is equal to that of the solid boundary.[1] Conceptually, one can think of the outermost molecules of fluid as stuck to the surfaces past which it flows.

Contents

Physical justification

Particles close to a surface do not move along with a flow when adhesion is stronger than cohesion.

Exceptions

As with most engineering approximations, the no-slip condition does not always hold in reality. For example, at very low pressure (e.g., at high altitude), even when the continuum approximation still holds there may be so few molecules near the surface that they "bounce along" down the surface. A common approximation for fluid slip is:

u - u_{Wall} = \beta \frac{\partial u}{\partial n}

where n is the coordinate normal to the wall and β is called the slip length. For an ideal gas, the slip length is often approximated as \beta \approx 1.15 \ell, where \ell is the mean free path.[2] Some highly hydrophobic surfaces have also been observed to have a nonzero but nanoscale slip length.

While the no-slip condition is used almost universally in modeling of viscous flows, it is sometimes neglected in favor of the 'no-penetration condition' (where the fluid velocity normal to the wall is set to the wall velocity in this direction, but the fluid velocity parallel to the wall is unrestricted) in elementary analyses of inviscid flow, where the effect of boundary layers is neglected.

The no-slip condition poses a problem in viscous flow theory at contact lines: places where an interface between two fluids meets a solid boundary. Here, the no-slip boundary condition implies that the position of the contact line does not move, which is not observed in reality. Analysis of a moving contact line with the no slip condition results in infinite stresses that can't be integrated over. The rate of movement of the contact line is believed to be dependent on the angle the contact line makes with the solid boundary, but the mechanism behind this is not yet fully understood.

See also

External links

References

  1. ^ Day, Michael A. (2004). "The no-slip condition of fluid dynamics". Erkenntnis 33 (3): 285–296. doi:10.1007/BF00717588. 
  2. ^ David L. Morris, Lawrence Hannon, Alejandro L. Garcia (1992). "Slip length in a dilute gas". Physical Review A 46 (8): 5279. Bibcode 1992PhRvA..46.5279M. doi:10.1103/PhysRevA.46.5279. 

Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • no-slip condition — prilipimo sąlyga statusas T sritis fizika atitikmenys: angl. no slip condition vok. Haftbedingung, f rus. условие прилипания, n pranc. condition d’adhérence, f …   Fizikos terminų žodynas

  • Slip — may refer to:* Packing slip, a shipping document that accompanies delivery packages * Slipway, a ramp on the shore by which ships or boats can be moved to and from the water * Ferry slip, a specialized docking facility that receives a ferryboat * …   Wikipedia

  • condition d’adhérence — prilipimo sąlyga statusas T sritis fizika atitikmenys: angl. no slip condition vok. Haftbedingung, f rus. условие прилипания, n pranc. condition d’adhérence, f …   Fizikos terminų žodynas

  • slip — slip1 [slip] vi. slipped, slipping [ME slippen < MLowG, akin to OHG slifan < IE * (s)leib , to glide, slip < base * (s)lei , slimy: see SLIDE] 1. to go quietly or secretly; move without attracting notice [to slip out of a room] 2. a) to… …   English World dictionary

  • Slip and fall — Slip and fall, in United States tort law, is a claim or case based on a person slipping (or tripping) and falling. It is a tort, and based on a claim that the property owner was negligent in allowing some dangerous condition to exist that caused… …   Wikipedia

  • slip — Ⅰ. slip [1] ► VERB (slipped, slipping) 1) lose one s balance or footing and slide unintentionally for a short distance. 2) accidentally slide or move out of position or from someone s grasp. 3) fail to grip or make proper contact with a surface.… …   English terms dictionary

  • slip|per|i|ness — «SLIHP uhr ee nihs, SLIHP ree », noun. slippery quality or condition: »the slipperiness of graphite …   Useful english dictionary

  • slip — slip1 W2S3 [slıp] v past tense and past participle slipped present participle slipping ▬▬▬▬▬▬▬ 1¦(fall or slide)¦ 2¦(go somewhere)¦ 3¦(put something somewhere)¦ 4¦(give something to somebody)¦ 5¦(move)¦ 6¦(knife)¦ 7¦(get worse)¦ …   Dictionary of contemporary English

  • slip — slip1 [ slıp ] verb *** 1. ) intransitive if you slip, your feet slide accidentally and you lose your balance or fall over: Margaret slipped and broke her arm. slip on: Be careful you don t slip on the wet floor. a ) intransitive if something… …   Usage of the words and phrases in modern English

  • slip — I UK [slɪp] / US verb Word forms slip : present tense I/you/we/they slip he/she/it slips present participle slipping past tense slipped past participle slipped *** 1) [intransitive] if you slip, your feet slide accidentally and you lose your… …   English dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”