Snmek 1

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Výzkumný ústav textilních stroju Liberec, a.s.
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Fabric air permeability(numerical modelling)

• Karel Adámek

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Definitions Permeability m/s Q m3/s / S
m2 Q air flow, S tested area Porosity Q
/ Qo Q flow with tested sample Qo flow
without sample
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3D model of satin 5/1 (one repeat of weave 5x5
yarns)
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Pressure distribution on fabric upper
surface(satin 5/1)
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Pressure distribution on fabric lower surface
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Velocity distribution in vertical cross-section
tangentially to one horizontal yarn
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Velocity distribution in vertical cross-section
in the middle between two adjoining yarns
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Velocity distribution slightly under the upper
fabric surface
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Velocity distribution in the middle of upper
yarns
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Velocity distribution in the middle between
upper and lower yarns
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Velocity distribution in the middle of lower
yarns
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Velocity distribution at level slightly above
the lower fabric surface
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Inlet level with inserted fabric
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Inlet level without inserted fabric
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Outlet level with inserted fabric
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Outlet level without inserted fabric
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Numerical evaluation of previous slides (pressure
gradient of 196 Pa)
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• The presented static flow modelling through an
  idealized fabric structure gives the good first
  imagination about the detailed influence of some
  parameters of fabric structure
• both warp / weft density,
• both warp / weft yarn diameters,
• type of binding,
• pressure difference etc.
• on the air flow around individual yarns and
  through the fabric structure and on the fabric
  air permeability, too.

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Numerical experiments

• For the flow modelling through the structure we
  can use the so-called porous jump
• dp / m Pa / m
• in any permeable structure. Comparing the
  geometry of numerical models, the porous jump is
  much more simple than real structure above.
• It is possible to determine two unknown
  parameters for porous jump definition from the
  relation
• dp f (v) const1 . v const2 . v2 .
• The first parameter is used in linear part of
  this relation (Darcys flow), the second one is
  used in quadratic part (dynamic pressure) of the
  relation.
• The necessary relation we can get by real
  experiment on measuring device or by numerical
  experiment by repeating above mentioned cases for
  several different inlet pressures.

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Pressure on yarn surfaces (flow in x direction
along the fabric surface)
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Flow in x direction along fabric surface path
lines
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Prepared under the support of Research Plan
No. MSM 4670900201 for 13th International
Conference Structure and Structural Mechanics of
Textiles TU Liberec, Czech Republic November
2006