Schlichting jet is a steady, laminar, round jet, emerging into a stationary fluid of the same kind with very high Reynolds number. The problem was formulated and solved by Hermann Schlichting in 1933,[1] who also formulated the corresponding planar Bickley jet problem in the same paper.[2] The Landau-Squire jet from a point source is an exact solution of Navier-Stokes equations, which is valid for all Reynolds number, reduces to Schlichting jet solution at high Reynolds number, for distances far away from the jet origin.

Flow description

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Consider an axisymmetric jet emerging from an orifice, located at the origin of a cylindrical polar coordinates  , with   being the jet axis and   being the radial distance from the axis of symmetry. Since the jet is in constant pressure, the momentum flux in the   direction is constant and equal to the momentum flux at the origin,

 

where   is the constant density,   are the velocity components in   and   direction, respectively and   is the known momentum flux at the origin. The quantity   is called as the kinematic momentum flux. The boundary layer equations are

 

where   is the kinematic viscosity. The boundary conditions are

 

The Reynolds number of the jet,

 

is a large number for the Schlichting jet.

Self-similar solution

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A self-similar solution exist for the problem posed. The self-similar variables are

 

Then the boundary layer equation reduces to

 

with boundary conditions  . If   is a solution, then   is also a solution. A particular solution which satisfies the condition at   is given by

 

The constant   can be evaluated from the momentum condition,

 

Thus the solution is

 

Unlike the momentum flux, the volume flow rate in the   is not constant, but increases due to slow entrainment of the outer fluid by the jet,

 

increases linearly with distance along the axis. Schneider flow describes the flow induced by the jet due to the entrainment.[3]

Other variations

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Schlichting jet for the compressible fluid has been solved by M.Z. Krzywoblocki[4] and D.C. Pack.[5] Similarly, Schlichting jet with swirling motion is studied by H. Görtler.[6]

See also

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References

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  1. ^ Schlichting, Hermann. "Laminare strahlausbreitung." ZAMM‐Journal of Applied Mathematics and Mechanics/Zeitschrift für Angewandte Mathematik und Mechanik 13.4 (1933): 260-263.
  2. ^ Schlichting, H (1979). Boundary-layer theory, Seventh Edition, McGraw-Hill Book Company
  3. ^ Schneider, W. (1981). Flow induced by jets and plumes. Journal of Fluid Mechanics, 108, 55-65.
  4. ^ Krzywoblocki, M. Z. (1949). On Steady, Laminar Round Jets in Compressible Viscous Gases for Behind the Mouth. Oesterr. Ing.-Arch, 3, 373-383.
  5. ^ Pack, D. C. (1954, January). Laminar flow in an axially symmetrical jet of compressible fluid, far from the orifice. In Mathematical Proceedings of the Cambridge Philosophical Society (Vol. 50, No. 1, pp. 98-104). Cambridge University Press.
  6. ^ Görtler, H. (1954). Decay of swirl in an axially symmetrical jet, far from the orifice. Revista matemática hispanoamericana, 14(4), 143-178.