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fluid dynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...
, Görtler vortices are secondary flows that appear in a boundary layer flow along a concave wall. If the boundary layer is thin compared to the radius of curvature of the wall, the pressure remains constant across the boundary layer. On the other hand, if the boundary layer thickness is comparable to the radius of curvature, the centrifugal action creates a pressure variation across the boundary layer. This leads to the centrifugal instability (Görtler instability) of the boundary layer and consequent formation of Görtler vortices. These phenomena are named after mathematician .


Görtler number

The onset of Görtler vortices can be predicted using the
dimensionless number Dimensionless quantities, or quantities of dimension one, are quantities implicitly defined in a manner that prevents their aggregation into unit of measurement, units of measurement. ISBN 978-92-822-2272-0. Typically expressed as ratios that a ...
called Görtler number (G). It is the ratio of centrifugal effects to the viscous effects in the boundary layer and is defined as : \mathrm = \frac \left( \frac \right)^ where : U_e = external velocity : \theta =
momentum thickness In Newtonian mechanics, momentum (: momenta or momentums; more specifically linear momentum or translational momentum) is the Multiplication, product of the mass and velocity of an object. It is a Euclidean vector, vector quantity, possessi ...
: \nu =
kinematic viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
: R = radius of curvature of the wall Görtler instability occurs when G exceeds about 0.3.


Other instances

A similar phenomenon arising from the same centrifugal action is sometimes observed in rotational flows which do not follow a curved wall, such as the rib vortices seen in the wakes of cylinders and generated behind moving structures.


References

* * {{DEFAULTSORT:Gortler Vortices Boundary layers Dimensionless numbers of fluid mechanics Fluid dynamics Fluid dynamic instabilities