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14.9: Wake Turbulence

With flying wings one often gets along with the usual rigid wake turbulence, since behind the wing no moments affecting surfaces are present. With multi-fixed-wing aircraft (tail, ducks, biplane) it is advisable, often even necessary to work with variable wake turbulence.

A lift-producing surface diverts the air flow, and at the wing tips vortices are formed. Surfaces located behind the wing are very strongly affected by this diverted flow. With the following functions one can start an iterative computation with variable wake turbulence.

To start an iterative computation with variable wake turbulence one of the following check-boxes must be selected:
'Wake Turbulence Corr. Single alignment'
or
'Wake Turbulence Corr. Complete alignment'.

The flow lines of wake turbulence consist of discrete pieces, which are one behind the other arranged as on a pearl necklet. Close behind the trailing edge these pieces have a small length, which becomes ever longer with increasing distance from trailing edge.
With the function 'Wake Turbulence Corr. Complete alignment' first all pieces of a flow line are aligned and than a new vortex computation is started.
With the function 'Wake Turbulence Corr. Single alignment' first the piece of a flow line near the trailing edge is aligned, than a new vortex computation is started. Afterwards the next piece of a flow line is aligned and again a new vortex computation is started and so on. The final result of the single alignment function is little more precise, on the other hand computing time increases significantly. In most cases the complete alignment function is sufficient.
Also a combination of the two functions is permitted, thus becomes the computation most exactly, results in however intolerable long computing times.



Select the marked button to make the wake turbulence visible.




The picture below shows rigid wake turbulence.



One can however see here only a small part of the wake turbulence, in reality the flow lines continues to the infinite. The program does well without a complete visualisation, since the graphic becomes otherwise very unclear.

The length of displayed wake turbulence can be entered manually into the input field 'Total length of elements [m]' or with the Up/Down-buttons near the input field. The dimensional unit for entered data is 'meter' [m].
This visible part of wake turbulence is divided into small elements, which become finer to the wing (sinusoidally). The number of visible elements can be set in the input field 'No. Elements Wake Turbulence'

The picture below shows the above wing computed with wake turbulence iteration. In the wing centre, the flow is diverted downwards and at the wing tips are vertices formed.



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