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I came across the term "Boundary layer tripping" but I can't really underastand it. After searching on internet I cannot find any video or an image explaining that concept. Could you please explain what is "Boundary Layer tripping" with some figures/illustrations if possible?

I appreciate your help.

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    $\begingroup$ would this answer help to answer your question? $\endgroup$
    – Peter Kämpf
    Commented Apr 13, 2020 at 5:39

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Tripping the boundary layer refers to the action of artificially transitioning a laminar boundary layer into a turbulent one. It can happen intentionally (via turbulator) or unintentionally (via imperfect aero-smoothness, such as rivets, bolts, counter-sinks). At the point of boundary layer tripping, the surface protrusion destabilizes the laminar boundary layer and causes the transition to occur earlier than via natural Tollmien-Schlichting instability.

The following is an example of a turbulator tape. It is attached spanwise along the surface of the wing (facing flat against the surface) at the desired chord-wise location where the laminar-turbulent transition is to take place:

Turbulator tape

Since turbulent boundary layer has higher skin-friction drag than a laminar one of the same Reynolds number, unintentional boundary layer tripping is undesired. That's why wing surfaces must be made flush and smooth. At the same time, since a turbulent boundary layer is much better at resisting flow separation than a laminar boundary layer, tripping the boundary layer can be used to improve stability & control at high angle of attack at the expense of increased skin-friction drag.

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  • $\begingroup$ You might want to note that the tape is applied flat to the surface, not standing up on edge like in the photo! If I hadn't seen it before on gliders I would be mis-led by the photo. Thanks! $\endgroup$
    – quiet flyer
    Commented Apr 12, 2020 at 22:33
  • $\begingroup$ @quietflyer Edited. Thanks. $\endgroup$
    – JZYL
    Commented Apr 12, 2020 at 23:07
  • $\begingroup$ Your zig-zag tape in the picture is merely destabilizing the boundary layer so it will transition downstream without a big separation bubble. Direct tripping is achieved with a trip wire or with dimple tape. And at high lift coefficient tripping is indeed used to lower drag by avoiding a lengthy separation bubble. $\endgroup$
    – Peter Kämpf
    Commented Apr 13, 2020 at 5:32
  • $\begingroup$ @PeterKämpf Agreed $\endgroup$
    – JZYL
    Commented Apr 13, 2020 at 19:42

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