The shape factor ($H=\frac{\delta^*}{\theta}$) is the ratio of displacement thickness, a measure of the thickness of the boundary layer, to the momentum thickness, a measure of the shear stress. I think that a larger shape factor indicates that the boundary layer is larger and there is less shear stress, so it seems like a larger shape factor should be associated with a greater likelihood of separation. Is that right? If not, why?

  • 2
    $\begingroup$ There is no need to close this question. It is very clear what OP is asking. $\endgroup$
    – Koyovis
    Jul 28, 2019 at 4:25
  • $\begingroup$ @Koyovis It might be that I used the separation tag wrong. $\endgroup$
    – kilojoules
    Jul 28, 2019 at 21:04

1 Answer 1


Yes you're reasoning is spot on. As the momentum thickness decreases, that indicates the velocity gradient at the wall is less, indicating a greater likelihood of separation occurring.

  • $\begingroup$ If you answer your own question, more explanation and background is useful. $\endgroup$
    – Koyovis
    Jul 30, 2019 at 22:30

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .