Find delta 99 of the boundary layer

I am trying to find the location of delta 99 (99 percent of the max velocity) in my velocity profile in a nozzle. I have the correct delta 99 value for the majority of my nozzle, but am having difficulty finding it near shocks (I understand that equations for boundary layers do not hold at shock/expansion fans).

Below is a snip of a velocity profile (Ux vs. y) near the shock. My current script searches for the first instance from the bottom by searching for when the derivative of Ux is negative and cutting off all points after. The current script finds delta 99 using a max velocity in the red circle. I would like to change the max velocity location to the green circle.

There isn't really a max velocity in the green circle, since the derivative is never negative, but ideally, I would like an artificial max velocity at the location show by the arrow below:

I would like to do it without knowing any of the values of velocity or height (completely soft coded). I already tried looking at the second derivative in Ux and y, but the grid spacing is so small, there is no noticable difference.

Any suggestions how I can soft code something for this and other profiles similar to this?

Answer 1

[Star Strider]

See if the findchangepts or ischange functions will do what you want. You may need to invert them (plot y vs Ux) for them to work.