Flow Past Sphere at High Re - Velocity Behavior

[redpepper303]

Hello,
I'm currently working on simulations in Solidworks of the flow of air (v = 450 m/s)
around a sphere (radius = 1.5 cm). The results have been used in a cut plot
representing the velocity in the x direction. The image is similar to this one:

https://www.llnl.gov/str/December01/gifs/Naka3.jpg

(Purple is high velocity and red is low velocity)
I was wondering why the velocity suddenly decreased so far in front of the
sphere and so spaced out (green zone), and then increases again.
Thank you for any answer!

 

[3DDave]

Under standard conditions your flow is supersonic. What you are seeing is a shock wave. This is where the velocity changes suddenly (slows) with an attendant increase in pressure and temperature. After a short time/distance the pressure re-accelerates the air, but to lower than stream velocity.

Since it is a blunt object, the shock wave is detached. If you substitute a sharp edged item, the shock wave will be an attached shock wave on the edge of the item. The shock wave can't attach to the sphere because the air at the sphere has already come to a stop and has stopped the air in front of it, up to the place that is in equilibrium with the shock wave.