Supersonic Pitot measurement in underexpanded jet

Schlieren visualization of a supersonic Mach 1.5 air jet issuing from a converging 2.54cm diameter nozzle (resulting in Mach 1 at the nozzle exit). A Prandtl Meyer expansion fan issues at the nozzle lip, and reflects on the opposing mixing layer as compression waves. These coalesce at around 1.1 jet diameter downstream, producing a small normal shock and oblique shocks. The whole process gives to the jet a barrel shape.
The pitot rake traverses the jet at two different downstream locations. Oblique shocks appear at the tip of the Pitot probes (except behind the small normal shock region, which is subsonic) and are reflected in the mixing layer. These shocks are being deflected as they go through expansion fans and compression waves.
Acquired at the Pennsylvania State University small scale jet noise laboratory.
Credit: J.Veltin and D.K.McLaughlin

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People & Blogs

Tags:

• supersonic
• pitot
• shocks
• expansion
• fan
• schlieren

[adamrisborg]

Is the purpose of this video to demonstrate that pitot measurements fundamentally alter the flow geometry within supersonic regimes, hence cannot be used to obtain useful pressure data?

Feel free to comment on some of my instability videos, your opinion would be great.

[JVeltin]

The flow geometry is essentially altered downstream of the probes, therefore not significantly affecting the measurement at the tip of the probes. What is mostly interesting is to see the reflection of the bow shocks in the mixing layer, as well as their deflection within the jet.

[mihir1310]

Have you performed CFD analsis on the free jet problem ? if yes, do you know what boundary conditions you use on the outlet ?

[bilimo]

This is a great video! Great work Dr. Veltin