ASME nozzles are used to calibrate the mass flow in blowdown test facilities tests. Understanding of the boundary layer displacement thickness for the calibration nozzle is necessary to apply the proper correction to the measured results. Tests conducted with a standard nozzle but with two differing entrance conditions denoted as “A” and “B” show a significant difference in the discharge coefficient. Comparison to the theoretical curves for laminar and turbulent boundary layers suggests that entrance geometry “A” causes earlier transition in the nozzle than entrance geometry “B.”

A pinhole microphone is mounted in the sidewall of the nozzle to register the  pressure fluctuations near the exit. A “shear layer wedge” with a closely coupled microphone monitor the instability frequency of the exiting boundary layer. These devices are used to determine if the boundary layer is turbulent or laminar. 

Pinhole
microphone
results