Flow characterization of supersonic gas jets: Experiments and Simulations

TL;DR

This study combines experiments and simulations to characterize supersonic helium and nitrogen jets, measuring the zone of silence and jet velocities without skimmers, and validates the results with computational models.

Contribution

It introduces a skimmer-free method for measuring jet velocities and compares experimental data with simulations for the first time in this context.

Findings

Measured ZOS matches empirical and mathematical models.

Jet velocities inside ZOS agree with simulations within uncertainties.

Helium jet velocity is lower than terminal velocity due to nozzle losses.

Abstract

In present work, we report an experimental setup that has been developed to characterize highly under-expanded helium and nitrogen jets confined in a vacuum chamber. The evolution of Zone of Silence (ZOS) is studied and found that experimentally measured ZOS for helium and nitrogen jets are in agreement with empirical relation and mathematical model. The velocity of the jet inside ZOS is measured using a developed time of flight (TOF) probe without using a skimmer. We are able to measures the velocity of the gas jet itself compared to a skimmer-based method which measures the velocity of gas that is subjected to further expansion after the skimmer. Moreover, this method is free from skimmer interference and calibration involved with it. We observe that the measured velocity for helium is smaller than the terminal velocity. This can be attributed to losses which can occur due to nozzle geometry. Simulations are carried out using available DS2V code. Experimentally observed velocities of jets inside ZOS are compared with simulated values and are found to be in agreement within experimental uncertainties.