Flow of a Free Air Jet

Summary

The purpose of the experiment was to investigate the profile created by an air jet with a cut conical nozzle, to better understand the regions usually called the core, mixing region and the edge. It was determined that past the core, the velocity of the profile begins to decrease, while the volume flow rate increases linearly with axial distance from the nozzle. In addition, radially from the peak at the centreline, the velocity at a given point decreases parabolically, until it is zero at the edge of the jet. The nozzle also tended to spread out, with a divergence angle of roughly 8o (the nozzle geometry was slightly asymmetric).

 

Results

Experimental data for distances of 60mm, 180mm and 300mm away from the nozzle respectively. Note the broadly parabolic shape of all the graphs. N.b. ‘r’ is referring to the radial distance away from the centerline of the jet.

 

Note the region up to around 4D (120mm) along the centerline where velocity is roughly equal to the nozzle output velocity, before beginning to decline sharply, roughly linearly immediately.

 

The volume flow rate seems to have increased linearly with axial distance, from its initial value at the nozzle, for this region investigated.

 

The higher end of the nozzle gives a divergence angle of 7.41 degrees, while the lower end of the nozzle gives an angle of 8.53o, representing the extent to which the nozzle’s output affects the surrounding area.

 

Summary plan view representation of the regions of the jet. The rough scale for the velocity profiles is 18m/s is 55mm on the axial distance axis, and the three profiles are in scale with each other.

 

Report

Due to the lab being repeated for other years, the full report has not been uploaded. It is however available on request, using the contact details available.