Effects of Injection Angle on the Structure of Choked Gaseous Jets

Abstract

The effects of injection angle on the structure of choked gaseous jets injected into quiescent air is investigated experimentally. The study is motivated by the use of choked gaseous jets in many industrial applications, including gas turbines, flares, and burners. The test conditions were as follows: a choked gas jet injected into a quiescent air environment, a straight cylindrical nozzle with an exit diameter of 1.6 mm, and three (3) injection angles of 0° (normal injection), 15°, and 30°. The diagnostics included particle image velocimetry using pulsed Nd:YAG lasers. The jet was seeded with aluminum oxide (1-micron) particles and was injected into an environment that was seeded with water-based fog. The field of view was limited to 22mm x 22mm. The results included jet and entrainment flow velocities and vorticity fields. A computational study of the present three nozzles, by our collaborators, was used to validate and interpret the present experimental results. The experimental results showed that the increase of the injection angle of the nozzle, from the normal position, caused the jet structure to become asymmetric and partially blocked the nozzle exit. This was due to the generation of a velocity slip plane inside the injection port initiating at the leading edge of the inlet section of the nozzle. The sharp entrance edge of the nozzle acted as the nozzle's throat and triggered an expansion fan that accelerated the flow to supersonic speeds of Mach 1.4 for the present test conditions from a simple straight cylindrical nozzle without the use of the traditional convergent-divergent (De Laval) nozzle geometry.