NUMERICAL INVESTIGATION OF CHOCKED CONVERGING-DIVERGING NOZZLES FOR THRUSTER APPLICATION

The need for low-thrust propulsion systems for small scale spacecraft is growing. Low thrust characteristics generally lead to low Reynolds number flows from propulsive devices that utilize converging-diverging nozzle. In the present work, seven choked converging-diverging nozzle flow characteristics operating at Reynolds number of 46000 are numerically investigated using a commercial software FLUENT 6.1.22. Computational work is carried out using axisymmetric flow Spalart-Allmaras model, twodimensional, axisymmetric, coupled solver and linearized using implicit scheme. The nozzles, which are intended to be used for thruster application, have a throat diameter of 11 mm and an area ratio of 4. All six nozzles are derived from a nozzle with divergence angle of 28°, where the divergence angle is reduced while maintaining the area ratio. The main objective of this work is to investigate the performance and flow characteristic of nozzles with different geometry. Numerical findings show that there is thrust reduction observed as the divergence angle reduces from 28° to 10°, except for nozzle with divergence angles of 16° and 18°, where they produce thrusts higher than their derivative one. Numerical result also reveals that the flow separation phenomenon occurs inside all nozzles, where normal shock forms inside nozzles with divergence angle of 20°, 14° and 10°, and this shock degrades the performance of the nozzle in term of the thrust produced.