Numerical investigation of chocked converging-diverging nozzles for thruster application (normal shock wave)

Small scale spacecraft generally need low thrust and these characteristics 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. A computational work is carried out using Spalart-Allmaras model, two-dimensional, axisymmetric, coupled solver and linearized using implicit scheme. The nozzles have a throat diameter of 11 mm, an area ratio of 4 and 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. Also, it can be observed that the strength of the normal shock depends on the viscous loss, where an increase in viscous loss tends to reduce the normal shock strength.