A Study On Unsteady Fully Pulsed Jet

The thrust is an important factor that can measure the advantage of rocket motors.Increasing the rocket thrust is significant to the promotion space technology and national defense strength.Recent researches show that the vortex ring generated by pulsed jet propulsion has the possibility to enhance the propulsive efficiency.Therefore,the purpose of this paper is to simulate the unsteady fully pulsed jet,to study the vortex formed by pulse-jet,to find whether the pulse jet propulsion method can improve the thrust and further reveal the mechanism,and to find factors that influence the impulse jet thrust.In this paper,FLUENT as a tool is used to simulate the process of fully pulsed jet with low Reynolds number and incompressible fluid.Use the experimental data in references to verify the accuracy of numerical simulation.The results show that,the propulsive efficiency of the pulse jet propulsion is higher than that of the steady jet under the same mass flow rate at low Reynolds number and incompressible flow.And also show that there are two reasons for the impulse jet to improve propulsive efficiency.First,there is a overpressure at the exit of the nozzle due to the impact of the vortex.The second is due to the non-steady state characteristics of pulse jet,making the combustion chamber pressure increases,resulting in increased thrust.For the different pulse distance to diameter ratio(L/D),the average thrust will be the largest when L/D is the formation number.The interaction of the vortex between the pulses causes the vorticity to decrease,vortex propagation velocity increases and the average pulse thrust decreased.The factors influencing the propulsive efficiency of pulsed jet are the nozzle outlet jet velocity function type,pulse distance to diameter ratio,nozzle diameter,nozzle geometry.