Dynamic characteristics study of regression rate in variable thrust hybrid rocket motor

This paper aims at the dynamic characteristics study of variable thrust HRMs, for which a two-dimensional transient numerical model of HRM is established. Complete transient simulation based on dynamic mesh has been performed sequentially. An HRM with a thrust of three stages is designed and tested. The pressure, regression rate and thrust of the simulation results are in good agreement with the experiment data, which verifies the feasibility of the dynamic mesh technique for fuel regression simulation in HRMs. Specifically, the maximum deviations of pressure and thrust are less than 3.6% and 3.2%, respectively at the large mass flow rate stage. The numerical simulations show that the regression rate is not only related to the oxidizer mass flux, but also affected by the dynamic regression process. Max deviation of regression rate is 35% at the same oxidizer mass flux. Moreover, it is also demonstrated that the presence of vortex near front edge of fuel grain has a great effect on motor performance. Regression rate at front part of solid fuel is significantly high at the initial stage of throttling process, and regression rate downstream of the vortex obviously increases with time. In addition, the gas temperature of the pre-combustion chamber continuously increases with regression of fuel surface. Gas temperature of the post-combustion chamber is positively correlated with the oxidizer mass flow rate. This research can predict performance of HRMs more accurately, and provide a valuable guidance for variable thrust HRMs design. •A numerical simulation model of variable thrust hybrid rocket motor is established.•Dynamic mesh technique is used to simulate the regression of solid fuel surface.•A firing test of variable thrust hybrid rocket motor are conducted.•Average regression rate is different at the same oxidizer mass flux.•Regression rate of downstream of the vortex obviously increases with time.