| A dual pulse solid rocket motor design consists of two burning combustion chambers which are separated by a pulse separation device(PSD).It can reasonably assign the thrust of the pulse motor and the ignition delay time.Dual pulse motors(DPM)have a good advantage of double range attack capability,large attack area,high maneuverability and small escape zone,and now it has become a new advanced flight power system.In this paper,the multi-physics coupling numerical methods were studied for engineering problems in the DPM.Then,a multi-physics coupling software platform was developed with dynamic overset grid method.After establishing the computational models for ignition process of the DPM with the metal diaphragm or elastomeric barrier type PSD,the gas impact characteristics,heat transfer characteristics of propellant,mechanical response of metal diaphragm or deformation characteristics of elastomeric barrier were analyzed deeply and systematically.The studies can provide an evaluable reference for the design of PSD and the project design of DPM.The main work of this paper is as follows.First,the governing equations of Reynolds Averaged Navier-Stokes equation and Fourier heat conduction were solved by the cell-center based multi-block finite volume method.One equation and two equation turbulence model were used for turbulence flow.The inviscid term was calculated by AUSMPW+schemes with reconstruction methods MUSCL.The viscous terms and diffusion terms were calculated by central difference scheme.The dual time-stepping approach in conjunction with LU-SGS implicit method was adopted for temporal discretization of unsteady flow.A finite element method was used to discretize structural dynamic equation in space,whereas the temporal time integration was achieved with the well-know Newmark algorithms.The reliability and accuracy of the current numerical approaches were validated by comparing with some complex experimental cases.Second,the loosely coupled partitioned method was addressed for the fluid-structure interaction problems,and the kinematic and kinetic continuum conditions were satisfied at the coupling interface.The dynamic overset grid method was used to deal with the boundary moving for large deformation and large displacement.The hole-map method was used to improve the efficiency of searching hole boundary,and a new overset grid method for multi-block patched grid was proposed for the numerical simulation of internal flow.A simple and practical method for searching donor cells of the interpolation points was proposed based on the vector identification method,and the information of overset region was transmitted using the bilinear interpolation method.The conjugate heat transfer process was addressed by a parallel approach with tight coupling algorithm,and heat flux consistent condition and equal temperature condition were used at the conjugate heat transfer surface.Thus,a number of classical complex multi-physics coupling cases were simulated,and the results show that the coupled numerical method was high reliability and high precision.Third,the multi-physics coupling software platform was developed based on the idea of structuralization and modularization.The key features of the platform include that the integration analysis ability of single physical and multi-physics coupling problem,flexibility of boundary condition processing,introducing periodic boundary condition,the ability to address boundary moving problem for large deformation and large displacement based on dynamic overset grid method,upgrading approach and expanding functional of the software in time.The verification experimental apparatus was designed for ignition process of a solid rocket motor and cool gas impact process.Afterward,the experimental models were simulated by the developed software platform,and a good agreement between simulated results and experimental data was found,indicating that the software platform was high credibility for engineering calculation.Fourth,the three-dimensional ignition transient of the second pulse in a metal diaphragm DPM was simulated with the developed software platform.Flow field characteristics of the combustion chamber before and after the rupture of the metal diaphragm and mechanical properties of metal diaphragm were analyzed,and the rupture time and burst pressure of the metal diaphragm were also obtained.The effects of ignition mass flow rate,metal diaphragm thickness and diameter,propellant burning rate on the ignition transient were studied.The results showed that flow field characteristics of the combustion chamber,the temperature distribution on the propellant surface and the pressure distribution on the metal diaphragm surface presented a very strong three-dimensional behavior at the initial stage of ignition.The rupture time and burst pressure of metal diaphragm were not only related to the pressure load on the surface of diaphragm,but also related to the history of the pressure load on it.Adjusting the thickness and diameter of metal diaphragm can effectively control the rupture time and burst pressure of the diaphragm,and the pressure spike in the combustion chamber.Fifth,the ignition transient of the second pulse in an elastomeric barrier DPM was simulated with the developed software platform.The deformation and swell process of elastomeric barrier were addressed by overset grid method.Flow field characteristics of the combustion chamber before and after the rupture of the elastomeric barrier and mechanical properties of elastomeric barrier were analyzed,and the rupture time and burst pressure of the elastomeric barrier were also obtained.The effects of ignition mass flow rate,propellant burning rate,and free volume of combustion chamber on the ignition transient were studied.The results showed that the rupture time and burst pressure of elastomeric barrier were related to the value,distribution and time history of the pressure load.The increase of igniter mass flow rate can reduce the rupture time of elastomeric barrier.The free volume of combustion chamber had a significant influence on the time for reaching a steady state of the dual pulse motor. |
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