| This paper focuses on the metal doped polymer and metal-mesh/polymer propellant,investigated the regulation mechanism on the propulsion performance of the doped metal particle and metal mesh structure numerically and experimentally,which lays a good foundation for further optimizing the propulsion performance of laser ablation propulsion.Numerical simulation of polymer doped with 20%metal by weight was carried out by numerical simulation system.The mechanism of metal doping structure on the propulsion performance of laser ablating polymer was analyzed from ablation morphology,shielding coefficient and flow field.It is found that the electron number density in the flow field is the key factor determining the shielding effect.When the peak electron number density in the flow field reaches the order of the critical electron number density,the absorption of laser ablated product on the incident laser is strong.The metal doping structure can increase the initial expanding velocity of polymer ablation products,but the grain-like erosion during the ablation process increases the final ablation mass,and along with it,the impulse and the specific impulse decreases.It is suggested that the doping ratio of metal particles can be decreased to reduce the erosion of metal particles.Preliminary experiments of POM doped with 1%and 10%aluminum and iron show that decreasing the metal doping ratio can improve the propulsion performance,with the maximum specific impulse reaching 313.0s,corresponding to the ratio of impulse to energy and specific impulse of 301.8N/MW and47.1%.Based on the problem of particle erosion in the presence of doped metal particle,the metal mesh/polymer propellant proposed was numerically investigated.It is found that the regulation mechanism of the metal mesh is mainly reflected in the metal mesh absorbs the laser energy to generate the high temperature and high pressure plasma in the vicinity of the metal mesh,which induces the polymer ablation product that reach the position of metal mesh to ionize and improve the axial expanding velocity of the ablation products,thus the impulse,ratio of impulse to energy and specific impulse were enhanced.The longer maintenance time of the high pressure on the ablation surface by metal mesh after the laser pulse is over also contributes to the improvement of propulsion performance.Besides,the effects of laser fluence and structure parameters of metal mesh on the regulation mechanism were investigated.The results show that the ionization effect is enhanced under high laser fluence,but the slowing down of the ablation rate of the polymer caused by the shielding effect limits the propulsion performance to further improve.The mesh spacing of metal mesh should be chosen to make the metal mesh play the role of induced ionization without deterring the expanding of polymer ablation products,and ensure that the high axial velocity region is large and complete,namely the LSD wave is complete.And the appropriate mesh height should ensure the polymer ablation products expanding axially and give the full play to its role in induced ionization at the same time.Finally,based on the numerical analysis results,a comparatively excellent metal mesh structure and low laser energy scheme was proposed,and the corresponding propulsion performance of the proposed scheme was verified through experiments.Under the conditions of mesh spacing of5mm,mesh height of 2mm and laser fluence of 14J/cm~2,the optimal specific impulse of386.7s was obtained,with ratio of impulse to energy and efficiency of 306.1N/MW and58.0%.In summary,the numerical and experimental study on the metal-particle-doped polymer and metal-mesh/polymer was carried out in this paper.Among which,the metal-mesh/polymer can greatly improve the propulsion performance of laser ablation propulsion,and the specific impulse of 386.7s was obtained.Definitely,this plan is the most promising method to realize the ground launch and single stage into orbit by laser ablation propulsion in the future. |
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