The nozzle of solid rocket motor (SRM) is easily ablated by high temperature, high pressure, high speed, and corrosive particles, which affects the stability of rocket flight. Therefore, the measurement and characterization of the nozzle ablation rate are helpful in providing some guidance for the design of nozzle material and structure. However, due to the high surface roughness of the composite nozzle after ablation, it is difficult to obtain an accurate ablation rate by contact measurement methods. The 3D laser scanning system is a 3D non-contact measurement technology using structured light technology, phase measurement technology, and computer vision technology. It has the advantages of non-contact, large scanning size, flexibility, and portability. In this paper, a 3D reconstruction of the ablation nozzle is carried out based on the 3D laser scanning system. Additionally, the ablation rate of the nozzle is measured without cutting the actual specimen. Furthermore, the pressure, temperature, and surface convective heat transfer coefficient trends are numerically calculated and compared with the ablation rate. Additionally, the empirical formula between ablation rate and pressure, temperature, convective heat transfer coefficient is obtained empirically by the inversion analysis method. The empirical formula can provide theoretical guidance for nozzle size design and optimization. The results show that the non-contact 3D laser scanning system is a valuable method for reconstructing the model of the ablated nozzle, and the empirical formula of ablation rate can accurately predict the ablation rate of the nozzle.

In order to study the flow characteristics of a nozzle with large expansion ratio and its influence on the force on the nozzle, ground cold flow test research and a fluid–structure coupling simulation analysis were carried out (maximum expansion ratio ε = 30.25). The variation and pulsation characteristics of the pressure near the measuring point area and the inlet pressure were obtained through experiments. Through the analysis of the peak-to-peak value and average value, it was found that the average pressure after separation increases by 90%, but the peak-to-peak value increases by about five times, indicating that the pressure fluctuation after separation is much larger than before separation. The separation flow field under cold flow conditions was simulated using the CFD commercial calculation software Fluent to verify the correctness of the numerical calculations. The fluid–structure coupling analysis was carried out on a large expansion ratio (maximum expansion ratio ε = 48) full-scale nozzle, and the structural deformation characteristics of the nozzle under the separation conditions were studied. The research results show that flow separation occurs in the nozzle with a large expansion ratio under ground conditions. Before the separation point, the pressure pulsation on the nozzle wall is small, and the turbulent pulsation effect is weak. After the separation point, the pressure pulsation increases, and the turbulent pulsation effect is enhanced. When the total pressure decreases, the separation area of the nozzle increases, and the separation flow field presents a strong asymmetry. Reducing the total inlet pressure by half resulted in approximately 50 times the lateral load. Under the combined influence of the ground conditions and low total pressure, the large lateral load caused by the asymmetry of the separation flow field will cause the deformation of the nozzle structure to increase by 5.5 times. This research provides an important reference for the design and experiment of nozzles with a large expansion ratio.

As a key component of the solid rocket motor, nozzle ablation is very important to the performance of the motor. In order to study the influence of the law of nozzle ablation on motor performance, a two-dimensional axisymmetric model of a ground state nozzle and vacuum state nozzle before and after ablation was constructed on the basis of a reference profile, and the change law of pressure, temperature and velocity with ablation were studied. The comprehensive performance of the nozzle before and after ablation was calculated to evaluate the influence of ablation on motor performance. It was found that the profile ablation changed the shock wave distribution in the flow field of the expansion section, and the appearance of the ablation step also led to a new internal shock wave. The gas was compressed, and the flow direction, velocity, pressure, temperature, etc., were changed. After the ablation, the temperature and pressure of the nozzle outlet location increased, the velocity decreased, and the total thrust and specific impulse decreased.