Study On Reducing Ablation Of Nozzle Throat By Boundary Layer Control Method

The high performance solid rocket motors(SRM) adopt a series of advanced technology, such as high pressure technology and new type high-energy propellant. The performance of SRM is advanced, while the recession of nozzle throat will be increased to an extreme extent. So it is significant to investigate nozzle erosion mechanisms and find effective methods to control nozzle throat erosion.Based on the throat material at present, a nozzle boundary layer control system is introduced in this paper which is an innovative design method of SRM. This method is used to control the boundary layer of nozzle throat, reduce the gas temperature and the concentration of oxidizing species in nozzle surface, and then decrease the recession of nozzle throat. The recession of nozzle throat is directly affected by the temperature of throat surface and the concentration of oxidizing species. An effective method to reduce throat erosion is found after the analysis of influence factors of nozzle throat erosion. The mechanism for decreasing the gas temperature and the concentration of oxidizing species in nozzle surface is illuminated through the mechanism analysis of nozzle erosion. Meanwhile, the effectiveness of this method for mitigating nozzle throat erosion is proved.A mathematical model is established using k -e two-equation model, which is applied to the calculation of NBLCS SRM field. In view of the erosion characteristic of graphite material, a two-equation model for thermochemistry erosion is found, which considers the erosion mechanism for both the kinetics and diffusion. The temperature within throat material is computed through instantaneous heat conduction equation. Gases and throat surface are connected with energy equation. The boundary layer for oxidizing species is considered in the surface of throat material. And the instantaneous recession of throat surface is also taken into account. Program MATLAB is used to compile Crank-Nicolson difference code for calculating nozzle erosion.A parametric study is conducted to determine the influence of NBLCS operating parameters as injection mass, orientation, temperature and the numbers of injection hole.The effectiveness of different parameters on reducing the gas temperature and the concentration of oxidizing species is compared. The influencing rule of these parameters on NBLCS is obtained ultimately. Under definite range, the effectiveness of NBLCS will become better with the increase of injection mass and the numbers of injection hole. The effectiveness of NBLCS will become better with the decrease of injection orientation and temperature. The recession of nozzle throat is calculated using the code compiled for the situation with and without NBLCS. Under an optimizing condition, NBLCS can decrease the recession of the nozzle throat by 80%. The feasibility of this method on mitigating nozzle erosion is testified in theoretical aspect.A nozzle assembly is designed to validate the effectiveness of the theoretical analysis of nozzle boundary layer control system on mitigating nozzle throat erosion. Parameters such as throat diameter, divergence ratio and inner outline for nozzle are confirmed. The emphases and difficulties on designing this experiment are discussed. Throat erosions with and without NBLCS are obtained in experiments. When nozzle boundary layer control system is adopted, the throat erosion of nozzle throat decreases by 57.71%. The validity of nozzle boundary layer control system for decreasing the recession of throat erosion is attested in experimental aspect.