Effects of Nozzle Throat and Combustion Chamber Design Variables on Divergent Portion of the Nozzle

The main objective of this work is to investigate the effects of combustion chamber pressure, combustion chamber temperature and nozzle throat radius on length, weight, exit area and maximum von Misses stress of divergent portion of an optimum expansion nozzle having constant thickness. To examine this issue, different alternative rocket motors that can provide 7500 N thrust at 3000 m altitude under the optimum expansion conditions are designed. An open source Matlab code applying method of characteristics is used to determine suitable nozzle geometries each of them satisfies the thrust requirements with an optimum expansion for each different motor design. Thus, convergent portion of the nozzle dimensions are determined and variation of the nozzle length, nozzle exit area with the response variables are determined using response surface method. After that, maximum von Misses stress values are determined as a result of finite element analysis performed in Abaqus environment. Both of pressure and temperature loads of the finite element models are calculated using isentropic relations. Then, maximum von Misses stress and weight of the divergent portion of the nozzle geometries for a certain thickness and material are determined for each different design. Finally, variation of maximum von Misses stress and weight of the divergent portion of the nozzle with the response variables are determined using response surface method.