Modal Analysis and Natural-frequency Testing of Supersonic Minimum-length Nozzles for Rocket Engines

Structural designers in the aerospace industry face challenges in developing good designs that consider both the structural performance and manufacturing cost during the early stages of development. In this work, detailed finite-element models for supersonic minimum length nozzles (MLNs) with centred expansion waves and variable exit sections are developed and analysed in order to study the natural frequencies of the nozzles. The MLN is designed using the method-of-characteristics under high temperatures to determine the appropriate nozzle contour that can achieve a uniform and parallel flow at the exit section. Experimental investigations and modal analyses are conducted for two types of three-dimensional supersonic nozzles with intensive aerospace application MLN and minimum-length dual-bell nozzle. The obtained results show a maximum difference of approximately ۹% for the first and second frequency modes and less than ۱۱% for the third frequency mode. The results of the equivalent model presented in this analysis exhibit good accuracy. This study focuses on the modal analysis of three-dimensional supersonic nozzles, based on several aspects, including the structural geometric variations (by considering different exit-section shapes such as square, elliptical, hexagonal and rectangular), material variations, exit Mach numbers, and thickness variations. The results of this study are encouraging and indicate that the geometry and type of material have significant effects on the values of the supersonic-nozzles’ modal frequencies.

کلیدواژه ها:

Supersonic nozzle ، Minimum length nozzle ، Analysis modal ، Frequencies ، Mode ، Msc.Patran/Nastran software