Lateral nozzle forces are known to cause severe structural damage during testing of any new rocket engine configuration under development. While three-dimensional computational fluid dynamics (CFD) methodology has been demonstrated to describe major side-load physics on rigid nozzles, actual hot-fire tests often show nozzle structure non-rigid flexing behavior during major side-load events. This can lead to structural damage.
Researchers at NASA Marshall have expanded and improved upon a rigid-wall analysis model to create new analysis software that provides an expanded modeling picture to account for the two-way responses between the rigid or flexible structure and fluid. This analysis capability now offers a more complete and realistic analysis of rocket-nozzle side-wall loading during the transient startup phase of hot-fire rocket engine testing.
The algorithm is based on an aeroelastic modeling capability that couples the necessary structural dynamics component into an anchored CFD methodology. The fluid dynamics component is an unstructured-grid, pressure-based computational formulation, whereas the structural dynamics component is based on the framework of modal analysis. Transient aeroelastic nozzle startup analyses at sea level have been conducted to demonstrate the successful simulation of nozzle-wall deformation with this tightly coupled algorithm.
The CFD methodology is based on a three-dimensional, finite-volume, viscous, chemically reacting, unstructured-grid, and pressure-based formulation. Time-varying transport equations of continuity, species continuity, momentum, total enthalpy, turbulent kinetic energy, and turbulent kinetic energy dissipation are solved using a time-marching subiteration scheme, thus providing transient load insights. The structural response due to fluid flow actions is analyzed using direct finite-element analysis.
The new capability has been demonstrated to provide computed generalized displacements, deformed nozzle shapes, deformation contours, physical lateral displacements, and axial nozzle-wall pressure profiles. Currently designed to be run on large computers, the software is ready for modification to enable use in a more practical parallel computing environment.