Numerical prediction of nozzle behavior of the CE-20 engine for developing a nozzle protection system (NPS) for testing at sea level

Overexpansion in a high area ratio rocket nozzle causes fluid pressure in the divergent part of the nozzle to drop below the ambient pressure. This leads to flow separation with formation of oblique shock waves. In this paper we present numerical investigations on the sea level performance of the cryogenic engine nozzle having an area ratio of 100. The modelling is done on a 2D axisymmetric plane using Ansys FluentTM (version 19.2). Meshing is done in ICEM CFD with closely spaced meshes near the throat and the nozzle wall for capturing the flow phenomena more closely and accurately in these areas. A density based K-ω SST model is used. Both free shock separation (FSS) and restricted shock separation (RSS) are detected for varying pressure ratios. Wall pressure is observed to reach higher peaks for RSS in comparison with FSS. Also, the nozzle is subjected to maximum thermal loading for RSS.