Transient Side-Load Analysis of Out-of-Round Film-Cooled Nozzle Extensions

摘要

Understanding the impact of out-of-round nozzle extension on the nozzle side load during engine transient startup operations has garnered special interest from design engineers of late. The out-of-round nozzle extension could be the result of asymmetric internal stresses, deformation induced by previous tests, and asymmetric loads induced by hardware attached to the nozzle. The objective of this study was to computationally investigate the effect of out- of-round nozzle extension on the nozzle side loads during an engine startup transient. The rocket engine studied encompasses a regeneratively cooled chamber and nozzle, along with a film-cooled nozzle extension. The computational methodology is based on an unstructured-grid pressure-based computational fluid dynamics formulation, and on transient inlet boundary flow properties derived from an engine system simulation. Six three- dimensional cases were performed, with the out of roundness achieved by three different degrees of ovalization, elongated on lateral v and z axes: one slightly ovalized, one more ovalized, and one significantly ovalized. The results show that the separation line jump was the primary peak side-load physics. Compared with the peak side load of the perfectly round nozzle, the peak side loads increased most for the slightly ovalized nozzle extensions. The peak side loads then reduced moderately from the slightly ovalized nozzle extensions to the more ovalized nozzle extensions. For the significantly ovalized nozzle extensions, the peak side loads dropped substantially from those of the slightly ovalized nozzle extensions, due to increased flow directionality.