Influence of divergent section on flow fields and discharge coefficient of ISO 9300 toroidal-throat sonic nozzle

• Inviscid transonic flow model and laminar boundary layer.
• Numerically and experimental data were conducted to verify the results of theory.
• The influence of divergent section was fully studied.
• A concept of effective critical flow was proposed.

The effect of divergent section of ISO 9300 toroidal-throat nozzle on discharge coefficient was analyzed based on the inviscid transonic flow model and laminar boundary layer theory. A series of numerical simulations were conducted to verify the results of theory, and investigate the effect of divergent section length L and diffuser angle θ operated at different Reynolds numbers. Combined with the numerical results in this study and the experimental data reported by Nakao, it showed the discharge coefficient increases with the rise of diffuser angle θ or the drop of divergent section length L. A lot of new results about the effect of divergent section were obtained. It indicated that the effect of divergent section on discharge coefficient of ISO 9300 toroidal-throat nozzle should be considered when Re<1.1×104. At last, a concept of effective critical flow was proposed to discuss the effect of divergent section on discharge coefficient.