Abstract

The convergent section of a converging-diverging (C-D) nozzle plays a fundamental role in accelerating subsonic flow to sonic conditions at the throat, directly influencing the overall efficiency of energy conversion in propulsion systems. This study investigates the effect of convergent angle on flow behavior using Computational Fluid Dynamics (CFD). A 2D axisymmetric C-D nozzle model was analyzed in ANSYS Fluent under steady, compressible, and near-isentropic flow assumptions. Simulations were conducted for convergent angles of 15° and 30°, while maintaining constant divergent angle (6°), throat diameter (0.404 m), and other geometric parameters. Results demonstrate that the convergent angle significantly influences inlet and centerline flow characteristics. The 15° convergent angle consistently produced higher velocities at the inlet and along the centerline, accompanied by sharper reductions in pressure, temperature, and density, indicating more effective energy conversion from thermal to kinetic energy. Conversely, the 30° convergent angle resulted in higher inlet pressure, suggesting milder acceleration but improved inlet pressure stability. Importantly, the convergent angle showed negligible influence on exit flow properties, as the exit conditions were primarily governed by the divergent section geometry and the overall pressure ratio. The study concludes that a smaller convergent angle (15°) is favorable for achieving higher flow acceleration and efficient energy conversion in C-D nozzles, providing valuable design guidelines for aerospace and industrial applications.