A modular method of characteristics framework for controllable-length axisymmetric high-speed wind tunnel nozzle design

Abstract This paper proposes a modular parametric framework for axisymmetric high-speed wind tunnel nozzle design, which innovatively introduces the Terminal Characteristic Line (TCL) theory to isolate upstream and downstream flow fields. It divides the wind tunnel nozzle into several modules for design. In the upstream initial expansion section module, this work improves the Method of Characteristics (MOC), which abandons empirical axial Mach number distributions and supports user-controlled length. In the downstream damping section module, it references the minimum-length nozzle (MLN) design method, serving as a case for modular design. The framework is developed in Python code and open-sourced on GitHub, which can design and output inviscid contours and boundary layer correction results based on user needs. Validation using Computational Fluid Dynamics (CFD), which covers multiple design cases from the framework, shows excellent outlet flow uniformity and demonstrates length-to-diameter ratio control capability.