An Experimental Configuration to Study High-Enthalpy Radiating Flows Under Nonequilibrium De-excitation

Abstract

This paper introduces an experimental configuration, called the Prandtl-Meyer plus duct arrangement (PMD), designed to study high-enthalpy radiating flows undergoing nonequilibrium de-excitation. The original design proposed by Wilson, developed without the benefit of modern computational fluid dynamics (CFD), was inadequate for generating a sufficiently large undisturbed zone or achieving a uniform flow along the centerline, necessitating further refinement. Consequently, significant modifications were implemented to enhance PMD's performance, resulting in an expanded undisturbed zone and a uniform centerline flow that facilitate the measurements of nonequilibrium de-excitation.} A general design method is introduced, combining theoretical analysis and numerical simulations to tailor the flow conditions for various research objectives. The implementation involves considerations of the shock tube conditions, PMD configuration, and the effective measurement zone. The interplay between shock tube conditions and airfoil geometry generates diverse de-excitation patterns. The shock tube test time, transition onset location, and radiance intensity determine the effective measurement zone. An example utilizing N2 as the test gas demonstrates the method, achieving one-dimensional flow with thermal nonequilibrium and chemical freezing along the centerline, validating the method's effectiveness. An effective measurement zone of 200 mm is obtained under this condition, and the primary constraint under high-enthalpy conditions is the limited shock tube test time due to the high shock velocity and low fill pressure.