Supersonic Nozzle Design for Arc Plasma Wind Tunnels

Abstract

A Mach 4 parallel flow supersonic nozzle, intended for arc-plasma wind tunnel applications, was designed for high-pressure and high-enthalpy working point conditions. The objective was to ensure effective cooling and structural integrity under conditions of no shock wave formation and parallel flow streamlines at the nozzle exit. The design was performed using a simplified approach, enabling the rapid examination of feasible design parameters, which were subsequently validated against Reynolds-Averaged Navier Stokes computational methods and finite-element structural simulations. The simplified approach was subdivided into the aerodynamic design, using the method of characteristics; aerodynamic-heating predictions, using integral and reference temperature methods; nozzle cooling-jacket performance predictions, based on semi-empirical correlations; and structural considerations, based on the pressure-induced and thermally-induced stresses in a circular cylinder. The simplified approach showed excellent agreement with computational methods and simulations. In particular, local cooling water temperature differences in the high heat-flux throat region never differed by more than 0.2°C. Moreover, small inner and outer nozzle wall temperature overpredictions, that resulted from neglecting axial conduction, validated our conservative design approach.