Analysis of mixing and thrust diagnostics for shock tunnel hot nozzle testing

Abstract

Transient testing of hot engine exhaust nozzle flows is being pursued to enable cost and time savings of one to two orders of magnitude over steady-state hot-flow testing. This thesis presents the design and assessment of mixing and thrust measurement systems for use with a shock tunnel for these applications. Results from preliminary testing of focused-Schlieren, shearing interferometer, and Mie-scattering systems are presented. The Mie-scattering method was judged to be most applicable to measure flow mixedness for this application. However, shortcomings in the tested Mie-scattering system were identified. An improved system is proposed which is expected to provide flow density measurements to within 5% uncertainty with an optical resolution on the order of 5-10 mm. Starting with the typical design for a steady-state thrust measurement facility and an understanding of the differences between steady-state and shock tunnel testing, a thrust measurement system for use with shock tunnel testing was also developed. The requirement for a high frequency response demanded high structural stiffness in the thrust measurement system. Dynamic modeling confirmed the proposed thrust measurement system will satisfy that requirement. A detailed uncertainty analysis was used to identify the most important factors in the system uncertainty. The analysis suggests that the proposed thrust measurement system could be used to measure thrust coefficient to within 1% accuracy.