Joule heated hot wall models in hypersonic wind tunnel facilities for energy deposition studies

Abstract

Joule heating is a useful experimental technique for ground based hypersonic testing as it allows replication of the governing wall-to-freestream temperature ratio and thus better simulation of the aerothermodynamic environment of high-speed flight vehicles. This paper presents design considerations for using this hot-wall method for hypersonic wind tunnel models. A numerical analysis of material choice and thickness for creating rapid uniform high-temperature model conditions is presented. The influence of the method and location of energisation and structural requirements for the integration of joule heating in a hypersonic wind tunnel model is also examined numerically. Experimental results of a bench-top study incorporating the design elements for joule heating for studies analogues to thermal energy deposition are also presented. To replicate thermal energy deposition, graphite plates with a 1.0 or 2.5mm thickness were heated via joule heating to a base level of either 30W or 100W. After 120s of heating the plates were then exposed to a thermal pulse of either 550, 1200 or 1300W. The thermal-structural response of the plate was experimentally recorded with a measurement system incorporating infrared thermal cameras, single and two-colour pyrometers, a load cell and a 520 nm light Digital Image Correlation system suitable for use on hot wall models. Results from this bench-top study demonstrate a proof-of-concept for using joule heating for analogue thermal deposition studies. Temperature rises of ΔT on the order of 500 - 1000K were achieved on models with base temperatures of 450 - 600K achieved with this technique. Plate deflections as high as 3.2 - 4.1mm were recorded for 1.0mm plates with both stress and strain of the heated models resolved experimentally for base heating and pulsed energy conditions.