Cryogenic hypersonic advanced tank Technologies Project final report

Abstract

In future aviation and particularly in hypersonic systems new propellants will be used, such as liquid hydrogen, liquid methane and possibly liquid oxygen. Previous FP7 funded studies in Europe such as FAST20XX, ATLLAS or LAPCAT investigated advanced vehicles with these fuels for passenger transport like the SpaceLiner or Lapcat A2 and some of their constituent materials and associated propulsion challenges. The question of cryogenic propellant storage inside an airliner – although of critical importance but by far not yet mastered – had not been addressed in Europe in comparable detail. The need for more detailed investigations on liquid hydrogen or methane tanks in future airliners is not only urgent in hypersonic aviation, but is also essential for environmental reasons in subsonic aviation. New materials and design concepts are required, such as fiber based composite materials, in order to reduce the tank weight and to increase the structural performance. This is particularly important if the tank has load carrying functions. Different to current rocket launch systems, the durability through hundreds or even thousands of flight cycles must be assured. Tank liners are another essential element of a tank design in order to assure the material compatibility over long durations. The Cryogenic Hypersonic Advanced Tank Technologies (CHATT) project addressed these challenges within a comprehensive and multifold approach. The focus has been on sophisticated experimental material research campaigns, culminating in the development, manufacturing and testing of four different demonstrator tank structures, each involving individual technologies or design philosophies. On the material research level various CFRP material and layup combinations as well as liner material and CFRP/liner combinations have been evaluated in order to assess their applicability for future advanced hydrogen tank structures. Special attention has been paid on material behavior in cryogenic temperature environments, including micro-crack initiation, thermal cycling, and fatigue. Based on these results, suitable material systems have been selected and utilized for manufacturing of the four tank structures. The largest tank built is a cylindrical vessel with approximately 3 m in length and 1 m in diameter, utilizing a CFRP shell design wound on a polymer liner. Another, smaller cylindrical vessel has been manufactured with innovative dry-wind technology. A third vessel employs a liner-less design, while the fourth tank has been designed and manufactured as a multi-bubble tank suited for non-circular fuselage cross-sections. Testing of the tank structures involved pressurization and mechanical loading tests, as well as cryogenic fluid fill and drain experiments using liquid nitrogen. The material research and tank manufacturing campaigns in CHATT have been complemented by comprehensive system investigations for different types of hypersonic vehicles. These not only provided the reference environmental and load conditions for material and tank research, but also included related topics such as propellant management, propellant cross-feed designs for parallel staged vehicles, cabin environment control and power generation by using cryogenic fluids, and flight control under presence of fluid movement. In particular the propellant sloshing problem has been addressed on a theoretical as well as experimental level. High-fidelity CFD codes have been improved enabling detail investigations of sloshing phenomena. Simultaneously, approximate analytic models were assessed on how far the impact of sloshing on flight vehicle control could be simulated in a fast way. Via coupled analysis, also the impact of sloshing on vehicle aero-elastics and structural sizing could be assessed. Furthermore, analytical and/or numerical analysis tools for cylinder, multi-lobe, and multi-bubble tanks including insulations were developed. These codes have been coupled with high-order optimization suites for overall optimization of tanks. Further associated topics to cryogenic tanks have been investigated as well, theoretically and experimentally, such as ceramic heat exchanger technologies, roughness induced boiling, aerogels for insulation applications, or tank structural health monitoring. One of the central findings of the CHATT-project supported by manufacturing and material tests is the very promising potential of thin-ply CFRP technologies for cryogenic tank applications. Extensive material research and demonstrator tube testing campaigns proved the superior performance of thin-ply approaches for delaying or even preventing cryogenic temperature induced micro-cracking. The results indicate that liner-less and ultra-lightweight cryogenic tank systems could be realized using thin ply approaches.