Strategies to protect ram accelerator projectiles from in-tube gasdynamic heating

A serious problem in advancing ram accelerator technology is the very high in-tube heat transfer rate to the projectile. Herein, we examine a number of strategies for protecting the projectile from gasdynamic heating. Radiation cooling of the projectile and flying the projectile through alternating regions of fuel-oxidizer-diluent drive gas and pure hydrogen are found to be totally unworkable. The ablative cooling technique has serious problems with a substantial retreat of the projectile surface. A transpiration cooling technique using liquid ammonia is calculated to provide adequate protection of the projectile for ram accelerator missions from 3 to 7 or 8 km/sec. Techniques for flying the projectile in pure hydrogen are also examined. One may have a vortex arrangement with a pure hydrogen core surrounded by a fuel-oxidizer-diluent mixture. The projectile may also fly in pure hydrogen while the driving energy is supplied by a deflagrating or detonating solid coating on the tube wall or by electrical energy input. The techniques for flying the projectile in pure hydrogen are judged to be extremely complex and expensive to implement. The transpiration technique appears to be the most viable way to protect projectiles flying in the 4 - 7 km/sec range

Supersonic mixing and combustion control using streamwise vortices

In this paper, we present our experimental and numerical results for the supersonic mixing and combustion control. Our strategy of enhancing supersonic mixing is to use streamwise vortices. The reasons are (1) that in supersonic flows streamwise vortices can be generated quite easily and almost without additional losses in total pressure such as those due to shock waves, (2) that their breakdown into smaller scale, which is essential for mixing enhancement, can be controlled by their geometry in spanwise row configurations and by various combinations of their scales, intensity of circulation and rotational directions, and (3)that the hydrogen fuel can be injected into their core region. Several kind of alternating wedge struts are tested to examine the effects of the cited various combinations on the mixing enhancement. By presenting those results, we will discuss the formation mechanism of streamwise vortices and their downstream development, in particular the interaction between themselves in spanwise row configurations, their eventual breakdown into turbulent eddies. Firing tests are also carried out and the results for alternating wedge strut will be presented together with the results for a generic fuel injection strut for comparison. The results show the effectiveness of the present streamwise vortices for supersonic mixing enhancement and combustion control