Targeted Research Division, Transdisciplinary Fluid Integration Research Center

Ultra-High-Enthalpy Flow Laboratory

Concurrent Professor

Shigeru Obayashi

How is a large amount of energy, with which atoms and molecules can be ionized, input to

flows? What are the characteristics of such ultra-high-enthalpy flows? Then, what are their useful applications? Those questions are our basic research problems.

It is easy to input a 100 MJ/kg to you computer program. Yet, experimental generation of such ultra-high-enthalpy flow is not an easy task. In order to realize this, we utilize laser, explosives, compressed gas and electrical discharge. Fundamental phenomena associated with shock waves and unsteady, compressible fluid dynamics are studied. Also, applications to non-chemical space propulsion, entry to atmosphere of planets and surface tension treatment of metals, for example, are explored.

‘Flow’ is a typical system in which practically infinite degrees of freedom are involved. Solutions are not necessarily unique also in studying ultra-high-enthalpy flows. It is important for us how much to find, understand and create out of such interesting systems. Laser-Driven In-Tube Accelerator, LITA This is a device that is developed here to launch a projectile by remotely supplying energy through a laser beam. The propellant is pre-charged in the acceleration tube so that the projectile does not need to carry it on board, thereby vastly increasing the payload capacity. Furthermore, the propellant is reusable. Hence, the launch cost can be reduced by a couple of orders in magnitude. Owing to a confinement effect in the tube, the thrust performance is almost doubled comparing to the existing device operating in an unconfined space. In the future, it is expected to be utilized as a driver in a space elevator, etc.

Projectile launch in LITA

Shock-wave-associated flow and impulse generation

Input a certain amount of energy to gas of a constant volume, the impulse that is generated as a

result of the interaction between the shock-induced flow and a body scales with the reciprocal of the speed of sound of the gas. This characteristic can be explained form the viewpoint of shock wave dynamics. Yet, the laser energy absorption involves in complicated process; the absorption occurs in a plasma core that does not shape into a sphere but into a complex geometry like ‘Daruma (Japanese doll).’ The blast waves that are driven by the plasma core are much influenced by the shape. It is a useful characteristic that the heavier the media the larger impulse is obtained. Utilizing much heavier media, not gas but condensed matter like water, a high pressure of the order of 2GPa can be readily generated form a laser energy of 200 mJ. Such a characteristic can be utilized for metal surface treatment etc.

Framing shadowgraphs of shock waves and plasma core that are driven by laser beam energy reflected from a parabolic mirror.

Experimental simulation of superorbital entry flow

An expansion tube can accelerate the test gas to a superorbital entry speed through unsteady expansion without stagnating the flow. The picture on the right-hand side shows a radiating shock layer around a 1/16-scaled Hayabusa capsule model. The flow speed in this case is 8 km/s. In the shock layer, the temperature exceeds 10,000 K

Radiation emission from shock layer around a 1/16 scaled ‘Hayabusa’ (Institute of Space and Astronautical Science) reentry capsule under its reentry condition.