IMPROVEMENT OF A FREE-PISTON DRIVER FOR A HIGH-ENTHALPY SHOCK TUNNEL

In order to improve the operation of a high-enthalpy free piston shock tunnel its tuned operation was studied analytically and experimentall y. First, the piston motion in the free piston driver tube was analyti cally solved by proposing a simple piston/gasdynamic model, and the tu ned operation condition was formulated as an eigenvalue with which the piston has sufficiently high speed at the moment of diaphragm rupture , so as to maintain a constant driver gas pressure, and reduces its sp eed to come to rest when very closely approaching the end of the drive r tube. Second, the result of this analysis was validated by its compa rison with experiments which were conducted in the medium-sized free p iston shock tunnel HEK installed at the NAL Kakuda Research Center. By observing the detail of piston landing at the end of the driver tube the present tuned operation was found to be successfully achieved with the operating condition given here. Its advantages in improving the p ressure recovery factor and in enhancing the stagnation enthalpy were successfully demonstrated.