EXPERIMENT INVESTIGATION OF OBLIQUE DETONATION WAVE STRUCTURE INDUCED BY HYPERSONIC PROJECTILES

By taking advantages of rapid heat release, high specific impulse and simple combustion chamber structure, oblique detonation plays an important role in hypersonic air-breathing propulsion systems, which has been attracted more attentions in recent decades. However, due to the existence of technical difficulties, such as high-speed test environment generating, fuel and oxidant mixing, and high-temperature combustion flow-field structure measurement, the ground experimental research about oblique detonation wave at home and abroad is still limited at present. Thus, it’s difficult to support the development of oblique detonation engines. To study the wave structures and dynamic characteristics of the self-sustained propagating oblique detonation wave, investigation on oblique detonation induced by a hypersonic projectile launching has been conducted based on a two-stage light-gas gun device. The spherical projectile with a diameter of 30 mm is launched into a test chamber, in which fills with stoichiometric hydrogen/oxygen combustible mixture to induce the initiation of the detonation wave. In this work, two different shadowgraph techniques have been employed to record the structures of shock induced by the projectile. Three kinds of shock structures have been observed with different projectile velocities and filling pressure: shock induced combustion, detonation wave initiated by the projectile and steady oblique detonation wave around the projectile. A decrease in the filling pressure results in increasing length of transverse wave and unsteady flow structure of detonation wave. The measured oblique detonation wave angle agrees well with the theoretical result. The discrepancy of the shock wave angle between experiment and theory exists due to large angle of attack of the projectile, which is caused by aerodynamic instability. The propagation velocity of the oblique detonation wave is determined by oblique detonation wave angle at various points of detonation wave. Moreover, it shows that the detonation propagation velocity decays to the CJ detonation velocity as moving away from the projectile, and thus accelerate the attenuation of propagation velocity of the oblique detonation wave.