21 Febbraio, 2012 14:15

Computational study on the propagation mechanism near detonation limit - galloping and spinning modes

Akiko Matsuo, Keio University, Department of Mechanical Engineering

Aula seminari MOX F. Saleri VI piano

One of the important technology for the new concept of supersonic propulsion system such as Pulse Detonation Engine (PDE) and Rotating Detonation Engine (RDE) is stabilizing
supersonic combustion . Supersonic premixed combustion, so called detonation , is ignited in a cylinder or square tube for PDE and in an annular tube for RDE, and propagates as a supersonic wave. An understanding of the propagation mechanism of detonation wave in such tubes near detonation limit is important for the product design of supersonic combustors. Since spinning and galloping detonations are distinctive features observed near detonation limit in tubes, they are numerically investigated in this work.
Spinning detonation propagating in circular tubes and galloping detonations propagating in circular and square tubes were reproduced with a simple two-step reaction model. The time evolution of the simulation results was utilized to reveal the propagation mechanism of spinning and galloping detonation. Soot track images on the wall and flow features agree with those by previous experiments. Galloping detonation shows strong pulsations in the longitudinal direction and repeats that its velocity varies from underdriven to overdriven in one cycle of pulsation. In order to discuss the one-dimensional features of galloping detonation, x-t diagrams of cross-sectionally averaged profile is directly compared with x-t diagram of one-dimensional detonation, and both agree well on the periodic manner. Therefore, galloping detonation is essentially one-dimensional phenomenon and is dominant to the longitudinal instability.