Cellular Structure And Stability Of Detonation Utilized In Propulsion System

How to confine detonations in a combustor is the key issue of the application of detonations to propulsion system. Based on the achieving schemes, detonations lying in the combustor can be divided into oblique detonation wave (ODW), rotating detonation wave (RDW) and pulsed detonation wave (PDW). Those detonations are different with that described by the classic CJ theory in fine structures and its self-sustaining mechanisms.The purpose of this thesis is to study flow field structures and propagation mechanism of a detonation in three combustors mentioned above based on numerical simulations. The computation was based on two-dimensional Euler equations and elementary reaction model, which included9species and48elementary reactions. The5th order WENO scheme was utilized to discretize the convection term, and ASIRK-2B was used to resolve the governing equations and treat the stiffness caused by the chemical source. In this paper, the experiment on the propagation of detonation was performed and the cellular structure was obtained. The main work of this thesis can be described as follows:(1) The numerical results show that three regions in the flow field behind ODW are defined:ZND model-like strcuture, single-sided triple point structure and dual-headed triple point strucuture according to the wavelet structures. The first structure is the smooth straight. The latter two structures are very complicated. In single-sided triple point structure all triple points facing upstream propagate dowanstream with almost same velocities and have the character of temporal periodicity. Simultaneously, the triple point trace is recorded to obtain cell structure of parallel straight lines. In the last structure the triple points move down with two different velocities. The velocity of triple points facing downstream is obviously faster than that facing upstream, which leads to the periodic collisions of the triple point. This period has the character of temporal and spatial periodicity. Cell structure is the inclining "fish scale" patterns. When ignoring the velocity component of the incoming flow tangential to the oblique detonation wave, the detonation cell symmetry axis is perpendicular to the oblique detonation front, and the width of cell is smaller than the normal detonation cell. It is because the transverse wave is the detonation wave in the former and is the shock wave in the latter.(2) Gaseous detonation propagating in an annular cylinder was studied for full of hydrogen/oxygen/argon mixture numerically and experimentally. The results show that the detonation is strengthened near the outer concave wall and weakened near the inner convex wall, so that the detonation front is continuously realigning itself to the local channel axis, to maintain the detonation steadily propagates with a planar front. In addition, the local explosion occurs on the inner wall periodically, which protects the detonation from quenches. The cellular size near the outer concave wall is smaller than that near the inner convex wall.For patially filled with hydrogen/oxygen/argon mixtures, a transmitted shock wave is connected with the detonation wavelet at the contact surface and a mach stem near inner wall or outer wall, forming a detonation-shock-mach combined wave. As for the proportion of O2/Ar and H2/O2/Ar in annular cylinder, there exists a critical value above which the detonation fails. For filling with H2/O2/Ar mixture near the inner wall, the critical proportion of02/Ar and H2/O2/Ar is9:21. While near the outer wall, the proportion is12:18.(3) This thesis emphasized detonation physics in the T-sharped tubes, simultaneously involving detonation self-propagation, diffraction, reflection, detonation failure and re-initiation. In a quiescent mixture system, the flow field is symmetrical about the axis of vertical detonation tube. The detonation fails on both the left and right side due to the detonation diffracting from confinement through an abrupt area expansion. With the development of shock wave, the detonation happens to re-initiate due to the reflection of incident shock from the upper wall. Since this mode of re-initiation is boundary inducd, it is referred to as "re-initiation by reflection". In a flow mixture system, the gas of combustible mixture flow from left to right, which forces the entire flow field to displace to the right side. On the right side, the mechanism of re-initiation is the same as in the quiescent. But on the left side, re-initiation commences by the formation of one or more re-ignition or explosion nuclei before the diffracted wave interacts with the upper wall. Since re-initiation occurs prior to the interaction of the wave with the upper, it will be referred as "spontaneous reinitiation’. The cellular structure, which is evident after the detonation has passed over, can be divided into six different zones in T-sharped tube. They include self-propagation zone, undisturbed zone, dead zone, induced by reflection zone, development of detonation zone and stability of detonation zone. For two systems, the size of cellular structure is different in the stability of detonation zone. The length of cell is in order of right side in the flow system> both sides in quiescent system>left side in the flow system, but the width is same.