Characteristic And Mechanism Study Of Detonation Wave Propagation On Curved Walls

On the background of the application of rotating detonation wave engine(RDE)in propulsion system,the influence mechanisms of curved wall on detonation wave propagation are studied through combination of numerical simulations,experimental observation and theoretical analysis.Especially for the detonation wave reflection and diffraction process over a curved wall,and the detonation propagation in an annular channel.The rules and characteristics for each process are analyzed in detail.The detonation wave reflections over cylindrical concave wedges are studied.The connections and diffrerences between the reflection of detonation and shock wave,which are the main reflection characteristics of detonation,are found by simulations,and the mechanism is explained to be the velocity variation of the corner signal which causes the Mach reflection.Besides,the parameter study indicates that the reaction and induction zone length ratio is the key parameter in deciding the detonation reflection characteristics,and the ratio has a positive correlation with the Mach stem height and MR-RR transition angle.While the increase of wedge curvature radius decreases the reflection paramters.A theoretical model for the triple-point trajectory of strong shock wave reflection is also built to predict the maximum Mach stem height and the corresponding position.The experimental study indicates that the compression effect increases along with the reflection process.The detonation wave diffractions over planar expansion wall with various expansion angles are investigated numerically.The results show that the re-initiation mechanism of detonation diffraction in small expansion angle is the collision between the transverse wave and the expansion wall,while with the large expansion angle,the diffracted detonation will generate transverse detonation to realize re-initiation.The critical expansion angle of these two mechanisms is also found.Additionally,the re-initiation characteristics in large expansion angle are analyzed,and a theoretical model for the trajectory of the transverse detonation in the re-initiation process is constructed.The movement rule of the transverse detonation,which is predicted by the model,agrees with the previous experimental study.The detonation wave diffractions over cylindrical convex expansion walls are studied.It is found that the curved convex wall can promote the re-intiation of the detonation diffraction by making the area divergence ratio change continuously,and the critical wall curvature radius for re-initiation decreases as the initial pressure and exit width increase.Moreover,the diffracted detonation wave can even realize stable propagation without decoupling under a large wall curvature radius,and the critical wall curvature radius for stable propagation decreases as the initial pressure increases.Simultaneously,the critical criterions for re-initiation and stable propagation are obtained by applying related theories,and verified by experiment observation.The detonation waves propagation in annular channels are investigated in detailed.The propagation modes are divided according to both the decoupling of the wave front and the development of the Mach stem.The structure and velocity of each mode is discussed.The distribustion of each propagation mode indicates that the ability of realizing stable propagation is promoted by the increased initial pressure,and as the ratio of wall curvature radius and the channel width increases,the Mach stem will be transformed from increase type to steady type and finally to decrease type.The critical criterions for propagation mode transition are obtained based on the previous theoretical studies,and the criterions are validated by the numerical and experimental results,which can predict the transition between the stable mode and the unstable mode precisely,thus can be applied for the design of the RDE annular combustor.