Experimental Studies On The Reflection Of Gaseous Detonations Over Plain And Sperieal Convex Wedges

The reflection of gaseous detonations waves over plain and sperieal convex wedges is basic problem regarding to detonations propagation.The propagation of gaseous detonation waves in many complex geometries involves the problem.The study on Mach and regular reflection of detonation waves has an important theoretical significance and an application value to(1)reduce the damage caused by the explosion by preventing the formation of detonations,(2)use the power of detonation waves to design propulsion devices.A detonation channel with rectangular cross section is designed to carry on experimental research on the reflection of detonations over over plain and sperieal convex wedges.The main studies of the thesis are described below:(1)The triple-point trajectory of Mach reflection can be obtained from the smoke foils.Through the three-point trajectory,it was found that the Mach reflection of a detonation is similar to the case of a shock reflection process near the wedge apex in the near field.In the far field,the Mach reflection process of a detonation tends to be self-similar.In the middle section,the triple-point trajectory is curved and non-self-similar.When the wedge angle approaches to 50 degree,the Mach reflection changes into a regular reflection.The distance required to obtain self-similarity in the equilibrium limit was found to be approximately(6–10)?,which essentially equates to a hydrodynamic thickness.Thus,the hydrodynamic thickness is a length scale to characterize a cellular detonation to describe self-similarity problem of Mach reflection.(2)The three-dimensional wave structures of Mach reflection over a wedge was studied.The cellular detonation is essentially three-dimensional,and the transverse waves along the thickness of the channel should be considered.The transition length associated with the equilibrium limit was found to be(5–6)L or(7–9)?,which is in agreement with the result from the triple-point trajectory measurement.However,in the case of a small wedge angle,the cell length variation along the wedge surface is not evident,which prevents the transition length associated with the equilibrium limit from being measured.(3)The experimental research on the reflection process of detonation waves on the sperieal convex wedges is carried out,by focusing on the critical angle of transition from regular reflection to Mach reflection.The activation energy and the ratio of radius to cell size,R/?,is a factor determining whether or not the detonation wave fails when the detonation wave passes the wedge surface.The unstable detonations with higher activation energy is less likely to fail as compared to relatively stable detonations with lower activation energy.The bigger R/? is,the harder it is to fail for a detonation wave.The critical angle was found to increase with the increase of R/?.With a certain radius,the critical angle increases as the cell size decreases(or R/? increases).