| Detonation combustion is the core working process of various detonation engines,and the rapid triggering detonation waves is the most basic and important topic in the field of detonation engines.In the research of detonation engine,predetonation tube is usually adopteded to trigger detonation wave quickly.Diffraction and reflection of detonation propagating from pre-detonator to main detonation tube is the key to detonate the main detonation tube.Related studies can provide theoretical guidance for the engineering application design and performance improvement of detonation engines.Based on the density-based compressible reactive flow solver DCRFoam,the propagation characteristics of gaseous/gas-liquid two-phase detonation waves in T-shaped channel and the mechanism of re-initiation are studied,especially the detonation wave diffraction and reflection process are deeply explored,and the detonation wave propagation characteristics and change laws under different environments are analyzed.The main research work is as follows:(1)Based on the open-source program OpenFOAM,DCRFoam is developed for the simulation of gaseous/gas-liquid two-phase detonation phenomena.For the gas phase governing equation,AUSM+-up scheme and second-order central difference scheme are used to discretize the convection term and diffusion term respectively.RK4 scheme is adopted to integrate ordinary partial equations.For the liquid phase governing equation,the first order Euler scheme is used for calculation,and the relevant parameters of the gas at the droplet location are obtained by linear interpolation.In order to reduce the computational cost and obtain the high-resolution flow field characteristic information,the adaptive mesh refinement method is used to dynamically encrypt and coarsen the local grid.The reliability of the solver and the accuracy of the established model are verified by comparing the simulation results with the theoretical and the experimental results of others through classical one-dimensional cases and two-dimensional cases related to the research content.(2)The detonation wave diffraction and re-initiation process under subcritical and supercritical conditions are studied,and the influence of different conditions on the secondary initiation process of detonation wave in T-shaped pipes is obtained.The results show that under supercritical condition,detonation wave can self-initiate by forming transverse detonation wave through local hot spots,and shear waves on the wave surface mainly come from transverse detonation waves and detonation waves in vertical channel.When the channel width is reduced,the detonation wave is mainly initiated by wall reflection.The re-initiation mechanism under different pressure is also revealed: for the high-pressure condition,the transverse wave interaction realizes the re-initiation,while for the low-pressure condition,the different wall reflection initiation mechanisms are realized by the shock wave compression and preheating of the unburned mixture and the wall hot jet effect.In the flow system,the upstream detonation wave can be reinitiated by self-initiation,while the downstream can only be re-initiated by wall reflection.(3)The influence of concentration gradient on the re-initiation process of gaseous detonation wave is studied,and the influence of concentration gradient grads and two different concentration gradient distribution modes on the propagation characteristics of detonation wave in T-shaped channels is obtained.The results show that two different concentration gradient distributions in the horizontal channel correspond to two different transverse wave formation modes.From fuelrich near the upper wall to fuel-lean near the lower wall(gradient > 0),the early transverse waves are mainly formed after the second reflection.From fuel-rich near the lower wall to fuel-lean near the upper wall(gradient < 0),the early transverse waves are mainly formed after the first reflection.However,the early transverse waves in the horizontal channel under the two different concentration gradient distributions are mainly formed on the fuel-lean side,and the early transverse waves in the horizontal channel are mainly from the transverse waves of the transverse detonation wave surface.With the increase of concentration gradient,the number and intensity of transverse waves tend to decrease,and the transition of detonation wave from multi-head propagation mode to single-head propagation mode,which is not conducive to the detonation wave re-initiation.(4)The re-initiation characteristics of detonation wave under gas-liquid two-phase conditions are studied to explore the feasibility of detonating gas-liquid two-phase unburned mixture by gasliquid detonation wave.For the gas-liquid two-phase condition in the stationary system,the detonation wave diffraction and reflection process in the two-phase condition and the pure gasphase condition is firstly compared,and then the influence of different parameters of the gas-liquid mixture on the re-initiation process of detonation wave is explored.The results show that due to the droplet breakup and evaporation process,the two-phase diffracted detonation wave is more easily decoupled,and it needs to be re-initiated by several wall reflections.There is an interaction between shock wave and droplets,and the droplet diameter changes gradually from breakup dominated to evaporation dominated.There exists a fuel-lean limit that can re-initiate the detonation wave,and the number of wall reflections required to re-initiate near the fuel-lean limit increases.Similar to the result of concentration gradient in the gas phase condition,the detonation wave in the two conditions with uneven droplet distribution can be re-initiated by one and two wall reflections respectively,but the early transverse wave is mainly formed after the first reflection.(5)The influence of the flowing state of gas-liquid mixture in the channels on the re-initiation of gas-liquid two-phase detonation waves is studied,and the upstream and downstream detonation wave diffraction and reflection characteristics at different Mach numbers and equivalence ratios in the flow system are obtained.The results show that the incoming flow contributes to the faster breakup and evaporation of droplets after the wavefront in the upstream,while the downstream flow is on the contrary.However,under the initial condition of this paper,the flow compression cannot make the upstream detonation wave realize self-initiation,and the detonation wave is still re-initiated through wall reflections.In addition,the flow system broadens the fuel-ean limit that can re-initiate detonation waves. |
PDF Full Text Request