Investigation On The Propagation Characteristics And Mode Control Of Rotating Detonation Wave

An energy conversion based on rotating detonation has the advantages of high thermal cycle efficiency,rapid energy release rate,and short combustion distance.The application of rotating detonation to rocket engine or aeroengine can reduce the combustor length and system complexity effectively.In this thesis,the propagation characteristics,adaptability,propagation modes and their control,as well as the velocity deficit of rotating detonation wave(RDW)were studied by the combination of experimental investigation and numerical simulation.The effects of mass flow rate and equivalence ratio on the propagation characteristics of RDW were conducted firstly,and the driving mechanism of the momentum flux ratio of hydrogen and air injection to the trend of measured velocity was revealed.It was found that the height and mixing degree of the fresh reactants depend on both the mass flow rate and global equivalence ratio in the non-premixed combustor.The result of three-dimentional simuation shows that there is a large gradient of hydrogen distribution along the radial direction of the combustor.The small equivalence ratio leads to the low height and chemical activity of reactant,which results in the unstable propagation of RDW.Increasing the mass flow rate and the equivalence ratio can increase the measured velocity,peak values of the instantaneous pressure and ion signal,and enhance the propagation stability of RDW.The influencing factors of the single-wave mode and multi-wave mode transitiona in rhe combustor were studied.It was found that the ratio of detonation height to the reaction length characterizing the activity of reactant is the main parameter that determines the number of detonation waves in the combustor,and the large value of the ratio favor the existence of multiple co-rotating waves.The mass flow rate,equivalence ratio,width of annulus and the backpressure affect the effective height of RDW,while the variations of air injection area,equivalence ratio,and backpressure lead to changes in activity of reactants.The mode transition from single-wave to multi-wave was analyzed in detail by the combination of instantaneous pressure signal and high-speed photography.Moreover,the promoting role of backpressure to the critical propagation of detonation was revealed numerically.For the leading oblique shock wave resulting from the over-expansion of detonation products,the effect of oblique shock wave on the flow field was analyzed,and a nozzle flow analogy was also established.The results show that increasing the injection area ratio,the ratio of the total pressure to the backpressure or reducing the combustor diameter can relieve or eliminate the over-expansion of the combustion products.However,the experimental results showed that an increase of chamber length leads to the mode transition from stable single wave to two counter-rotating waves for the case of low mass flow rate,the mechanism behind the transition and the details of transition process were revealed numerically.The longitudinal pulsed detonation(LPD)phenomenon in the annular combustor with high backpressure or high blockage ratio were also studied,and the increase of combustor length decreases the critical equivalence ratio for the occurrence of LPD.It demonstrated that the RDW has the ability to propagates continuously from the wide range of equivalence ratio to the subsequent large gradients of equivalence ratio without the decoupling or unstable propagation.The feasibility of thrust control was also validated by regulating the mass flow rate of fuel based on the strong adaptability of RDW.The controllable transition between the single wave and two co-rotating waves was realized by regulating the equivalence ratio during the test,and the corresponding process was simulated in detail.Moreover,the feasibility of mode transition between the transverse and longitudinal propagation of detonation wave was demonstrated experimentally by changing the combustor length and equivalence ratio.Numerical simulation of the velocity deficit of RDW was conducted,including the effect of non-ideal mixing of fuel and oxidizer,lateral expansion of reaction zone,and the different curvatures of inner and outer walls.It was shown that the calculated velocity from the premixed and non-premixed injection matched the experimental results well.The mixing degree plays a dominant role in the stable propagation of RDE for the case of low mass flow rate.The lateral expansion of reaction zone decreases the propagation velocity significantly.The relationship between the propagation velocity and detonation height was built through integrating the ZND model with area expansion,and a critical detonation height was obtained.The curvatures of inner and outer wall leads to a decrease of velocity about 6-7%,and the non-uniform distribution of fuel will aggravate the velocity deficit of the detonation wave.