Investigation On Structure And Stability Of Oblique Detonation Waves In Supersonic Flows

On the background of the application of oblique detonation wave engine(ODWE)in hypersonic propulsion,the flow structure and stability of oblique detonation waves(ODWs)in supersonic combustible mixtures are investigated through combination of theoretical analysis,numerical simulations and experiments,especially for ODWs in complicated turbulence flows.Firstly,the formation mechanisms of the two kinds of transition structures are studied based on inviscid condition,and it is found that the state difference between the areas behind the induced shock and the ODW is the direct cause of different transition structures.When the state difference is large,the state match between the two areas requires transverse wave,leading to the formation of an abrupt transition.When the state difference is small,only weak compressional waves are needed rather than shock waves,so a smooth transition forms.Besides,an empirical method is proposed for the prediction of transition structures based on inflow conditions.Secondly,stability and thermodynamic efficiency of ODWs with different transition structures are investigated and the results show that ODWs with smooth transitions are more stable but the thermodynamic efficiency decreases obviously.On the contrary,thermodynamic efficiency of ODWs with abrupt transitions are relatively higher,but the stability of this kind of ODWs is weaker.Therefore,the shift area between abrupt and smooth transitions is more applicable for ODWE.Besides,the empirical method can be used for the estimation of inflow condition,which may play an important role in the design of ODWE.Then,the initiation and flow structure of ODWs in turbulence flows are investigated.Results show that autoignition delay of the premixed mixture is shorter in turbulence flows,which leads to the decrease of the initiation length of ODW and benefits size reduction of the combustion chamber in ODWE.Meanwhile,the initiation limits of ODWs in turbulence flows are broadened and the initiation limits become lower with the increase of the turbulence intensity.In addition,the transition structure of ODWs are affected by turbulence intensity,that means,when the inflow condition is unchanged,a smooth transition is more likely to be formed in a strongly turbulent flow.Finally,shock wave-boundary layer interactions(SBLI)in oblique detonations are investigated and it is analyzed how it affects the structure and stability of ODWs.It is shown that ODWs with smooth transitions are mainly affected by inflow boundary layer,which makes the initiation lengths increase with little changes in the overall structure.However,ODWs with abrupt transitions are affected by both inflow boundary layer and post-wave boundary layer.Two kinds of SBLIs(the ramp-induced shock and the incident shock)exist in the ODW flowfields.The initiation lengths are increased by the inflow boundary layer,which is similar to ODWs with smooth transitions.The transition structures are changed by the post-wave SBLI and the stability is weakened.Besides,with the increase of abrupt degree or thickness of inflow boundary layer,the ramp-induced separation merges with the post-wave subsonic area and an extended separation forms,leading to the failure of ODWs.