Backpressure Characteristics Of Annular Isolator In CRDR

As a new propulsion system,continuous rotating detonation ramjet(CRDR)has a broad application prospect.At the same time,the harsh backpressure environment produced by the high speed rotating detonation wave also brings great challenges to the design of isolator.In this paper,the backpressure characteristics of isolator and the process of fuel jet and mixing are studied by means of numerical simulation.Firstly,the characteristics of shock train motion under dynamic backpressure in a two-dimensional straight isolator are studied systematically.When subjected to sinusoidal backpressure,the shock train undergoes a consistent and repeatable oscillation.The frequency of oscillation is the same with the backpressure frequency.The structure and length of shock train vary slightly during moving,which is related to the changing relative Mach number ahead of the shock train.The impacts of dynamic backpressure parameters on shock train motions are summarized.It is found that the average backpressure has a great influence on the location of shock train oscillating region,while the amplitude of backpressure has a noticeable effect on the size of oscillating region.The frequency affects both the location and size of oscillating region.The velocity of shock train reaches its peak when the shock train passes the mean position,and the maximum velocity largely depends on the amplitude of backpressure.As the amplitude increases,the maximum velocity becomes larger.However,the velocity is approximately independent of the frequency and the average backpressure.The size of region affected by the shock train oscillation is positively correlated with the degree of wall pressure fluctuation.Keeping backpressure with the same maximum,minimum and frequency,the square-wave backpressure obtains the largest affected region and the most violent wall pressure oscillation,followed by sinusoidal-wave,sawtooth-wave and triangle-wave.Subsequently,the annular isolator of CRDR is studied.The flowfield structure of annular isolator under rotating backpressure is reconstructed,and the influence law of rotating backpressure parameters on flow characteristics of isolator is summarized.It is found that the oblique shock induced by rotating backpressure becomes weakened gradually in the process of propagating upstream and terminated in the first shock ring finally.The first shock ring is perpendicular to the axis of isolator,and its position and intensity are basically unchanged.A method of rapidly predicting the position of first shock ring by the simplified 2-D model is proposed.The existence of rotating backpressure makes the total pressure loss of isolator slightly larger than that of non-backpressure condition.It is mainly due to the introduction of new shock wave system to the flow.Increasing the frequency and reducing the amplitude will make the first shock ring move downstream,which can also help to reduce the total pressure loss and improve the isolator performance.At last,by comparing the fuel jet-mixing process with or without the backpressure effect,this paper illustrates the influence mechanism of rotating backpressure on the jet-mixing process,and analyzes the efficiency of fuel jet-mixing process and the isolator performance under the effect of rotating backpressure.It is found that the oblique shock induced by the rotating backpressure deflects the flow direction and promotes the large-scale convective mixing of fuel and the mainstream.The fuel distribution of isolator exit also becomes more uniform.The frequency and amplitude of backpressure have no impact on the fuel mixing efficiency and total pressure loss,but a little influence on the penetration depth of fuel.And the difference in penetration depth can be attributed to the varying intensities of oblique shock induced by different backpressures.