Experimental And Theoretical Research On Detonation Noise Characteristics Of Multi-tube Pulse Detonation Engine

Compared with the single tube PDE,the multi-tube PDE with increased detonation tube has the advantages of stable thrust and wide thrust range.However,as a power device,the instantaneous pressure release will cause large vibration and large noise.The flow field of multi-tube PDE is more complicated than that of the single tube PDE tube,so the acoustic source and physical characteristics of its noise are more complex.It is an urgent problem to study and utilize the physical characteristics and propagation laws of the multi-tube PDE detonation noise to effectively reduce the interference and harm of noise to the related personnel and equipment itself.In this paper,the effects of detonation tube number,filling fraction,and different shape nozzle on the detonation noise of multi tube PDE are analyzed by experimental test and numerical simulation,and the coordination characteristics of multi-tube PDE are studied.Also,the influence of the arrangement of multiple detonation tubes and the influence of tube spacing to the noise are discussed.The numerical simulation of the complex flow field,the detonation noise and the propagation process from near field to far field are carried out for multi-tube PDE.The main contents are as follows:(1)The experimental system of multi-tube PDE is set up to investigate the propagation characteristics and the physical parameters such as the waveform,sound pressure level,attenuation law,radiation characteristics,A/B duration and spectrum characteristics of detonation noise at different angles and propagation distances are obtained.The research shows that the detonation noise of multi-tube PDE is a typical impulse noise,which is mainly composed of the impact noise generated by the detonation wave and the jet noise formed by the ejection of the high temperature and high pressure gas to the tube.The peak sound pressure level of detonation noise attenuates faster in the area near the tube exit,and the attenuation speed is proportional to the cube of l/r,and the attenuation velocity in the area far away from the tube exit is proportional to the l/r.The directivity of detonation noise changes with the increase of propagation distance,and the maximum value changes from 0 degrees to 30 degrees.At the same distance,higher sound pressure level corresponds longer A duration.The B duration is mainly affected by the size of the jet disturbance and increases with the increase of the detonation tube number.Detonation noise is a broadband signal,and the energy mainly concentrates in the middle and low frequency range below 2kHz.(2)The formation of detonation noise and propagation process from near field to far field is numerically simulated for multi-tube PDE.The CE/SE method is used to simulate the complex flow field of multi-tube exit.It is found that the multi-tube PDE outflow field wave system is relatively complex,and there is a shock wave and expansion wave influenced by multi-channel interaction.With the increase of the propagation distance,the flow field of the front guided wave front is gradually confluent and eventually converge into a uniform spherical shock wave to propagate forward.According to the difference of nonlinear intensity of detonation noise,the propagation process from near field to far field is divided into three parts,i.e.,strong nonlinear zone,weak nonlinear zone and linear region,and the corresponding control equations are solved by different methods.It is found that the conception of the partition calculation can simulate the propagation process of the detonation wave with the near field intensity shoek wave to the remote linear sound wave,and also has a better simulation effect on the process of the sound wave from the strong nonlinear region to the linear transformation.Due to the filling process and the exhaust process of the last cycle in the PDE multi-cycle process,the guided wave front wave front produces a gourd-shaped convex in the vicinity of the central axis.With the guiding shock wave spreads forward,the peak pressure near the central axis attenuates fastest,and the acoustic pressure level of the multi-cycle 0 degree is less than that of 30 degree.(3)The influences of the combination mode,the distance between tube and other important factors on the detonation noise in the multi-tube PDE design scheme are studied experimentally.At the same time,the detonation noise distribution in different test planes is analyzed.The results show that the superposition of the detonation noise in the horizontal arrangement is more obvious,the distribution of the noise energy distribution is relatively scattered,the symmetrical arrangement of the noise energy is relatively concentrated,and the noise peak pressure level on the small azimuth is larger than that of the horizontal arrangement.The A duration of symmetrical arrangement is generally larger than that of horizontal arrangement.When symmetrical arrangement is applied,the peak frequency points of spectrum are all larger than horizontal arrangement,and the sound pressure level of frequency points is larger.In the case of different tube spacing,the detonation noise presents the same directivity,the sound pressure in the direction of o degrees increases and the pressure in the direction of 30 degrees decreases with the increase of the distance between the tubes.The peak sound pressure and A duration on the vertical test surface are generally larger than those of the horizontal test surface,but the distribution of acoustic energy on the horizontal test surface is more than that in the vertical plane.(4)The influence of the multi-tube PDE thrust performance and detonation noise on the independent and common nozzle with convergent,divergent and convergent-divergent are added.The interaction between the adjacent detonating tubes under the different ignition schemes is also analyzed.It is found that the convergent and convergent-divergent of independent nozzles increase the thrust of multi-tube PDE and suppress detonation noise as well.While the convergent common nozzle can provide positive thrust,the divergent and convergent-divergent common nozzle will reduce the thrust.Although the common nozzle can solve the eccentric thrust of multi-tube PDE under different ignition schemes,the adjacent detonating tubes can be influenced mutually,which can be seen that the detonation wave in the first detonated tube spilts the tube,degenerates to shock wave without chemical reaction and then spreads into next tube to affect its normal progress.The laser Doppler velocity measurement method is used to test the impulse of PDE in the process of gas emission.The internal mechanism of the effect of gas emission on the thrust of PDE under different nozzles structures is analyzed.(5)The influence of filling fraction on the detonation noise of multi-tube PDE is studied experimentally.In order to measure the filling fraction of the PDE tube,a test method for the filling fraction of the detonation tube based on the spectral radiation signal is proposed,which avoids the interference of the contact measurement method on the flow field.The experimental results show that the detonation noise increases with the increase of the filling fraction.When overfilled,detonation will form outside the tube,and the sound pressure peak of the detonation noise will become relatively large.When the filling fraction is small,detonation waves cannot be formed in the detonation tube.The detonation and detonation conditions have distinct differences in the radiation signal,and the detonation radiation signal is much larger than the deflagration radiation signal.The spectrometer in the visible light range is used to measure and analyze the detonation combustion process of gasoline/oxygen/nitrogen in the detonation tube,and the changes of important intermediates such as OH,CH,and C2 radicals were obtained.In view of the uneven distribution of oil and gas caused by the spoiler,an on-line measurement method based on the monitoring of C radical concentration is proposed.(6)For the phenomenon of non-synchronous work in the process of multi-tube PDE,dual-tube PDE is used as the research object,and ion probe technology and pressure sensor are used to test signals at different test positions on the detonation tube.The experimental results show that detonation may occur in the spoiler,and the wave velocity and pressure are greater than the C?J theoretical value.The instability of the deflagration-to-detonation process is the main intrinsic factor that causes non-synchronous work.The active control of the multi-tube PDE ignition time can greatly reduce the time difference between the detonation and detonation waves in multiple detonation tubes caused by external factors and reach the nozzle,so that the multi-tube PDEs are in synchronous operation.The measurement of the detonation noise outside the tube shows that the peak value of the sound pressure of the detonation noise during the synchronization work is large.When the work is not synchronized,the peak value of the noise pressure is small,and the A duration is relatively large due to the superposition of the waveform.