Investigation On Detonation Noise Characteristics Of Pulse Detonation Engine

Pulse Detonation Engine(PDE)is an innovative propulsion system that utilizes repetitive high temperature and high pressure gas generated by detentions to produce thrust and power.It has a broad application prospect in future aerospace and weapon fields with the advantages of high thermal cycle efficiency,high specific impulse,hardware simplicity,light weight and high Thrust-to-Weight ratio.When PDE works,it produces strong impulse noise and vibration,The PDE noise radiation and vibration will directly affect the aircraft stealth and structural fatigue,which is one of the most serious threats to PDE performance and vehicle safety.With the rapid development of the PDE technology and the breakthrough of the key technical,the acoustical performance of PDE is valued,so the research on the acoustical performance of the PDE is a necessity.The experiment system of gas-liquid two-phase pulse detonation engine,where filling fraction could be regulated accurately,was set up to investigate the detonation acoustical characteristic with different tube types and loading condition(including the filling fraction and equivalence ratio).A theory modeling for process of formation and propagation of detonation waves was set up and its numerical procedure has been programmed in this paper.The main work and achievements are described mainly as follows:(1)The experiment system of gas-liquid two-phase pulse detonation engine was set up to investigate the physical characteristics of detonation noise in time domain.The result shows that detonation noise is mainly composed of impact noise and jet noise.As the distance increasing,there are decreases in amplitudes of impact noise and jet noise.When the distance is shorter,the speed of jet noise attenuation is lower than the impact noise attenuation;however,when the distance is longer,the speed of jet noise attenuation is higher than the impact noise attenuation.The detonation pressure curve takes on an "L" changing law.Pulsed detonation engine detonation noise amplitude is proportional to the radial distance power of-3 before the inflection point,while,it is proportional to the radial distance power of-1 after the inflection point.With increased distance,the duration of A firstly decreases and then increases and the duration of B is increaseing with increased distance.When the distance is shorter,impact noise and jet noise is decreaseing with increased angle,however,when the distance is longer,the maximal impact noise and jet noise are obtained in 30 deg.(2)The fields of detonation noise are successfully divided into three ideal regions,which are strongly nonlinear region,weak nonlinear region and linear region respectively,through the analysis on the features of detonation noise.Formation and propagation of detonation noise is numerically simulated.The space-time conservation element and solution element(The CE/SE method)was used to solve the viscous Navier-Stokes equation in strongly nonlinear region.Using time split algorithm,The Nonlinear Progressive-wave Equation(the NPE equation)was solved with CE/SE method and C-N method.The result shows that the formation and evolution of vortex have a major impact on formation of expansion chamber,leading to waveform oscillator for jet noise.In the weak nonlinear region,nonlinear accumulation leads to waveform distortion of detonation wave noise and moving backwards of the peak of detonation wave noise.(3)The investigation of physical characteristics of detonation noise characteristic of the part and total is carried out by using Fourier transform and wavelet transform.A new avenue for detection of the working state of pulse detonation engine is proposed,according to the energy proportion of detonation noise in different wavelet coefficients.In deflagration stage,η11/η5 is less than 5,while η11/η5 is large than 5 in detonation stage.The result shows that detonation noise is belong to broadband noise which is composed of fundamental frequency and harmonic-frequency.With increased frequency,the detonation noise strength have remained about the same at 10～100Hz;the detonation noise strength firstly decreases and then increases at100～1000Hz;the detonation noise strength decreases at 1000～100kHz.As the angle increasing,there are decreases in amplitudes of the detonation noise at 100～1000Hz.The acoustic signal of experiment system is mainly at high frequency range 500-1000kHz.The energy of impulsive rise of impact noise and jet noise is mainly at 15.62～125kHz.The energy distribution of detonation noise is mainly at 0～0.98kHz.In deflagration stage the concentrate of PDE acoustic signal energy is obvious and in detonation stage the concentration in low frequency is more obvious,while,in external detonation stage energy is more concentrated in low frequency.(4)The experiment system of pulse detonation engine is set up to investigate the detonation noise characteristic of pulse detonation engine with different PDE diameters,different nozzles,and different ejectors.The result shows that as the PDE diameter increasing,there are increases in amplitudes of impact noise and jet noise at all angles,and the smaller PDE diameter is,the distance of most obvious directivity at 0 deg turning to most obvious directivity at 30 deg is shorter.When the distance is shorter,the duration of A is increasing with the increase of PDE diameter,however,when the distance is longer,it is just the opposite.The nozzle shows significant influence on detonation noise to reduce the amplitude,and the convergent-divergent nozzle is the most effective.A large convergence angle would lead to more obvious directivity for convergent nozzles.The obvious directivity would be also obtained by divergent and convergent-divergent nozzles with small exit area.The reference radius of detonation noise can be effectively slowed down with nozzles.The larger convergence angle,the smaller reference radius for detonation noise with convergent nozzles is obtained.The larger divergence angle,the smaller reference radius for detonation noise with divergent nozzles is obtained too.The detonation noise strength decreases at all frequency almost with divergent nozzles,and the large divergence angle,the effect of decrease of detonation noise strength is more obvious.The thrust augmentation generally increases and OASPL decreases with an increase in LEjector/DEjector.Thrust augmentation increases and OASPL decreases are obtained with all ejectors,and the divergent ejector is the most effective.With increased x/DpDE,the thrust augmentation and reductions in OASPL firstly increase and then decrease.The optimum ejector based on thrust augmentation and reductions in OASPL is determined to at x/DPDE =2、LEjector/DEjector=2.61.(5)The experiment system of gas-liquid two-phase pulse detonation engine,where filling fraction could be regulated accurately,was set up to investigate the detonation noise characteristic with different equivalence ratios and filling fractions,and the time error of detonation acoustic characteristic in process of formation and propagation.Based on laser absorption spectroscopy technology,H2O in reaction product was measured.The result shows that as the filling fraction increasing,there are increases in firing time interval,but it is not a direct proportion relationship between filling fraction and firing time interval.As the filling fraction increasing,there are increases in amplitudes of impact noise and jet noise at all angles.A significant increase in amplitude of impact noise and jet noise are observed at the turning point from deflagration stage to detonation stage.With increased filling fraction,the detonation noise directivity becomes obvious at short distance,but ambiguously at long distance.As the filling fraction increasing,the detonation noise strength increases at 10～50Hz,contrastly,decreases at 50～200Hz.The amplitude of detonation noise,the duration of A and the detonation noise strength firstly increase and then decrease with increased equivalence ratio.The maximal detonation noise,the duration of A and the detonation noise strength are obtained at equivalence ratio 1.1.Based on optical signal collected through infrared sensing units,time error of ignition can be negligible.The maximum average arrival time error of detonation acoustic,about 328.22μs,is obtained with the highest filling fraction at 0 deg.The maximum detonation acoustic average relative error is achieved in overdriven detonation event produced stage inside PDE,while,in strongly nonlinear region outside PDE.The convergent nozzle exhibits a marked decrease in detonation acoustic average relative error;the maximum is appeared at the same location,where a maximum reduction of 56.13 percent is achieved.In this paper,the formation and propagation of pulse detonation engine noise was studied by combining the experimental and numerical methods,which reveals the transmission characteristics of gas-liquid two-phase pulse detonation engine detonation noise.The effects of different tube types and loading condition on the PDE detonation noise were studied.The results are of great significance for studying the mechanism of detonation noise and expediting the process of the engineering application.