Study On Flow Field Optimization And Erosion Test Of A Self Excited Oscillating Pulsed Jet

Self excited oscillation pulsed jet relies on fluid to generate self-excited oscillation in a specially designed oscillating chamber,converting continuous jet into pulsed jet,without additional excitation elements and devices,which is a new and efficient pulsed jet.Self excited oscillation pulsed jet is widely used in the production of coal-bed methane because of its advantages of simple structure,easy installation,good sealing and no open fire in industrial operation.In order to increase the permeability of deep coal seams,the properties of self-excited oscillating pulsed jets are studied by means of theoretical analysis,numerical simulation and experimental research.First of all,the mechanism of self excited oscillating pulsed jet is analyzed by theoretical research.It is known that the effective matching of pressure disturbance wave and the amplification effect of shear layer on vortex ring are the key to produce effective pulsed jet.Based on the theory of similar network,the formula of amplitude frequency characteristics of self excited oscillating pulse jet is derived.The results show that the main factors affecting the frequency of pulsed jet are the structure parameters and disturbance wave velocity of self excited oscillating pulsed jet.The theory of rock destruction by the erosion of the self excited oscillation pulsed jet is analyzed,and the process of destroying rock by the impact of the jet impingement is learned.Secondly,on the basis of theoretical analysis,the self-excited oscillating pulse jet is numerically simulated.By using the large eddy model?LES?,it is found by numerical simulation that the variation of the velocity cloud pattern of the self-excited oscillating pulse jet accords with the generation principle of the self-excited oscillating pulse jet.Under certain parameters?the diameter of the upper nozzle is d₁=1.2mm,the diameter of the lower nozzle is d₂=1.3mm,the length of the cavity is L=3.0mm,the diameter of the cavity is D=10.5mm,the convergent angle of the collision wall is?=120^?,and the length of the lower nozzle is L₂=4mm?,the maximum velocity increment at the outlet of the nozzle under the self excited oscillation cavity is the largest and the effect of the pulse jet is the best.The peak velocity of the self-excited oscillating pulse jet and the peak velocity of the outlet of the continuous jet are compared.The results show that the peak velocity of the self-excited oscillating pulsed jet is 1.53 times that of the continuous jet.The fast Fourier transform?FFT?method is used to analyze the velocity of the self-excited oscillating pulse jet exit with time,The frequency characteristic curve of the self excited oscillation pulsed jet is obtained.The results show that the exciting frequency of the pulse jet is about 27.1 kHz,which has a multiple relation with the natural frequency derived from the theory,which shows that the pulse jet has a good exciting effect.Finally,on the basis of theoretical research and numerical simulation,the erosion test of self-excited oscillating pulse jet is carried out.Through the experiment,the optimal cavity length of erosion test and numerical simulation of the optimal cavity length of line,are L=3.0mm,which verify the correctness of numerical simulation.The test results obtained influence of pressure,target distance and time parameters of the target erosion erosion effect,when the cavity length of L=3.0mm,erosion time t=60s,target distance s=30mm,self-excited oscillation pulsed jet erosion effect.The diameter and volume of the erosion pits caused by the erosion target of the self excited oscillation pulsed jet are found to be larger than the diameter and volume of the erosion pits caused by the continuous jet erosion target.,which indicates that the erosion effect of the pulsed jet on the target is stronger than that of the continuous jet on the target.