Study On Jet Flow And Noise Prediction Of Edge Scarfer

The edge scarfer,where small scale parallel circular jets(d=1.5mm,s/d=4)combine with high aspect ratio rectangular jet(b/a=44),is a device utilizing compressible jet to clean surface deficiency of slabs.In the paper,the experimental and numerical methods are used to study the characteristics of the jet flow and noise of the edge scarfer.The feasibility of the noise reduction is experimentally studied by main jet accompanying with different second flow.The flow field characteristics are calculated by simulation,and the noise reduction ability of various structures is analyzed.Furthermore,the layout scheme of the shielding plates is given from the angle of sound propagation.Finally,a technical scheme to reduce the noise of the edge scarfer is formed.Cold and hot tests are carried out by edge scarfer test-bed,which can analyze the noise characteristics,including circumferential distribution,propagation and attenuation characteristics and spectrum analysis.The noise of edge scarfer belongs to the broadband noise,when the jet exit pressure is low,which is under middle-high frequency noise.And in contrary,it is under high frequency noise;With the increase of the jet pressure,the frequency of the noise from 500Hz and 8kHz in middle-high frequency region is close to 3kHz in high frequency region.The oxygen jet in a rectangular groove is the main source of noise generation;Far field noise has obvious directivity.Thermal experimental study found that the highest sound pressure level(SPL)of noise is in the direction deviated from streamwise of 30 DEG?60 DEG.And cold test study found that 15 DEG deviated from streamwise is the maximum SPL direction in the preheating condition.In the addition,30 DEG?60 DEG is the maximum SPL direction in cleaning condition noise.Finally,the main noise source is the dipole and quadrupole.The numerical simulation of the near flow field and the far field noise is carried out by the finite volume method.The large eddy simulation(LES)is used to calculate the near-field flow structure of the nozzle.Based on the Ffowcs Williams-Hawkings integral equation(FW-H integral method),the noise features are obtained.Near-field flow structure can be roughly divided into three regions,mixed region,transition region and development region.Noise source characteristics of the edge scarfer is analyzed through the vortex-sound theory,which points out the determining factor of noise pollution and controllable factors of noise reduction in working process of the edge scarfer.By optimizing the structure of the rectangular nozzle,the changes of the flow and sound field are observed,and the noise reduction scheme of the edge scarfer is formulated from the noise source.The calculation results show that with the increase of the aspect ratio of the rectangular nozzle,the spanwise mean velocity distribution changes from the "saddle-type" gradually to the"bell-type" characteristics,and potential core length and width shorten.The broken distance of large scale continuous structure shortens,so that,in the mixed region,the ability to roll up the surrounding fluid becomes stronger.Small vortexes are closer to the nozzle,leading to the faster velocity attenuation,which make high frequency noise decrease;Potential core of round-side nozzle is slightly smaller than the straight-side nozzle,but in the transition zone,jet angle is far greater than that of rectangular nozzle,which indicates that its interaction with the surrounding environment becomes stronger,so that the high frequency noise will decrease.The noise spectrum characteristics and circumferential sound pressure level are consistent with the experimental results greatly.The calculation of aerodynamic noise by the finite element method is a hybrid method.The law of the propagation of the far field noise can be obtained.The rectangular nozzle is changed into the circle-corner nozzle,the divergent nozzle,and the chamfered-corner nozzle.The calculation results show that in preheating conditions,these nozzles can't reduce the noise;The noise pollution in the pipe(inside the nozzle and distributor)is much larger than that in the free space,and the maximum turbulence intensity is near the nozzle mixing area,where the sound pressure is also in the largest area.The Maher number of the second flow and its angle of the jets are particularly important.It is found that decreasing the velocity gradient in the shear zone of the mixing zone and transition zone can effectively reduce the noise,and the effect of the noise reduction is about 3dB.Round-side nozzle in the transition zone can increase the jet angle,and its interaction with the surrounding environment becomes stronger.In this way,the SPL can be reduced by more than 3?5dB.The layout of the sound absorption material is expected to reduce the noise by more than 5?10dB.The three noise reduction methods can eventually reach the noise reduction ability of more than 15dB,which can basically guarantee the noise of the indoor staff to reach the national standard.