| Perforated liner ducts have wide sound absorption band and good absorption characteristics,so they are widely used in sound-absorbing of power equipments and air ducts.No matter whether the cavity is filled with porous sound absorbing material or not,the vicinity of the perforated wall both exist strong and complex vortex flows which will cause the large flow resistance loss.In structure design of noise elimination,the noise induction index and the aerodynamic performance of the equipment are both needed to take into account.Thus,it is necessary to accurately estimate the flow resistance in the perforated liner ducts for sound-absorbing needs.Current work focus on the frictional drag performance of the perforated liner ducts which are filled with porous material in cavity,by the numerical simulation and experimental methods.And the total flow resistance of chip muffler is also to be simulated at the same time.The main research contents and results are summarized as follows.(1)Find and validate the numerical simulation method of the frictional drag of the perforated liner ducts.When the cavity is filled with porous material,the quantity of flow in and out the holes will become very small,to simplify,the flow out and in the porous material by holes is ignored in the calculation.The math and physical models were established under the initial conditions that the punching rate was 20%,the arrangement relative angle of holes was 60,the pore diameter was 3mm and the size of ducts sections was fixed at 200mm×200mm.In the simulation,used the Realizable k-? turbulence model and the most suitable wall function was chosen from four different functions.Chose the flow velocities of 6m/s,9m/s and 12m/s,respectively.It turned out that,the combine of the Realizable k-? turbulence model and the enhanced wall function could get a more accurate result of flow frictional resistance of ducts,by which,the deviation between numerical simulation and experiment was less than 10%.This work provided a reasonable scheme for model simplifying and mesh generation of the next study.(2)The study of the equivalent roughness of the perforated liner ducts.The equivalent roughness,i.e.,the roughness was obtained by plugging the flow resistance datas,which were got through simulation,into the Colebrook equation.The simulation were performed under the conditions that pore diameters were 1mm,2mm,3mm and 4mm,and the corresponding punching rates were 6.7%,11.3%,14.5% and 20.0%,respectively.The results showed that when the flow velocities were 6m/s,9m/s and 12m/s,the fluctuation range of equivalent roughnesses were less than 10%.Based on the mean equivalent roughnesses,the deviation between the flow resistance datas attained by the empirical formula and the numerical simulation datas was less than 10%,which verified the method of equivalent roughness.These offered a workable method for calculating the frictional drag of the perforated liner ducts in the real engineering design.(3)The study of the chip muffler.The design of shunt channels can improve the broadband sound-absorbing property,but also will remarkable increase the flow resistance.To improve the performance of sound-absorbing and satisfy the design requirement of smaller flow resistance,this paper studied the total flow resistance of chip muffler.Designed the reducing pipe and other three schemes for the sudden contraction section,designed the increasing pipe and other two schemes for the sudden expansion section,and increased the guide vane and smooth transition pipe schemes for channel shunting.The results indicated that,when the tapering angel was 32,the expanding angle was 15,could get the smallest local resistance,the schemes of channel shunting could induce the local resistance slightly.Thus,a low flow resistance chip muffler was proposed,and by the numerical simulation and experiment finding this duct structure could induce the flow resistance effectively. |
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