Study On Acoustic Performance And Flow Field Characteristics Of Light Truck Engine Intake System

In recent years,the rapid development of automobile industry has made urban noise pollution and air pollution more serious.With the gradual tightening of emission laws and regulations,it is urgent to solve these problems effectively.In the intake system,the air intake tube and the air filter are the main components of noise reduction and filtration respectively.And their performances determine the sound quality,the engine life and components of exhaust emissions.Therefore,the optimizations for the air intake tube and air filter were based on the study which was discussed from two aspects of acoustic performance and flow field characteristics.The conclusions obtained not only improve the sound quality and life of the car,but also have practical guiding significance for reducing noise pollution and air pollution.Firstly,the optimization of the air intake tube was carried out in this study.According to the noise test experimental results,contribution frequency of noise was obtained.Then the mufflers were designed.The acoustic performance and flow field characteristics of the original and optimized air intake tube were simulated by LMS virtual.lab and fluent15.0 software,respectively.And the influence of the mufflers on the sound field and flow field was analyzed.Then the noise test of the optimized air intake tube was carried out to verify the noise reduction effect of mufflers.Next,the flow field characteristic of the flat air filter was simulated based on the porous medium theory.By comparing the simulation results with the experimental results,a numerical model suitable for the simulation of the air filter in this study was obtained.Finally,the obtained numerical model was applied to the flow field simulation of honeycomb air filter.The model adopted the same filter element(pleat height h=5 mm),while the series of combinations of the inlet and outlet shapes of the housing were respectively round and round(scheme 1),round and ellipse(scheme 2),ellipse and round(scheme 3),ellipse and ellipse(scheme 4).Then the optimized housing and the honeycomb filter elements with pleat heights of 5mm,7.5mm,10 mm,12.5mm and 15 mm were combined to study the effect of pleat height on the flow field.The results showed that:(1)Through the noise test of the original air intake tube,it is found that the total noise value of the intake port basically meets the limit requirement under the idling condition.In the accelerated condition,the total noise of the intake port exceeds the limit value when the engine speed is in 2125r/min.The noises of 2,6,8 orders exceed the limit at certain speeds.The contribution frequencies of noise are calculated to be 125 Hz,180Hz,465 Hz and 640 Hz.Four resonator cavities are designed for these four frequencies.(2)The acoustic finite element calculation shows that the acoustic pressure level of the intake tube can be obviously reduced by adding resonator cavities.And the transmission loss increases 19.79 dB,22.91 dB,18.06 dB and 43.62 dB at 125 Hz,180Hz,465 Hz and 640 Hz,respectively.The flow field simulation analysis shows that adding resonator cavities have little influence on the flow field,and the pressure drop has a small increase of 6%.Therefore,the simulation shows that the optimization of the structure is feasible.Subsequently,the noise test of the optimized air intake tube shows that the total noise value of the inlet is below the limit value under idle condition.And under the accelerated condition the total noise and the order noise are also less than the limit value.Therefore,the above indicates that the resonator cavities have achieved a good noise reduction effect.(3)Comparing the numerical simulation results and experimental results of the flat air filter,the simulated values have the same regularity as the experimental values.That is,as the flow rate increases,the inlet resistance increases and the increasing rate increases gradually.The simulation results using the Standard k-? turbulence model has the lowest error and higher coincidence with the experimental results.Therefore,the Standard k-? turbulence model is suitable for the numerical study of the air filter in this study.And this method will also be applied to the simulation analysis of the honeycomb air filter.(4)Comparing the flow field distribution of the honeycomb air filter under the four schemes,the flow field distribution of scheme 2 is more uniform.The flow velocity and pressure distribution of the filter core are more uniform as a whole,and the velocity and pressure gradient are smaller.So the filter element is evenly used.The pressure drop increases approximately linearly with the increase of flow rate.When the flow rate is less than 60% of the rated flow,the values of pressure drop of these four schemes are similar.However,the pressure drop of scheme 2 was smaller than that of schemes1,3 and 4 when the flow rate is greater than 60% of the rated flow.Therefore,it is concluded that the housing with circular inlet and elliptic outlet is more suitable for the honeycomb air filter.Different pleat heights have a certain influence on the flow field characteristics and pressure drop.The larger the flow rate,the more significant the pressure drop is affected by the change of pleats height.At the same flow rate,the pressure drop first decreases and then increases with the increase of pleat height.What?s more,the pressure drop reaches the minimum when the pleat height is 10 mm.Therefore,there is an optimum pleat height to minimize the pressure drop in the range of 7.5-12.5mm,which provides a theoretical basis for the optimum design of honeycomb air filter.