Research On High Temperature Airflow Condition Simulation Of Muffler Experiment Technology

As an important noise reduction component of an automobile,muffler with poor acoustics performance and will lead to noise pollution and unsatisfying driving comfort.The muffler performance tests are conducted in the case of no airflow during design procedure,ignoring the influence of flow velocity and temperature on the acoustic performance.Actual noise reduction effectiveness couldn't match design goals,resulting in the waste of manpower and material resources.Therefore,a test bench with controllable airflow velocity and temperature,which can be applied to performance test of muffler with different structural parameters,will be able to develop mufflers from the aspect of practicability,improving design efficiency and reduce design cost.In this paper,the performance test bench of muffler consists of a vortex fan,an air heater and a harmonic source system.An air heater is designed at ultimate working condition for test bench to warm the air,of which aerodynamic noise characteristics is obtained.Sound source front-end muffler is designed based on vortex fan noise characteristics at different airflow velocity combined with aerodynamic noise of heater,in order to improve signal to noise ratio of sound source and guarantee correct test results.Influence of airflow and temperature on the acoustic performance is then analyzed.To achieve automatic control of the test bench,the inverter and differential pressure meter interact with PC through serial communication on basis of RS485 data bus,which is accomplished with VB.net program.Velocity of airflow is under feedback control on basis of incremental PI algorithm.Acoustics test of sample muffler is realized through two-load method and integrated controllable effectiveness of airflow velocity and muffler performance testing is finally verified.As is what analysis results show,The air heater could heat airflow to 485? with velocity of 35.3m/s,at which condition aerodynamic noise of air heater is less than 70 dB in the frequency range of 50-1500 Hz and makes little difference to sound source.Average static transmission loss of sound source front-end reactive muffler can be up to 30 dB in frequency range of 100-1500 Hz.The transmission loss curve is stretched and overall noise reduction is still over 25 dB when velocity and temperature of airflow at the entrance reach 40m/s and 500?.The resistance muffler works well in medium and high frequency.Feedback control is successfully accomplished.Velocity of airflow reaches stability within 10 s and overshoot is less than 3%.Transmission loss of sample muffler is tested with airflow velocity at 18m/s,and satisfying results proves integration of airflow control and performance testing has been successfully achieved.