Numerical modeling of an active noise reduction system in the engine exhaust pipe

Numerical simulations of the exhaust pipe of the internal combustion engine with an active noise cancellation system are being reported. It is proposed to introduce an additional controlled sound source opposite in phase to the sound waves coming from the engine into the engine exhaust pipe. A round plate that performs rotational vibrations with a given frequency and amplitude is assumed to be the sound source. The ideal gas model is taken as an equation of state. The realizable k-ε turbulence model is applied to simulate the compressible gas flow. Using a direct method based on changing the position of the damper at each time step, the additional sound source created by the damper was modeled. The damper motion was realized within the framework of the sliding mesh approach. A spherical mesh segment capable of rotating during calculations was created. The influence of the plate size and the incoming sound wave parameters on the operation of the active noise cancellation system of an internal combustion engine was evaluated. The dependences of the amplitude of oscillations of static and total pressure at the output of the noise reduction system on the amplitude and radius of the oscillating damper were obtained. The simulations were conducted for various values of the exhaust radius, and the effect of the size of the expansion chamber in front of the oscillating damper was studied. The obtained results indicate that the proposed active noise cancellation system is able to reduce the engine noise level by 10 dB. It is shown that an increase in the plate radius leads to an increase in the efficiency of the noise suppression system. However ,at the same time, the level of aerodynamic resistance that the noise suppression system provides to the gas flow also increases, which can lead to a decrease in engine power characteristics.