Browse Publications Technical Papers 2019-01-1569
2019-06-05

Multi-Physics and CFD analysis of an Enclosed Coaxial Carbon Nanotube Speaker for Automotive Exhaust Noise Cancellation 2019-01-1569

Automotive exhaust noise is one of the major sources of noise pollution and it is controlled by passive control system (mufflers) and active control system (loudspeakers and active control algorithm). Mufflers are heavy, bulky and large in size while loudspeakers have a working temperature limitation. Carbon nanotube (CNT) speakers generate sound due to the thermoacoustic effect. When an alternating current is passed through the CNT film having low heat capacity per unit area, their surface temperature undergoes rapid oscillations. These oscillations create density variation in the surrounding medium, resulting in generation of pressure waves or sound. CNT speakers are also lightweight, flexible, have acoustic and light transparency as well as high operating temperature. These properties make them ideal to overcome the limitations of the current exhaust noise control systems. An enclosed, coaxial CNT speaker is designed for exhaust noise cancellation application. The development of a 3D multi-physics (coupling of electrical, thermal and acoustical domains) model, for the coaxial speaker is discussed in this paper. The acoustic transparency of the CNT film is modeled using interior impedance boundary condition. The model is used to simulate the sound pressure level, input power versus ambient temperature and efficiency. The model is validated by comparing the experimental results with the simulation results. Along with multi-physics simulation, CFD analysis of the coaxial speaker is also studied in this paper. The CFD analysis is focused on the backpressure generated by the speaker and the flow path of the exhaust gases inside the CNT speaker.

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