Computation of internal aerodynamic noise from a quick-opening throttle valve using frequency-domain acoustic analogy

Recently, plastic products in air-intake parts of automotive engines have become very popular due to advantages that include reduced weight, constricted cost, and lower intake air temperature. However, flow-induced noise in air-intake parts becomes a more serious problem for plastic intake-manifolds than for conventional aluminum-made manifolds. This is due to the fact that plastic manifolds transmit more noise owing to their lower material density. Internal aerodynamic noise from a quick-opening throttle valve is computed by using a frequency-domain acoustic analogy, which is based on the integral formula derived by using the General Green Function, Lighthill's acoustic analogy and Curle's extension of Lighthill's. The integral formula is arranged in such a manner that allows a frequency-domain acoustic signal to be predicted at any location in a duct through the use of unsteady flow data in space and time, which can be obtained by applying Computational Fluid Dynamics techniques. The prediction of the acoustic pressure level from the quick-opening throttle valve shows good agreement with actual measurement. Through the detailed analysis of the flow-noise generation mechanism it was found that the anti-vortex lines, formed behind the throttle valve during the quick-opening behavior, feed the large-scale coherent turbulence and, as a result, play a crucial role in generating the dipolar sound from unsteady loading of the quick-opening throttle valve. From this, it can be inferred that the low-noise design of the throttle-duct system can be made by using this concept to break the large-scale vortex structure.