The air noise generated by automotive climate control systems is today emerging as one of the main noise sources in a vehicle interior. In the confined instrument panel (I.P.) ducts, that lead the air flow from the HVAC outlets to the cabin, the highly constrained geometry generally leads to flow separation and to complex flow structures that contribute to the noise perceived in the car.
Numerical simulation offers a good way to analyze these mechanisms and to identify the aerodynamic noise sources, in an industrial context driven by permanent reduction of programs timing and development costs, implying no physical prototype of ducts before serial tooling. This paper presents an example of aero-acoustic study of simple I.P. ducts performed with the finite element code ACTRAN to estimate the sound produced by the turbulent flow. For this type of configuration, the acoustic propagation is decoupled from the noise generation mechanism that is essentially of aerodynamic nature.
The methodology is the following: the unsteady flow field is first computed using a CFD solver -here FLUENT™- which provides the aero-dynamic quantities at each time step. Then, the finite element acoustic solver computes the acoustic sound sources according to the theory developed by Lighthill [1] and leading to the so called Lighthill's equation. The sources are converted in the frequency domain and propagated into the vehicle interior.
Acoustic maps allow the identification of the noise source locations within the turbulent flow. Another advantage of the technique is that the CFD computations are completely separated from the acoustic computations. This allows reusing one CFD computation for many different acoustic computations. Consequently, the method fully suits for the acoustic design of I.P. ducts of VISTEON.
In this paper, the mathematical aspects of the method are first briefly introduced. Then, the method is applied to real I.P. components.. The LES CFD computations are presented as well as the acoustic simulations. The accuracy of the method is demonstrated by comparing the numerical results to experimental results available for several basic I.P. ducts configurations.