Car Sound Generation: with and without Spoiler

Description

This project simulates aeroacoustic noise generation around an Audi car body, comparing configurations with and without a rear spoiler, using ANSYS Fluent. Aeroacoustics studies how sound arises from turbulent fluid motion and from aerodynamic forces striking surfaces; turbulent flow carries oscillating pressure and density gradients, and it's these oscillations, propagating as pressure waves, that constitute the generated sound. The subject matters well beyond automotive design, since the same mechanisms govern the very high noise levels produced around aerospace surfaces like airfoils. The car geometries, both with and without spoiler, are built in three dimensions in Design Modeler and meshed in ICEM, with airflow directed at the body at 70 m/s.

Methodology

Turbulence is resolved with the SST k-omega model, and the acoustic field is predicted using Fluent's Broadband Noise Sources model, which derives sound generation from the statistics of the turbulent flow rather than resolving acoustic waves directly. The acoustic setup uses standard air properties as reference: a density of 1.225 kg/m³, a sound speed of 340 m/s, and a reference acoustic power of 1×10⁻¹² Pa. Both the spoiler and no-spoiler configurations are run under identical inflow conditions so the two cases can be compared directly.

Analysis

The solution yields 2D pressure and velocity contours for both configurations, along with plots of velocity and acoustic power level along the car's longitudinal axis, sampled from a few meters upstream, across the car body, to a few meters downstream. These results show that adding the spoiler noticeably reduces the acoustic power generated by the airflow striking the body, from roughly 95 dB without the spoiler to about 70 dB with it. Interestingly, this trend reverses in the far wake behind the car, where the spoiler configuration actually shows higher acoustic power than the case without one, suggesting the spoiler suppresses near-body noise generation at the cost of somewhat more turbulent, noise-generating structure further downstream.