Computational Analysis of Noise Generation and Propagation Mechanisms using the Example of an HVAC Blower

H1 - Lattice Boltzmann Methods (ii)

This paper describes a computational approach to simulate passenger car HVAC blower noise. Besides validation, the purpose of the study is also to analyze flow structures that might influence noise generation.
In general, in early product development phases, fans and blowers are typically evaluated "standalone" in experiment, without the HVAC system or cooling package, but mounted in a test environment instead, nevertheless representing the crucial mechanisms that lead to noise generation and affect the fan or blower performance. The test environment used for the examinations discussed in this paper consists of a settling box, placed inside an anechoic chamber, with an imposed mass flow, where the rotating blower is mounted at an opening. Outside the box, within the anechoic environment, microphones are positioned.
The experiment can give overall results, like e.g. sound pressure measured in different microphone positions, showing general differences and enabling the comparison of different designs in terms of the noise generated. But this means that for each variation a prototype is necessary. By performing simulations, on the other hand, the variations can be tested virtually, thus reducing the number of physical prototypes. In order to validate such approach, microphone results were compared to experiments and showed good correlation.
Analyzing in detail the flow properties inside the system that lead to the generation of sound is costly if not impossible at all. So, another advantage of simulation is the possibility to gain more insight into the flow. Detailed analysis both in time and frequency domain are done to analyze and understand better the noise generation and propagation mechanisms.
In order to avoid a two-step approach where first a fluid simulation is performed and then e.g. acoustic analogies are used to predict sources for a standalone acoustic propagation simulation, the Lattice-Boltzmann method, a kinetic scheme modeling the dynamics of particle distributions, was used in combination with rotating meshes to represent the blower movement. This allows the prediction of both the transient hydrodynamic flow structures as well as the generation and propagation of the acoustic waves within the fluid at the same time.