In-Duct Acoustic Source Data for Roots Blowers

Increased demands for reduction of fuel consumption and CO2 emissions are driven by the global warming. To meet these challenges with respect to the passenger car segment the strategy of utilizing IC-engine downsizing has shown to be effective. In order to additionally meet requirements for high power and torque output supercharging is required. This can be realized using e.g. turbo-chargers, roots blowers or a combination of several such devices for the highest specific power segment. Both turbo-chargers and roots blowers can be strong sources of sound depending on the operating conditions and extensive NVH abatements such as resonators and encapsulation might be required to achieve superior vehicle NVH. For an efficient resonator tuning process in-duct acoustic source data is required. No published studies exists that describe how the gas exchange process for roots blowers can be described by acoustic sources in the frequency domain. This paper presents an experimental study that aims to investigate if a linear time invariant acoustic 1-port model can represent the in-duct sound source of a roots blower in- and outlet. Different operating conditions are investigated for a wide rotation speed range. The results show that it is possible to use a linear acoustic source model to represent a roots blower and that sound predictions can be performed with good accuracy.