Abstract

During acceleration of a vehicle the turbocharger operates very close to the surge line. At this operating regime of the turbocharger, the pressure ratio increases substantially in comparison to the increase in airflow. This leads to a NVH error state generically known as whoosh noise which is a broadband noise between 4000 Hz to 11000 Hz. A test for whoosh noise is usually performed late on the design stages and usually performed on the vehicle. This late testing in the design phase, increases risk of late changes if whoosh is detected. This also inhibits any design changes that could have mitigated the issue and requiring to take only palliative measures such as silencers or damping pads. These palliative measures to contain whoosh noise can be significantly expensive. Therefore, an analytical method becomes more desirable that could potentially save cost if whoosh noise is predicted early in the design process. These in-vehicle tests are performed with a microphone at the air induction system orifice location. So, the analytical model would not only need to predict the source accurately, but also it must predict the propagation of acoustic energy through the AIS without numerical loss to predict sound pressure level at the orifice location accurately. This CFD investigation aims to achieve the above; asses sound pressure level at different location in the air induction system including at the orifice. The results are then validated with actual gas turbine lab test results. The CFD uses transient aeroacoustics (CAA) along with rigid body motion to assess sound pressure level. The simulation demands a high level of spatial and temporal accuracy because the speed of rotation of turbocharger could be more than 100,000 RPM and to minimize numerical loss. The current investigation takes 6 weeks of CPU time on 384 Processors. The software StarCCM+ is used for CFD analyses & visual post-processing and LMS Testlab is used for NVH post-processing.