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We study in detail the flow mechanism, the aeroacoustic sources and its sound propagation in turbochargers by applying numerical simulations based on an appropriate aeroacoustic formulation. Thereby, we consider Lightill’s analogy for the investigation of the different noise mechanisms. The flow inside a turbocharger is highly turbulent and compressible. Thus, all three terms of Lighthill’s tensor are examined: (1) the Reynolds stress term, (2) the excess term and (3) the viscosity term. The investigations will be performed both in time and frequency domain, and we do a detailed study of the influences of different spatial and temporal discretizations.

Raising demands towards lightweight design paired with a loss of originally predominant engine noise pose significant challenges for NVH engineers in the automotive industry. From an aeroacoustic point of view, low frequency buffeting ranks among the most frequently encountered issues. The phenomenon typically arises due to structural transmission of aerodynamic wall pressure fluctuations and/or, as indicated in this work, through rear vent excitation. A possible workflow to simulate structure-excited buffeting contains a strongly coupled vibro-acoustic model for structure and interior cavity excited by a spatial pressure distribution obtained from a CFD simulation. In the case of rear vent buffeting no validated workflow has been published yet. While approaches have been made to simulate the problem for a real-car geometry such attempts suffer from tremendous computation costs, meshing effort and lack of flexibility.

Using existing aeroacoustic wave equations, we propose a general hybrid aeroacoustic method, based on compressible flow data. By applying the Helmholtz-Hodge decomposition on arbitrary domains, we extract the incompressible projection (non-radiating base flow) of the compressible flow velocity by solving the vector valued curl-curl equation with the vorticity as forcing term. The resulting vortical flow part is used for computing the acoustic source term. This method maintains the favorable properties of the hybrid aeroacoustic method, while still considering acoustic feedback on the flow field.

Reliable tools for the prediction of aeroacoustic noise are of major interest for the car industry and also for the vendors of heating, ventilation and air conditioning (HVAC) systems whose aim is to reduce the negative impact of HVAC noise onto passengers. In this work a hybrid approach based on the acoustic perturbation equations is tested for this purpose. In a first step, the incompressible flow field is computed by means of a commercial finite volume solver. A large eddy simulation turbulence model is used to obtain time resolved flow data, which is required to accurately predict acoustic phenomena. Subsequently, the aeroacoustic sources are computed and conservatively interpolated to a finite element grid, which is used to calculate the sound radiation. This procedure is tested for an HVAC unit, a radial blower and finally for a complete system, which combines these two components.

A shortcoming of widely-used integral methods for prediction of flow-induced sound emission of rotating systems is that the rotation of the impeller can be included in the calculation, but not reflections of sound from the housing, rotor blades and attached ducts. This paper introduces a finite element method that correctly maps both the sound sources rotating with the impeller and the reflections of the sound from the rigid surfaces of the components of the blower. For the prediction of flow-induced sound a hybrid approach is employed using separate CFD and acoustic simulations. It is based on a decomposition of flow (incompressible part) and acoustic (compressible part) quantities and is applicable to high-Reynolds-number and low-Mach-number flows. It features only a scalar unknown (i.e. the acoustic velocity potential), thus reducing the computational effort significantly.

To reduce noise in a HVAC system for railway application the usage of micro-perforated panels (MPP) is proposed. MPPs offer some favorable characteristics, like robustness and durability in harsh environments and the possibility to optimize absorption in desired frequency bands. The underlying acoustic mechanism can be modelled via an equivalent fluid in accordance with the Johnson-Champoux-Allard (JCA) approach, treating the MPPs as a porous material with rigid frame. This allows to conduct the necessary acoustic pre-evaluation in complex HVAC application scenarios in order for the MPPs to substitute the commonly used foam and fibrous absorber materials.

We present a recently developed computational scheme for the numerical simulation of flow induced sound for rotating systems. Thereby, the flow is computed by scale resolving simulations using an arbitrary mesh interface scheme for connecting rotating and stationary domains. The acoustic field is modeled by a perturbation ansatz resulting in a convective wave equation based on the acoustic scalar potential and the substational time derivative of the incompressible flow pressure as a source term. We use the Finite-Element (FE) method for solving the convective wave equation and apply a Nitsche type mortaring at the interface between rotating and stationary domains. The whole scheme is applied to the numerical computation of a side channel blower.

A low pressure axial fan for benchmarking numerical methods in the field of aerodynamics and aeroacoustics is presented. The generic fan for this benchmark is a typical fan to be used in commercial applications. The design procedure was according to the blade element theory for low solidity fans. A wide range of experimental data is available, including aerodynamic performance of the fan (fan characteristic curve), fluid mechanical quantities on the pressure and suction side from laser Doppler anemometer (LDA) measurements, wall pressure fluctuations in the gap region and sound characteristics on the suction side from sound power and microphone array measurements. The experimental setups are described in detail, as to ease reproducibility of measurement positions. This offers the opportunity of validating aerodynamic and aeroacoustic quantities, obtained from different numerical tools and procedures.

A low pressure axial fan for benchmarking numerical methods in the field of aerodynamics and aeroacoustics is presented. The generic fan for this benchmark is a typical fan to be used in commercial applications. The design procedure was according to the blade element theory for low solidity fans. A wide range of experimental data is available, including aerodynamic performance of the fan (fan characteristic curve), fluid mechanical quantities on the pressure and suction side from laser Doppler anemometer (LDA) measurements, wall pressure fluctuations in the gap region and sound characteristics on the suction side from sound power and microphone array measurements. The experimental setups are described in detail, as to ease reproducibility of measurement positions. This offers the opportunity of validating aerodynamic and aeroacoustic quantities, obtained from different numerical tools and procedures.