Noise and Vibration Research Group - Aeroacoustics Research Group - Jobs

Open positions in Aeroacoustics

We are seeking early-stage as well as experienced researchers to join the Aeroacoustics Research Group of the Department of Mechanical Engineering of the K.U.Leuven, Belgium.

• prof. dr. ir. Martine Baelmans
• prof. dr. ir. Wim Desmet

General scope
The general scope of the Aeroacoustic Research Group is the development and experimental validation of hybrid numerical methodologies for the aeroacoustic analysis of noise generation and noise propagation in low-Mach number confined engineering flows, with particular focus on (automotive) muffler and ducted fan applications.
The simulation of noise generation in flows requires the use of advanced Computational Fluid Dynamics (CFD) techniques, whereas for noise propagation, more efficient simulation methods from (linear) acoustics can be used. A multidisciplinary approach from fluid mechanics and acoustics is therefore necessary. This research area, known as Computational Aero-Acoustics (CAA), is a highly innovative, emerging discipline with enormous numerical challenges resulting from the large disparity in energy levels and length- and time scales between flow perturbations and acoustic waves.
From a theoretical point of view, all aeroacoustic problems can be described by the compressible Navier-Stokes (NS) equations. CAA problems can therefore, in principle, be solved using CFD techniques only, such as Direct Numerical Simulation (DNS) and/or Large Eddy Simulation (LES) techniques. These are referred to as direct methods.
A more pragmatic and practically feasible approach is to use a hybrid method where the noise generation and noise propagation processes are considered separately. The same (non-linear) CFD techniques used in direct methods are still applied, but now only to identify and quantify the noise sources. These are then coupled to (linear) methods that calculate the noise propagation and radiation into the far field. Because of the linearization, this hybrid approach excludes a feedback of the acoustic waves on the flow field, unless the feedback mechanism is correctly captured by a high-order CFD scheme, and the propagation region is defined outside of this extended source region. Hybrid methods alleviate, however, the computational burden and allow tackling engineering applications.

Activities within the research group
The K.U.Leuven Aeroacoustics Research Group is developping a suite of hybrid CAA methodologies for subsonic confined flow analysis.
For noise generation modelling, an LES-based approach is adopted. LES provides a good compromise between accuracy and computational effort, by filtering the Navier-Stokes equations in space and solving them on a grid that allows representing the turbulent scales that are bigger than the filter size, while the effect of the small scales is modelled with a subgrid-scale model. Given their simplicity and ease-of-implementation, eddy-viscosity models are currently applied, assuming that the subgrid-stress tensor is proportional to the resolved rate of strain.
For (time-domain) noise propagation modelling, an LEE-based approach is adopted. Convection and refraction effects have an important influence on the propagation of acoustic waves in a moving medium. These flow effects are not taken into account in the linear acoustic or the convected wave equation. The Linearised Euler Equations (LEE) can be used to describe the noise propagation in the presence of a non-uniform mean flow. Due to the specific character of acoustic waves, numerical schemes for solving the LEE should have, as compared to classical CFD-computations, a high accuracy with minimum dispersion and dissipation errors. Moreover, boundary conditions may not introduce spurious reflections back into the computational domain. Numerical solution schemes for the LEE equations are being developped using both a finite difference (2D) and discontinuous Galerkin (3D) formulations. The former propagation code uses a Dispersion Relation Preserving (DRP) finite difference scheme and a Low-Dispersion and Dissipation Runge-Kutta scheme to obtain fourth-order accuracy overall. It allows the use of several methods to describe the aeroacoustic sources and supports different types of non-reflecting boundary conditions. The second propagation code uses a Discontinuous Galerkin Method for the spatial discretisation and a low-storage optimized Runge-Kutta method for the time discretisation. The Discontinuous Galerkin Method has good dispersion and dissipation properties. It is also very compact, which makes it very suitable for unstructured grids and parallelisation. Also here, many types of boundary conditions are available, including a Perfectly Matched Layer (PML).
These propagation schemes can be driven with conventional acoustic source terms, with aero-acoustic analogy source terms and with (aero-)acoustic boundary conditions. In this way, the LEE can be used both to solve acoustic propagation applications in a moving medium and to solve aero-acoustic applications. Besides the LEE, the research also focuses on the validation of other formulations, similar to the LEE, to describe the sound propagation in subsonic confined flows. Alternative formulations include the Acoustic Perturbation Equations (APE) and the Expansion about Incompressible Flow (EIF) formulation.

The sollicitated early-stage and experienced researchers are invited to join our efforts in the further improvement and validation of the LES- and/or the LEE-based numerical schemes, as well as the hybrid coupling strategies.

Project framework
The research activities are part of a 4-year research project, entitled ‘Simulation and design tools towards the reduction of aerodynamic noise in confined flows’, starting on June 1, 2006. The project consortium consists of several Belgian research laboratories and companies, including the Departments of Mechanical Engineering of the Katholieke Universiteit Leuven (K.U.Leuven) and the Free University of Brussels (VUB), the von Karman Institute for Fluid Dynamics, LMS International and NUMECA International. The project is part of the SBO programme, funded by the Flemish Government.

Eligibility and desired background
We are seeking both early-stage researchers, pursuing a Ph.D. degree, as well as experienced researchers. The Ph.D. candidates should hold an Engineering Degree (M.Sc. in Mechanical, Electrical, Computer Science, Civil, Aerospace, Physics Engineering, or equivalent). The experienced researchers, seeking a one- or two-years research position in support of our CAA activities, should have a solid background in computational dynamics, preferably in computational aeroacoustics.
K.U.Leuven is an equal opportunity employer.

Specific technical competencies:

• Knowledge of FE and/or CFD solvers is an asset;
• Knowledge in fluid dynamics, acoustics or aero-acoustics is a strong advantage;
• Programming skills are a significant advantage;
• Knowledge in numerical acoustics is a definitive advantage;
• Good English redaction skills for scientific reporting;

Benefits:
The K.U.Leuven Department of Mechanical Engineering offers to the selected candidates a very competitive salary, including social security. Funding for participation to courses, workshops and international conferences is ensured. The city of Leuven, just 20 km east of Brussels, the heart of Europe, offers a stimulating, young and multicultural working environment.