5 FRIA doctoral fellowships have been granted by FNRS

We are pleased to announce that 5 FRIA doctoral fellowships have been granted by FNRS during its Board meeting of 6 December 2016 to PhD candidates enrolled in the VKI PhD program.

FRIA stands for "Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture" and is managed by FNRS (Belgian Scientific Research Foundation for the Fédération Wallonie-Bruxelles).

The candidates who obtained the grant are:

FRIA 1st grant - first year

- Nicolas Coudou (VKI supervisor Prof. Jeroen van Beeck – Prof. L. Bricteux (Université de Mons, Belgium) and Prof. Philippe Chatelain (Université catholique de Louvain, Belgium) - see the abstract below

- Ludovico Zanus (VKI supervisor Prof. Olivier Chazot –& Prof. G. Degrez(Université Libre de Bruxelles, Belgium) - see the abstract below

FRIA 1st grant - second year

- Elissavet Boufidi (VKI supervisor Prof. Fabrizio Fontaneto & UCL supervisor Prof. Tony Arts ) - see the abstract below

FRIA 2nd grant

- Gori Gian Luca (VKI and UCL supervisor Prof. Tony Arts)- see the abstract below

- Orkun Temel (VKI supervisor Prof. Jeroen van Beeck & Prof. L. Bricteux (Université de Mons, Belgium) - see the abstract below

Abstract of Nicolas Coudou

Study of wake meandering phenomenon

Nicolas CoudouLarge wind farms with installed capacities that reach up to 1GW cover 11.5% (end 2015) of the electrical power demand in the European Union for a normal wind year. This share is foreseen to increase dramatically by the year 2020 ; it will be translated in more, and larger, clustered wind farms.

An important aspect of wind farm design is the farm layout optimization. It consists in optimally positioning the wind turbines within the wind farm so that the wake effects are minimized in order to maximize the efficiency and the lifetime of downstream turbines. It is therefore essential to have an in-depth knowledge of wind turbine wake flow physics. More specifically, the vortical wake meandering is a well-known phenomenon for which the fundamental turbulence mechanisms are not yet well understood. This phenomenon causes the wake to be swept in and out of the rotor disk of downstream turbines. It is thus critical to understand it to predict mechanical fatigue and loading on the downstream turbines.

The aim of this project is to study in-depth the wake meandering phenomenon using a combination of advanced experimental and numerical tools.

The numerical studies will rely on a high performance implementation of a state-of-the-art Vortex Method. The advanced turbulence models (Large Eddy Simulation, LES) implemented as well as an original actuator line model will allow to capture very fine physical details of the wake turbulence to better understand the physical phenomenon considered.

The phenomenon will be also studied on a scaled wind farm located in an atmospheric boundary layer wind tunnel (VKI atmospheric wind tunnel, 2x3m section, 50m/s, a remarkable facility at European scale). The experiments to be carried will provide stereoscopic particle image velocimetry (PIV) results to validate the numerical approach.

Abstract of Ludovico Zanus

Numerical study of chemically reacting hypersonic boundary layer by means of Nonlinear Parabolized Stability Equations

Ludovico ZanusThe study of stability and laminar-turbulent transition is one of the most relevant problems in fluid dynamics. Accurate predictions of the transition location have a fundamental importance in many applications, being directly related to accurate heat flux and skin friction estimations. This is a particularly delicate aspect when related to hypersonic flows, where the physics complexity and the lack of experiments often lead to large uncertainty design margins.

The common and widely used eN method based on Linear Stability Theory (LST) results presents some limitations related to the local assumption underlying this theory. These deficiencies can be overcome by using the so called Nonlinear Parabolized Stability Equations (NPSE) technique. In this way, the streamwise development of the instability can be captured and effects like nonparallelism and curvature can be taken into account. Moreover, by considering physical nonlinearities the analysis can be conducted up to the final stages of the transition process, thus determining with a quite good accuracy the turbulent breakdown location.

The goal of this project is to study the stability and predict transition of a realistic hypersonic flow such the one faced by space vehicles during ann atmospheric re-entry or by future high speed spaceplanes. In order to have an accurate and reliable description of the investigated phenomenon high temperature gas effects have to be taken into account, such for example Thermo-Chemical Non-Equilibrium conditions (TCNEQ).

The NPSE method in TCNEQ will be developed inside the framework of the VKI Extensible Stability and Transition Analysis (VESTA) toolkit. The results obtained by the numerical investigation will be compared against the inflight data collected by the re-enty Intermediate eXperimental Vehicle (IXV), developed by a partnership of European countries and launched by the ESA in 2015. This project may exploit the IXV data and provide new knowledge on similar applications

Abstract of Elissavet Boufidi

The characterization of turbulence in high speed, compressible and complex industrial flows

Elissavet BoufidiA rigorous characterization of flow turbulence (i.e. turbulence intensity, time and length scales, spectrum) is needed to understand in depth loss mechanisms and heat transfer in complex turbomachinery flows. Moreover, the extensive use of high-fidelity CFD requires accurate boundary conditions at the borders of the computational domain, as well as data to improve and validate turbulence models. Nevertheless, due to the limitations of currently established measurement techniques, turbulence data at engine representative flow conditions are very limited in literature.

The goal of this project is to fill this gap by developing a measurement methodology based on Fast Response Aerodynamic Pressure Probes (FRAPPs), to exploit their robustness and large bandwidth. The Hot Wire Anemometry (HWA) technique is employed as well to act as reference tool. HWA is a traditionally used tool for accurate turbulence measurements, but due to its fragility it cannot be used in high temperature flows and harsh environments.

The first phase of the project focuses on the development of the measurement methodology. The HWA will be enhanced to retrieve velocity fluctuations in conditions where its application is particularly complex. Using HWA as a reference tool, the capabilities of FRAPPs to measure turbulence will be systematically investigated. The second phase of the project then consists in the application of the developed measurement methodology to test cases of increasing complexity: a low pressure turbine linear cascade with simulation of the incoming wakes and a 1.5 high pressure turbine stage test section, both at engine similar operating conditions. The methodology is thus tested in 2D and 3D unsteady compressible flows with complex turbulence topology. These measurements will constitute a significant contribution to our knowledge of turbulence in high speed turbomachinery flows, leading to a better understanding of loss mechanisms and turbulence generation in these two cases.

Abstract of Gian Luca Gori

Determination and Modeling of the Aero-Thermal Behavior of a Cooling Channel

Gian Luca GoriCooling channels have wide applications, ranging from aeronautics to oil, automotive and nuclear industry. Initially designed with smooth walls, their surface has rapidly been equipped with various obstacles to increase the thermal exchange area and the local mixing. The main objective is to maximize the wall heat transfer while keeping the channel pressure drop as low as possible. The proposed research focuses on an aeronautical application (gas turbines), but is of definite interest to many other fields of engineering.

The thermal efficiency of a gas turbine cycle increases with the Turbine Inlet Temperature. The limits are set by the blades and endwalls material resistance against thermal and mechanical loads. Their life time will increase by using efficient cooling techniques. A major contribution to the heat extraction is ensured by forced convection. Although known for a long time, it still has margin for important improvements. The classical CFD codes approaches based on isotropic turbulence and constant Prt models provide limited fidelity. High resolution reliable experimental data are therefore needed for the validation and new modeling purposes. Their actual lack is mainly due to the complexity and availability of measurement techniques and representative facilities.

In addition to the of the wall heat transfer and the flow velocity available in literature, the present research wants to provide the flow temperature. Laser-Induced Fluorescence, however difficult to apply in gas-phase, will provide a 2D distribution of the temperature non-intrusively. Never applied in Internal Cooling and, so far, in internal continuous flows, it represent the main challenge of the research. Further, synchronized measurements with PIV will provide information of Prt, never measured and of particular interest for CFD modeling.

The main goal is to provide an intermediate link between the already available PIV and LCT data for the understanding of the physical phenomena. Moreover, with the determination of Prt this study might provide important statements for CFD modeling improvements.

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