Gregoire Winckelmans

• PhD Aeronautics
• Catholic University of Louvain

Large eddy simulation (LES) can be performed using general-purpose flow solvers such as Fluent or OpenFOAM. These solvers typically require regular grids with high orthogonality and low skewness for explicit LES. Consequently, most existing LES studies of indoor airflows rely on structured grids. Given this grid constraint, this paper presents a no...

Depending on the application, both RANS and LES can be relevant for the simulation of airflows inside buildings. Although high-resolution LES can be performed using general-purpose flow solvers such as Fluent or OpenFoam, regular grids with good orthogonality and limited skewness are required. Therefore, most existing LES for airflows inside buildi...

This paper investigates the impact of blade flexibility on the aerodynamics and wake of large offshore turbines using a flexible actuator line method (ALM) coupled to the structural solver BeamDyn in large-eddy simulations. The study considers the IEA 15 MW reference wind turbine in close-to-rated operating conditions. The flexible ALM is first com...

The actuator line method (ALM) is a commonly used technique to simulate slender lifting and dragging bodies such as wings or blades. However, the accuracy of the method is significantly reduced near the tip. To quantify the loss of accuracy, translating wings with various aspect and taper ratios are simulated using several methods: wall-resolved Re...

The interest towards supersonic ejectors as replacement for compressors in various industrial applications has grown over the last decade. In contrast with the simplicity of their working principle, the turbulent phenomena responsible for the entrainment and mixing are still not fully understood nor well captured by numerical simulations. Indeed, m...

In scale-resolving simulations such as Large Eddy Simulations (LES), the spatial discretization scheme of the convective term plays a crucial role in avoiding interference between the numerical errors and the subgrid-scale model. Accurate schemes lead to lower truncation errors and better predictions of turbulent flows without the need for an exces...

This paper investigates the impact of rotor size on the structural displacements and loads of large wind turbines during power production. The actuator line method is used in Large Eddy Simulations and is coupled to a structural solver for the blades. The latter consists either of a linear solver based on the Euler-Bernoulli beam theory, or uses Be...

Airborne Wind Energy Systems (AWES) consist of tethered wings harvesting power from the wind. Rigid-wing (aircraft) pumping-mode AWES are considered here: they generate power during the reel-out phase and consume a fraction of this power during the reel-in phase. Those devices fly complex trajectories that require advanced control strategies. In th...

Wind energy is playing an essential role in the energy transition towards a carbon-neutral system, for which wind turbine wakes are one of the most important aspects. By extracting energy from the flow, the turbine generates power but also decreases the production and increases the loading of downstream wind turbines; and potentially affects nearby...

A turbulent two-vortex system (T-2VS) is obtained by inserting analytical model wake vortices into very weak homogeneous isotropic turbulence (HIT) and by evolving them in time using large-eddy simulation until a turbulent state at statistical equilibrium is reached. The T-2VS is characterised as follows: circulation distribution of the vortices; e...

This paper investigates the impact of the blades flexibility on the aerodynamics and wake of large offshore turbines using a flexible actuator line method (ALM) coupled to the structural solver BeamDyn in Large Eddy Simulations. The study considers the IEA 15-MW reference wind turbine in close-to-rated operating conditions. The flexible ALM is firs...

Wall modelling in large-eddy simulation (LES) is of high importance to allow scale resolving simulations of industrial applications. Numerous models were developed and validated for incompressible flows, including a simple quasi-analytical model based on Reichardt’s formula that approximates the law of the wall. In this paper, a scaling is proposed...

This work presents an investigation of the aeroelastic effects occurring on the IEA 15-MW reference wind turbine in a turbulent atmospheric boundary layer. Large Eddy simulation is carried out using an actuator line method coupled to the finite element beam solver BeamDyn . The results show that the blades experience significant displacements, lead...

Wind energy is usually harnessed using wind turbines but it is not the only way of collecting this energy. In this paper, Airborne Wind Energy Systems (AWES) are considered. The understanding of the wake shed by such devices is of primary importance when considering farms, yet it has not been much studied so far, and even less so when considering k...

Turbulent flows are most often wall-bounded, rendering the treatment of the wall essential. In this work, the near-wall layer is modelled in large eddy simulations which enables simulating high Reynolds number flows. An algebraic wall model has been implemented in the spectral element code Nek5000. It consists of an approximate boundary condition t...

We introduce and validate a weak coupling approach between a body-fitted velocity-pressure solver and a Vortex Particle-Mesh (VPM) method in 2D for the simulation of incompressible external aerodynamics. The approach does not involve inner iterations, conserves circulation up to interpolation accuracy without resorting to a panel method, and accomm...

Wall models reduce the computational cost of large eddy simulations (LES) by modeling the near-wall energetic scales and enable the application of LES to complex flow configurations of engineering interest. However, most wall models assume that the boundary layer is fully turbulent, at equilibrium, and attached. Such models have also been successfu...

From small drones to large Urban Air Mobility vehicles, the market of vertical take-off and landing (VTOL) aircraft is currently booming. Modern VTOL designs feature a variety of configurations involving rotors, lifting surfaces and bluff bodies. The resulting aerodynamics are highly impacted by the interactions between those components and their w...

The current trend of wind turbine upscaling has led to the use of long and slender blades prone to large structural deformations. In the present study, the impact of the aeroelastic effects is assessed for the NREL-5MW wind turbine in a turbulent wind. To this end, an actuator curve method coupled to a one-dimensional finite-element structural solv...

A recent challenge in the modeling of particle flows is to build microstructure-informed drag models to overcome the average description of the fluid-particle force in the drag force correlations currently used in Euler–Lagrange and Euler-Euler models. To that end, we study through particle-resolved direct numerical simulations (PR-DNS) the flow pa...

We focus on the wake function F(Y), where Y=y/δ: the excess velocity above the logarithmic profile in wall-bounded turbulence. It is first measured using direct numerical simulation data of turbulent channel flow at Reτ≃5200, which has a distinguishable overlap layer. The function Q(Y)=YF′(Y) is seen to be significant only beyond Yc≃0.16, and also...

The impact of the blade support structures (the struts) on the performance of vertical-axis turbines at a high Reynolds number is investigated here. Numerical simulations of a single-blade turbine with different strut configurations are carried out and the results are compared to a reference hypothetical turbine without strut. The results show that...

Midway between a vortex method and a grid-based CFD, the Vortex Particle-Mesh method with Immersed Lifting Lines is intended to provide medium-fidelity results on rotor loadings, together with a realistic representation of the 3-D vortical wakes and their dynamics over long distances. We assess the potential of this hybrid approach for the Large-Ed...

We perform direct numerical simulation (DNS) and large eddy simulation (LES) of an initially spherical region of turbulence evolving in free space. The computations are performed with a lattice Green's function method, which allows the exact free-space boundary conditions to be imposed on a compact vortical region. LES simulations are conducted wit...

We perform direct numerical simulation (DNS) and large eddy simulation (LES) of an initially spherical region of turbulence evolving in free space. The computations are performed with a lattice Green's function method, which allows the exact free-space boundary conditions to be imposed on a compact vortical region. LES simulations are conducted wit...

The advance in wind turbine technology has led to a tendency to gather the turbines into wind farms to benefit from economies of scale. However, the farm configuration often leads to a drastic power loss due to the interactions between the turbines. To mitigate this issue, the turbines are typically misaligned with the dominant wind direction to de...

We perform the large-eddy simulation of the flow past a helicopter rotor to support the investigation of rotorcraft wake characteristics and decay mechanisms. A hybrid Lagrangian-Eulerian Vortex Particle-Mesh method is employed to simulate the wake development, with the blades modeled using immersed lifting lines. The validity of the numerical appr...

We perform the large-eddy simulation of the flow past a helicopter rotor to support the investigation of rotorcraft wake characteristics and decay mechanisms. A hybrid Lagrangian–Eulerian vortex particle–mesh method is employed to simulate the wake development with the blades modeled using immersed lifting lines. The validity of the numerical appro...

We perform the large-eddy simulation of the flow past a helicopter rotor to support the investigation of rotorcraft wake characteristics and decay mechanisms. A hybrid Lagrangian–Eulerian vortex particle–mesh method is employed to simulate the wake development with the blades modeled using immersed lifting lines. The validity of the numerical appro...

We perform the large-eddy simulation of the flow past a helicopter rotor to support the investigation of rotorcraft wake characteristics and decay mechanisms. A hybrid Lagrangian–Eulerian vortex particle–mesh method is employed to simulate the wake development with the blades modeled using immersed lifting lines. The validity of the numerical appro...

The numerical study of the wake of full-scale slender devices such as aircraft wings and wind turbine blades requires high-fidelity large eddy simulation tools. The broad spectrum of scales involved entails the use of coarse-grain models for the devices. Actuator disk or line methods have been developed for that purpose, and are to date the most em...

To detect wake vortices in all weather conditions, lidar and radar sensors are complementary. It is important to determine accurately the limitations of the radar detection in clear air and to determine the parameters influencing the detection. This paper is the first study to present the simulation and analysis of the radar signatures of wake vort...

In this paper, the Brinkman penalization method is extended to the weakly compressible formulation of the Navier-Stokes equations to study gas-particle flows with reactions and coupled heat and mass transfer. The weakly compressible approximation removes the acoustic modes from the solution while allowing a variable density. The Brinkman volume pen...

We present an Immersed Interface Vortex Particle-Mesh (IIVPM) method in 2D and validate our approach. Unlike other VPM-based approaches, it converges in time and space up to the boundary, and hence it offers a sharp and accurate way to take the presence of obstacles into account. We first present the methodology and investigate its convergence. We...

Wall-Modeled Large-Eddy Simulation (WMLES) alleviates the near-wall grid requirement by employing a wall-model to reconstruct the wall shear-stress. In this way, WMLES simultaneously reduces the computational cost associated with Wall-Resolved LES (WRLES) and opens the door towards higher Reynolds numbers (Piomelli, Wall-modeled large-eddy simulati...

Building on the well-known Prandtl lifting line, this work proposes an extended framework for mollified lifting lines, which is valid for multidimensional Gaussian smoothings. The smoothing length scale σ can be taken as constant or variable across the span. In this framework, slender lifting device and its wake are represented by a mollified vorte...

In most Rapid Compression Machine (RCM) operations, it is sought to have a homogeneous temperature field inside the core region of the reaction chamber so that the adiabatic core assumption may be appropriately applied. Pistons with crevice on their side have shown to be effective in producing a uniform temperature field at the end of the compressi...

In this paper, we derive the non-singular Green's functions for the unbounded Poisson equation in one, two and three dimensions using a spectral cut-off function approach to impose a minimum length scale in the homogeneous solution. The resulting non-singular Green's functions are relevant to applications which are restricted to a minimum resolved...

This paper presents an in-depth study, using wall-resolved Large-Eddy Simulation (wrLES), of a high Reynolds number airfoil in a near-stall condition. The flow around the NACA4412 airfoil, a widely used test case for turbulence modeling validation, is computed at Reynolds number Re = 1.64 × 10⁶ and angle of attack α = 12∘. In the first part of the...

The study of wind turbines requires a multidisciplinary approach that covers the electrical, mechanical and aerodynamic aspects. Most wind turbine studies focus their modelization effort on a single aspect and rely on simplified models for the other ones. The present paper aims at a complete modelization and investigation of the energy conversion c...

This work aims at assessing the performance of a tip‐loss correction for advanced actuator disk (AD) methods coupled to large eddy simulation and making this correction possible in a wind farm configuration. The classical Glauert tip‐loss factor, commonly used in the blade element momentum method, is added here to correct the tip and the root induc...

Abstract We present a fast and efficient Fourier-based solver for the Poisson problem around an arbitrary geometry in an unbounded 3D domain. This solver merges two rewarding approaches, the lattice Green's function method and the immersed interface method, using the Sherman-Morrison-Woodbury decomposition formula. The method is intended to be seco...

This paper presents the implementation and validation of a remeshed Vortex Particle-Mesh (VPM) method capable of simulating complex compressible and viscous flows. It is supplemented with a radiation boundary condition in order for the method to accommodate the radiating quantities of the flow. The efficiency of the methodology relies on the use of...

Vortex methods are presented, from the fundamentals to the advanced subjects. These methods are well suited to simulating unsteady, convection-dominated, flows (inviscid and viscous). The spectrum of applicability is thus quite large. Examples are presented in incompressible flows (unbounded flows and bluff-body flows) and in combustion.

The present work focuses on the Large Eddy Simulation of the wake flow behind an advancing rotor, to support the investigation of rotorcraft wake characteristics and decay mechanisms. A mixed Lagrangian-Eulerian Vortex Particle-Mesh (VPM) method was employed to simulate the near to far wake development of a four-bladed rotor. The rotor configuratio...

The present work focuses on the Large Eddy Simulation of the wake flow behind an advancing rotor, to support the investigation of rotorcraft wake characteristics and decay mechanisms.

Wall-resolved Large-Eddy Simulations (LES) are still limited to moderate Reynolds number flows due to the high computational cost required to capture the inner part of the boundary layer. Wall-modeled LES (WMLES) provide more affordable LES by modeling the near-wall layer. Wall function-based WMLES solve LES equations up to the wall, where the coar...

We formulate the penalization problem inside a vortex particle-mesh method as a linear system. This system has to be solved at every wall boundary condition enforcement within a time step. Furthermore, because the underlying problem is a Poisson problem, the solution of this linear system is computationally expensive. For its solution, we here use...

A vortex particle-mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity–velocity formulation of the Navier–Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early...

The temperature perturbation method (TPM) is used as an alternative technique to the classical velocity perturbations to generate inflow turbulence for LES or DNS simulations. The TPM consists in seeding the flow with random temperature perturbations which, through a buoyancy triggered mechanism, will induce the creation of turbulent structures. Na...

The aerodynamics of Vertical Axis Wind Turbines (VAWTs) is inherently unsteady, which leads to vorticity shedding mechanisms due to both the lift distribution along the blade and its time evolution. In this paper, we perform large-scale, fine-resolution Large Eddy Simulations of the flow past Vertical Axis Wind Turbines by means of a state-of-the-a...

The objective of the present work is to develop a tool able to predict, in a computationally affordable way, the unsteady wind turbine power production and loads as well as its wake dynamics, as a function of the turbine dynamics and incoming wind conditions. Based on the lessons learned from a previous study about the characterization of the unste...

In this paper, we derive the non-singular Green's functions for the unbounded Poisson equation in two and three dimensions using a spectral approach to regularize the homogeneous equation. The resulting Green's functions are relevant to applications which are restricted to a minimum resolved length scale (e.g. a mesh size h) and thus cannot handle...

We present an cheaper iterative penalization method based on recycled Krylov subspaces. It uses the previous time-steps information.

A Vortex Particle-Mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity-velocity formulation of the Navier-Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early...

Simulation of aircraft wake-vortex encounters is regularly applied in the research toward revised aircraft separation minima. Most encounter flight simulation studies have used a pair of straight counter-rotating vortices. However, after being shed by the generating aircraft, the wake vortices begin to develop a growing deformation due to the long-...

A Vortex Particle-Mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity-velocity formulation of the Navier-Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early...

Large eddy simulations coupled to Actuator Disks are used to investigate wake effects in wind farms. An effort is made on the wind turbine model: it uses the prevailing velocities at each point of the disk to estimate the aerodynamic loads and is improved using a tip-loss correction and realistic control schemes. This accurate and efficient tool is...

This paper aims at evaluating the potential of the Discontinuous Galerkin (DG) methodology for Large-Eddy Simulation (LES) of wind turbine airfoils. The DG method has shown high accuracy, excellent scalability and capacity to handle unstructured meshes. It is however not used in the wind energy sector yet. The present study aims at evaluating this...

The sharp and high-order treatment of arbitrary boundaries immersed in the computational domain remains a challenge to particle methods. While several techniques have been proposed to modify numerical stencils, e.g. Finite Difference ones, near the walls, the particle–mesh interpolation component of particle methods also has to be modified. This op...

A Vortex Particle-Mesh (VPM) method with immersed lifting lines has been developed and validated. Based on the vorticity-velocity formulation of the Navier-Stokes equations, it combines the advantages of a particle method and of a mesh-based approach. The immersed lifting lines handle the creation of vorticity from the blade elements and its early...

The present paper describes a method to quantify the vortical structure characteristics from simulation results of the flow past a wind turbine, with the aim to develop an accurate, physics-based operational wake model. The wake centerline is first identified. Then, the flow characteristics are extracted by fitting a vorticity-based wake skeleton o...

Implementation of WMLES approach on a Discontinuous Galerkin Methodology. Sensitivity analysis on the plane channel flow at Re_tau=5200. Demonstration of the importance of the input position and the polynomial order. Work presented in the session: MS409 Current trends in modelling and simulation of turbulent flows.

A Vortex Particle-Mesh (VPM) method with immersed lifting lines (ILL) has been developed and validated, in a HPC framework. The vorticity-velocity formulation of the Navier-Stokes equations is treated in a hybrid way: particles handle advection while the mesh is used to evaluate the differential operators and for the fast Poisson solvers (here a Fo...

In the large-eddy simulation (LES) of turbulent flows, models are used to account for the subgrid-scale (SGS) stress. We here consider LES with “truncation filtering only” (i.e., that due to the LES grid), thus without regular explicit filtering added. The SGS stress tensor is then composed of two terms: the cross term that accounts for interaction...

This paper aims at presenting an alternative and more consistent way to account for bodies in the framework of computing incompressible external flows in aerodynamics using vortex particle-mesh methods (VPM). More specifically, we present a purely grid-based numerical technique using an immersed interface method and the James-Lackner algorithm to c...

We present the treatment of lifting lines with a Vortex Particle-Mesh (VPM) methodology. The VPM method relies on the Lagrangian discretization of the Navier-Stokes equations in vorticity-velocity formulation. The use of this hybrid discretization offers several advantages. The particles are used solely for the advection, thereby waiving classical...

Vortex methods solve the NS equations in vorticity-velocity formulation. The present Particle-Mesh variant exploits the advantages of a hybrid approach: advection is handled by the particles while the mesh allows the evaluation of the differential operators and the use of fast Poisson solvers (here a Fourier-based solver which allows for unbounded...

Because of its take-off, an aircraft generates a wake essentially made of a pair of counter-rotating vortices notably characterized by their total circulation. In this test case, we analyze the evolution of wake vortex total circulation with the extreme value theory. It consists in estimating the probability that a wake vortex circulation exceeds a...

WakeNet3 Europe results and findings on aircraft wake vortex state of the art and research needs

Vortex particles methods are applied to the aeroelastic simulation of a wind turbine in sheared and turbulent inflow. The possibility to perform large-eddy simulations of turbulence with the effect of the shear vorticity is demonstrated for the first time in vortex methods simulations. Most vortex methods formulation of shear, including segment for...

This paper presents the second validation step of a compressible discontinuous Galerkin solver with symmetric interior penalty (DGM/SIP) for the direct numerical simulation (DNS) and the large eddy simulation (LES) of complex flows. The method has already been successfully validated for DNS of an academic flow and has been applied to flows around c...

This paper presents a severity metric supporting the characterization of the effect of a wake vortex encounter on a follower aircraft. The proposed metric is the Rolling Moment Coefficient computed using various simplified assumptions that lead to a simple and usable metric. The metric can indeed be computed using available aircraft data. The paper...

This report has been compiled by the partners of the WakeNet3-Europe consortium with the support of several external experts. It describes the present international state-of-the-art in wake vortex research and application – focusing on recent developments in the various involved disciplines – and specifically evaluates research activities needed in...

Wake vortex behaviour modelling is the technology relating to the operational (thus necessarily simplified) modelling of aircraft wake vortex behaviour: the transport and the decay of the port and starboard vortices of the two-vortex system formed after complete rollup of the wake behind an aircraft. Those vortices are influenced by various paramet...

Most promising Generation IV nuclear reactor concepts are based on a liquid metal coolant. However, at low Prandtl (Pr ) numbers such as those of liquid metal, classical approaches derived for unity, or close to unity, Pr fail to accurately predict the heat transfer. This paper assesses the RANS modeling of forced turbulent convection at low Pr and...

This paper focuses on the assessment of a discontinuous Galerkin method for the simulation of vortical flows at high Reynolds number. The Taylor–Green vortex at Re = 1600 is considered. The results are compared with those obtained using a pseudo-spectral solver, converged on a 512³ grid and taken as the reference. The temporal evolution of the diss...

We develop a Vortex Particle-Mesh (VPM) method for the Large Eddy Simulation of wind turbine wakes and coarse scale aerodynamics. Based on the vorticity formulation of the Navier-Stokes equations, the approach combines the advantages of two discretizations. The particles handle the advection of vorticity, and exploit its compact support. The mesh i...

We present the coupling of a vortex particle-mesh method with immersed lifting lines for the Large Eddy Simulation of wind turbine wakes. The method relies on the Lagrangian discretization of the Navier–Stokes equations in vorticity-velocity formulation. Advection is handled by the particles while the mesh allows the evaluation of the differential...

A fast-time model for wake vortex behavior prediction in ground proximity is presented. This model takes into account the combined effects of ground proximity and wind (both crosswind and headwind components) on the wake vortex transport and decay. It aims to mimic the whole flow using a limited set of vortex particles to model both the primary two...

This paper presents the second step of the validation of a compressible discontinuous Galerkin method (DGM) for the direct numerical simulation (DNS) and the large eddy simulation (LES) of turbomachinery flows. The method has already been successfully validated for the DNS of academic flows as well as for the flow around complex geometries. During...

This study investigates the influence, on aircraft wake vortex behavior, of atmospheres that are stably stratified (neutral to very strong) and weakly turbulent, by means of large-eddy simulations at very high Reynolds number and on relatively fine grids. The atmospheric fields are first generated using large-eddy simulations of forced and stratifi...

During two field measurement campaigns aircraft wake vortex trajectory and wind measurement data have been collected at Frankfurt airport. Three different approaches to analyse the data have been used in order to estimate crosswind threshold values supporting vortex-free corridors for departing aircraft. Although several competing effects as wake v...

This paper is concerned with the ability of a flow solver using a high-order discontinuous Galerkin method (DGM) to perform large eddy simulation (LES) of turbulent flows. Several modeling approach are considered: the Smagorinsky model (Smag), the regularized variational multiscale model (RVMs) and the implicit LES (ILES). Results on decaying homog...

This coupling aims at improving the computational efficiency of high Reynolds number bluff body flow simulations by using two complementary methods and exploiting their respective advantages in distinct parts of the domain. Vortex particle methods are particularly well suited for free vortical flows such as wakes or jets (the computational domain -...

This paper deals with the issue of modeling convective turbulent heat transfer of a liquid metal with a Prandtl number down to 0.01, which is the order of magnitude of lead–bismuth eutectic in a liquid metal reactor. This work presents a DNS (direct numerical simulation) and a LES (large eddy simulation) of a channel flow at two different Reynolds...

2D shear layers are studied using a high accuracy vortex-in-cell (VIC) method. The case investigated is U2/U1=0.38, as in the Brown and Rhosko experiment. The inflow corresponds to a regularized vortex sheet with momentum thickness theta0=pi/4 and Re0=54. It then growths and smoothly undergoes transition, through TS waves and then K-H instabilities...

The WAKE4D is a "3-D space + time" wake vortex (WV) prediction platform software developed at UCL. It allows to handle complete flight scenarios in 3-D space, and with given met conditions. It simulates the transport and decay of the WV generated by an aircraft evolving along a given flight path and under those met conditions. It uses many "computa...