Matthieu Duponcheel

LES investigation of the transport and decay of various-strengths wake vortices in ground effect and subjected to a turbulent crosswind

This study is concerned with the investigation of two-vortex systems (2VS) of various strengths that are released near the ground and evolve in the presence of a turbulent crosswind. We analyze the physics of the vortices interactions with the turbulent wind and with the ground during the rebound phase, and that lead to the fully developed turbulent flow and interactions. The transport and decay of the vortices are also analyzed. The turbulent wind itself is obtained by direct numerical simulation using a half channel flow. The flow is then supplemented with the 2VS, using vortices with a circulation distribution that is representative of vortices after roll-up of a near wake. The vortex strengths, Γ0, are such that ReΓ = Γ0/ν = 2.0 × 104 for the baseline; there is then a case with twice weaker vortices, and a case with twice stronger vortices. The simulations are run in wall-resolved Large Eddy Simulation (LES) mode. The baseline is in line with the wall-resolved LES study of a similar case [A. Stephan e...

Numerical prediction of turbulent heat transfer at low prandlt number

This paper is concerned with comparing different approaches for the numericalprediction of heat transfer in a turbulent channel flow at very low Prandtl number and highReynolds number. Results obtained with a Reynolds Averaged Navier Stokes (RANS) approachat relevant Reynolds numbers for the liquid metal reactor problematic (Reτ = 590, Reτ = 1020),are presented and discussed. Original results obtained with a wall resolved Large EddySimulations (LES) at Reτ = 2000 are provided. The velocity profile agrees very well withthat of a reference Direct Numerical simulation (DNS). The obtained temperature profile canserve as a reference as the energy equation is computed without any Subgrid Scale (SGS) modelat this low Pr.

Vortex Particle-Mesh simulations of Vertical Axis Wind Turbine flows: from the blade aerodynamics to the very far wake

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 development. LES of Vertical Axis Wind Turbine (VAWT) flows are performed. The complex wake development is captured in details and over very long distances: from the blades to the near wake coherent vortices, then through the transitional ones to the fully developed turbulent far wake (beyond 10 rotor diameters). The statistics and topology of the mean flow are studied. The computational sizes also allow insights into the detailed unsteady vortex dynamics, including some unexpected topological flow features.

LES of wind farm response to transient scenarios using a high fidelity actuator disk model

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 used to study the wind farm response in terms of flow and power production during an unsteady scenario: this work focuses on an emergency shutdown of one rotor inside a wind farm.

A New Multiscale Model with Proper Behaviour in Both Vortex Flows and Wall Bounded Flows

A new subgrid-scale (SGS) model which has an adequate behaviour in both vortical flows and wall-bounded flows is proposed. In wall-bounded flows computed using wall-resolved LES, the theory predicts that the SGS dissipation should vanish with a y +3 behaviour near the wall. In the case of vortex flows, one needs to have models which do not dissipate energy in the strongly vortical and essentially laminar part of the flow, e.g. in vortex core regions. The model presented here aims at combining the strengths of two models as it is a regularized variational multiscale (RVM) model (as in Jeanmart and Winckelmans [3]), thus acting on the high pass filtered LES field, and for which the subgrid-scale viscosity is evaluated using the WALE (wall adapting local eddy viscosity) scaling of Nicoud and Ducros [5], itself computed using the high pass filtered LES field. Thus this model is only active when there is a significant high wavenumber content in the flow and it has a natural near wall damping behaviour. The ability of this model to simulate vortex and wall-bounded flows is demonstrated on three test cases. The first case is the turbulent channel flow. The second case concerns a four-vortex system. The third case concerns a two-vortex system in ground effect. It is shown that this new model allows to perform successfully LES of these flows with the proper dissipative behaviour in both near wall and vortical regions. The LES are performed using a parallel fourth order code based on finite differences.