Sylvain Lardeau

Siemens Digital Industries Software

div class="section abstract"> Increasing fuel and electricity prices create high pressure to develop efficient external aerodynamics of road cars. At the same time, development cycles are getting shorter to meet changing customer preferences while physical testing capacities remain limited, creating a pressing need for fast and accurate turbulence...

View Video Presentation: https://doi.org/10.2514/6.2022-2568.vid Validation study of the intermittency-based transition prediction models available in Simcenter STAR-CCM+ is presented. Both the two-equation γ-Re_θ the one-equation γ models coupled to the k-w SST turbulence model are extensively studied on a range of cases with increasing complexity...

View Video Presentation: https://doi.org/10.2514/6.2021-2762.vid Simulating the flow over a smooth cylinder with low-level inlet turbulence for a Reynolds number equal to 140,000 remains a robust test case to evaluate the performance of turbulence closure models and numerical methods. This study considers a variety of closure levels, Reynolds-Avera...

A set of Direct Numerical Simulations in a heated square cavity invoking the Boussinesq approximation was carried out at Rayleigh numbers ranging between 1e8 and 1e11 and Prandtl number of 0.71. The three dimensional configurations studied represent an infinitely deep cavity, thus corresponding to a statistically two-dimensional flow with an impose...

The paper presents a comparison of two hybridization techniques between RANS and LES, and their potential and limitations in an industrial context. The first part of the paper also attempts to address an often eluded problem in the hybrid RANS/LES scommunity: the importance of the baseline statistical model. A new robust low-Reynolds number eddy-vi...

Flows in pipe bends and T-Junctions are of great interest to the nuclear power industry, as turbulent temperature fluctuations in coolant flow can cause high cycle thermal fatigue in pipe walls. However, these flows often feature separation, streamline curvature and Reynolds stress anisotropy; as a result, they are challenging for RANS eddy viscosi...

Liquid metal cooled reactors are envisaged to play an important role in the future of nuclear energy production because of their possibility to use natural resources efficiently and to reduce the volume and lifetime of nuclear waste. Typically, sodium and lead(-alloys) are envisaged as coolants for such reactors. Obviously, in the development of th...

Turbulent heat transfer is an extremely complex phenomenon, which has challenged turbulence modellers over various decades. The limitations of the commonly used eddy diffusivity approach have become more evident specially for innovative nuclear reactor applications with low-Prandtl fluids like liquid metals. One of the objectives of the THINS (Ther...

The individual and coupled effects of the incoming free-stream turbulence (FST) and surface roughness on the transition of a separated shear layer over a flat plate is numerically investigated using Large eddy simulation (LES). The upper wall of the test section is inviscid and specifically contoured to impose a streamwise pressure distribution ove...

A direct numerical simulation study is presented, which examines the response of a spatially developing boundary layer to oscillatory spanwise wall motion imposed over a limited streamwise stretch. At the heart of the study is the dependence of the streamwise variations in skin friction and turbulence properties on the period of the oscillatory mot...

One of the objectives of the THINS (Thermal Hydraulics of Innovative Nuclear Systems) sponsored by the European Commission is to push forward the validation and adoption of more accurate closures for single-phase turbulence for innovative reactors in engineering codes. As a part of this THINS project, CD-adapco has implemented in its commercial cod...

The objective of this numerical study is to increase the base pressure on a backward-facing step via linear feedback control, to be ultimately translated to a drag reduction on a blunt-based bluff body. Two backward-facing step cases are simulated: a laminar two-dimensional (2D) flow at a Reynolds number of , and a turbulent three-dimensional (3D)...

The ability of Large-Eddy Simulation (LES) to predict transitional separation bubbles is investigated, with particular emphasis being placed on the response to free-stream-turbulence. The principal objective is to quantify the penalties, relative to Direct Numerical Simulations (DNS), that arise from the coarser resolution and the use of subgrid-sc...

Highly resolved large-eddy simulation (LES) is used to investigate the characteristics of a canonical boundary layer separating from a curved step in a channel of height 8.5 times that of the step. The flow is treated as statistically spanwise homogeneous, in line with the conditions of a related experimental study in a large aspect ratio channel,...

The paper provides a broad discussion of multiscale and structural features of sheared turbulent flows. Basic phenomenological aspects of turbulence are first introduced, largely in descriptive terms with particular emphasis placed on the range of scales encountered in turbulent flows and in the identification of characteristic scale ranges. There...

A computational large eddy simulation (LES) study is presented of the interaction between a turbulent boundary layer separating from a rounded ramp in a duct and a pair of spanwise-periodic, round synthetic jets, actuated upstream of the nominal separation line. Several scenarios are considered, for different injection angles and velocity ratios. I...

A three-equation model has been applied to the prediction of separation-induced transition in high-lift low-Reynolds-number cascade flows. Classical turbulence models fail to predict accurately laminar separation and turbulent reattachment, and usually over-predict the separation length, the main reason for this being the slow rise of the turbulent...

Synthetic jets--also referred to as mass-less jets--offer the potential of effective, on-demand, fluid-based control of separating boundary layers on highly loaded aerodynamic surfaces, without the need for a mass source. However, the control authority that may optimally be derived from such jets, and any generality of the underlying flow physics a...

In this paper, a new characterisation and quantification of lamination are presented. The lamination is identified by tracking material lines and the estimation of the ratio between the length of the material lines within circles and the diameter of the circles. The quantification of the lamination rate relies on the interlaced structure of velocit...

The three-dimensional structure and behaviour of the rate of rotation and strain rate tensors is examined in the far field of a turbulent planar two dimensional mixing layer. The mixing layer is simulated using the incompact3d DNS code at Reynolds number based on inlet conditions of 1000. The study looks at the effect of spatial resolution on the l...

A new technique for extracting information about cyclic and periodic features in turbulent-flow fields is proposed. This is based on a combination of proper orthogonal decomposition, applied to DNS and LES flow data, and the use of ‘recurrence plots’, the latter being a tool often adopted for analysing dynamical systems outside the field of fluid m...

In this numerical study, the flow obtained behind a trailing edge separating two streams of different velocities is studied by means of direct numerical simulation. The main originality of this work is that the splitter plate itself is included in the computational domain using an immersed boundary method. The influence of the trailing-edge shape i...

Time-resolved simulations of simple shear flows, such as boundary layers and channel flows, are often used as precursor simulations that provide the inflow-boundary conditions for simulations of turbulent flows in and around more complex geometries. For both the precursor and main simulations, the accuracy of the calculated mean flow relies on the...

Large Eddy Simulations for two flows separating from a two-dimensional hump in a duct are reported and discussed. The flows differ through the presence or absence of a synthetic slot-jet injected in a sinusoidal manner, i.e. at zero net mass-flow rate, close to the location of separation and intended to reduce (“control”) the extent of the separate...

Large eddy simulation (LES) is now seen more and more as a viable alternative to current industrial practice, usually based on problem-specific Reynolds-averaged Navier-Stokes (RANS) methods. Access to detailed flow physics is attractive to industry, especially in an environment in which computer modelling is bound to play an ever increasing role....

This paper presents conceptual experiments and simulations aiming at controlling flow geometries. Such flow design is performed by driving electromagnetically a shallow layer of brine, the forcing being generated by a transverse electrical current and different combinations of permanent magnets placed underneath the brine supporting wall. It is sho...

Three-dimensional 3D direct numerical simulations of a flow driven by multiscale electromagnetic forcing are performed in order to reproduce with maximum accuracy the quasi-two-dimensional 2D flow generated by the same multiscale forcing in the laboratory. The method presented is based on a 3D description of the flow and the electromagnetic forcing...

Large-eddy simulations of transitional flows over a flat plate have been performed for different sets of free-stream-turbulence conditions. Interest focuses, in particular, on the unsteady processes in the boundary layer before transition occurs and as it evolves, the practical context being the flow over low-pressure turbine blades. These consider...

An unsteady Reynolds-averaged Navier-Stokes (URANS) strategy is applied to the problem of wake-induced transition at high freestream turbulence on the suction side of two blades representative of those used in low-pressure turbines. Experimentally, the blades are arranged in high-aspect-ratio linear cascades, with upstream circular bars generating...

Turbulent inflow condition generation for large eddy simulation (LES) was investigated using a purely numerical approach, based on 3D direct numerical simulation (DNS). The inflow condition generation methodology was only tested and validated on a specific flow test case. The purely numerical approach showed that the inflow condition generation met...

An investigation is presented of the ability of the unsteady RANS approach to represent, from a numerical point of view, the characteristics and evolution of moving wakes as they interact with the flow around a turbine blade and in a related variable-passage configuration. The context of the study is wake-induced transition in unsteady turbomachine...

The interaction between wakes generated by a moving array of cylindrical bars and the transitional boundary layer over a low-pressure turbine blade located downstream of the bars is studied by means of an unsteady Reynol-averaged Navier-Stokes (RANS) method that incorporates a recent low-Reynolds-number, nonlinear eddy-viscosity turbulence model. T...

THe ability of two nonlinear, low-Reynolds-number eddy viscosity models, one cubic and the other quadratic, to predict transitional boundary laters was investigated. The choice of low Reynolds-number models was motivated by the fact that transitional flows in turbomachinery featured both transition and relaminarization in different parts of the sam...

Due to the difficulty of specifying realistic inflow conditions for numerical simulations, a new method has been recently developed permitting to use time-dependent highly turbulent velocity field as inflow condition for spatially developing Large Eddy Simulation. This methodology is based on experimental time histories obtained at few selected ref...

A method for generating realistic (i.e., reproducing in space and time the large-scale coherence of the flows) inflow conditions based on two-point statistics and stochastic estimation is presented. The method is based on proper orthogonal decomposition and linear stochastic estimation. This method allows a realistic representation with a minimum o...

A method for generating realistic (i.e. reproducing in space and time the large-scale coherence of the flows) inflow conditions based on two-point statistics and stochas-tic estimation is presented. The method is based on Proper Orthogonal Decomposition and Linear Stochastic Estimation. This method allows for a realistic representation with a minim...

The improvement of mixing in free-shear flows via external jets has been proven efficient in subsonic and supersonic flows as well. However, the hyper-mixing process is not well known. The present study deals with an experimental and a numerical approach of the interaction of an external control jet with a turbulent mixing layer. The main conclusio...

A method for generating realistic (i.e. reproducing in space and time the large-scale coherence of the flows) inflow conditions based on two-point statistics and stochas-tic estimation is presented. The method is based on Proper Orthogonal Decomposition and Linear Stochastic Estimation. This method allows for a realistic representation with a minim...

This study is concerned with direct numerical simulations of jet control carried out by means of secondary jets. The use of realistic inflow conditions enables us to examine the influence of the side jets on the vortical structure dynamics in the main jet. Four control configurations are presented for several positions and flow rates of the control...

The RANS and LES simulations were performed on a 1:5 scale simplified model of a Citroën C5. The cross- wind effect was produced with the model placed at a yaw angle of 20°. The Reynolds number of the flow, based on the incoming velocity and car height, H, was 6.19 x 10 5 . The surface mesh (around 730,000 elements) was generated with ANSA™ and was...