Joëlle Caro

Free surface flows simulations in Pelton turbines using an hybrid SPH-ALE method

An Arbitrary Lagrange Euler (ALE) description of fluid flows is used together with the meshless numerical method Smoothed Particle Hydrodynamics (SPH) to simulate free surface flows. The ALE description leads to an hybrid method that can be closely connected to the finite volume approach. It is then possible to adapt some common techniques like upwind schemes and preconditioning to remedy some of the well known drawbacks of SPH like stability and accuracy. An efficient boundary treatment based on a proper upwinding of fluid information at the boundary surface is settled. The resulting SPH-ALE numerical method is applied to simulate free surface flows encountered in Pelton turbines.

Numerical studies towards practical large-eddy simulation

Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and “low-cost” shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra. Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.

Large-eddy simulation of a single airfoil tip-clear ance flow

The tip-clearance flow induced by a static blade loc ated above a plane is investigated by large-eddy simulation (LES), in comparison with a recent experiment. A shear-improved subgrid-scale model is employed in the computation, paying particular attention to the influence of mean flow structures. Indeed, the comp utation is shown to capture the main flow topology, governed by three major vortices: the tip-leakage vortex, the induced counter-rotating vortex, and the tip-separation vor tex. Mean and fluctuating quantities are correctly simulated within the gap and the tip-leak age vortex. However, it is shown that a particular care should be put on the incoming boundary layer calibration in order to represent more precisely the turbulence dragged by the counter vortex. Finally, fluctuating pressure spectra are analyzed, in good comparison between the computation and the experiment.

Tip-Leakage Flow: a Detailed Simulation with a Zonal Approach

The secondary flow generated by the clearance between an isolated airfoil tip and anend-plate is analyzed by means of a zonal large-eddy simulation, in comparison with avail-able experimental data. The flow around the tip clearance is described with full large-eddysimulation, while Reynolds-averaged Navier-Stokes is employed in the rest of the compu-tational domain in order to limit computational cost. The various analyses of the flowcharacteristics (mean velocities, Reynolds stresses, spectra) show a very good agreementbetween the experiment and the simulation. Looking at the mean velocities, an intensetip-leakage vortex is observed on the suction side. The Reynolds stresses are used toevaluate the anisotropy of the vortex. Finally, the spectral content is investigated in thenear-field and the far-field, and the leakage flow is shown to be characterized by a dominantcontribution in the range [0.7 kHz; 7 kH z].

Next-generation Multi-mechanics Simulation Engine in a Highly Interactive Environment

We describe the development of a highly interactive approach to simulation of engineering multi-mechanics problems, using the smoothed particle hydrodynamics mesh-free method as the computational engine, for applications including ship survival, medical devices and Pelton turbines.

Budget Analysis of Turbulent Kinetic Energy in a Tip-Leakage Flow of a Single Blade: RANS Vs Zonal LES

This study aims at analyzing the modeling of turbulence in a tip-leakage flow. The academic configuration considered is made of a single airfoil and a flat casing, with clearance, at Re=9.3e5. For characterising the turbulence, a zonal large-eddy simulation (ZLES), validated against experimental data, is considered as reference. ZLES was previously shown to describe precisely the flow features in the tip region, including the Reynolds stresses. Two steady Reynolds-averaged Navier-Stokes (RANS) simulations, using Wilcox’s k-ω model, are evaluated against this reference. The first simulation uses the Boussinesq constitutive relation, whereas the second simulation relies on the quadratic constitutive relation (QCR). The analysis focuses on the mean velocities, the Reynolds stresses and a term-to-term decomposition of the turbulent kinetic energy budget. RANS is shown to under-estimate the vorticity of the flow, the Reynolds stresses and the turbulent kinetic energy budget terms. The QCR has little effects on these deficits.

Smoothed Particle Hydrodynamics: benchmarking on selected test cases within the NextMuSE initiative

In this paper are presented comparisons of SPH variants on academic test cases classically used to validate numerical fluid dynamics software. These comparisons are extracted from NextMuSE FP7 project activities which will be published more extensively in the near future. One of the goals of this project was to better understand the SPH method and to leave the path to its establishment within CFD methods. An important work load was thus dedicated to benchmark SPH variants on selected test cases.A number of results and conclusions of this comparative study are presented in this paper. The studied variants are: standard weekly-compressible SPH, δ-SPH, Riemann-SPH, incompressible SPH, and FVPM. The majority of the test cases also present a reference solution, either experimental or computed using a mesh-based solver. Test cases include: wave propagation, flow past a cylinder, jet impact, floating body, bubble rise, dam break on obstacle, floating body dynamics, etc. Conclusions may help SPH practitioners to choose one variant or another and shall give detailed understanding necessary to derive further improvements of the method.Copyright