Simulation des écoulements à surface libre dans les turbines Pelton par une méthode hybride SPH-ALE

International audienceAn 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.La méthode numérique sans maillage Smoothed Particle Hydrodynamics (SPH) est modifiée par l'adoption d'une description Arbitrary Lagrange Euler (ALE) des écoulements fluides, dans le but de simuler des écoulements à surface libre. Le formalisme ALE conduit à une méthode numérique hybride s'apparentant sur de nombreux points à une approche volumes finis. Il est alors possible d'adapter des techniques numériques courantes comme les schémas décentrés et le préconditionnement pour résoudre certains défauts majeurs de la méthode SPH, comme la stabilité numérique ou le manque de précision. Par ailleurs, le traitement des conditions limites est réalisé par un décentrement approprié des informations fluides sur les surfaces frontières. La méthode numérique SPH-ALE résultante est appliquée à la simulation d'écoulements à surface libre tels que ceux rencontrés dans les turbines Pelton

Zonal large-eddy simulation of a tip leakage flow

The flow induced by the clearance between the tip of an isolated airfoil and an end-plate is investigated numerically, using a zonal approach with large-eddy simulation in the region of interest. The results are analyzed in comparison with available experimental data, presented in a companion paper. The incoming boundary layer and the pressure distribution around the blade are evaluated. The description of the inflow-jet deviation, with an averaged approach, enables to represent the proper loading on the airfoil. Also, particular attention is paid to the powerful tipleakage vortex. The vortex characteristics are investigated using specific functions to locate its center and quantify its width. Overall, good results are obtained for the flow statistics and spectra. Furthermore, a very good description of the far-field pressure is achieved using the acoustic analogy, and the results confirm that the tip-flow essentially radiates in the central frequency range (0.7 kHz, 7 kHz)

Wavelet Analysis of a Blade Tip-Leakage Flow

The secondary flow generated by the clearance between an isolated airfoil tip and an end-plate is analyzed by means of a zonal large-eddy simulation, in comparison with available experimental data. The flow around the tip clearance is described with full large-eddy simulation, while Reynolds-averaged Navier-Stokes is employed in the rest of the computational domain in order to limit the computational cost. The various analyses of the flow characteristics (mean velocities, Reynolds stresses, spectra) show a very good agreement between the experiment and the simulation. Furthermore, a detailed analysis is carried out from the numerical results. The flow separations on the blade tip are related with the leakage distribution along the chord, which generates an intense tip-leakage vortex on the suction side. Finally, a hump in the pressure spectra at tip is investigated by means of a wavelet conditional average, and related to the unsteadiness of the aft tip separatio

Simulation des écoulements à surface libre dans les turbines Pelton par une méthode hybride SPH-ALE

International audienceAn 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.La méthode numérique sans maillage Smoothed Particle Hydrodynamics (SPH) est modifiée par l'adoption d'une description Arbitrary Lagrange Euler (ALE) des écoulements fluides, dans le but de simuler des écoulements à surface libre. Le formalisme ALE conduit à une méthode numérique hybride s'apparentant sur de nombreux points à une approche volumes finis. Il est alors possible d'adapter des techniques numériques courantes comme les schémas décentrés et le préconditionnement pour résoudre certains défauts majeurs de la méthode SPH, comme la stabilité numérique ou le manque de précision. Par ailleurs, le traitement des conditions limites est réalisé par un décentrement approprié des informations fluides sur les surfaces frontières. La méthode numérique SPH-ALE résultante est appliquée à la simulation d'écoulements à surface libre tels que ceux rencontrés dans les turbines Pelton

Discovery and progress in our understanding of the regulated secretory pathway in neuroendocrine cells

In this review we start with a historical perspective beginning with the early morphological work done almost 50 years ago. The importance of these pioneering studies is underscored by our brief summary of the key questions addressed by subsequent research into the mechanism of secretion. We then highlight important advances in our understanding of the formation and maturation of neuroendocrine secretory granules, first using in vitro reconstitution systems, then most recently biochemical approaches, and finally genetic manipulations in vitro and in vivo

Combined experimental/computational study of tip clearance flow and acoustics

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Combined experimental/computational study of tip clearance flow and acoustics

International audienc

Tip Leakage Flow: Advanced Measurements and Analysis

Advanced measurements of a tip clearance flow are carried out in the large subsonic anechoic wind tunnel of the LMFA in Lyon. The experimental set-up is obtained by placing the airfoil between two plates into the potential core of a turbulent rectangular jet, the upper plate being the hub and the lower the casing. The jet that exits a converging nozzle has a 450 mm cross-stream width and a 200 mm height in the span-wise direction. An h=10 mm gap is maintained between the blade and the casing plate. The incoming free stream turbulence u’/U0 is 0.5%, and the flat plate boundary layer half a chord upstream of the airfoil leading edge is about 8 mm thick. Except for the thickness being halved, the configuration is the same as the one discussed by Jacob et al.1, I.J.A, 9(3), (2010) , and Camussi et al.2, J.F.M., 660, (2010): a M ~ 0.2 and Rec ~ 950000 jet flow past a NACA5510 airfoil with 15° angle of attack. Measurements are carried out in the region of the Tip Leakage Vortex (TLV) in order to characterise its unsteady velocity. Both 2D–2 Component and stereo Time Resolved PIV techniques are successfully applied in order to provide an insight into the low frequency content of the velocity field, that are compared to LDV measurements. This experiment corresponds to a novel type of configuration that has only been studied by Jacob et al. Moreover, the TR-PIV and specifically the stereo-TR PIV are quite new techniques that have not often been applied to such complex configurations at such high speeds. The benefits of the time resolution are promising for the understanding of such broadband noise sources. Among the findings, there is a low frequency oscillation of the TLV, whose mechanism is yet unclear but which does not seem to radiate into the far field. Additionally, a hump at medium and high frequencies (0.7 – 7 kHz) is found in the far field. It can also be related to time decay double space-time correlations

SPH truncation error in estimating a 3D function

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A high-order SPH method by introducing inverse kernels

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