The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Nicholas J. Hills - One of the best experts on this subject based on the ideXlab platform.
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Large-Eddy Simulations of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques
Journal of Turbomachinery, 2015Co-Authors: Dario Amirante, Nicholas J. HillsAbstract:Large-eddy simulations (LES) of wall bounded, low Mach Number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES (ILES) procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds Number Reb = 44 × 103 based on the pipe diameter, and a confined rotor–stator flow at the Rotational Reynolds Number ReΩ = 4 × 105 based on the outer radius. In both cases, the mean flow and the turbulent statistics agree well with existing direct numerical simulations (DNS) or experimental data.
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LES OF WALL BOUNDED TURBULENT FLOWS USING UNSTRUCTURED LINEAR RECONSTRUCTION TECHNIQUES
Volume 2B: Turbomachinery, 2014Co-Authors: Dario Amirante, Nicholas J. HillsAbstract:Large-Eddy Simulations of wall bounded, low Mach Number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds Number Reb = 44 × 103 based on the pipe diameter, and a confined rotor-stator flow at the Rotational Reynolds Number ReΩ = 4 × 105 based on the outer radius. In both cases the mean flow and the turbulent statistics agree well with existing DNS or experimental data.
Sébastien Poncet - One of the best experts on this subject based on the ideXlab platform.
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High-order direct numerical simulations of a turbulent round impinging jet onto a rotating heated disk in a highly confined cavity
International Journal of Heat and Fluid Flow, 2016Co-Authors: Romain Oguic, Sébastien Poncet, Stéphane ViazzoAbstract:The present work reports Direct Numerical Simulations (DNS) of an impinging round jet onto a rotating heated disk in a confined rotor-stator cavity. The geometrical characteristics of the system correspond to the experimental set-up developed by u. Pelle and S. Harmand. Heat transfer study in a rotor-stator system air-gap with an axial inflow. Applied Thermal Engineering, 29:1532-1543, 2009.]. The aspect ratio of the cavity G = h/R-d between the interdisk spacing h and the rotor radius R-d is fixed to 0.02 corresponding to a narrow-gap cavity. The axial Reynolds Number Red based on the jet characteristics is also fixed to Re-j = 5300, while the Rotational Reynolds Number Re-Omega may vary to preserve the swirl parameter N proportional to Re(Omega)dRe(j) (0
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Numerical Simulations of Co- and Counter-Taylor-Couette Flows: Influence of the Cavity Radius Ratio on the Appearance of Taylor Vortices
American Journal of Fluid Dynamics, 2015Co-Authors: Nabila Ait-moussa, Sébastien Poncet, Abdelrahmane GhezalAbstract:Taylor-Couette flows in the annular region between rotating concentric cylinders are studied numerically to determine the combined effects of the co- and counter-rotation of the outer cylinder and the radius ratio on the system response. The computational procedure is based on a finite volume method using staggered grids. The axisymmetric conservative governing equations are solved using the SIMPLER algorithm. One considers the flow confined in a finite cavity with radius ratios η = 0.25, 0.5, 0.8 and 0.97. One has determined the critical points and properties for the bifurcation from the basic circular Couette flow (CCF) to the Taylor Vortex Flow (TVF) state. Indeed, the results are presented in terms of the critical Reynolds Number Rei of the inner cylinder that depends on the Rotational Reynolds Number of the outer cylinder Reo and η. To show the capability of the present code, excellent quantitative agreement has been obtained between the calculations and previous experimental measurements for a wide range of radius ratios and rotation rates.
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Large Eddy Simulation and Measurements of Turbulent Rotor-Stator Flows
2007Co-Authors: Eric Serre, Sébastien Poncet, Eric Séverac, Marie-pierre ChauveAbstract:Comparisons between large eddy simulation (LES) and velocity measurements have been performed for the turbulent flow in a real shrouded rotor-stator configuration. To investigate turbulent flow regimes, LES numerical results (Spectral Vanishing Viscosity technique) and experimental data have been favourably compared for a large range of Rotational Reynolds Number in an annular cavity of curvature parameter Rm=1.8 and of aspect ratio G=5. All the characteristics of 3D turbulent boundary layers have been found and coherent structures have been shown under the form of annuli or spiral arms.
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Turbulent Von Kármán flow between two counter-rotating disks
2007Co-Authors: Sébastien Poncet, Roland Schiestel, Romain MonchauxAbstract:The present work considers the turbulent Von Kármán flow generated by two coaxial counter-rotating smooth (viscous stirring) or bladed (inertial stirring) disks enclosed by a cylindrical vessel. Numerical predictions based on one-point statistical modeling using a low Reynolds Number second-order full stress transport closure (RSM) are compared to velocity measurements performed at CEA. An efficient way to model the rule of straight blades is proposed. The influences of the Rotational Reynolds Number, the aspect ratio of the cavity, the rotating disk speed ratio and of the presence or not of impellers are investigated to get a precise knowledge of the dynamics and the turbulence properties in the Von Kármán configuration. In particular, we highlighted the transition be-tween the Batchelor and the Stewartson flow structures and the one between the merged and separated boundary layer regimes in the smooth disk case. We determined also the transition between the one cell and the two cell regimes for both viscous and inertial stirrings.
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Turbulence characteristics of the B\"{o}dewadt layer in a large shrouded rotor-stator system
arXiv: Classical Physics, 2006Co-Authors: Sébastien Poncet, Anthony RandriamampianinaAbstract:A three-dimensional direct numerical simulation (3D DNS) is performed to describe the turbulent flow in an enclosed rotor-stator cavity characterized by a large aspect ratio $G=(b-a)/h=18.32$ and a small radius ratio $a/b=0.15$ ($a$ and $b$ the inner and outer radii of the rotating disk and $h$ the interdisk spacing). Recent comparisons with velocity measurements have shown that, for the Rotational Reynolds Number $Re=\Omega b^2/\nu=95000$ ($\Omega$ the rate of rotation of the rotating disk and $\nu$ the kinematic viscosity of water) under consideration, the stator boundary layer is 3D turbulent and the rotor one is still laminar. Budgets for the turbulence kinetic energy are here presented and highlight some characteristic features of the effect of rotation on turbulence. A quadrant analysis of conditionally averaged velocities is also performed to identify the contributions of different events (ejections and sweeps) on the Reynolds shear stress.
Souad Harmand - One of the best experts on this subject based on the ideXlab platform.
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Convective Heat Transfer in a Rotor–Stator System Airgap With a Centered Natural Suction of Fluid
Journal of Heat Transfer, 2011Co-Authors: Julien Pellé, Souad HarmandAbstract:The present work relates to an experimental study of the local convective heat transfer over the rotor surface in the air-gap of a discoidal rotor–stator system. This configuration is of interest namely, in electrical machines or tubomachinery. Following precedent studies obtained for a single rotating disk or a closed (but unshrouded) rotor–stator system, an air suction comes through the stator and enters the air-gap in this particular work. Determination of Nusselt Numbers is based on the use of infrared thermography. The influence of the suction is discussed for an interdisk dimensionless spacing interval, G ranging from 0.01 to 0.16 and for a Rotational Reynolds Number, Re between 30,000 and 5,16,000. Results shows that the suction could locally provide better cooling than in the closed rotor–stator and in the single disk configurations, even if the main influence is a decrease in the convective heat transfer.
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Heat transfer study in a discoidal system: The influence of rotation and space between disks
International Journal of Heat and Mass Transfer, 2008Co-Authors: Julien Pellé, Souad HarmandAbstract:Abstract This article presents an experimental study of the local heat transfer on the rotor surface in a discoidal rotor–stator system air-gap in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance was used to identify the local convective heat transfer coefficient. The influence of the dimensionless spacing interval G between the disks and of the Rotational Reynolds Number Re was measured and compared with the data available in bibliography. Local convective heat transfer coefficients were obtained for an axial Reynolds Number Rej = 41.6 × 103, a Rotational Reynolds Number Re between 0.2 × 105 and 5.16 × 105, and a dimensionless spacing interval G ranging from 0.01 to 0.16.
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Heat transfer measurements in an opened rotor-stator system air-gap
Experimental Thermal and Fluid Science, 2007Co-Authors: Julien Pellé, Souad HarmandAbstract:Abstract This article presents an experimental study of the heat transfers in a discoidal rotor–stator system air-gap. Measurements are performed over the rotor, using an experimental technique based on infrared thermography, in order to determine the surface temperatures. Using a thermal balance, the local convective heat transfer coefficient is identified. The influences of the Rotational Reynolds Number Re and the dimensionless spacing between the two disks G are carried out and compared with literature data when available. Local convective heat transfer coefficients are obtained for Re ranging from 1.29 × 105 to 6.45 × 105 and for G between 0.01 and 0.16. Four heat transfer regimes are identified then correlated. Comparisons with our previous results concerning flow and heat transfers over a single rotating disk in still air are also carried out.
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Local convective heat transfer for laminar and turbulent flow in a rotor-stator system
Experiments in Fluids, 2005Co-Authors: Rachid Boutarfa, Souad HarmandAbstract:The aim of this work is to show a better comprehension of the flow structure and thermal transfer in a rotor-stator system with a central opening in the stator and without an airflow imposed. The experimental technique uses infrared thermography to measure the surface temperatures of the rotor and the numerical solution of the steady-state heat equation to determine the local heat transfer coefficients. Analysis of the flow structure between the rotor and the stator is conducted by PIV. Tests are carried out for Rotational Reynolds Numbers ranging from 5.87×10^4 to 1.4×10^6 and for gap ratios ranging from 0.01 to 0.17. Analysis of the experimental results has determined the influence of the Rotational Reynolds Number, the gap ratio and system’s geometry on the flow structure, and the convective exchanges in the gap between the rotor and the stator. Some correlations expressing the local Nusselt Number as a function of the Rotational Reynolds Number and the gap ratio are proposed.
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Experimental study using infrared thermography on the convective heat transfer of a TGV brake disk in the actual environment
Optical Engineering, 2002Co-Authors: Monica Siroux, Souad Harmand, Bernard DesmetAbstract:We present an experimental identification of the local and mean Nusselt Number from a rotating TGV brake disk model in the actual environment and exposed to an air flow parallel to the disk surface. This method is based on the use of a heated thermally thick disk combined with the technique of temperature measurement by infrared thermography. The local and mean convective heat transfer coefficient from the disk surface is identified by solving the steady state heat equation by a finite difference method using the experimental temperature distribution as boundary conditions. The experimental setup is constituted of a model disk with all the representative parts of the actual TGV brake system. The disk and its actual environment are inside a wind tunnel test section, so that the Rotational disk speed and the air flow velocity can be varied. Tests were carried out for Rotational speeds w between 325 and 2000 rpm (Rotational Reynolds Number Re between 88,500 and 545,000), and for an air flow velocity U ranging between 0 and 12 m.•s-1 (air flow Reynolds Number Re0 between 0 and 153,000).
Zhenhua Xiao - One of the best experts on this subject based on the ideXlab platform.
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Flow and Heat Transfer in an Industrial Rotor-Stator Rim Sealing Cavity
Volume 3: Heat Transfer; Electric Power; Industrial and Cogeneration, 2000Co-Authors: Alexander Mirzamoghadam, Zhenhua XiaoAbstract:Flow and heat transfer in the row-1 upstream rotor-stator disc cavity of a large 3600-rpm industrial gas turbine was investigated using an integrated approach. A 2D axisymmetric transient thermal analysis using aero engine-based correlations was performed to predict the steady state metal temperatures and hot running seal clearances at ISO rated power condition. The cooling mass flow and the flow pattern assumption for the thermal model were obtained from the steady state 2D axisymmetric CFD study. The CFD model with wall heat transfer was validated using cavity steady state air temperatures and static pressures measured at inlet to the labyrinth seal and four cavity radial positions in an engine test which included the mean annulus static pressure at hub radius. The predicted wall temperature distribution from the matched thermal model was used in the CFD model by incorporating wall temperature curve-fit polynomial functions. Results indicate that although the high rim seal effectiveness prevents ingestion from entering the cavity, the disc pumping flow draws air from within the cavity to satisfy entrainment leading to an inflow along the stator. The supplied cooling flow exceeds the minimum sealing flow predicted from both the Rotational Reynolds Number-based correlation and the annulus Reynolds Number correlation. However, the minimum disc pumping flow was found to be based on a modified entrainment expression with a turbulent flow parameter of 0.08. The predicted coefficient of discharge (Cd) of the industrial labyrinth seal from CFD was confirmed by modifying the carry-over effect of a correlation reported recently in the literature. Moreover, the relative effects of seal windage and heat transfer were obtained and it was found that contrary to what was expected, the universal windage correlation was more applicable than the aero engine-based labyrinth seal windage correlation. The CFD predicted disc heat flux profile showed reasonably good agreement with the free disc calculated heat flux. The irregular cavity shape and high Rotational Reynolds Number (in the order of 7×107) leads to entrance effects that produce a thicker turbulent boundary layer profile compared to that predicted by the 1/7 power velocity profile assumption.
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Flow and Heat Transfer in an Industrial Rotor-Stator Rim Sealing Cavity
Journal of Engineering for Gas Turbines and Power, 2000Co-Authors: Alexander Mirzamoghadam, Zhenhua XiaoAbstract:Flow and heat transfer in the row-1 upstream rotor-stator disk cavity of a large 3600-rpm industrial gas turbine was investigated using an integrated approach. A two dimensional axisymmetric transient thermal analysis using aeroengine-based correlations was performed to predict the steady-state metal temperatures and hot running seal clearances at ISO rated power condition. The cooling mass flow and the flow pattern assumption for the thermal model were obtained from the steady-state two dimensional axisymmetric CFD study. The CFD model with wall heat transfer was validated using cavity steady-state air temperatures and static pressures measured at inlet to the labyrinth seal and four cavity radial positions in an engine test which included the mean annulus static pressure at hub radius. The predicted wall temperature distribution from the matched thermal model was used in the CFD model by incorporating wall temperature curve-fit polynomial functions. Results indicate that although the high rim seal effectiveness prevents ingestion from entering the cavity, the disk pumping flow draws air from within the cavity to satisfy entrainment leading to an inflow along the stator. The supplied cooling flow exceeds the minimum sealing flow predicted from both the Rotational Reynolds-Number-based correlation and the annulus Reynolds Number correlation. However, the minimum disk pumping flow was found to be based on a modified entrainment expression with a turbulent flow parameter of 0.08. The predicted coefficient of discharge (Cd) of the industrial labyrinth seal from CFD was confirmed by modifying the carryover effect of a correlation reported recently in the literature. Moreover, the relative effects of seal windage and heat transfer were obtained and it was found that contrary to what was expected, the universal windage correlation was more applicable than the aeroengine-based labyrinth seal windage correlation. The CFD predicted disk heat flux profile showed reasonably good agreement with the free disk calculated heat flux. The irregular cavity shape and high Rotational Reynolds Number (in the order of 7×107) leads to entrance effects that produce a thicker turbulent boundary layer profile compared to that predicted by the 1/7 power velocity profile assumption.
Dario Amirante - One of the best experts on this subject based on the ideXlab platform.
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Large-Eddy Simulations of Wall Bounded Turbulent Flows Using Unstructured Linear Reconstruction Techniques
Journal of Turbomachinery, 2015Co-Authors: Dario Amirante, Nicholas J. HillsAbstract:Large-eddy simulations (LES) of wall bounded, low Mach Number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES (ILES) procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds Number Reb = 44 × 103 based on the pipe diameter, and a confined rotor–stator flow at the Rotational Reynolds Number ReΩ = 4 × 105 based on the outer radius. In both cases, the mean flow and the turbulent statistics agree well with existing direct numerical simulations (DNS) or experimental data.
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LES OF WALL BOUNDED TURBULENT FLOWS USING UNSTRUCTURED LINEAR RECONSTRUCTION TECHNIQUES
Volume 2B: Turbomachinery, 2014Co-Authors: Dario Amirante, Nicholas J. HillsAbstract:Large-Eddy Simulations of wall bounded, low Mach Number turbulent flows are conducted using an unstructured finite-volume solver of the compressible flow equations. The numerical method employs linear reconstructions of the primitive variables based on the least-squares approach of Barth. The standard Smagorinsky model is adopted as the subgrid term. The artificial viscosity inherent to the spatial discretization is maintained as low as possible reducing the dissipative contribution embedded in the approximate Riemann solver to the minimum necessary. Comparisons are also discussed with the results obtained using the implicit LES procedure. Two canonical test-cases are described: a fully developed pipe flow at a bulk Reynolds Number Reb = 44 × 103 based on the pipe diameter, and a confined rotor-stator flow at the Rotational Reynolds Number ReΩ = 4 × 105 based on the outer radius. In both cases the mean flow and the turbulent statistics agree well with existing DNS or experimental data.
