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http://hdl.handle.net/10985/8914
Numerical investigation of the real and ideal gap profiles in the calculation of the pressure distortion coefficient and piston fall rate of an LNE 200 MPa pressure balance
WONGTHEP, Padipat; RABAULT, Thierry; NOGUERA, Ricardo; SARRAF, Christophe
This paper aims to investigate, by means of numerical simulation, the effect of gap profiles on the calculation of the pressure distortion coefficient (λ) and the piston fall rate (vf) of two piston-cylinder units used in a Laboratoire National de Métrologie et d'Essais (LNE) 200 MPa pressure balance. The ideal mean gap width between the piston and the cylinder was obtained after measuring the piston fall rate at a low pressure, while the piston radius was obtained from the cross-float experiments at a low pressure. The real gap width was obtained from dimensional measurements by measuring the diameter and straightness of the piston and the cylinder. The piston and cylinder radial distortions were calculated using the finite element method. The pressure distribution in the gap was calculated on the basis of the Navier-Stokes equation for Newtonian viscous flow. The results such as pressure distributions, radial distortions, the pressure distortion coefficient and the piston fall rate were presented for the free-deformation operating mode of the assemblies. The calculation resulted in ideal and real gap profiles indicating that the average pressure distortion coefficient was in good agreement within 0.017 × 10-6 MPa-1 and the calculations of piston fall rate depended on the gap profile especially at the inlet and outlet zones of the engagement length.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/89142013-01-01T00:00:00ZWONGTHEP, PadipatRABAULT, ThierryNOGUERA, RicardoSARRAF, ChristopheThis paper aims to investigate, by means of numerical simulation, the effect of gap profiles on the calculation of the pressure distortion coefficient (λ) and the piston fall rate (vf) of two piston-cylinder units used in a Laboratoire National de Métrologie et d'Essais (LNE) 200 MPa pressure balance. The ideal mean gap width between the piston and the cylinder was obtained after measuring the piston fall rate at a low pressure, while the piston radius was obtained from the cross-float experiments at a low pressure. The real gap width was obtained from dimensional measurements by measuring the diameter and straightness of the piston and the cylinder. The piston and cylinder radial distortions were calculated using the finite element method. The pressure distribution in the gap was calculated on the basis of the Navier-Stokes equation for Newtonian viscous flow. The results such as pressure distributions, radial distortions, the pressure distortion coefficient and the piston fall rate were presented for the free-deformation operating mode of the assemblies. The calculation resulted in ideal and real gap profiles indicating that the average pressure distortion coefficient was in good agreement within 0.017 × 10-6 MPa-1 and the calculations of piston fall rate depended on the gap profile especially at the inlet and outlet zones of the engagement length.A new model of fluid flow to determine pressure balance characteristics
http://hdl.handle.net/10985/8900
A new model of fluid flow to determine pressure balance characteristics
WONGTHEP, Padipat; RABAULT, Thierry; NOGUERA, Ricardo; SARRAF, Christophe
Some projects such as the EUROMET project 463 have underlined the lack of agreement between experimental measurements and calculations by the finite element method (FEM), used to determine the piston fall rate of a high-pressure balance used in primary standards. This is significant because the piston fall rate is an essential parameter to characterize experimentally the mean gap between the piston and the cylinder and to determine the effective area (A p) at each pressure (p) point. By improving the method used to estimate the piston fall rate it is possible to improve the determination of the gap, the effective area and consequently the pressure distortion coefficient. One possible cause of the lack of agreement between the calculated and measured piston fall rates could be inappropriate modelling of the fluid flow. In fact, the former quasi-1D Stokes model assimilates the gap between the piston and the cylinder as formed by two parallel walls, which is an approximation. In addition, the velocity of the piston wall was neglected. In order to evaluate the influence of this model, the equations of the fluid flow are modified and are presented in this paper. Equations that were defined in a parallel-plane model are defined in an annular gap model. In addition to this, corrections due to the velocity of the piston wall are inserted. This research work is applied on a Desgranges et Huot DH 7594 piston-cylinder unit of PTB with a pressure up to 1 GPa, in the continuity of the EUROMET project 463 in order to quantify the influence of each correction that has been inserted in the new equations. This is carried out using the FEM. This analysis will allow us to evaluate the improvement of our knowledge of the behaviour of piston gauges and consequently to better evaluate the uncertainties due to the models.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/89002013-01-01T00:00:00ZWONGTHEP, PadipatRABAULT, ThierryNOGUERA, RicardoSARRAF, ChristopheSome projects such as the EUROMET project 463 have underlined the lack of agreement between experimental measurements and calculations by the finite element method (FEM), used to determine the piston fall rate of a high-pressure balance used in primary standards. This is significant because the piston fall rate is an essential parameter to characterize experimentally the mean gap between the piston and the cylinder and to determine the effective area (A p) at each pressure (p) point. By improving the method used to estimate the piston fall rate it is possible to improve the determination of the gap, the effective area and consequently the pressure distortion coefficient. One possible cause of the lack of agreement between the calculated and measured piston fall rates could be inappropriate modelling of the fluid flow. In fact, the former quasi-1D Stokes model assimilates the gap between the piston and the cylinder as formed by two parallel walls, which is an approximation. In addition, the velocity of the piston wall was neglected. In order to evaluate the influence of this model, the equations of the fluid flow are modified and are presented in this paper. Equations that were defined in a parallel-plane model are defined in an annular gap model. In addition to this, corrections due to the velocity of the piston wall are inserted. This research work is applied on a Desgranges et Huot DH 7594 piston-cylinder unit of PTB with a pressure up to 1 GPa, in the continuity of the EUROMET project 463 in order to quantify the influence of each correction that has been inserted in the new equations. This is carried out using the FEM. This analysis will allow us to evaluate the improvement of our knowledge of the behaviour of piston gauges and consequently to better evaluate the uncertainties due to the models.Comparison of various hemodynamic models for applications to CFD in stent arteries
http://hdl.handle.net/10985/10255
Comparison of various hemodynamic models for applications to CFD in stent arteries
CHABI, Fatiha; NOGUERA, Ricardo; MAUREL, Blandine; CHAMPMARTIN, Stephane; SARRAF, Christophe
This work assesses three hemodynamic models for the numerical modeling of intra-stent flows. These are the classical Poiseuille model (PM), the simplified pulsatile model (SPM) and the complete pulsatile model (CPM) based on the analysis of Womersley. They are applied to the physiological flow rate of a stented left coronary artery. The CFD package "Ansys Fluent 14.5" is used to compute the main features of the flows. The results show large differences between the steady and unsteady models notably for the wall shear stress and the re-circulation lengths, which are known to promote intra-stent restenosis. The PM is obviously not pertinent to calculate the flows involved in intra-stent restenosis. The CPM and SPM give close results but the latter model is by far less time-demanding and should be preferred.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/102552014-01-01T00:00:00ZCHABI, FatihaNOGUERA, RicardoMAUREL, BlandineCHAMPMARTIN, StephaneSARRAF, ChristopheThis work assesses three hemodynamic models for the numerical modeling of intra-stent flows. These are the classical Poiseuille model (PM), the simplified pulsatile model (SPM) and the complete pulsatile model (CPM) based on the analysis of Womersley. They are applied to the physiological flow rate of a stented left coronary artery. The CFD package "Ansys Fluent 14.5" is used to compute the main features of the flows. The results show large differences between the steady and unsteady models notably for the wall shear stress and the re-circulation lengths, which are known to promote intra-stent restenosis. The PM is obviously not pertinent to calculate the flows involved in intra-stent restenosis. The CPM and SPM give close results but the latter model is by far less time-demanding and should be preferred.Study of passive control study of the cavitation instability on a venturi profile
http://hdl.handle.net/10985/11254
Study of passive control study of the cavitation instability on a venturi profile
DANLOS, Amélie; MEHAL, Jean-Elie; RAVELET, Florent; SARRAF, Christophe
This paper presents experimental and numerical results concerning the operation of a configuration that includes an axial pump and a bundle of tubes that mimics the cool source of a heat exchanger. The pump used in the tests has a low solidity and two blades designed in forced vortex, the tip clearance is approximately 3.87% of tip radius. The experimental measures of the characteristic curves and of the wall static pressure fluctuations signals upstream and downstream the pump and the exchanger were compared to the numerical results. The numerical simulations were carried out by using a Fluent code, with URANS (Unsteady Reynolds Averaged Navier-Stokes) approach and k-w SST turbulence model.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/112542010-01-01T00:00:00ZDANLOS, AmélieMEHAL, Jean-ElieRAVELET, FlorentSARRAF, ChristopheThis paper presents experimental and numerical results concerning the operation of a configuration that includes an axial pump and a bundle of tubes that mimics the cool source of a heat exchanger. The pump used in the tests has a low solidity and two blades designed in forced vortex, the tip clearance is approximately 3.87% of tip radius. The experimental measures of the characteristic curves and of the wall static pressure fluctuations signals upstream and downstream the pump and the exchanger were compared to the numerical results. The numerical simulations were carried out by using a Fluent code, with URANS (Unsteady Reynolds Averaged Navier-Stokes) approach and k-w SST turbulence model.Thickness effect of NACA foils on hydrodynamic global parameters, boundary layer states and stall establishment
http://hdl.handle.net/10985/10295
Thickness effect of NACA foils on hydrodynamic global parameters, boundary layer states and stall establishment
DJERIDI, Henda; PROTHIN, Sébastien; BILLARD, Jean-Yves; SARRAF, Christophe
The present study investigates experimentally the hydrodynamic behavior of 2D NACA (15, 25, 35%) symmetric hydrofoils at Reynolds number 0.5 106 . A particular attention is paid on the hysteretic behavior at static stall angle and a detailed cartography of boundary layer structures (integral quantities and velocity profiles) is given in order to put in evidence the mechanism of the detachment and the onset of von Karman instability for thick profile
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10985/102952010-01-01T00:00:00ZDJERIDI, HendaPROTHIN, SébastienBILLARD, Jean-YvesSARRAF, ChristopheThe present study investigates experimentally the hydrodynamic behavior of 2D NACA (15, 25, 35%) symmetric hydrofoils at Reynolds number 0.5 106 . A particular attention is paid on the hysteretic behavior at static stall angle and a detailed cartography of boundary layer structures (integral quantities and velocity profiles) is given in order to put in evidence the mechanism of the detachment and the onset of von Karman instability for thick profileComparison of various hemodynamic models for applications to cfd in stented arteries
http://hdl.handle.net/10985/15875
Comparison of various hemodynamic models for applications to cfd in stented arteries
CHABI, Fatiha; NOGUERA, Ricardo; MAUREL, Blandine; CHAMPMARTIN, Stephane; SARRAF, Christophe
A design study of propeller hydrokinetic turbines is explored in the present paper, where the optimized blade geometry is determined by the classical Glauert theory applicable to the design of axial flow turbines (hydrokinetic and wind turbines). The aim of the present study is to evaluate the optimized geometry for propeller hydrokinetic turbines, observing the effect of the number of blades in the runner design. The performance of runners with different number of blades is evaluated in a specific low-rotational-speed operating conditions, using blade element momentum theory (BEMT) simulations, confirmed by measurements in wind tunnel experiments for small-scale turbine models. The optimum design values of the power coefficient, in the operating tip speed ratio, for two-, three- and four-blade runners are pointed out, defining the best configuration for a propeller 10 kW hydrokinetic machine.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/158752014-01-01T00:00:00ZCHABI, FatihaNOGUERA, RicardoMAUREL, BlandineCHAMPMARTIN, StephaneSARRAF, ChristopheA design study of propeller hydrokinetic turbines is explored in the present paper, where the optimized blade geometry is determined by the classical Glauert theory applicable to the design of axial flow turbines (hydrokinetic and wind turbines). The aim of the present study is to evaluate the optimized geometry for propeller hydrokinetic turbines, observing the effect of the number of blades in the runner design. The performance of runners with different number of blades is evaluated in a specific low-rotational-speed operating conditions, using blade element momentum theory (BEMT) simulations, confirmed by measurements in wind tunnel experiments for small-scale turbine models. The optimum design values of the power coefficient, in the operating tip speed ratio, for two-, three- and four-blade runners are pointed out, defining the best configuration for a propeller 10 kW hydrokinetic machine.Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows
http://hdl.handle.net/10985/9961
Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows
CHABI, Fatiha; NOGUERA, Ricardo; CHAMPMARTIN, Stephane; SARRAF, Christophe
We evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/99612015-01-01T00:00:00ZCHABI, FatihaNOGUERA, RicardoCHAMPMARTIN, StephaneSARRAF, ChristopheWe evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations.Experimental study of blade thickness effects on the overall and local performances of a Controlled Vortex Designed axial-ﬂow fan
http://hdl.handle.net/10985/11220
Experimental study of blade thickness effects on the overall and local performances of a Controlled Vortex Designed axial-ﬂow fan
NOURI, Hussain; RAVELET, Florent; SARRAF, Christophe; BAKIR, Farid
The purpose of this work is to study the effects of blade thickness on the performances of an axial-ﬂow fan. Two fans that differ only in the thickness of their blades were studied. The ﬁrst fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin blades. The second fan has much thicker blades compatible with the rotomoulding conception process. The overall perfor-mances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus ﬂow-rate) is slightly steeper for the fan with thick blades, and the nominal point is shifted towards lower ﬂow-rates. The efﬁciency of the thick blades fan is lower than the efﬁciency of the fan with thin blades but remains high on a wider ﬂow-rate range. The mean velocity ﬁelds downstream of the rotors are very similar at nominal points with less centrifu-gation for the thick blades fan. Moreover, the thick blades fan maintains an axial exit-ﬂow on a wider range of ﬂow-rates. The main differences concern local properties of the ﬂow: phase-averaged velocities and wall pressure ﬂuctuations strongly differ at the nominal ﬂow-rates. The total level of ﬂuctuations is lower for the thick blades fan that for the thin blades fan and the spectral decomposition of the wall ﬂuc-tuations and velocity signals reveal more harmonics for the thick blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/112202011-01-01T00:00:00ZNOURI, HussainRAVELET, FlorentSARRAF, ChristopheBAKIR, FaridThe purpose of this work is to study the effects of blade thickness on the performances of an axial-ﬂow fan. Two fans that differ only in the thickness of their blades were studied. The ﬁrst fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin blades. The second fan has much thicker blades compatible with the rotomoulding conception process. The overall perfor-mances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus ﬂow-rate) is slightly steeper for the fan with thick blades, and the nominal point is shifted towards lower ﬂow-rates. The efﬁciency of the thick blades fan is lower than the efﬁciency of the fan with thin blades but remains high on a wider ﬂow-rate range. The mean velocity ﬁelds downstream of the rotors are very similar at nominal points with less centrifu-gation for the thick blades fan. Moreover, the thick blades fan maintains an axial exit-ﬂow on a wider range of ﬂow-rates. The main differences concern local properties of the ﬂow: phase-averaged velocities and wall pressure ﬂuctuations strongly differ at the nominal ﬂow-rates. The total level of ﬂuctuations is lower for the thick blades fan that for the thin blades fan and the spectral decomposition of the wall ﬂuc-tuations and velocity signals reveal more harmonics for the thick blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range.Design and Experimental Validation of a Ducted Counter-rotating Axial-flow Fans System
http://hdl.handle.net/10985/8541
Design and Experimental Validation of a Ducted Counter-rotating Axial-flow Fans System
NOURI, Hussain; SARRAF, Christophe; REY, Robert; RAVELET, Florent; BAKIR, Farid
An experimental study on the design of counter-rotating axial-flow fans was carried out. The fans were designed using an inverse method. In particular, the system is designed to have a pure axial discharge flow. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The relative axial spacing between fans can vary from 17% to 310%. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system has a very flexible use, with a large patch of high efficient operating points in the parameter space. The increase of axial spacing causes only a small decrease of the efficiency
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/85412012-01-01T00:00:00ZNOURI, HussainSARRAF, ChristopheREY, RobertRAVELET, FlorentBAKIR, FaridAn experimental study on the design of counter-rotating axial-flow fans was carried out. The fans were designed using an inverse method. In particular, the system is designed to have a pure axial discharge flow. The counter-rotating fans operate in a ducted-flow configuration and the overall performances are measured in a normalized test bench. The rotation rate of each fan is independently controlled. The relative axial spacing between fans can vary from 17% to 310%. The results show that the efficiency is strongly increased compared to a conventional rotor or to a rotor-stator stage. The effects of varying the rotation rates ratio on the overall performances are studied and show that the system has a very flexible use, with a large patch of high efficient operating points in the parameter space. The increase of axial spacing causes only a small decrease of the efficiencyÉtude expérimentale de l’influence du blocage aval sur les performances de ventilateurs axiaux
http://hdl.handle.net/10985/8590
Étude expérimentale de l’influence du blocage aval sur les performances de ventilateurs axiaux
RAVELET, Florent; SARRAF, Christophe; BAKIR, Farid
L’étude a pour objet l’aide au développement d’une méthode de pré-dimensionnement des ventilateurs axiaux opérant en champs contraints. L’influence d’un obstacle situé à l’aval d’un ventilateur est étudiée expérimentalement sur quatre rotors de vitesses angulaires spécifiques différentes. Les rotors sont testés sur un banc d’essais normalisé de type caisson aspirant. Les rotors fonctionnent en champ libre et en champs contraints par 15 configurations de blocage. Les blocages sont réalisés par une plaque plane, perpendiculaire à l’axe de rotation du rotor, modélisant par exemple l’obstruction d’un bloc moteur automobile à combustion interne. Les quatre jeux de performances globales (élévation de pression, débit et rendement statique) évoluant avec la distance à l’obstacle sont comparés pour mettre en évidence leurs similarités. On observe des variations d’élévation de pression en fonction du débit quand l’obstacle se rapproche du ventilateur. Les courbes caractéristiques semblent évoluer autour d’un pivot dont la position par rapport au débit nominal du rotor en champ libre pourrait être en relation avec la vitesse angulaire spécifique.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/85902013-01-01T00:00:00ZRAVELET, FlorentSARRAF, ChristopheBAKIR, FaridL’étude a pour objet l’aide au développement d’une méthode de pré-dimensionnement des ventilateurs axiaux opérant en champs contraints. L’influence d’un obstacle situé à l’aval d’un ventilateur est étudiée expérimentalement sur quatre rotors de vitesses angulaires spécifiques différentes. Les rotors sont testés sur un banc d’essais normalisé de type caisson aspirant. Les rotors fonctionnent en champ libre et en champs contraints par 15 configurations de blocage. Les blocages sont réalisés par une plaque plane, perpendiculaire à l’axe de rotation du rotor, modélisant par exemple l’obstruction d’un bloc moteur automobile à combustion interne. Les quatre jeux de performances globales (élévation de pression, débit et rendement statique) évoluant avec la distance à l’obstacle sont comparés pour mettre en évidence leurs similarités. On observe des variations d’élévation de pression en fonction du débit quand l’obstacle se rapproche du ventilateur. Les courbes caractéristiques semblent évoluer autour d’un pivot dont la position par rapport au débit nominal du rotor en champ libre pourrait être en relation avec la vitesse angulaire spécifique.