https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Sun, 10 May 2026 09:16:13 GMT 2026-05-10T09:16:13Z http://hdl.handle.net/10985/9961 Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows CHABI, Fatiha; CHAMPMARTIN, Stephane; SARRAF, Christophe; NOGUERA, Ricardo 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 GMT http://hdl.handle.net/10985/9961 2015-01-01T00:00:00Z CHABI, Fatiha CHAMPMARTIN, Stephane SARRAF, Christophe NOGUERA, Ricardo 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. http://hdl.handle.net/10985/10296 POD study of aerated cavitation in a venturi nozzle TOMOV, Petar; DANLOS, Amélie; RAVELET, Florent; SARRAF, Christophe; BAKIR, Farid; KHELLADI, Sofiane The fact of injecting bubbles into a cavitating flow influences typical cavitating behavior. Cavitation and aerated cavitation experiments has been carried out on a symmetrical venturi nozzle with convergent/divergent angles of 18 ◦ and 8 ◦ , respectively. A snapshot Proper Orthogonal Decomposition (POD) technique is used to identify different modes in terms of discharge flow velocity, pressure and injected quantity of air. The energy spectrum per given mode is also presented. The first four modes are outlined in the present paper for an aerated and non-aerated cavitating flows. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/10296 2015-01-01T00:00:00Z TOMOV, Petar DANLOS, Amélie RAVELET, Florent SARRAF, Christophe BAKIR, Farid KHELLADI, Sofiane The fact of injecting bubbles into a cavitating flow influences typical cavitating behavior. Cavitation and aerated cavitation experiments has been carried out on a symmetrical venturi nozzle with convergent/divergent angles of 18 ◦ and 8 ◦ , respectively. A snapshot Proper Orthogonal Decomposition (POD) technique is used to identify different modes in terms of discharge flow velocity, pressure and injected quantity of air. The energy spectrum per given mode is also presented. The first four modes are outlined in the present paper for an aerated and non-aerated cavitating flows. 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 GMT http://hdl.handle.net/10985/11254 2010-01-01T00:00:00Z 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. 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 GMT http://hdl.handle.net/10985/15875 2014-01-01T00:00:00Z 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. http://hdl.handle.net/10985/17815 A New Hemodynamic Ex Vivo Model for Medical Devices Assessment MAUREL, Blandine; CHAI, Feng; MATON, Mickael; SOBOCINSKI, Jonathan; HERTAULT, Adrien; BLANCHEMAIN, Nicolas; HAULON, Stephan; LERMUSIAUX, Patrick; SARRAF, Christophe; BAKIR, Farid Introduction: In stent restenosis (ISR) remains a major public health concern with an increased morbidity, mortality and health-related costs. Drug-eluting stents (DES) have reduced ISR, but are associated with healing-related issues or hypersensitivity reactions, leading to an increased risk of late acute stent thrombosis. Evaluations of new DES are based on animal models or in vitro release systems which show several limitations. The role of flow and shear stress on endothelial cell and ISR has also been emphasized. The aim of this work was to design and first evaluate an original bioreactor, reproducing ex vivo hemodynamic and biological conditions similar to human conditions, to further evaluate new DES. Methods & Results: This bioreactor was designed to study up to 6 stented arteries connected in bypass, immersed in a culture box, in which circulated a physiological systolo-diastolic resistive flow. Two centrifugal pumps drove the flow. The principal pump generated pulsating flows by modulation of rotation velocity, and the second pump worked at constant rotation velocity, ensuring the counter pressure levels and backflows. The flow rate, the velocity profile, the arterial pressure and the resistance of the flow were adjustable. The bioreactor was placed in an incubator to reproduce a biological environment. A first experience of feasibility was realized over a period of 24 days. Three rat aortic thoracic arteries were placed into the bioreactor, immersed in cell culture medium change every 3 days, and with a circulating systole diastolic flux circulating among the entire experimentation. There was no infection, no leak. At the end of experimentation, a morphometric analysis was performed confirming the viability of the arteries. Conclusion: We design and patent an original hemodynamic ex vivo model to further study new DES and ISR. We will next validate this ex vivo model of ISR reproducing this experimentation with stented arteries. Once validated, this bioreactor will allow characterization of the velocity field and drug transfers within a stented artery with new functionalized DES, with experimental means not available in vivo. Another main point will be the reduction of animal experimentation, and the availability of first results of new DES in human tissues (human infra popliteal or coronary arteries collected during human donation). Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/17815 2015-01-01T00:00:00Z MAUREL, Blandine CHAI, Feng MATON, Mickael SOBOCINSKI, Jonathan HERTAULT, Adrien BLANCHEMAIN, Nicolas HAULON, Stephan LERMUSIAUX, Patrick SARRAF, Christophe BAKIR, Farid Introduction: In stent restenosis (ISR) remains a major public health concern with an increased morbidity, mortality and health-related costs. Drug-eluting stents (DES) have reduced ISR, but are associated with healing-related issues or hypersensitivity reactions, leading to an increased risk of late acute stent thrombosis. Evaluations of new DES are based on animal models or in vitro release systems which show several limitations. The role of flow and shear stress on endothelial cell and ISR has also been emphasized. The aim of this work was to design and first evaluate an original bioreactor, reproducing ex vivo hemodynamic and biological conditions similar to human conditions, to further evaluate new DES. Methods & Results: This bioreactor was designed to study up to 6 stented arteries connected in bypass, immersed in a culture box, in which circulated a physiological systolo-diastolic resistive flow. Two centrifugal pumps drove the flow. The principal pump generated pulsating flows by modulation of rotation velocity, and the second pump worked at constant rotation velocity, ensuring the counter pressure levels and backflows. The flow rate, the velocity profile, the arterial pressure and the resistance of the flow were adjustable. The bioreactor was placed in an incubator to reproduce a biological environment. A first experience of feasibility was realized over a period of 24 days. Three rat aortic thoracic arteries were placed into the bioreactor, immersed in cell culture medium change every 3 days, and with a circulating systole diastolic flux circulating among the entire experimentation. There was no infection, no leak. At the end of experimentation, a morphometric analysis was performed confirming the viability of the arteries. Conclusion: We design and patent an original hemodynamic ex vivo model to further study new DES and ISR. We will next validate this ex vivo model of ISR reproducing this experimentation with stented arteries. Once validated, this bioreactor will allow characterization of the velocity field and drug transfers within a stented artery with new functionalized DES, with experimental means not available in vivo. Another main point will be the reduction of animal experimentation, and the availability of first results of new DES in human tissues (human infra popliteal or coronary arteries collected during human donation). http://hdl.handle.net/10985/17781 Experimental study of aerated cavitation in a horizontal venturi nozzle TOMOV, Petar; VERTENOEUIL, P.; RAVELET, Florent; SARRAF, Christophe; BAKIR, Farid; KHELLADI, Sofiane The injection of bubbles into an already cavitating flow is a way of influencing the typical cavitating behaviour. The present article deals with experiments on aerated and non-aerated cavitation in a transparent horizontal venturi nozzle. The observations are done by means of a high-speed camera. In such a way the extremely rapid cavitation and cavitation–aeration flows are captured and further analysed. The post-processing techniques is based on the detection of the grey level on the series of images. As a result, three different regimes are identified: sheet cavitation, cloud cavitation and “supercavitation”. Those regimes are further aerated by injecting air bubbles. Standard deviations, time–space diagrams and frequency spectrum based on the vertical distribution of the grey level along a monitored line are plotted for all of the observed regimes. In the pure cavitation cases we obtain statistically symmetrical structures with characteristic lengths and frequencies. On the other hand, with aeration present, the symmetry is broken and characteristic lengths and frequencies are deeply modified, until a complete disappearance when “supercavitation” is reached. Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10985/17781 2016-01-01T00:00:00Z TOMOV, Petar VERTENOEUIL, P. RAVELET, Florent SARRAF, Christophe BAKIR, Farid KHELLADI, Sofiane The injection of bubbles into an already cavitating flow is a way of influencing the typical cavitating behaviour. The present article deals with experiments on aerated and non-aerated cavitation in a transparent horizontal venturi nozzle. The observations are done by means of a high-speed camera. In such a way the extremely rapid cavitation and cavitation–aeration flows are captured and further analysed. The post-processing techniques is based on the detection of the grey level on the series of images. As a result, three different regimes are identified: sheet cavitation, cloud cavitation and “supercavitation”. Those regimes are further aerated by injecting air bubbles. Standard deviations, time–space diagrams and frequency spectrum based on the vertical distribution of the grey level along a monitored line are plotted for all of the observed regimes. In the pure cavitation cases we obtain statistically symmetrical structures with characteristic lengths and frequencies. On the other hand, with aeration present, the symmetry is broken and characteristic lengths and frequencies are deeply modified, until a complete disappearance when “supercavitation” is reached. http://hdl.handle.net/10985/9481 Banc de test pour stent MAUREL, Blandine; LERMUSIAUX, Patrick; SARRAF, Christophe; BAKIR, Farid L'invention concerne un banc test pour stents, caractérisé en ce qu'il comprend une pompe (2) non volumétrique dont l'entrée est raccordée à un réservoir (4) de liquide sanguin ouvert et dont la sortie est reliée à une canalisation (6) d'alimentation d'au moins une éprouvette (8), formée d'un tronçon artériel (10) équipé d'un stent et une canalisation de by-pass (13) équipée d'une restriction (14) de section réglable, l'éprouvette étant reliée à un collecteur (12) de retour du fluide au réservoir (4), les moyens (11) de connexion de l'éprouvette au circuit étant démontables, ce collecteur (12) étant équipé d'un régulateur (17) de pression et un capteur de débit (16) à la sortie de l'éprouvette, la canalisation d'alimentation (6) comportant un capteur de pression à la sortie de la pompe (1), la commande de la pompe étant assurée par une électronique (3) de commande de l'alimentation électrique de son moteur (2) apte à reproduire les phases systoliques et diastoliques du cycle cardiaque, lesdits capteurs (15,16) étant reliés à une carte d'acquisition de données de manière à surveiller le fonctionnement de la pompe, l'éprouvette étant logée dans un milieu nutritif (18) pour le tissu artériel, le réservoir ouvert (4) étant adapté à une oxygénation du liquide sanguin et l'ensemble du circuit hydraulique étant logé dans une enceinte (21) à température régulée. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/9481 2013-01-01T00:00:00Z MAUREL, Blandine LERMUSIAUX, Patrick SARRAF, Christophe BAKIR, Farid L'invention concerne un banc test pour stents, caractérisé en ce qu'il comprend une pompe (2) non volumétrique dont l'entrée est raccordée à un réservoir (4) de liquide sanguin ouvert et dont la sortie est reliée à une canalisation (6) d'alimentation d'au moins une éprouvette (8), formée d'un tronçon artériel (10) équipé d'un stent et une canalisation de by-pass (13) équipée d'une restriction (14) de section réglable, l'éprouvette étant reliée à un collecteur (12) de retour du fluide au réservoir (4), les moyens (11) de connexion de l'éprouvette au circuit étant démontables, ce collecteur (12) étant équipé d'un régulateur (17) de pression et un capteur de débit (16) à la sortie de l'éprouvette, la canalisation d'alimentation (6) comportant un capteur de pression à la sortie de la pompe (1), la commande de la pompe étant assurée par une électronique (3) de commande de l'alimentation électrique de son moteur (2) apte à reproduire les phases systoliques et diastoliques du cycle cardiaque, lesdits capteurs (15,16) étant reliés à une carte d'acquisition de données de manière à surveiller le fonctionnement de la pompe, l'éprouvette étant logée dans un milieu nutritif (18) pour le tissu artériel, le réservoir ouvert (4) étant adapté à une oxygénation du liquide sanguin et l'ensemble du circuit hydraulique étant logé dans une enceinte (21) à température régulée. 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 GMT http://hdl.handle.net/10985/8900 2013-01-01T00:00:00Z 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. 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 GMT http://hdl.handle.net/10985/8914 2013-01-01T00:00:00Z 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. http://hdl.handle.net/10985/10255 Comparison of various hemodynamic models for applications to CFD in stent arteries CHABI, Fatiha; CHAMPMARTIN, Stephane; SARRAF, Christophe; NOGUERA, Ricardo; MAUREL, Blandine 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 GMT http://hdl.handle.net/10985/10255 2014-01-01T00:00:00Z CHABI, Fatiha CHAMPMARTIN, Stephane SARRAF, Christophe NOGUERA, Ricardo MAUREL, Blandine 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.