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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 08 Aug 2024 20:14:51 GMT2024-08-08T20:14:51ZNew high-resolution-preserving sliding mesh techniques for higher-order finite volume schemes
http://hdl.handle.net/10985/17818
New high-resolution-preserving sliding mesh techniques for higher-order finite volume schemes
RAMÍREZ, Luis; FOULQUIÉ, Charles; NOGUEIRA, Xesús; CHASSAING, Jean-Camille; COLOMINAS, Ignasi; KHELLADI, Sofiane
This paper presents a new sliding mesh technique for the computation of unsteady viscous flows in the presence of rotating bodies. The compressible Euler and incompressible Navier–Stokes equations are solved using a higher-order (>2) finite volume method on unstructured grids. A sliding mesh approach is employed at the interface between computational grids in relative motion. In order to prevent loss of accuracy, two distinct families of higher-order sliding mesh interfaces are developed. These approaches fit naturally in a high-order finite volume framework. To this end, Moving Least Squares (MLS) approximants are used for the transmission of the information from one grid to another. A particular attention is paid for the study of the accuracy and conservation properties of the numerical scheme for static and rotating grids. The capabilities of the present solver to compute complex unsteady vortical flow motions created by rotating geometries are illustrated on a cross-flow configuration.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/178182015-01-01T00:00:00ZRAMÍREZ, LuisFOULQUIÉ, CharlesNOGUEIRA, XesúsCHASSAING, Jean-CamilleCOLOMINAS, IgnasiKHELLADI, SofianeThis paper presents a new sliding mesh technique for the computation of unsteady viscous flows in the presence of rotating bodies. The compressible Euler and incompressible Navier–Stokes equations are solved using a higher-order (>2) finite volume method on unstructured grids. A sliding mesh approach is employed at the interface between computational grids in relative motion. In order to prevent loss of accuracy, two distinct families of higher-order sliding mesh interfaces are developed. These approaches fit naturally in a high-order finite volume framework. To this end, Moving Least Squares (MLS) approximants are used for the transmission of the information from one grid to another. A particular attention is paid for the study of the accuracy and conservation properties of the numerical scheme for static and rotating grids. The capabilities of the present solver to compute complex unsteady vortical flow motions created by rotating geometries are illustrated on a cross-flow configuration.Experimental study of aerated cavitation in a horizontal venturi nozzle
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 GMThttp://hdl.handle.net/10985/177812016-01-01T00:00:00ZTOMOV, PetarVERTENOEUIL, P.RAVELET, FlorentSARRAF, ChristopheBAKIR, FaridKHELLADI, SofianeThe 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.Numerical Analysis of a Novel Twin-Impeller Centrifugal Compressor
http://hdl.handle.net/10985/21358
Numerical Analysis of a Novel Twin-Impeller Centrifugal Compressor
NGUYEN, Van Thang; DANLOS, Amélie; SOLIS, Moises; RAVELET, Florent; DELIGANT, Michael; BAKIR, Farid; KHELLADI, Sofiane
Centrifugal compressors are widely used in many industrial fields such as automotive, aviation, aerospace. However, these turbomachines suffer instability phenomenon when the flow rate is too high or too low, called rotating stall and surge. These phenomena cause the operation failure, pressure fluctuations and vibrations of the thorough system. Numerous mechanical solutions have been presented to minimize these instabilities and expand the operating range towards low-flow rates like active control of the flow path, variable inlet guide vane and casing treatment. Currently, our team has developed a novel compressor composed of a twin-impeller powered by autonomous systems. We notice the performance improvement and instabilities suppression of this compressor experimentally. In this paper, an active control method is introduced by controlling the speed and rotation direction of the impellers to expand the operating range. A CFD study is then conducted to analysis flow morphology and thermodynamic characteristics based on the experimental observations at three special points. Numerical results and experimental measurements of compressor maps are consistent.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/213582021-01-01T00:00:00ZNGUYEN, Van ThangDANLOS, AmélieSOLIS, MoisesRAVELET, FlorentDELIGANT, MichaelBAKIR, FaridKHELLADI, SofianeCentrifugal compressors are widely used in many industrial fields such as automotive, aviation, aerospace. However, these turbomachines suffer instability phenomenon when the flow rate is too high or too low, called rotating stall and surge. These phenomena cause the operation failure, pressure fluctuations and vibrations of the thorough system. Numerous mechanical solutions have been presented to minimize these instabilities and expand the operating range towards low-flow rates like active control of the flow path, variable inlet guide vane and casing treatment. Currently, our team has developed a novel compressor composed of a twin-impeller powered by autonomous systems. We notice the performance improvement and instabilities suppression of this compressor experimentally. In this paper, an active control method is introduced by controlling the speed and rotation direction of the impellers to expand the operating range. A CFD study is then conducted to analysis flow morphology and thermodynamic characteristics based on the experimental observations at three special points. Numerical results and experimental measurements of compressor maps are consistent.Multi-scale damage analysis and fatigue behavior of PLA manufactured by fused deposition modeling (FDM)
http://hdl.handle.net/10985/21762
Multi-scale damage analysis and fatigue behavior of PLA manufactured by fused deposition modeling (FDM)
VANAEI, Hamid Reza; SHIRINBAYAN, Mohammadali; VANAEI, Saeedeh; TCHARKHTCHI, Abbas; FITOUSSI, Joseph; KHELLADI, Sofiane
Purpose Fused deposition modeling (FDM) draws particular attention due to its ability to fabricate components directly from a CAD data; however, the mechanical properties of the produced pieces are limited. This paper aims to present the experimental aspect of multi-scale damage analysis and fatigue behavior of polylactic acid (PLA) manufactured by FDM. The main purpose of this paper is to analyze the effect of extruder temperature during the process, loading amplitude, and frequency on fatigue behavior. Design/methodology/approach Three specific case studies were analyzed and compared with spool material for understanding the effect of bonding formation: single printed filament, two printed filaments and three printed filaments. Specific experiments of quasi-static tensile tests coupled with microstructure observations are performed to multi-scale damage analysis. A strong variation of fatigue strength as a function of the loading amplitude, frequency and extruder temperature is also presented. Findings The obtained experimental results show the first observed damage phenomenon corresponds to the inter-layer bonding of the filament interface at the stress value of 40 MPa. For instance, fatigue lifetime clearly depends on the extruder temperature and the loading frequency. Moreover, when the frequency is 80 Hz, the coupling effect of thermal and mechanical fatigue causes self-heating which decreases the fatigue lifetime. Originality/value This paper comprises useful data regarding the mechanical behavior and fatigue lifetime of FDM made PLA specimens. In fact, it evaluates the effect of process parameters (extruder temperature) based on the nature of FDM that is classified as a thermally-driven process.
Fri, 01 Jan 2021 00:00:00 GMThttp://hdl.handle.net/10985/217622021-01-01T00:00:00ZVANAEI, Hamid RezaSHIRINBAYAN, MohammadaliVANAEI, SaeedehTCHARKHTCHI, AbbasFITOUSSI, JosephKHELLADI, SofianePurpose Fused deposition modeling (FDM) draws particular attention due to its ability to fabricate components directly from a CAD data; however, the mechanical properties of the produced pieces are limited. This paper aims to present the experimental aspect of multi-scale damage analysis and fatigue behavior of polylactic acid (PLA) manufactured by FDM. The main purpose of this paper is to analyze the effect of extruder temperature during the process, loading amplitude, and frequency on fatigue behavior. Design/methodology/approach Three specific case studies were analyzed and compared with spool material for understanding the effect of bonding formation: single printed filament, two printed filaments and three printed filaments. Specific experiments of quasi-static tensile tests coupled with microstructure observations are performed to multi-scale damage analysis. A strong variation of fatigue strength as a function of the loading amplitude, frequency and extruder temperature is also presented. Findings The obtained experimental results show the first observed damage phenomenon corresponds to the inter-layer bonding of the filament interface at the stress value of 40 MPa. For instance, fatigue lifetime clearly depends on the extruder temperature and the loading frequency. Moreover, when the frequency is 80 Hz, the coupling effect of thermal and mechanical fatigue causes self-heating which decreases the fatigue lifetime. Originality/value This paper comprises useful data regarding the mechanical behavior and fatigue lifetime of FDM made PLA specimens. In fact, it evaluates the effect of process parameters (extruder temperature) based on the nature of FDM that is classified as a thermally-driven process.High Accuracy Volume Flow Rate Measurement Using Vortex Counting
http://hdl.handle.net/10985/8577
High Accuracy Volume Flow Rate Measurement Using Vortex Counting
ZAARAOUI, Abdelkader; MARGNAT, Florent; RAVELET, Florent; KHELLADI, Sofiane
A prototype device for measuring the volumetric flow-rate by counting vortices has been designed and realized. It consists of a square-section pipe in which are placed a two-dimensional bluff body and a strain gauge force sensor. These two elements are separated from each other, unlike the majority of vortex apparatus currently available. The principle is based on the generation of a separated wake behind the bluff body. The volumetric flow-rate measurement is done by counting vortices using a flat plate placed in the wake and attached to the beam sensor. By optimizing the geometrical arrangement, the search for a significant signal has shown that it was possible to get a quasi-periodic signal, within a good range of flow rates so that its performances are well deduced. The repeatability of the value of the volume of fluid passed for every vortex shed is tested for a given flow and then the accuracy of the measuring device is determined. This quantity is the constant of the device and is called the digital volume (V_p). It has the dimension of a volume and varies with the confinement of the flow and with the Reynolds number. Therefore, a dimensionless quantity is introduced, the reduced digital volume (V_r) that takes into account the average speed in the contracted section downstream of the bluff body. The reduced digital volume is found to be independent of the confinement in a significant range of Reynolds numbers, which gives the device a good accuracy.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/85772013-01-01T00:00:00ZZAARAOUI, AbdelkaderMARGNAT, FlorentRAVELET, FlorentKHELLADI, SofianeA prototype device for measuring the volumetric flow-rate by counting vortices has been designed and realized. It consists of a square-section pipe in which are placed a two-dimensional bluff body and a strain gauge force sensor. These two elements are separated from each other, unlike the majority of vortex apparatus currently available. The principle is based on the generation of a separated wake behind the bluff body. The volumetric flow-rate measurement is done by counting vortices using a flat plate placed in the wake and attached to the beam sensor. By optimizing the geometrical arrangement, the search for a significant signal has shown that it was possible to get a quasi-periodic signal, within a good range of flow rates so that its performances are well deduced. The repeatability of the value of the volume of fluid passed for every vortex shed is tested for a given flow and then the accuracy of the measuring device is determined. This quantity is the constant of the device and is called the digital volume (V_p). It has the dimension of a volume and varies with the confinement of the flow and with the Reynolds number. Therefore, a dimensionless quantity is introduced, the reduced digital volume (V_r) that takes into account the average speed in the contracted section downstream of the bluff body. The reduced digital volume is found to be independent of the confinement in a significant range of Reynolds numbers, which gives the device a good accuracy.Experimental investigation of an actively controlled automotive cooling fan using steady air injection in the leakage gap
http://hdl.handle.net/10985/17889
Experimental investigation of an actively controlled automotive cooling fan using steady air injection in the leakage gap
AZZAM, Tarik; PARIDAENS, Richard; OUALLI, Hamid; RAVELET, Florent; BAKIR, Farid; KHELLADI, Sofiane
In an axial fan, a leakage flow driven by a pressure gradient between the pressure side and the suction side occurs in the gap between the shroud and the casing. This leakage flow is in the opposite direction to the main flow and is responsible for significant energy dissipation. Therefore, many authors have worked to understand this phenomenon in order to reduce these inherent energy losses. Up to now, most of the studies reported in the literature have been passive solutions. In this paper, an experimental controlling strategy is suggested to reduce the leakage flow rate. To this end, a fan with hollow blades and a specific drive system were designed and built for air injection. Air is injected in the leakage gap at the fan periphery. The experiment was performed for three rotation speeds, five injection rates and two configurations: 16 and 32 injection holes on the fan's circumference. The experimental results of this investigation are presented in this article
ne pas mettre sur hal c'est déjà fait
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10985/178892017-01-01T00:00:00ZAZZAM, TarikPARIDAENS, RichardOUALLI, HamidRAVELET, FlorentBAKIR, FaridKHELLADI, SofianeIn an axial fan, a leakage flow driven by a pressure gradient between the pressure side and the suction side occurs in the gap between the shroud and the casing. This leakage flow is in the opposite direction to the main flow and is responsible for significant energy dissipation. Therefore, many authors have worked to understand this phenomenon in order to reduce these inherent energy losses. Up to now, most of the studies reported in the literature have been passive solutions. In this paper, an experimental controlling strategy is suggested to reduce the leakage flow rate. To this end, a fan with hollow blades and a specific drive system were designed and built for air injection. Air is injected in the leakage gap at the fan periphery. The experiment was performed for three rotation speeds, five injection rates and two configurations: 16 and 32 injection holes on the fan's circumference. The experimental results of this investigation are presented in this articleExperimental study of yawed inflow around wind turbine rotor
http://hdl.handle.net/10985/8967
Experimental study of yawed inflow around wind turbine rotor
NOURA, Belkheir; DOBREV, Ivan; DIZENE, Rabah; MASSOUH, Fawaz; KHELLADI, Sofiane
In this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and topredict the performance of wind turbines as well.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/89672012-01-01T00:00:00ZNOURA, BelkheirDOBREV, IvanDIZENE, RabahMASSOUH, FawazKHELLADI, SofianeIn this article, we present an experimental study in a wind tunnel of a three-bladed, Rutland 503 model, horizontal axis yawed wind turbine. Power measurement and an exploration downstream wake of the turbine using particle image velocimetry measurements are performed. The variation of power coefficient as a function of rotational velocity is presented for different yaw angles. The results show a loss of power from the wind turbine when the yaw angle increases. The velocity field of the downstream wake of the rotor is presented in an azimuth plane, which passes through the symmetry axis of the rotor. The instantaneous velocity field is measured and recorded to allow for obtaining the averaged velocity field. The results also show variations in the wake downstream due to decelerating flow caused by the yawed turbine rotor. Analysis of this data shows that the active control of yaw angles could be an advantage to preserve the power from the wind turbine and that details near rotor wake are important for wake theories and topredict the performance of wind turbines as well.3D Model for Powder Compact Densification in Rotational Molding
http://hdl.handle.net/10985/9894
3D Model for Powder Compact Densification in Rotational Molding
ASGARPOUR, Monir; KHAVANDI, Alireza; TCHARKHTCHI, Abbas; BAKIR, Farid; KHELLADI, Sofiane
During rotational molding, a loosely packed, low-density powder compact transforms into a fully densified polymer part. This transformation is a consequence of particles sintering. Powder compact density evolution of the polymer powder is measured experimentally. Obtained results show that the powder densification process consists of two stages, and its mechanism during these two stages is not the same. During the first stage, densification occurs by grains coalescence, and air between the grains escape by open pores between particles. These open pores close in time by particles coalescence progress, and remaining air entrapped in polymer melt becomes air bubbles. Surface tension, viscosity, grains size, and temperature are the controlling parameters during first stage. A three-dimensional model is proposed for the densification of polymer powder during first stage. Second stage starts after bubble forming. Diffusion is the controlling phenomena during this stage. A diffusion-based model is used for the second stage of densification. By comparing with the other models, proposed model exhibits several advantages: it is proposed in three-dimensional and takes into account the nature of layer-by-layer powder densification. Model verification by experimental data obtained for densification of two different polymers shows a close agreement between model prediction and experiments.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10985/98942012-01-01T00:00:00ZASGARPOUR, MonirKHAVANDI, AlirezaTCHARKHTCHI, AbbasBAKIR, FaridKHELLADI, SofianeDuring rotational molding, a loosely packed, low-density powder compact transforms into a fully densified polymer part. This transformation is a consequence of particles sintering. Powder compact density evolution of the polymer powder is measured experimentally. Obtained results show that the powder densification process consists of two stages, and its mechanism during these two stages is not the same. During the first stage, densification occurs by grains coalescence, and air between the grains escape by open pores between particles. These open pores close in time by particles coalescence progress, and remaining air entrapped in polymer melt becomes air bubbles. Surface tension, viscosity, grains size, and temperature are the controlling parameters during first stage. A three-dimensional model is proposed for the densification of polymer powder during first stage. Second stage starts after bubble forming. Diffusion is the controlling phenomena during this stage. A diffusion-based model is used for the second stage of densification. By comparing with the other models, proposed model exhibits several advantages: it is proposed in three-dimensional and takes into account the nature of layer-by-layer powder densification. Model verification by experimental data obtained for densification of two different polymers shows a close agreement between model prediction and experiments.POD study of aerated cavitation in a venturi nozzle
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 GMThttp://hdl.handle.net/10985/102962015-01-01T00:00:00ZTOMOV, PetarDANLOS, AmélieRAVELET, FlorentSARRAF, ChristopheBAKIR, FaridKHELLADI, SofianeThe 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.An efficient reduced-order method with PGD for solving journal bearing hydrodynamic lubrication problems
http://hdl.handle.net/10985/17776
An efficient reduced-order method with PGD for solving journal bearing hydrodynamic lubrication problems
CHERABI, Bilal; HAMRANI, Abderrachid; BELAIDI, Idir; BAKIR, Farid; KHELLADI, Sofiane
In the present work, a reduced-order method, “Proper Generalized Decomposition (PGD)” is extended and applied to the resolution of the Reynolds equation describing the behavior of the lubricant in hydrodynamic journal bearing. The PGD model is employed to solve the characteristic ‘Reynolds’ partial differential equation using the separation technique through the alternating direction strategy. The resulting separated-dimension system has a low computation cost compared to classical finite-difference resolution. Several numerical benchmark examples are investigated to verify the validity and accuracy of the proposed method. It has been found that numerical results obtained by the PGD method can achieve an improved convergence rate with a very low computation cost.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10985/177762016-01-01T00:00:00ZCHERABI, BilalHAMRANI, AbderrachidBELAIDI, IdirBAKIR, FaridKHELLADI, SofianeIn the present work, a reduced-order method, “Proper Generalized Decomposition (PGD)” is extended and applied to the resolution of the Reynolds equation describing the behavior of the lubricant in hydrodynamic journal bearing. The PGD model is employed to solve the characteristic ‘Reynolds’ partial differential equation using the separation technique through the alternating direction strategy. The resulting separated-dimension system has a low computation cost compared to classical finite-difference resolution. Several numerical benchmark examples are investigated to verify the validity and accuracy of the proposed method. It has been found that numerical results obtained by the PGD method can achieve an improved convergence rate with a very low computation cost.