SAM
https://sam.ensam.eu:443
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Fri, 08 Nov 2024 18:11:53 GMT2024-11-08T18:11:53ZEffects of Surface Tension and Yield Stress on Mucus Plug Rupture: a Numerical Study
http://hdl.handle.net/10985/17733
Effects of Surface Tension and Yield Stress on Mucus Plug Rupture: a Numerical Study
HU, Yingying; ROMANO, Francesco; GROTBERG, James B.
We study the effects of surface tension and yield stress on mucus plug rupture. A three-dimensional simplified configuration is employed to simulate mucus plug rupture in a collapsed lung airway of the 10 th generation. The Herschel-Bulkley model is used to take into account the non-Newtonian viscoplastic fluid properties of mucus. Results show that the maximum wall shear stress greatly changes right prior to the rupture of the mucus plug. The surface tension influences mainly the late stage of the rupture process when the plug deforms greatly and the curvature of the mucus-air interface becomes significant. High surface tension increases the wall shear stress and the time needed to rupture since it produces a resistance to the rupture, as well as strong stress and velocity gradients across the mucus-air interface. The yield stress effects are pronounced mainly at the beginning. High yield stress makes the plug take long time to yield and slows down the whole rupture process. When the effects induced by the surface tension and yield forces are comparable, dynamical quantities strongly depend on the ratio of the two forces. The pressure difference (the only driving in the study) contributes to wall shear stress much more than yield stress and surface tension per unit length. Wall shear stress is less sensitive to the variation in yield stress than that in surface tension. In general, wall shear stress can be effectively reduced by the smaller pressure difference and surface tension.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/177332019-01-01T00:00:00ZHU, YingyingROMANO, FrancescoGROTBERG, James B.We study the effects of surface tension and yield stress on mucus plug rupture. A three-dimensional simplified configuration is employed to simulate mucus plug rupture in a collapsed lung airway of the 10 th generation. The Herschel-Bulkley model is used to take into account the non-Newtonian viscoplastic fluid properties of mucus. Results show that the maximum wall shear stress greatly changes right prior to the rupture of the mucus plug. The surface tension influences mainly the late stage of the rupture process when the plug deforms greatly and the curvature of the mucus-air interface becomes significant. High surface tension increases the wall shear stress and the time needed to rupture since it produces a resistance to the rupture, as well as strong stress and velocity gradients across the mucus-air interface. The yield stress effects are pronounced mainly at the beginning. High yield stress makes the plug take long time to yield and slows down the whole rupture process. When the effects induced by the surface tension and yield forces are comparable, dynamical quantities strongly depend on the ratio of the two forces. The pressure difference (the only driving in the study) contributes to wall shear stress much more than yield stress and surface tension per unit length. Wall shear stress is less sensitive to the variation in yield stress than that in surface tension. In general, wall shear stress can be effectively reduced by the smaller pressure difference and surface tension.Experimental Analysis of an Axial Compressor Operating under Flow Distorsion
http://hdl.handle.net/10985/22722
Experimental Analysis of an Axial Compressor Operating under Flow Distorsion
BARETTER, Alberto; ROUSSETTE, Olivier; ROMANO, Francesco; DAZIN, Antoine; JOSEPH, Pierric
In aircraft engines, compressor stages can encounter situations in which the flow is distorted at rotor inlet, for example during particular flight maneuvers, or due to the shape of the inlet of the airframe. The main objective of this paper is to investigate experimentally the effect of an inlet flow distortion on the internal flow dynamic and its consequences on the performance and operability of these machines. The distortion was generated by a porous plate grid installed upstream of the compressor. Eight total pressure rakes placed downstream of the grid were used to evaluate the distortion. Unsteady pressure measurements were performed on the casing at different axial and azimuthal positions to investigate the dynamic flow behavior at nominal conditions, at an operating point close to stall and during the transition to stall. 2D-2C PIV maps, synchronized with the runner position, were obtained on rotor blade-to-blade planes at three different spanwise positions (79%, 51%, 18% of the blade span). Three relative angular positions of the grid to the laser sheet were investigated at two different flow rates, namely the nominal flow rate and a flow rate close to stall. These three positions are corresponding to the laser sheet cutting through i/ the center of the grid’s wake and ii/ the two edges of the grid. The impact of the distortion on the performance of the compressor is analyzed and compared to existing models. The impact of the flow dynamic will also be considered, especially in operations close to the stall limit.
Wed, 01 Jun 2022 00:00:00 GMThttp://hdl.handle.net/10985/227222022-06-01T00:00:00ZBARETTER, AlbertoROUSSETTE, OlivierROMANO, FrancescoDAZIN, AntoineJOSEPH, PierricIn aircraft engines, compressor stages can encounter situations in which the flow is distorted at rotor inlet, for example during particular flight maneuvers, or due to the shape of the inlet of the airframe. The main objective of this paper is to investigate experimentally the effect of an inlet flow distortion on the internal flow dynamic and its consequences on the performance and operability of these machines. The distortion was generated by a porous plate grid installed upstream of the compressor. Eight total pressure rakes placed downstream of the grid were used to evaluate the distortion. Unsteady pressure measurements were performed on the casing at different axial and azimuthal positions to investigate the dynamic flow behavior at nominal conditions, at an operating point close to stall and during the transition to stall. 2D-2C PIV maps, synchronized with the runner position, were obtained on rotor blade-to-blade planes at three different spanwise positions (79%, 51%, 18% of the blade span). Three relative angular positions of the grid to the laser sheet were investigated at two different flow rates, namely the nominal flow rate and a flow rate close to stall. These three positions are corresponding to the laser sheet cutting through i/ the center of the grid’s wake and ii/ the two edges of the grid. The impact of the distortion on the performance of the compressor is analyzed and compared to existing models. The impact of the flow dynamic will also be considered, especially in operations close to the stall limit.Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion
http://hdl.handle.net/10985/24441
Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion
BARETTER, Alberto; GODARD, Benjamin; JOSEPH, Pierric; ROUSSETTE, Olivier; ROMANO, Francesco; BARRIER, Raphael; DAZIN, Antoine
On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells.
Mon, 01 Nov 2021 00:00:00 GMThttp://hdl.handle.net/10985/244412021-11-01T00:00:00ZBARETTER, AlbertoGODARD, BenjaminJOSEPH, PierricROUSSETTE, OlivierROMANO, FrancescoBARRIER, RaphaelDAZIN, AntoineOn many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells.Stability of generalized Kolmogorov flow in a channel
http://hdl.handle.net/10985/24541
Stability of generalized Kolmogorov flow in a channel
ROMANO, Francesco
The Kolmogorov flow is a paradigmatic model flow used to investigate the transition from laminar to turbulent regimes in confined and, especially, in unbounded domains. It represents a solution of the forced Navier–Stokes equation, where the forcing term is sinusoidal. The resulting velocity profile is also sinusoidal with the same wavenumber of the forcing term. In this study, we generalize the Kolmogorov flow making use of a generic forcing term defined by a Fourier series that bridges the classical Kolmogorov flow to an arbitrary even-degree power-law profile. Thereafter, we perform a linear stability analysis on the power-law profiles for exponents, α=2, 4, 6, 8, and 10, and the corresponding generalized Kolmogorov flows, varying the truncation index K of the Fourier series. Several neutral stability curves are computed numerically for wall-bounded flows and the relevant critical conditions are compared in terms of critical Reynolds number, critical wavelength, and eigenspectrum at criticality. The most dangerous perturbations are thoroughly characterized, and we identify three qualitatively different most dangerous modes, depending on α, K, the Reynolds number, and the perturbation wavelength.
Mon, 01 Feb 2021 00:00:00 GMThttp://hdl.handle.net/10985/245412021-02-01T00:00:00ZROMANO, FrancescoThe Kolmogorov flow is a paradigmatic model flow used to investigate the transition from laminar to turbulent regimes in confined and, especially, in unbounded domains. It represents a solution of the forced Navier–Stokes equation, where the forcing term is sinusoidal. The resulting velocity profile is also sinusoidal with the same wavenumber of the forcing term. In this study, we generalize the Kolmogorov flow making use of a generic forcing term defined by a Fourier series that bridges the classical Kolmogorov flow to an arbitrary even-degree power-law profile. Thereafter, we perform a linear stability analysis on the power-law profiles for exponents, α=2, 4, 6, 8, and 10, and the corresponding generalized Kolmogorov flows, varying the truncation index K of the Fourier series. Several neutral stability curves are computed numerically for wall-bounded flows and the relevant critical conditions are compared in terms of critical Reynolds number, critical wavelength, and eigenspectrum at criticality. The most dangerous perturbations are thoroughly characterized, and we identify three qualitatively different most dangerous modes, depending on α, K, the Reynolds number, and the perturbation wavelength.Laminar–turbulent intermittency in pipe flow for an Herschel–Bulkley fluid: Radial receptivity to finite-amplitude perturbations
http://hdl.handle.net/10985/24522
Laminar–turbulent intermittency in pipe flow for an Herschel–Bulkley fluid: Radial receptivity to finite-amplitude perturbations
CHARLES, Antoine; ROMANO, Francesco; RIBEIRO, Thierry; AZIMI, Sam; ROCHER, Vincent; BAUDEZ, Jean-Christophe; BAHRANI, S. Amir
We investigate the laminar-to-turbulent transition for non-Newtonian Herschel–Bulkley fluids that exhibit either a shear-thinning or shear-thickening behavior. The reduced-order model developed in this study also includes the effect of yield-stress for the fluid. Within our model framework, we investigate how the Newtonian dynamics change when significant non-Newtonian effects are considered either via the flow index n or the yield-stress τ0 or both. We find that an increase in τ0 as well as a decrease in n lead to a delayed transition if a perturbation of the given turbulent intensity is injected at various radial locations. As the radial position of the injection for the perturbation is varied in this study, our reduced-order model allows for the investigation of the flow receptivity to the finite-amplitude perturbations and to their radial position of inception. We observe that, for a given mean flow profile, the same perturbation becomes more prone to induce turbulence the closer it approaches the wall because of its initial amplitude being relatively higher with respect to the local mean flow. An opposite trend is found when the perturbation amplitude is rescaled on the local mean flow.
Tue, 01 Nov 2022 00:00:00 GMThttp://hdl.handle.net/10985/245222022-11-01T00:00:00ZCHARLES, AntoineROMANO, FrancescoRIBEIRO, ThierryAZIMI, SamROCHER, VincentBAUDEZ, Jean-ChristopheBAHRANI, S. AmirWe investigate the laminar-to-turbulent transition for non-Newtonian Herschel–Bulkley fluids that exhibit either a shear-thinning or shear-thickening behavior. The reduced-order model developed in this study also includes the effect of yield-stress for the fluid. Within our model framework, we investigate how the Newtonian dynamics change when significant non-Newtonian effects are considered either via the flow index n or the yield-stress τ0 or both. We find that an increase in τ0 as well as a decrease in n lead to a delayed transition if a perturbation of the given turbulent intensity is injected at various radial locations. As the radial position of the injection for the perturbation is varied in this study, our reduced-order model allows for the investigation of the flow receptivity to the finite-amplitude perturbations and to their radial position of inception. We observe that, for a given mean flow profile, the same perturbation becomes more prone to induce turbulence the closer it approaches the wall because of its initial amplitude being relatively higher with respect to the local mean flow. An opposite trend is found when the perturbation amplitude is rescaled on the local mean flow.Transition to turbulence in a heated non-Newtonian pipe flow
http://hdl.handle.net/10985/24542
Transition to turbulence in a heated non-Newtonian pipe flow
ROMANO, Francesco; CHARLES, Antoine; DOTTORI, François; AMIR BAHRANI, S.
A simplified mono-dimensional model for investigating the transition to turbulence in nonisothermal and non-Newtonian pipe flows is proposed. The flow stability is analyzed within the framework of such a model, showing that uniformly heating the pipe wall leads to an earlier transition to turbulence, while differentially heating the pipe wall produces a stabilizing effect. For power-law fluids, we also demonstrate that an increase in the power-law index, i.e., passing from shear-thinning to shear-thickening fluids, leads to a stabilization of the system.
Wed, 01 Sep 2021 00:00:00 GMThttp://hdl.handle.net/10985/245422021-09-01T00:00:00ZROMANO, FrancescoCHARLES, AntoineDOTTORI, FrançoisAMIR BAHRANI, S.A simplified mono-dimensional model for investigating the transition to turbulence in nonisothermal and non-Newtonian pipe flows is proposed. The flow stability is analyzed within the framework of such a model, showing that uniformly heating the pipe wall leads to an earlier transition to turbulence, while differentially heating the pipe wall produces a stabilizing effect. For power-law fluids, we also demonstrate that an increase in the power-law index, i.e., passing from shear-thinning to shear-thickening fluids, leads to a stabilization of the system.The effect of viscoelasticity in an airway closure model
http://hdl.handle.net/10985/24486
The effect of viscoelasticity in an airway closure model
ROMANO, Francesco; MURADOGLU, M.; FUJIOKA, H.; GROTBERG, J.B.
Abstract
Mon, 01 Feb 2021 00:00:00 GMThttp://hdl.handle.net/10985/244862021-02-01T00:00:00ZROMANO, FrancescoMURADOGLU, M.FUJIOKA, H.GROTBERG, J.B.AbstractForces and torques on a sphere moving near a dihedral corner in creeping flow
http://hdl.handle.net/10985/24421
Forces and torques on a sphere moving near a dihedral corner in creeping flow
ROMANO, Francesco; DES BOSCS, P.-E.; KUHLMANN, H.C.
The low-Reynolds-number flow past a sphere moving near a right dihedral corner made by a stationary and a tangentially sliding wall is considered. Using the superposition principle, the arbitrary motion of the sphere is decomposed into simple elementary motions. Fully-resolved spectral-element simulations are carried out in the frame of reference translating and rotating with the particle such that the velocity on the particle’s surface vanishes. Forces and torques on the sphere are obtained as functions of the particle position near the corner. The data obtained are fitted by closed-form expressions which take into account symmetries of the problem, exact solutions, and asymptotic solutions from lubrication theory. The correlations obtained can easily be implemented in larger-scale one-way-coupled particulate-flow simulations to correct the particle motion near dihedral corners where mere point-particle models break down.
Sun, 01 Nov 2020 00:00:00 GMThttp://hdl.handle.net/10985/244212020-11-01T00:00:00ZROMANO, FrancescoDES BOSCS, P.-E.KUHLMANN, H.C.The low-Reynolds-number flow past a sphere moving near a right dihedral corner made by a stationary and a tangentially sliding wall is considered. Using the superposition principle, the arbitrary motion of the sphere is decomposed into simple elementary motions. Fully-resolved spectral-element simulations are carried out in the frame of reference translating and rotating with the particle such that the velocity on the particle’s surface vanishes. Forces and torques on the sphere are obtained as functions of the particle position near the corner. The data obtained are fitted by closed-form expressions which take into account symmetries of the problem, exact solutions, and asymptotic solutions from lubrication theory. The correlations obtained can easily be implemented in larger-scale one-way-coupled particulate-flow simulations to correct the particle motion near dihedral corners where mere point-particle models break down.Coherent Particle Structures in High-Prandtl-Number Liquid Bridges
http://hdl.handle.net/10985/24485
Coherent Particle Structures in High-Prandtl-Number Liquid Bridges
BARMAK, Ilya; ROMANO, Francesco; KANNAN, Parvathy Kunchi; KUHLMANN, Hendrik C.
Clustering of small rigid spherical particles into particle accumulation structures (PAS) is studied numerically for a high-Prandtl-number (Pr = 68) thermocapillary liquid bridge. The one-way-coupling approach is used for calculation of the particle motion, modeling PAS as an attractor for a single particle. The attractor is created by dissipative forces acting on the particle near the boundary due to the finite size of the particle. These forces can dramatically deflect the particle trajectory from a fluid pathline and transfer it to certain tubular flow structures, called Kolmogorov–Arnold–Moser (KAM) tori, in which the particle is focused and from which it might not escape anymore. The transfer of particles can take place if a KAM torus, which is a property of the flow without particles, enters the narrow boundary layer on the flow boundaries in which the particle experiences extra forces. Since the PAS obtained in this system depends mainly on the finite particle size, it can be classified as a finite-size coherent structure (FSCS).
Mon, 01 Feb 2021 00:00:00 GMThttp://hdl.handle.net/10985/244852021-02-01T00:00:00ZBARMAK, IlyaROMANO, FrancescoKANNAN, Parvathy KunchiKUHLMANN, Hendrik C.Clustering of small rigid spherical particles into particle accumulation structures (PAS) is studied numerically for a high-Prandtl-number (Pr = 68) thermocapillary liquid bridge. The one-way-coupling approach is used for calculation of the particle motion, modeling PAS as an attractor for a single particle. The attractor is created by dissipative forces acting on the particle near the boundary due to the finite size of the particle. These forces can dramatically deflect the particle trajectory from a fluid pathline and transfer it to certain tubular flow structures, called Kolmogorov–Arnold–Moser (KAM) tori, in which the particle is focused and from which it might not escape anymore. The transfer of particles can take place if a KAM torus, which is a property of the flow without particles, enters the narrow boundary layer on the flow boundaries in which the particle experiences extra forces. Since the PAS obtained in this system depends mainly on the finite particle size, it can be classified as a finite-size coherent structure (FSCS).Capillary instability of a two-layer annular film: an airway closure model
http://hdl.handle.net/10985/24444
Capillary instability of a two-layer annular film: an airway closure model
ERKEN, O.; ROMANO, Francesco; GROTBERG, J.B.; MURADOGLU, M.
Capillary instability of a two-layer liquid film lining a rigid tube is studied computationally as a model for liquid plug formation and closure of human airways. The two-layer liquid consists of a serous layer, also called the periciliary liquid layer, at the inner side and a mucus layer at the outer side. Together, they form the airway surface liquid lining the airway wall and surrounding an air core. Liquid plug formation occurs due to Plateau–Rayleigh instability when the liquid film thickness exceeds a critical value. Numerical simulations are performed for the entire closure process, including the pre- and post-coalescence phases. The mechanical stresses and their gradients on the airway wall are investigated for physiologically relevant ranges of the mucus-to-serous thickness ratio, the viscosity ratio, and the air–mucus and serous–mucus surface tensions encompassing healthy and pathological conditions of a typical adult human lung. The growth rate of the two-layer model is found to be higher in comparison with a one-layer equivalent configuration. This leads to a much sooner closure in the two-layer model than that in the corresponding one-layer model. Moreover, it is found that the serous layer generally provides an effective protection to the pulmonary epithelium against high shear stress excursions and their gradients. A linear stability analysis is also performed, and the results are found to be in good qualitative agreement with the simulations. Finally, a secondary coalescence that may occur during the post-closure phase is investigated.
Sat, 01 Jan 2022 00:00:00 GMThttp://hdl.handle.net/10985/244442022-01-01T00:00:00ZERKEN, O.ROMANO, FrancescoGROTBERG, J.B.MURADOGLU, M.Capillary instability of a two-layer liquid film lining a rigid tube is studied computationally as a model for liquid plug formation and closure of human airways. The two-layer liquid consists of a serous layer, also called the periciliary liquid layer, at the inner side and a mucus layer at the outer side. Together, they form the airway surface liquid lining the airway wall and surrounding an air core. Liquid plug formation occurs due to Plateau–Rayleigh instability when the liquid film thickness exceeds a critical value. Numerical simulations are performed for the entire closure process, including the pre- and post-coalescence phases. The mechanical stresses and their gradients on the airway wall are investigated for physiologically relevant ranges of the mucus-to-serous thickness ratio, the viscosity ratio, and the air–mucus and serous–mucus surface tensions encompassing healthy and pathological conditions of a typical adult human lung. The growth rate of the two-layer model is found to be higher in comparison with a one-layer equivalent configuration. This leads to a much sooner closure in the two-layer model than that in the corresponding one-layer model. Moreover, it is found that the serous layer generally provides an effective protection to the pulmonary epithelium against high shear stress excursions and their gradients. A linear stability analysis is also performed, and the results are found to be in good qualitative agreement with the simulations. Finally, a secondary coalescence that may occur during the post-closure phase is investigated.