Yvan Maciel - Academia.edu (original) (raw)

Papers by Yvan Maciel

Proceeding of Seventh International Symposium on Turbulence and Shear Flow Phenomena, 2011

... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médeci... more ... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médecine, Quebec City, Quebec, G1V0A6, Canada saeed.rahgozar.1@ulaval ... high speed (in average 2-3 of each) thus fields containing only SS of both high and low momen-tum are ...

International Journal of Computational Fluid Dynamics, 2008

ABSTRACT End-wall effects for high aspect ratio (AR) turbulent duct flows under moderate spanwise... more ABSTRACT End-wall effects for high aspect ratio (AR) turbulent duct flows under moderate spanwise rotation are investigated using Reynolds-Averaged Navier–Stokes (RANS) calculations with a Reynolds stress turbulence closure model. It is shown that despite an important uniformisation of the mean streamwise flow compared to the non-rotating case, the channel flow solution (AR = ∞) is not recovered in practical high AR ducts used in experiments. The unavoidable end-wall generated secondary flow causes transverse advection which is capable of altering the mean velocity profile, even for AR as high as 22. In addition, for Re = 40,000 and Ro = 0.22, persistent longitudinal roll cells are found in the RANS solutions. The results suggest that their interaction with the secondary flow may challenge the prospect of formally reaching a steady, streamwise invariant regime in actual rotating duct experiments.

Bulletin of the American Physical Society, Nov 23, 2020

The spectral distributions of the transport equation budgets of all Reynolds stresses in adverse ... more The spectral distributions of the transport equation budgets of all Reynolds stresses in adverse gradient pressure (APG) turbulent boundary layers (TBLs) are examined to understand the energy transfer mechanisms in the inner and outer layers of APG TBLs. The spectra of the budget terms are obtained for two streamwise positions, which correspond to small and large velocity defect situations, of a non-equilibrium APG TBL using temporally collected data. The turbulence production is predominantly in the inner layer and due to small-scale structures for the small defect case, although there are energy-carrying large-scale structures in the outer layer. In the large defect situation, there is significant production in both inner and outer layers at small and large scales, respectively. Furthermore, the behavior of the pressure-strain rate and production spectra illustrates that the inter-component energy transfer from the streamwise component to the other components and production happen at similar wavelengths and wall-normal positions. More detailed results about energy transport between the inner and outer layers will be presented at the meeting.

Bulletin of the American Physical Society, Nov 21, 2017

ERCOFTAC series, Aug 18, 2015

The existence of the outer region “hairpins” and “hairpin packets” is visually assessed in a well... more The existence of the outer region “hairpins” and “hairpin packets” is visually assessed in a well-resolved DNS of a zero-pressure-gradient turbulent boundary layer at moderately high Reynolds number. For this purpose, 50 independent 2D streamwise–wall-normal slices at \(Re_{\theta }=4300\) are extracted. The slices are then used to mimic the coarser resolution PIV velocity fields of Adrian et al. J. Fluid Mech, 422:1–54, 2000 [2] using the mimicking procedure of Rahgozar et al. J. Turbul, 14(10):37–66, 2013 [5] based on Gaussian filtering and linear interpolation. Afterwards, in the same manner as Adrian et al. J. Fluid Mech, 422:1–54, 2000 [2], the mimicked fields are inspected in order to discover the signatures of hairpin and hairpin packets. The vortices that are identified as hairpins are then isolated and visualized in three dimensions using the fully resolved DNS data. In agreement with Adrian et al. J. Fluid Mech, 422:1–54, 2000 [2], signatures associated by them to hairpin and hairpin packets are observed frequently in the mimicked planes. However, the 3D character of the 2D signatures is found to be more convoluted than the proposed hairpin packet model.

Physical review fluids, Jan 16, 2018

This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations... more This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations for zero-pressure-gradient turbulent boundary layers (ZPG TBLs). It has long been observed that the scaling of the mean streamwise velocity in turbulent boundary layer flows differs in the near surface region and in the outer layer. In the inner region of small-velocity-defect boundary layers, it is generally accepted that the proper velocity scale is the friction velocity, u τ , and the proper length scale is the viscous length scale, ν/u τ. In the outer region, the most generally used length scale is the boundary layer thickness, δ. However, there is no consensus on velocity scales in the outer layer. Zagarola and Smits [ASME Paper No. FEDSM98-4950 (1998)] proposed a velocity scale, U ZS = (δ 1 /δ)U ∞ , where δ 1 is the displacement thickness and U ∞ is the freestream velocity. However, there are some concerns about Zagarola-Smits scaling due to the lack of a theoretical base. In this paper, the Zagarola-Smits scaling is derived directly from a combination of integral, similarity, and order-of-magnitude analysis of the mean continuity equation. The analysis also reveals that V ∞ , the mean wall-normal velocity at the edge of the boundary layer, is a proper scale for the mean wall-normal velocity V. Extending the analysis to the streamwise mean momentum equation, we find that the Reynolds shear stress in ZPG TBLs scales as U ∞ V ∞ in the outer region. This paper also provides a detailed analysis of the mass and mean momentum balance in the outer region of ZPG TBLs.

IOP conference series, Sep 1, 2022

Proceeding of Fifth International Symposium on Turbulence and Shear Flow Phenomena, 2007

Coherent structures in the outer region of a turbulent boundary layer subjected to a strong adver... more Coherent structures in the outer region of a turbulent boundary layer subjected to a strong adverse pressure gradient have been studied using particle image velocimetry (PIV). The experimental setup is designed to achieve flow conditions corresponding to trailing-edge stall of an airfoil. Large sets of instantaneous velocity fields are acquired by PIV in streamwise-wall-normal planes at three different streamwise locations. Signatures of hairpin vortices are found in all the fields and hairpin packets occur in the majority of them. The essential features of the hairpins and hairpin packets are similar to those found in zero-pressuregradient turbulent boundary layers. The hairpin vortices are however slightly more inclined with respect to the wall in the present flow, and the upward growth of the hairpin packets in the streamwise direction is more important. The characteristics of the spanwise vortices are also documented.

Bulletin of the American Physical Society, Nov 25, 2014

Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a stron... more Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a strongly decelerated boundary layer 1 AYSE G. GUNGOR, Istanbul Technical University, YVAN MACIEL, Laval University, MARK P. SIMENS, U. Politécnica Madrid-The characteristics of three-dimensional intense Reynolds shear stress structures (Qs) are presented from a direct numerical simulation of an adverse pressure gradient boundary layer at Re θ = 1500 − 2175. The intense Q2 (ejections) and Q4 (sweeps) structures separate into two groups: wall-attached and wall-detached structures. In the region where turbulent activity is maximal, between 0.2δ and 0.6δ, 94% of the structures are detached structures. In comparison to canonical wall flows, the large velocity defect turbulent boundary layers are less efficient in extracting turbulent energy from the mean flow. There is, furthermore, much less turbulence activity and less velocity coherence near the wall. Additionally, the wall-detached structures are more frequent and carry a much larger amount of Reynolds shear stress.

International Journal of Molecular Sciences, Aug 2, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Proceeding of Fifth International Symposium on Turbulence and Shear Flow Phenomena, 2007

The near-field characteristics of a turbulent jet with moderate swirl generated by a fully develo... more The near-field characteristics of a turbulent jet with moderate swirl generated by a fully developed, axially rotating pipe flow are investigated with LDV, time-resolved stereoscopic PIV measurements, as well as with large-eddy simulations. Large-scale vortical structures in either double, triple or even quadruple-helix configuration are found at the pipe exit but rapidly break down or amalgamate after two jet diameters. Further downstream, the swirling jet is dominated by large-scale sweeping motions not present at such a scale and strength in the non-swirling case. Of special interest is the recently discovered counter-rotating core (in the mean) which develops about six jet diameters downstream the jet exit. Data for all six Reynolds stresses is reported at this position and it is argued that the counter-rotation is the result of the transport of angular momentum radially outward by the radial-azimuthal Reynolds shear stress. The mechanisms behind this transport are discussed by qualitative analysis of the time-resolved PIV and LES data and comparisons with the non-swirling case are made.

35th AIAA Fluid Dynamics Conference and Exhibit, Jun 6, 2005

ABSTRACT The experimental study of the turbulent boundary layer under external flow conditions si... more ABSTRACT The experimental study of the turbulent boundary layer under external flow conditions similar to those found on the suction side of airfoils in trailing-edge post-stall conditions has been performed. Detailed boundary layer measurements were carried out with a PIV system and a two-sensor wall probe. They cover the region downstream of the suction peak where the boundary layer is subjected to a very strong adverse pressure gradient and has suffered from an abrupt transition from strong favorable to strong adverse pressure gradients. The experiments show that in spite of these severe conditions, the boundary layer is surprisingly able to recover a state of near-equilibrium before separating. In this near-equilibrium zone, the mean velocity defect and all the measured Reynolds stresses are self-similar (in the outer region) with respect to the outer scales δ and U e δ*/δ. The mean momentum balance indicates that for the upper half of the outer region, the advection terms dominate all the stress-gradient terms in the zone prior to separation. A large portion of the outer region has therefore become essentially an inertial flow zone where an approach toward equilibrium is expected.

Journal of Fluids and Structures, Sep 1, 1990

Using the Krylov & Bogoliubov (1949, Introduction to Non-Linear Mechanics, Princeton: Princeton U... more Using the Krylov & Bogoliubov (1949, Introduction to Non-Linear Mechanics, Princeton: Princeton University Press) method of averaging, solutions have been obtained to the previously developed nonlinear equations of motion for wake-induced flutter of one circular cylinder in the wake of a fixed similar cylinder. The results obtained have been compared with previously obtained ones via numerical integration of the same equations; the agreement is excellent, but there is a considerable saving in computational time using the Krylov and Bogoliubov method. It has been reconfirmed that, when the windward cylinder is held fixed, increasing mechanical damping is not a very efficient way of decreasing the amplitude of oscillation of the leeward cylinder. Provided the same set of aerodynamic force coefficients are employed the nonlinear analysis predicts essentially the same lower flutter boundary as that obtained via a linearized analysis. There is, however, evidence th~/t the leeward cylinder acts as a hard oscillator, resulting in a considerable difference in the upper flutter boundary obtained via the nonlinear analysis visa -vis the linearized theory.

International Journal of Molecular Sciences

Every year, thousands of aortic valve replacements must take place due to valve diseases. Tissue-... more Every year, thousands of aortic valve replacements must take place due to valve diseases. Tissue-engineered heart valves represent promising valve substitutes with remodeling, regeneration, and growth capabilities. However, the accurate reproduction of the complex three-dimensional (3D) anatomy of the aortic valve remains a challenge for current biofabrication methods. We present a novel technique for rapid fabrication of native-like tricuspid aortic valve scaffolds made of an alginate-based hydrogel. Using this technique, a sodium alginate hydrogel formulation is injected into a mold produced using a custom-made sugar glass 3D printer. The mold is then dissolved using a custom-made dissolving module, revealing the aortic valve scaffold. To assess the reproducibility of the technique, three scaffolds were thoroughly compared. CT (computed tomography) scans showed that the scaffolds respect the complex native geometry with minimal variations. The scaffolds were then tested in a cardi...

Proceeding of Seventh International Symposium on Turbulence and Shear Flow Phenomena

... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médeci... more ... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médecine, Quebec City, Quebec, G1V0A6, Canada saeed.rahgozar.1@ulaval ... high speed (in average 2-3 of each) thus fields containing only SS of both high and low momen-tum are ...

IOP Conference Series: Earth and Environmental Science, 2019

Physical Review Fluids, 2018

This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations... more This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations for zero-pressure-gradient turbulent boundary layers (ZPG TBLs). It has long been observed that the scaling of the mean streamwise velocity in turbulent boundary layer flows differs in the near surface region and in the outer layer. In the inner region of small-velocity-defect boundary layers, it is generally accepted that the proper velocity scale is the friction velocity, u τ , and the proper length scale is the viscous length scale, ν/u τ. In the outer region, the most generally used length scale is the boundary layer thickness, δ. However, there is no consensus on velocity scales in the outer layer. Zagarola and Smits [ASME Paper No. FEDSM98-4950 (1998)] proposed a velocity scale, U ZS = (δ 1 /δ)U ∞ , where δ 1 is the displacement thickness and U ∞ is the freestream velocity. However, there are some concerns about Zagarola-Smits scaling due to the lack of a theoretical base. In this paper, the Zagarola-Smits scaling is derived directly from a combination of integral, similarity, and order-of-magnitude analysis of the mean continuity equation. The analysis also reveals that V ∞ , the mean wall-normal velocity at the edge of the boundary layer, is a proper scale for the mean wall-normal velocity V. Extending the analysis to the streamwise mean momentum equation, we find that the Reynolds shear stress in ZPG TBLs scales as U ∞ V ∞ in the outer region. This paper also provides a detailed analysis of the mass and mean momentum balance in the outer region of ZPG TBLs.

Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a stron... more Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a strongly decelerated boundary layer 1 AYSE G. GUNGOR, Istanbul Technical University, YVAN MACIEL, Laval University, MARK P. SIMENS, U. Politécnica Madrid-The characteristics of three-dimensional intense Reynolds shear stress structures (Qs) are presented from a direct numerical simulation of an adverse pressure gradient boundary layer at Re θ = 1500 − 2175. The intense Q2 (ejections) and Q4 (sweeps) structures separate into two groups: wall-attached and wall-detached structures. In the region where turbulent activity is maximal, between 0.2δ and 0.6δ, 94% of the structures are detached structures. In comparison to canonical wall flows, the large velocity defect turbulent boundary layers are less efficient in extracting turbulent energy from the mean flow. There is, furthermore, much less turbulence activity and less velocity coherence near the wall. Additionally, the wall-detached structures are more frequent and carry a much larger amount of Reynolds shear stress.

Proceeding of Seventh International Symposium on Turbulence and Shear Flow Phenomena, 2011

... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médeci... more ... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médecine, Quebec City, Quebec, G1V0A6, Canada saeed.rahgozar.1@ulaval ... high speed (in average 2-3 of each) thus fields containing only SS of both high and low momen-tum are ...

International Journal of Computational Fluid Dynamics, 2008

ABSTRACT End-wall effects for high aspect ratio (AR) turbulent duct flows under moderate spanwise... more ABSTRACT End-wall effects for high aspect ratio (AR) turbulent duct flows under moderate spanwise rotation are investigated using Reynolds-Averaged Navier–Stokes (RANS) calculations with a Reynolds stress turbulence closure model. It is shown that despite an important uniformisation of the mean streamwise flow compared to the non-rotating case, the channel flow solution (AR = ∞) is not recovered in practical high AR ducts used in experiments. The unavoidable end-wall generated secondary flow causes transverse advection which is capable of altering the mean velocity profile, even for AR as high as 22. In addition, for Re = 40,000 and Ro = 0.22, persistent longitudinal roll cells are found in the RANS solutions. The results suggest that their interaction with the secondary flow may challenge the prospect of formally reaching a steady, streamwise invariant regime in actual rotating duct experiments.

Bulletin of the American Physical Society, Nov 23, 2020

The spectral distributions of the transport equation budgets of all Reynolds stresses in adverse ... more The spectral distributions of the transport equation budgets of all Reynolds stresses in adverse gradient pressure (APG) turbulent boundary layers (TBLs) are examined to understand the energy transfer mechanisms in the inner and outer layers of APG TBLs. The spectra of the budget terms are obtained for two streamwise positions, which correspond to small and large velocity defect situations, of a non-equilibrium APG TBL using temporally collected data. The turbulence production is predominantly in the inner layer and due to small-scale structures for the small defect case, although there are energy-carrying large-scale structures in the outer layer. In the large defect situation, there is significant production in both inner and outer layers at small and large scales, respectively. Furthermore, the behavior of the pressure-strain rate and production spectra illustrates that the inter-component energy transfer from the streamwise component to the other components and production happen at similar wavelengths and wall-normal positions. More detailed results about energy transport between the inner and outer layers will be presented at the meeting.

Bulletin of the American Physical Society, Nov 21, 2017

ERCOFTAC series, Aug 18, 2015

The existence of the outer region “hairpins” and “hairpin packets” is visually assessed in a well... more The existence of the outer region “hairpins” and “hairpin packets” is visually assessed in a well-resolved DNS of a zero-pressure-gradient turbulent boundary layer at moderately high Reynolds number. For this purpose, 50 independent 2D streamwise–wall-normal slices at \(Re_{\theta }=4300\) are extracted. The slices are then used to mimic the coarser resolution PIV velocity fields of Adrian et al. J. Fluid Mech, 422:1–54, 2000 [2] using the mimicking procedure of Rahgozar et al. J. Turbul, 14(10):37–66, 2013 [5] based on Gaussian filtering and linear interpolation. Afterwards, in the same manner as Adrian et al. J. Fluid Mech, 422:1–54, 2000 [2], the mimicked fields are inspected in order to discover the signatures of hairpin and hairpin packets. The vortices that are identified as hairpins are then isolated and visualized in three dimensions using the fully resolved DNS data. In agreement with Adrian et al. J. Fluid Mech, 422:1–54, 2000 [2], signatures associated by them to hairpin and hairpin packets are observed frequently in the mimicked planes. However, the 3D character of the 2D signatures is found to be more convoluted than the proposed hairpin packet model.

Physical review fluids, Jan 16, 2018

This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations... more This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations for zero-pressure-gradient turbulent boundary layers (ZPG TBLs). It has long been observed that the scaling of the mean streamwise velocity in turbulent boundary layer flows differs in the near surface region and in the outer layer. In the inner region of small-velocity-defect boundary layers, it is generally accepted that the proper velocity scale is the friction velocity, u τ , and the proper length scale is the viscous length scale, ν/u τ. In the outer region, the most generally used length scale is the boundary layer thickness, δ. However, there is no consensus on velocity scales in the outer layer. Zagarola and Smits [ASME Paper No. FEDSM98-4950 (1998)] proposed a velocity scale, U ZS = (δ 1 /δ)U ∞ , where δ 1 is the displacement thickness and U ∞ is the freestream velocity. However, there are some concerns about Zagarola-Smits scaling due to the lack of a theoretical base. In this paper, the Zagarola-Smits scaling is derived directly from a combination of integral, similarity, and order-of-magnitude analysis of the mean continuity equation. The analysis also reveals that V ∞ , the mean wall-normal velocity at the edge of the boundary layer, is a proper scale for the mean wall-normal velocity V. Extending the analysis to the streamwise mean momentum equation, we find that the Reynolds shear stress in ZPG TBLs scales as U ∞ V ∞ in the outer region. This paper also provides a detailed analysis of the mass and mean momentum balance in the outer region of ZPG TBLs.

IOP conference series, Sep 1, 2022

Proceeding of Fifth International Symposium on Turbulence and Shear Flow Phenomena, 2007

Coherent structures in the outer region of a turbulent boundary layer subjected to a strong adver... more Coherent structures in the outer region of a turbulent boundary layer subjected to a strong adverse pressure gradient have been studied using particle image velocimetry (PIV). The experimental setup is designed to achieve flow conditions corresponding to trailing-edge stall of an airfoil. Large sets of instantaneous velocity fields are acquired by PIV in streamwise-wall-normal planes at three different streamwise locations. Signatures of hairpin vortices are found in all the fields and hairpin packets occur in the majority of them. The essential features of the hairpins and hairpin packets are similar to those found in zero-pressuregradient turbulent boundary layers. The hairpin vortices are however slightly more inclined with respect to the wall in the present flow, and the upward growth of the hairpin packets in the streamwise direction is more important. The characteristics of the spanwise vortices are also documented.

Bulletin of the American Physical Society, Nov 25, 2014

Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a stron... more Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a strongly decelerated boundary layer 1 AYSE G. GUNGOR, Istanbul Technical University, YVAN MACIEL, Laval University, MARK P. SIMENS, U. Politécnica Madrid-The characteristics of three-dimensional intense Reynolds shear stress structures (Qs) are presented from a direct numerical simulation of an adverse pressure gradient boundary layer at Re θ = 1500 − 2175. The intense Q2 (ejections) and Q4 (sweeps) structures separate into two groups: wall-attached and wall-detached structures. In the region where turbulent activity is maximal, between 0.2δ and 0.6δ, 94% of the structures are detached structures. In comparison to canonical wall flows, the large velocity defect turbulent boundary layers are less efficient in extracting turbulent energy from the mean flow. There is, furthermore, much less turbulence activity and less velocity coherence near the wall. Additionally, the wall-detached structures are more frequent and carry a much larger amount of Reynolds shear stress.

International Journal of Molecular Sciences, Aug 2, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Proceeding of Fifth International Symposium on Turbulence and Shear Flow Phenomena, 2007

The near-field characteristics of a turbulent jet with moderate swirl generated by a fully develo... more The near-field characteristics of a turbulent jet with moderate swirl generated by a fully developed, axially rotating pipe flow are investigated with LDV, time-resolved stereoscopic PIV measurements, as well as with large-eddy simulations. Large-scale vortical structures in either double, triple or even quadruple-helix configuration are found at the pipe exit but rapidly break down or amalgamate after two jet diameters. Further downstream, the swirling jet is dominated by large-scale sweeping motions not present at such a scale and strength in the non-swirling case. Of special interest is the recently discovered counter-rotating core (in the mean) which develops about six jet diameters downstream the jet exit. Data for all six Reynolds stresses is reported at this position and it is argued that the counter-rotation is the result of the transport of angular momentum radially outward by the radial-azimuthal Reynolds shear stress. The mechanisms behind this transport are discussed by qualitative analysis of the time-resolved PIV and LES data and comparisons with the non-swirling case are made.

35th AIAA Fluid Dynamics Conference and Exhibit, Jun 6, 2005

ABSTRACT The experimental study of the turbulent boundary layer under external flow conditions si... more ABSTRACT The experimental study of the turbulent boundary layer under external flow conditions similar to those found on the suction side of airfoils in trailing-edge post-stall conditions has been performed. Detailed boundary layer measurements were carried out with a PIV system and a two-sensor wall probe. They cover the region downstream of the suction peak where the boundary layer is subjected to a very strong adverse pressure gradient and has suffered from an abrupt transition from strong favorable to strong adverse pressure gradients. The experiments show that in spite of these severe conditions, the boundary layer is surprisingly able to recover a state of near-equilibrium before separating. In this near-equilibrium zone, the mean velocity defect and all the measured Reynolds stresses are self-similar (in the outer region) with respect to the outer scales δ and U e δ*/δ. The mean momentum balance indicates that for the upper half of the outer region, the advection terms dominate all the stress-gradient terms in the zone prior to separation. A large portion of the outer region has therefore become essentially an inertial flow zone where an approach toward equilibrium is expected.

Journal of Fluids and Structures, Sep 1, 1990

Using the Krylov & Bogoliubov (1949, Introduction to Non-Linear Mechanics, Princeton: Princeton U... more Using the Krylov & Bogoliubov (1949, Introduction to Non-Linear Mechanics, Princeton: Princeton University Press) method of averaging, solutions have been obtained to the previously developed nonlinear equations of motion for wake-induced flutter of one circular cylinder in the wake of a fixed similar cylinder. The results obtained have been compared with previously obtained ones via numerical integration of the same equations; the agreement is excellent, but there is a considerable saving in computational time using the Krylov and Bogoliubov method. It has been reconfirmed that, when the windward cylinder is held fixed, increasing mechanical damping is not a very efficient way of decreasing the amplitude of oscillation of the leeward cylinder. Provided the same set of aerodynamic force coefficients are employed the nonlinear analysis predicts essentially the same lower flutter boundary as that obtained via a linearized analysis. There is, however, evidence th~/t the leeward cylinder acts as a hard oscillator, resulting in a considerable difference in the upper flutter boundary obtained via the nonlinear analysis visa -vis the linearized theory.

International Journal of Molecular Sciences

Every year, thousands of aortic valve replacements must take place due to valve diseases. Tissue-... more Every year, thousands of aortic valve replacements must take place due to valve diseases. Tissue-engineered heart valves represent promising valve substitutes with remodeling, regeneration, and growth capabilities. However, the accurate reproduction of the complex three-dimensional (3D) anatomy of the aortic valve remains a challenge for current biofabrication methods. We present a novel technique for rapid fabrication of native-like tricuspid aortic valve scaffolds made of an alginate-based hydrogel. Using this technique, a sodium alginate hydrogel formulation is injected into a mold produced using a custom-made sugar glass 3D printer. The mold is then dissolved using a custom-made dissolving module, revealing the aortic valve scaffold. To assess the reproducibility of the technique, three scaffolds were thoroughly compared. CT (computed tomography) scans showed that the scaffolds respect the complex native geometry with minimal variations. The scaffolds were then tested in a cardi...

Proceeding of Seventh International Symposium on Turbulence and Shear Flow Phenomena

... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médeci... more ... Saeed Rahgozar Department of Mechanical Engineering Laval University 1065 avenue de la médecine, Quebec City, Quebec, G1V0A6, Canada saeed.rahgozar.1@ulaval ... high speed (in average 2-3 of each) thus fields containing only SS of both high and low momen-tum are ...

IOP Conference Series: Earth and Environmental Science, 2019

Physical Review Fluids, 2018

This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations... more This Rapid Communication derives the Zagarola-Smits scaling directly from the governing equations for zero-pressure-gradient turbulent boundary layers (ZPG TBLs). It has long been observed that the scaling of the mean streamwise velocity in turbulent boundary layer flows differs in the near surface region and in the outer layer. In the inner region of small-velocity-defect boundary layers, it is generally accepted that the proper velocity scale is the friction velocity, u τ , and the proper length scale is the viscous length scale, ν/u τ. In the outer region, the most generally used length scale is the boundary layer thickness, δ. However, there is no consensus on velocity scales in the outer layer. Zagarola and Smits [ASME Paper No. FEDSM98-4950 (1998)] proposed a velocity scale, U ZS = (δ 1 /δ)U ∞ , where δ 1 is the displacement thickness and U ∞ is the freestream velocity. However, there are some concerns about Zagarola-Smits scaling due to the lack of a theoretical base. In this paper, the Zagarola-Smits scaling is derived directly from a combination of integral, similarity, and order-of-magnitude analysis of the mean continuity equation. The analysis also reveals that V ∞ , the mean wall-normal velocity at the edge of the boundary layer, is a proper scale for the mean wall-normal velocity V. Extending the analysis to the streamwise mean momentum equation, we find that the Reynolds shear stress in ZPG TBLs scales as U ∞ V ∞ in the outer region. This paper also provides a detailed analysis of the mass and mean momentum balance in the outer region of ZPG TBLs.

Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a stron... more Submitted for the DFD14 Meeting of The American Physical Society Turbulence structures in a strongly decelerated boundary layer 1 AYSE G. GUNGOR, Istanbul Technical University, YVAN MACIEL, Laval University, MARK P. SIMENS, U. Politécnica Madrid-The characteristics of three-dimensional intense Reynolds shear stress structures (Qs) are presented from a direct numerical simulation of an adverse pressure gradient boundary layer at Re θ = 1500 − 2175. The intense Q2 (ejections) and Q4 (sweeps) structures separate into two groups: wall-attached and wall-detached structures. In the region where turbulent activity is maximal, between 0.2δ and 0.6δ, 94% of the structures are detached structures. In comparison to canonical wall flows, the large velocity defect turbulent boundary layers are less efficient in extracting turbulent energy from the mean flow. There is, furthermore, much less turbulence activity and less velocity coherence near the wall. Additionally, the wall-detached structures are more frequent and carry a much larger amount of Reynolds shear stress.