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Research paper thumbnail of A Microscopic Particle Image Velocimetry Study of Transition to Turbulence in Microscale Capillaries

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

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Research paper thumbnail of Turbulence Modifications in the Roughness Sublayer of Flow over a Highly-Irregular Surface Topology

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

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Research paper thumbnail of Direct Assessment of the Accuracy of Stereo PIV in Turbulent Channel Flow

Volume 1, 2004

ABSTRACT

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Research paper thumbnail of A Comparison of Real and Simulated Surface Roughness Characterizations

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

ABSTRACT

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Research paper thumbnail of Outer-Layer Similarity in the Presence of Highly-Irregular Surface Roughness

45th AIAA Aerospace Sciences Meeting and Exhibit, 2007

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Research paper thumbnail of Structural Characteristics of Flow Over a Highly-Irregular Surface Topography

46th AIAA Aerospace Sciences Meeting and Exhibit, 2008

ABSTRACT

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Research paper thumbnail of Observations of meandering superstructures in the roughness sublayer of a turbulent boundary layer

International Journal of Heat and Fluid Flow, 2014

ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irre... more ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irregular roughness is explored with high-frame-rate particle-image velocimetry measurements within the roughness sublayer at moderate Reynolds number. Elongated streamwise fields of view reconstructed from this data using a Taylor’s hypothesis approach revealed spanwise-meandering regions of low-streamwise-momentum fluid that extended several boundary-layer thicknesses in the streamwise direction. Such signatures are consistent with previous observations of superstructures in smooth-wall turbulence. Counter-rotating wall-normal vortex cores were found to reside along the spanwise boundaries of these superstructure patterns, consistent with the spatial characteristics of hairpin vortex packets.

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Research paper thumbnail of The Combined Impact of Irregular Roughness and Favorable-Pressure-Gradient Conditions on Wall Turbulence Structure

41st AIAA Fluid Dynamics Conference and Exhibit, 2011

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Research paper thumbnail of Combined Irregular Roughness and Favorable-Pressure-Gradient Effects in a Turbulent Boundary Layer

40th Fluid Dynamics Conference and Exhibit, 2010

ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradi... more ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradient (FPG) conditions (K 2.5 x10-7) on the structure of a turbulent boundary layer is assessed using two-dimensional particle image velocimetry (PIV) measurements in the streamwise--wall-normal plane. The roughness under consideration is replicated from a turbine blade damaged by deposition of foreign materials and contains a broad range of topographical scales. These measurements are compared to measurements of smooth-wall flow under both identical FPG conditions as well as zero-pressure-gradient (ZPG) conditions in order to reveal the synergistic impact of roughness and FPG conditions on the underlying structure of the flow. While vortex organization is found to persist under both smooth- and rough-wall FPG conditions, its characteristics are altered compared to smooth-wall ZPG flow. Inspection of instantaneous velocity fields reveals this organization to be focused closer to the wall in the smooth- wall FPG case, with a shallower inclination angle noted as well as an elongated streamwise extent. In contrast, the rough-wall FPG results reveal packet structures more consistent with the smooth-wall ZPG case, indicating that roughness mitigates the FPG-induced focusing of these structural attributes toward the wall. Two-point correlations of streamwise velocity support these instantaneous observations.

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Research paper thumbnail of Interaction of the 20 kDa and 63 kDa fragments of anthrax protective antigen: kinetics and thermodynamics

Biochemistry, Jan 25, 2005

The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a... more The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a mammalian cell-surface receptor and is cleaved by a furin-family protease into two fragments: PA(20) (20 kDa) and PA(63) (63 kDa). After PA(20) dissociates, receptor-bound PA(63) spontaneously oligomerizes to form a heptameric species, which is able to bind the two enzymatic components of the toxin and transport them to the cytosol. Treatment of PA(83) with trypsin yielded PA(63) and a form of PA(20) lacking unstructured regions at the N- and C-termini. We labeled these fragments with dyes capable of fluorescence resonance energy transfer to quantify their association in solution. We kinetically determined that the equilibrium dissociation constant is 190 nM with a dissociation rate constant, k(off), of 3.3 x 10(-)(2) s(-)(1) (t(1/2) of 21 s). A two-step association process was observed using stopped-flow: a fast bimolecular step (k(on) = 1.4 x 10(5) M(-)(1) s(-)(1)) was followed by a s...

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Research paper thumbnail of Observation of yeast cell movement and aggregation in a small-scale MHz-ultrasonic standing wave field

Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been mon... more Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quan- tified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 µl. The aggreg- ation process was observed from above the transducer

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Research paper thumbnail of Anderson localization in one-dimensional randomly disordered optical systems that are periodic on average

Physical review. B, Condensed matter, Jan 15, 1993

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Research paper thumbnail of A microscopic particle image velocimetry method for studying the dynamics of immiscible liquid–liquid interactions in a porous micromodel

Microfluidics and Nanofluidics, 2015

ABSTRACT The development of an experimental protocol to investigate the flow field produced by th... more ABSTRACT The development of an experimental protocol to investigate the flow field produced by the interaction of two immiscible liquids flowing through a porous network is reported. The experimental protocol allows simultaneous quantification of the velocity distribution in a multi-liquid system based on the microscopic particle image velocimetry technique. The experimental challenges associated with this unique application are discussed, including two-liquid imaging and interface tracking, and solutions that couple refractive index matching and fluorescent signal separation are described. The technique was applied to both single- and two-liquid flows in a two-dimensional pore network comprising a staggered array of circular pillars wherein the flow was driven by a steady pressure gradient. Both drainage and imbibition were considered herein with a focus on fluid–fluid front migration and effects owing to the passage of the interface. The velocity distribution obtained for these two-liquid-phase flow scenarios revealed several peculiarities when compared to the reference case of single-liquid-phase flow. In particular, the instabilities associated with the interfacial processes propagate downstream and perturb the flow field, resulting in dramatic differences from the regular and periodic flow paths typical of steady-state, single-phase flow. Additionally, the passage of the interface does not restore previous flow patterns, but instead yields complex preferential flow paths that mutually interact with residual trapped pockets of fluid. Such dynamical events must be quantified in order to properly model the pore-scale physics central to fully understanding the wealth of practical applications represented by this model flow system.

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Research paper thumbnail of Modi 칌 ations of the Structure of Turbulent Flow by a Rough Surface

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Research paper thumbnail of Development of Fluorescent Thermometry Methods for Microfluidic Systems

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Research paper thumbnail of Contributions of coherent structures to subgrid-scale energy transfer in low-Re channel and higher-Re boundary-layer flows

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Research paper thumbnail of The Role of Coherent Structures in Subgrid-Scale Energy Transfer in Turbulent Channel Flow

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Research paper thumbnail of Reynolds Number Versus Roughness Effects in the Princeton``Super-Pipe''Re-examined in the Context of Large Reynolds Number Asymptotics*

Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion con... more Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion concerning the reasons for systematic deviations with Re's (Reynolds numbers) in the Princeton ``Super-Pipe'' data. Perry et al. demonstrate that the deviation of the constant within the ``log-law'' is compatible with the ``Colebrook formula'' for transitionally rough pipes. Since the experiments were completed, Lex

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Research paper thumbnail of The Structure of Turbulent Boundary Layers Subjected to Non-Zero Streamwise Pressure Gradients

ABSTRACT

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Research paper thumbnail of The Structure of Transitional Wall-Bounded Microscale Flows

ABSTRACT

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Research paper thumbnail of A Microscopic Particle Image Velocimetry Study of Transition to Turbulence in Microscale Capillaries

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Turbulence Modifications in the Roughness Sublayer of Flow over a Highly-Irregular Surface Topology

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Direct Assessment of the Accuracy of Stereo PIV in Turbulent Channel Flow

Volume 1, 2004

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A Comparison of Real and Simulated Surface Roughness Characterizations

37th AIAA Fluid Dynamics Conference and Exhibit, 2007

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Outer-Layer Similarity in the Presence of Highly-Irregular Surface Roughness

45th AIAA Aerospace Sciences Meeting and Exhibit, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Structural Characteristics of Flow Over a Highly-Irregular Surface Topography

46th AIAA Aerospace Sciences Meeting and Exhibit, 2008

ABSTRACT

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Research paper thumbnail of Observations of meandering superstructures in the roughness sublayer of a turbulent boundary layer

International Journal of Heat and Fluid Flow, 2014

ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irre... more ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irregular roughness is explored with high-frame-rate particle-image velocimetry measurements within the roughness sublayer at moderate Reynolds number. Elongated streamwise fields of view reconstructed from this data using a Taylor’s hypothesis approach revealed spanwise-meandering regions of low-streamwise-momentum fluid that extended several boundary-layer thicknesses in the streamwise direction. Such signatures are consistent with previous observations of superstructures in smooth-wall turbulence. Counter-rotating wall-normal vortex cores were found to reside along the spanwise boundaries of these superstructure patterns, consistent with the spatial characteristics of hairpin vortex packets.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Combined Impact of Irregular Roughness and Favorable-Pressure-Gradient Conditions on Wall Turbulence Structure

41st AIAA Fluid Dynamics Conference and Exhibit, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Combined Irregular Roughness and Favorable-Pressure-Gradient Effects in a Turbulent Boundary Layer

40th Fluid Dynamics Conference and Exhibit, 2010

ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradi... more ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradient (FPG) conditions (K 2.5 x10-7) on the structure of a turbulent boundary layer is assessed using two-dimensional particle image velocimetry (PIV) measurements in the streamwise--wall-normal plane. The roughness under consideration is replicated from a turbine blade damaged by deposition of foreign materials and contains a broad range of topographical scales. These measurements are compared to measurements of smooth-wall flow under both identical FPG conditions as well as zero-pressure-gradient (ZPG) conditions in order to reveal the synergistic impact of roughness and FPG conditions on the underlying structure of the flow. While vortex organization is found to persist under both smooth- and rough-wall FPG conditions, its characteristics are altered compared to smooth-wall ZPG flow. Inspection of instantaneous velocity fields reveals this organization to be focused closer to the wall in the smooth- wall FPG case, with a shallower inclination angle noted as well as an elongated streamwise extent. In contrast, the rough-wall FPG results reveal packet structures more consistent with the smooth-wall ZPG case, indicating that roughness mitigates the FPG-induced focusing of these structural attributes toward the wall. Two-point correlations of streamwise velocity support these instantaneous observations.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Interaction of the 20 kDa and 63 kDa fragments of anthrax protective antigen: kinetics and thermodynamics

Biochemistry, Jan 25, 2005

The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a... more The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a mammalian cell-surface receptor and is cleaved by a furin-family protease into two fragments: PA(20) (20 kDa) and PA(63) (63 kDa). After PA(20) dissociates, receptor-bound PA(63) spontaneously oligomerizes to form a heptameric species, which is able to bind the two enzymatic components of the toxin and transport them to the cytosol. Treatment of PA(83) with trypsin yielded PA(63) and a form of PA(20) lacking unstructured regions at the N- and C-termini. We labeled these fragments with dyes capable of fluorescence resonance energy transfer to quantify their association in solution. We kinetically determined that the equilibrium dissociation constant is 190 nM with a dissociation rate constant, k(off), of 3.3 x 10(-)(2) s(-)(1) (t(1/2) of 21 s). A two-step association process was observed using stopped-flow: a fast bimolecular step (k(on) = 1.4 x 10(5) M(-)(1) s(-)(1)) was followed by a s...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Observation of yeast cell movement and aggregation in a small-scale MHz-ultrasonic standing wave field

Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been mon... more Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quan- tified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 µl. The aggreg- ation process was observed from above the transducer

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Anderson localization in one-dimensional randomly disordered optical systems that are periodic on average

Physical review. B, Condensed matter, Jan 15, 1993

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A microscopic particle image velocimetry method for studying the dynamics of immiscible liquid–liquid interactions in a porous micromodel

Microfluidics and Nanofluidics, 2015

ABSTRACT The development of an experimental protocol to investigate the flow field produced by th... more ABSTRACT The development of an experimental protocol to investigate the flow field produced by the interaction of two immiscible liquids flowing through a porous network is reported. The experimental protocol allows simultaneous quantification of the velocity distribution in a multi-liquid system based on the microscopic particle image velocimetry technique. The experimental challenges associated with this unique application are discussed, including two-liquid imaging and interface tracking, and solutions that couple refractive index matching and fluorescent signal separation are described. The technique was applied to both single- and two-liquid flows in a two-dimensional pore network comprising a staggered array of circular pillars wherein the flow was driven by a steady pressure gradient. Both drainage and imbibition were considered herein with a focus on fluid–fluid front migration and effects owing to the passage of the interface. The velocity distribution obtained for these two-liquid-phase flow scenarios revealed several peculiarities when compared to the reference case of single-liquid-phase flow. In particular, the instabilities associated with the interfacial processes propagate downstream and perturb the flow field, resulting in dramatic differences from the regular and periodic flow paths typical of steady-state, single-phase flow. Additionally, the passage of the interface does not restore previous flow patterns, but instead yields complex preferential flow paths that mutually interact with residual trapped pockets of fluid. Such dynamical events must be quantified in order to properly model the pore-scale physics central to fully understanding the wealth of practical applications represented by this model flow system.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modi 칌 ations of the Structure of Turbulent Flow by a Rough Surface

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Development of Fluorescent Thermometry Methods for Microfluidic Systems

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Contributions of coherent structures to subgrid-scale energy transfer in low-Re channel and higher-Re boundary-layer flows

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Role of Coherent Structures in Subgrid-Scale Energy Transfer in Turbulent Channel Flow

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Reynolds Number Versus Roughness Effects in the Princeton``Super-Pipe''Re-examined in the Context of Large Reynolds Number Asymptotics*

Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion con... more Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion concerning the reasons for systematic deviations with Re's (Reynolds numbers) in the Princeton ``Super-Pipe'' data. Perry et al. demonstrate that the deviation of the constant within the ``log-law'' is compatible with the ``Colebrook formula'' for transitionally rough pipes. Since the experiments were completed, Lex

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Structure of Turbulent Boundary Layers Subjected to Non-Zero Streamwise Pressure Gradients

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Structure of Transitional Wall-Bounded Microscale Flows

ABSTRACT

Bookmarks Related papers MentionsView impact