Most flow visualizations and flow measurements to understand particle mobility in porous media are typically performed in transparent microfluidic devices (micro-models) with 2D pore-throat networks. Nano-particle mobility studies to date have been limited to micro-models made of transparent thermoplastic or silicone-based materials. In an effort to fabricate materials close to reservoir rock, ceramic micro-model has been designed and micro fabricated by our group to study nano-particle transport in rock-based ceramic micro-model. A Confocal Micro-Particle Image Velocimetry (C-μPIV) technique augmented with associated post processing algorithms [1] is used in obtaining 3D distributions of nano-particle velocity and concentration at selected locations of the ceramic micro-model. Furthermore, a novel in-situ, nondestructive method of measuring 3D geometry of non-transparent ceramic micro-model is described and validated. The particle experiment uses 860 nm fluorescence labeled polystyrene neutrally buoyant, and electrically neutral nano-particles. The data was acquired using confocal laser-scanning microscope to quantify 3D particle transport at selected observation locations. In addition, fluorescence microscope was used to measure in-situ geometry of porous media. Results of detailed 3D measurements of nano-particle velocity and particle concentration from experiment conducted at a constant flow rate of 30 nL/min in the rock-based micro-model are presented and discussed. Particle velocities range from 0 to 20.93 μm/sec in magnitude, and average concentration range from 6.02 × 103 to 6.79 × 103 particles at inlet channel while velocities range from 0 to 73.63 μm/sec and concentration range from 4.9 × 101 to 1.45 × 103 particles at selected observation locations of the ceramic micro-model. 3D velocity fields at selected locations also indicate that mean velocity closer to the top wall is comparatively higher than bottom wall, because of higher planar porosity and smooth pathway for the nano-particles closer to the top wall. The three dimensional micro-model geometry reconstructed from the fluorescence data can be used to conduct numerical simulations of the flow in the as-tested micro-model for future comparisons to experimental results after incorporating particle transport and particle-wall interaction models.

A ceramic-based micromodel was fabricated with batching of green alumina ceramics mixed with polymer binders, extrusion of the green alumina tapes, and hot embossing of the green tapes with a metal mold. The metal mold fabricated using optical lithography of SU8 and electroforming of nickel contained 2.5D pore network geometry in 13 layers of a rock, Boise sandstone. The hot embossing process enabled the generation of the pore network geometries with a minimum feature size of 25 μm and for distinct formation of the 13 layers of the 2.5D pore geometry of the rock. The green ceramic micromodels were processed with solvent extraction, thermal debinding, and sintering. The sintered micromodels showed significant shrinkages at all directions of the micromodels, which were 17.6% in x, 17.5% in y, and 14.6% in z. The sintered, 2.5D rock-based ceramic micromodel was capped with a thin glass cover slide and used for flow visualization with a fluorescent dye and fluorescent nano-particles. The dye-filled micromodel showed good flow connectivity and fluorescence signal intensity dependence on depth. It was observed that the peak particle concentration close to the observation window and gradual decrease in particle concentration along the depth. The higher velocities were measured in the low flow resistance region with velocity variations along the depth. The microfabricated 2.5D ceramic micromodels will allow resistance to harsh experimental conditions such as high temperature and pressure, and opportunity for investigation of the complex flow patterns in 3D.

Fabrication of 2.5D rock-based micromodels with high resolution features is presented using SU-8 multi-layer lithography and nickel electroforming for nickel molds. Processes associated with SU-8 were carefully optimized by the use of the vacuum contact, the use of UV filter, and controls of UV exposure doses and baking times. The use of SU-8 Micro Spray enabled the easy fabrication of multi-layers of SU-8, while exhibiting some total thickness variations. The thirteen layered SU-8 samples showed reliable patterning results for features at 10 and 25 gm resolutions, and minor pattern distortions of features at the 5 gm resolution. Flycutting method employed in multi-layer lithography of SU-8 yielded accurate total thickness control within 1.5 gm and excellent pattern formation for all of 5, 10, and 25 gm features. Electroforming of nickel was optimized with electroplating bath composition and electroplating parameters such as current density to realize the high resolution nickel mold. The fabricated nickel molds from flycutting based SU-8 samples revealed the feasibility of manufacturing the minimum features down to 5 gm for thirteen layers without any pattern distortions. The replication-based micromolding method will allow for fabrication of micromodels in a variety of materials such as polymers and ceramics. The high resolution, 2.5D micromodels will be used for investigation of pore-scale fluid transport, which will aid in understanding the complicated fluidic phenomena occurring in the 3D reservoir rock.

Evaluation of the safety and performance of road vehicles in windy conditions requires accurate descriptions of wind loads on vehicles. However, the research in this area has been far from comprehensive. In the present study, wind tunnel tests were carried out on various vehicle models under different flow conditions, including smooth flow, turbulent flow, and boundary layer flow. The lift, drag, and side forces, and the pitching, rolling, and yawing moments for these vehicle models were measured and analyzed to interpret the effects of flow conditions on these forces. The results were also compared with other wind tunnel tests results published in the literature. The experimental results reveal that the flow conditions did have effects on the variation of wind loads; the smooth flow case is a conservative estimation in general. The height of the center of gravity of the vehicle will significantly affect the results of the aerodynamic moment coefficients, which causes the significant difference between different studies. The results under the boundary layer flow also provide a good reference guide for the context of applications such as stability problem of still vehicles under extreme wind events.

A confocal Micro-Particle Image Velocimetry (C-μPIV) technique along with associated post image processing algorithms is established to quantify three dimensional distributions of nano-particle velocity and concentration at the micro-scale (pore-scale) in 2.5D porous media designed from a Boise rock sample. In addition, an in-situ, non-destructive method for measuring the geometry of the micro-model, including its depth, is described and demonstrated. The particle experiments use 900 nm fluorescence labeled polystyrene particles at a flow rate of 10 nLmin−1 and confocal laser scanning microscopy (CLSM), while in-situ geometry measurements use regular microscope along with Rhodamine dye and a depth-to-fluorescence-intensity calibration. Image post-processing techniques include elimination of background noise and signal from adsorbed nano-particle on the inner surfaces of the micro-model. In addition, a minimization of depth of focus technique demonstrates a capability of optically thin slice allowing us to measure depth wise velocity in 2.5D micro-model. The mean planar components of the particle velocity of the steady-state flow and particle concentration distributions were measured in three dimensions. Particle velocities range from 0.01 to 122 μm s−1 and concentrations from 2.18 × 103 to 1.79 × 104 particles mm−2. Depth-wise results show that mean velocity closer to the top wall is comparatively higher than bottom walls, because of higher planar porosity and smooth pathway for the nano-particles closer to the top wall. The three dimensional micro-model geometry reconstructed from the fluorescence data can be used to conduct numerical simulations of the flow in the as-tested micro-model for future comparisons to experimental results after incorporating particle transport and particle-wall interaction models.

A new cascade wind tunnel has been designed and constructed at the LSU Wind Tunnel Laboratory. The objective was to develop a versatile test facility, suitable for a wide range of experimental studies and measurements on turbine airfoils, especially with regards to film-cooling incorporating realistic unsteady effects due to passing wakes. The test section consists of a four passage linear cascade composed of three full blades and two shaped wall blades. The 2D blade shape profile of the cascade is a high-lift, low-pressure turbine L1A profile provided by the US Air Force Research Laboratories (AFRL), with a 152-mm axial chord. The Reynolds number based on the axial chord length at the nominal freestream velocity of 50 ms−1 is 500,000. A conveyor-based system was designed and fabricated to simulate the passing wakes of the upstream vanes (or blades) on the test blades (or vanes) depending on which airfoil types are put on the stationary frame and the moving frame of the conveyor. The original implementation uses blade profiles on the stationary frame and thick plate wake generators on the translating frame. Results are presented from hot-wire surveys conducted to characterize and qualify the velocity and turbulence intensity distributions and associated spectral characteristics at the cascade test section inlet, in the wake of the vanes and in the wake of the test blade. A blade instrumented with 123 pressure taps was used to acquire static pressure profiles of the cascade central blade, which were compared to the ones from the nominal airfoil design as well as to those obtained from a CFD simulation of the cascade flow. Incoming velocity and temperature profiles were found to be uniform to within a few percentage points, and the pressure coefficient distribution was found to be in good agreement with design values. The passage periodicity of the conveyor-belt-driven, flat-plates was verified and their wake was characterized. These results verified that the cascade wind tunnel operates according to design, thus proving to be a reliable test-bed for film cooling studies with and without unsteady wake effects. The design also incorporates an in-house-designed, miniature periscopic and adjustable laser sheet generating system integrated within the “dummy” blades to enable Particle Image Velocimetry measurements in the intra-blade domain.

There is potential for flight time based DNA sequencing involving disassembly into individual nucleotides which would pass through a nanochannel with two or more detectors. We performed molecular dynamics simulations of electrophoretic motion of single DNA nucleotides through 3 nm wide hydrophobic slits with both smooth and rough walls. The electric field (E) varied from 0.0 to 0.6 V/nm. The nucleotides adsorb and desorb from walls multiple times during their transit through the slit. The nucleotide-wall interactions differed due to nucleotide hydrophobicities and wall roughness which determined duration and frequency of nucleotide adsorptions and their velocities while adsorbed. Transient association of nucleotides with one, two, or three sodium ions occurred, but the mean association numbers (ANs) were weak functions of nucleotide type. Nucleotide-wall interactions contributed more to separation of nucleotide flight time distributions than ion association and thus indicate that nucleotide-wall interactions play a defining role in successfully discriminating between nucleotides on the basis of their flight times through nanochannels/slits. With smooth walls, smaller nucleotides moved faster, but with rough walls larger nucleotides moved faster due to fewer favorable wall adsorption sites. This indicates that roughness, or surface patterning, might be exploited to achieve better time-of-flight based discrimination between nucleotides.

Numerical approaches are presented to minimize the statistical errors inherently present due to finite sampling and the presence of thermal fluctuations in the molecular region of a hybrid computational fluid dynamics (CFD) — molecular dynamics (MD) flow solution. Near the fluid-solid interface the hybrid CFD-MD simulation approach provides a more accurate solution, especially in the presence of significant molecular-level phenomena, than the traditional continuum-based simulation techniques. It also involves less computational cost than the pure particle-based MD. Despite these advantages the hybrid CFD-MD methodology has been applied mostly in flow studies at high velocities, mainly because of the higher statistical errors associated with low velocities. As an alternative to the costly increase of the size of the MD region to decrease statistical errors, we investigate a few numerical approaches that reduce sampling noise of the solution at moderate-velocities. These methods are based on sampling of multiple simulation replicas and linear regression of multiple spatial/temporal samples. We discuss the advantages and disadvantages of each technique in the perspective of solution accuracy and computational cost.

Film cooling jets were simulated using Large Eddy Simulation (LES) at blowing ratios of 0.150, 0.50 and 1.0. The results were analyzed using Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) as a statistical analysis tool and the first step toward reduced order modeling. The results of both decompositions are presented and put in perspective with dominant vortical structures and heat transfer mechanisms observed in the instantaneous velocity and temperature fields. Assessment of the performance of the decompositions is provided in terms of energy content and rendered dominant frequencies. Evolution of the dominant modes and decomposition metrics are discussed as the blowing ratio is increased.

The present experimental and numerical study focuses on the vortical structures encountered in steady and pulsed low-blowing-ratio transverse jets (0.150 <= BR <= 4.2), a configuration hardly discussed in the literature. Under unforced conditions at low blowing ratio, a stable leading-edge shear-layer rollup is identified inside the jet pipe. As the blowing ratio is increased, the destabilization and evolution of this structure sheds light on the formation mechanisms of the well-known transverse jet vortical system. A discussion on the nature of the counter-rotating vortex pair in low-blowing-ratio transverse jets is also provided. Under forced conditions, the experimental observations support and extend numerical results of previous fully modulated jet studies. Large-eddy simulation results provide scaling parameters for the classification of starting vortices for partly modulated jets, as well as information on their three-dimensional dynamics. The counter-rotating vortex pair initiation is observed and detailed in both Mie scattering visualizations and simulations. The observations support a mechanism based on stretching of the starting vortical structures because of inviscid induction and partial leapfrogging. Two modes of cross-flow ingestion inside the jet pipe are described as the pulsed jet cycles from high to low values of blowing ratio.

This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A2 at the mismatch plane to the original cross-sectional area A1. Multiple simulations were performed for varying degrees of area reduction i.e. 0–75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition.

Minimizing misalignments during the interconnection of microfluidic modules is extremely critical to develop a fully integrated microfluidic device. Misalignments arising during chip-to-chip or world-to-chip interconnections can be greatly detrimental to efficient functioning of microfluidic devices. To address this problem, we have performed numerical simulations to investigate the effect of misalignments arising in three types of interconnection methods: (i) end-to-end interconnection (ii) channel overlap when chips are stacked on top of each other, and (iii) tube-in-reservoir misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. In the channel overlap interconnection method, various possible misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction). The effect of misalignment in a tube-in-reservoir interconnection was investigated by positioning the tube at an offset of 164 μm from the reservoir center. All the results were evaluated in terms of the equivalent length of a straight pipe. The effect of Reynolds number (Re) was also taken into account by performing additional simulations of aforementioned cases at Re ranging between 0.075 ≤ Re ≤ 75. Correlations were developed and the results were interpreted in terms of equivalent length (Le ). Equivalent length calculations revealed that the effect of misalignment in tube-in-reservoir interconnection method was the least significant when compared to the other two methods of interconnection.

Transport of single molecules in nanochannels or nanoslits might be used to identify them via their transit (flight) times. In this paper, we present molecular dynamics simulations of transport of single deoxynucleotide 5'-monophoshates (dNMP) in aqueous solution under pressure-driven flow, to average velocities between 0.4 and 1.0 m/s, in 3 nm wide slits with hydrophobic walls. The simulation results show that, while moving along the slit, the mononucleotides are adsorbed and desorbed from the walls multiple times. For the simulations, the estimated minimum slit length required for separation of the dNMP flight time distributions is about 5.9 μm, and the minimum analysis time per dNMP is about 10 μs. These are determined by the nature of the nucleotide-wall interactions, channel width, and by the flow characteristics. A simple analysis using realistic dNMP velocities shows that, in order to reduce the effects of diffusional broadening and keep the analysis time per dNMP reasonably small, the nucleotide velocity should be relatively high. Tailored surface chemistry could lead to further reduction of the analysis time toward its minimum value for a given driving force.

Liquid-liquid segmented flows in microchannels fabricated on polycarbonate test chips were investigated experimentally. Three different cross-sectional expansion ratios of 16, 4, and 2 from the injection to the test channels were used to observe the effect of different cross-sectional areas of the injection channel on the segmented flow regimes in the test channel. Flow regime maps and the transitions between flow regimes were determined for the different expansion ratios. The effect of the cross-sectional expansion ratio was determined by mutual comparison of these results. The measured length of the dispersed fluid segments was found to scale inversely with the carrier fluid volumetric flow ratio (beta(C)). A simplified geometric model for the volume of the dispersed and the carrier fluid plugs provided good estimates of the carrier plug length, which scaled inversely with (1 - beta(C)). Velocity and pressure drop measurements of the liquid-liquid segmented flows were carried out for all flow regimes, and the associated trends were correlated with changes in the flow topology. Most previous homogeneous and separated flow models based on the viscous frictional pressure drop underestimated the measured pressure drops. Including the contribution of the capillary pressure drop in addition to the frictional pressure drop improved the agreement with the measured data. (C) 2013 Elsevier Ltd. All rights reserved.

Microfluidic polymethylmethacrylate (PMMA) devices for study of particle transport in artificial porous media were designed and microfabricated using hot embossing with a brass mold insert containing a microchannel network with eight layers. After thermal bonding to enclose the microchannel network, a process protocol was applied to successfully remove bubbles in the PMMA device. Characterization protocols were developed for study of fluorescent particle tracking, accumulation, and retention in these microfluidic chip artificial porous media. Particle accumulation and retention was observed throughout the microfluidic network domain and predominantly at the inlet section of the PMMA device due to entrance effects. Particle Image Velocimetry of the PMMA device allowed for generating velocity profiles in the chip microchannel networks.

The effects of jet flow-rate modulation were investigated in the case of a 35° inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records and large eddy simulations (LES). An unforced jet study was conducted over a wide range of blowing ratios to provide a baseline for comparison to the pulsed results. The two distinct and well known steady jet regimes (attached jet with high film cooling performance for BR<0.4 and detached jet with poor film cooling performance for BR>1.0) were related to the dynamics of characteristic vortical structures, significant in the transition from one regime to the other. Similarity of the inclined jet results with a past vertical jet study are also put in perspective when comparing wall adiabatic effectiveness results. 3D Proper Orthogonal Decomposition (3D-POD) was performed on LES results of an unforced case at BR = 0.15 to provide an analysis of dominant modes in the velocity and temperature fields. Error calculations on the reconstructed fields provided an estimation of the number of modes necessary to obtain satisfactory reconstruction while revealing some of the shortcomings associated with POD.

A parallel CFD code is being modified to improve performance for multiphase flows. The code uses a hybrid front-tracking/front-capturing technique to solve for two immiscible fluids simultaneously on a regular 3D Cartesian grid. The pressure solver uses a multigrid method to solve a Poisson-like equations with variable coefficients. A Schwarz–Aitken acceleration technique is applied to the solver, and the results analysed.