Hydrodynamic Drag Research Articles

Vertical Array of Graphite Oxide Liquid Crystal by Microwire Shearing for Highly Thermally Conductive Composites.

Excellent through-plane thermally conductive composites are highly demanded for efficient heat dissipation. Giant sheets have large crystalline domain and significantly reduce interface phonon scattering, making them promising to build highly thermally conductive composites. However, realizing vertical orientation of giant sheets remains challenging due to their enormous mass and huge hydrodynamic drag force. Here, we achieve highly vertically ordered liquid crystals of giant graphite oxide (more than 100μm in lateral dimension) by microwire shearing, which endows the composite with a recorded through-plane thermal conductivity of 94W m-1 K-1 . Microscale shearing fields induced by vertical motion of microwires conquer huge hydrodynamic energy barrier and vertically reorient giant sheets. The resulting liquid crystals exhibit extremely retarded relaxation and impart large-scale vertical array with bidirectional ordering degree as high as 0.82. The graphite array-based composites demonstrate an ultrahigh thermal enhancement efficiency of over 35 times per unit volume. Furthermore, the composites improve cooling efficiency by 93% for thermal management tests compared to commercial thermal interface materials. Our work offers a novel methodology to precisely manipulate the orientation of giant particles and promote large-scale fabrication of vertical array with advanced functionalities. This article is protected by copyright. All rights reserved.

Monitoring Cardiac Biomarkers with Aptamer‐Based Molecular Pendulum Sensors

AbstractReagent‐free electronic biosensors capable of analyzing disease markers directly in unprocessed body fluids will enable the development of simple & affordable devices for personalized healthcare monitoring. Here we report a powerful and versatile nucleic acid‐based reagent‐free electronic sensing system. The signal transduction is based on the kinetics of an electrode‐tethered molecular pendulum—a rigid double stranded DNA with one of the strands displaying an analyte‐binding aptamer and the other featuring a redox probe—that exhibits field‐induced transport modulated by receptor occupancy. Using chronoamperometry, which enables the sensor to circumvent the conventional Debye length limitation, the binding of an analyte can be monitored as these species increase the hydrodynamic drag. The sensing platform demonstrates a low femtomolar quantification limit and minimal cross‐reactivity in analyzing cardiac biomarkers in whole blood collected from patients with chronic heart failure.

Monitoring Cardiac Biomarkers with Aptamer-Based Molecular Pendulum Sensors.

Reagent-free electronic biosensors capable of analyzing disease markers directly in unprocessed body fluids will enable the development of simple & affordable devices for personalized healthcare monitoring. Here we report a powerful and versatile nucleic acid-based reagent-free electronic sensing system. The signal transduction is based on the kinetics of an electrode-tethered molecular pendulum - a rigid double stranded DNA with one of the strands displaying an analyte-binding aptamer and the other featuring a redox probe - that exhibits field-induced transport modulated by receptor occupancy. Using chronoamperometry, which enables the sensor to circumvent the conventional Debye length limitation, the binding of an analyte can be monitored as these species increase the hydrodynamic drag. The sensing platform demonstrate a low femtomolar quantification limit and minimal cross-reactivity in analyzing cardiac biomarkers in whole blood collected from patients with chronic heart failure.

Validation of a control-oriented point vortex model for a cyclorotor-based wave energy device

Recently conducted analytical assessment of the potential performance of cyclorotor wave energy converters (WECs) have shown that such devices offer the best wave absorption behaviour, if energy capture can be optimised through suitable control. Such claims require additional investigation. This article is dedicated to validation of the control-oriented point vortex model of cyclorotor WECs against numerical and experimental assessments conducted by various research groups. The validation is conducted in terms of the traditional metrics for cyclorotor WECs: (a) cancellation of incoming waves; (b) generation of lift and drag forces (c) mechanical power generation.It is shown that the point vortex model generally confirms the previously conducted analytical assessment of device performance. However, accounting for the influence of the hydrofoil induced wakes decreases performance estimates to some extent. It is also shown that, overall, wave cancellation metrics are more optimistic than actual shaft power generation.Analysis of the lift and drag coefficients, which were derived from experimental data, reveal a range of hydrodynamic and mechanic effects which could influence actual device performance. It has been shown that, due to the complexity of hydrodynamic effects, lift and drag coefficients for the control-oriented model should be considered not only as functions of the Reynolds number and angle of attack, but also related to submergence of the foils and direction of their rotation with respect to the free surface. This method allows us to achieve the best validation against experimental results in terms of generation of tangential and radial forces.

Cation-controlled permeation of charged polymers through nanocapillaries.

Molecular dynamics simulations are used to study the effects of different cations on the permeation of charged polymers through flat capillaries with heights below 2nm. Interestingly, we found that, despite being monovalent, Li^{+}, Na^{+}, and K^{+} cations have different effects on polymer permeation, which consequently affects their transmission speed throughout those capillaries. We attribute this phenomenon to the interplay of the cations' hydration free energies and the hydrodynamic drag in front of the polymer when it enters the capillary. Different alkali cations exhibit different surface versus bulk preferences in small clusters of water under the influence of an external electric field. This paper presents a tool to control the speed of charged polymers in confined spaces using cations.

Hydrodynamics of a slip-stick sphere with a non-axisymmetric patch

We study the low Reynolds number hydrodynamics of a slip-stick sphere suspended in an arbitrary ambient Stokes flow, whose surface is partitioned into two regions with different slip lengths. The fore-aft symmetry of the sphere breaks due to the varied slip length over the surface, which causes translational and rotational motion of the slip-stick sphere. An analytical solution is developed using the double curl method to evaluate Faxén's formulae for the hydrodynamic drag and torque exerted on the slip-stick sphere for the sub-cases, namely, (a) cap/strip model and (b) patch model. Subsequently, we compute the flow field, velocity, and rotation rate, which strongly depend on the slip lengths and configuration of the patch. As a specific example, we consider the slip-stick sphere immersed in a Poiseuille flow. For the cap/strip model, we find an optimal configuration for which the velocity of the slip-stick sphere is maximum compared to the slip-stick sphere with uniform slip. We also find configurations for which the velocity is independent of the slip lengths. Subsequently, in the patch model, we obtain the optimal azimuthal angles for the maximum rotation rate of the slip-stick sphere. We observe near-field deviations in streamlines due to the heterogeneous nature of the surface of the slip-stick sphere. These findings help design efficient artificial passive swimmers with prescribed slip lengths.

Intracycle Velocity Variation in Swimming: A Systematic Scoping Review.

Intracycle velocity variation is a swimming relevant research topic, focusing on understanding the interaction between hydrodynamic propulsive and drag forces. We have performed a systematic scoping review to map the main concepts, sources and types of evidence accomplished. Searches were conducted in the PubMed, Scopus and Web of Science databases, as well as the Biomechanics and Medicine in Swimming Symposia Proceedings Book, with manual searches, snowballing citation tracking, and external experts consultation. The eligibility criteria included competitive swimmers' intracycle velocity variation assessment of any sex, distance, pace, swimming technique and protocol. Studies' characteristics were summarized and expressed in an evidence gap map, and the risk of bias was judged using RoBANS. A total of 76 studies, corresponding to 68 trials involving 1440 swimmers (55.2 and 34.1% males and females), were included, with only 20 (29.4%) presenting an overall low risk of bias. The front crawl was the most studied swimming technique and intracycle velocity variation was assessed and quantified in several ways, leading to extremely divergent results. Researchers related intracycle velocity variation to coordination, energy cost, fatigue, technical proficiency, velocity, swimming techniques variants and force. Future studies should focus on studying backstroke, breaststroke and butterfly at high intensities, in young, youth and world-class swimmers, as well as in IVV quantification.

Modal analysis of underwater hull cleaning robot considering environmental interaction

Cleaning ship's fouling can increase the speed up to 95–98% of the original value, decrease fuel costs, increase the ship's maneuverability, and reduce impeller damage by reducing cavitation. In this paper, the dynamic behavior of an underwater cleaning brush system is investigated using modal analysis while the brushing robot is in contact with an underwater ship's hull. The environmental interaction forces on the rotating filaments are considered, resulting from rotating inertia, hydrodynamic drags, and surface contact with external substances such as twisted algae and sediments with different hardness. A prototype robot is designed and built to test and valid the presented theory. Vibrational interaction forces and bending moments of the rotating brush system are investigated by acceleration sensor ADXL345, Arduino UNO and MATLAB software, and compared with the real experimental data. The experimental results demonstrated the theory which are essential to design a hull cleaning robot's suspension system and increase the surface cleaning quality without damaging the ship's hull and antifouling coating.

Eco-friendly biodegradable polyurethane based coating for antibacterial and antifouling performance

Biofouling, which comprises the absorption of proteins and the adhesion of bacteria to the surface of living entities, is a severe concern for the maritime sector since it ultimately leads to hydrodynamic drag, resulting in a higher increase in fuel consumption. As a result, polymer resins are crucial in the marine sector for anti-biofouling coatings. In this work, the poly(caprolactone-ethylene glycol-caprolactone)-polyurethane (PECL-PU) are prepared through ε -caprolactone (CL), poly(ethylene glycol) (PEG), 4,4′-methylene bis(cyclohexyl isocyanate ) and 1,4 butanediol. Our study demonstrate that the PECL-PU copolymer degraded in artificial seawater (5.21%), enzymatic solution (12.63%), and seawater (13.75%) due to the presence of PEG segments in the laboratory-based test under static condition. Because the addition of PEG segments are increased the polymer's amorphous area and decreased the crystallization of the polycaprolactone (PCL) in the copolymer, as demonstrated by differential scanning calorimetry, X-ray diffraction, and water contact angle studies. Therefore, the hydrolysis rates of PECL-PU were higher than the caprolactone-co-polyurethane (CL-PU). The antifouling test showed that PECL-PU3 copolymer had about 90.29% protein resistance, 85.2% Escherichia coli ( E. coli ) reduction and 94.61% marine diatom Navicula incerta reduction comparison to the control. We have developed an eco-friendly and inexpensive promising degradable polyurethane for reduction of bacterial biofilm, which can preserve the formation of biofouling on marine coating under practical sea conditions.

Role of DNA sliding friction and nonequilibrium dynamics in viral DNA ejection and packaging.

In many viruses DNA is packaged to high densities, resulting in high “internal force” inside the capsid shell. This helps drive DNA ejection through the portal channel when viruses infect cells. Imaging of the in vitro ejection of fluorescent-labeled DNA from phages T5 and lambda found that it was initially slow despite the internal force being highest when the capsid is full. This was attributed to hydrodynamic drag on the tightly-packed DNA, but this hypothesis has not been tested. Here we introduce a new method for probing the DNA mobility by using optical tweezers to pull it out from phage phi29 capsids. This allows us to measure the dynamics with higher precision, avoid using DNA-binding dyes that alter the dynamics, and apply variable forces. We measure even slower DNA exit than reported previously, a steeper, exponential velocity increase as the first 20% of the genome length exits, and find that exit velocity is not proportional to driving force as expected for hydrodynamic friction. Rather, our findings are consistent with theoretical predictions for DNA-DNA sliding friction. We also observe large heterogeneity in the exit dynamics and stochastic pausing, indicating that ejection is a nonequilibrium process, in qualitative agreement with simulations. Features of the pausing suggest it is related to the phenomenon of “clogging” in soft-matter physics, which occurs in the flow of disordered materials through constrictions. Our results indicate that intramolecular friction and nonequilibrium pausing control the kinetics of ejection but that this friction does not significantly affect DNA packaging.

Numerical investigation of flow past a circular cylinder modified with a single groove at low Reynolds number

Flow past a circular cylinder modified by grooves is one of the passive control techniques to control the drag and lift forces. The presence of grooves tends to reduce the hydrodynamic drag and lift. The aim of this work was to numerically investigate the influence of a single groove modification on a circular cylinder and how it was impacting the hydrodynamic coefficients based on its position and shape at low Reynolds numbers. Three types of grooves were considered, namely, dimple, square, and triangular, with identical width and depth which is 0.1 times the diameter. The Reynolds numbers considered were 100, 150, and 200. The computational domain was set to a blockage ratio of 0.01 after carrying out a detailed domain independence test. It was observed that the drag and lift reduction was maximum at groove location 90° with the decrements being more for the square groove shape. The viscous drag showed a decrease in its values for all the groove positions located on the flow-facing side of the cylinder; however, the pressure drag showed an increment in its values for these groove locations, and these increments were relative of larger magnitudes, thus influencing a net increase in the total mean drag when compared to the smooth case; this was evident at groove locations 120° and 150°. The vorticity patterns for the grooves located on the front side showed large irregularities in magnitude between the anticlockwise and the clockwise vortices with the groove side vortices being of larger magnitudes, and for the wake side, the irregularities were negligible. The coefficient of pressure and separation angles were also investigated. The CP vs θ plots showed discontinuity at groove locations with abrupt variations at the front face of the cylinder; for the wake side grooves, these discontinuities were low and almost coincided with the CP vs θ plots of the smooth cylinder. The grooves located at 90° showed a delay in separation and at 60° the boundary layer tends to detach earlier.

Persistent reshaping of cohesive sediment towards stable flocs by turbulence

Cohesive sediment forms flocs of various sizes and structures in the natural turbulent environment. Understanding flocculation is critical in accurately predicting sediment transport and biogeochemical cycles. In addition to aggregation and breakup, turbulence also reshapes flocs toward more stable structures. An Eulerian–Lagrangian framework has been implemented to investigate the effect of turbulence on flocculation by capturing the time-evolution of individual flocs. We have identified two floc reshaping mechanisms, namely breakage-regrowth and restructuring by hydrodynamic drag. Surface erosion is found to be the primary breakup mechanism for strong flocs, while fragile flocs tend to split into fragments of similar sizes. Aggregation of flocs of sizes comparable to or greater than the Kolmogorov scale is modulated by turbulence with lower aggregation efficiency. Our findings highlight the limiting effects of turbulence on both floc size and structure.

Magneto-thermal convection in partially heated novel cavity with multiple heaters at bottom wall: A numerical solution

It is well consensus that magneto-thermal convection claims various applications in thermal engineering like cancer treatment, drug delivery, and anti-vibration systems to mention just a few. Owing to such importance we explore the heat transfer in a magnetized thermal flow field in the novel cavity with convection mode. Three different heaters are varied at the bottom wall of the enclosure. At the inlet, fluid enters the cavity having a parabolic velocity profile and exits at the right side with the Neumann condition. The upper wall, lower wall, and boundary of the obstacle are kept at no-slip condition. Adiabatic condition is imposed at the lower wall by omitting ribs while all other walls are taken at cold temperature. The mathematical formulations are tackled using the finite element method. Various values of Reynolds and Hartmann numbers are used in this study and observations are concluded by using graphical and tabular outcomes. The numerical findings are displayed as velocity plots, pressure plots, and temperature plots by regulating the Reynolds and Hartmann numbers. For three different installations of heaters, we evaluated the hydrodynamic (drag and lift) forces. These forces are expressed as lift and drag coefficients with the help of line integration around the heated obstacle at different refinement levels. We have noticed that with the occurrence of a magnetic field, the values of lift and drag coefficients are higher for a rectangular heater in comparison with triangular and semi-circular heaters.

Prediction model for multidirectional vortex-induced vibrations of catenary riser in convex/concave and perpendicular flows

This study presents an advanced numerical prediction model based on nonlinear wake oscillators for the investigation of multidirectional vortex-induced vibration (VIV) responses of a long catenary riser depending on the structural curved configuration versus the incoming flow direction. By considering a uniform free-stream flow aligned with the initial curvature plane of the catenary riser in a convex or concave shape, the normal flow velocity component is nonlinearly sheared owing to the spanwise variation of inclination angles. This is different from the perpendicular flow case in which the normal flow velocity is spatially constant. To capture the influence of flow direction on the three-dimensionally coupled cross-flow and in-line VIV, distributed wake oscillators are introduced and applied to simulate the fluctuating hydrodynamic lift and drag forces that account for the important effects of cylinder inclination, variable vortex excitation frequencies, global–local​ displacement relationships, and relative flow-cylinder velocities. The amplified mean drag force and the axial force depending on the tangential flow velocity are also considered. These empirical hydrodynamic effects are nonlinearly coupled with the equations of riser three-dimensional motion, and the overall governing equations are numerically solved to assess the multimode, multi-frequency and multi-degree-of-freedom responses. Validation of the model is carried out for VIV of flexible straight and curved cylinders based on experimental results in the literature. Parametric investigations are performed by varying the incoming flow velocities in perpendicular, convex and concave configurations for a long catenary riser with a low mass-damping ratio. In-plane (horizontal and vertical) and out-of-plane VIV features are presented and discussed in terms of space–time varying amplitudes, drag-amplified shape reconfigurations, oscillation frequencies, lock-in occurrences, dual resonances, orbital motion trajectories, fluid–structure energy transfer, and multimodal contributions. Overall prediction results highlight the influence of the cylinder geometric configuration versus the incoming flow orientation on multidirectional VIV characteristics that should be recognised and incorporated into practical analysis tools.

Impact of Limited Degree of Freedom Drag Coefficients on a Floating Offshore Wind Turbine Simulation

The worldwide effort to design and commission floating offshore wind turbines (FOWT) is motivating the need for reliable numerical models that adequately represent their physical behavior under realistic sea states. However, properly representing the hydrodynamic quadratic damping for FOWT remains uncertain, because of its dependency on the choice of drag coefficients (dimensionless or not). It is hypothesized that the limited degree of freedom (DoF) drag coefficient formulation that uses only translational drag coefficients causes mischaracterization of the rotational DoF drag, leading to underestimation of FOWT global loads, such as tower base fore-aft shear. To address these hydrodynamic modeling uncertainties, different quadratic drag models implemented in the open-source mid-fidelity simulation tool, OpenFAST, were investigated and compared with the experimental data from the Offshore Code Comparison Collaboration, Continued, with Correlation (OC5) project. The tower base fore-aft shear and up-wave mooring line tension were compared under an irregular wave loading condition to demonstrate the effects of the different damping models. Two types of hydrodynamic quadratic drag formulations were considered: (1) member-based dimensionless drag coefficients applied only at the translational DoF (namely limited-DoF drag model) and (2) quadratic drag matrix model (in dimensional form). Based on the results, the former consistently underestimated the 95th percentile peak loads and spectral responses when compared to the OC5 experimental data. In contrast, the drag matrix models reduced errors in estimates of the tower base shear peak load by 7–10% compared to the limited-DoF drag model. The underestimation in the tower base fore-aft shear was thus inferred be related to mischaracterization of the rotational pitch drag and the heave motion/drag by the limited-DoF model.

A versatile and high-throughput flow-cell system combined with fluorescence imaging for simultaneous single-molecule force measurement and visualization.

A flow-cell offers many advantages for single-molecule studies. But, its merit as a quantitative single-molecule tool has long been underestimated. In this work, we developed a gas-pumped fully calibrated flow-cell system combined with fluorescence imaging for simultaneous single-molecule force measurement and visualization. Such a flow-cell system has considered the hydrodynamic drags on biomolecules and hence can apply and measure force up to more than 100 pN in sub-pN precision with an ultra-high force stability (force drift <0.01 pN in 10 minutes) and tuning accuracy (∼0.04 pN). Meanwhile, it also allows acquiring force signals and fluorescence images at the same time, parallelly tracking hundreds of protein motors in real time as well as monitoring the conformational changes of biomolecules under a well-controlled force, as demonstrated by a series of single-molecule experiments in this work, including the studies of DNA overstretching dynamics, transcription under force and DNA folding/unfolding dynamics. Interesting findings, such as the very tight association of single-stranded binding (SSB) proteins with ssDNA and the reversed transcription, have also been made. These results together lay down an essential foundation for a flow-cell to be used as a versatile, quantitative and high-throughput tool for single-molecule manipulation and visualization.

Velocity distribution and hydrodynamic drag in turbulent flow

This work aims to study the vertical velocity distribution in the near-wall layer of a pipe, channel, and boundary layer of a flat plate because these issues are of great practical and theoretical importance. Until now, engineering calculations of turbulent flows have been based on empirical formulas derived in the last century. The theory of turbulent fluid motion has not been completed, and the issues of velocity distribution and hydraulic resistance remain open for further study. It is known that velocity distribution in the flow is intricately linked to hydraulic resistance. Therefore, the study’s objectives also include determining the position of the point of maximum turbulent tangential stresses and comparing the change in tangential stresses with the logarithmic velocity profile. Based on calculation and analytical methods, we have researched the distribution of the turbulent component of the tangential stress along the depth of the flow. Derived an expression determining the position of the maximum point of the turbulent component of the tangential stress for smooth tubes. The contribution of the viscous component of the tangential stress at different points along the flow depth has been evaluated. The calculation results determining the position of the maximum point of the turbulent component of the tangential stress were compared with experimental data on velocity distribution in the flow. With the decrease of the hydraulic resistance coefficient, the point of maximum turbulent tangential stresses shifts towards the solid flow boundary. Based on the results of comparing the maximum turbulent tangential stresses with the total tangential stress, we can conclude that the contribution of the viscous component of the tangential stress to the total amount of friction and its influence on velocity distribution is significant. The angular coefficient of the velocity profile for the flow core is determined.

A Sea Surface–Based Drag Model for Large-Eddy Simulation of Wind–Wave Interaction

Abstract Monin–Obukhov similarity theory (MOST) is a well-tested approach for specifying the fluxes when the roughness surfaces are homogeneous. For flow over waves (inhomogeneous surfaces), phase-averaged roughness length scales are often prescribed through models based on the wave characteristics and the wind speed. However, such approaches lack generalizability over different wave ages and steepnesses due to the reliance on model coefficients tuned to specific datasets. In this paper, a sea surface–based hydrodynamic drag model applicable to moving surfaces is developed to model the pressure-based surface drag felt by the wind due to the waves. The model is based on the surface gradient approach of Anderson and Meneveau applicable to stationary obstacles and extended here to the wind–wave problem. The wave drag model proposed specifies the hydrodynamic force based on the incoming momentum flux, wave phase speed, and the surface frontal area. The drag coefficient associated with the wind–wave momentum exchange is determined based on the wave steepness. The wave drag model is used to simulate turbulent airflow above a monochromatic wave train with different wave ages and wave steepnesses. The mean velocity profiles and model form stresses are validated with available laboratory-scale experimental data and show good agreement across a wide range of wave steepnesses and wave ages. The drag force is correlated with the wave surface gradient and out-of-phase with the wave height distribution by a factor of π/2 for the sinusoidal wave train considered. These results demonstrate that the current approach is sufficiently general over a wide parameter space compared to wave phase-averaged models with a minimal increase in computational cost. Significance Statement Understanding the physics of wind waves plays an important role in the context of numerous geophysical and engineering applications. A drag-based model is developed that characterizes the effect of the sea surface waves on the wind above. The model is validated with existing experimental datasets and is shown to be effective in predicting the average wind velocity and stress over waves with varied steepnesses and phase speeds. The ease of implementation and low computational cost of the model make it useful for studying turbulent atmospheric-scale flows over the sea surface important in offshore wind energy research as well as for modeling air–sea fluxes of momentum, heat, and mass.

Study on high-speed water entry of the projectile passing through an ice hole in a low-temperature environment based on a modified thermodynamic cavitation model

It is a complicated problem to study high-speed water entry of a projectile passing through an ice hole in a polar environment. This involves the constraint of the ice hole on the free surface and low-temperature cavitation during the water entry. In this paper, a numerical method involving a modified thermodynamic cavitation model is introduced to study the water entry process. The numerical method is validated by comparing the numerical results of cavity evolution with the experimental data. The cavity dynamics of the projectile passing through the overwater ice hole at high speed and different ambient temperatures are studied. The cavity evolution, flow field, and motion state of the projectile are analyzed. The results show that a nested cavity forms when the projectile passes through the ice hole at high speed. The drop in temperature accelerates the surface closure and deep pinch-off. The effect of the temperature on cavity evolution weakens as the Froude number (Fr) increases. Moreover, at high Fr, the temperature alters the appearance of the ripple on the cavity surface and the growth trend of the cavity size. The drop in temperature reduces the content of the vapor in the cavity and changes the flow characteristics. At a low temperature, the hydrodynamic drag of the projectile passing through the ice hole increases, and the pressure distribution on the surface of the projectile is different.

Electric field gradient focusing with electro-osmotic flow to reduce analyte dispersion: Concept and numerical investigation

In proteomics, the need to precisely examine the protein compounds of small samples, requires sensitive analytical methods which can separate and enrich compounds with high precision. Current techniques require a minimal analysis time to obtain satisfactory compound separation where longer analysis time means better separation of compounds. But, molecular diffusion will create broadening of the separated compound bands over time, increasing the peak width, and thus reducing the resolution and the enrichment.Electric field gradient focusing (EFGF) is a separation technique, in which proteins are simultaneously separated and enriched by balancing a gradient electrostatic force with a constant hydrodynamic drag force. Because of this balance, analytes are continuously pushed back to their focusing point, limiting the time-dependent peak broadening due to molecular diffusion. Current EFGF techniques are however still suffering from peak broadening because of flow-profile inhomogeneities.In this paper, we propose to use AC electro-osmotic flow (AC EOF) to create a homogeneous flow in EFGF. The interference between the electric field gradient and the AC EOF was thoroughly analysed and the concept was validated using numerical simulations. The results show that a plug flow is obtained on top of a small, distorted boundary layer. While applying different DC electric fields in the electrolyte, a constant flow velocity can be obtained by including a DC offset to the electrodes generating the AC EOF. The plug flow is then maintained over the whole separation channel length, while an electric field gradient is applied. This way, the flow-induced contribution to peak broadening can be minimized in EFGF devices. By modelling the separation of green fluorescent protein (GFP) and R-Phycoerythrin (R-PE), it was shown that the peak width of separated compounds can be reduced and that the separation resolution can be improved, compared to current EFGF methods.