Hydrodynamic Part Research Articles

Optimal decay of the Boltzmann equation

The Boltzmann equation is a typical example of partially dissipative equations, where the linearized collision operator is positive definite with respect to the microscopic part and the dissipation of the hydrodynamic part is discovered from the coupling structure between the transport operator and the linearized collision operator. Guo and Wang (Comm. Partial Differential Equations, 37, 2012) developed a general energy method for proving the optimal time decay rates of the solution to such type of equations in the whole space; however, the decay rate of the highest order spatial derivatives of the solution is not optimal. In this paper, by incorporating the high‐low frequency decomposition in the energy estimates, both linearly and nonlinearly, we prove the optimal decay rates of any high order spatial derivatives of the low frequency part of the solution to the Boltzmann equation and the almost exponential decay rate of the high frequency part, which imply in particular the optimal decay rate of the highest order spatial derivatives of the solution. Moreover, the velocity‐weighted assumption of the initial data required in Guo and Wang (Comm. Partial Differential Equations, 37, 2012) is removed by capturing the time‐weighted dissipation estimates via the time‐weighted energy method. The method can be applied to the compressible Navier–Stokes equations and many partially dissipative equations in kinetic theory and fluid dynamics.

Theoretical Perspectives on Viscous Nature of Strongly Interacting Systems

Matter prevailing during the early stages of the Universe or under extreme conditions in high-energy heavy-ion experiments supposedly possesses a rich phase structure. During the evolution of such a system, the complicated pictures of transitions among various phases are studied as part of hydrodynamics. This system, on most occasions, is considered to be non-viscous. However, various theoretical studies reveal the importance of incorporating viscous effects into the analysis. Here, the paper discusses the behavioral patterns of transport coefficients with varying temperatures and chemical potentials to obtain a qualitative, if not quantitative, picture of the same. Discussions are also shared regarding their impacts on such an exotic system for different energies, as explored in the experimental domain. This theoretical analysis, made using the structure of the Polyakov–Nambu–Jona-Lasinio (PNJL) model with a 2+1-flavor quark–antiquark system reveals important aspects of the inclusion of viscous effects in the hydrodynamic studies of QGP.

Hydrodynamic Study of a Hybrid Electro-Flotation Column

Bubble columns are used in the mining industry for mineral recovery but are also widely utilized in the chemical and petrochemical industry. The hydrodynamic characteristics of their performance is a field of interest with a number of points, which are nonetheless poorly understood, and a considerable amount of methods have aimed to shed light on the flow regimes that prevail in the columns. The study of the hydrodynamic part of a flotation process should consider characteristics such as air flow, volumetric gas fraction, flow field, and bubble size, along with the mechanical and design factors and pulp properties. The present work aims to elucidate the characteristics of the gas phase of a hybrid flotation system. For this purpose, a hybrid flotation column was designed and constructed and the bubbles size distributions at different radial positions in the flotation column were computed by analyzing high resolution digital images. A patented electrical impedance technique was employed to instantaneously measure the local volumetric gas fraction. Flow dispersion in the column was studied by residence time distributions using conductivity tracers. The experimental results are discussed to comprehend the variation in the gas fraction in the column. In particular, the study showed that the size of the bubbles changed from the center to the walls of the column, and this was observed both radically and vertically. Moreover, the size of the bubbles affected the volume fractions, and no coalescence of the bubbles was observed. Finally, the dispersion of the tracer in the working solution was distributed uniformly in the volume of the column, with a time difference for the four positions of the column.

Artificial compressibility method for high-pressure transcritical fluids at low Mach numbers

Supercritical fluids possess unique properties that makes them relevant in various scientific and engineering applications. However, the experimental investigation of these fluids is challenging due to the high pressures involved and their complex thermophysical behavior. To overcome these limitations, computational researchers employ scale-resolving methods, such as direct numerical simulation and large-eddy simulation to study them. Nonetheless, these methods require substantial computational resources, especially in the case of low-Mach-number regimes due to the disparity between acoustic and hydrodynamic/thermal time scales. This work, therefore, addresses this problem by extending the artificial compressibility method to high-pressure transcritical fluids. This method is based on decoupling the thermodynamic and hydrodynamic parts of the pressure field, such that the acoustic time scales can be externally modified without severely impacting the flow physics of the problem. In addition, the method proposed has two key characteristics: (i) the splitting method presents low computational complexity, and (ii) an automatic strategy for selecting the speedup factor of the approach is introduced. The effectiveness of the resulting methodology is demonstrated through comprehensive numerical tests of increasing complexity, showcasing its ability to accurately simulate a wide range of high-pressure transcritical flows including turbulence. The results obtained indicate that the approach proposed can readily lead to computational speedups larger than 10× without significantly compromising the accuracy of the numerical solutions.

Development of technology for ingots production using electroslag remelting at direct current with consumable electrode rotation

The paper describes the problem of increasing the productivity of electroslag remelting (ESR) furnaces. The remelting technology on direct current is proposed as the most effective method. The description of the technology touches upon positive and negative effects affecting the specific productivity of smelting, energy consumption, and quality of the obtained ingots in terms of their physical and mechanical properties and chemical purity. The authors proposed the electroslag remelting method with rotation of the consumable electrode as a new technology, and realized a brief comparison with the external magnetic field application technology. The schemes that clearly demonstrate the principle of controlling the crystallization front shape and the thermal center localization in the slag bath are considered. A stationary numerical model for the slag bath of the operating semi-industrial furnace ESR A-550 on direct current with polarity reversing ability was developed. The mathematical apparatus consisting of electrothermal, hydrodynamic and convective parts was constructed. The authors designed the mesh domain for a slag bath located between the consumable electrode and the water-cooled crystallizer with diameters of 60 and 90 mm, respectively. The height of the sub-electrode zone is 10 mm. The current limit is 800 A and the voltage is 46 V. Numerical fields of current density and temperature distribution in the slag bath volume are obtained. The range of temperature values is located in the range from 1400 to 2200 °C at the peripheral and subelectrode zones of the slag bath, respectively. The scheme of the ESR furnace modernization is given in terms of mechanical part automation and transferring to direct current.

Nonlinear dynamics of novel flight-style autonomous underwater vehicle with bow wings, Part I: ASE and CFD based estimations of hydrodynamic coefficients, Part II: Nonlinear dynamic modeling and experimental validations

Accurate dynamic modeling is essential for precise prediction of six degrees-of-freedom (6-DOF) motion and model-based controller design of an autonomous underwater vehicle (AUV). The accuracy of dynamic model of an AUV largely depends upon the precise estimation of hydrodynamic coefficients. Accordingly, to establish the dynamic model based on ASE-estimated hydrodynamic coefficients of the novel flight-style AUV and experimental validations, the study is presented in two parts (Part I: ASE and CFD based estimations of hydrodynamic coefficients and Part II: Nonlinear dynamic modeling and experimental validations).Part I: In this part complete set of nonlinear hydrodynamic coefficients including, added mass, drag, and lift forces and moment coefficients are estimated using ASE technique, which is specifically developed to accurately comprehend the novel AUV design including, AUV hull, fixed wings, control fins, and appendages. Additionally, an improved ASE approach is also proposed to estimate cross flow drag force coefficients. In proposed improved ASE technique, (Cdc) in mathematical formulation is taken from the experimental results of 3D flow past over circular cylinder instead of 2D, as followed previously to estimate the nonlinear cross-flow drag force and moment coefficients (Yvv,Zww,Mww,Nvv,Yrr,Zqq,Mqq&Nrr). The proposed ASE technique is verified and validated in two stages: first, by comparing the ASE-estimated results with CFD-based estimations, and second, by investigating the 6-DOF motion response of the AUV. When compared ASE-estimations with the CFD results for the cross-flow drag force and moment coefficients, the proposed ASE technique has shown a significant improvement (approximately 20%) over the previously employed ASE method. The ASE-estimated results are validated through 6-DOF motion response of AUV during free-running underwater experiments, provided in ‘Part II’. Overall, the proposed ASE technique is considered more effective, direct, and less costly in terms of time and computational efforts, compared to CFD-based or experimental-based estimations of hydrodynamic coefficients of AUVs, particularly torpedo-shaped AUVs.Part II: This part presents a nonlinear dynamic model for a newly designed torpedo-shaped flight-style AUV having complex bow and stern fixed wings and control fins configuration. The model includes precise mathematical formulations to accurately represent the physics of the AUV and underwater environment in terms of hydrodynamic derivatives such as added mass, drag, and lift forces and moment coefficients. These coefficients have been estimated using an ASE method provided in ‘Part I’. The 6-DOF motion response of the AUV has been simulated in both horizontal and vertical planes which includes, zigzag yaw, circle, zigzag pitch, and spiral maneuvers. The lift generated by the bow and stern control fins has been investigated both separately and collectively, especially during complex spiral ascending maneuvers. Moreover, improved ASE technique for cross flow drag coefficients has also been validated through 6-DOF free-running underwater experiments of AUV and insights on impact of cross flow drag coefficients on 6-DOF motion response of AUV has also been provided. Overall, the comparison between the simulated AUV motion and free-running underwater experiments demonstrated consistency, thereby validating the accuracy of the nonlinear dynamic modeling, ASE-based hydrodynamic coefficient predictions, and effectiveness of the newly designed flight-style AUV for underwater operations.

Similarity solutions of heat transfer in shear flow over an otherwise still fluid

Thermal energy and momentum transport in two-fluid systems are investigated. The hydrodynamic part of the problem was considered by Wang [“The boundary layers due to shear flow over a still fluid,” Phys. Fluids A 4, 1304–1306 (1992)] and Andersson and Mukhopadhyay [“Boundary layers due to shear flow over a still fluid: A direct integration approach,” Appl. Math. Comput. 242, 856–862 (2014)], whereas the accompanying heat transfer analysis is new and fills a gap in the literature. Momentum and thermal boundary layers form on both sides of the planar interface between a shear-driven upper fluid and an underlying still fluid. Similarity transformations reduce the governing partial differential equations to sets of ordinary differential equations for each fluid, coupled by boundary conditions at the interface. The thermal part of the transformed two-fluid problem depends explicitly on the ratios between the kinematic viscosities, the thermal conductivities, the Prandtl numbers, and the temperatures of the lower and upper fluids. Moreover, an implicit dependence on the density ratio appears due to the fluid velocities. Similarity solutions obtained by means of a direct integration approach are presented for six different two-fluid systems. The computed results show that the temperature and velocity fields in the upper and lower fluid depend crucially on the mechanical and thermophysical properties of the two fluids, as does the heat flux through the interface between the two immiscible fluids.

Fully coupled aero-hydrodynamic modelling of floating offshore wind turbines in nonlinear waves using a direct time-domain approach

In standard operating conditions, a floating offshore wind turbine (FOWT) suffers from the combined action of nonlinear waves and wind. It is important to explore the effect of higher-order hydrodynamic loads induced by the nonlinear waves on its motion response. In this work, a fully coupled aero-hydrodynamic analysis method for FOWT is developed. The hydrodynamic part is based on the nonlinear potential flow theory and the perturbation approach, using a higher-order boundary element method in the time domain. Blade element momentum theory is applied to evaluate the aerodynamic load on the turbine rotor. The mooring system is modelled by the catenary theory. The developed method is verified against the published data of the NREL's 5-MW baseline wind turbine supported by the DeepCwind semi-submersible platform. The verifications are conducted stepwise in the following ways, including hydrodynamic wave excitation load, free-decay response, the load-displacement relationship of the mooring line, the steady-state response of the wind turbine, and fully coupled aero-hydrodynamic interaction. It is found that the nonlinear effect mainly influences the surge motion. The coupled configuration has little effect on the linear wave force and platform displacement but notably impacts the nonlinear wave force and displacement. The FOWT motion is found to be critical in changing the wave field, the maximum wave elevation position around the platform, and the nonlinear wave force acting on the floating platform. The results illustrate that the traditional indirect time-domain method using the Quadratic Transfer Function (QTF) based on assumed response cannot appropriately evaluate the nonlinear wave force of a FOWT in coupled motions. The results also reveal that nonlinear wave hydrodynamics is necessary to understand the motion response of a fully coupled FOWT.

The influence of the configurations of multiple-impeller on canrenone bioconversion using resting cells of Aspergillus ochraceus

Abstract 11 α-Hydroxycanrenone is a key intermediate in the synthesis of eplernone which is a drug that protects the cardiovascular system. It can be obtained by microbial transformation of canrenone using Aspergillus ochraceus. The impeller configuration has a great impact on the microbial transformation efficiency. In this study, three kinds of multiple-impeller including six-blade Rushton turbine (lower) and six-blade Rushton turbine (upper) (RT + RT), six-blade Rushton turbine (lower) and six-arrow blade turbine (upper) (RT + ABT), six-blade Rushton turbine impeller (lower) and six-blade Chemineer CD6 impeller (upper) (RT + CD6) were employed to carry out the microbial conversion process, which was investigated by experiments and computational fluid dynamic (CFD) simulations. The CFD simulation was performed only for the hydrodynamic part of the bioreactor in this article. The results showed that RT + CD6 gave better conversion ratio compared to the other two multiple impellers. It had higher axial flow and better air volume fraction distribution which was benefit for the biotransformation process. A certain amount of cell content should be guaranteed in order to obtain a good substrate conversion (45 % approximately). The final conversion ratio of canrenone was proportional to the content of mycelium at the late stage of conversion, while the content of mycelium at the early stage had a subtle effect. Besides, A. ochraceus resting cells could tolerate the maximum and average shear strain rate in the order of 2598 s−1 and 52 s−1, respectively. The research results provided a guide for the selection of impeller for the biotransformation of canrenone in biopharmaceutical industry.

Water Quality Analysis of a Tropical Reservoir Based on Temperature and Dissolved Oxygen Modeling by CE-QUAL-W2

Water quality impacts on water bodies such as reservoirs are strongly influenced by the hydrodynamics of the system. Although multiple models might be applied, they are limited by the simplification of the variables. In this study, a two-dimensional public domain model, CE-QUAL-W2, was adapted to test whether it would generate an accurate hydrodynamic simulation of the URRÁ Reservoir in Córdoba, Colombia, to understand water quality. The variables to be modeled were temperature and dissolved oxygen due to their importance in ecological terms. Thus, trial and error techniques were used to calibrate and validate the model, varying different parameters such as the wind shelter coefficient (WSC). Although the model accurately predicted the hydrodynamic part by having daily flow information, significant modifications to the eddy diffusivity coefficient were required to simulate acceptable longitudinal currents. This research shows that the CE-QUAL-W2 model fits adequately to tropical lentic systems. However, it is recommended that, for future studies, the modeling be adjusted using hourly data, especially in areas where inflow and boundary conditions are unstable.

Near wake hydrodynamics and structural design of a single foil cycloidal rotor in regular waves

We present a hydrodynamic and structural model to design a single foil wave cycloidal rotor in regular waves. The hydrodynamic part considers potential flow and represents the foil as a point vortex. Unsteady effects are accounted for through Theodorsen’s function. The structural part utilises beam theory to compute the bending moments and stresses on the foil of the cyclorotor. The validity of the hydrodynamic model is explored with the aid of CFD, and the CFD results are bench marked versus experimental measurements. Results show that the hydrodynamic model estimates the mean radial loading on the foil within 20%–25% in attached flow conditions, whilst it is accurate to predict the mean tangential loading only when operating close to stall, at maximum lift conditions. Because the optimal structural operation of the rotor is in attached flow conditions, and close to stall, we utilise the coupled model to design a rotor that operates optimally for a range of different sea conditions. We find that with careful dimensioning of the radius and span, power extraction in regular waves can be optimised, whilst the structural penalty is kept constant at the allowable stress level.

Heat treatment effect of 65G and 60C2A steels on strength characteristics of the hydrodynamic oscillator built-in drill head

The ways of improving the physical and mechanical properties of the components of a hydromonitor drill head with an integrated generator of hydrodynamic oscillations are reviewed. On the basis of the results of this consideration, an improvement of the working body of the HDD technique is proposed. On the example of 60S2A and 65G steels, the influence of different modes of heat treatment of the improved drilling head on the ultimate strength, relative lengthening, and surface hardness of the detail petal, which is the basic loaded element of the generator of hydrodynamic vibrations, is examined. The analysis of physical and mechanical properties has shown a significant increase of parameters influencing the increase of rigidity properties of the investigated hydrodynamic oscillator part, which allows us to make a conclusion about the effectiveness of its application for the increase of drill bit operational life. An experimental and analytical method was carried out to describe the increase of physical-mechanical properties of the part - petal, which is the main loaded element of the generator of hydrodynamic oscillations. Increase of durability of rock destruction tool for pilot hole laying by increasing of physical-mechanical properties of used material for individual parts of hydrodynamic oscillator.

Temperature and net baryochemical potential dependence of η/s in a hybrid approach

In this work, the qualitative impact of the net baryochemical potential dependence of the shear viscosity to entropy density ratio $\eta/s$ in hydrodynamical simulations is studied. The effect of a predicted non-constant $\eta/s$($\mu_B$) is largely unexplored in hydrodynamic simulations. Previous studies focus only on a temperature dependence or even only a constant effective shear viscosity. This work addresses this issue by studying qualitatively the effect of a generalized $\eta/s$($T,\mu_B$) in the hybrid approach SMASH-vHLLE, composed of the hadronic transport approach SMASH and the (3+1)d viscous hydrodynamic code vHLLE. In order to reduce the bias of the result on the equation of state used in the hydrodynamic part of the model, $\eta/s$ is parameterized directly in the energy density and net baryon number density. The parameterization takes into account the constraints of matching to the transport coefficients in the hadronic phase, as well as pQCD results. This work compares the impact of the density dependence for different system sizes and energies and compares the observables with experimental results in the RHIC - BES region $\sqrt{s_{NN}}$ =7.7 - 39.0 GeV, as the effect of this generalization is especially relevant for intermediate collision energies, for which the system is in equilibrium for a relevant amount of time, but the net baryochemical potential does not vanish. It is shown that the effect of an explicit net baryon number dependence on the elliptic flow is negligible and only relevant in the early stages of the collision. Additionally, we find that the proposed parameterization could be a good proxy for the shear viscosity in the non-equilibrium hadronic transport stage.

A numerical method to compute flexible vertical responses of containerships in regular waves

In this paper, a series of simulations of hydroelastic problems of containerships are conducted by a nonlinear 3D panel method which is based on the generalized Taylor Expansion Boundary Element Method (TEBEM). In the structure part, the Transfer Matrix Method is selected to perform a modal analysis which provides key parameters of hydroelastic calculation. In the hydrodynamic part, the nonlinearities arising from the variations of instantaneous wetted surface area are considered in the solutions of hydrostatic restoring forces as well as 1st order incident wave forces. Meanwhile, an extended Modified Logvinovich Model (MLM) is presented to predict the slamming forces due to the large-amplitude incident waves. The numerical predictions of the hydroelastic responses of a 6750-TEU containership and S175 in regular waves are presented. The effects of wave steepness and sailing speed as well as the variation characteristics of load components against with wave direction are studied. The numerical and experimental results are in acceptable agreement which proves the accuracy of the proposed method.

Mathematical modelling of salt ion transfer in the three-dimensional desalting channel of an electrodialysis apparatus

A new 3D model of 1:1 salt ion transfer in the desalting channel of an electrodialysis apparatus is presented and investigated in this paper. For the first time a three-dimensional mathematical model of salt ion transfer in the desalting channel taking into account the electroconvection based on the system of Nernst – Planck, Poisson and Navier – Stokes equations with the electric force and the natural boundary conditions is proposed. To solve the boundary value problem, the finite element method is used in the cross-platform numerical analysis software COMSOL Multiphysics in combination with the method of successive approximations, when the electrochemical and hydrodynamic parts of the problem are solved one by one on the current layer. In turn, the electrochemical and hydrodynamic parts of the problem are solved by Newton’s method. As a result of numerical analysis, the fundamental regularities of salt ion transfer in a three-dimensional channel, the emergence and development of electroconvective vortices, including the discovery of new three-dimensional spiral forms of salt ions, are established for the first time. It is shown that electroconvective vortices exist in the form of clusters, within which vortex bifurcations can occur. Thus, the currently existing simplified view of the structure of electroconvective vortices is clarified and developed.

Combined experimental and simulative approach for friction loss optimization of DLC coated piston rings

Piston rings cause significant friction losses within internal combustion engines. Especially the first compression ring, which is pressed onto the liner by high cylinder pressure, contributes significantly to the total friction loss of the piston assembly. The tribological behavior of the oil scraper ring is mainly related to the pretensioning force and can lead to high losses even at low and idle speed. Due to this, there is always a markable risk of wear for the contact surfaces of the piston rings and the cylinder. “Diamond-like carbon” coatings on the surface of the piston rings can prevent wear and are able to reduce friction in the ring-liner-contact. The purpose of this work was to investigate the tribological benefit of this coating-system on the compression and oil scraper ring. Experimental studies were carried out on a fired single-cylinder engine using the Indicated Instantaneous Mean Effective Pressure-method (IIMEP) for the crank angle-resolved detection of the piston assembly’s friction force. To be able to determine the component-related fractions of the friction loss and to quantify the hydrodynamic and asperity related parts locally and time dependent, an EHD/MBS model of the engine was created in AVL EXCITE and a simulative investigation was performed. This simulation was validated by the experimental work and provided detailed information about the individual contact conditions and gap height of each tribological contact of the piston group. The combined approach of measurement and simulation enabled the prediction of tribological aspects and performance in parameter studies on a virtual engine test bed.

Estimating the equilibrium scour depth around two side-by-side piers with different spacing ratios in live-bed conditions

The aim of this research was to numerically investigate the flow behaviour and evolution of the local scour around a group of two side-by-side piers in live-bed conditions. A coupled hydro-morphodynamic model was developed in OpenFOAM®. The hydrodynamic part of the model solved the unsteady Reynolds Averaged Navier-Stokes equations. The morphodynamic part of the model entailed solving both bedload and suspended load sediment transport. The model validation was performed for the available experimental data in the literature. The modelling for the pier groups was carried out with three different spacing ratios of G/D = 1, 2, and 3, where G represents the distance between the piers and D is the pier diameter. The results presented detailed information regarding the flow field and scour hole progression adjacent to two side-by-side piers. The dimensionless equilibrium scour hole depths of 1.74, 1.38 and 1.29 were predicted for the pier groups with G/D = 1, 2, and 3, respectively. The results showed an inverse correlation between the spacing ratio and the scour hole depth adjacent to the piers. The results were generalised, and an equation was obtained for the prediction of the equilibrium scour hole depth as a function of the spacing ratio.

Equilibrium model of titanium laser induced plasma in air with reverse deposition of titanium oxides

A chemical-hydrodynamic model of laser induced plasma is developed to study a process of deposition of titanium oxides from titanium laser induced plasma to the titanium target surface. The model is relevant to texturing and coating of titanium bone implants that is done by scanning the ablation laser across implant surfaces. Such the procedure improves the biocompatibility and durability of the implants. The model considers plasma chemical reactions, formation of condensed species inside the plasma plume, and deposition and accumulation of these species on the ablation surface. A chemical part of the model is based on minimization of Gibbs free energy of the chemical system; it is used to calculate the chemical composition of the plasma. A hydrodynamic part uses the 2D fluid-dynamic equations that model a 3D axisymmetric plasma plume and assumes the mass and energy exchange between the plasma and the surface. The initial parameters for the model are inferred from experiment. The model shows that condensed titanium oxides, mostly TiO2, form in a peripheral plasma zone and gradually adhere to the surface during the plasma plume evolution. The model predicts the major component and thickness of the deposit and can be applied for the optimization of experiments aimed at surface modification.

TEBEM for springing responses of a container ship with forward speed and nonlinear effects in time domain

In this paper, springing responses of a container ship with forward speed in regular waves are studied by a time-domain TEBEM which is generalized to elastic modes. TEBEM is used principally to solve the steady and unsteady flow and the infinity radiation condition is achieved by the Damping Zone Method. In the structure part, the Transfer Matrix Method is used to get the generalized structural mass, damping, stiffness and principal mode of displacement and rotation of vertical oscillation modes which will participate in the subsequent hydrodynamic calculation. In the hydrodynamic part, the fourth-order Runge–Kutta method is used to solve the hydroelasticity equations. The effects of forward speed and 2nd order wave forces generated by 1st order velocity potential in head sea are analyzed. Meanwhile, the variation of different load components against wave direction for corresponding different stations and contribution of different part of ship for different load components in head sea are studied. Compared with the experimental results, the motions and loads of a 6750-TEU container ship with different forward speeds predicted by TEBEM show an acceptable agreement.

Particle/wall electroviscous effects at the micron scale: comparison between experiments, analytical and numerical models

We report a experimental study of the motion of 1 μm single particles interacting with functionalized walls at low and moderate ionic strengths conditions. The 3D particle’s trajectories were obtained by analyzing the diffracted particle images (point spread function). The studied particle/wall systems include negatively charged particles interacting with bare glass, glass covered with polyelectrolytes and glass covered with a lipid monolayer. In the low salt regime (pure water) we observed a retardation effect of the short-time diffusion coefficients when the particle interacts with a negatively charged wall; this effect is more severe in the perpendicular than in the lateral component. The decrease of the diffusion as a function of the particle–wall distance h was similar regardless the origin of the negative charge at the wall. When surface charge was screened or salt was added to the medium (10 mM), the diffusivity curves recover the classical hydrodynamic behavior. Electroviscous theory based on the thin electrical double layer (EDL) approximation reproduces the experimental data except for small h. On the other hand, 2D numerical solutions of the electrokinetic equations showed good qualitative agreement with experiments. The numerical model also showed that the hydrodynamic and Maxwellian part of the electroviscous total drag tend to zero as h → 0 and how this is linked with the merging of both EDL’s at close proximity.