Influence Of Wall Effects Research Articles

The influence of wall effects on self-propelled performance of brown trout swimming

When benthic fish engage in predation, they often swim near the riverbank or close to hard rocks, where they are subjected to the combined effects of side and benthic walls. This study focuses on the brown trout and employs a three-dimensional numerical model to simulate the process of brown trout accelerating from a stationary state to a cruising state under the influence of wall effects. A self-developed subroutine algorithm is applied to solve the various hydrodynamic parameters of brown trout swimming. By varying the distance between the fish's center of gravity and the wall, this study explores the self-propelled performance and efficiency of fish swimming affected by the sidewall as well as the combined influence of the side and benthic walls. This study also reveals the hydrodynamic mechanism of wall effects that impact the performance of fish swimming in the body/caudal fin (BCF) mode. The results demonstrate that when the distance is less than 0.5 times the body length of the fish, swimming near the sidewall can enhance speed and thrust, but the swimming efficiency will reduce. Closer proximity to the benthic wall leads to increased power consumption and decreased efficiency, which is disadvantageous for fish swimming. The findings of this study reveal the unstable wall effects experienced by fish and offer insights for designing biomimetic underwater vehicles that leverage wall effects as well as for creating habitats that support fish swimming in the BCF mode.

Design of tandem wing layout of pneumatic cooperative lift train

Pneumatic lift train together is the concept of under the background of further accelerate the speed of high-speed train running speed, in order to under higher speed train the whole life cycle cost, the researchers put forward the concept of aerodynamic lift high-speed train together, break through the traditional high-speed train aerodynamic shape design concept, combined with high speed trains and aircraft their respective advantages, hope that through increasing train aerodynamic lift, It is hoped that by increasing the aerodynamic lift of the train, the overall energy saving and consumption reduction of the high-speed train can be achieved. In this paper, a high lift airfoil is optimized to improve the lift coefficient as much as possible while the drag coefficient is basically unchanged. The thickness and drag coefficient of the optimized airfoil are almost unchanged at the designed Angle of attack, and the lift coefficient is increased by 13%. A flat wing is designed based on the optimized airfoil, and the influence of wall effect and tandem wing layout on the lift drag coefficient of the wing is studied. A better aerodynamic lift cooperative train tandem wing layout is obtained, which can reduce the weight of a single train by 17%.

Influence of Wall Effect on the Measurement of Permeability in High Porosity Fibrous Porous Media

Influence of Wall Effect on the Measurement of Permeability in High Porosity Fibrous Porous Media

A Flow Resistance Model for Power Law Fluid in Granular Porous Media with Wall Effect

For an important engineering application background, a new resistance model for predicting power law fluid flowing through granular porous medium with homogeneous spherical particles was developed in this study. By considering the influence of wall effect, every parameter in the modified Ergun type equation hadits clear physical meaning. The analysis results showed that the influence of wall effect on the inertia item pressure loss was closely related to the Reynolds number and D/d. The correlations of critical Reynolds number, the modified permeability, the inertia coefficient and dimensionless equivalent viscosity ratio for power law fluid were derived and described in detail.

Frictional pressure drop characteristics of air flow through sinter bed layer in vertical tank

The experimental investigations on the pressure drop behavior of air flow in packed bed with sinter particles were performed for different air superficial velocity and particle diameters. Based on a homemade gas flow experimental platform, the pressure drop of air flow through sinter bed layer was measured under different experimental cases. Considering the influence of wall effect on the pressure drop behavior, the experimental correlation of air flow pressure drop through sinter bed layer was redefined through the experimental data fitting, and the applicability of experimental correlation was also checked. The results show that, the increase in reduced pressure drop, ΔP/Hu, shows a first power relationship with the air superficial velocity for a given particle diameter. The curve slope of frictional pressure drop of wall correction, fw, is basically unchanged with the increase of particle Reynolds number of wall correction, Rew, and the frictional pressure drop of wall correction also increases as a first power relationship with the particle Reynolds number of wall correction. In addition, the modified viscous and inertia coefficients, k1 and k2, both decrease as an exponential relationship with the increase of bed geometric factor, D/dp. The redefined experimental correlation of air flow pressure drop in sinter bed layer predicts the whole experimental data best, and the mean deviation of redefined correlation is 4.44%.

Aerodynamic Performance of a Flapping Foil with Asymmetric Heaving Motion near a Wall

The effect of asymmetric heaving motion on the aerodynamic performance of a two-dimensional flapping foil near a wall is studied numerically. The foil executes the heaving and pitching motion simultaneously. When the heaving motion is symmetric, the mean thrust coefficient monotonically increases with the decrease in mean distance between foil and wall. Meanwhile, the mean lift coefficient first increases and then decreases sharply. In addition, the negative mean lift coefficient appears when the foil is very close to the wall. After the introduction of asymmetric heaving motion, the influence of wall effect on the force behavior becomes complicated. The mean thrust coefficient is enhanced when the duration of upstroke is reduced. Moreover, more and more enhancement can be achieved when the foil approaches the wall gradually. On the other hand, the positive mean lift coefficient can be observed when the duration of downstroke is shortened. By checking the flow patterns around the foil, it is shown that the interaction between the vortex shed from the foil and the wall can greatly modify the pressure distribution along the foil surface. The results obtained here might be utilized to optimize the kinematics of the Micro Aerial Vehicles (MAVs) flying near a solid wall.

Influence of Wall Effects on Filter Upscaling during Solid‐Liquid Filter Tests

AbstractIndustrial solid‐liquid filtration units are upscaled based on laboratory tests, often by a resistance meter. Wall or boundary effects are more pronounced during lab tests compared with full‐scale units where these effects might be negligible. Thus, simply using area‐specific rates from lab tests may lead to a significant upscaling error. Intentional alterations of wall lengths and filtration areas are performed to allow quantitative description of this effect. Smaller area and longer wall length result in faster cake buildup as well as higher air consumption during subsequent cake drying. This indicates that the permeability close to the walls is different. Extrapolation towards negligible specific wall areas is used to improve upscaling calculations.

Numerical Simulation and Analysis for Influence of Wall Effect on Cavity Shape

In the experiment of cavitation, the same water tunnel with different model size will get cavity shape that is different from the result of the empirical formula under the same cavitation number. In this article, we studied the impact of wall effect on natural cavity shape and the resistance of cavitator. We get the cavity shape and resistance of cavitator under different diameter ratio. We also get the law how cavity shape and resistance of cavitator change with the diameter ratio. The results provide a reference for experiment in water tunnel and the simulation model.

Unsteady Flow Mixing Effect in Bionic Micro-Flow Channel

Micro-mixers are studied extensively due to their high mixing efficiency. A periodic flow variation at the channel entrance will be used to drive fluids in this study to achieve a mixing effect. Numerical analysis is used and verified by experiment in the study to identify the group of operating factors, such as Reynolds number Re, the driving phase difference ? and the driving frequency ratio Fr, needed for the fluid to achieve the best mixing result for a bionic micro-mixer. It is found in this study that the mixing efficiency is related to the velocity period distribution; the more even the velocity period distribution becomes, the better the mixing efficiency and the best group of operating factors is found (Re2 = 1, Rer = 0.85, Fr = 1, F2 = 50 Hz, I/Am = 1, ? = 3/4 ?). Furthermore, a larger aspect ratio results in a better mixing efficiency. The influence of wall-effect on the flow mixing decreases with AR. It is found that there exists an optimal mixing efficiency at aspect ratio AR = 10. These research results could be used to improve the design of a bionic micro-mixer.

Unsteady Flow Mixing Effect in Bionic Micro-Flow Channel

Micro-mixers are studied extensively due to their high mixing efficiency. A periodic flow variation at the channel entrance will be used to drive fluids in this study to achieve a mixing effect. Numerical analysis is used and verified by experiment in the study to identify the group of operating factors, such as Reynolds number Re, the driving phase difference ? and the driving frequency ratio Fr, needed for the fluid to achieve the best mixing result for a bionic micro-mixer. It is found in this study that the mixing efficiency is related to the velocity period distribution; the more even the velocity period distribution becomes, the better the mixing efficiency and the best group of operating factors is found (Re2 = 1, Rer = 0.85, Fr = 1, F2 = 50 Hz, I/Am = 1, ? = 3/4 ?). Furthermore, a larger aspect ratio results in a better mixing efficiency. The influence of wall-effect on the flow mixing decreases with AR. It is found that there exists an optimal mixing efficiency at aspect ratio AR = 10. These research results could be used to improve the design of a bionic micro-mixer.

Experimental investigation of inertial flow processes in porous media

Summary The hydraulic behavior of inertial flows in porous media is experimentally investigated. A vertical metal column was constructed, of dimensions 0.5 m in diameter and 2.30 m in height. Eight different porous media were used in the experiments. Head loss was measured. A total of 454 experimental data were collected. The experimental data indicate that, for a wide spectrum of velocities, both the Forchheimer and Izbash equations offer excellent descriptions of the flow processes. For moderate values of the Reynolds number, a discontinuity in the velocity–hydraulic gradient curve was detected, a behavior also predicted by former numerical studies. The analysis of the hydraulic behavior of bidisperse media indicate the influence of wall effects taking place at the interface between small and large grains. The data are used to validate semi-empirical relations, and give also some insight on the flow processes taking place at the pore-scale for the case of non-Darcian flows.

Wall effects in non-Boussinesq density currents

We report on the results of a numerical study of nearly immiscible contrasted density currents aimed at shedding light on the influence of wall effects on current dynamics in the lock-exchange configuration. The numerical approach is an interface-capturing method which does not involve any explicit reconstruction of the interface. Navier–Stokes equations are solved on a fixed grid and a hyperbolic equation is used for the transport of the local volume fraction of one of the fluids. This allows us to describe the density currents for the complete range of density contrast 10−3≤ρL/ρH≤0.99 (ρL and ρH being the density of the light and heavy fluids) and a wide range of Reynolds number 70≤Re≤5×104 (based on the channel height and the viscosity of the heavy fluid). The use of free-slip vs. no-slip boundary conditions enables us to separate the dissipation at the interface from the dissipation at the boundaries. Present results reveal that wall effects play a significant role on the propagation of contrasted density currents, unlike dissipation at the interface. It is first shown that when wall friction can be neglected, theoretical models based on the inviscid shallow-water approximations and Benjamin's steady-state result describe fairly well the light and heavy front velocities of density currents for the complete range of density ratio. However, when wall friction cannot be neglected, the results depart significantly from the prediction of inviscid theories. It is observed that most of the dissipation in highly contrasted currents takes place at the bottom wall and is a maximum at the head of the heavy current. This dissipation is shown to be responsible for the decrease of the front velocity. We propose a simple model based on Benjamin's analysis that includes wall friction. Keeping in mind the simplicity and limitations of the present model, the prediction of the front velocity of both the heavy and light currents is observed to be in good agreement with the numerical results for the complete range of density contrast. This gives further support to the idea that wall effects are the crucial ingredient for accurately predicting the front velocity of highly contrasted density currents.

Experimental study on the hydrodynamic forces induced by a twin-propeller ferry during berthing

The paper presents the experimental study on the influence of wall effect on the hydrodynamic forces induced by the propellers and thrusters of a ferry during the berthing. The program of the model tests was developed for the twin-propeller, twin-rudder, man-manned model of a car–passenger ferry in 1:16 scale, equipped with two bow thrusters. The different combinations of the operational settings of bow thrusters and propellers operating in the push–pull mode allowed to observe and quantify the variation of the hydrodynamic forces due to the changes of the water depth to draft ratios and distances to the quay. The results of model tests are introduced and discussed in the paper. The difference between the measured total hydrodynamic force and superposition of the component forces induced by the propellers and thrusters has been investigated. According to the structure of the generally accepted modular manoeuvring model, the proposition of the weight factors for the component forces comprising the interaction effects has been introduced and discussed.

A model for the frequency response of a near-wall hot wire: velocity perturbation and sine-wave voltage perturbation tests

A simplified 1-D model is developed to compute the response of a near-wall hot wire as subjected to a velocity perturbation and sine-wave voltage perturbation tests. The calculated frequency response, f D (according to the velocity perturbation test) and f bulge (according to the sine-wave perturbation test) are compared to previous experimental works, and to ascertain the relationship proposed by Teo et al. [Meas. Sci. Technol. 12 (2001) 37] between f D and f bulge. The behavioral trends of f D and f bulge are evaluated in terms of varying convection velocity, influence of wall effects and other pertinent factors. Although f D and f bulge share many similar characteristics and trends, the differences between the two responses give rise to the suggestion that while f D measures the response of heat lost from the wire in near-wall vicinity by velocity perturbation, f bulge measures the frequency response to the total heat lost from the wire.

On the Effect of Free Surface to the Flow Resistance in Rectangular Channels

Friction facter and boundary shear stress distributions are ditermined for rectangular channels of a wide renge of Reynolds number and a renge of width-to-depth ratios (B/H) 0.5 to 10. The influence of wall effect on the boundary shear and maximum-velocity point occuring below the water surface are examined. The boundary shear distributions of open channels are discussed indetailed. By using the maximum-velocity point, the calculation method of the boundary shear distributions are proposed.

Many-sphere hydrodynamic interactions

A scheme for the evaluation of many-sphere hydrodynamic interactions including interactions with container walls is presented. For a system consisting of a suspension of N spherical particles in an unbounded incompressible viscous fluid general formulae for the many sphere mobility tensors were obtained with explicit expressions for three- and four-body contributions up to order R–7 with R a typical interparticle distance. Explicit expressions were also obtained to order R–n R0–m, n+m⩽ 3, for the three-body problem consisting of two suspended spheres at arbitrary positions within a spherical container of radius R0. The influence of hydrodynamic interactions on transport properties, in particular their essential non-additivity and the influence of wall effects, is then discussed for self-diffusion and sedimentation.

Surface and Magnetic Orientation in a Type II Nematic Lyomesophase

Abstract A type II nematic lyomesophase formed by a quaternary system (K decanoate/water/decanol/KCI) has been studied by X-ray diffraction (XD) and optical microscopy (OM) at room temperature. Samples in capillaries of various thicknesses, materials and geometries have been studied under the influence of wall effects, residual magnetic orientation and orientation in presence of magnetic fields. Results evidence that surface orientation extend typically up to 0.5 mm. The planar diffracting units have a characteristic distance in the director direction of 36 A. The analysis of the compromise between surface and magnetic orientation by XD allowed to determine a critical field of 200 G for a 0.5 mm thickness; the elastic constant is estimated as 10−-7 dynes. Analised by OM, the sample is axially positive, but shows also a weak biaxiality.