LIFTING FORCE ACTING ON A GATE WITH HIGH HEAD

The hydrodynamic lifting force acting on a gate with high head is one of the key factors concerning the safety and reliability of gates. The lifting force is closely related to hydrodynamic pressure, and generally, is obtained through the model test. This work presents a method of numerical simulation based on the VOF method for the flow and FEM for the structure of a gate to investigate this kind of the lifting force. The physical model experiments were conducted about the hydrodynamic pressure and the lifting force to verify the numerical results. The comparisons of those two methods show that the maximum relative error is smaller than 11.40 % and the method presented in this paper is feasible and could be used in the designs of hydropower projects.

Influence of Anteroposterior Symmetrical Aero-Wings on the Aerodynamic Performance of High-Speed Train

The running stability of high-speed train is largely constrained by the wheel-rail coupling relationship,and the continuous wear between the wheel and rail surfaces will profoundly affect the dynamic performance of the train.In recent years,under the background of increasing train speed,some scientific researchers have proposed a new idea of using the lift force generated by the aerodynamic wings(aero-wing)installed on the roof to reduce the sprung load of the carriage in order to alleviate the wear and tear of the wheel and rail.Based on the bidirectional running characteristics of high-speed train,this paper proposes a scheme to apply aero-wings with anteroposterior symmetrical cross-sections on the roof of the train.After the verification of the wind tunnel experimental data,the relatively better airfoil section and extension formof anteroposterior symmetrical aero-wing is selected respectively in this paper,and the aero-wings are fixedly connected to the roof of the train through the mounting column to conduct aerodynamic simulation analysis.The research shows that:compared with the circular-arc and oval crosssections,this paper believes that the crescent cross-section can form greater aerodynamic lift force in a limited space.Considering factors such as aerodynamic parameters,ground effect,and manufacturing process,this paper proposes to adopt aero-wings with arc type extension form and connect them to the roof of the train through mounting columns with shuttle cross-section.When the roof of the train is covered with aero-wings and runs at high speed,the sprung load of the carriages can be effectively reduced.However,there are certain hidden dangers in the tail carriage due to the large amount of lift force,so,the intervention of the aero-wing lifting mechanism is required.At the same time,it is necessary to optimize the overall aerodynamic drag force reduction in the followup work.

几何形状对气垫升力的影响研究

One of the crucial and challenging issues for researchers is presenting an appropriate approach to evaluate the aerodynamic characteristics of air cushion vehicles(ACVs)in terms of system design parameters.One of these issues includes introducing a suitable approach to analyze the effect of geometric shapes on the aerodynamic characteristics of ACVs.The main novelty of this paper lies in presenting an innovative method to study the geometric shape effect on air cushion lift force,which has not been investigated thus far.Moreover,this paper introduces a new approximate mathematical formula for calculating the air cushion lift force in terms of parameters,including the air gap,lateral gaps,air inlet velocity,and scaling factor for the first time.Thus,we calculate the aerodynamic lift force applied to nine different shapes of the air cushions used in the ACVs in the present paper through the ANSYS Fluent software.The geometrical shapes studied in this paper are rectangular,square,equilateral triangle,circular,elliptic shapes,and four other combined shapes,including circle-rectangle,circle-square,hexagonal,and fillet square.Results showed that the cushion with a circular pattern produces the highest lift force among other geometric shapes with the same conditions.The increase in the cushion lift force can be attributed to the fillet with a square shape and its increasing radius compared with the square shape.

Experimental and Numerical Investigation on the Aerodynamic Characteristics of High-Speed Pantographs with Supporting Beam Wind Deflectors

Aiming to mitigate the aerodynamic lift force imbalance between pantograph strips,which exacerbates wear and affects the current collection performance of the pantograph-catenary system,a study has been conducted to support the beam deflector optimization using a combination of experimental measurements and computational fluid dynamics(CFD)simulations.The results demonstrate that the size,position,and installation orientation of the wind deflectors significantly influence the amount of force compensation.They also indicate that the front strip deflectors should be installed downwards and the rear strip deflectors upwards,thereby forming a“π”shape.Moreover,the lift force compensation provided by the wind deflectors increases with the size of the deflector.Alternative wind compensation strategies,such as control circuits,are also discussed,putting emphasis on the pros and cons of various pantograph types and wind compensation approaches.

Viscous Effects on Wave Forces on A Submerged Horizontal Circular Cylinder

Numerical simulations are carried out for wave action on a submerged horizontal circular cylinder by means of a viscous fluid model, and it is focused on the examination of the discrepancies between the viscous fluid results and the potential flow solutions. It is found that the lift force resulted from rotational flow on the circular cylinder is always in anti-phase with the inertia force and induces the discrepancies between the results. The influence factors on the magnitude of the lift force, especially the correlation between the stagnation-point position and the wave amplitude, and the effect of the vortex shedding are investigated by further examination on the flow fields around the cylinder. The viscous numerical calculations at different wave frequencies showed that the wave frequency has also significant influence on the wave forces. Under higher frequency and larger amplitude wave action, vortex shedding from the circular cylinder will appear and influence the wave forces on the cylinder substantially.

EFFECT OF INTERPHASE LIFT FORCE ON THE FLUID FLOW IN AN AIR-STIRRED CYLINDRICAL VESSEL

In the present paper, based on the two-phase model (Eulerian model), the two dimensional fluid flow liz air-stirred water systems is simulated, and the effect of interphase lift force on the fluid flow is specially discussed. In the Eulerian two-phase model, gas and liquid phase are considered to be two different continuous fluids interacting with each other through the finite inter-phase areas. The exchange between the phases is represented by source terms in conversation equations. Turbulence is assumed to be a property of the liquid phase, k - ε model is used to describe the behavior of the liquid phase. The dispersion of phases due to turbulence is represented by introducing a diffusion term in mass consecrvation equation. The contribution of bubble movement to the turbulent energy and its dissipation rate is taken into accounted by adding extra volumetric source terms to the equations of turbulent enemy and its dissipation rate. The comparison between the mathematical simulation and experiment data indicates that the interphase lift force has a big effect on the flow behavior, and considering both drug force and lift force as interphase forces is important to accurately simulate the gas-water two-phase fluid flow in air-stirred systems. The interphase lift force makes bubbles move away from the centerline, the gas concentration is decreased near the centerline, and increased near the wall. The lift force is smaller than drug force at the same place, especially far away from the centerline.

A Study of Lift Force and Instantaneous Velocity Field Around an Oscillating Circular Cylinder

Force measurements of oscillatory flow acting on a single circular cylinder have been carried out. The experiments were done by oscillating a circular cylinder in still water. Instantaneous forces and velocity fields around the cylinder were measured by Particle Image Velocimetry (PIV). The Keulegan-Carpenter number (KC) varied in the range from 5 to 20 and the viscous parameter beta = Re / KC was set at 500 (Re is Reynolds number). It was found that the strength and frequency of the lift force increased with KC number, the main frequency of the lift force being three times the frequency of the oscillatory flow at KC = 20. The movement and strength of the vortices around the cylinder are discussed for different KC numbers.

Effect of the particle temperature on lift force of nanoparticle in a shear rarefied flow

The nanoparticles suspended in a shear flow are subjected to a shear lift force,which is of great importance for the nanoparticle transport.In previous theoretical analysis on the shear lift,it is usually assumed that the particle temperature is equal to the temperature of the surrounding gas media.However,in some particular applications,the particle temperature can significantly differ from the gas temperature.In the present study,the effect of particle temperature on the shear lift of nanoparticles is investigated and the corresponding formulas of shear lift force are derived based on the gas kinetic theory.For extremely small nanoparticles(with radius R<2 nm)or large nanoparticles(R>20 nm),the influence of the particle temperature can be neglected.For the intermediate particle size,the relative error induced by the equal gas–particle temperature can be significant.Our findings can bring an insight into accurate evaluation of the nanoparticle transport properties.

Lift Force at Equatorial Sea Level Due to Compressed Air Dynamics of the Trade Wind’s Boundary Layer

Starting with a recent unconventional explanation of the lift force on a wing, featuring compressibility of the air, an application of the same concept is made to the lift force on the equatorial sea surface due to the Trade Winds, by greatly increasing the spatial scales. If the equatorial sea level does rise up, the northward slope to the sea level should facilitate the poleward flux of summer heat in both the North Pacific and North Atlantic Oceans, as two examples, in accordance with the heat budget requirements of these oceans. Compressed air dynamics consists of Bernoulli’s law applied to the streamlines of the Trade Winds, the force balance between the upward centrifugal force of the curved streamlines at the earth’s surface and a downward pressure force, and the perfect gas law for air.

A novel method of evaluating the lift force on the bluff body based on Noca's flux equation

The influence of experimental error on lift force evaluated by Noca’s flux equation is studied based on adding errors into the direct numerical simulation data for flow past cylinder at Re = 100. As Noca suggested using the low-pass filter to get rid of the high-frequency noise in the evaluated lift force, we verify that his method is inapplicable for dealing with the dataset of 1% experimental error, although the precision is acceptable in practice. To overcome this defect, a novel method is proposed in this paper. The average of the lift forces calculated by using multiple control volume is taken as the evaluation before applying the low-pass filter. The method is applied to an experimental data for flow past a cylinder at approximately Re = 900 to verify its validation. The results show that it improves much better on evaluating the lift forces.

The Lift Forces Acting on a Submarine Composite Pipeline in a Wave-Current Coexisting Field

A composite pipeline is defined as a main big pipe composed of one or several small pipes. The flow behaviour around a submarine composite pipeline is more complicated than that around a single submarine pipeline. A series model test of composite pipelines in a wave-current coexisting field was conducted by the authors. Both in-line and lift forces were measured, and the resultant forces were also analyzed. The results of lift forces and resultant forces are reported in this paper. It is found that the lift force coefficients for composite pipelines are well related to the KC number. The lift force coefficients for an irregular wave-current coexisting field are smaller than those for a regular wave-current coexisting field. The frequency of lift force is usually twice the wave frequency or higher. The authors test indicates that the resultant forces are about 10 to 20 percent larger than in-line forces (horizontal forces). The effect of water depth is analyzed. Finally, the relationship between lift force coefficient CL and KC number, the statistical characteristics of lift and resultant forces, are given in this paper, which may be useful for engineering practice.

Study of the Lift Force Induced by An Interceptor on A High-Speed Mono-Hull:The Affecting Factors and Estimation Formula

To find a better way to estimate the lift force induced by an interceptor on a high-speed mono-hull ship,a series of high-speed mono-hull ship models are designed and investigated under different conditions.Different lift forces are obtained by numerical calculations and validated by a model test in a towing tank.The factors that influence the force are the interceptor height,velocity,draft,and deadrise angle.The relationship between each factor and the induced lift force is investigated and obtained.We found that the induced lift mainly depends on the interceptor height and advancing velocity,and is proportional to the square of the interceptor height and velocity.The results also showed that the effects of the draft and deadrise angle are relatively less important,and the relationship between the induced lift and these two factors is generally linear.Based on the results,a formula including the combined effect of all factors used to estimate the lift force induced by the interceptor is developed based on systematic analysis.The proposed formula could be used to estimate the lift force induced by interceptors,especially under high-speed condition.

Numerical simulation of low-Reynolds number flows past two tandem cylinders of different diameters

The flow past two tandem circular cylinders of different diameters was simulated using the finite volume method. The diameter of the downstream main cylinder （D） was kept constant, and the diameter of the upstream control cylinder （d） varied from 0.1D to D. The studied Reynolds numbers based on the diameter of the downstream main cylinder were 100 and 150. The gap between the control cylinder and the main cylinder （G） ranged from 0.1D to 4D. It is concluded that the gap-to-diameter ratio （G/D） and the diameter ratio between the two cylinders （d/D） have important effects on the drag and lift coefficients, pressure distributions around the cylinders, vortex shedding frequencies from the two cylinders, and flow characteristics.

Impact Dynamics of a Dragonfly Wing

The lift force was reported not to be high enough to support the dragonfly’s weight during flight in some conventional investigations,and higher lift force is required for its takeoff.In this study,by employing a thin plate model,impact effect is investigated for the wing deformation in dragonfly flapping during takeoff.The static displacement is formulated to compare with the dynamical displacement caused by impact.The governing equation of motion for the impact dynamics of a dragonfly wing is derived based on Newton’s second law.Separation of variables technique and assumed modes method are introduced to solve the resulting equations.Further,lift force is presented for the cases of considering and without considering the impact on the wing flapping which indicates that the impact has prominent effects for the dragonfly’s aerodynamic performance.Numerical simulations demonstrate that considering the impact effect on the wing flapping can increase the wing deformation,which results in the rise of the lift force.The enhanced lift force is of critical importance for the dragonfly’s takeoff.

Effect of turbulence intensity on airfoil flow:numerical simulations and experimental measurements

The effect of the turbulence intensity of the oncoming stream on the aerodynamic characteristics of the NACA-0012 airfoil is investigated by a direct numerical simulation. The numerical results are found to be consistent with the experimental measurements. Based on the finite spectral QUICK scheme, the simulation gets the high accuracy results. Both the simulation and the experiment reveal that the airfoil stall does not exist for the low turbulence intensity, however, occurs when the turbulence intensity increases sufficiently. Besides, the turbulence intensity has a significant effect on both the airfoil boundary layer and the separated shear layer.

THE DISTRIBUTION OF PARTICLES IN A SHOCK-INDUCED BOUNDARY LAYER OF A DUSTY GAS OVER A SOLID SURFACE

The laminar boundary layer behind a constant-speed shock wave moving through a dusty gas along a solid surface is studied.The Saffman lift force acting on a spherical particle in a gas boundary layer is taken into account.A method for calculating the density profile of dispersed phase near the wall is pro- posed and some numerical results are given.It is shown that behind the shock wave,there exists a curved thin layer where the density of particles is many times higher than the original one.This dust collection effect may be of essential importance to the problem of dust explosion in industry.

Aeolian Tone from a Semi-Circular Cylinder in a Stream

Aeolian tone from a semi-circular cylinder in a uniform flow is studied experimentally for various angles of attack. It is found that the peak sound spectrum of the Aeolian tone from the semi-circular cylinder is smaller than that from the circular cylinder and the lowest sound is observed around the zero angle of attack. This is due to the reduction in the fluctuating lift force on the semi-circular cylinder compared to that of the circular cylinder. This result suggests the validity of the analogy between the sound pressure level and the fluctuating lift force on a semi-circular cylinder in a stream. The flow visualization study also supports these results.

Vibrational Suspension of Two Cylinders in a Rotating Liquid-Filled Cavity with a Time-Varying Rotation Rate

The dynamics of rotating hydrodynamic systems containing phase inclusions are interesting due to the related widespread occurrence in nature and technology.The influence of external force fields on rotating systems can be used to control the dynamics of inclusions of various types.Controlling inclusions is of current interest for space technologies.In low gravity,even a slight vibration effect can lead to the appearance of a force acting on phase inclusions near a solid boundary.When vibrations are applied to multiphase hydrodynamic systems,the oscillating body intensively interacts with the fluid and introduces changes in the related flow structure.Asymmetries in the fluid flow lead to the appearance of an averaged force.As a result,the body is repelled from the cavity boundary and takes a position at a certain distance from it.The vibrationally-induced movement of phase inclusions in liquids can be used to improve various technological processes(for example,when degassing and cleaning liquids from solid inclusions,mixing various components,etc.).This study presents a relevant methodology to study the averaged vibrational force acting on a pair of free cylindrical bodies near the oscillating wall of a cavity.Attention is paid to the region of moderate and low dimensionless frequencies when the size of the inclusion is consistent with the thickness of the Stokes boundary layer.The dynamics of these bodies is considered in a horizontal cylindrical cavity with a fluid undergoing modulated rotation.The average lift force of a vibrational nature is measured by the method of quasi-stationary suspension of bodies whose density differs from the density of the liquid in a static centrifugal force field.The developed technique makes it possible to determine the dependence of the lift force on vibration parameters and the distance from the oscillating boundary at which solid inclusions are located.It is shown that in the region of moderate dimensionless frequencies,the average lift force acting on an inclusion near the boundary undergoing modulated rotation almost linearly depends on the dimensionless frequency.

Numerical simulation and scaling analysis of elasticity-induced lift force in a viscoelastic fluid between confining surfaces

How to accurately characterize the lift force on the particles near the solid surfaces is an ongoing challenge in fluid mechanics and microfluidic techniques, especially in a complex system with viscoelastic fluid or/and soft surface that is commonly encountered in a biological system. The motions of the particles in vicinity of a surface can be simplified to be a rigid cylinder surrounded by the viscoelastic fluid moving along a substrate which can be rigid or soft according to different cases. In such an inertial free system with a wide range of Weissenberg number (Wi < 5.00, representing the ratio of the elastic force to the viscous force), firstly we numerically evaluate the influence of the systematic parameters, including the polymer viscosity, the geometry and Wi, on the net normal force for a cylinder closely moving along a rigid substrate, and the elasticity-induced lift force in a scaled form. It is shown that a strong shear arises in the viscoelastic confinement between the moving cylinder and the rigid substrate, it leads to the asymmetry of the first normal stress distribution around the cylinder, and thus the lift force. Then, the influence of a soft substrate on the lift force is considered, and we find that the lift force induced by the viscoelastic fluid always dominates in magnitude over that induced by the soft substrate deformation. This work provides a reliable scaling that can be utilized to quantify the elasticity-induced lift force on the particles in a viscoelastic system, such as the micro- and nanofluidic systems in biological applications.

Numerical and experimental investigation to design a novel morphing airfoil for performance optimization

Optimizing flying objects’wing performance has attracted a significant attention in the last few decades.In this article,some of the main mechanisms for changing the geometry of the wing were investigated and a new mechanism is proposed to improve the aerodynamic performance of the airplane wing.The designs have been simulated and analyzed from both aerodynamic and control points of view.In aerodynamic simulations using CFD methods,two airfoils of NACA series 6 with specifications 65-212 and 65-2012 were modeled.The results indicated that both airfoils used have a better performance compared to others in a certain range of the angle of attack.Subsequently,a new mechanism is proposed to change the wing geometry to optimize its structure.In the proposed mechanism,the structures of airfoils and wings consist of two fixed and moving parts,which can change their geometry with the help of a control circuit.The fixed part has a grooved track,and as the moving part moves in the direction of the grooves,the curvature of the upper and lower parts of the wing changes.The design control circuit includes an angle sensor,a micro controller,and a servomotor.The CFD results are entered into the micro controller as code.At any moment,the micro controller receives the angle data from the angle sensor and by comparing them with the CFD data,and issuing a command to the servomotor,it situates the wing curvature in the optimal state at all times.The built mechanism was tested at an attack angle of 0°and 25°.The results showed that the different parts of the mechanism work with very high precision and put the geometric shape of the wing in an optimal state in a completely intelligent way.It should be noted that the average error in test for t/c and Xt/c was 15.3% and 9%,respectively.