Fluid Dynamic Pressure Research Articles

Experimental Data Mining Research on Factors Influencing Friction Coefficient of Wet Clutch

Abstract In this study, an experiment is conducted for assessing the friction characteristics of a wet clutch on actual working conditions, to determine how various factors influence the friction coefficient in the actual working process of a wet clutch. Based on the experimental data of a wet clutch under different engagement conditions, a data surrogate model construction method is proposed for the friction coefficient. According to this model, the decoupling between different influencing factors of friction coefficient is realized, and their influence on friction coefficient is obtained. To reveal the change mechanism of the friction coefficient, a theoretical analysis model of the friction coefficient is established by using the elastic contact theory and the elastic fluid dynamic pressure lubrication theory. In addition, based on the constructed friction coefficient data surrogate model, the sensitivity of different influencing factors on the friction coefficient and the coupling relationship between the different influencing factors are studied.

Spatio-temporal aeroacoustic–structural responses of cavity-backed elastic panel liner exposed to grazing duct flow

An in-duct device laid with acoustic liner is a popular noise control option for extensive ductworks carrying unsteady flow in various engineering applications. Besides the conventional absorptive liner, elastic panel liner backed by a cavity emerges as a promising alternative concept that has advantages in providing effective broadband reduction at low frequencies yet with significantly low fluid dynamic pressure loss. The present paper reports a numerical study of aeroacoustic–structural interaction of elastic panel liner exposed to subsonic duct boundary layer flow in time domain and explores its role in liner mitigation of plane wave broadband acoustic excitation. The aeroacoustics of the duct flow and panel dynamics are respectively modeled by the two-dimensional compressible Navier–Stokes equations that solved by the conservation element and solution element (CE/SE) method, and one-dimensional elastic panel equation that is solved with finite difference method. The interaction between aeroacoustics and panel dynamics is resolved with a monolithic coupling scheme that is well validated down to acoustic scales. Special attention is placed on the sensitivity of liner acoustic performance to duct flow Mach number (M≤0.3) and the relative directions between duct flow and acoustic excitation. Extensive cross-spectral analyses of acoustic results reveal that the transmission loss of the elastic panel liner is primarily a result of the destructive interference of the incident wave with the scattered wave as well as the dissipation of non-planar waves radiated by the panel vibration. The contribution of interference and dissipation to liner reflection and absorption are particularly pronounced at low and high frequencies respectively. In addition, the effect of flow is not strong for M≤0.1. The presence of flow with the incident wave in the flow direction mainly weakens the reflection. However, the effect of flow with incident waves against the flow largely enhances the absorption. Overall, the elastic panel liner is much more effective when the noise source radiates against the flow.

Experimental study of internal forces and moments generated by strut injection in a supersonic cross-flow in a C-D nozzle

An experimental investigation was conducted to obtain wall pressure distribution in a convergent divergent nozzle with a strut inserted through the diverging wall and to find out the possible generation of side force. The strut inserted through the nozzle wall represented an active control method for thrust vector control. Laboratory tests were carried out to examine whether this type of strut injection would be effective and serve as an alternative thrust vector control method for the other widely used such as secondary injection thrust vector control. The nozzle model used in the experiments had a design Mach number of 1.84 with a corresponding area ratio of 1.48. The solid strut which was inserted through the diverging wall of the nozzle had a square cross section. Experiments were conducted for identifying three different strut positions from the nozzle throat, i.e. at Ld/3, Ld/2, and 2Ld/3, where Ld was the length of the diverging section of the nozzle. At each strut position, the strut height was varied and the maximum strut height corresponded to the radius of the local cross section where the strut was inserted. The nozzle was operated at overexpansion conditions such as nozzle pressure ratios of 3.4 and 5. The strut side and the opposite side of the nozzle wall had eight wall pressure tappings each and the wall pressure data were obtained using a pressure scanner. The asymmetrical pressure distributions of the strut side and the non-strut side (opposite side) of nozzle wall were used for the calculation of side force and pitching moment in the nominal plane through the wall pressure ports of both sides. The calculated two-dimensional side force, axial force, and pitching moment coefficients were plotted against strut height at each strut position from the nozzle throat. From the experimental data and calculations, it was found that the axial force varied more or less linearly with strut height irrespective of the strut position. However, the side force and pitching moments varied nonlinearly with strut height and the nature of variation of the two was similar. Both the side force and pitching moment exhibited maximum and minimum values at two specific values of the strut height. The change in the strut position did not alter the nature of the above variations and the strut height values for maximum and minimum. The magnitude of the side force was found to be 1–10% of the axial force generated as a fluid dynamic pressure drag. Both positive and negative side force and pitching moments were produced with increase in the strut height.

Numerical and experimental study on the ultrasonic-assisted soft abrasive flow polishing characteristics

To resolve the low-polishing efficiency problem caused by the turbulent layer separation in soft abrasive flow (SAF) processing, an ultrasonic-assisted SAF (UA-SAF) method is proposed based on the vibration effect. The coupled computational fluid dynamics (CFD)-discrete element method (DEM) modeling method (CFD-DEM) and the dynamic mesh are used to represent the UA-SAF flow and the periodic moving boundary caused by ultrasonic vibration, while the particle-wall erosion is calculated by the Archard model. Through tracking the abrasive particle motion in the simulation, the particle-wall collision states and the particle cutting effect are revealed, which mainly includes the particle plowing and the particle impact erosion. It has been found from the simulation that the fluid turbulent motion and the fluid dynamic pressure which are the power source for the particles to obtain the anisotropic cutting kinetic energy can be strengthened obviously by the ultrasonic vibrating, which results in the increase of the probability of particle impacting the target surface, and then the particle-wall wear rate and the wear area can be improved. A set of comparative experiments, including the rough and precision polishing procedures, are then conducted to evaluate the polishing performance by using the SAF and UA-SAF, respectively. The variations of the surface roughness and the workpiece mass are obtained, and the surface morphologies are observed. The experimental results prove that the ultrasonic vibration can effectively improve the abrasive flow polishing efficiency and precision without producing cavitation erosion.

Numerical study on the fluid dynamic pressure effect of convex-shaped texuture under fluid lubrication

Numerical study on the fluid dynamic pressure effect of convex-shaped texuture under fluid lubrication

Blockage and cavitation detection in centrifugal pumps from dynamic pressure signal using deep learning algorithm

Centrifugal pumps play an important role in many industrial applications even in harsh environment for prolong duration. High efficiency with very low power consumption makes them very popular in industry. However, during their operation, they may fail due to some operationally developed faults, which may subsequently lead to the interruption in the continuous operation of pumps. Therefore, monitoring the health status of the centrifugal pumps is essential to prevent unwanted stoppage, which may further lead to the breakdown of the whole system. The main focus of this study is to propose a methodology to identify the presence and severity of blockages, and cavitation in the centrifugal pump using fluid pressure, which is very vital for fluid related faults. To simulate the blockage in the pump, the flow area of the suction pipe is restricted by dividing into six equal intervals (i.e., 0%, 16.7%, 33.3%, 50%, 66.6% and 83.33%) using a mechanical modulating valve. Due to blockage and cavitation, the main parameter which directly gets affected is the fluid dynamic pressure. Hence, in the present study, pressure signatures were captured at different blockage levels and at different running speeds with the help of a pressure transducer, which was mounted on the circumference of the centrifugal pump casing. Deep learning based binary data classification methodology is used to classify the data acquired from the pressure transducer. To get better performance of the data classifier, statistical features are extracted from time domain pressure signals. In order to identify the severity of the faults, binary classification of the data is performed at different blockage levels and running speeds. Finally, based on the results obtained from the classifier, existence of the faults (i.e., blockage and the cavitation), their severity levels are presented.

Performance Analysis of Hydrodynamic Pressure Finger Seal by Wall Slip Effect

Hydrodynamic pressure finger seal1 is a kind of flexible noncontact dynamic sealing device with good application potential. It relies on the ultrathin dynamic pressure film effect produced by the rotation of finger boot and rotor to realize the design of noncontact and low leakage and is suitable for high-speed dynamic sealing parts. However, under the high-speed condition, there is a wall slip effect when the gas flows in the microchannel with a thickness of about 10 μm between the finger boot and rotor, which affects the stability of the dynamic pressure air film and also affects the change of the air film bearing capacity and the leakage rate of the finger seal. Therefore, based on the theory of microflow, the interstitial flow field model of finger seal under fluid dynamic pressure is established, and its slip effect under high speed is analyzed. The results show that the slip ratio of the sealing medium temperature of 500°C and 0.1 MPa conditions reached 27.28%. When considering the slip effect of the wall surface generated by the gas under shear driving, the gas film bearing capacity decreased and the leakage rate increased. When the pressure difference between the upper and lower reaches of the seal is 0.1 MPa, and the rotor line speed is 400 m/s, the gas film bearing capacity decreases by 17.39% after considering the slip effect of the wall surface, and the leakage rate increases by 14.06%. The results provide an important reference for the structural design and leakage control of hydrodynamic finger seal.

Effect of Surface Texture Distribution Parameters on Hydrodynamic Lubrication and Numerical Optimization

Surface texture technology has been proven to be an effective way to improve the lubrication performance of friction surfaces. In order to obtain the optimal surface texture distribution parameters, taking the spherical crown pit texture model as the research object, and selecting the unequal rectangular control unit to establish the surface texture distribution model with different horizontal and vertical distribution distances (densities).According to the principle of fluid dynamic pressure lubrication, a two-dimensional Reynolds equation based on the N-S equation is established and solved by the multigrid method to study the effect of texture distribution parameters on the surface hydrodynamic lubrication under plane motion. The results show that when the texture unit Lx is 3.4r and the aspect ratio Ly / Lx is 0.82, the optimal oil film bearing capacity can be obtained. When the control unit of the boundary pit is appropriately increased so that the left and right sides of the pit at the boundary are about 3.4r, the oil film pressure stability can be effectively improved.

Investigating the Effect of Fluid Pressure on the Vibrational Behavior of Annular Sector Plate

In this article, the effect of fluid dynamic pressure on the linear vibration of the annular sector plate has been investigated. The pressure introduced from the fluid to the plate is determined by solving the Laplace equation and satisfying its boundary conditions. Also, the governing equations of plate motion are determined using the first-order shear deformation plate theory and the Hamilton principle. The shape of the modes is based on the satisfaction of the boundary conditions of the plate. By using shape modes and Galerkin method, the governing equations have become linear differential equations based on time. Then, by considering the harmonic response and solving the characteristic equation, the natural frequency will be determined. At the end, the numerical results are presented for a sample plate and the effect of parameters such as aspect ratio, sector angle, boundary conditions, fluid density and fluid height has been investigated. Also, the results obtained are verified with the current research and FEM (ANSYS software), which shows good accuracy.

Optimization of Performance Parameters and Mechanism of Bionic Texture on Friction Surface

In this paper, a variety of micro-textures made by imitating the biological body surface are mentioned, and four common biomimetic texture types—convex hull, pit, groove and corrugation—are summarized by referring to a large number of literatures. These texture types that are widely used are those of the grooves and the pits of non-smooth surface because their viscosity drag reduction effects are relatively optimal for wear-resistance; in view of these two types of textures (with others including pit diameter, groove width, depth and area of share, and morphology spacing), we use data analysis and comparisons to find optimal parameter values in order to find the optimal effect of drag reduction and anti-sticking wear-resistance. Several texture processing methods are briefly introduced through case analysis and an illustration of the viscosity drag reduction mechanism of wear-resistance, and general fluid dynamic pressure is deduced from a theory formula in order to facilitate future research work on the basis of the optimal parameters to further improve the friction, wear lubrication, and hydrophobic properties, thus improving the bionic texture surface efficiency of saving energy and reducing consumption in industrial applications.

A Momentum-Based Method for the Mass Concentration Measurement of Pneumatically Conveyed Solid: Computational Verification

A momentum-based method is proposed to measure the mass concentration of solids in pneumatic pipelines. The mechanism relies on the fact that particles flowing with the fluid will exert drag force and thus induce pressure increase on the fluid phase when they decelerate as approaching a static object or space in the flow domain. The pressure increase is expected to increase with the mass concentration of particles and the fluid velocity, and is also affected by the particles size and density. A conversion factor that indicates the extent to which particle momentum is converted to the fluid static pressure increase was defined. Computational verification of the mechanism was carried out with pulverized coal flow around a one-end closed tube with its opening facing towards the incoming flow. The pressure increase was quantitatively comparable to the fluid dynamic pressure when the solid-to-fluid mass ratio was of the same order of magnitude. The conversion factor was found insensitive to particle size over a wide range, which is advantageous since particle size distribution are usually not known in advance. Compared to most existing techniques, current mechanism is more robust and economic in industry field measurements.

Polynomial profile optimization method of a magnetic petal-shaped capsule robot

Based on the multiple wedge effects, magnetically manipulated petal-shaped capsule robots (PCRs) using circle-based profiles have achieved an advantageous comprehensive driving performance, which lies in acquiring the high fluid dynamic pressure to ensure the good self-centering ability inside the pipe, the fast steady swimming speed and the low fluid resistance torsion moment. Nevertheless, the limited parametric choice of the circle-based profile hinders the further improvement in the comprehensive driving performance. This paper presents a general profile optimization method using polynomial curve for PCRs to further enhance the comprehensive driving performance. Applying the fluid lubrication theory, the fluid dynamic pressure, the steady swimming speed and the fluid resistance torsion moment are derived under the polynomial profile constraints. Selecting the steady swimming speed and the fluid resistance torsion moment as the optimization objectives, the PCR is optimized using the polynomial profile by the proposed method. Afterwards, a comparative investigation into the optimized and the circle-based PCRs and the non-PCR (the ordinary spiral-type capsule robot) has been conducted both theoretically and experimentally, showing that the optimized PCR using the polynomial profile improves the comprehensive driving performance significantly compared with its counterparts.

Investigation of the optimal parameters for the surface finish of K9 optical glass using a soft abrasive rotary flow polishing process

A workpiece polished by soft abrasive flow polishing has the advantages of low damage and ultrasmoothness. However, due to the need to use a constrained flow path, the fluid dynamic pressure on the near wall surface of the workpiece has a gradient distribution, so achieving uniform polishing of workpieces of large size is difficult. To address this problem, this paper proposes a new method of soft abrasive rotary flow (SARF) polishing to achieve low damage, ultrasmooth, uniform polishing of a large-size K9 optical glass surface. A new SARF polishing system and a 6-outlet rotary polishing tool are designed. The SARF polishing principle is analyzed, and a polishing experiment is conducted on K9 glass. The experiment of surface roughness improvement of the K9 optical glass is designed by Taguchi method. Orthogonal arrays and the signal-to-noise ratio (S/N) are used to determine the optimal parameters for SARF polishing. Analysis of variance (ANOVA) is used to determine the effect of the main polishing parameters on the surface roughness of K9 glass. According to the results of the polishing experiment using a Taguchi L18 orthogonal array and S/N ratio analysis, the optimal parameters for K9 glass SARF polishing are revealed to be as follows: the abrasive material is CeO2, the polishing pressure is 0.35 MPa, the abrasive particle concentration is 5 wt.%, the average size of the abrasive particles is 0.7 μm, the polishing time is 1.5 h and the platform rotation speed is 10 rpm. After polishing the sample for 1.5 h under these parameters, the surface roughness decreases from the original value of Ra = 37.28 nm to Ra = 4.51 nm, and the surface roughness improves by 87.9 %.

Imperfect bifurcations in an initially curved plate loaded by incompressible axial airflow

This paper is concerned with the static bifurcations in a simply supported nonlinear curved plate subjected to a steady incompressible axial airflow. The fluid velocity potential of the flow is considered as the sum of two parts: One is due to the plate deformation, and the other is to the plate initial shape. The fluid force theoretically solved from the Bernoulli’s equation has been successfully verified through a wind tunnel experiment. The von Karman’s theory for large deflection of plates is used for the plate modeling. Results show that the plate loses symmetry and becomes imperfect due to its initial shape. The system has a fundamental and another two asymmetric bifurcated equilibrium solutions. Compared with the symmetric bifurcations in a flat plate, these bifurcations are called as the imperfect ones. The imperfect pitchfork-like bifurcation has a non-bifurcating branch and an additional imperfect bifurcation. The bifurcation regions and features are explored in detail in various parametric planes. There are two types of imperfect pitchfork-like bifurcations. The first type involves an additional saddle-node bifurcation and could be either supercritical or subcritical. However, the second type is associated with a transcritical-like bifurcation and represents the coexistence of both the supercritical and the subcritical bifurcations. The hysteresis in nature is due to the asymmetry of the system and can be restrained by increasing the tension and the fluid dynamic pressure.

Tribological characteristics of a cemented carbide friction surface with chevron pattern micro-texture based on different texture density

Abstract The influence of the drawing area on the tribological properties was studied using femtosecond laser processing of four kinds of chevron pockets of cemented carbides with 5.05%, 9.5%, 13.02%, and 15.2% texture density. The results show that the chevron pattern texture with a certain texture density helps decrease the friction of a YT15 cemented carbide surface compared with un-textured specimens. This surface texture minimizes and stabilizes the friction coefficient, while the fluid dynamic pressure increased in the specimen with 9.5% texture density. Wear occurs due to abrasive and adhesive wear. Therefore, designing a reasonable shape and selecting appropriate texture density will be the focus of further research on surface micro-texture.

Stochastic inverse modeling and global sensitivity analysis to assist interpretation of drilling mud losses in fractured formations

This study is keyed to enhancing our ability to characterize naturally fractured reservoirs through quantification of uncertainties associated with fracture permeability estimation. These uncertainties underpin the accurate design of well drilling completion in heterogeneous fractured systems. We rely on monitored temporal evolution of drilling mud losses to propose a non-invasive and quite inexpensive method to provide estimates of fracture aperture and fracture mud invasion together with the associated uncertainty. Drilling mud is modeled as a yield power law fluid, open fractures being treated as horizontal planes intersecting perpendicularly the wellbore. Quantities such as drilling fluid rheological properties, flow rates, pore and dynamic drilling fluid pressure, or wellbore geometry, are often measured and available for modeling purposes. Due to uncertainty associated with measurement accuracy and the marked space–time variability of the investigated phenomena, we ground our study within a stochastic framework. We discuss (a) advantages and drawbacks of diverse stochastic calibration strategies and (b) the way the posterior probability densities (conditional on data) of model parameters are affected by the choice of the inverse modeling approach employed. We propose to assist stochastic model calibration through results of a moment-based global sensitivity analysis (GSA). The latter enables us to investigate the way parameter uncertainty influences key statistical moments of model outputs and can contribute to alleviate computational costs. Our results suggest that combining moment-based GSA with stochastic model calibration can lead to significant improvements of fractured reservoir characterization and uncertainty quantification.

Effect of Surface Topography Parameters on Friction and Wear of Random Rough Surface.

In order to explore the relationship between the surface topography parameters and friction properties of a rough contact interface under fluid dynamic pressure lubrication conditions, friction experiments were carried out. The three-dimensional surface topography of specimens was measured and characterized with a profile microscopy measuring system and scanning electron microscope. The friction coefficient showed a trend of decreasing first and then increasing with the increase in some surface topography parameters at lower pressure, such as the surface height arithmetic mean Sa, surface height distribution kurtosis Sku, surface volume average volume Vvv, and surface center area average void volume Vvc, which are the ISO 25178 international standard parameters. The effects of surface topographic parameters on friction were analyzed and the wear mechanism of the worn surface was presented. The wear characteristics of the samples were mainly characterized as strain fatigue, grinding, and scraping. The results provide a theoretical basis for the functional characterization of surface topography.

Effects of different inlet velocity on the polishing quality of abrasive flow machining

In order to study the effect of different inlet velocity on the polishing quality of abrasive flow machining, this paper takes the variable diameter pipe as an example. The fluid dynamic pressure and total energy of abrasive particles under coupling field with different inlet velocities were carried out by using computational fluid dynamics software. The results of numerical analysis show that the polishing quality becomes better with the increase of the inlet velocity. At the same inlet velocity, the smaller the pipe diameter is, the higher the polishing quality will be. Therefore, the optimum inlet velocity can be selected by numerical simulation according to the size of the aperture of workpiece in the actual processing, which can provide technical support for the production.

Fabricating the Superhydrophobic Nickel and Improving Its Antifriction Performance by the Laser Surface Texturing.

The superhydrophobic surface can change the friction property of the material, reduce the adhesion of the friction interface, and produce a certain slip, thereby reducing the friction coefficient. The laser has high energy, high density, and is especially suitable for the surface treatment of materials. The laser surface texturing is a good way to construct superhydrophobic surfaces. The experiment uses a nanosecond pulse laser to construct the groove texture on the nickel surface. The contact area between the air and the droplets retained on the rough surface is increased, effectively preventing the water droplets from entering the gully of the surface microstructure, reducing the water droplets and the solid surface. The contact area ultimately makes the surface exhibit excellent superhydrophobicity. A superhydrophobic nickel surface having an apparent contact angle of water (ACAW) of 160° and a sliding angle (SA) of less than 10° was prepared. The MM-W1B vertical universal friction and wear tester was used to test the groove texture samples with different depths. The surface texture can capture the wear debris generated by the wear and store the lubricant, which is beneficial to the formation of fluid dynamic pressure lubrication and improve the load. The friction coefficient is reduced from 0.65 of the unprocessed surfaces to 0.25 after the texturing, and the friction performance is greatly improved.

Dynamic Stability Analysis of a Flexible Rotor Filled With Liquid Based on Three-Dimensional Flow

This paper deals with the dynamic stability of a flexible liquid-filled rotor. On the basis of three-dimensional flow, the fluid perturbation motion is analyzed and the fluid–structure interaction equation is established, combining with continuity equation, the expression of fluid force exerted on rotor is derived in terms of Fourier series expansion. Considering the complex nonlinear relationship between fluid dynamic pressure and the rotor deformation function, they are expanded in terms of the eigenfunction of a dry rotor. The whirling frequency equation of a flexible rotor partially filled with liquid is obtained based on the rotor static equilibrium equation. Finally, the numerical technique is used to analyze the dynamic stability of the rotor system, and the influences of system parameters on unstable region are discussed.