Radial Gap Research Articles

Thrust actuator with passive restoration force for wide gap magnetic bearings

Abstract Active thrust magnetic bearings provide an axial force to balance the moving parts of machines. However, most devices produce null or unbalancing passive forces. Furthermore, reported designs usually feature very small axial and radial gaps. This paper presents a thrust actuator for wide axial gaps that produces both passive and active restoring axial forces. It features a long biconical rotor and a stator housing a single winding and two permanent magnets. Simulations are done using finite-element-analysis (FEA) and compared to magnetic circuit analysis and experimental results from a prototype with a diameter of 48 mm and 20 mm axial displacement.

Numerical modeling and analysis of the noncontacting impulse gas face seals

Noncontacting mechanical seals with various kinds of face surface modifications have established their position in the sealing technique. Over the last few years, a lot of works dedicated to the impact of various surface modifications on the dynamics of working rings have been created. This paper presents model studies regarding relatively unknown noncontacting impulse gas face seals. Here, a mathematical model of impulse gas face seals is developed including the nonlinear Reynolds equation and stator dynamics equations, which were solved simultaneously using numerical methods. An original computer software written in C + + language was developed. A number of numerical tests were conducted and the phenomena occurring in the radial gap during seal operation were analyzed. Final conclusions were drawn and several features were indicated characterizing impulse face seals. It should be emphasized that numerical research on this type of seals has not been published yet. The literature usually presents simplified models for the noncompressible medium, which can be solved with the use of analytical methods.

FLOW MODELLING AND PERFORMANCE ASSESSMENT OF ROTARY SLIDING VANE PUMP USING COMPUTATIONAL FLUID DYNAMICS

A pump is a mechanical device that converts mechanical energy into hydraulic energy. The aim of the current work is to examine the behavior of fluid flow inside a rotary sliding vane pump and assessing the performance by studying the effect of change of the rotational speed, number of vanes and the radial clearance gap size between vane tips and stator surface on the performance of the pump. The commercial finite-volume solver ANSYS Fluent was used to simulate flow behavior in the pump with an additional C source code for the description of the dynamic mesh motion. Pump flow has been studied using lubricating oil, 5W-30, as the working fluid. Several computational configurations were used for the numerical simulation. The numerical results showed that 100% increase of the number vanes decreases the overall efficiency by 46.5%, while increasing the clearance gap size from 0.025 to 0.05 decreases the overall efficiency by 9.72%, and results in a 42.85% increase in the internal leakage within the pump.

INFLUENCING FACTORS OF SELF-PRIMING TIME OF MULTISTAGE SELF-PRIMING CENTRIFUGAL PUMP

Self-priming centrifugal pump are a type of drainage and irrigation equipment applied in crop irrigation, urban landscaping, dust prevention and cooling, and building water supply. At present, single-stage self-priming centrifugal pumps dominate the pump market. Hence, the market share for multistage self-priming pumps, which can provide high-pressure liquid, is barely adequate. Self-priming time is an important parameter that measures the self-priming performance of multistage self-priming centrifugal pumps. Although many studies have focused on the influences of a single factor on the self-priming time of single-stage self-priming centrifugal pumps, only a few have discussed the self-priming time of multistage self-priming pumps. In the current work, we conducted an experimental study that combined the orthogonal, grey correlation, and self-priming time tests to investigate the influencing factors of the self-priming time of a multistage self-priming centrifugal pump and shorten the corresponding self-priming time. The outlet width of the impeller blade, the radial gap between the impeller and the diffuser, the area of backflow hole, and the number of stages of the multistage self-priming centrifugal pump were selected as the influencing factors in the orthogonal test. The orthogonal analysis of the self-priming time of the multistage self-priming centrifugal pump was conducted, and the results were used as the basis in obtaining the order of importance of all influencing factors through the grey correlation test. Results demonstrate that self-priming time increases gradually with an increase in impeller blade outlet width but that it decreases continuously with an increase in stage number and area of backflow hole. As radial gap increases, self-priming time increases and then decreases. In summary, the area of backflow hole is the most important influencing factor of self-priming time of the multistage self-priming centrifugal pump, followed by impeller blade outlet width, radial gap, and stage number. These findings provide important references for shortening the self-priming time of multistage self-priming centrifugal pumps. Keywords: Multistage self-priming centrifugal pump, Grey correlation test, Orthogonal test; Self-priming time rrelation test, Bomba centrífuga autocebante multietapa, Ensayo de correlación Grey, Ensayo orthogonal, Ensayo de rrelación de tiempo autocebante

반경 공극에 따른 제어봉구동장치 인양 하중 영향 연구

반경 공극에 따른 제어봉구동장치 인양 하중 영향 연구

Performance Simulation Analysis for Magnetorheological Damper with Internal Meandering Flow Valve

Magnetorheological (MR) damper as a semi-active system for a vehicle suspension is simulated in this study. The proposed design of Magnetorheological (MR) valve consists of meandering flow channel or gaps that fixed in the piston of the damper. The focus of this study is to estimate the performance of proposed MR valve based on actual front suspension parameter of a vehicle. Annular and radial gaps are combined to produce an MR valve with meandering fluid flow path. Furthermore, the damper is filled with Magnetorheological (MR) fluid to energize the damper under the presence of magnetic fields. The magnetic flux density within each gap is obtained via the Finite Element Method Magnetics (FEMM) software. Therefore, the yield stress of MR fluid and magnetic flux relationships both can be predicted. The present paper shows a reduction in pressure drop when the thickness of each gap is increased. Pressure drop is closely affected by the fluid flow rate that enters each gap. This means that the lower flow rate increases the pressure drop of MR valve at various current.

Bearing Fault Analysis in Induction Motor Drives Using Finite Element Method

Diagnosis of faults in induction motor is an indispensable process in industries to improve the reliability of the machine and reduce the financial loss. Among the various faults occurring in induction motors (IM), bearing fault is the predominant one which covers nearly 60% of faults. In this paper, a study of the electromagnetic field of an induction motor with bearing fault fed from both the mains and a three phase voltage source PWM inverter in open loop is carried out using Finite element method (FEM). Electromagnetic field parameters like flux lines distribution, flux density distribution and radial air gapflux density are analyzed. The presence of bearing fault can be detected from the spatial FFT spectrum of radial air gap flux density. From the FFT spectrum, it is seen that the amplitude of fundamental component of radial air gap flux density decreases and those around 100 mm distance increases with the severity of fault.

Flow characteristics in a volute-type centrifugal pump using large eddy simulation

The flow characteristics in a volute-type centrifugal pump operating at design (Qd = 35 m3/h) and off-design (Qoff = 20 m3/h) conditions are investigated using large eddy simulation. Numerical results indicate that separation bubbles are generated on both the pressure and suction sides of impeller blades. At the off-design condition, the blade pressure side contains a larger recirculation zone with highly unsteady characteristics due to impeller-volute interactions. The vortices shed from a blade trailing edge due to its rotation strongly interact with those from the following blade and leakage through radial gaps at the off-design condition, generating stronger vortices in a wider region inside the volute, whereas this mutual interaction is weak at the design condition. Flow separation also occurs around the volute tongue at both operating conditions. At the off-design condition, a part of high-pressure fluid discharged from the volute does not follow the main stream to the outlet duct but re-enters into the volute area near the volute tongue. This pressurized fluid forms a high adverse pressure gradient on the blade pressure side, resulting in strong unsteady separation there. Also, a high pressure gradient in the axial direction at the radial gaps is formed especially near the volute tongue, creating the leakage into the cavities. Inside the volute, azimuthal vortices exist and grow along the volute passage. A secondary motion induced by these vortices also significantly affects the leakage to the cavities. All of these flow losses contain unsteady features that are strongly influenced by impeller-volute interactions, especially at the off-design condition.

Differences in the Gas and Dust Distribution in the Transitional Disk of a Sun-like Young Star, PDS 70

Abstract We present ALMA 0.87 mm continuum, HCO+ J = 4–3 emission line, and CO J = 3–2 emission line data of the disk of material around the young, Sun-like star PDS 70. These data reveal the existence of a possible two-component transitional disk system with a radial dust gap of 0.″42 ± 0.″05, an azimuthal gap in the HCO+ J = 4–3 moment zero map, as well as two bridge-like features in the gas data. Interestingly these features in the gas disk have no analog in the dust disk making them of particular interest. We modeled the dust disk using the Monte Carlo radiative transfer code HOCHUNK3D using a two-disk component. We find that there is a radial gap that extends from 15 to 60 au in all grain sizes, which differs from previous work.

Ducted wind turbine optimization and sensitivity to rotor position

Abstract. The design of a ducted wind turbine modeled using an actuator disc was studied using Reynolds-averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) simulations. The design variables included the rotor thrust coefficient, the angle of attack of the duct cross section, the radial gap between the rotor and the duct, and the axial location of the rotor in the duct. Two different power coefficients, the rotor power coefficient (based on the rotor swept area) and the total power coefficient (based on the exit area of the duct), were used as optimization objectives. The optimal value of thrust coefficients for all designs was nearly constant, having a value between 0.9 and 1. The rotor power coefficient was sensitive to rotor gap but was insensitive to the rotor's axial location for positions ranging from upstream of the throat to nearly half the distance down the duct. Compared to the design that maximized rotor power coefficient, the design for maximal total power coefficient was characterized by a smaller angle of attack, a smaller rotor gap, and a downstream placement of the rotor. The insensitivity of power output to the rotor position implies that a rotor placed further downstream in the duct could produce the same power with a considerably smaller duct exit area and thus a greater total power coefficient. The design for that maximized total power coefficient exceeded Betz's limit with a total power coefficient of 0.67.

Inferring giant planets from ALMA millimeter continuum and line observations in (transition) disks

Context. Radial gaps or cavities in the continuum emission in the IR-mm wavelength range are potential signatures of protoplanets embedded in their natal protoplanetary disk are. Hitherto, models have relied on the combination of mm continuum observations and near-infrared scattered light images to put constraints on the properties of embedded planets. Atacama Large Millimeter/submillimeter Array (ALMA) observations are now probing spatially resolved rotational line emission of CO and other chemical species. These observations can provide complementary information on the mechanism carving the gaps in dust and additional constraints on the purported planet mass. Aims. We investigate whether the combination of ALMA continuum and CO line observations can constrain the presence and mass of planets embedded in protoplanetary disks. Methods. We post-processed azimuthally averaged 2D hydrodynamical simulations of planet-disk models, in which the dust densities and grain size distributions are computed with a dust evolution code that considers radial drift, fragmentation, and growth. The simulations explored various planet masses (1 MJ ≤ Mp ≤ 15 MJ) and turbulent parameters (10−4 ≤ α ≤ 10−3). The outputs were then post-processed with the thermochemical code DALI, accounting for the radially and vertically varying dust properties. We obtained the gas and dust temperature structures, chemical abundances, and synthetic emission maps of both thermal continuum and CO rotational lines. This is the first study combining hydrodynamical simulations, dust evolution, full radiative transfer, and chemistry to predict gas emission of disks hosting massive planets. Results. All radial intensity profiles of 12CO, 13CO, and C18O show a gap at the planet location. The ratio between the location of the gap as seen in CO and the peak in the mm continuum at the pressure maximum outside the orbit of the planet shows a clear dependence on planet mass and is independent of disk viscosity for the parameters explored in this paper. Because of the low dust density in the gaps, the dust and gas components can become thermally decoupled and the gas becomes colder than the dust. The gaps seen in CO are due to a combination of gas temperature dropping at the location of the planet and of the underlying surface density profile. Both effects need to be taken into account and disentangled when inferring gas surface densities from observed CO intensity profiles; otherwise, the gas surface density drop at the planet location can easily be overestimated. CO line ratios across the gap are able to quantify the gas temperature drop in the gaps in observed systems. Finally, a CO cavity not observed in any of the models, only CO gaps, indicating that one single massive planet is not able to explain the CO cavities observed in transition disks, at least without additional physical or chemical mechanisms.

Global Search of a Three-dimensional Low Solidity Circular Cascade Diffuser for Centrifugal Blowers by Meta-model Assisted Optimization

A three-dimensional blade of a low solidity circular cascade diffuser in centrifugal blowers is designed by means of a multi-point optimization technique. The optimization aims at improving static pressure coefficient at a design point and at a small flow rate condition. Moreover, a clear definition of secondary flow expressed by positive radial velocity at hub side is taken into consideration in constraints. The number of design parameters for three-dimensional blade reaches to 10 in this study, such as a radial gap, a radial chord length and mean camber angle distribution of the LSD blade with five control points, control point between hub and shroud with two design freedom. Optimization results show clear Pareto front and selected optimum design shows good improvement of pressure rise in diffuser at small flow rate conditions. It is found that three-dimensional blade has advantage to stabilize the secondary flow effect with improving pressure recovery of the low solidity circular cascade diffuser.

Steam Turbine Flow Path Seals (a Review)

Various types of shroud, diaphragm, and end seals preventing idle leak of working steam are installed in the flow paths of steam turbine cylinders for improving their efficiency. Widely known labyrinth seals are most extensively used in the Russian turbine construction industry. The category of labyrinth seals also includes seals with honeycomb inserts. The developers of seals with honeycomb inserts state that the use of such seals makes it possible to achieve certain gain due to smaller leaks of working fluid and more reliable operation of the system under the conditions in which the rotor rotating parts may rub against the stator elements. However, a positive effect can only be achieved if the optimal design parameters of the honeycomb structure are fulfilled with due regard to the specific features of its manufacturing technology and provided that this structure is applied in a goal-seeking manner in the seals of steam and gas turbines and compressors without degrading their vibration stability. Calculated and preliminary assessments made by experts testify that the replacement of conventional labyrinth seals by seals with honeycomb inserts alone, due to which the radial gaps in the shroud seal can be decreased from 1.5 to 0.5 mm, allows the turbine cylinder efficiency to be increased at the initial stage by approximately 1% with the corresponding gain in the turbine set power output. The use of rectangular-cellular seals may result, according to estimates made by their developers, in a further improvement of turbine efficiency by 0.5–1.0%. The labor input required to fabricate such seals is six to eight times smaller than that to fabricate labyrinth seals with honeycomb inserts. Recent years have seen the turbine construction companies of the United States and Germany advertising the use of abradable (sealing) coatings (borrowed from the gas turbine construction technology) in the turbine designs instead of labyrinth seals. The most efficient performance of such seals in the turbine flow path is achieved with the sealing material-to-blade linear wear ratio equal to 10 : 1. According to estimates of the developers, application of abradable (sealing) coatings to all problem surfaces (resulting in the power output increased by 0.5–1.0%) is economically profitable even if this procedure is carried out under field conditions at a thermal power plant.

Effect of the ratio of radial gap to radius of the coils on the transmission efficiency of wireless power transfer via coupled magnetic resonances

Wireless power transfer (WPT) via coupled magnetic resonance is a promising technology to be applied in many fields. In general, there will be a radial gap in practical application, and some special application environments need to limit the radius of the coils. Therefore, in this paper, considering the comprehensive analysis of the radial gap and the radius of the coils, the concept of the ratio of radial gap to the radius of the coils was proposed. Based on the circuit theory, the formula between the ratio and transmission efficiency of WPT was deduced, and the effects of the ratio on the transmission efficiency were studied respectively at different axial distances. Simulation experiments were carried out and the results not only demonstrate the influence law of the ratio on transmission efficiency, but also validate the value of the ratio which the axial distance has the greatest effect on the transmission efficiency. Besides, the results shows the relationship between the effect of the ratio on the efficiency and the effect of the axial distance on the efficiency. The experimental results show that the theoretical analysis is correct, thus providing an useful theoretical reference for the design and further research on the wireless power transfer system in complicated environment.

Enactment-Based Direct-Drive Test of a Novel Radial-Gap Helical RotLin Machine

The future trend of mechanical systems is to substitute most of them by permanent magnet (PM) and/or electromagnetic based ones. This current research highlights a paradigm for future studies of the advanced direct-drivable safe and precise motion actuators, and headlines design, modeling, simulation, and implementation-based control of a novel RotLin (rotary–linear) radial gap helical machine. The machine is comprised of stator, midlayer rotor, and the inner layer translator. This is a hybrid of magnetic screw with a synchronous motor by modifying the design concept. Structurally, it is made using smartly piecewise helical-shaped PM that are radially magnetized, and helically layered on both rotor and translator. This machine has a wide range of applications, it can be used for linear actuation or for wave energy harvesting. The three-dimensional finite element analysis simulation results and calculations confirmed the realization of rotary and linear motions. To confirm this model, a prototype was enacted and experimental verifications of its performance in terms of direct-drive position and speed control were conducted. This compact machine can realize high thrust-force densities when used as a linear actuator.

Thermomagnetic effects on the stability of Taylor-Couette flow of a ferrofluid in the presence of azimuthal magnetic field

A stability analysis is conducted for the non-isothermal Taylor-Couette flow of a non-conductive ferrofluid under the action of an azimuthal magnetic field. The transition from steady flow to Taylor vortex flow is investigated in terms of the critical Taylor number and with respect to the changes in the magnetic field strength, radial temperature gradient, gap ratio, ferroparticle concentration and size. For the linear stability analysis, infinitesimal perturbations to the velocity, temperature and magnetization fields are considered and the resulting linear system of stability equations is solved using Chebyshev collocation method. Also, the original nonlinear system of equations is solved numerically using a finite element analysis software, and the results are compared with the linear stability analysis results. A significant stabilization is observed under strong magnetic fields for all cases. It is also observed that radial temperature difference has a destabilizing effect on the flow and this effect is amplified when the magnetic field strength is increased. Higher ferroparticle volume fraction and size lead to a strong degree of magnetization of the fluid and amplifies the stabilizing effect of magnetic fields. The stabilization under azimuthal magnetic forces is observed to be smaller for the narrow gap case compared to the wide gap case.

Theoretical and experimental models for the synthesis of single-walled carbon nanotubes and their electrochemical properties

A major challenge in the field of selective synthesis of single-walled carbon nanotubes (SWCNTs) via chemical vapor deposition (CVD) method is lack of established theoretical model for direct selection of metal/support catalyst to grow the corresponding SWCNTs. This has limited the application of these materials, especially, in electronics. In this report, we introduced circumferential and axial distortions in the Extended Tight Binding (ETB) equations to generate our model equations which correlated the numerical magnitude of chiral index (n, m) of SWCNTs directly with mass fractions of metal/support catalyst matrix, respectively. Theoretical predictions of our model equations showed acceptable deviations with ETB model, and two Fe2O3/Al2O3 catalysts were prepared according to this model to grow corresponding SWCNTs (10, 7) and (8, 8) via CVD pyrolysis of C6H14/N2 feedstock. High-resolution transmission electron microscopy analysis revealed bundled SWCNTs while analysis of their Raman profiles showed consistency with the radial breathing modes, diameter and energy band gaps of SWCNTs (10, 7) and (8, 8). Electrochemical analysis of the samples suggested potentials as pseudocapacitor electrodes. If fully explored and optimized, this model may complement or augment the existing in-situ epitaxial growth model.

Slip line model for forces estimation in the radial-axial ring rolling process

In the research presented in this paper, a slip line-based model is proposed for the estimation of both radial and axial force in the radial-axial ring rolling (RARR) process. Based on the shape of the contact arcs between ring and tools in the two deformation gaps present in the ring rolling process, a recursive algorithm for the calculation of the two slip line fields starting from the two pairs of opposite tools is derived and implemented in a commercial spreadsheet software (MS Excel). By considering the stress boundary conditions applied to the portion of material undergoing the deformation, both for the radial and axial deformation gaps, the pressure factors those make the two slip line fields starting from the two opposite tools to intersect are calculated and utilized for the estimation of radial and axial forces, for each round of the process. The developed model has been validated by cross-comparing its results with those of laboratory experiment and numerical simulation. For the validation study case, the average deviations, in comparison to the experimental results, are calculated in 1.86% and 4.55% for the slip line force model whereas in 6.86% and 0.88% for the numerical simulation, for the radial and axial forces respectively. The proposed slip line model has been also utilized for the estimation of radial and axial forming forces of nine different study cases of flat rings having the outer diameter ranging from 800 mm to 2000 mm, observing a maximum deviation, in comparison to the relevant FEM simulation, of 4.92% (radial force) and 5.88% (axial force). The developed slip line force model allows estimating almost in real time and with a reasonable accuracy the process forces and, for this reason, it may be of interest for both industrial and academic researchers dealing with the set-up and control of the radial-axial ring rolling process.

Effect of Radial Resistance Gap on the Pressure Drop of a Compact Annular-Radial-Orifice Flow Magnetorheological Valve

A compact annular-radial-orifice flow magnetorheological (MR) valve was developed to investigate the effects of radial resistance gap on pressure drop. The fluid flow paths of this proposed MR valve consist of a single annular flow channel, a single radial flow channel and an orifice flow channel through structure design. The finite element modelling and simulation analysis of the MR valve was carried out using ANSYS/Emag software to investigate the changes of the magnetic flux density and yield stress along the fluid flow paths under the four different radial resistance gaps. Moreover, the experimental tests were also conducted to evaluate the pressure drop, showing that the proposed MR valve has significantly improved its pressure drop at 0.5 mm width of the radial resistance gap when the annular resistance gap is fixed at 1 mm.

Experimental determination and study of horizontal forces during rolling

Results of experimental and theoretical studies of horizontal accelerations of rolls, chocks and housings of strip/sheet rolling stands are shown. Relations between horizontal forces and dynamic rolling torques, sequence of their arise are described. Significant influence of gaps in system ‘chock – housing’ and radial gaps in main drive lines on values of work rolls chocks horizontal impacts against housings is proved. Influence of rolled metal dimensions, mass and speed of rolled metal before metal-in on dynamic forces of work rolls chocks horizontal impacts against housings is described by means of developed mathematical relation.