Disk Rotation Research Articles

ENTROPY ANALYSIS OF HYBRID NANOFLUID FLOW OVER A ROTATING POROUS DISK: A MULTIVARIATE ANALYSIS

This article discusses the flow of a time-dependent biviscosity hybrid nanofluid boundary layer across a rotational permeable disk with effects of magnetic field and thermal radiation, and the subjective and quantitative transfer of heat flow. In the classic Von Karman issue, nanofluids comprising volume fractions of Ag-MgO/60% water and 40% ethylene glycol are considered instead of Newtonian regular fluids. The governing equations are transformed nonlinear ordinary differential equations using Von Karman transformations. The equation for the generation of entropy is calculated as a function of velocity and temperature gradient. This equation is made nondimensional by adding geometric and physical flow field-dependent parameters. The velocity profiles in the radial, tangential, and axial directions, as well as the axial pressure gradient, nanoparticle temperature distribution, local skin friction, Nusselt number, and Bejan number, are calculated by using MATLAB bvp4c. The multivariate analysis is implemented in the numerical results of the Nusselt number. A rotation parameter is generated by the spinning phenomena, which regulates the disk's movement. Increasing the rotation of the disk causes fluid velocity to accelerate in both the radial and cross-radial directions, while contrasting phenomena can be noticed in the axial velocity of the flow. The temperature and wall shear stress of a nanofluid both rise with the disc's Brinkman number and the volume fraction of nanoparticles. Increasing the thickness of the thermal boundary layer raises the axial pressure gradient. Entropy measured by the Bejan number Influences the magnetic field and the Biot number. Physical parameters presented in this article may be used to optimize the system's performance. A magnetic rotating porous disk drives could be used in nuclear space propulsion engines and in heat transfer augmentation in thermal management and renewable energy sources.

Rotor Air-Friction Loss and Thermal Analysis of IPM Rotors for High Speed Axial-Flux Machine

This paper focuses on the temperature rise of high-speed disc rotor considering the air-friction loss for an axial flux permanent magnet (AFPM) motor with double rotors and sandwiched stator. The air-friction loss and the heat transfer coefficient on the rotor surface at different speed are obtained based on the formula method and Fluid-Thermal coupling analysis. The rotor temperature distribution based on the coupling analysis of temperature and fluid field is obtained considering various losses and the impact of heat dissipation of air flowing in the motor cavity. Finally, the temperature variation of rotor disc considering the rotating speed is presented for the AFPM motor in this paper. The heat dissipation mechanism of rotor disc for the AFPM motor are revealed. It provides a significant guideline for the cooling design and the efficiency enhancement of high speed AFPM motor.

Modeling the Mechanical Properties and Stress Mapping of Aluminium Based Metal Matrix Composite Used in Brake Disc Rotor

Modeling the Mechanical Properties and Stress Mapping of Aluminium Based Metal Matrix Composite Used in Brake Disc Rotor

Термообработка слизистых субпродуктов под воздействием электрофизических факторов: разработка установки

Low efficiency of equipment for heat treatment, disinfection and removal of unpleasant odour of substandard mucous by-products urges the development of an installation that provides for the complex effect of ultra-high frequency electromagnetic field, ozone and bactericidal flow of ultraviolet rays. The paper presents the technology and describes the installation developed by the authors. The installation ensures electromagnetic safety and uniformity of loading according to the penetration depth of the wave. The duration of raw material treatment is matched with the specific power of the microwave generator, the power of the lamps and with the rotation frequency of the compartment disc. The electric field strength has been studied in the CST Microwave Studio program. The developed installation contains a resonator in the form of a flattened spheroid with diameters of the main axes multiple of half the wavelength. Magnetrons are placed on the upper surface of the spheroid along the perimeter. On the inner surface of the spheroid, where there are corona needles, ring electro-gas-discharge lamps powered from pulsed modeled high-frequency generators are uniformly installed along the perimeter through the gap. The source of radiation in the bactericidal lamp is an electric discharge in a mixture of mercury vapour and argon. A fluoroplastic perforated disc is installed at the level of the large diameter of the spheroid, on which mucous by-products are treated. The conducted research shows that the intrinsic factor of quality of the spheroid resonator is 9000. The heat treatment and disinfection of raw materials is most effective at the plant productivity of 50 kg/h, electric field strength of 3 to 4 kV/cm, disc rotation frequency of 0.17 to 0.2 rpm and a specific power of the microwave generator of 1.2 W/g. Power consumption amounted to 6.6 kW, while energy costs were 0.132 kW∙h/kg.

Халькогениды висмута, полученные различными методами

The microstructure and thermoelectric properties of a Bi2Te3–Bi2Se3 solid solution samples containing 20 mol. % Bi2Te3 doped with Hg2Cl2 of n-type conductivity obtained by hot pressing, extrusion and spark plasma sintering of powders prepared by melt spinning and grinding the ingot in a ball mill were studied. Optical and electron scanning microscopy methods were used. The effect of the disk rotation speed on the morphology of particles obtained by melt spinning is investigated. The Seebeck coefficient, electrical conductivity and thermal conductivity were measured at room temperature and in the temperature range 100 – 700 K and the thermoelectric figure of merit was calculated. The samples had anisotropy of electrical conductivity (σ) and thermal conductivity (κ) in the direction perpendicular and parallel to the pressing, the Seebeck coefficient (α) was isotropic. At 300 K anisotropy factors σ┴/σ// ~ 2, κ┴/κ// ~ 2, α┴/α// ~ 1. The highest thermoelectric figure of merit (ZT)max = 1,0 ± 0,1 at ~ 470 K was obtained for extruded samples from powders prepared by grinding the ingot and for hot-pressed samples from powders obtained by melt spinning.

STUDY OF THE MOVEMENT OF A MATERIAL PARTICLE ON A FLAT DISK ROTATING AROUND A PERPENDICULAR AXIS INCLINED TO THE HORIZON

The movement of material particles along rotational planes is complex, since it should be considered as the result of the movement of the plane itself and the particle along this plane. The task becomes more difficult if the moving plane is inclined at a certain angle to the horizon. Its solution makes it possible to find out the regularities of the movement of a particle along an inclined plane, which rotates around an axis perpendicular to it. The purpose of the study is to establish the patterns of movement of material particles on a flat disc with and without blades, which rotates around a perpendicular axis inclined to the horizon. If a round disk rotating around an axis perpendicular to it is located horizontally, then the kinematic parameters of the particle's motion on it do not depend on the point of impact of the particle on the disk. If the disk is tilted at a certain angle β to the horizon, it is obvious that the absolute trajectories of the particle's movement and other parameters of the movement will not be the same and will depend on the sector of the disk from which the particle starts its movement. The relative and absolute motion of a particle on an inclined disk with and without rectilinear blades is considered. A system of differential equations of particle motion has been compiled using the accompanying trihedron of the transfer trajectory, which is a circle, and Frenet's formulas. Numerical integration of the system was carried out. The obtained results were visualized. It was established that when particles hit an inclined disk that rotates around its own axis, the absolute trajectories of motion differ significantly from the trajectories of motion along a horizontal disk, and the difference in trajectories increases with an increase in the angle of inclination β. If rectilinear vanes are installed on the disc in the radial direction, the difference between the particle motion parameters will increase insignificantly as the angle β increases. When increasing the angular speed of rotation of the disk at a given angle, the shape of the absolute trajectories of particle motion practically does not change, but they are different depending on the point of impact on the disk. There is a certain area of impact and a certain sector of trajectories, after passing which the particle flies up after leaving the disc. Among this set, it is possible to analytically find the point of impact and the corresponding trajectory, which provide the maximum angle of elevation of the particle (equal to the angle β).

Effect of TiO2 inoculants on the wear conduct of the aluminium AA 6061/red mud high performance hybrid composite

The current work focuses on the manufacturing of aluminium AA 6061 composites and its tribological characterization. This is achieved by reinforcing the matrix with red mud. However, the uniform dispersion of red mud requires ultrasonic assisted stir casting and the use of optimum wt.% of TiO2 inoculants. In this regard, the composition of red mud is fixed at 2 wt.%, since the addition of red mud beyond 2 wt.% results in the agglomeration, while the wt.% of TiO2 inoculants is varied from 2 wt.% to 6 wt.%. The wear tests are conducted as per the L9- Orthogonal Array (OA) for a load range of 10 N to 30 N, sliding distance of 500 m to 2500 m, disk rotation speed of 200 RPM to 600 RPM. The regression coefficients are more than 0.9 and close to unity and the error between the experimental outcomes and statistical values are within the tolerance band. The SWR and COF is minimized for 2 wt.% of red mud, 4 wt.% of TiO2, beyond which there is a slight increase in the wear of the composites attributed to the agglomeration of the reinforcments in certain localized regions and the presence of voids in other regions.

Turbulence in Particle-laden Midplane Layers of Planet-forming Disks

We examine the settled particle layers of planet-forming disks in which the streaming instability (SI) is thought to be either weak or inactive. A suite of low-to-moderate-resolution 3D simulations in a 0.2H-sized box, where H is the pressure scale height, are performed using PENCIL for two Stokes numbers, St = 0.04 and 0.2, at 1% disk metallicity. We find that a complex of Ekman-layer jet flows emerge subject to three co-acting linearly growing processes: (1) the Kelvin–Helmholtz instability (KHI), (2) the planet-forming disk analog of the baroclinic Symmetric Instability (SymI), and (3) a later-time weakly acting secondary transition process, possibly a manifestation of the SI, producing a radially propagating pattern state. For St = 0.2 KHI is dominant and manifests as off-midplane axisymmetric rolls, while for St = 0.04 the axisymmetric SymI mainly drives turbulence. SymI is analytically developed in a model disk flow, predicting that it becomes strongly active when the Richardson number (Ri) of the particle–gas midplane layer transitions below 1, exhibiting growth rates , where Ω is the local disk rotation rate. For fairly general situations absent external sources of turbulence it is conjectured that the SI, when and if initiated, emerges out of a turbulent state primarily driven and shaped by at least SymI and/or KHI. We also find that turbulence produced in 2563 resolution simulations are not statistically converged and that corresponding 5123 simulations may be converged for St = 0.2. Furthermore, we report that our numerical simulations significantly dissipate turbulent kinetic energy on scales less than six to eight grid points.

Disc Brake Run-Out Detection System

Abstract: Disc brakes failure had become a major issue in vehicles these days, some of the common reasons for brake failures are reported to be a disc wobble, as it affects the overall braking, and the wobble caused on disc brakes generates a shudder at the passenger cabin through the brake pedal, which adds to a jagged movement of the vehicle. After carrying out deep research on this issue, an idea was formed to sense the wobble on the disc rotor. So, based on this idea a new concept for the Data Acquisition system is presented, namely: a Brake Disc Run-Out Sensor, which is designed on browser-based simulation software, Tinker-Cad. A Circuit diagram along with a block diagram is displayed and explained, addressing the main idea and objective of this prototype, this system will show the disc brake wobble or run-out data to the driver or controller via a visual indication. In this system, a tilt sensor is used and is interfaced with a microcontroller, every code is explained in detail with comments on each step. This system will increase the overall life of the brake rotor and the vibrations caused on the vehicle will be avoidable up to some extent. Therefore, reducing the maintenance cost of the vehicle

Collective behavior of soft self-propelled disks with rotational inertia

We investigate collective properties of a large system of soft self-propelled inertial disks with active Langevin dynamics simulation in two dimensions. Rotational inertia of the disks is found to favor motility induced phase separation (MIPS), due to increased effective persistence of the disks. The MIPS phase diagram in the parameter space of rotational inertia and disk softness is reported over a range of values of translation inertia and self-propulsion strength of the disks. Our analytical prediction of the phase boundary between the homogeneous (no-MIPS) and MIPS state in the limit of small and large rotational inertia is found to agree with the numerical data over a large range of translational inertia. Shape of the high density MIPS phase is found to change from circular to rectangular one as the system moves away from the phase boundary. Structural and dynamical properties of the system, measured by several physical quantities, are found to be invariant in the central region of the high density MIPS phase, whereas they are found to vary gradually near the peripheral region of the high density phase. Importantly, the width of the peripheral region near the phase boundary is much larger compared to the narrow peripheral region far away from the phase boundary. Rich dynamics of the disks inside the high density MIPS phase is addressed. Spatial correlation of velocity of the disks is found to increase with rotational inertia and disk hardness. However, temporal correlation of the disks’ velocity is found to be a function of rotational inertia, while it is independent of disk softness.

Aero-Engine Rotor Assembly Process Optimization Based on Improved Harris Hawk Algorithm

Multi-stage disc rotor assembly is an important part of the aero-engine rotor manufacturing process. To solve the problem that excessive unbalance of assembly affects the vibration of the whole machine, this paper presents an optimization method for aero-engine rotor assembly balance based on an improved Harris Hawk algorithm. Firstly, the assembly sequence model of the single-stage disc blade and the phase assembly model of a multi-stage disc of the engine rotor is established. Secondly, by using the initial population generation based on dynamic opposing learning and the escape energy function of the non-linear logarithmic convergence factor, the search mechanism of the whale optimization algorithm is introduced in the global exploration, and the adaptive weight strategy and mutation strategy of the genetic algorithm is introduced in the development to improve the algorithm. Then, the effectiveness of the algorithm is verified by experiments and compared with particle swarm optimization, genetic algorithm, and Harris Hawk algorithm, the unbalance of the optimal blade assembly sequence is reduced by 91.75%, 99.82%, and 83.39%, respectively. The algorithm comparison and analysis are carried out for all disc-blade assembly optimization of the rotor. The optimal unbalance of the improved Harris Hawk optimization algorithm is reduced by 79.71%, 99.48%, and 54.92% on average. The unbalance of the algorithm in this paper is the best. Finally, the improved Harris Hawk algorithm is used to find the best assembly phase, and the optimized unbalanced force and moment are reduced by 84.22% and 98.05%, respectively. The results of this study prove that the improved Harris Hawk algorithm for aero-engine rotor assembly balance optimization can effectively reduce the unbalance of rotor disc blade assembly and rotor unbalance and provide a powerful solution for solving engine vibration.

Numerical Study on Tandem-Rotor Autorotation in Forward Flight

This work presents a systematic approach to analyzing the aerodynamic characteristics of tandem rotor forward autorotation considering rotor-to-rotor interference. The single-rotor computational model trimmed from a generic helicopter flight dynamics analysis program was used as the baseline model. The effectiveness of the baseline model is demonstrated by a comparison with data from wind tunnel tests performed in this work. The rotor disk angle of attack and driven moment distribution obtained by the modified model indicate the fact that the rotor acceleration is primarily caused by the higher angle of attack region of the disk. This is of great significance in the rotor blade design, in terms of the drag-to-lift ratio characteristics of the airfoil under different angle-of-attack ranges. The influence of wind speed, rotor shaft angle, and collective pitch on the steady-state rotor speed was then studied. The results show a nonlinear nature of the variation of steady rotor speed with collective pitch, which can cause a thrust control reverse problem during flight operations. To reveal the flow field details of rotor-to-rotor interference, the flow field Navier–Stokes equations of tandem rotor autorotation were solved. Computational results of both rotors’ inflow velocities were considered when deriving the empirical model of interference. The refined interference model was compared to the wind tunnel test data of the tandem rotor autorotation and showed good performance. This synthetical methodology, which combines mechanism analysis with CFD-aided refinement and experiment verification, achieves a balance between computational costs and accuracy and thus can be readily applied to engineering practices.

Numerical Investigations on Gas Ingestion Mechanism Based on Flow Instabilities in Rim Seal and Cooling Characteristics of Endwall in a 1.5-Stage Axial Turbine

Abstract The sealant flow and rim seal at the periphery of cavities formed between rotor and stator disks prevent the high-temperature gas from ingesting into disk cavities and reduce the use of secondary air bleeding from a compressor. The unsteady sealing performance of rim seal and the cooling characteristics of sealant flow on endwall of a 1.5-stage axial turbine are studied by solving the three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations via shear stress transfer (SST) turbulence model. Besides, mass transfer analogy is introduced to predict the sealant distribution which makes the numerical sealing effectiveness in front and aft cavities agree well with experimental data. The accuracy of the numerical method is verified. The sealing effectiveness in cavities and the flow field in rim seal clearance are analyzed, and the film cooling performance on endwall is explored. The results show that, compared with Φ0=0.0170, the area-averaged sealing effectiveness εc on stator face is increased by 19.05% when Φ0=0.500 in the front cavity, and compared with Φ0=0.0042, the area-averaged sealing effectiveness εc on stator face is increased by 9.82% when Φ0=0.096 in the aft cavity. The nonaxisymmetric pressure on the endwall near rim seal and Kelvin Helmholtz unstable vortices arise due to the circumferential velocity difference between main flow and cavity flow. The flow field in the rim seal clearance is jointly affected by these two factors. The flow pattern in the front rim seal clearance is mainly affected by unstable vortex while the flow pattern in the aft rim seal clearance depends on the circumferential pressure distribution. According to FFT, the most significant frequency of flow field variety is about 1200 Hz and 400 Hz (corresponding to two and six blades passing periods) in front and aft rim seals, respectively. The time-averaged cooling effectiveness increases with the increase of sealant flow on endwall and decreases gradually in the axial direction. The unsteady flow behavior of cooling effectiveness on endwall is also discussed in detail.

Flow structures and heat transfer characteristics in a vaneless counter-rotating turbine cavity with different cooling inflows

The cooling air is used in the gas turbine to prevent the hot gas ingress and overheating of turbine disks. In this paper, the flow structures and heat transfer characteristics of vaneless counter-rotating turbine (VCRT) with different types of cooling inflows are numerically analyzed. The three-dimensional unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a Shear Stress Transport (SST) turbulence model are adopted. The results reveal that the inertia force, rotating effect and mainstream dominate the flow fields in VCRT cavity. The axial cooling inflow promotes the heat transfer characteristic in low pressure rotor (LPR) disk meanwhile the radial cooling inflow improves the heat transfer performance in high pressure rotor (HPR) disk. The vortexes interaction, viscous dissipation and heat transportation result in the decrease of heat transfer characteristic in the high radius region of rotor disk. The combined cooling inflow is adopted to solve the problem. It is the combination of radial cooling inlet and high position cooling inlet. The cooling air injected axially from the high position cooling inlet moves outward along the HPR disk which enhances the heat transfer characteristic. It is found that the Nusselt number and the amount of cooling air is not the simple linear relationship. The Nusselt number in HPR disk no longer increases if the high position cooling flow rate exceeds the threshold value. Compared with other types of cooling inflows, the needed amount of cooling air reduces when the combined cooling inflow is adopted. There is an optimum combined cooling flow rate which obtains the excellent heat transfer characteristics in the HPR disk.

Wake transitions behind a streamwise rotating disk

Direct numerical simulations are performed to investigate the wake transitions of the flow normal to a circular rotating disk. The diameter-thickness aspect ratio of the disk is $\chi =50$ . The Reynolds number of the free stream is defined as $Re_s=U_\infty D/\nu$ , with incoming flow velocity $U_\infty$ , disk diameter $D$ , and kinematic viscosity of the fluid $\nu$ . The rotational motion of the disk is described by the Reynolds number of rotation $Re_r=\varOmega Re_s$ , with non-dimensional rotation rate $\varOmega =\frac {1}{2}\omega D/U_\infty$ , where $\omega$ is the angular rotation speed of the disk. Extensive numerical simulations are performed in the parameter space $50 \leqslant Re_s \leqslant 250$ and $0 \leqslant Re_r \leqslant 250$ , in which six flow regimes are identified as follows: the axisymmetric state, the low-speed steady rotation (LSR) state, the high-speed steady rotation (HSR) state, the low-speed unsteady rotation (LUR) state, the rotational vortex shedding state, and the chaotic state. Although plane symmetry exists in the wake when the disk is stationary, a small rotation will immediately destroy its symmetry. However, the vortex shedding frequencies and wake patterns of the stationary disk are inherited by the unsteady rotating cases at low $Re_r$ . A flow rotation rate jump is observed at $Re_s\approx 125$ . The LUR state is intermediate between the LSR and HSR states. Due to the rotational motion, the wake of the disk enters the steady rotation state earlier at large $Re_r$ , and is delayed into the vortex shedding state in the whole range of $Re_r$ . In the steady rotation states (LSR and HSR), the steady flow rotation rate is linearly correlated with the disk rotation rate. It is found that the rotation of the disk can restrain the vortex shedding. The chaotic state can be regularized by the medium rotation speed of the disk.

Experimental Investigations to Study the Influence of Thickness and Speed of Aluminum Discs on Brake Parameters with Neodymium – Iron – Boron Magnets

In the existing friction brakes there are several problems such as squealing, judder, thermal and mechanical failures, disc distortions etc. Hence, in the current work an effort is made to develop contactless braking system using eddy current principles. Aluminum disc along with Neodymium – Iron – Boron (NdFeB) permanent magnets are used for investigations. Thickness of discs considered are 4, 6 and 8 mm. Speeds of disc rotation are equivalent of 75.39 Km/hr, 113 Km/hr, 150.8 Km/hr and 188.5 Km/hr. Considered brake parameters are percentage of reduction in speed, negative acceleration and time consumed. In lone magnet situation with gradual application, higher percentage of reduction in speed, good negative acceleration and less time consumed were observed in 4 mm disc thickness. Hence is suitable for faster train applications. In lone magnet with rapid application situation, superior negative acceleration and lesser time consumed were found in 4 mm disc thickness. This situation is beneficial for high speed automobile applications.

Fluid Dynamics of Turbine Rim Seal Structures: A Physical Interpretation Using URANS

Abstract Unsteady Reynolds-averaged Navier–Stokes modeling (URANS) is a valuable and cost-effective tool for computational fluid dynamics (CFD), including the investigation of mainstream–cavity interaction in turbines. Despite the gap in accuracy with higher order CFD methodologies, URANS is among the few simulation strategies of industrial interest suitable for predicting ingress/egress over a wide range of conditions. This paper presents a numerical study of the flow-field in the upstream double-radial seal of a 1.5 stage turbine. Various configurations are tested, including nonpurged and purged conditions. Rigor of the approach is ensured by a set of sensitivity analyses, allowing the delineation of a best practice on the use of URANS in rim seal simulations: this includes an assessment of the effects of sector size, cavity domain size, and blade count. Time-averaged and time-resolved flow predictions capture coherent structures in the rim gap. An association between the three-dimensional (3D) morphology of these structures and different ingress/egress mechanisms is proposed. Regions of enhanced radial activity are identified to correspond with the blade leading edges. A frequency analysis of unsteady pressure signals probed in the rim gap leads to a calculation of the structure number and speed. The structures are synchronous with the disk rotation for nonpurged cases but rotate at slower speed when purge is introduced. The relative number of blades and vanes directly influences the structure count and velocity. The configuration with no blades is characterized by the slowest structures. The calculations have been conducted at three different flow coefficients for the annulus flow. There is a reduction in radial activity and structure speed at lower flow coefficient, fundamentally related to the reduced pressure asymmetry and gradient of swirl across the rim seal.

Tip vortex trajectory in proximity to the heliport

The last decade has brought a significant increase in the number of heliports built in Poland mostly for medical purposes to enable helicopter medical transport directly to the hospital. Some hospitals, however, could not build ground-level heliports due to limited space in densely populated areas. The solution to this problem can be elevated rooftop heliports. The main drawback of elevated heliports can be vibrations of the whole building, caused primarily by unsteady rotor slipstream which impinges on the heliport surface during take-off and landing. It is especially awkward in case of medical heliports due to strict vibration requirements. The frequency of these vibrations is known to equal a blade passing frequency of about 25 Hz for the Eurocopter EC-135 that is commonly used by, e.g. Polish medical service. However, the pressure measurements made by the authors showed that a low-frequency component of pressure oscillations of a significant amplitude is recorded in the outer part of the rotor disc. To explain the source of this component, we performed a PIV measurement of the velocity field in rotor slipstream. An object of investigation was the remotely controlled T-REX 450 Pro helicopter with a rotor diameter of 0.7 m. A key conclusion is that tip vortices from blade tips are located roughly along the Archimedean spiral, but vortices distanced from the blade tip shift up and down (or towards the blade tip and rotor axis) in a periodical manner.

Nonlinear Dynamic Numerical Analysis of Solid-liquid Separation Rolling Bearing-Rotor System Finite Element Discrete Modeling

Based on a rolling bearing-single disc rotor, centrifugal force is generated due to the influence of unbalanced factors such as rotor eccentric excitation, bearing restraint stiffness, and rotating stator clearance, which leads to the imbalance of the rotor system, resulting in the problem of friction between the rotor and the stator. This paper establishes a dynamic model of a single-disk rotor supported by rolling bearings, and the fourth-order Runge-Kutta numerical integration method is used to solve it. Bifurcation behavior and nonlinear dynamic response at a rotational speed. The results show that the nonlinear dynamic characteristics of the system are significantly different due to changes in elliptic eccentricity, rotational speed, and bearing constraint stiffness; when the rotational speed increases, the system gradually appears bifurcation, quasi-periodic motion, and instability increases. Therefore, reasonable selection of the working speed of the rotor and the gap between the stator and the rotor can reduce the non-periodic vibration caused by the unbalanced force and improve the stability of the system operation.

Snapshot of a magnetohydrodynamic disk wind traced with water masers

AbstractDisk-jet systems are common in astrophysical sources of different nature, from black holes to gaseous giant planets. The disk drives the mass accretion onto a central compact object and the jet ejects material along the disk rotation axis. Magnetohydrodynamic disk winds can provide the link between mass accretion and ejection, which is essential to ensure that the excess angular momentum is removed and accretion can proceed. However, up to now, we have been lacking direct observational proof of disk winds. This work presents a direct view of the velocity field of a disk wind around a forming massive star. Achieving a very high spatial resolution of 0.05 au, our water maser observations trace the velocities of individual streamlines emerging from the disk orbiting the forming star. We find that, at low elevation above the disk midplane, the flow co-rotates with its launch point in the disk, in agreement with magneto-centrifugal acceleration. Beyond the co-rotation point, the flow rises spiraling around the disk rotation axis along a helical magnetic field. We have performed (resistive-radiative-gravito-) magnetohydrodynamic simulations of the formation of a massive star and record the development of a magneto-centrifugally launched jet presenting many properties in agreement with our observations.