Viscous Drag Torque Research Articles

Calculating the Torques and Meter Factor of Turbine Flow Meter with Numerical Simulation

The torque balancing equations and the torque equation of the turbine flow meter is deduced in the paper. The driving torque, the viscous drag torque and the bearing friction drag torque on the impeller is calculated by unsteady numerical simulation methods. The change rule of the various torques is gotten considering or not the influence of bearing drag torque. Also, the effect of different viscosity on the torque is calculated, which is used to explain the phenomenon of meter factor change law with the viscosity. It makes clear that the possibilities to improve the accuracy of the meter and to predicate the meter factor by unsteady numerical simulation.

Magnetic fluid control for viscous loss reduction of high-speed MRF brakes and clutches with well-defined fail-safe behavior

No-load losses within brakes and clutches based on magnetorheological fluids are unavoidable and represent a major barrier towards their wide-spread commercial adoption. Completely torque free rotation is not yet possible due to persistent fluid contact within the shear gap. In this paper, a novel concept is presented that facilitates the controlled movement of the magnetorheological fluid from an active, torque-transmitting region into an inactive region of the shear gap. This concept enables complete decoupling of the fluid engaging surfaces such that viscous drag torque can be eliminated. In order to achieve the desired effect, motion in the magnetorheological fluid is induced by magnetic forces acting on the fluid, which requires an appropriate magnetic circuit design. In this investigation, we propose a methodology to determine suitable magnetic circuit designs with well-defined fail-safe behavior. The magnetically induced motion of magnetorheological fluids is modeled by the use of the Kelvin body force, and a multi-physics domain simulation is performed to elucidate various transitions between an engaged and disengaged operating mode. The modeling approach is validated by captured high-speed video frames which show the induced motion of the magnetorheological fluid due to the magnetic field. Finally, measurements performed with a prototype actuator prove that the induced viscous drag torque can be reduced significantly by the proposed magnetic fluid control methodology.

Experimental Research on Drag Torque for Single-plate Wet Clutch

The relative motion between the friction and separate plates in a disengaged wet clutch causes viscous drag torque when the lubrication fluid flows through the clearance. Reduction of the drag torque is one of the important potentials for the improvement of transmission efficiency. The objective of this study is to set up an experimental rig to measure drag torque for a single-plate wet clutch. Visualization of the flow pattern in the clearance through transparent quartz was presented. Design factors and lubrication conditions were tested to evaluate the effects on drag torque. A comparison between the nongrooved plate and grooved plate was made. Plates made up of different materials were also tested to reveal the effects caused by the contact angle. Drag torque increases linearly at low rotating speeds and gradually decreases at high rotating speeds. It is confirmed that fluid completely covers the plate surface at a low rotating speed and air mixes with the fluid at a high rotating speed. A low feeding flow rate is useful to reduce drag torque. The reduction of the drag torque benefits from radial and deep grooves compared to a flat plate. A small contact angle near the stationary plate plays an important role in maintaining the oil film, however, it has little effect on the drag torque at the rotating side because the hydrodynamic force becomes dominant compared to the surface tension force. The test results help to build an accurate mathematical model based on two-phase flow lubrication.

Optical angular momentum transfer to microrotors fabricated by two-photon photopolymerization

We design, fabricate and test optically driven microrotors a few microns in size. The rotors are trapped and rotated in optical tweezers using an LG02 Laguerre–Gaussian laser beam. We verify that we can accurately measure the total optical torque by measuring the spin angular momentum transfer for three different polarizations, by comparing the optical torque with the optical torque calculated using computational electrodynamics and the viscous drag torque determined from the rotation rate and computational fluid dynamics. The torque agrees with that expected from the design principles and electromagnetic modelling of the torque within the optical trap.

Viscous Drag Torque on a Rotating Nanofabricated Cylinder Near an Infinite Plane Boundary

Microrheological and single molecule biological measurements often involve the use of a microscopic probe particle near a surface. On such systems a precise understanding of the hydrodynamic interactions between the particle and the surface is required. Recently nanofabricated nearly cylindrical quartz particles have been used as ideal trapping particles for an angular optical trap. Here the rotational viscous drag torque imposed on a nanofabricated quartz cylinder near a surface is measured with the angular optical trap. The deviation of torque from the Stokes drag relation in solution is measured as a function of distance from the plane surface of a microscope cover glass. The surface effect is found to be significant for distances on the order of the characteristic dimension of the cylinder. These findings will allow for more accurate and quantitative torsional measurements of angular trapping systems.

Theoretical Calculation of Laser Driving 3-D Microrotors

In this paper, we propose the new theoretical investigation on the optical forces and torques on complex microrotors. Based on R. C. Gauthier’s modified ray model, the optical forces and toques on a complex micro-object, the conical microrotor, are analyzed. The viscous drag torque is estimated by Stokes flow to obtain the rotational speed. The results of our computation agree well with the previously published experimental results, which indicates that our approach of the optical torque calculation is suitable for complex microrotors and that the theoretical calculation is very helpful to optimum design of light-driven microrotors. The primary experimental results of one kind of microrotors driven are also presented.

Electric and fluid field analysis of side-drive micromotors

Motive torque, axial force, and viscous drag torque in variable-capacitance side-drive micromotors are analyzed by finite-element modeling of electric and fluid fields. For electric field modeling, the focus is on surface-micromachined salient-pole polysilicon micromotors with 12 stator poles and eight rotor poles, and their three-dimensional geometry is considered. Comparison with results of two-dimensional in-plane and axial-plane analysis of the same motors indicates that 3-D finite-element analysis (FEA) of the electric field is required to accurately calculate the motive torque and axial force acting on the rotor. The 3-D results are in good agreement with available experimental data. For fluid field modeling, a simple axisymmetric model geometry that consists of a thin flat disk is used, and the bushing, stator, and bearing are added incrementally. The viscous drag coefficient from steady-state FEA is within 30% of the value estimated from experimental measurement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radiation torque on a sphere caused by a circularly-polarized electromagnetic wave

The cross sections associated with absorption, scattering, extinction, and radiation pressure for homogenous isotropic spheres illuminated by plane waves are well known. We derive a new fundamental cross section, namely, the one which gives the time-averaged torque caused by circularly-polarized illumination. Consider a $z$-directed wave with pure circular polarization corresponding to a positive value for the $z$ projection of the photon spin. Formulation of the Maxwell stress dyad of the total (incident + scattered) field gives the following torque relative to the sphere's center, ${\ensuremath{\Gamma}}_{z}=\frac{{I}_{L}\ensuremath{\pi}{\ensuremath{\alpha}}^{2}{Q}_{\mathrm{abs}}}{\ensuremath{\omega}}$. Here ${I}_{L}$ and $\ensuremath{\omega}$ are the incident wave's irradiance and angular frequency and $\ensuremath{\alpha}$ and ${Q}_{\mathrm{abs}}$ are the sphere's radius and Mie-theoretic absorption efficiency. Consequently the effective cross section for torque is the same as that for energy absorption $\ensuremath{\pi}{\ensuremath{\alpha}}^{2}{Q}_{\mathrm{abs}}$ as might be expected since the scattered radiation is shown to have the same ratio of $z$ component of angular momentum to energy as the incident wave. This result is rigorous for stationary isotropic spheres in vacuo. It may be used to estimate the steady-state angular velocity ${\ensuremath{\omega}}_{\mathrm{sz}}$ of a sphere in a gas which is achieved when ${\ensuremath{\Gamma}}_{z}$ is balanced by the viscous-drag torque. A Rayleigh-scattering approximation for ${Q}_{\mathrm{abs}}$, which should be useful for small spheres, gives ${\ensuremath{\omega}}_{\mathrm{sz}}\ensuremath{\simeq}\frac{{I}_{L}{M}_{g}{M}^{\ensuremath{'}}{M}^{\ensuremath{'}\ensuremath{'}}}{\ensuremath{\eta}c({M}^{\ensuremath{'}2}+2)}$ where the sphere's refractive index is ${M}^{\ensuremath{'}}+{\mathrm{iM}}^{\ensuremath{'}\ensuremath{'}}$ relative to that of the gas ${M}_{g}$, $\ensuremath{\eta}$ is the viscosity of the gas, and $c$ is the speed of light. The radiation torque caused by elliptically-polarized illumination and the torque on stratified spheres are also discussed.