Dynamics and interactions of active rotors

We consider a simple model of an internally driven self-rotating object; a rotor, confined to two dimensions by a thin film of low Reynolds number fluid. We undertake a detailed study of the hydrodynamic interactions between a pair of rotors and find that their effect on the resulting dynamics is a combination of fast and slow motions. We analyse the slow dynamics using an averaging procedure to take account of the fast degrees of freedom. Analytical results are compared with numerical simulations. Hydrodynamic interactions mean that while isolated rotors do not translate, bringing together a pair of rotors leads to motion of their centres. Two rotors spinning in the same sense rotate with an approximately constant angular velocity around each other, while two rotors of opposite sense, both translate with the same constant velocity, which depends on the separation of the pair. As a result a pair of counter-rotating rotors are a promising model for controlled self-propulsion.Comment: 6 pages, 6 figure

Longitudial fluctuations of rotors of disk knife refiners

The subject of the study is the longitudinal fluctuations of the rotors of disk knife refiners. The dynamic and mathematical models of rotors of disk mills are developed. As a result of the research, a methodology for calculating the longitudinal fluctuations of rotors is proposed and tested. The error in determining the lower frequencies of free fluctuations of the mill rotors does not exceed 9%. The lowest frequencies of free longitudinal fluctuations of the rotors of existing mills are in the range of 85-165 Hz, and the second and subsequent frequencies of free fluctuations are in the frequency range above 1 kHz. When designing and operating disk knife refiners, it is necessary that the minimum inter-knife gap between the rotor and stator does not exceed the amplitude of fluctuations of the mill disk. The developed calculation procedure can be used in other industries, for example, mining and metallurgy. © Published under licence by IOP Publishing Ltd

The velocity field of a system of unsteady cycloidal vorticies

An essential difference between two-dimensional and three-dimensional models of cycloidal rotors, the presence of unsteady trailing cycloidal vorticies in the wake, was studied. The velocity induced by these vorticies is the primary mechanism producing flow retardation for low span/radius ratio, finite blade number rotors. Results of using idealized rigid wake model of finite blade cycloidal rotors to investigate some cycloidal rotor problems are presented

On the Classification of Universal Rotor-Routers

The combinatorial theory of rotor-routers has connections with problems of statistical mechanics, graph theory, chaos theory, and computer science. A rotor-router network defines a deterministic walk on a digraph G in which a particle walks from a source vertex until it reaches one of several target vertices. Motivated by recent results due to Giacaglia et al., we study rotor-router networks in which all non-target vertices have the same type. A rotor type r is universal if every hitting sequence can be achieved by a homogeneous rotor-router network consisting entirely of rotors of type r. We give a conjecture that completely classifies universal rotor types. Then, this problem is simplified by a theorem we call the Reduction Theorem that allows us to consider only two-state rotors. A rotor-router network called the compressor, because it tends to shorten rotor periods, is introduced along with an associated algorithm that determines the universality of almost all rotors. New rotor classes, including boppy rotors, balanced rotors, and BURD rotors, are defined to study this algorithm rigorously. Using the compressor the universality of new rotor classes is proved, and empirical computer results are presented to support our conclusions. Prior to these results, less than 100 of the roughly 260,000 possible two-state rotor types of length up to 17 were known to be universal, while the compressor algorithm proves the universality of all but 272 of these rotor types

Quality Assurance Testing for Screening Defective Aluminum Die-cast Rotors of Squirrel Cage Induction Machines

The recent trend in squirrel cage induction motor manufacturing is to replace fabricated copper rotors with aluminum die-cast rotors to reduce manufacturing cost to stay competitive in the global market. Porosity in aluminum die-cast squirrel cage rotors is inevitably introduced during the die cast process. Porosity can cause degradation in motor performance and can lead to a forced outage causing irreversible damage in extreme cases. Many offline and online quality assurance test methods have been developed and applied for assessment of rotor quality. However, years of experience with the existing test methods revealed that they are not suitable for quality testing or capable of providing a quantitative assessment of rotor porosity with sufficient sensitivity. In this paper, a new offline test method capable of providing sensitive assessment of rotor porosity is proposed. It is shown that rotors with minor and distributed porosity that are difficult to detect with other tests can be screened out during manufacturing. The proposed method is verified through a 3-D finite element analysis and experimental testing on closed and semiopen slot aluminum die cast rotors of 5.5 kW induction motors with porosity

Simulation of wind turbine wake interaction using the vorticity transport model

The aerodynamic interactions that can occur within a wind farm can result in the constituent turbines generating a lower power output than would be possible if each of the turbines were operated in isolation. Tightening of the constraints on the siting of wind farms is likely to increase the scale of the problem in the future. The aerodynamic performance of turbine rotors and the mechanisms that couple the fluid dynamics of multiple rotors can be most readily understood by simplifying the problem and considering the interaction between only two rotors. The aerodynamic interaction between two rotors in both co-axial and offset configurations has been simulated using the Vorticity Transport Model. The aerodynamic interaction is a function of the tip speed ratio, and both the streamwise and crosswind separation between the rotors. The simulations show that the momentum deficit at a turbine operating within the wake developed by the rotor of a second turbine is governed by the development of instabilities within the wake of the upwind rotor, and the ensuing structure of the wake as it impinges on the downwind rotor. If the wind farm configuration or wind conditions are such that a turbine rotor is subject to partial impingement by the wake produced by an upstream turbine, then significant unsteadiness in the aerodynamic loading on the rotor blades of the downwind turbine can result, and this unsteadiness can have considerable implications for the fatigue life of the blade structure and rotor hub

Performance and wake analysis of rotors in axial flight using computational fluid dynamics

Flow field around rotors in axial flight is known to be complex especially in steep descent where the rotor is operating inside its own wake. It is often reported that, in this flight condition, the rotor is susceptible to severe wake interactions causing unsteady blade load, severe vibration, loss of performance, as well as poor control and handling. So far, there is little data from experimental and numerical analysis available for rotors in axial flight. In this paper, the steady Reynolds-Averaged Navier-Stokes Computational Fluid Dynamics solver Helicopter Multi-Block was used to predict the performance of rotors in axial flight. The main objective of this study was to improve the basic knowledge about the subject and to validate the flow solver used. The results obtained are presented in the form of surface pressure, rotor performance parameters, and vortex wake trajectories. The detailed velocity field of the tip vortex for a rotor in hover was also investigated, and a strong self-similarity of the swirl velocity profile was found. The predicted results obtained when compared with available experimental data showed a reasonably agreement for hover and descent rate, suggesting unsteady solution for rotors in vortex-ring state

Orienting coupled quantum rotors by ultrashort laser pulses

We point out that the non-adiabatic orientation of quantum rotors, produced by ultrashort laser pulses, is remarkably enhanced by introducing dipolar interaction between the rotors. This enhanced orientation of quantum rotors is in contrast with the behavior of classical paired rotors, in which dipolar interactions prevent the orientation of the rotors. We demonstrate also that a specially designed sequence of pulses can most efficiently enhances the orientation of quantum paired rotors.Comment: 7 pages, 5 figures, to appear in Phys. Rev.

Manufacturing method and performance assessment for variable lead vacuum rotors

In recent years variable lead rotors have been produced, mainly for vacuum applications, involving a multiple pass manufacturing process which is necessarily time-consuming. A faster method of manufacturing such rotors uses a full profiled disc-type milling or grinding tool but involves clearance variations along the length. These effects have been assessed by computer modelling to quantify any disadvantages. The results indicate that the effects on performance are negligible and the profiled disk tool process is suitable for such components

Simulating wind turbine interactions using the vorticity transport equations

The aerodynamic interactions that can occur within a wind farm result in the constituent turbines generating a lower power output than would be possible if each of the turbines were operated in isolation. Tightening of the constraints on the siting of wind farms is likely to increase the scale of the problem in the future. The aerodynamic performance ofturbine rotors and the mechanisms that couple the fluid dynamics of multiple rotors can be understood best by simplifying the problem and considering the interaction between only two rotors. The aerodynamic interaction between two rotors in both axial and yawed wind conditions has been simulated using the Vorticity Transport Model. The aerodynamic interaction is a function of the tip speed ratio, the separation between the rotors, and the angle of yaw to the incident wind. The simulations show that the momentum deficit at a turbine operating within the wake developed by the rotor of a second turbine can limitsubstantially the mean power coefficient that can be developed by the turbine rotor. In addition, the significant unsteadiness in the aerodynamic loading on the rotor blades that results from the inherent asymmetry of the interaction, particularly in certain configurations and wind conditions, has considerable implications for the fatigue life of the blade structure and rotor hub. The Vorticity Transport Model enables the simulation the wakedynamics within wind farms and the subsequent aerodynamic interaction to be evaluated over a broad range of wind farm configurations and operating conditions