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1
Hou, Xukui, Ende Wang, Hui Cao, Yalong Zhu e Kai Qi. "Research on Dynamic Balance Adjustment Method of Single Braced Frame Gyroscope Rotor". MATEC Web of Conferences 256 (2019): 02005. http://dx.doi.org/10.1051/matecconf/201925602005.
Testo completoAbstract (sommario):
The uneven mass distribution of gyro rotors results in vibration, rotation and drift of gyro rotors, which seriously affect the performance index and life of gyro rotors. However, because there is no rigid connection between the rotary shaft and the shell of the gyro rotor, the dynamic balancing machine can only balance the vibration component of the single braced frame gyroscope rotor, and can’t measure the gyro rotor’s rotation component. By analyzing the influence of uneven rotor mass distribution on the gyro rotor performance, a method of eliminating two rotational degrees of freedom of the gimbal in gyro rotor by mandrel is proposed, which makes the dynamic balancing machine directly measure the vibration component and the moving component of the gyroscope rotor, and simplifies the dynamic balancing debugging process.
2
Kay, Matthew W., Gregory P. Walcott, James D. Gladden, Sharon B. Melnick e Jack M. Rogers. "Lifetimes of epicardial rotors in panoramic optical maps of fibrillating swine ventricles". American Journal of Physiology-Heart and Circulatory Physiology 291, n. 4 (ottobre 2006): H1935—H1941. http://dx.doi.org/10.1152/ajpheart.00276.2006.
Testo completoAbstract (sommario):
During ventricular fibrillation (VF), electrical activation waves are fragmented, and the heart cannot contract in synchrony. It has been proposed that VF waves emanate from stable periodic sources (often called “mother rotors”). The objective of the present study was to determine if stable rotors are consistently present on the epicardial surface of hearts comparable in size to human hearts. Using new optical mapping technology, we imaged VF from nearly the entire ventricular surface of six isolated swine hearts. Using newly developed pattern analysis algorithms, we identified and tracked VF wave fronts and phase singularities (PS; the pivot point of a reentrant wave front). We introduce the notion of a compound rotor in which the rotor's central PS can change and describe an algorithm for automatically identifying such patterns. This prevents rotor lifetimes from being inappropriately abbreviated by wave front fragmentation and collision events near the PS. We found that stable epicardial rotors were not consistently present during VF: only 1 of 17 VF episodes contained a compound rotor that lasted for the entire mapped interval of 4 s. However, shorter-lived rotors were common; 12.2 (SD 3.3) compound rotors with lifetime >200 ms were visible on the epicardium at any given instant. We conclude that epicardial mother rotors do not drive VF in this experimental model; if mother rotors do exist, they are intramural or septal. This paucity of persistent rotors suggests that individual rotors will eventually terminate by themselves and therefore that the continual formation of new rotors is critical for VF maintenance.
3
Prasad Rao, Jubilee, Jonathan E. Holzsager, Marco M. Maia e Javier F. Diez. "Experimental Study into Optimal Configuration and Operation of Two-Four Rotor Coaxial Systems for eVTOL Vehicles". Aerospace 9, n. 8 (17 agosto 2022): 452. http://dx.doi.org/10.3390/aerospace9080452.
Testo completoAbstract (sommario):
Coaxial rotors are utilized in multirotor aerial vehicles for the added thrust compared to independent rotors while keeping similar area footprints; however, performance losses should be considered. This experimental study analyzes the effects of varying motor duty cycle and propeller pitch values in motor-propeller systems with two to four coaxial rotors. The results demonstrate that in a two-rotor coaxial system, to lessen the adverse effects of a front rotor’s backwash and operate at the maximum performance, only the back motor should be operated initially up to 75% duty cycle before using the front motor up to its 75% duty cycle. Additional thrust requirements should be generated from the back rotor and then from the front rotor up to their maximum duty cycles. In two, three, and four-rotor coaxial setups, total thrust output generated is 1.6, 2.1, and 2.5 times the thrust output at system thrust performance of 86%, 76%, and 66%, respectively, of that of an isolated rotor. In a four-rotor coaxial setup, the maximum system performance is achieved when the propeller pitch values gradually increase from the first to the last rotor. The gradual increments in propeller pitch values also result in more uniform thrust sharing among rotors.
4
Liu, Bao Guo, Hai Feng Hua, Long Wang Yue e Xiao Ding Xu. "Design of the Post-Processor for Rotors Dynamics Based on the STEP Standard". Advanced Materials Research 706-708 (giugno 2013): 1871–76. http://dx.doi.org/10.4028/www.scientific.net/amr.706-708.1871.
Testo completoAbstract (sommario):
The STEP standard is an international standard for data expressing and exchanging during the whole life cycle of the product, the neutral file is an universal data exchange form for the data exchanging. In order to develop a STEP post-processer for the rotor dynamics analysis software-Rotors Dynamics, the author elaborates the lexical analysis module and data mapping module, studies the rotor model parameter extraction based on STEP neutral file, and realizes the seamless connectivity between the Rotors Dynamics and the rotor’s CAD model.
5
Andrew, Philip L. "GE Power Services Ships First F-class Extended-Life Rotors". Mechanical Engineering 138, n. 05 (1 maggio 2016): 54–55. http://dx.doi.org/10.1115/1.2016-may-4.
Testo completoAbstract (sommario):
This article presents an overview of technical aspects of the first F-class gas turbine life-extended rotors. Power Services, a GE Power Business, has shipped from the Greenville, S.C., facility its two F-class extended-life rotors, building upon a foundation of experience gained by executing more than 20 E-class rotor life extensions (RLEs). Experience has shown that additional features that require inspection, including rabbet fillets on wheels other than on stage one, cannot be inspected without a complete rotor disassembly. Each rotor is uniquely characterised by the combination of its particular configuration and operational history. Expanding the value of an RLE upgrade also requires that it be executed at the right point in the rotor’s life. For the two rotors evaluated to date, there have been no unexpected issues uncovered from the part inspections as compared to analytical predictions.
6
Laube, Tomasz, e Janusz Piechna. "Analytical and Numerical Feasibility Analysis of a Contra-Rotary Ramjet Engine". Energies 13, n. 1 (30 dicembre 2019): 163. http://dx.doi.org/10.3390/en13010163.
Testo completoAbstract (sommario):
A new idea for a contra-rotary ramjet engine is presented. To define the theoretical limits of the non-typical, contra-rotary ramjet engine configuration, its analytical model was developed. The results obtained from that model and the analytical results were compared with those received from numerical simulations. The main weakness of existing rotary ramjet engine projects is the very high rotational speed of the rotor required for achieving supersonic inlet flow. In this paper, a new idea for a contra-rotary ramjet engine (CORRE) is presented and analyzed. This paper presents the results of analytical analysis and numerical simulations of a jet engine system with two rotors rotating in opposite directions. Contra-rotating rotors generate a supersonic air velocity at the inlet to the compressor at two times slower rotor’s speed. To determine the flow characteristics, combustion process, and engine efficiency of the double-rotor engine, a numerical solution of the average Navier-Stokes equations was used with the k-eps turbulence model and the non-premixed combustion model. The results of numerical simulations of flow and the combustion process inside the contra-rotary jet engine achieving a shockwave compression are shown and compared with similar data for a single-rotor engine design and analytical data. This paper presents only the calculation results of the flow processes and the combustion process, indicating the advantages of the proposed double-rotor design. The results of the numerical analysis were presented on the contours and diagrams of the pressure and flow velocity, temperature distribution, and mass fraction of the fuel.
7
Pervushin, Vladimir F. "Classification of rotary cultivation tools of agricultural machines and their motion trajectories". Agricultural Engineering, n. 3 (2023): 57–64. http://dx.doi.org/10.26897/2687-1149-2023-3-57-64.
Testo completoAbstract (sommario):
The rotary machines and implements used for the cultivation of agricultural crops do not fully meet the agrotechnical requirements. To determine the parameters of the working tools, the authors studied the absolute trajectory of their movement and classified rotary working tools of agricultural machines according to the special location of their rotation axis, dividing them into four groups and seven subgroups: A – the first group of rotors with a horizontal-transverse axis of rotation; B – the second group of rotors with a vertical axis of rotation; C – the third group of rotors with a longitudinal axis of rotation; D, D, E and F are the fourth group of rotors with the axis of rotation located in space relative to the coordinate system XYZ at angles α, β, and γ. The article presents kinematic analysis results for rotary working tools of classes G, D, E, W having a complex location of the axis of rotation in the space. The analysis of calculating the coordinates of the motion trajectory of rotary working tools showed that for the group of rotors of class G, D, E, the motion trajectory corresponds to a compressed cycloid, and for a rotor of class G, the trajectory represents a helicoid. The obtained motion trajectories of material points of rotary working tools can be used to evaluate the process of interaction of working tools with the soil and plant material, to determine the geometric parameters of working tools, the rotor speed, and the translational speed of an agricultural machine.
8
Kong, Yong-Boon, J. V. R. Prasad, Lakshmi N. Sankar e Chengjian He. "Finite State Inflow Flow Model for Coaxial Rotor Configuration". Journal of the American Helicopter Society 65, n. 3 (1 luglio 2020): 1–11. http://dx.doi.org/10.4050/jahs.65.032002.
Testo completoAbstract (sommario):
An analytical coaxial rotor inflow model has been developed from potential flow theory using the pressure potential superposition approach. The coaxial rotor pressure potential superposition inflow model (PPSIM) is formulated in statespace form with structure similar to the Peters–He model, except that additional off-diagonal blocks are included in the apparent mass (M-matrix) and influence coefficient matrices (L-matrix). These off-diagonal blocks take into account mutual interference effects present in a coaxial rotor system by relating the rotor's inflows due to other rotor's pressure loadings. Induced inflow distributions on both upper and lower rotors are computed using PPSIM for comparison against predictions from high-fidelity models such as GT-Hybrid and the viscous vortex particle method (VVPM). Good agreement between PPSIM-induced inflow results and GT-hybrid as well as VVPM data has been shown for hover flight condition. At low advance ratio, there are differences in fore-to-aft inflow states between PPSIM and the high-fidelity models. This is because PPSIM assumed rigid, skewed cylindrical wake geometries for both upper and lower rotors during forward flight. But in GT-Hybrid and VVPM, wake structures are allowed to move freely in space and are mainly affected by rotor-induced velocities at low advance ratios. Owing to the close proximity between upper and lower rotors, mutual interference-induced velocities significantly distorted the rotors' wake geometries. The rigid rotor wake geometry assumptions in PPSIM and the distortion captured in higher fidelity models are the reasons behind differences in rotor-induced inflows. At higher advance ratios, wake distortion effects are less prominent since free-stream inflows are significantly larger than rotorinduced velocities. Hence, smaller differences between PPSIM inflow states and those extracted from GT-Hybrid as well as VVPM are observed at high advance ratios.
9
Mimmi, G., e P. Pennacchi. "Analytical model of a particular type of positive displacement blower". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 213, n. 5 (1 maggio 1999): 517–26. http://dx.doi.org/10.1243/0954406991522743.
Testo completoAbstract (sommario):
Many papers exist in the literature that deal with the twin-screw compressor. This usually has two different rotors, a male and a female, and is commonly used to produce compressed gas for industrial uses. However, a different type of positive displacement rotary compressor with two screws is sometimes used, one of its typical applications being in car engine supercharging. The present paper deals with the latter type, which is defined as a two-screw blower. This blower has two identical helical rotors, each with three lobes. The kinematics and the geometry of the rotors are analysed here, and a complete mathematical model for the rotor is defined. Moreover, different possible shapes of the rotors, depending on the design parameters, are analysed and the limitations in the choice of the design parameters are presented. Finally, an analysis of the theoretical specific slipping of the rotors is presented, showing which zones of the profile are the most stressed. This model will be useful for further studies on rotor pressure loads and blower dynamics.
10
Qian, Kun Xi, Z. H. Xu e H. Wang. "Effects of Rotational Inertia and Bearing Force on Stability of Permanent Maglev Rotator". Applied Mechanics and Materials 150 (gennaio 2012): 50–56. http://dx.doi.org/10.4028/www.scientific.net/amm.150.50.
Testo completoAbstract (sommario):
The authors’ former works demonstrated that a passive magnetic (PM) rotator supported merely by PM bearings has a minimal speed, above which it can stabilize its equilibrium, under the function of a so-called Gyro-effect. It is unclear, however, by which factors is this minimal speed determined. This paper investigated the factors affecting the minimal stable speed of permanent maglev rotator, namely, the rotating inertia and PMB force. Two novel permanent maglev turbine models were designed: Model A---one stator and three rotors which have the same size but different rotational inertias; Model B---one rotor and one stator, but the stator has been devised with three different passive magnetic bearings: 1. a pair of small magnetic rings; 2. a pair of big magnetic rings; and 3. both of the two pairs of magnetic rings. Four Hall sensors distributed evenly at the turbine’s stator were used to detect the rotor’s eccentricity, and the speed sensor measured rotating speed. The calculated models of rotor’s eccentricity were established respectively for the two turbine models; the rotor’s eccentricity measuring system was built up and the rotor’s eccentricity of the two turbines was measured. The experimental data demonstrated that the rotational inertia of three rotors in the model A is 6.293×10-5 kg•m2, 1.074×10-4 kg•m2 and 2.081×10-4 kg•m2 respectively, and the corresponding minimal speed for suspension are 4597rpm, 3030rpm and 2222rpm respectively; in the model B, the magnetic force between the stator and rotor in the three cases is 92.12N, 123.48N, 212.66N respectively, corresponding to the minimal speed for suspension---3730rpm, 3120rpm and 2195rpm respectively. The results exhibited that same as the permanent maglev heart pump, permanent maglev turbines also have gyroscopic effect, which makes the rotors maintain stable suspension. And the minimal speed for suspension has a negative correlation with the rotor’s rotational inertia, namely, the bigger the inertia of the rotor, the smaller the required speed for suspension; the minimal speed for suspension also has a negative correlation with the magnetic force between the stator and rotor, that is, the larger the magnetic force, the smaller the rotating speed for suspension. Smaller minimal speed means better stability of the system, thereafter larger inertia or larger bearing force means better stability; besides, larger difference between minimal speed and performance speed of the rotator means better stability, it’s suggested permanent maglev be applied in high speed rotary machines.
11
Mao, Xiaochen, e Bo Liu. "Numerical investigation of tip clearance size effect on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 231, n. 3 (15 febbraio 2017): 474–84. http://dx.doi.org/10.1177/0954410016638878.
Testo completoAbstract (sommario):
Based on a validation of the numerical methods with an experiment, numerical simulations are carried out to study the effect of tip clearance size on the performance and tip leakage flow in a dual-stage counter-rotating axial compressor. The predicted results showed that the variation of the tip clearance size in rotor2 has a more significant impact on the overall performance and stall margin of the compressor. In addition, the impact of the tip clearance size effect is mainly on the rotor with the tip clearance size variation. The variation of the tip clearance size in rotor2 almost has no influence on the performance of rotor1, while the performance of rotor2 is increased about 1.37% at near-stall point when the tip clearance size of rotor1 is increased to 1.0 mm from 0.5 mm. At peak efficiency condition, the tip clearance size variation in rotor1 has remarkable influence on the tip leakage vortex intensity, onset point and trajectory in rotor1, but has little influence on those in rotor2. However, the tip clearance size variation in rotor2 has remarkable effect on those in both rotors. Different tip clearance size combination schemes can impact the stall-free characteristic in the counter-rotating axial compressor.
12
Povarov, Sergii. "Determination of the aerodynamic characteristics of the tiltrotor with the wingtip-mounted coaxial rotors". MECHANICS OF GYROSCOPIC SYSTEMS, n. 40 (26 dicembre 2021): 108–16. http://dx.doi.org/10.20535/0203-3771402020248778.
Testo completoAbstract (sommario):
The article describes the study of rotor-to-wing aerodynamic interaction for the wingtip-mounted coaxial rotors configuration of the tiltrotor aircraft.
The influence of the rotor slipstreams on lift-to-drag ratio characteristic was determined. Obtained results were compared with similar characteristics of the equivalent in thrust conventional single rotor slipstreams impact.
Using the computational aerodynamics methods (panel-vortex method) the flow around the tiltrotor model with the wingtip-mounted single and coaxial rotors has been simulated. A study of the basic model configuration with conventional single rotors, based on the technical characteristics of the AgustaWestland AW609 tiltrotor, was conducted. Further researches were conducted for a modified model where single rotors were replaced with equivalent in thrust coaxial rotors. The influence of the rotor slipstreams on the aerodynamic characteristics of the model for both directions of rotors rotation in coaxial combination is considered. Also, the dependence of the maximum lift-to-drag characteristic due to the coaxial rotor diameters change has been determined.
The results show that the coaxial rotor slipstreams-to-wing aerodynamic interaction effect is the similar to the effect of conventional single rotor, but less intensive. Comparison of the results showed that a tiltrotor equipped with wingtip-mounted single rotors has approximately 20% greater maximum lift-to-drag characteristic than one equipped with coaxial rotors with the same thrust. However, the use of coaxial rotors allows getting higher maximum speed, when conventional single rotors lose the efficiency significantly. Therefore, it is advisable to conduct further research for the possibility of using coaxial rotors for tiltrotor aircrafts.
The research results are presented in graphical form. The obtained data provides a basis for further studies of the described problem, and also will be useful for new tiltrotor design works.
13
Povarov, Sergey. "Comparison of aerodynamic characteristics of convertible models with single and coaxial schemes of propellers". MECHANICS OF GYROSCOPIC SYSTEMS, n. 39 (20 maggio 2020): 96–105. http://dx.doi.org/10.20535/0203-3771392020229110.
Testo completoAbstract (sommario):
The article describes the study of rotor-to-wing aerodynamic interaction for the wingtip-mounted coaxial rotors configuration of the tiltrotor aircraft.
The influence of the rotor slipstreams on lift-to-drag ratio characteristic was determined. Obtained results were compared with similar characteristics of the equivalent in thrust conventional single rotor slipstreams impact.
Using the computational aerodynamics methods (panel-vortex method) the flow around the tiltrotor model with the wingtip-mounted single and coaxial rotors has been simulated. A study of the basic model configuration with conventional single rotors, based on the technical characteristics of the AgustaWestland AW609 tiltrotor, was conducted. Further researches were conducted for a modified model where single rotors were replaced with equivalent in thrust coaxial rotors. The influence of the rotor slipstreams on the aerodynamic characteristics of the model for both directions of rotors rotation in coaxial combination is considered. Also, the dependence of the maximum lift-to-drag characteristic due to the coaxial rotor diameters change has been determined.
The results show that the coaxial rotor slipstreams-to-wing aerodynamic interaction effect is the similar to the effect of conventional single rotor, but less intensive. Comparison of the results showed that a tiltrotor equipped with wingtip-mounted single rotors has approximately 20% greater maximum lift-to-drag characteristic than one equipped with coaxial rotors with the same thrust. However, the use of coaxial rotors allows getting higher maximum speed, when conventional single rotors lose the efficiency significantly. Therefore, it is advisable to conduct further research for the possibility of using coaxial rotors for tiltrotor aircrafts.
The research results are presented in graphical form. The obtained data provides a basis for further studies of the described problem, and also will be useful for new tiltrotor design works.
14
Kosushkin, K. G., B. S. Kritsky e R. M. Mirgazov. "Computational studies of the rotors aerodynamic characteristics of multirotor drones". Civil Aviation High Technologies 24, n. 5 (1 novembre 2021): 60–75. http://dx.doi.org/10.26467/2079-0619-2021-24-5-60-75.
Testo completoAbstract (sommario):
The article presents the results of computational studies of aerodynamic characteristics for unmanned lift-generating multi-rotor drones of various configurations. The distinctive features of rotors flow were characterized. The rotor interaction was evaluated. The computations were based on the nonlinear rotor blade vortex theory in a non-stationary arrangement. The combinations of four, eight (four coaxial) and fourteen two-bladed rotors at velocity V = 100, 150, 200 km/h were considered. Semi-empirical methods were employed to select the rotor angles of attack, rotation speed, blade installation angles and geometric parameters at the given take-off weight for each combination of rotors and flight airspeed. The computations showed that for a four-rotor lift-generating design (quad-rotor), two rotors installed downstream, depending on the velocity due to the mutual effect, have values of the thrust coefficients ≈10...20% less than those of the rotors located upstream. For a coaxial quad-copter, the effect of the upper front rotor on the upper rear rotor is similar to the effect of the front rotors on the rear ones in a four-rotor lift-generating design. The effect of the upper front rotor on the lower rear rotor does not vary in terms of the average thrust value, and variations are only local in nature. The interaction of other rotors is identical to that of the four-rotor version. A fourteen-rotor lift-generating multi-rotor drone has a complex flow pattern, which generates deviance in the thrust coefficients variation with respect to time. Depending on the mode and rotors location, the average rotor thrust coefficient can vary approximately twice. The computations showed that with the similar geometric parameters and kinematics characteristics, rotors thrust is substantially subject to variation, which causes destabilizing moments to a significant degree without additional control input. Thrust pulsations and, respectively, vibrations grow in intensity as the flight airspeed increases. Probably, the right choice of the rotor configuration and the automatic control system can counterbalance thrust surge by so-called "phasing", i.e. selecting an initial azimuth angle for each rotor.
15
Kim, Pan Soo, e James L. White. "Flow Visualization of Intermeshing and Separated Counter-Rotating Rotor Internal Mixer". Rubber Chemistry and Technology 67, n. 5 (1 novembre 1994): 880–91. http://dx.doi.org/10.5254/1.3538719.
Testo completoAbstract (sommario):
Abstract A flow visualization investigation of material motions and compounding in an internal mixer with intermeshing rotors is described. Rotors based on the design of R. T. Cooke of Francis Shaw and Company are used. Compared with separated rotor designs developed by F. H. Banbury, the distinctive feature is the passage of the rubber and compounding ingredients through the calendering gap between the rotors during mixing. The intermeshing rotors were found to rapidly circulate the materials from rotor to rotor around the mixing chamber and to more rapidly incorporate carbon black and oil relative to double-flighted separated rotors.
16
Saini, Gaurav, e Ashoke De. "ON THE SELF-STARTING COMPARATIVE PERFORMANCE EVALUATION OF DARRIEUS AND HYBRID HYDROKINETIC ROTOR". International Journal of Energy for a Clean Environment 24, n. 5 (2023): 67–91. http://dx.doi.org/10.1615/interjenercleanenv.v24.i5.50.
Testo completoAbstract (sommario):
Darrieus rotor is a promising technology for hydrokinetic and wind energy harvesting applications. However, the Darrieus rotor suffers from the problem of poor starting performance. The present research highlights solutions to improve the poor starting performance of the Darrieus rotor by introducing the hybrid rotor. Further, a comparative performance evaluation of conventional vertical axis Darrieus and hybrid rotors has been investigated numerically. The most widely used S-series S-1046 hydrofoil has been utilized by hybrid and Darrieus rotors. Further, two semicircular blades are used for the Savonius part of the hybrid rotor. The size of the Savonius part is optimized to obtain maximum performance from the hybrid rotor. Analyzing the flow field distributions across the turbine vicinity has highlighted various possible reasons. The study results have demonstrated that the hybrid rotor yields an exceptional increment of about 159.41% in the torque coefficient under low tip speed ratio (TSR) regimes (during initial starting) compared to the Darrieus rotor. However, due to the Savonius rotor's presence, the hybrid rotor's maximum power coefficient is reduced slightly compared to the maximum operating point of the Darrieus rotor. Further, the hybrid rotor yields a wider operating range than the single maximum operating point by the Darrieus rotor. The present investigations will assist the designers in selecting the site-specific hydrokinetic technology suitable for efficient and optimum use of hydrokinetic potential.
17
Tucker, V. A. "Using a Collision Model to Design Safer Wind Turbine Rotors for Birds". Journal of Solar Energy Engineering 118, n. 4 (1 novembre 1996): 263–69. http://dx.doi.org/10.1115/1.2871791.
Testo completoAbstract (sommario):
A mathematical model for collisions between birds and propellor-type turbine rotors identifies the variables that can be manipulated to reduce the probability that birds will collide with the rotor. This study defines a safety index—the “clearance power density”—that allows rotors of different sizes and designs to be compared in terms of the amount of wind energy converted to electrical energy per bird collision. The collision model accounts for variations in wind speed during the year and shows that for model rotors with simple, one-dimensional blades, the safety index increases in proportion to rotor diameter, and variable speed rotors have higher safety indexes than constant speed rotors. The safety index can also be increased by enlarging the region near the center of the rotor hub where the blades move slowly enough for birds to avoid them. Painting the blades to make them more visible might have this effect. Model rotors with practical designs can have safety indexes an order of magnitude higher that those for model rotors typical of the constant speed rotors in common use today. This finding suggests that redesigned rotors could have collision rates with birds perhaps an order of magnitude lower than today’s rotors, with no reduction in the production of wind power. The empirical data that exist for collisions between raptors, such as hawks and eagles, and rotors are consistent with the model: the numbers of raptor carcasses found beneath large variable speed rotors, relative to the numbers found under small constant speed rotors, are in the proportions predicted by the collision model rather than in proportion to the areas swept by the rotor blades. However, uncontrolled variables associated with these data prevent a stronger claim of support for the model.
18
Doerffer, Krzysztof, Janusz Telega, Piotr Doerffer, Paulina Hercel e Andrzej Tomporowski. "Dependence of Power Characteristics on Savonius Rotor Segmentation". Energies 14, n. 10 (18 maggio 2021): 2912. http://dx.doi.org/10.3390/en14102912.
Testo completoAbstract (sommario):
Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.
19
Liu, Yongmeng, Yingjie Mei, Chuanzhi Sun, Pinghuan Xiao, Ruirui Li, Xiaoming Wang e Chengtian Li. "Multistage Asymmetric Rotors Coaxial Measurement Stacking Method Based on Minimization of Exciting Force". Symmetry 13, n. 6 (11 giugno 2021): 1054. http://dx.doi.org/10.3390/sym13061054.
Testo completoAbstract (sommario):
The unbalanced exciting force of high-speed rotary asymmetric rotor equipment is the main factor causing rotor vibration. In order to effectively suppress the vibration of the asymmetric rotor equipment, the paper establishes a multistage asymmetric rotor coaxial measurement stacking method that minimizes the exciting force. By analyzing the propagation process of the centroid of the multistage asymmetric rotor assembly and analyzing the relationship between the geometric center and the centroid of a single asymmetric rotor, a multistage asymmetric unbalanced rotor propagation model based on geometric center stacking is established. The genetic algorithm is used to optimize the unbalance of the multistage asymmetric rotors. Combined with the vibration principle under the exciting force, the vibration amplitude of the left bearing at different rotation speeds under the minimization of the exciting force and the random assembly phase is analyzed. Finally, the experimental asymmetric rotors are dynamically measured, combined with the asymmetric rotors’ geometric error measurement experiment. The experimental results confirm that the vibration amplitude of the assembly phase with the minimum exciting force is smaller than the vibration amplitude under the random assembly phase at three-speed modes, and the optimization rate reached 73.2% at 9000 rpm, which proves the effectiveness of the assembly method in minimizing the exciting force.
20
He, Xing Zhu, Shu Nan Liu, Yan Li Chen, Chun Xue Wang e Song Yang. "Research on Hover Characteristics of Ducted Fan with Coaxial Rotors". Applied Mechanics and Materials 427-429 (settembre 2013): 216–20. http://dx.doi.org/10.4028/www.scientific.net/amm.427-429.216.
Testo completoAbstract (sommario):
The method of handling respectively is used to refine the grid of ducted fan with coaxial rotors. Research the complex flow field of the ducted fan by numerical simulation to analyze its hover characteristics. The curve of the upper rotors lift, the lower rotors lift, the ducts lift with collective and the distance between rotors is got respectively. By comparing with the aerodynamic characteristics of ducted fan with a single rotor, results show that there is interference between the upper and lower rotors, the upper one interferes the lower one more heavily and interference is reduced with the increase of distance between the rotors; the duct of ducted fan with coaxial rotors can provide more lift than the one with a single rotor.
21
Sineglazov, Victor, e Oleksandr Stanislavchuk. "Automation Disign of Hybrid Vertical-axial Rotors". Electronics and Control Systems 4, n. 70 (1 aprile 2022): 44–50. http://dx.doi.org/10.18372/1990-5548.70.16755.
Testo completoAbstract (sommario):
The paper proves the need to create vertical-axial rotors of wind power plants in the city strip, which can be placed on roofs, which makes it possible to increase their energy efficiency by 60-70%. It is shown that the placement of such rotors on the roofs has its own characteristics, which is the need to take into account the relief of the roof of the house, its surface area, rose and wind speed over it and others. Examples of wind farms are considered and it is proved that their energy efficiency can be increased by using hybrid vertical-axial rotors, which consist of a combination of Darrieus and Savonius rotors, where the Darrieus rotor is the main source (s) of wind energy conversion. in electric, while the rotor (s) of Savonius provide acceleration of Darrieus rotors. In order to improve the quality of design, an automated design system was developed, which includes the following blocks: determining the forces affecting the rotor, choosing the type of main and accelerating rotors, determining the optimal number of blades, optimal rotor placement, calculation of dynamic rotor characteristics, analysis of probable wind speed characteristics and strength calculation.
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Dayhoum, Abdallah, Mohamed Etewa, Alejandro Ramirez-Serrano e Robert Martinuzzi. "Enhancing VTOL Performance: Shrouded Rotor BLDC Motor Model and Validation". Journal of Physics: Conference Series 2784, n. 1 (1 giugno 2024): 012004. http://dx.doi.org/10.1088/1742-6596/2784/1/012004.
Testo completoAbstract (sommario):
Abstract One prominent area of current research interest, driven by a multitude of factors and considerations, centers around drone technology. A primary challenge currently faced in the realm of small-scale Unmanned Aerial Vehicles (UAVs) is the increasing demand for increased power coupled with the constraint of limited flight duration provided by available battery technology. These vehicles fall into two overarching categories based on the presence or absence of shrouding around their rotor(s). Shrouded rotors play a pivotal role in augmenting aerodynamic performance by enhancing thrust while mitigating blade-tip vortex losses and numerous other aspects that are not presented in open rotors. Although such characteristics contribute to an expanded effective rotor diameter and optimized airflow within the shroud. There are numerous aspects related to power, shroud and rotor characterization, etc. that need to be understood before shrouded rotors are commonly used. This paper presents the implementation of an effective mathematical model for Brushless Direct Current (BLDC) motors, specifically tailored for application in conjunction with shrouded rotors aimed at enhancing thrust and reducing power consumption. The proposed model serves to predict the performance characteristics of the utilized motor within the context of the specified shrouded rotor combination. In order to identify the effects of the induced load torque on the rotor’s dynamic response, a methodical analysis is conducted on the numerical simulation of the proposed model. The results are experimentally verified for hover flying in a case study of a scalable and highly maneuverable vertical takeoff and landing aircraft developed for operations in highly confined spaces. The adoption of this modeling technique is anticipated to significantly streamline the shrouded rotor combination design and selection process, particularly in the selection of an appropriate motor.
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McKay, Michael E., Robert Niemiec e Farhan Gandhi. "Performance Comparison of Quadcopters with Variable-RPM and Variable-Pitch Rotors". Journal of the American Helicopter Society 64, n. 4 (1 ottobre 2019): 1–14. http://dx.doi.org/10.4050/jahs.64.042006.
Testo completoAbstract (sommario):
Use of variable-pitch rotors was compared against variable-RPM rotors on a 2-kg (20 N) quadcopter in simulation. To generate 5 N of thrust in hover while maintaining a 2:1 maximum thrust-to-weight ratio, the variable-pitch rotor required 29% more power. At low climb rates the variable-RPM rotor requires less power, but near its maximum rate it required more power than the variable-pitch rotor. The maximum climb rate for the variable-pitch rotor was up to 70% greater than that of the variable-RPM rotor. A quadcopter equipped with variable-pitch rotors required more power to operate compared to the aircraft with variable-RPM rotors over its operational airspeed range. The variable-pitch quadcopter required 30% more power at best-endurance speed and had 18% less range than the variable-RPM quadcopter (at maximum-range speed). The 1/rev root drag shear was 42% larger for the variable-RPM rotor, and the 2/rev H- and Y-forces were 37% and 50% larger. The 2/rev thrust vibration was 6.5% smaller for the variable-RPM rotor, and the hub pitching and rolling moments were 11% and 9% smaller, respectively. Unlike the quadcopter equipped with variable-pitch rotors, the quadcopter equipped with variable-RPM rotors experienced a beating phenomenon in the aircraft-level vibratory loads.
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Noor Al-Fauzan Syahputra, Muhammad, Subekti Subekti e Nur Indah. "Effect of eccentric mass on rotor dynamics as a source of harvesting energy vibration". JTTM : Jurnal Terapan Teknik Mesin 5, n. 1 (30 aprile 2024): 54–61. http://dx.doi.org/10.37373/jttm.v5i1.855.
Testo completoAbstract (sommario):
This research focuses on the potential for vibration energy from the use of eccentric masses in dynamic rotors to become an electrical energy source. Prior studies on eccentric mass in dynamic rotors were primarily concerned with examining the rotor's vibrational characteristics; however, little research was done on converting vibrational energy into electrical energy. The purpose of this study is to ascertain the maximum amount of electrical energy that can be produced by dynamic rotor vibrations using an eccentric mass. Utilizing an electromagnetic energy harvester, an experimental study is the methodology used. With a rotor rotation speed of 450 rpm, the eccentric mass variations used are 6.5 grams, 8.5 grams, and 10.5 grams. Matlab is used in this research to process data. The highest energy, using an eccentric mass of 8.5 grams, was found to be 24.15 mV. Nevertheless, this study shows that while the eccentric mass has an impact on the amplitude, it has no effect on the voltage. In order to increase and improve the efficiency of the electrical energy produced, further research on the utilization of vibration energy from dynamic rotors can be guided by the findings of this study
25
Bian, Hui Guang, Cui Wen Fu e De Wei Zhang. "Three Dimension Fluid Field of Mixer with Synchronous Rotors". Advanced Materials Research 87-88 (dicembre 2009): 323–28. http://dx.doi.org/10.4028/www.scientific.net/amr.87-88.323.
Testo completoAbstract (sommario):
The flow field analyzed method about mixer flow in chamber has been introduced, Synchronous rotor three dimension flow field simulation rubber with the Finite Element Analysis is reported. The physical and three dimension Finite Element Method models for synchronous rotors flow field has been built for the first time. Isothermal flow field simulation with synchronous rotor has been made, the pressure field, velocity field and viscosity field had been obtained from numerical simulation. The results showed flow field’s change rule in a circle clearly, which are useful to improve mixer rotor’s structure.
26
Bensason, David, Andrea Sciacchitano e Carlos Ferreira. "Experimental study of the impact of blade-tip mounted rotors on the X-Rotor vertical-axis wind turbine". Journal of Physics: Conference Series 2767, n. 7 (1 giugno 2024): 072016. http://dx.doi.org/10.1088/1742-6596/2767/7/072016.
Testo completoAbstract (sommario):
Abstract The Horizon 2020 European Commission-funded project - X-ROTOR - proposes a radical rethink of the traditional vertical-axis wind turbine geometry. The X-Rotor vertical axis wind turbine relies on blade-tip mounted rotors, referred to as secondary rotors, for power generation and takeoff. This study examines the aerodynamic effects of secondary rotors on a scaled X-Rotor model’s loading in an open-jet wind tunnel. Particle image velocimetry measurements are taken at two cross-stream planes within the volume of rotation of a scaled turbine model at two phase-locked positions. The measurements are compared with cases without secondary rotors present to understand the local impact of the blade-tip mounted devices on the wake and vortex strengths. The results indicate an accelerated turbulent diffusion of the trailing tip-vortex of the X-Rotor, and the subsequent local in-plane velocity gradients induced by the trailing tip-vortex are diminished. These insights and experimental database contribute to the development and validation of numerical models of the X-Rotor with blade-tip mounted rotors.
27
Gan, Wenbiao, Yunpeng Wang, Hongbo Wang e Junjie Zhuang. "Aerodynamic Investigation on a Coaxial-Rotors Unmanned Aerial Vehicle of Bionic Chinese Parasol Seed". Biomimetics 9, n. 7 (2 luglio 2024): 403. http://dx.doi.org/10.3390/biomimetics9070403.
Testo completoAbstract (sommario):
Aerodynamic investigation of a bionic coaxial-rotors unmanned aerial vehicle (UAV) is performed. According to Chinese parasol seed features and flight requirements, the bionic conceptual design of a coaxial-rotors UAV is described. A solution procedure for the numerical simulation method, based on a multi-reference frame (MRF) model, is expressed, and a verification study is presented using the typical case. The aerodynamic design is conducted for airfoil, blade, and coaxial-rotors interference. The aerodynamic performance of the coaxial rotors is investigated by numerical simulation analysis. The rotor/motor integrated experiment verification is conducted to assess the performance of the coaxial-rotors UAV. The results indicate that the UAV has excellent aerodynamic performance and bionic configuration, allowing it to adapt to task requirements. The bionic UAV has a good cruise power load reach of 8.36 kg/kw, and the cruise flying thrust force is not less than 78 N at coaxial-rotor and rotor-balloon distance ratios of 0.39 and 1.12, respectively. It has the “blocks stability phenomenon” formed by the rotor downwash speed decreases and the balloon’s additional negative pressure. The present method and the bionic configuration provide a feasible design and analysis strategy for coaxial-rotors UAVs.
28
Shchur, Ihor, Volodymyr Klymko, Shengbai Xie e David Schmidt. "Design Features and Numerical Investigation of Counter-Rotating VAWT with Co-Axial Rotors Displaced from Each Other along the Axis of Rotation". Energies 16, n. 11 (2 giugno 2023): 4493. http://dx.doi.org/10.3390/en16114493.
Testo completoAbstract (sommario):
In this paper, dual-rotor counter-rotating (CR) configurations of vertical axis wind turbines (VAWTs) are briefly inspected and divided into three types. This investigation was focused on one of these types—the CR-VAWT with co-axial rotors, in which two equal rotors are placed on the same shaft, displaced from each other along it and rotated in opposite directions. For this CR-VAWT with three-blade H-Darrieus rotors, the properties of the design in terms of aerodynamics, mechanical transmission and electric generator, as well as control system, are analyzed. A new direct-driven dual-rotor permanent magnet synchronous generator was proposed, in which two built-in low-power PM electric machines have been added. They perform two functions—starting-up and overclocking of the rotors to the angular velocity at which the lifting force of the blades is generated, and stabilizing the CR-VAWT work as wind gusts act on the two rotors. Detailed in this paper is the evaluation of the aerodynamic performance of the CR-VAWT via 3D computational fluid dynamics simulations. The evaluation was conducted using the CONVERGE CFD software with the inclusion of the actuator line model for the rotor aerodynamics, which significantly reduces the computational effort. Obtained results show that both rotors, while they rotate in opposite directions, had a positive impact on each other. At the optimal distance between the rotors of 0.3 from a rotor height, the power coefficients of the upper and lower rotors in the CR-VAWT increased, respectively, by 5.5% and 13.3% simultaneously with some increase in their optimal tip-speed ratio compared to the single-rotor VAWT.
29
Lin, Jau-Wen, e M. D. Bryant. "Reductions in Wear Rate of Carbon Samples Sliding Against Wavy Copper Surfaces". Journal of Tribology 118, n. 1 (1 gennaio 1996): 116–24. http://dx.doi.org/10.1115/1.2837065.
Testo completoAbstract (sommario):
Wear rates (μgm/s) versus rotor speed for carbon samples sliding against smooth and wavy copper rotors (250 μm thick copper sheets were attached to smooth and wavy steel and polycarbonate backings) were identical at some speeds, but at other speeds wear rates for the wavy rotors were almost half those of the smooth rotors. Slider vibrations (periodic, with period set by rotation) perpendicular to the sliding surface were measured and Fourier analyzed. Comparison of vibration spectral amplitudes to spectral amplitudes derived from surface profiles identified vibration modes dynamically enhanced by surface waviness on the wavy rotor. At speeds where wear rates on the wavy rotor were most reduced, amplitudes of certain modes in the vibration spectrum were most enhanced. For all these cases, the product of mode number times speed was nearly constant, suggesting resonance. Contact forces and contact voltage drop (due to a mA current flowing from slider to rotor) were measured and plotted versus time during all experiments. Friction coefficients rapidly varied between 0.1 and 0.4, but averaged 0.2. Traces of friction coefficient versus time for both wavy and smooth rotors were similar, even when wear rates plunged on the wavy rotor. There were no large jumps in the contact voltage drop data, suggesting that the slider never disconnected from any of the rotors. Photoelastic visualizations (Bryant and Lin, 1993) of slider-rotor interfaces revealed concentrated contact on the smooth rotors, but none on the wavy rotors. The absence (induced by vibration) of concentrated contact may have caused differences in wear rates. Appreciable reductions (up to 50 percent) in wear rate are possible by adding small surface waves to a rotor that induce micro-vibrations of the slider-spring-rotor contact system. The effect appears most pronounced at resonance.
30
Elgamal, Mohamed, Karim Kriaa e Mohamed Farouk. "Drainage of a Water Tank with Pipe Outlet Loaded by a Passive Rotor". Water 13, n. 13 (5 luglio 2021): 1872. http://dx.doi.org/10.3390/w13131872.
Testo completoAbstract (sommario):
The optimal design of pipe outlets is an essential objective for many engineering projects. For the first time, this paper reports the results of a laboratory investigation on the effect of using a passive rotor (added at the pipe outlet) on the outlet performance. Different sizes and numbers of blades of rotors were considered. Through the Tracker software package, video and image processing techniques were applied to capture the temporal variations of the tank water depth and the passive rotor’s angular speed. In addition, a normalized average drainage rate (NADR) parameter is defined to quantify the changes in the tank drainage rate as a result of passive rotor utilization. It is noted that adding a 4-bladed symmetric passive rotor will increase NADR by up to 9.0%. The study also shows that the highest increase in NADR is attained when the rotor diameter size is approximately 1.73 times the pipe outlet’s diameter for the case of symmetric 4-blade rotors, and the corresponding average tip rotor speed ratio is 1.65. It is also found that using an asymmetric 3-blade rotor has a negative impact on the NADR due to the significant perturbation produced by the rotor asymmetry.
31
Gan, Ze Feng (Ted), Vitor Tumelero Valente, Kenneth S. Brentner e Eric Greenwood. "Multirotor broadband noise modulation". Journal of the Acoustical Society of America 155, n. 3_Supplement (1 marzo 2024): A111. http://dx.doi.org/10.1121/10.0026987.
Testo completoAbstract (sommario):
Rotor broadband noise spectra are typically analyzed over time scales on the order of one or more rotor periods. However, modulation of the broadband noise spectrum with the blade passage frequency (BPF) has been shown to be significant for noise levels and perception of wind turbines and helicopters. In contrast, time-varying broadband noise has not been extensively studied for aircraft with many rotors, such as unmanned aerial vehicles (UAVs) or advanced air mobility aircraft. In this work, significant broadband noise modulation was measured in flight and anechoic chamber tests of hexacopter UAVs at various observer angles. This modulation is aperiodic with the BPF such that the modulation amplitude varies substantially between blade passages, even when the BPFs are controlled to be nearly constant between all rotors at all times. Furthermore, the azimuthal phasing between rotors greatly affects the measured modulation, such that the modulation of multiple rotors may be less than or greater than for a single rotor, depending on the phase offsets. The effects of phase variations on acoustic interactions between rotors is studied by comparing the sum of the modulation of individual rotors to the modulation of those rotors operating simultaneously. This is done not only using measurements, but also noise predictions made using PSU-WOPWOP. These results contribute understanding to how the noise modulation of rotors sum together, including the resulting directivity and aperiodicity.
32
Ahmad Adib Najib, Djamal Hissein Didane, Mostafa Radwan Behery e Hashim Ahmed Kabrein. "Comparison of 2D and 3D Simulations on Predicting the Performance of a Savonius Wind Turbine". CFD Letters 16, n. 7 (4 marzo 2024): 71–88. http://dx.doi.org/10.37934/cfdl.17.6.7188.
Testo completoAbstract (sommario):
The performance of Savonius rotors plays a vital role in harnessing wind energy for various applications. This study aims to investigate and compare the performance characteristics of Savonius rotors using two-dimensional (2D) and three-dimensional (3D) analysis approaches. The primary objective is to determine the optimal analysis method for evaluating the rotor's performance. The simulations were conducted using ANSYS software, considering six different tip-speed ratios (TSRs) ranging from 0.2 to 1.2, and three wind speed categories (7 m/s, 5 m/s, and 3 m/s). The hybrid shear-stress transport (SST) k-omega was used as the turbulence model. The results indicate that the 2D analysis approach, which simplifies the rotor's geometry by assuming rotational symmetry, provides reasonable estimations of the rotor's performance. However, the 3D analysis captures the intricacies of the rotor's actual geometry, accounting for the effects of non-uniform flow and vortex shedding, which can significantly influence the rotor's performance. The comparative analysis reveals that the 3D analysis predicts higher torque and power coefficients than the 2D approach, especially at higher wind speeds. At TSR 1.0, the torque and power coefficient obtained from the 3D approach are 6.56 Nm and 0.102, respectively meanwhile 2D approach gains 6.28 Nm torque and 0.098 for power coefficient. This research contributes to a better understanding of the performance characteristics of Savonius rotors and highlights the importance of considering three-dimensional effects in their analysis. The findings can guide the design and optimization of Savonius rotor systems, leading to improved wind energy conversion efficiency and enhanced utilization of renewable energy resources.
33
Kaleta, Jiří, Josef Michl, Cécile Mézière, Sergey Simonov, Leokadiya Zorina, Pawel Wzietek, Antonio Rodríguez-Fortea, Enric Canadell e Patrick Batail. "Gearing motion in cogwheel pairs of molecular rotors: weak-coupling limit". CrystEngComm 17, n. 41 (2015): 7829–34. http://dx.doi.org/10.1039/c5ce01372k.
Testo completoAbstract (sommario):
Investigation of the rotor dynamics by X-ray diffraction, spin–lattice relaxation, and DFT modelling of the two rotational barriers in arrays of rod-like molecules with 1,3-bis(ethynyl)bicyclo[1.1.1]pentane rotators conclude to gearing motion between two rotors in a pair.
34
Chen, Guang Zhong, Bing Zhang, Yue Yang, Jin Han e Lin Jun Tong. "3D Visualization Automatic Modeling of Helical Rotors". Applied Mechanics and Materials 321-324 (giugno 2013): 1721–24. http://dx.doi.org/10.4028/www.scientific.net/amm.321-324.1721.
Testo completoAbstract (sommario):
Structure of Helical rotor is complicated.3D visualization automatic modeling of Helical Rotors with CAD could make the design of product more efficient. Scheme of 3D visualization automatic modeling of Helical Rotors is described in detail and Generation Principle of end surface curve of rotor and Scanning helix is analyzed deeply in the paper. With the further development of SolidWorks by Visual C#, 3D Visualization Automatic Modeling of Helical Rotors is accomplished .
35
Wang, Chuan Sheng, Wei Shuai Lv e Hui Guang Bian. "Finite-Element Comparative Analysis of Two Kinds of Meshing Rotor". Key Engineering Materials 501 (gennaio 2012): 16–21. http://dx.doi.org/10.4028/www.scientific.net/kem.501.16.
Testo completoAbstract (sommario):
This paper mainly introduces two kinds of internal mixer rotor. The professional visco-elastic fluid software--Polyflow is used to obtain dynamic simulation analysis process of the two different types of meshing rotors. The transient flow field model’s simulation results of the two intermeshing rotors which have rotated for 180 seconds are used to analyze the performance of the two rotors. And these analyses can be theoretical references for optimal design of the rotor.
36
Peng, Jifeng. "Effects of Aerodynamic Interactions of Closely-Placed Vertical Axis Wind Turbine Pairs". Energies 11, n. 10 (21 ottobre 2018): 2842. http://dx.doi.org/10.3390/en11102842.
Testo completoAbstract (sommario):
In this study, a numerical model was developed to study the effects of aerodynamic interactions between a pair of counter-rotating vertical axis wind turbines (VAWTs) in close proximity. In this model, the rotor rotation is not prescribed as a constant as in most other studies, but is determined by the moment of inertia and the total torque of the rotor, including the aerodynamic torque, generator torque, and a torque representing friction. This model enables study of the behavior of the rotor under an arbitrary ambient wind profile. The model was applied to an isolated rotor with five straight J-blades and pairs of identical rotors placed in close proximity. Compared with an isolated rotor, the aerodynamic interactions between the pair of rotors enhance the aerodynamic torques on the rotors and significantly increase the turbine power output on a per unit basis. The enhancement in turbine power output due to aerodynamic enhancement decreases with the distance between the pair of rotors.
37
Mimmi, G., e P. Pennacchi. "INTERNAL LOBE PUMP DESIGN". Transactions of the Canadian Society for Mechanical Engineering 21, n. 2 (giugno 1997): 109–21. http://dx.doi.org/10.1139/tcsme-1997-0008.
Testo completoAbstract (sommario):
The subject of this paper is the theoretical analysis of the internal lobe pump which is a particular type of positive displacement rotary pump. The main components of the pump are the rotors: usually the outer one is characterised by lobes with circular shape, while the inner rotor profile is determined as conjugate to the other. For this reason the first topic presented here is the definition of the geometry of the rotors starting from the design parameters. The choice of these parameters is subject to some limitations in order to avoid inner rotor undercutting and to limit the pressure angle between the rotors. Now we will consider the design optimisation. The first step is the determination of the instantaneous flow rate as a function of the design parameters. This allows us to calculate two performance indexes commonly used for the study of positive displacement pumps: the flow rate irregularity and the specific flow rate. These indexes are used to optimise the design of the pump and to obtain the sets of optimum design parameters. Finally further considerations are presented regarding the calculation and the use of other performance indexes, the specific slipping and the rotor curvature, which are particularly suitable for giving more elements for the analysis of this case.
38
Tulwin, Tytus. "Low Reynolds Number Rotor Blade Aerodynamic Analysis". MATEC Web of Conferences 252 (2019): 04006. http://dx.doi.org/10.1051/matecconf/201925204006.
Testo completoAbstract (sommario):
Maintaining a steady hover flight in a rotorcraft usually requires high energy input. The aim of the paper is to prove that it is possible to vastly reduce energy use in a rotorcraft by reducing the disc loading. The energy consumption reduction is especially important in electric rotorcraft, where the energy source is characterized by low energy density when compared to the hydrocarbon fuel in ICE rotorcraft. The paper presents results of CFD simulations on low Reynolds Number operating rotors. For low RE rotors tip vortex induced drag is highly affecting the rotor’s Figure of Merit, thus reducing rotor performance. Even though FM is reduced, the low RE setup is still beneficial in terms of reduced Power Loading, the main factor responsible for hover endurance.
39
Tanabe, Yasutada, Hideaki Sugawara, Shigeru Sunada, Koichi Yonezawa e Hiroshi Tokutake. "Quadrotor Drone Hovering in Ground Effect". Journal of Robotics and Mechatronics 33, n. 2 (20 aprile 2021): 339–47. http://dx.doi.org/10.20965/jrm.2021.p0339.
Testo completoAbstract (sommario):
A variable-pitch-controlled quadrotor drone was simulated in the ground effect using a high-fidelity CFD solver. In contrast to a single rotor in the ground effect, which has been extensively studied for conventional helicopters, the flow fields around multiple rotors are complex. In this study, the rotating speed of the rotors was maintained constant, and the blade pitch angles were adjusted so that the total thrust of the multicopter was the same regardless of the rotor height from the ground. It was observed that the power required for the quadrotors, which generate the same thrust, decreases when the rotors are approaching the ground from the height where they can be considered to be out of the ground effect, but increases locally when the rotor height is approximately the rotor radius, owing to flow recirculation into the rotor, and then decreases abruptly when the rotors further approach the ground. The outwash from the quadrotors depends heavily on the direction relative to the quadrotor layout. Along the plane crossing the diagonal rotor centers, the outwash velocity profiles resemble those of a single rotor; however, the outwash from the rotor gaps is stronger and extends to a much higher altitude.
40
Shen, ZhiHuang, Bin Yao, BinQiang Chen, Wei Feng e XiangLei Zhang. "A Novel Rotor Profile Error Tracing and Compensation Strategy for High Precision Machining of Screw Rotor Based on Trial Cutting of Limited Samples". Shock and Vibration 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/978325.
Testo completoAbstract (sommario):
The machining precision plays an important role in the operation reliability and service life of screw rotors. However, the actual machined rotor profile of screw rotors is different from its theoretical profile due to the errors of the machine tool. This paper proposes a novel method of error tracing and compensation to reduce the machined errors of rotor profile on the basis of the limited sample trials, and the method is based on a matrix of error compensation. The errors of rotor profile are obtained based on limited sample trials machining of screw rotors,and fitted into piecewise smooth data. A matrix of error compensation is established to compute the errors of rotor profile to generate a compensated rotor profile. The compensated rotor profile is then used to regenerate forming tool and a new rotor product is processed on the same machine tool. And the errors of new rotor profile are smaller and can be reduced within (−0.01 mm, 0.01 mm) after compensations. Finally, the actual machining examples illustrate that the method of error compensation can not only satisfy the machining requirement of high-precision rotors, but also has the characteristics of good stability and applicability.
41
Wileman, J., e I. Green. "Parametric Investigation of the Steady-State Response of a Mechanical Seal With Two Flexibly Mounted Rotors". Journal of Tribology 121, n. 1 (1 gennaio 1999): 69–76. http://dx.doi.org/10.1115/1.2833813.
Testo completoAbstract (sommario):
A parametric analysis is performed to investigate the steady-state dynamic response of a mechanical seal with two flexibly mounted rotors. The effect of changing various inertia, support, and fluid film properties is examined. Short rotors are shown to benefit from gyroscopic aligning moments and to exhibit their maximum steady-state misalignment when one of the shaft speeds is zero. Long rotors experience misaligning gyroscopic moments, but if only one of the two rotors is long then aligning moments from the short rotor can be transmitted through the fluid and counteract the detrimental gyroscopic effect in the long rotor. In this case rotors which corotate are shown to have a higher steady-state misalignment than those which counterrotate because of the reduction of the hydrodynamic moments, thus leading to increased leakage and a higher probability of face contact.
42
Sharma, P. B., Y. P. Jain e D. S. Pundhir. "A Study of Some Factors Affecting the Performance of a Contra-Rotating Axial Compressor Stage". Proceedings of the Institution of Mechanical Engineers, Part A: Power and Process Engineering 202, n. 1 (febbraio 1988): 15–21. http://dx.doi.org/10.1243/pime_proc_1988_202_003_02.
Testo completoAbstract (sommario):
An experimental investigation of the performance of a contra-rotating stage is reported. The influence of factors such as speed ratio of the two rotors, rotor stagger, pitch-chord ratio and axial spacing between the rotors is examined from tests on a 0.66 hub-tip ratio compressor. The study reveals that the performance of a contra-rotating stage is affected by all these factors. Axial spacing between the rotors and the speed ratio of the rotors both exhibit a strong influence on the stalling behaviour of the stage. It has been found that in a stage with close axial gap, rotating stall on the first rotor is suppressed if the second rotor is contra-rotated at a speed 50 per cent faster than the first rotor. This unique advantage of contra-rotation is not obtained if the axial gap is large. Measurements of sound pressure level are also reported to highlight the high noise problems associated with a contra-rotating stage.
43
Song, Wenda, Zhengzhi Mu, Yufei Wang, Zhiyan Zhang, Shuang Zhang, Ze Wang, Bo Li et al. "Comparative Investigation on Improved Aerodynamic and Acoustic Performance of Abnormal Rotors by Bionic Edge Design and Rational Material Selection". Polymers 14, n. 13 (23 giugno 2022): 2552. http://dx.doi.org/10.3390/polym14132552.
Testo completoAbstract (sommario):
Rotor plays a vital role in the dynamical system of an unmanned aerial vehicle (UAV). Prominent aerodynamic and acoustic performance are a long-term pursuit for the rotor. Inspired by excellent quiet flight characteristics of owls, this work adopted bionic edge design and rational material selection strategy to improve aerodynamic and acoustic performance of the rotor. A reference model of rotor prototype with streamlined edges was firstly generated by reverse engineering method. With inspiration from owl wings and feathers, bionic rotors with rational design on leading and trailing edges were obtained. Original and bionic rotors were fabricated with polyamide PA 12 and Resin 9400 by 3D printing technique. Aerodynamic and acoustic performance of the as-fabricated rotors were experimentally measured and analyzed in detail using a self-established test system. Comparative experimental results indicated that the aerodynamic and acoustic performance of the rotors was closely related to the bionic structures, material properties, and rotational speeds. At the same rotational speed, bionic rotor fabricated with Resin 9400 can produce a higher thrust than the prototype one and its power consumption was also reduced. The resulting noise of different bionic rotors and their directivities were comparatively investigated. The results verified the bionic edge design strategy can effectively control the turbulent flow field and smoothly decompose the airflow near the tailing edge, which resulting in enhancing the thrust and reducing the noise. This work could provide beneficial inspiration and strong clues for mechanical engineers and material scientists to design new abnormal rotors with promising aerodynamic and acoustic performance.
44
Kaltenbacher, Wenzel, Markus Rottmann e Olaf Dössel. "An algorithm to automatically determine the cycle length coverage to identify rotational activity during atrial fibrillation – a simulation study". Current Directions in Biomedical Engineering 2, n. 1 (1 settembre 2016): 167–70. http://dx.doi.org/10.1515/cdbme-2016-0038.
Testo completoAbstract (sommario):
AbstractAtrial fibrillation is the most common cardiac arrhythmia. Many physicians believe in the hypothesis that persistent atrial fibrillation is maintained by centers of rotatory activity. These so called rotors are sometimes found by physicians during catheter ablation or electrophysiological studies but there are also physicians who claim that they did not find any rotors at all. One reason might be that today rotors are mainly identified by visual inspection of the data. Thus we are aiming at an algorithm for rotor detection. We first developed an algorithm based on the local activation times of the intracardiac electrograms recorded by a multielectrode catheter that can automatically determine the cycle length coverage. This was done to get an objective view on possible rotors and therefore help to quantify whether a rotor was found or not. The algorithm was developed and evaluated in two different simulation setups, where it could reliably determine cycle length coverage. But we found out that effects like wave collision and slow conduction have strong influence on cycle length coverage. This prevents cycle length coverage from being suited as the only parameter to quantify whether a rotor is present or not. On the other hand we could confirm that rotors imply a cycle length coverage of >70% if the multielectrode catheter is centered in an area of <5 mm away from the rotor tip. Therefore cycle length coverage can at least be used in some situations to exclude the presence of possible rotors.
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Jalal, Sara, Fernando Ponta, Apurva Baruah e Anurag Rajan. "Dynamic Aeroelastic Response of Stall-Controlled Wind Turbine Rotors in Turbulent Wind Conditions". Applied Sciences 11, n. 15 (27 luglio 2021): 6886. http://dx.doi.org/10.3390/app11156886.
Testo completoAbstract (sommario):
With the current global trend of the wind turbines to be commissioned, the next generation of state-of-the-art turbines will have a generating capacity of 20 MW with rotor diameters of 250 m or larger. This systematic increase in rotor size is prompted by economies-of-scale factors, thereby resulting in a continuously decreasing cost per kWh generated. However, such large rotors have larger masses associated with them and necessitate studies in order to better understand their dynamics. The present work regarding the aeroelastic behavior of stall-controlled rotors involves the study of the frequency content and time evolution of their oscillatory behavior. A wide range of experiments were conducted to assess the effects of rapid variations on the rotor’s operational conditions. Various gust conditions were tested at different wind speeds, which are represented by pulses of different intensities, occurring suddenly in an otherwise constant wind regime. This allowed us to observe the pure aero-elasto-inertial dynamics of the rotor’s response. A reduced-order characterization of the rotor’s dynamics as an oscillatory system was obtained on the basis of energy-transfer principles. This is of fundamental interest for researchers and engineers working on developing optimized control strategies for wind turbines. It allows for the critical elements of the rotor’s dynamic behavior to be described as a reduced-order model that can be solved in real time, an essential requirement for determining predictive control actions.
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Liu, Hung-Cheng, Shih-Hsi Tong e Daniel C. H. Yang. "Trapping-Free Rotors for High-Sealing Lobe Pumps". Journal of Mechanical Design 122, n. 4 (1 luglio 1999): 536–42. http://dx.doi.org/10.1115/1.1311611.
Testo completoAbstract (sommario):
In this paper a method for the design of new rotor profiles for high-sealing lobe pump is presented. The objective of this research is to improve the sealing property of lobe pumps by designing chamber profile conforming rotors. The deviation function method is adopted for the design. The resultant rotors are trapping-free and have C1 continuity. A design procedure for rotor generation is also developed. A sealing index is defined to evaluate the sealing property of lobe pumps. Our results show that it is possible to design many new rotor profiles that have better sealing property than conventional involute rotors. [S1050-0472(00)01304-0]
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Lu, Jie, Zhiqin Cai, Sijie Cai, Bin Yao e Binqiang Chen. "A Novel Engagement-Pixel Tracking Method for Meshing Clearance Layout of Twin-Screw Rotors". Mathematical Problems in Engineering 2019 (22 settembre 2019): 1–12. http://dx.doi.org/10.1155/2019/6316538.
Testo completoAbstract (sommario):
The performance of dry twin-screw compressors is primarily affected by the meshing clearance between a pair of meshing rotors. In this paper, a novel method for meshing clearance layout (MCL) is presented. The presented method is based on the engagement-pixel tracking (EPT) technique, which utilizes discrete-pixel curves generated by the two rotors. An algorithm for the proposed method is put forward. Firstly, when the profile of one rotor is known, the discrete point coordinates of the two rotor profiles and their thermal expansion profiles can be obtained. Secondly, the instantaneous contact models of the two rotors at special meshing positions are acquired under pixel coordinate system. Thirdly, through inspecting the pixels on the profile of a rotor and establishing the corresponding normal vector, the meshing clearance of the two rotors is extracted. Then, the meshing clearances can be generated by extracting the boundary pixels on the other rotor profile. Finally, the meshing clearance layout method is proposed. To verify the effectiveness of the presented method, a case study was conducted on a pair of meshing rotors to extract its meshing clearance. It was shown that the proposed method can be used as a tool for evaluating the clearance distribution of actual machined profiles.
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Mohammad, Al-Zgoul, e Attila Szilágyi. "Dynamical Simulation of A CNC Turning Centre (Survey Paper)". Design of Machines and Structures 10, n. 2 (2020): 85–90. http://dx.doi.org/10.32972/dms.2020.018.
Testo completoAbstract (sommario):
This paper shows the most common rotor systems which can be used to analyse a CNC turning center. Starting with the simplest rotor system representation (single-degree-offreedom) up to analysing multi-degree-of-freedom and infinite-degree-of-freedom rotor systems using the TMM (Transfer Matrix Method) when it comes to cases like multi desk rotors and Jeffcott-rotors.
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Pacholczyk, Michał, e Dariusz Karkosiński. "Parametric Study on a Performance of a Small Counter-Rotating Wind Turbine". Energies 13, n. 15 (29 luglio 2020): 3880. http://dx.doi.org/10.3390/en13153880.
Testo completoAbstract (sommario):
A small Counter-Rotating Wind Turbine (CRWT) has been proposed and its performance has been investigated numerically. Results of a parametric study have been presented in this paper. As parameters, the axial distance between rotors and a tip speed ratio of each rotor have been selected. Performance parameters have been compared with reference to a Single Rotor Wind Turbine (SRWT). Simulations were carried out with Computational Fluids Dynamics (CFD) solver and a Large Eddy Scale approach to model turbulences. An Actuator Line Model has been chosen to represent rotors in the computational domain. Summing up the results of simulation tests, it can be stated that when constructing a CRWT turbine, rotors should be placed at a distance of at least 0.5 D (where D is rotor outer diameter) or more. One can then expect a noticeable power increase compared to a single rotor turbine. Placing the second rotor closer than 0.5 D guarantees a significant increase in power, but in such configurations, dynamic interactions between the rotors are visible, resulting in fluctuations in torque and power. Dynamic interactions between rotor blades above 0.5 D are invisible.
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Lee, Yu-Been, e Jae-Sang Park. "Hover Performance Analyses of Coaxial Co-Rotating Rotors for eVTOL Aircraft". Aerospace 9, n. 3 (9 marzo 2022): 152. http://dx.doi.org/10.3390/aerospace9030152.
Testo completoAbstract (sommario):
Hover performance analyses of coaxial co-rotating rotors (or stacked rotors), which can be used as lifting rotors for electric VTOL (eVTOL) aircraft, are conducted here. In this study, the rotorcraft comprehensive analysis code, CAMRAD II, is used with the general free-wake model. The generic coaxial co-rotating rotor without the blade taper and built-in twist is considered as the baseline rotor model, and the rotor is trimmed to match a prescribed rotor thrust value. The hover performance, including the rotor power and Figure of Merit (FM), is investigated for various index angles, axial spacings, blade taper ratios, and built-in twist angles. A maximum FM value is obtained near an index angle of 0° and 10° when the axial spacing is below and above 5.27%R, respectively. When the index angle is 0° and axial spacing is 1.44% R, the maximum increments in the FM are 3.03% and 6.06%, respectively, for a rotor with a blade taper ratio of 0.8 and a built-in twist angle of −12°. Therefore, this simulation study demonstrates that the hover performance of coaxial co-rotating rotors can be changed by adjusting the index angle or the axial spacing.