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Keywords = viscous torque loss

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20 pages, 7581 KiB  
Article
Kinematics Analysis and Oil Film Lubrication Characteristics in the Piston–Cylinder Interface of a Bent-Axis-Type Piston Motor
by Jinlin Yu and Xiaozhou Hu
Energies 2024, 17(23), 6080; https://doi.org/10.3390/en17236080 - 3 Dec 2024
Viewed by 1038
Abstract
Hydraulic piston motors are characterized by their excellent starting performance, high transmission torque, good sealing performance, compact design, and lightweight. These attributes make them highly applicable in fields such as construction machinery and marine applications. With the advancement of hydraulic transmission technology, higher [...] Read more.
Hydraulic piston motors are characterized by their excellent starting performance, high transmission torque, good sealing performance, compact design, and lightweight. These attributes make them highly applicable in fields such as construction machinery and marine applications. With the advancement of hydraulic transmission technology, higher performance requirements have been set for hydraulic motors. While extensive research has been conducted on hydraulic pumps, studies focusing on the performance of hydraulic motors remain relatively limited. Therefore, this paper is novel in that, based on the motion and force conditions of the piston, it differs from previous research on swashplate-type machinery by considering the complex structure of the bent-axis motor; it employs a micro finite element method to analyze the oil film characteristics at the piston–cylinder interface in a bent-axis piston motor, the structural changes in the piston assembly in the bent-axis motor are comprehensively considered, and a fluid–structure coupling model for the piston–cylinder interface is established. The leakage and viscous friction power loss equations for the piston–cylinder interface are derived. Simulation analyses are conducted using MATLAB R2016a to reveal the variation patterns of leakage and viscous friction power loss under different operating conditions and structural parameters, providing valuable insights for the operation analysis, energy loss evaluation, structural design optimization, and engineering applications of bent-axis piston motors. Full article
(This article belongs to the Section H: Geo-Energy)
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20 pages, 4980 KiB  
Article
Theoretical and Numerical Investigation of Reduction of Viscous Friction in Circular and Non-Circular Journal Bearings Using Active Lubrication
by Denis Shutin and Yuri Kazakov
Lubricants 2023, 11(5), 218; https://doi.org/10.3390/lubricants11050218 - 13 May 2023
Cited by 9 | Viewed by 2400
Abstract
Reducing friction losses is one of the most common ways to improve fluid film bearings, whose adjustable design provides additional opportunities to improve their dynamic and tribological properties. Previous studies have shown the possibility of reducing viscous friction in actively lubricated bearings by [...] Read more.
Reducing friction losses is one of the most common ways to improve fluid film bearings, whose adjustable design provides additional opportunities to improve their dynamic and tribological properties. Previous studies have shown the possibility of reducing viscous friction in actively lubricated bearings by adjusting the rotor position. This work provides a theoretical justification for the mechanism of this effect for the cases of purely laminar lubricant flows in journal bearings. The operating modes connected with the transition to turbulent phenomena and the occurrence of Taylor vortices are beyond the scope of this paper. Conditions that ensure the minimization of friction losses in hydrodynamic and hybrid bearings with hydrostatic parts are determined based on the equations describing viscous friction in a fluid film. In non-adjustable plain hydrodynamic bearings, the minimum of friction is achieved with the centered shaft position that is actually unstable due to the resulting forces configuration. In actively lubricated hybrid bearings, a further reduction in viscous friction is possible by combining film thickness and pressure distributions. Recombining them, along with adjustment of the shaft position, allows the optimization of the distribution of shear stresses in the fluid film. As a result, the shear stresses caused by the rotation of the shaft can be partially compensated by the stresses caused by the pressure gradient, reducing the torque-resisting rotation. In addition, additional benefits can be obtained in the minimum friction state by the reduced lubricant flow and power losses to its pumping. A series of numerical calculations for elliptical, 3-, and 4-lobe bearings show that non-circular bores provide additional variability in film thickness distribution and a premise for optimizing the bearing tribological parameters. Four-lobe bearing demonstrated the best ability for reducing viscous friction among the considered designs. The results obtained can be used as a basis for further optimization of the geometry of fluid film bearings of both active and passive designs by reducing power losses due to viscous friction. Full article
(This article belongs to the Special Issue Tribology Problems in Rotating Machinery)
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44 pages, 15880 KiB  
Article
Improved Prediction of Aerodynamic Loss Propagation as Entropy Rise in Wind Turbines Using Multifidelity Analysis
by Kiran Siddappaji and Mark Turner
Energies 2022, 15(11), 3935; https://doi.org/10.3390/en15113935 - 26 May 2022
Cited by 6 | Viewed by 2290
Abstract
Several physics-based enhancements are embedded in a low-fidelity general unducted rotor design analysis tool developed, py_BEM, including the local Reynolds number effect, rotational corrections to airfoil polar, stall delay model, high induction factor correction, polar at large angle of attack, exergetic efficiency calculation [...] Read more.
Several physics-based enhancements are embedded in a low-fidelity general unducted rotor design analysis tool developed, py_BEM, including the local Reynolds number effect, rotational corrections to airfoil polar, stall delay model, high induction factor correction, polar at large angle of attack, exergetic efficiency calculation and momentum-based loss. A wind turbine rotor is analyzed in high fidelity designed from py_BEM using a 3D blade generator. It is a design derived from the NREL Phase VI rotor. Three design variations are analyzed using steady 3D CFD solutions to demonstrate the effect of geometry on aerodynamics. S809 and NACA 2420 airfoil properties are used for calculating the aerodynamic loading. Momentum, vorticity and energy transport are explained in depth and connected to entropy production as a measure of performance loss. KE dissipation downstream of the rotor is shown to be a significant contributor of entropy rise. Wake analysis demonstrates mixing with the free stream flow, which begins after 3 diameters downstream of the rotor and extends to about 25 diameters until the decay is very small. Vorticity dynamics is investigated using a boundary vorticity flux technique to demonstrate the relationship between streamwise vorticity and lift generated in boundary layers. Drag components are accounted as well. It is demonstrated using rothalpy that shaft power is not only torque multiplied by rotational velocity but a viscous power loss term must also be included. A multifidelity analysis of wind turbine aerodynamics is demonstrated by capturing flow physics at several levels. Full article
(This article belongs to the Special Issue The Nexus among Sustainable Development Goals and Clean Energies)
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16 pages, 6237 KiB  
Article
Numerical Simulation on Windage Power Loss of High-Speed Spur Gear with Baffles
by Yuzhe Zhang, Xiangying Hou, Hong Zhang and Jiang Zhao
Machines 2022, 10(6), 416; https://doi.org/10.3390/machines10060416 - 25 May 2022
Cited by 8 | Viewed by 2179
Abstract
Windage power loss (WPL) is significant and cannot be neglected in a study on transmission efficiency and reducing the energy consumption of high-speed gear. The influence mechanism of the baffle on the reduction of WPL needs to be further studied. Based on computational [...] Read more.
Windage power loss (WPL) is significant and cannot be neglected in a study on transmission efficiency and reducing the energy consumption of high-speed gear. The influence mechanism of the baffle on the reduction of WPL needs to be further studied. Based on computational fluid dynamics (CFD) technology, this paper puts stress on analyzing the influence of axial and radial baffles on viscous and pressure effects in WPL and the influence of baffles with groove structures on reducing WPL. The numerical calculation model of windage torque considering the baffle’s regulation is established, and the calculation results of WPL with different baffle configurations are obtained. The results indicate that the radial baffle mainly reduces pressure loss, while power loss caused by the viscous effect is mainly affected by the axial baffle. The baffle with the smallest clearance achieves the most significant suppression effect on windage. On this basis, adding groove structures to a smooth baffle can have a positive or negative impact on reducing WPL, and the baffles with circular grooves can further promote the reduction of WPL by 8.2%, compared with smooth baffles. This paper provides a reference for the optimal design of baffles in engineering applications. Full article
(This article belongs to the Section Machine Design and Theory)
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18 pages, 5730 KiB  
Article
Verification and Validation of Large Eddy Simulation for Tip Clearance Vortex Cavitating Flow in a Waterjet Pump
by Chengzao Han, Yun Long, Mohan Xu and Bin Ji
Energies 2021, 14(22), 7635; https://doi.org/10.3390/en14227635 - 15 Nov 2021
Cited by 12 | Viewed by 2106
Abstract
In this paper, large eddy simulation (LES) was adopted to simulate the cavitating flow in a waterjet pump with emphasis on the tip clearance flow. The numerical results agree well with the experimental observations, which indicates that the LES method can make good [...] Read more.
In this paper, large eddy simulation (LES) was adopted to simulate the cavitating flow in a waterjet pump with emphasis on the tip clearance flow. The numerical results agree well with the experimental observations, which indicates that the LES method can make good predictions of the unsteady cavitating flows around a rotor blade. The LES verification and validation (LES V&V) analysis was used to reveal the influence of cavitation on the flow structures. It can be found that the LES errors in cavitating region are larger than those in the non-cavitating area, which is mainly caused by more complicated cavitating and tip clearance flow structures. Further analysis of the interaction between the cavitating and vortex flow by the relative vorticity transport equation shows that the stretching, dilatation and baroclinic torque terms have major effects on the generation and transport of vortex structure. Meanwhile the Coriolis force term and viscosity term also exacerbate the vorticity transport in the cavitating region. In addition, the flow loss characteristics of this pump are also revealed by the entropy production theory. It is indicated that the tip clearance flow and trailing edge wake flow cause the viscous dissipation and turbulent dissipation, and the cavitation can further enhance the instability of the flow field in the tip clearance. Full article
(This article belongs to the Special Issue Advances in Pumped Storage Hydraulic System)
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10 pages, 4277 KiB  
Article
An Investigation of Viscous Torque Loss in Ball Bearing Operating in Various Liquids
by Martin Dobrovolný, Vladimír Habán, Jana Tancjurová and Jan Zbavitel
Water 2021, 13(10), 1414; https://doi.org/10.3390/w13101414 - 18 May 2021
Cited by 2 | Viewed by 3565
Abstract
The limited functionality of seals that are used in hydraulic machines to prevent the liquid from leaking into the bearings may result in decrease in machine efficiency and reliability and may cause an accident of the whole hydraulic machine. However, not every damage [...] Read more.
The limited functionality of seals that are used in hydraulic machines to prevent the liquid from leaking into the bearings may result in decrease in machine efficiency and reliability and may cause an accident of the whole hydraulic machine. However, not every damage of seals must result in a shutdown of the whole machine. In case of partially or fully flooded bearings, the machine can temporarily operate with significantly increased input power and with lower efficiency. Such a limited operation of the machine shortens its lifetime and is accompanied by the presence of torque loss on the shaft. The measurement of torque loss can be helpful during the design process of new machines as well as for an analysis of hydraulic losses and efficiency of prototypes. Moreover, the real-time measurement of torque loss can be used for remote online monitoring of hydraulic machines. The aim of this paper is to present primarily an experimental investigation of the viscous torque loss for ball bearings submerged into liquid. The CFD simulation is also included to distribute the total torque loss between the hub and the bearing. The main goal is to modify the drag coefficient, respectively the friction loss coefficient in SKF’s and Palgrem’s empirical model. The new coefficients may provide a prediction of torque loss in the fully flooded bearings which is not possible with existing models. The torque loss characteristics are determined for specific ball bearings too. In contradiction to partially flooded bearing situation, it is obvious from a experiment, that some coefficients in Palgrem’s model and SKF model are dependent on revolutions when bearings are fully flooded. The experimental investigation of viscous torque loss are carried out for various types of ball bearings, all fully submerged into two various liquids, i.e., oil and water. Full article
(This article belongs to the Section Hydraulics and Hydrodynamics)
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13 pages, 1391 KiB  
Article
Push/Pull Inequality Based High-Speed On-Chip Mixer Enhanced by Wettability
by Toshio Takayama, Naoya Hosokawa, Chia-Hung Dylan Tsai and Makoto Kaneko
Micromachines 2020, 11(10), 950; https://doi.org/10.3390/mi11100950 - 21 Oct 2020
Cited by 1 | Viewed by 2721
Abstract
In this paper, a high-speed on-chip mixer using two effects is proposed, i.e., push/pull inequality and wettability. Push/pull inequality and wettability are effective for generating a rotational fluid motion in the chamber and for enhancing the rotational speed by reducing the viscous loss [...] Read more.
In this paper, a high-speed on-chip mixer using two effects is proposed, i.e., push/pull inequality and wettability. Push/pull inequality and wettability are effective for generating a rotational fluid motion in the chamber and for enhancing the rotational speed by reducing the viscous loss between the liquid and channel wall, respectively. An on-chip mixer is composed of three components, a microfluidic channel for making the main fluid flow, a circular chamber connected to the channel for generating a rotational flow, and an actuator connected at the end of the channel allowing a push/pull motion to be applied to the liquid in the main channel. The flow patterns in the chamber under push/pull motions are nonreversible for each motion and, as a result, produce one-directional torque to the fluid in the circular chamber. This nonreversible motion is called push/pull inequality and eventually creates a swirling flow in the chamber. Using hydrophilic treatments, we executed the experiment with a straight channel and a circular chamber to clarify the mixing characteristics at different flow speeds. According to the results, it is confirmed that the swirling velocity under appropriately tuned wettability is 100 times faster than that without tuning. Full article
(This article belongs to the Special Issue Micro Process-Devices)
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17 pages, 2005 KiB  
Article
Rheological, Thermal, Superficial, and Morphological Properties of Thermoplastic Achira Starch Modified with Lactic Acid and Oleic Acid
by Carolina Caicedo, Rocío Yaneli Aguirre Loredo, Abril Fonseca García, Omar Hernán Ossa, Aldo Vázquez Arce, Heidy Lorena Calambás Pulgarin and Yenny Ávila Torres
Molecules 2019, 24(24), 4433; https://doi.org/10.3390/molecules24244433 - 4 Dec 2019
Cited by 20 | Viewed by 4722
Abstract
The modification of achira starch a thermoplastic biopolymer is shown. Glycerol and sorbitol, common plasticizers, were used in the molten state with organic acids such as oleic acid and lactic acid obtaining thermodynamically more stable products. The proportion of starch:plasticizer was 70:30, and [...] Read more.
The modification of achira starch a thermoplastic biopolymer is shown. Glycerol and sorbitol, common plasticizers, were used in the molten state with organic acids such as oleic acid and lactic acid obtaining thermodynamically more stable products. The proportion of starch:plasticizer was 70:30, and the acid agent was added in portions from 3%, 6%, and 9% by weight. These mixtures were obtained in a torque rheometer for 10 min at 130 °C. The lactic acid managed to efficiently promote the gelatinization process by increasing the available polar sites towards the surface of the material; as a result, there were lower values in the contact angle, these results were corroborated with the analysis performed by differential scanning calorimetry and X-ray diffraction. The results derived from oscillatory rheological analysis had a viscous behavior in the thermoplastic starch samples and with the presence of acids; this behavior favors the transitions from viscous to elastic. The mixture of sorbitol or glycerol with lactic acid promoted lower values of the loss module, the storage module, and the complex viscosity, which means lower residual energy in the transition of the viscous state to the elastic state; this allows the compounds to be scaled to conventional polymer transformation processes. Full article
(This article belongs to the Special Issue Structural Mechanics of Composite Materials and Structures)
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25 pages, 9823 KiB  
Article
Performance Analysis of Hydrofoil Shaped and Bi-Directional Diffusers for Cross Flow Tidal Turbines in Single and Double-Rotor Configurations
by Stefania Zanforlin, Fulvio Buzzi and Marika Francesconi
Energies 2019, 12(2), 272; https://doi.org/10.3390/en12020272 - 16 Jan 2019
Cited by 15 | Viewed by 4286
Abstract
With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. [...] Read more.
With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better CP were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a CP loss is expected. Full article
(This article belongs to the Section A: Sustainable Energy)
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