Viscous Power Losses Research Articles

Kinematics Analysis and Oil Film Lubrication Characteristics in the Piston–Cylinder Interface of a Bent-Axis-Type Piston Motor

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.

Decreased erythrocyte aggregation in Glenn and Fontan: univentricular circulation as a rheologic disease model.

In the Fontan palliation for single ventricle heart disease (SVHD), pulmonary blood flow is non-pulsatile/passive, low velocity, and low shear, making viscous power loss a critical determinant of cardiac output. The rheologic properties of blood in SVHD patients are essential for understanding and modulating their limited cardiac output and they have not been systematically studied. We hypothesize that viscosity is decreased in single ventricle circulation. We evaluated whole blood viscosity, red blood cell (RBC) aggregation, and RBC deformability to evaluate changes in healthy children and SVHD patients. We altered suspending media to understand cellular and plasma differences contributing to rheologic differences. Whole blood viscosity was similar between SVHD and healthy at their native hematocrits, while viscosity was lower at equivalent hematocrits for SVHD patients. RBC deformability is increased, and RBC aggregation is decreased in SVHD patients. Suspending SVHD RBCs in healthy plasma resulted in increased RBC aggregation and suspending healthy RBCs in SVHD plasma resulted in lower RBC aggregation. Hematocrit corrected blood viscosity is lower in SVHD vs. healthy due to decreased RBC aggregation and higher RBC deformability, a viscous adaptation of blood in patients whose cardiac output is dependent on minimizing viscous power loss. Patients with single ventricle circulation have decreased red blood cell aggregation and increased red blood cell deformability, both of which result in a decrease in blood viscosity across a large shear rate range. Since the unique Fontan circulation has very low-shear and low velocity flow in the pulmonary arteries, blood viscosity plays an increased role in vascular resistance, therefore this work is the first to describe a novel mechanism to target pulmonary vascular resistance as a modifiable risk factor. This is a novel, modifiable risk factor in this patient population.

Lubrication characteristics of valve plate pair of balanced large flow pump based on elastic deformation

In this paper, the balanced large flow pump is taken as the research object. Considering the elastic deformation of the surface of the valve plate pair, the oil film dynamic model and the power loss model of valve plate pair are established, and the influence of different working conditions on the lubrication characteristics of valve plate pair is analyzed. The results show that the oil film parameters and performance parameters of valve plate pair change periodically. The power loss of valve plate pair is mainly viscous friction power loss, and the leakage power loss is small; considering the elastic deformation, the viscous friction power loss is reduced by 2.73 %–3.61 %, and the leakage power loss is increased by 21.8 %–25.3 %. The increase of working pressure and rotating speed will increase friction and leakage power loss. The increase of internal and external swash plate inclination will reduce the friction power loss and increase the leakage power loss. Compared with the traditional single-row axial piston pump, the viscous friction torque of the balance pump decreases and the leakage increases, but the total power loss decreases, which makes the balance pump more efficient than the traditional pump.

Analysis and design of the optimal radius gap of the piston pair

The axial piston pump plays a crucial role as a power component in the hydraulic system. As one of the important friction pairs, the piston pair has a significant influence on the mechanical and volumetric efficiency of the axial piston pump, where the gap of the piston pair has a considerable effect on the lubrication and overall efficiency of the piston. However, there are a few studies on the gap of the piston pair and there is a lack of relevant theoretical support for the design of the gap of the piston pair, especially when the piston has spin motion. To tackle this problem, we propose a CORG (critical and optimal radius gap) design method for the gap of the piston pair based on the critical radius gap and the optimal radius gap. Specifically, we first provide a theoretical proof for the existence of the critical radius gap. Then, considering that the piston has spin motion, we analyze the power loss of the piston pair and define the leakage power loss and viscous dissipation power loss according to the physical meaning. Meanwhile, the minimum value of the total power loss of a single piston pair is taken as the optimization metric of the piston pair, and we further propose the optimal radius gap. Then, by combining the critical radius gap and the optimal radius gap of the piston pair, we propose the CORG design method for the radius gap of the piston pair and obtain a dimensionless CORG constant that should be satisfied in the design of the radius gap of the piston pair. In framework of the CORG design method, it can not only ensure that the total power loss of a single piston pair is minimized but also prevent the volumetric efficiency of the piston pair from being too low. Finally, the simulation model of the piston pair is built by AMESim software, and the correctness of the theoretical calculation results are further verified by comparing the simulation results with the theoretical calculation results. The CORG design method can further provide theoretical references for the design of the piston pair.

Improved Prediction of Aerodynamic Loss Propagation as Entropy Rise in Wind Turbines Using Multifidelity Analysis

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.

Modeling and Optimization of Compensating Oil Viscous Power for a Deep-Sea Electric Manipulator

The dynamic performance and load capacity of a deep-sea electric manipulator are obviously affected by the viscous resistance of compensating oil. However, the complex geometric clearance of the oil-filled joint of the manipulator makes it difficult for existing theoretical models to accurately model this problem. Based on the existing theoretical models, a viscous power model considering the influence of the surface grooves of the rotor and stator is proposed. To reduce the viscous power loss, an optimization method for the clearance geometry is proposed. This optimization method is carried out by filling the surface grooves of the motor rotor and stator with epoxy resin. This method makes the clearance geometry of the compensated oil more regular. The modified model and optimization method are validated by designing an experimental installation and method. The experimental results demonstrate the accuracy and effectiveness of the modified theoretical model and optimization method.

Research and Comparative Analysis of Flow Field Characteristics and Load-Independent Power Losses of Internal and External Gear Pairs

Power loss analysis of gear transmission in a transmission system is of great significance to improve the efficiency of the power system, and load-independent power losses are an important part of the power losses of gear transmission. Based on the computational fluid dynamics (CFD) method, the hydrodynamic models of internal and external gear pairs are established. By analyzing the pressure field and the velocity field, the windage and squeezing power losses and the pressure and viscous power losses, the influence of rotation speed and tooth width on flow field characteristics, and load-independent power losses of internal gear pair are studied. In addition, we compare the flow field characteristics and the load-independent power losses between external and internal gear pairs and discuss the difference between them. The results show that the pressure and fluid velocity in the meshing area of the gear pair are greatly affected by rotation speed and tooth width, and the load-independent power losses increase with the increase of rotation speed and tooth width. At the same rotation speed, the transmission ratio and number of teeth, windage, and squeezing power losses of the external gear pair are smaller than those of the internal gear pair. Compared with the internal gear pair, the external gear pair has more advantages in controlling the load-independent power losses. The difference of the load-independent power losses of the two meshing modes mainly comes from the viscous power losses of the wheel gear of internal gear pair. This paper provides a basis for the selection of the gear meshing mode and the analysis of load-independent power losses of the transmission system.

Research on fluid-structure interaction for piston/cylinder tribopair of seawater hydraulic axial piston pump in deep-sea environment

Abstract Seawater hydraulic axial piston pump (SHAPP) is a critical power component in underwater operating systems. A parameterized elasto-hydrodynamic (EHD) lubrication model of the piston/cylinder tribopair in the SHAPP is originally established, which considers the elasto-hydrodynamic behavior, viscosity temperature effect and deep-sea environmental pressure. The deformation of piston bush, bearing mechanism and energy loss characteristics of the water film under different operating conditions are discussed. The results show that the deformation of piston bush made of polyetheretherketone (PEEK) is in micron-scale under water film and deep-sea pressure, which could increase the leakage and viscous friction power loss of piston/cylinder tribopair. In deep-sea environment, the leakage and viscous friction power loss calculated by EHD are always greater than those calculated by hydrodynamic (HD), and increase with the increase of working pressure, shaft speed, gap size, sea depth and piston bush thickness. Besides, the increase of sea surface temperature could increase the leakage and decrease the viscous friction power loss of the piston/cylinder tribopair, respectively. Finally, design instructions to optimize the piston/cylinder tribopair are presented, therefore the proposed methodology can be used as a designing tool for SHAPP.

Power loss characteristics analysis of slipper pair in axial piston pump considering thermoelastohydrodynamic deformation

AbstractThe power loss characteristics of slipper pair in an axial piston pump considering the thermoelastohydrodynamic deformation are investigated based on a transient power loss model. The simulation results indicate that the leakage power loss of the slipper pair increases with increasing the thermoelastohydrodynamic deformation. The viscous friction power loss decreases with an increase in the thermoelastohydrodynamic pressure. The viscous friction becomes sufficiently large under the influence of slipper surface roughness that it leads to an increase in viscous friction power loss. The pump displacement decreases with increasing the leakage rate and results in higher leakage power loss and higher friction power loss. To achieve minimum power loss in the slipper, an objective optimization study using Newton's method is applied to calculate structural parameters such as slipper inner diameter, slipper outer diameter, and orifice diameter. The proposed structural parameter optimization can be used as theoretical evidence for slipper pair design.

A novel fluid structure interaction model for the grooved piston-cylinder interface in axial piston pump

In the design of high pressure and high speed axial piston pump, grooves on piston are often used to improve the lubrication condition of piston-cylinder interface. However, the position and parameters of grooves are still depending on experience and experiment. A novel fluid structure interaction (FSI) model for the grooved piston-cylinder interface is formulated in this study, which aims to reveal the performance of oil film. Based on the kinematic analysis of piston, the instantaneous pressure of displacement chamber in piston pump is calculated. Reynolds equation is discretized and solved on the oil film mesh to obtain the pressure distribution of oil film. Eccentricities of piston center is iterated out with force balance loop. Influence method is used to calculate the deformation of both piston and cylinder. Six types of piston are introduced and compared in this study. Simulation results indicate that the grooves near displacement chamber can improve the trajectory of the micro motion of piston, which finally avoid contact between piston and cylinder and reduce viscous friction power loss. The grooves far from displacement chamber could store oil and reduce the leakage flow piston-cylinder interface.

On the performance of foil thrust bearing with misaligned bearing runner

PurposeCompliant foil thrust bearings are promising bearings for high-speed oil-free turbomachinery. However, most previous experimental and numerical approaches to investigate the performance of these bearings have ignored the effect of bearing runner misalignment. Therefore, this paper aims to evaluate the effects of static and dynamic angular misalignments of the bearing runner on the performance of a gas-lubricated foil thrust bearing.Design/methodology/approachThe bearing runner is allowed a maximum angular misalignment that produces a minimum gas film thickness as low as 20 per cent of the nominal clearance. Then, the variations of bearing load carrying capacity, viscous power loss and stiffness and damping coefficients of the gas film with runner misalignment are thoroughly analyzed. The flow in the gas film is modeled with compressible Reynolds equation along with the Couette approximation technique, and the deformation of the compliant bearing is calculated with a robust analytical model. Small perturbations method is used to calculate the force and moment dynamic coefficients of the gas film.FindingsThe results show that misaligned foil thrust bearings are capable of developing a restoring moment sufficient enough to withstand the imposed misalignments. Furthermore, the enhanced hydrodynamic effect ensures a stable operation of the misaligned bearing, and the results highlighted the role of the compliant bearing structure to maintain foil bearing prominent features even at misaligned conditions.Originality/valueThe value of this study is the evaluation of the effects of runner angular misalignments on the static and dynamic characteristics of Generation II bump-type foil thrust bearing.

EFFECT OF MISALIGNMENT ON THE DURABILITY OF GAS-LUBRICATED FOIL THRUST BEARING

The present study aims to evaluate the effects of static and dynamic angular misalignments of the runner surface on the performance of a gas-lubricated foil thrust bearing. The responses of the bearing load capacity, viscous power loss, and the stiffness and damping coefficients of the gas film to small angular misalignments are thoroughly analyzed. The compressible Reynolds equation along with the Couette Approximation technique is used to model the flow in the gas film. The deformation of the compliant bearing is calculated with a robust analytical model, and small perturbations method is used to calculate the dynamic coefficients of the gas film. The results show that misaligned foil thrust bearings are capable of developing a restoring moment sufficient enough to withstand the imposed mechanical distortions. Furthermore, the enhanced hydrodynamic effect ensures a stable operation of the misaligned foil thrust bearing at very thin gas films.

Optimum Design of Compound Helicopters that Use Higher Harmonic Control

The optimal design of a compound helicopter comprised of counterrotating coaxial rotors, a propeller, and optionally a fixed wing is investigated. The blade geometry, azimuthal blade pitch inputs, optimal shaft angle (rotor angle of attack), and division of propulsive and lifting forces among the components that minimize the total power for a given flight condition are determined. The optimal design problem is cast as a variational statement that minimizes the sum of induced and viscous power losses for a prescribed lift, propulsive force, and vehicle trim condition. The rotor, propeller, and wing geometry and control inputs are related to the far-field circulation through a lifting-line model that accounts for experimentally or computationally determined nonlinear lift and drag polars. The variational statement is discretized using a vortex lattice wake, and the resulting nonlinear constrained optimization problem is solved via Newton iteration. Results show that varying the prescribed propulsive force of the system affects the optimal shaft angle and rotor design, that higher harmonic control reduces the total vehicle power loss (inefficiency) in high-speed flight by as much as 15%, and that imposing a maximum allowable lateral lift offset can greatly increase the power loss of the coaxial rotors.

Brownian motion in a viscoelastic medium modelled by a Jeffreys fluid

The theory of Brownian motion of a particle in a viscoelastic Jeffreys fluid is extended for the case of rotational motion. The employed rheological model combines two viscous mechanisms (instantaneous and retarded) and, in contrast to the Maxwell model, does not produce artifacts and works robustly when applied to the diffusion of tracer particles in real complex fluids. With the aid of this model, specific features of the dynamic susceptibility of a magnetic Jeffreys suspension and the viscous power losses induced by an ac field are analyzed and conclusions are derived that are valid for active microrheology and magnetic hyperthermia. In general, it is shown that the developed phenomenology provides an archetypal “frame” for a number of mesoscopic models used to describe confined random walk transport processes in a variety of systems of both biological and inorganic origin.

A Three-Dimensional Foil Bearing Performance Map Applied to Oil-Free Turbomachinery

To effectively apply compliant foil gas bearings to increasingly larger and more challenging turbomachinery, a comprehensive method that compares a foil bearing's capabilities with the application's operating requirements is needed. Extensive laboratory and field experience suggests that foil bearing failure is generally due to thermal stress brought on by excessive viscous power loss; therefore, a map that graphically relates component- and system-level parameters (bearing size, applied loads, and shaft rotational speeds) directly to bearing power loss is more elucidating than a map based on a lumped speed/load parameter like the Sommerfeld number. In this article we describe a performance map featuring a three-dimensional contour plot that illustrates the expected power loss in a foil bearing as a function of applied load and shaft speed. Using this performance map, bearing capabilities can be examined at the anticipated system operating conditions and safety margins between an operating point and incipient bearing failure can be ascertained. To demonstrate the concept's features and usefulness, we present a performance map generated from foil bearing power loss test data. We expect that these maps, combined with other predictive tools, will help evaluate a foil bearing's general suitability for a candidate rotor system and will lead to more robust and successful oil-free turbomachinery designs.

Design basis and hydrodynamic performance analysis of single‐screw extruders. II – viscous power loss

PurposeThe purpose of this paper is to investigate the design dimensions in pressure or metering region of a single‐screw extruder by determining viscous power loss. The paper is the second part of a series.Design/methodology/approachViscous power loss formed in the extruder screw channel and the radial clearance is determined and evaluated in terms of non‐dimensional parameters in order to obtain a theoretical model.FindingsThe theoretical model developed is capable of estimating the viscous power loss in the extruder metering region. With the model developed, extruder geometry and viscous power loss under different operating conditions can be predicted.Originality/valueThis paper offers a quick and easy opportunity to examine the viscous power loss in the extruder.

Temperature variations in the simulation of high-pressure injection-system transient flows under cavitation

Temperature variations and their effects on the simulation of unsteady pipe flows, in the presence of pressure-wave induced cavitation, were investigated with reference to high-pressure fuel injection systems. The thermal effects due to the compressibility of the liquid and to the thermodynamic process in the cavitating flow mixture were analyzed. To that end, the energy conservation equation was applied, in addition to the mass-continuity and momentum-balance equations, along with the constitutive state equation of the fluid. In particular, for the liquid, the physical properties (i.e., bulk modulus of elasticity, density, isothermal speed of sound, thermal expansivity, kinematic viscosity, specific heat at constant pressure) were implemented as functions of pressure and temperature in a closed analytical form matching carefully determined experimental data. Consistent with virtually negligible combined effects of heat transfer and viscous power losses involved in the flow process, the equation of energy was reduced to a state relation among the fluid thermodynamic properties, leading to a barotropic flow model. A comparison between isentropic and isothermal evolutions in the pure liquid regions was carried out for evaluating the influence of the temperature variation simulation on the macroscopic results given by local pressure time-histories. Besides, for cavitation analysis, different thermodynamic transformations of the vapor–liquid mixture were considered and compared.A recently developed conservative numerical model of general application, based on a barotropic flow model, was applied and further assessed through the comparison of prediction and measurement results on injection-system performance.A conventional pump-line-nozzle system was considered for this purpose, being relevant to model evaluation for its pressure-wave dynamics and also because it was subject to severely cavitating flow conditions at part loads. Predicted time-histories of injector-needle lift and pressure at two pipe locations were compared to experimental results. This substantiated the validity and robustness of the conservative model taking temperature variation effects into account, in the simulation of high-pressure injection-system transient flows with great degree of accuracy, even in the presence of cavitation induced discontinuities. The thermal effects due to the temperature variations in the liquid fuel and in the cavitating mixture were analyzed and discussed.

Dynamic characteristics and optimization design for disc-shape electro-rheological actuator

A disc-shape electro-rheological actuator was developed. The torque generated by a pair of rotary discs consists of two components: the torque from the viscosity of electro-rheological fluid(ERF) and the torque owing to the field-dependent yield shear stress. The former contributes to the viscous power loss. Changing the application of electric field between the two discs, the output torque of ER actuator can be controlled to amplify the torque of input signal to overcome the load and friction. Relationships between the main structure parameters, the dynamic characteristics of the device, the physical properties of ERF and the torque transmission, range of speed regulation, power loss, stiffness of system were discussed. A multi-object programming model was set up for the optimization design. Experimental simulations with step and pulse signals were presented.

Viscous and Joulean power losses in liquid-metal sliding electrical contacts with finite electrically conducting electrodes

Designing high performance liquid-metal sliding electrical contacts for homopolar machinery requires a precise knowledge of the magnitudes of the viscous and Joulean losses under various operating conditions. The liquid metal, which is confined to a channel between a rotor and stator, is subjected to a large external magnetic induction while transporting current. Significant power losses can occur in these devices. The geometry and electrical conductivity of the channel walls have a significant effect on these losses. In past theoretical work, copper electrodes were generally treated as perfect electrical conductors as compared to liquid metals. Calculations based on this perfectly conducting electrode approximation predicted unrealistically high power losses. In the present study, the effects of electrodes with finite conductivity on both the viscous dissipation and Joulean heating are explored. Numerical results are presented for both radial and axial magnetic inductions. It is found that the magnetic induction orientation has a significant impact on the losses. The results of this type of analysis can be used to minimize the power losses in the design of liquid-metal sliding electrical contacts.

Liquid-metal flows and power losses in ducts with moving conducting wall and skewed magnetic field

Fully developed, laminar liquid-metal flows, currents, and power losses in a rectangular channel in a uniform, skewed high external magnetic field were studied for high Hartmann numbers, high interaction numbers, low magnetic Reynolds numbers, and different aspect ratios. The channel has insulating side walls that are skewed to the external magnetic field. Both the perfectly conducting moving top wall with an external potential and the stationary perfectly conducting bottom wall at zero potential act as electrodes and are also skewed to the external magnetic field. A solution is obtained for high Hartmann numbers by dividing the flow into three core regions, connected by two free-shear regions, and Hartmann layers along all the channel walls. Mathematical solutions are presented in each region in terms of singular perturbation expansions in negative powers of the Hartmann number. The free-shear layers are treated rigorously and in detail with fundamental magnetohydrodynamic theory. Numerical calculations are presented for the total current carried by the core region between top and bottom electrodes, Joulean and viscous power losses, and channel resistance at different skewed external magnetic field angles. With the high external magnetic field, the current through the central core region between the electrodes must be parallel to the external magnetic field lines. The two side core regions carry no current to the zeroth order. The two free-shear layers carry less current than the central core region. The theoretical magnetohydrodynamic model derived here was developed to provide data to help in the design of liquid-metal current collectors.