Drag Losses Research Articles

Investigation on Tripping in Magnetic Generator in Steam-Assisted Gravity Drainage Wells Based on Numerical Simulation

Abstract Magnetic Guidance Technology can meet the precise measurement requirements when drilling steam-assisted gravity drainage (SAGD) oil wells. Magnetic generator is a key part in the Magnetic Guidance Technology. When magnetic generator is tripped into horizontal well, pump pressure and passing capacity of the magnetic source generator in the curved section need to be analyzed. So, a mathematical model of tripping in the magnetic generator is established. If curvature radius, deviation angle, and friction factor are known, the forces acting on the magnetic generator in different positions could be calculated. The finite element (FE) results show that: (1) with depth increasing in the curved section, the equivalent stress on the magnetic generator increases in a fluctuating manner, the contact area, friction drag, and energy loss increase. (2) The greater the hole curvature, the greater tripping in force and the higher pump pressure are needed. The lower friction coefficient is favorable to tripping in the magnetic generator. (3) The friction between the magnetic generator and tubing wall in the horizontal section is much less than that in the curved section. Field applications have shown that the maximum downforce is close to the result of finite element analysis. The research results provide a reasonable reference basis for smooth running of magnetic source generators with different trajectory conditions.

Pumping Loss of Shrouded Meshed Spur Gears

Abstract High speed rotorcraft transmissions are subject to load-independent power losses consisting of drag loss and pumping loss. Tightly conforming shrouds enclosing the transmission gears are often incorporated to reduce the drag component of the total load-independent losses. However, tightly conforming axial shrouds can result in an increase in the pumping loss component. Quantifying the pumping loss of shrouded gear transmissions has been the subject of many studies. This study presents a new approach for estimating pumping loss based on the concept of swept volume and examines the applicability of the approach to various shroud configurations. The drag loss and pumping loss of a shrouded spur gear pair have been determined through testing using the NASA Glenn Research Center (GRC) Gear Windage Test Facility. The results from this testing have been compared to theoretical results using the formulations presented in this study. In addition, computational fluid dynamics (CFD) analysis has been conducted for the various shroud configurations tested at NASA GRC. The results from the CFD analysis confirm the theoretical and empirical results and provide insight into the applicability of the swept volume approach for estimating pumping power loss of shrouded gear transmissions.

Peak thermoelectric power factor of holey silicon films

The thermoelectric properties of nanostructured silicon are not fully understood despite their initial promise. While the anomalously low thermal conductivity has attracted much work, the impact of nanostructuring on the power factor has mostly escaped attention. While initial reports did not find any significant changes to the power factor compared to the bulk, subsequent detailed measurements on p-type silicon nanowires showed a stark reduction in the Seebeck coefficient when compared to similarly doped bulk. The reduction is consistent with the disappearance of the phonon drag contribution, due to phonon boundary scattering. Here, we report measurements on a different nanostructure, holey silicon films, to test if similar loss of phonon drag can be observed. By devising experiments where all properties are measured on the same sample, we show that though these films possess electrical conductivity close to that in the bulk at comparable doping, they exhibit considerably smaller thermopower. The data are consistent with loss of phonon drag. At neck distances between 120 and 230 nm, the power factor at optimal doping is ∼50% that of the bulk. These insights are useful in the practical design of future thermoelectric devices based on nanostructured silicon.

Experimental Investigations About the Power Loss Transition Between Churning and Windage for Spur Gears

Abstract Oil sump lubrication is commonly used in gearboxes. When considering consistent speeds, oil immersion is usually set to low level in order to reduce associated power losses. This configuration is already used in some parts of helicopter mechanical transmissions, and it is under consideration as a lubrication solution for future electric powertrain where gearbox input speeds may be very high. The gear drag power losses are generally evaluated from either a churning power loss model for classic oil sump lubrication or a windage power loss model for oil jet lubrication. One may thus wonder how to estimate drag losses when considering a gear that only a small part is immersed. In this study, the authors investigate the transition between churning and windage phenomena for a spur gear. A series of torque measurements on a single spur gear rotating in an oil bath at numerous oil immersion levels have been carried out. Based on these results, a criterion to indicate which power loss model to use is proposed.

Thermodynamics-Acoustics Coupling Studies on Self-Excited Combustion Oscillations Maximum Growth Rate

Unlike electric vehicles and electric aircrafts, hydrocarbon-fuelled (fossil) engine systems are much noisier. By conducting one-step chemical reaction-thermodynamics-acoustics coupling studies and experimental measurements, we explore the universal physics of how hydrocarbon-fuelled combustion is a noise maker. We also explain that how combustion-sustained noise at a particular frequency ω is intrinsically selected. These frequencies correspond to the acoustic resonance nature of the combustor. We find that a reacting gas in which the rate of chemical reacting increases with temperature is intrinsically and naturally unstable with respect to acoustic wave motion, since its modal growth rate α is greater than 0. Acoustic disturbances tend to exponentially i.e. exp(αt) increase first and then are limited by nonlinear effects and finally grow into limit cycle oscillations. The growth rate α is found to increase first and then decrease with the gradient of the heat release rate with respect to the temperature change, i.e. heat capacity. The maximum (α/ω)max depends on the specific heat ratio γ, which is related to the speed of sound. The unstable nature could be changed by introducing some acoustic dissipative/damping mechanisms, such as the boundary layer viscous drag and boundary losses. It is shown that such losses could lead to increased critical heat capacity, below which stable combustors can be designed. Finally, the acoustical energy consisting of both potential and kinetic energy is found to grow exponentially faster by 100% than the acoustic disturbance amplitude.

Aerodynamic Investigation on Performance Enhancement of NACA 2412 Airfoil with Suction Assistance

Advanced transport aircraft concept has active boundary-layer control by slot suction which reduces drag by stabilizing the laminar boundary. Thus, the prevention of transition and delaying the boundary layer separation will lead to a higher lift co-efficient. The influence of location and position of suction, suction flow rate and suction hole width on aerodynamic performance have greater influence. These examine the potential payoff for boundary-layer control as applied to the advanced-concept wings. An experimental work deals with the continuous normal suction from the wing upper surface effects on the aerodynamic forces. The wing model with NACA-2412 has been made to achieve normal suction from the wing upper surface by means of four slot channels. The results showed that the continuous normal suction can significantly increase the lift to drag force ratio and this ratio is increasing as the strength of suction increases. There is a convincing decrease in drag and pressure loss and an increase in max lift, which in turn improves the overall performance of the aircraft. While multi-hole suction control can reduce drag much more efficiently than single hole suction control, the position of the suction hole has a greater effect on reducing pressure losses than the suction flow rate.

Forebody Wake Effects on Parachute Performance for Re entry Space Application

Forebody generates its own wake that influences the performance of aerodynamic decelerators during the flights. Many parachute Jumpers have experienced the failure of an ejected pilot chute as the parachute canopy collapsed and fell back on the Jumper because of wake developed behind the Jumper. In the available literature, limited data is available to predict the exact loss of parachute drag in presence of the forebody (FB). The purpose of this paper is to generate a comprehensive aerodynamic data to study the behaviour of FB-parachute dynamics by conducting the wind tunnel experiments. Wind tunnel test has been carried out to establish the initial design parameters of aerodynamic parachute. The experiment was carried out on a scale down model of 20 degree conical ribbon drogue parachute and FB with and without each of them at a subsonic speed for studying dynamic stability characteristic for different orientation of FB. The test results indicate that to ensure adequate stability for the capsule to descend vertically at a low subsonic speed, a cluster of two drogue parachutes be used. Under such condition, the overall drag coefficient found to be above 0.50 providing not only a safe descends velocity but increasing reliability of mission as well.

Methods to reduce drag losses of long cryogenic pipelines

Methods to reduce drag losses of long cryogenic pipelines

Multi-rotor helicopter type platform capacities research

The development of multi-rotor helicopter concepts, driven by the active introduction of brushless electric motors, leads to the necessity of assessing the multi-rotor scheme main advantages implementing possibility and determining the rational areas of its application. The article analyzes the concept of a multi-rotor platform with a distributed power plant. Parametric study of characteristics depending on the number of rotors for a line of multi-propeller aircraft with take-off weight from 0.5 to 120 tons was carried out. Evaluation of weight and dimensional characteristics of blades, main rotor heads, gear boxes, as well as power wires of electric motors and structure beams connecting the elements of the distributed power plant is obtained. Evaluation of drag and thrust losses on blowing, as well as power requirements for typical flight modes was carried out. Estimation of the required number of rotors for the implementation of the gearless condition and flight safety with one engine failed are obtained. Rational areas of multi-rotor scheme application are defined.

Magnetic Drag and Energy Losses in Noncontact Bearings Based on Superconducting Tapes

In the paper, the problem of magnetic drag and origination of energy losses in noncontact bearings based on high-temperature superconducting tapes is considered. The model configurations of bearings in which a superconducting tape is a stator and a set of permanent magnets is a rotor are investigated. It is shown that the magnetic friction can be neglected in the case where more than eight permanent magnets compose the rotor. This result indicates the possibility to create scaled magnetic bearings for the systems of long-term energy storage, for example, flywheel energy storage systems.

Hydrodynamic Lubricant Film Separation During Codirectional and Counter-Directional Rotations of Disengaged Wet Clutch Packs

Abstract The parasitic drag losses incurred by wet clutches, used in transmission systems, can significantly affect vehicular powertrain efficiency. This paper presents a novel implicit solution for hydrodynamic parasitic drag losses of disengaged clutches. These are generated by conjunctional friction, taking into account lubricant film separation during codirectional and counter-directional disk pair rotations. Lubricant film rupture is considered through application of incipient reverse flow boundary condition, which is representative of lubricant film separation. The results point to the operating conditions at which significant power losses occur. In particular, the time efficient model is able to represent the small losses incurred during codirectional rotation of disk pairs.

Analysis of Counter-Rotating Roller Bearing in Different Mounting Configurations

Advanced engine configuration studies have shown large advantages for an engine with counter-rotating spools with intershaft counter-rotating roller bearings. Mounted on two counter-rotating differential-speed hollow rotors, the bearing internal kinetic behavior, dynamic behavior, and then thermal behavior change greatly, causing a severe challenge to engine designers using traditional analysis methods. A special quasi-dynamic model for counter-rotating roller bearing is proposed, considering rings deformation and windage effects, to analyze the bearing mechanical and thermal behavior in different mounting configurations. Roller sliding and bearing heat generation are calculated and compared with experimental data to verify the model capabilities. It shows that the configuration that connects the inner ring to the high-speed rotor has life cycle advantage with more uniform load distribution, smaller roller/ring clearance, and lower cage speed. This leads to less drag loss due to the rotation of the rollers and cage assembly. The decrease of the total power loss is a key element to minimize the quantity of oil required to lubricate the roller bearing.

A design framework for realizing multifunctional wings for flapping wing air vehicles using solar cells

Long flight durations are highly desirable to expand mission capabilities for unmanned air systems and autonomous applications in particular. Flapping wing aerial vehicles are unmanned air system platforms offering several performance advantages over fixed wing and rotorcraft platforms, but are unable to reach comparable flight times when powered by batteries. One solution to this problem has been to integrate energy harvesting technologies in components, such as wings. To this end, a framework for designing flapping wing aerial vehicle using multifunctional wings using solar cells is described. This framework consists of: (1) modeling solar energy harvesting while flying, (2) determining the number of solar cells that meet flight power requirements, and (3) determining appropriate locations to accommodate the desired number of solar cells. A system model for flapping flight was also developed to predict payload capacity for carrying batteries to provide energy only for power spikes and to enable time-to-land safely in an area where batteries can recharge when the sun sets. The design framework was applied to a case study using flexible high-efficiency (>24%) solar cells on a flapping wing aerial vehicle platform, known as Robo Raven IIIv5, with the caveat that a powertrain with 81% efficiency is used in place of the current servos. A key finding was the fraction of solar flux incident on the wings during flapping was 0.63 at the lowest solar altitude. Using a 1.25 safety factor, the lowest value for the purposes of design will be 0.51. Wind tunnel measurements and aerodynamic modeling of the platform determined integrating solar cells in the wings resulted in a loss of thrust and greater drag, but the resulting payload capacity was unaffected because of a higher lift coefficient. A time-to-land of 2500 s was predicted, and the flight capability of the platform was validated in a netted test facility.

Open Rotor Engines—Still an Open Question?

A major factor in the continued domination of turbofan engines for economic airline propulsion, is the ability to increase bypass ratios. However, increasing fan diameters to go to ever higher bypass ratios increases nacelle weight, aerodynamic drag and duct losses. By eliminating the need for a fan duct, open rotor engines can effectively in-crease bypass ratios, resulting in a significant savings in fuel consumption. Open rotor engines have been under intermittent development since the 1980s, sub-ject to rising and falling of fuel prices. Technical challenges that continue in their de-ployment include noise reduction, airframe integration and protection from propel-ler/fan blade failure.

Validation of a Coupled Electrical and Hydrodynamic Simulation Model for a Vertical Axis Marine Current Energy Converter

This paper validates a simulation model that couples an electrical model in Simulink with a hydrodynamic vortex-model by comparing with experimental data. The simulated system is a vertical axis current turbine connected to a permanent magnet synchronous generator in a direct drive configuration. Experiments of load and no load operation were conducted to calibrate the losses of the turbine, generator and electrical system. The power capture curve of the turbine has been simulated as well as the behaviour of a step response for a change in tip speed ratio. The simulated results agree well with experimental data except at low rotational speed where the accuracy of the calibration of the drag losses is reduced.

Nonpropagating Form Drag and Turbulence due to Stratified Flow over Large-Scale Abyssal Hill Topography

AbstractDrag and turbulence in steady stratified flows over “abyssal hills” have been parameterized using linear theory and rates of energy cascade due to wave–wave interactions. Linear theory has no drag or energy loss due to large-scale bathymetry because waves with intrinsic frequency less than the Coriolis frequency are evanescent. Numerical work has tested the theory by high passing the topography and estimating the radiation and turbulence. Adding larger-scale bathymetry that would generate evanescent internal waves generates nonlinear and turbulent flow, driving a dissipation approximately twice that of the radiating waves for the topographic spectrum chosen. This drag is linear in the forcing velocity, in contrast to atmospheric parameterizations that have quadratic drag. Simulations containing both small- and large-scale bathymetry have more dissipation than just adding the large- and small-scale dissipations together, so the scales couple. The large-scale turbulence is localized, generally in the lee of large obstacles. Medium-scale regional models partially resolve the “nonpropagating” wavenumbers, leading to the question of whether they need the large-scale energy loss to be parameterized. Varying the resolution of the simulations indicates that if the ratio of gridcell height to width is less than the root-mean-square topographic slope, then the dissipation is overestimated in coarse models (by up to 25%); conversely, it can be underestimated by up to a factor of 2 if the ratio is greater. Most regional simulations are likely in the second regime and should have extra drag added to represent the large-scale bathymetry, and the deficit is at least as large as that parameterized for abyssal hills.

Star-planet interactions

Context. When planets are formed from the protoplanetary disk and after the disk has dissipated, the evolution of their orbits is governed by tidal interactions, friction, and gravitational drag, and also by changes in the mass of the star and planet. These interactions may change the initial distribution of the distances between the planets and their host star by expanding the original orbit, by contracting it (which may cause an engulfment of the planet by the star), or by destroying the planet. Aims. We study the evolution of the orbit of a planet orbiting its host star under the effects of equilibrium tides, dynamical tides, drag (frictional and gravitational), and stellar mass loss. Methods. We used the Geneva stellar evolution code to compute the evolution of stars with initial masses of 1 and 1.5 M⊙ with different rotation rates at solar metallicity. The star is evolved from the pre-main-sequence (PMS) up to the tip of the red giant branch. We used these models as input for computing the evolution of the planetary orbits. We explored the effects of changing the planet masses (of 1 Earth mass up to 20 Jupiter masses), the distance between the planet and the star (of 0.015 and more than 3 au), the mass, and the spin of the star. We present results when only the equilibrium tide was accounted for and when both equilibrium and dynamical tides were accounted for. The expression for the dynamical tide is a frequency-averaged dissipation of tidally excited inertial waves, obtained from a piecewise homogeneous two-layer stellar model. Gravity wave damping was neglected. Results. Dynamical tides in convective zones have a significant effect on planetary orbits only during the PMS phase and only for fast-rotating stars. They have no significant effects during the PMS phase for initially slow-rotating stars and during the red giant branch phase, regardless of the initial rotation. In the plots of initial orbital distance versus planetary mass, we show the regions that lead to engulfment or any significant changes in the orbit. As a result of orbital evolution, a region near the star can become devoid of planets after the PMS phase. We call this zone the planet desert, and its extent depends sensitively on stellar rotation. An examination of the planet distribution as a function of distance to the host star and mass can provide constraints on current computations.

Parametric analysis of the drag torque model of wet multi-plate friction clutch with groove consideration

PurposeThe purpose of this paper is to reduce the drag loss and study the effects of operating conditions and groove parameters such as flow rate and temperature of automatic transmission fluid, clearance between plates, groove depth and groove ratio on the drag torque of a wet clutch for vehicles, parametric analysis of the drag torque model of wet multi-plate friction clutch with groove consideration.Design/methodology/approachBoth experimental and numerical research was carried out in this work. Parametric groove models, full film lubrication flow model and pressure distribution model are established to investigate the effects of the grooves on drag torque of a wet clutch. Multigrid method is used to simplify the solution.FindingsIn this paper, a drag torque model of a wet multi-plate friction clutch based on the basic theory of viscous fluid dynamics is examined through experimental and numerical methods that take grooves into account, and the change trend of drag torque with operating conditions and groove parameters is analyzed.Originality/valueMultigrid method is used to solve the governing equations, which simplifies the solution process because of the restrictions and interpolation operations between the adjacent layers of coarser and fine grids. These works provide insight into the effect regularity of operating conditions and groove parameters on drag torque of a wet multi-plate friction clutch. Furthermore, variable test conditions and sufficient experimental data are the main functions in the experimental research.

Simulation and experiment of viscous torque for disengaged wet clutches of tracked vehicle

In order to predict the viscous drag loss for tracked vehicles, the drag torque of the friction pair with different grooves was investigated in this paper. The traditional computation method is difficult to adapt for the new kinds of friction plates with complex grooves. A numerical method with the help of CFD models is adopted to simulate the fluid flow status in the grooves and the drag torque was obtained by the accumulation of the discrete viscous force. The simulation results implied that the plates with different kinds grooves were provided with various characteristics of viscous torque and these characteristics could be affected by the rotation direction for the plate with spiral grooves, which are proved in experiment. Meanwhile, it was also found that the two kinds of plates with double arc or spiral grooves, which have different sensitive parameters in drag dissipation, have to perform accurate flow control and clearance design respectively. The simulations and experiments showed that the ‘positive spiral grooves’ friction plates had minimum drag torque in regular heavy-duty conditions. It can be used in transmission system with requirements of limited space and high mobility, which can lead to better heat dissipation and less power loss.

Understanding boundary layer suction and its e ect on wings - A review

Boundary layer suction reduces drag by stabilizing the laminar boundary preventing transition and conceding higher regions of laminar ow. Boundary layer suction(BLS) also postpones boundary layer separation resulting in higher CLmax. This phenomenon is particularly useful in the Aerospace sector and many applications are found and hence understanding the mechanics of BLS becomes critical. Consequently it becomes vital to understand the e ect of BLS during di erent ight regimes and mission pro les. The objective of this review is to understand and document the understanding on BLS and its e ects. The in uence of location and position of suction, suction ow rate and suction hole width on aerodynamic performance by experiments and numerical analysis have been reviewed. It has been brought out that there is a convincing decrease in drag and pressure loss and an increase in max lift which in turn improves the overall performance of the aircraft. While multi-hole suction control can reduce drag much more e ciently than single hole suction control, position of the suction hole has a greater e ect on reducing pressure losses than the suction ow rate. The factors a ecting BLS and its e ects on aerodynamic performance and overall performance of the aircraft has been discussed in this review.