Effect Of Centrifugal Force Research Articles

Large-eddy simulation of non-isothermal flow and heat transfer in an enclosed rotor–stator cavity

This paper presents a numerical study of non-isothermal flow and heat transfer in an enclosed rotor–stator disk cavity. Wall-resolved large-eddy simulation is implemented with attention focused on the Reynolds number effect (Reϕ=105 and 5×105) and non-isothermal effects, including different thermal Rossby numbers (βΔT=0.05–0.25) and heat convection types (axial heat convection, axial and radial heat convection). Verification and validation are implemented by comparing with available experimental data and examining the resolution of the present LES. Although the Batchelor flow type is unchanged, the non-isothermal effect is found to be responsible for the acceleration of flow in both disk boundary layers and cavity core. Temperature in the cavity is negatively correlated with the Rayleigh number. The radial inward temperature gradient is found to be responsible for destabilizing the flow near the cylinders, due to the effect of centrifugal buoyant force. Transition from laminar to turbulent is shown in the rotor boundary layer for Reϕ=5×105 conditions. The non-isothermal effect increases flow unsteadiness in both rotor and stator boundary layers, but it has little to no effect on the transition position, as well as the kinematic and thermal boundary layer thicknesses, which are mainly controlled by Reϕ. Spectral proper orthogonal decomposition is implemented to explore the Reynolds number effect. Analyzing the most energetic mode and its energy spectra provides some insights into the understanding of non-isothermal rotor–stator disk cavity flows.

Investigation on the compressibility characteristics of laminar flow in rotating channel

In high-speed rotating channels, significant compressive effects are observed, resulting in distinct flow characteristics compared to incompressible flows. This study employs a finite volume method, based on the implicit formulation, to solve for low-speed compressible laminar flow in rotating channels using an orthogonal uniform grid. The governing equations include the full Navier–Stokes equations and the energy equation. The alterations in flow within rotating channel are primarily influenced by the compressive effects of centrifugal force and the compressibility of fluid within the flow's normal section. The first effect involves a reduction in the velocity due to centrifugal force, leading to an increasing influence of the Coriolis force compared to inertial forces. This trend change aligns closely with the increase in rotation speed. The second effect arises from the increase in the rotating Mach number and the Coriolis compression, resulting in slight density differences within the cross section. Strong centrifugal forces generate significant centrifugal additional force (buoyancy force). Consequently, under the same local rotation number, the velocity profiles of the mainstream experience considerable changes. Additionally, a higher rotating Mach number significantly impacts wall shear stress, with the leading side being notably affected. For instance, at cross-sectional Ro = 0.6 and MaΩ = 2.1, the dimensionless shear stress on the leading side decreased by 13%. Furthermore, while an increase in the rotating Mach number has minimal impact on the cross-sectional secondary flow structure, changes in mainstream velocity profiles influence secondary flow intensity, resulting in an enhanced velocity peak and a shift toward the trailing side.

Effect of Centrifugal Force of Gas Film on the Load Capacity of Thrust Gas Bearing

Abstract A modified Reynolds equation including centrifugal force of gas film was derived, and it was used to study the effect of gas film centrifugal force and associated streamline on the load capacity of both rigid and foil thrust bearings operating in hydrodynamic and hybrid modes. The thrust bearings have six pads with an outer diameter of 82 mm and an inner diameter of 47 mm with typical aper-flat geometry. The setup for the simulations is a single-acting air thrust bearing operating at various ambient pressures and isothermal temperature. Air was chosen for the gas film for the investigations, but the modified Reynolds equation can handle any general gas films through nondimensional parameter governing the centrifugal force. The simulations were performed with varying ambient pressure from 1 to 9 bar. The simulation results at different ambient pressures and temperatures are presented in forms of pressure profiles, streamlines, and bearing's load capacity. The bearings' load capacity becomes worse when the centrifugal force is considered at very low temperature, and the reduction of the load capacity grows more noticeable with the increase of the ambient pressure and the decrease of the ambient temperature. However, at higher temperature where centrifugal force is not large enough to create large leakage, the centrifugal force helps to redistribute the streamline to favorable way to increase the load capacity.

Nonlinear Structural Vibration of Multi-Megawatt Vertical Axis Wind Turbine Blades-Part 1: Derivation of Motion Equations

Replacing fossil fuels with renewable energy is one of the important means to improve energy scarcity and environmental protection, and is of great significance for achieving sustainable development of human society. Vertical axis wind turbine (VAWT) is one of the key equipment for applying green energy — wind energy. During the operation of VAWT, its blades not only have to withstand periodic aerodynamic loads, but also suffer from centrifugal force effects and the Coriolis force effect caused by coupling with multi-dimensional deformation. The complex stress situation makes the blades susceptible to damage, resulting in structural resonance and instability of aeroelastic stability. This paper applies the Euler beam model and Hamilton principle to establish a nonlinear structural vibration motion equation for large-span vertical axis wind turbine blades with fully coupled four-dimensional deformation (i.e. lateral bending deformation, chord bending deformation, axial torsion deformation, and axial tensile deformation), and retains the nonlinear term of the motion equation to the third-order infinitesimal. Separating the motion equation into equilibrium equation and dynamic equation, it can be seen that the displacement of equilibrium state caused by the centrifugal force of the rigid body exists in the form of a coefficient in the dynamic equation, which will have an impact on the dynamic characteristics. This modeling work can provide a research foundation for exploring the dynamic characteristics and aeroelastic stability of VAWT blades in the future.

Study on one-dimensional performance prediction of multi-stage axial turbine based on the blade height

Abstract As turbine operating conditions change, the blade height and tip clearance undergo continuous alterations due to the combined effects of thermal stress, aerodynamic forces and centrifugal forces, subsequently influencing the turbine performance. To take this effect into account in turbine performance prediction, this study considers the influence of fluid-heat-structure coupling on blade height and tip clearance and establishes a one-dimensional comprehensive prediction method for multi-stage axial turbine performance considering blade height. When compared with experimental results from a four-stage axial turbine, by considering the fluid-thermal-solid coupling effects, the average relative error in total pressure ratio prediction is reduced from 3.76 % to 1.99 % and the average relative error in total temperature ratio prediction is reduced from 2.03 % to 1.26 %. Compared with the traditional flow prediction method, the prediction results of turbine characteristics considering blade height and tip clearance changes in this paper are closer to the experimental results.

Investigation on Free Vibration of Rotating Cylindrical Shells with Variable Thickness

In order to improve the performance and efficiency of the rotating cylindrical shell (RCS), one of the effective ways reduces the mass of the RCS. The scientific and effective method is to design the variable thickness of RCS (VTRCS) along the axial direction in response to this demand. Then, the vibration traveling wave characteristics of VTRCS are investigated by Chebyshev–Ritz method. The displacement field of the cylindrical shell is expanded in the form of the product of the Chebyshev polynomial and the boundary function. The kinetic and potential energies of the VTRCS are calculated based on the Sanders shell theory considering the effects of Coriolis forces and centrifugal forces. Also, the frequency equation of the VTRCS is obtained according to the Ritz method. The accuracy of the modeling method is verified by comparing the present results with literature that had done, and the convergence of the calculated results is studied. Finally, the free-vibration traveling wave characteristics of the VTRCS in different thickness variations are compared, and the parameters such as the rotational speed, thickness variation parameters, and aspect ratio on the free-vibration traveling wave characteristics of the VTRCS are discussed. The influence of thickness variation on the vibration characteristics is analyzed, which has significance for the lightweight design for VTRCS.

Centrifugal forces enable band gaps that self-adapt to synchronous vibrations in rotating elastic metamaterial

The rotation of mechanical systems can greatly change their modal and wave propagation response. In the classic example of the Foucault pendulum, the Coriolis force from the Earth’s rotation causes the pendulum path to appear deflected to an observer on Earth. More recently, Coriolis forces and gyroscopic effects from rotation have been shown to break time-reversal symmetry, induce non-reciprocity, and change the band structure of phononic crystals. However, rotation also introduces centrifugal forces that can considerably affect the vibration response through stress stiffening and spin softening effects. Although this is well studied in the field of rotor dynamics, the effects of centrifugal forces on the dynamic behavior of acoustic metamaterials (AMs) are still unexplored. In this paper, we study the dependence of torsional band gaps on rotational speed in a rotating shaft with attached local resonances. Different from previous studies, we explicitly consider the effects of stress stiffening in local resonances by introducing a stress stiffening function in a reduced order model of the rotating AM. We then calculate the stress stiffening function for beam-tip-mass resonators and show that these resonators have a resonant frequency that scales linearly with the rotational speed in the asymptotic limit, which in turn causes the band gaps of the AM to depend linearly on the rotational speed. Motivated by the presence of synchronous vibrations in rotating machinery, in which frequency is also linearly dependent on rotational speed, we show that this rotating AM supports band gaps that self-adjust to the synchronous vibration frequency, resulting in attenuation over a wide range of frequencies and thus rotational speeds. Finally, we validate the reduced order model of the rotating AM using 3D finite element analysis. This work contributes a foundational understanding of the effects of rotation in AMs and builds a connection between the AM and rotor dynamics communities, with the potential to introduce novel vibration control in rotor dynamics problems.

A comparative study on inflow schemes of radial throughflow cooling for thermal management of a specific multi-layer gas foil thrust bearing

In order to illustrate the effects of radial cooling throughflow on the aerodynamic and thermal behaviors of gas foil thrust bearing, a three-dimensional fluid-solid coupled numerical investigation is conducted for a specific multi-layer gas foil thrust bearing under stable operating conditions in the present study, with two inflow schemes adopted, referred as radially-inward inflow scheme and radially-outward inflow scheme, respectively. The results show that the flow fields and the thermal behavior within the gas foil thrust bearings under the two inflow schemes are significantly different due to the difference in the inflow direction and the effect of centrifugal force caused by the high-speed rotation. The radial cooling throughflow can greatly alleviate the high temperatures in the film layer and improve the cooling capacity, but the increase of mass flow rate causes a non-monotonic change of static bearing load and an enhancement of viscous-shearing heat, as well as a significant rise of the air supply pressure. The radially-inward inflow scheme allows a lower peak temperature and a more uniform temperature distribution on the thrust plate and foil surfaces, while the radially-outward inflow scheme provides a lower area-averaged temperature and consumes less air supply pressure.

Free-vibration analysis of rim-driven rotating composite plate using NURBS-based isogeometric approach and HSDT

This paper presents free-vibration analysis of a rim-driven rotating composite plate. Based on higher-order shear deformation theory (HSDT) and the isogeometric approach (IGA), the formulations are developed. The effects of Coriolis and centrifugal forces due to rotation are considered. The present formulation results are compared and validated with the existing results for the hub-driven rotating plate, non-rotating plate, etc. A parametric study is conducted to investigate effect of the lamination sequence, pitch angle, material anisotropy, thickness ratio, and aspect ratio on natural frequency, critical buckling speed, and resonance speed. Natural frequency crossing and mode shape interchange are observed.

Effect of Centrifugal Forces on the Structure of an ESR Ingot Produced by DC Remelting

Effect of Centrifugal Forces on the Structure of an ESR Ingot Produced by DC Remelting

Analysis of Sliding Contact of Armature Inside the Vertical Curved Rails in Electromagnetic Railgun

In previous studies, the armature–rail sliding contact interface is usually considered to be an ideal slide in which both rails are parallel and symmetric. However, due to the influence of structural deformation of the barrel affected by boundary constraints and the manufacturing errors of rails and armature, it often leads to a variety of nonideal the armature–rail matching such as space curved or twisted rails, offset or deflected armature, and so on. This article focuses on the common vertical curved rail in electromagnetic railgun. By introducing centrifugal force effects and coupling electromagnetic force, the armature–rail contact pressure is analyzed theoretically. According to the 3-D finite-element simulation results, the effect of centrifugal force on sliding contact pressure should not be ignored. The effects of different curved radii, velocities, and densities of armature on the contact pressure are compared and analyzed. The influence law on the contact pressure is obtained, which provides a theoretical basis for the design of the railgun.

Analysis of Factors Affecting Strand Tension in Cable-Twisting Equipment and Method for Equilibrated Control

To address the issue of tension fluctuations and deviations among the strands during cable-twisting production, it is necessary to establish a relationship model between the centrifugal force, frictional force, and tension experienced by each strand in a single span range under the state of traveling and rotating. Considering the differences of strand alignment at the distribution reel, the effects of centrifugal force and friction on strand tension under different twisting-deflection paths and cylinder-traveling paths should be analyzed. In our study, different stress states of each strand were applied to simulate and verify the tension fluctuations and deviations of every strand under various traveling and deflection paths. The experimental results show that the increasing travel path of the strand cylinder will cause an increase in the average strand tension. Different deflection paths in the distribution reel will affect the range of the strand tension fluctuation. A sliding mode controller based on a discrete system was designed in MATLAB to control the tension fluctuation and deviation among the strands. The results indicated that this control method can effectively reduce the tension deviation between strands, and the average tension fluctuation range of each strand was reduced by 79.5%.

Numerical study on heat transfer characteris tics of supercritical water in straight and helical tubes

The subcritical steam generators in high-temperature gas-cooled reactor pebble-bed modules can be replaced by supercritical steam generators to improve thermal efficiency. The axial and circumferential nonuniform flow and heat transfer characteristics of supercritical water in straight and helical tubes with varying inclinations (0–90°) are simulated to investigate the combined effects of tube structure, flow direction, thermophysical properties, property variations, buoyancy, and centrifugal forces. With heat fluxes of 233–930 kW/m2 and inlet mass fluxes of 225 or 1260 kg/(m2 s) under a working pressure of 24.5 MPa, the friction coefficients, turbulent kinetic energy, secondary flow, temperature, and heat transfer coefficients are studied in the cross section of variable structure tubes. The wall temperature and heat transfer coefficients of four regions are compared in straight and helical tubes; the maximum heat transfer coefficient appeared before the pseudo-critical point. The heat transfer coefficients are the greatest at the bottom of the straight tubes, where fluidity was high, and at the outer of the helical tubes, where the fluid velocity was high under centrifugal force. The secondary flow in the helical tubes causes a nonuniformity in the wall temperature, causing the circumferential maximum wall temperature to move.

Numerical Calculations and Analysis of the Effects of Centrifugal Force and Viscous-Energy Dissipation on the Operation of High-Speed Ferrofluid Sealer

Numerical Calculations and Analysis of the Effects of Centrifugal Force and Viscous-Energy Dissipation on the Operation of High-Speed Ferrofluid Sealer

Dynamic analysis of a rigid-flexible inflatable space structure coupled with control moment gyroscopes

The vibration generated by the inflatable structure after deployment has a great impact on the performance of the payloads. In this paper, the influence of the control moment gyroscopes (CMGs) on the dynamic responses and characteristics of an inflatable space structure is studied, based on the flexible multibody dynamics in a combination of the absolute nodal coordinate formulation (ANCF) and the natural coordinate formulation (NCF). Firstly, the ANCF and NCF are used to accurately describe the large deformations and large overall motions of flexible inflatable tubes and rigid satellites, respectively. Then, instead of modeling gyroscopic flexible bodies, this paper pioneers a rigid body dynamic model of the CMG in detail by using the NCF modeling scheme, which can be attached to and coupled with any flexible bodies without any assumptions. Then, the orbital dynamic equations of the inflatable space structure coupled with distributed CMGs are obtained by considering the effects of Coriolis force, centrifugal force, and gravity gradient through coordinate transformation. The dynamic characteristics of the inflatable space structure are also analyzed by deriving the eigenvalue problem of a flexible multibody system. Finally, the accuracy of the CMG dynamic model is verified via a classic heavy top example. Several numerical examples are presented to study the influence of the magnitudes and directions of the rotor angular momentum of the CMGs on the dynamic responses and characteristics of the inflatable space structure.

The configurational effects of centrifugal and centripetal forces on firms' breakthrough innovation and strategic performance in the artificial intelligence context

PurposeThe purpose of this study is to empirically explore how firms configure centrifugal and centripetal forces in promoting breakthrough innovation (BI), thus improving their strategic performance (SP) in the artificial intelligence (AI) context.Design/methodology/approachThis study applies the centrifugal and centripetal forces model to a survey sample of 285 Chinese AI firms. Fuzzy-set qualitative comparative analysis (fsQCA) and propensity score matching (PSM) are integrated to explore the configurational effects of three centrifugal forces—the autonomy of technical experts, knowledge search and alliance network—and two centripetal forces—strictness of organisational institutions (SOI) and human–human–AI collaboration (HHAC)—on BI, examining whether the configurations that enhance BI can further improve SP.FindingsThe results indicate that the strictness of innovation institutions (SII) and strictness of ethical institutions (SEI) are equally important for determining SOI. Three configurations can improve BI when SOI and HHAC are the core conditions; only one of three configurations can further improve SP significantly.Originality/valueBy introducing SOI composed of equally important levels of SII and SEI and HHAC, this research is one of the few empirical studies to explore the mechanisms behind the impact of centrifugal and centripetal forces on BI and SP, which may help researchers and managers address innovation challenges in the AI context.

Investigation of sludge disintegration using vortex cavitation circulating fluidised grinding technology

Waste-activated sludge (WAS) is regarded as a source of hazardous waste pollution from sewage treatment plants. To efficiently deal with WAS, vortex cavitation circulating fluidised grinding technology (VCCFGT) was proposed as a novel circulating fluidisation technology (CFT) to disintegrate WAS. To be specific, we investigated the effects of disintegration duration, pressure, and filling ratio of mill balls on sludge disintegration. The results of chemical and physical evaluation showed that the values of soluble chemical oxygen demand (SCOD), disintegration degree (DDSCOD), DNA, protein, carbohydrate, and NH4+-N increased with the increase in the filling ratio of the mill balls. Under a pressure and filling ratio of 0.30 MPa and 1.6%, respectively, the maximum effect was achieved after 60 min of treatment. Compared to those in the treatment without mill balls, the values of SCOD, DDSCOD, DNA, protein, carbohydrate, and NH4+-N in the treatment using mill balls increased by 218, 229, 230, 177, 371, and 190%, respectively. As a result of this technology, the temperature of the sludge dramatically increased, rising approximately 42.9 °C. Compared to that of the raw sludge, the sludge particle size after treatment was reduced by 83.25% at most, and the morphology of the sludge comprised smaller flocs. Compared to that of the ball-milling method, the mill balls filling ratio of VCCFGT reduced by 93.60–98.12%. Compared to that of sludge disintegration by the vortex cavitation method, VCCFGT indicating good disintegration degree (increased by 229%) and economic feasibility. VCCFGT has good application prospects for sludge disintegration. The main mechanisms of sludge disintegration and organic release include centrifugal force, grinding, shear force, cavitation, and cyclic fatigue effects, among which grinding plays a leading role. This study concluded that CFT can effectively disintegrate sludge flocs and disrupt bacterial cell walls.

Numerical calculation and analysis of the effects of centrifugal force and viscous energy dissipation on the functioning of high-speed ferrofluid sealers

Numerical calculation and analysis of the effects of centrifugal force and viscous energy dissipation on the functioning of high-speed ferrofluid sealers

Superhydrophobic Strategy for Nature-Inspired Rotating Microfliers: Enhancing Spreading, Reducing Contact Time, and Weakening Impact Force of Raindrops

Wind-dispersal of seeds is a remarkable strategy in nature, enlightening the construction of microfliers for environmental monitoring. However, the flight of these microfliers is greatly affected by climatic conditions, especially in rainy days, they suffer serious raindrop impact. Here, a hierarchical superhydrophobic surface is fabricated and a novel strategy is demonstrated that the superhydrophobic coating can enhance spreading while reduce contact time and impact force of raindrops, all of which are beneficial for the rotating microfliers. When the surface rotating speed exceeds a critical value, the effect of centrifugal force becomes considerable so that the droplet spreading is enhanced. The rotating superhydrophobic surface can rotate an impacting droplet by the tangential drag force from the air boundary layer, and the rotation of the droplet generates a negative pressure zone inside it, reducing the contact time by more than 30%. The impact force by the droplet on the rotating superhydrophobic surface also has a remarkable reduction of 53% compared to that on unprocessed hydrophilic surfaces, which helps maintain the flight stability of the microfliers. This work pioneers in revealing the droplet impact effect on rotating microflier surfaces and demonstrates the effectiveness of protecting microfliers with superhydrophobic coatings, which shall guide the manufacture and flight of microfliers in rainy conditions.

A single quasi-cubic test mass configuration for space-based gravitational wave detection

Two test masses per spacecraft configuration is the main scheme and exhibits a high level of maturity for space-based gravitational wave detection. However, the single test mass configuration is continuously discussed with different designs to reduce technical complexities such as spacecraft control. This paper proposes a new configuration with a single quasi-cubic test mass per spacecraft. The new configuration inherits the existing capacitance displacement sensor and electrostatic actuator. It has the advantage of the suppression of centrifugal force effect due to the coincidence of the center of mass between the spacecraft and test mass. In addition, it has the advantages of simplifying the self-gravity compensation strategy and the drag-free attitude and orbit control strategy due to using a single test mass.