Showing papers on "Slip ratio published in 2015"

Simulation of copper-water nanofluid in a microchannel in slip flow regime using the lattice Boltzmann method

Abstract: Laminar forced convection heat transfer of water–Cu nanofluids in a microchannel was studied utilizing the lattice Boltzmann method (LBM). The entering flow was at a lower temperature compared to the microchannel walls. Simulations were performed for nanoparticle volume fractions of 0.00 to 0.04 and slip coefficient from 0.005 to 0.02. The model predictions were found to be in good agreement with earlier studies. The effects of wall slip velocity and temperature jump of the nanofluid were studied for the first time by using lattice Boltzmann method. Streamlines, isotherms, longitudinal variations of Nusselt number, slip velocity and temperature jump as well as velocity and temperature profiles for different cross sections were presented. The results indicate that LBM can be used to simulate forced convection for the nanofluid micro flows. Moreover, the effect of the temperature jump on the heat transfer rate is significant. Also, the results showed that decreasing the values of slip coefficient enhances the convective heat transfer coefficient and consequently the Nusselt number (Nu) but increases the wall slip velocity and temperature jump values.

Model-Based Range Extension Control System for Electric Vehicles With Front and Rear Driving–Braking Force Distributions

Abstract: This paper proposes a model-based range extension control system for electric vehicles. The proposed system optimizes the front and rear driving–braking force distributions by considering the slip ratio of the wheels and the motor loss. The optimal distribution depends solely on vehicle acceleration and velocity. Therefore, this system is effective not only at constant speeds but also in acceleration and deceleration modes. Bench tests were conducted for more precise evaluation and to realize experimental results with high reproducibility. The effectiveness of the proposed system was verified through field and bench tests.

Radiative Convective Nanofluid Flow Past a Stretching/Shrinking Sheet with Slip Effects

Abstract: Steady two-dimensional laminar mixed convective boundary-layer slip nanofluid flow in a Darcian porous medium due to a stretching/shrinking sheet is studied theoretically and numerically. A thermal radiative effect is incorporated in the model. The governing transport, partial differential equations, along with the boundary conditions, are transformed into a dimensionless form and then, via a linear group of transformation, a system of coupled similarity differential equations is derived. The transformed equations are solved numerically using the Runge–Kutta–Fehlberg fourth–fifth-order numerical quadrature method from Maple symbolic software. The effects of the controlling parameters (namely, stretching/shrinking, velocity slip, thermal slip, mass slip, Darcy number, radiation conduction, buoyancy ratio parameter, and Lewis number) on the dimensionless velocity, temperature, nanoparticle volume fraction, velocity gradient, temperature gradient, and nanoparticle volume fraction gradient are shown in graphi...

Magnetohydrodynamic (MHD) flow of Cu-water nanofluid due to a rotating disk with partial slip

Abstract: This paper investigates MHD steady flow of viscous nanofluid due to a rotating disk. Water is treated as a base fluid and copper as nanoparticle. Nanofluid fills the porous medium. Effects of partial slip, viscous dissipation and thermal radiation are also considered. Similarity transformations reduce the nonlinear partial differential equations to ordinary differential equations. Flow and heat transfer characteristics are computed by HAM solutions. Also computations for skin friction coefficient and Nusselt number are presented and examined for pertinent parameters. It is noted that higher velocity slip parameter decreases the radial and azimuthal velocities while temperature decreases for larger values of the thermal slip parameter. Also the rate of heat transfer enhances when the nanoparticle volume fraction increases.

Interaction Mechanics Model for Rigid Driving Wheels of Planetary Rovers Moving on Sandy Terrain with Consideration of Multiple Physical Effects

Abstract: Predicting wheel-terrain interaction with semiempirical models is of substantial importance for developing planetary wheeled mobile robots rovers. Primarily geared toward the design of manned terrestrial vehicles, conventional terramechanics models do not provide the sufficient fidelity required for application on autonomous planetary rovers. To develop a high-fidelity interaction mechanics model, in this study the physical effects of wheel lug, slip sinkage, wheel dimension, and load are analyzed based on experimental results, including wheel sinkage, drawbar pull, normal force, and moment, which are measured on a single-wheel test bed. The mechanism of lug-terrain interaction is investigated systematically to clarify the principle of increasing shear stress, conditions of forming successive shearing among adjacent lugs, and the influence on shear displacement of soil. A mathematical model for predicting the concentrated forces and torque of rigid wheels with lugs for planetary rovers moving on sandy terrain is derived by integrating the improved models of normal and shearing stress distributions. In addition to the wheel parameters, terrain parameters, and motion state variables, wheel-terrain interaction parameters, such as the linear varying sinkage exponent, the soil displacement radius, and load effect parameters, were proposed and explicitly included in the model. In the single-wheel experiments, the slip ratio was increased approximately from 0.05 to 0.6, and the relative errors of the predicted results using the proposed model are less than 10% for all the wheels when compared with the experimental data. The proposed model has been used in the simulation of a four-wheeled rover, and its effectiveness is evaluated by comparing the simulation results with experimental results.

Effects of radiation on MHD free convection of a Casson fluid from a horizontal circular cylinder with partial slip in non-Darcy porous medium with viscous dissipation

Abstract: In the present study, the effects of radiation on MHD free convection from a cylinder with partial slip in a Casson fluid in non-Darcy porous medium is investigated The surface of the cylinder is heated under constant surface temperature with partial slip Partial slip factors are considered on the surface for both velocity and temperature The boundary layer equations are normalized into a system of non-similar partial differential equations and are then solved using a bi-variate quasilinearization method (BQLM) The boundary layer velocity and temperature profiles are computed for different values of the physical parameters Increasing the Forchheimer parameter decreases the temperature profiles The decrease of the velocity profiles with the increase in magnetic parameter is more enhanced in the presence of the velocity slip factor Increasing the Eckert number increases the temperature profiles in both suction and blowing cases This study considers the unique problem of the effect of transpiration in a Casson fluid in the presence of radiation, a magnetic field, and viscous dissipation The results obtained in this study are compared with other numerical methods and were found to be in excellent agreement

Heat Transfer in a Casson Rheological Fluid from a Semi-infinite Vertical Plate with Partial Slip

Abstract: The laminar boundary layer flow and heat transfer of Casson non-Newtonian fluid from a semi-infinite vertical plate in the presence of thermal and hydrodynamic slip conditions is analyzed. The plate surface is maintained at a constant temperature. Increasing velocity slip induces acceleration in the flow near the plate surface and the reverse effect further from the surface. Increasing velocity slip consistently enhances temperatures throughout the boundary layer regime. An increase in thermal slip parameter strongly decelerates the flow and also reduces temperatures in the boundary layer regime. An increase in the Casson rheological parameter acts to elevate considerably the skin friction (non-dimensional wall shear stress) and this effect is pronounced at higher values of tangential coordinate. Temperatures, however, are very slightly decreased with increasing values of Casson rheological parameter. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21115

Analysis of heat transfer due to stretching cylinder with partial slip and prescribed heat flux: A Chebyshev Spectral Newton Iterative Scheme

Abstract: This study is dedicated to analyze the combined effects of partial slip and prescribed surface heat flux when the fluid is moving due to stretching cylinder. A very moderate and powerful technique Chebyshev Spectral Newton Iterative Scheme is used to determine the solution of the present mathematical model. Involved physical parameters, namely the slip parameter, Casson fluid parameter, curvature parameter and Prandtl number are utilized to control the fluid moments and temperature distribution. The results show that the fluid velocity and the skin friction coefficient on the stretching cylinder are strongly influenced by the slip parameter. It is further analyzed that hydrodynamic boundary layer decreases and thermal boundary layer increases with the slip parameter. Influence of Casson fluid parameter on temperature profile provides the opposite behavior as compared to the slip parameter. The comparison of numerical values of skin friction coefficient and the local Nusselt number is made with the results available in the literature. The accuracy and convergence of Chebyshev Spectral Newton Iterative Scheme is compared with finite difference scheme (Keller box method) through tables. The CPU time is calculated for both schemes. It is observed that CSNIS is efficient, less time consuming, stable and rapid convergent.

Theoretical analysis of slip flow on a rotating cone with viscous dissipation effects

Abstract: This paper is concerned with the mutual effects of viscous dissipation and slip effects on a rotating vertical cone in a viscous fluid. Similarity solutions for rotating cone with wall temperature boundary conditions provides a system of nonlinear ordinary differential equations which have been treated by optimal homotopy analysis method (OHAM). The obtained analytical results in comparison with the numerical ones show a noteworthy accuracy for a special case. Effects for the velocities and temperature are revealed graphically and the tabulated values of the surface shear stresses and the heat transfer rate are entered in tables. From the study it is seen that the slip parameter γ enhances the primary velocity while the secondary velocity reduces. Further it is observed that the heat transfer rate NuRe x −½ increases with Eckert number Ec and Prandtl number Pr.

Thermally stratified stagnation point flow of Casson fluid with slip conditions

Abstract: Purpose – The purpose of this paper is to focus on the stratified phenomenon through vertical stretching cylinder in the region of stagnation point with slip effects. Design/methodology/approach – Homotopy analysis method is used to find the series solutions of the governing equations. Findings – Velocity profile decreases with an increase in stratified parameters due to temperature and concentration. Velocity and thermal slips cause a reduction in the velocity profile. Thermally stratified and thermal slip parameters reduce the temperature field. Originality/value – The present analysis has not been existed in the literature yet.

Effect of interfacial slip on the cross-stream migration of a drop in an unbounded Poiseuille flow.

Abstract: We analyze the motion and deformation of a buoyant drop suspended in an unbounded fluid which is undergoing a quadratic shearing flow at small Reynolds number in the presence of slip at the interface of the drop. The boundary condition at the interface is accounted for by means of a simple Navier slip condition. Expressions for the velocity and the shape deformation of the drop are derived considering small but finite interface deformation, and results are presented for the specific cases of sedimentation, shear flow, and Poiseuille flow with previously reported results as the limiting cases of our general expressions. The presence of interfacial slip is found to markedly affect axial as well as cross-stream migration velocity of the drop in Poiseuille flow. The effect of slip is more prominent for drops with larger viscosity wherein the drop velocity increases. The presence of significant interface slippage always leads to migration of a deformed drop towards the centerline of the channel for any drop-to-medium viscosity ratio, which is in contrast to the case of no slip at the interface, which allows drop migration towards or away from the centerline depending on the viscosity ratio. We obtain the effect of slip on the cross-stream migration time scale, which quantifies the time required to reach a final steady radial position in the channel. The presence of slip at the drop interface leads to a decrease in the cross-stream migration time scale, which further results in faster motion of the drop in the cross-stream direction. Gravity in the presence of Poiseuille flow is shown to affect not only the axial motion, but also the cross-stream migration velocity of the drop; interfacial slip always increases the drop velocities.

An ABS Control Strategy for Commercial Vehicle

Abstract: This paper proposes an antilock braking system (ABS) control method for maximizing tire-road friction and minimizing yaw moment of a commercial vehicle. First, a target slip ratio-based ABS control strategy has been described based on Lyapunov theory. Under this method, slip ratio is controlled in stable range precisely and rapidly. As fixed target slip ratio of ABS controller is not able to provide optimal road friction when a vehicle brakes on butt road and μ-split road, a variable target slip ratio method has been proposed to further improve tire-road friction and decrease yaw moment caused by longitudinal tire-road friction. Vicinity estimation and actual adhesion-based estimation have been introduced to estimate optimal target slip ratio. After a series of simulation tests, the method proposed in this paper has been proven to be effective.

Slip regulation for anti-lock braking systems using multiple surface sliding controller combined with inertial delay control

Abstract: In this paper, a multiple surface sliding controller is designed for an anti-lock braking system to maintain the slip ratio at a desired level. Various types of uncertainties coming from unknown road surface conditions, the variations in normal force and the mass of the vehicle are estimated using an uncertainty estimation technique called the inertial delay control and then the estimate is used in the design of the multiple surface sliding controller. The proposed scheme does not require the bounds of uncertainties. The ultimate boundedness of the overall system is proved. The proposed scheme is validated by simulation under various scenarios of road friction, road gradient and vehicle loading followed by experimentation on a laboratory anti-lock braking set-up for different friction conditions.

Three Three-Axis IEPE Accelerometers on the Inner Liner of a Tire for Finding the Tire-Road Friction Potential Indicators

Abstract: Direct tire-road contact friction estimation is essential for future autonomous cars and active safety systems. Friction estimation methods have been proposed earlier for driving conditions in the presence of a slip angle or slip ratio. However, the estimation of the friction from a freely-rolling tire is still an unsolved topic. Knowing the existing friction potential would be beneficial since vehicle control systems could be adjusted before any remarkable tire force has been produced. Since accelerometers are well-known and robust, and thus a promising sensor type for intelligent tires, this study uses three three-axis IEPE accelerometers on the inner liner of a tire to detect friction potential indicators on two equally smooth surfaces with different friction levels. The equal roughness was chosen for both surfaces in order to study the friction phenomena by neglecting the effect of surface texture on vibrations. The acceleration data before the contact is used to differentiate the two friction levels between the tire and the road. In addition, the contact lengths from the three accelerometers are used to validate the acceleration data. A method to differentiate the friction levels on the basis of the acceleration signal is also introduced.

Boundary layer flow due to a stretching sheet with a variable thickness and slip velocity

Abstract: This article presents a numerical solution for the flow of a Newtonian fluid over an impermeable stretching sheet with a power-law surface velocity, slip velocity, and variable thickness The flow is caused by nonlinear stretching of the sheet The governing partial differential equations are transformed into a nonlinear ordinary differential equation with appropriate boundary conditions for various physical parameters The remaining ordinary differential equation is solved numerically by using the Chebyshev spectral method The effects of the slip parameter and the wall thickness parameter on the flow profile and local skin friction are presented A comparison of obtained numerical results is made with previously published results in some special cases, and excellent agreement is noted

Lie group analysis and numerical solution of magnetohydrodynamic free convective slip flow of micropolar fluid over a moving plate with heat transfer

Abstract: In this paper, we investigate magnetohydrodynamic free convective flow of micropolar fluid over a moving flat plate using the Lie group transformations and numerical methods. Instead of using conventional no-slip boundary conditions, we used both the velocity and thermal slip boundary conditions to achieve physically realistic and practically useful results. The governing boundary layer equations are non-dimensionalized and transformed into a set of coupled ordinary differential equations (ODEs) using similarity transformations generated by the Lie group, before being solved numerically using Matlab stiff ODE solver ode15s and Matlab trust-region-reflective algorithm lsqnonlin. The effects of governing parameters on the dimensionless velocity, angular velocity, temperature, skin friction and heat transfer rate are investigated. Our analysis revealed that the dimensionless velocity and angular velocity decrease whilst the dimensionless temperature increases with the velocity slip parameter. Thermal slip reduces the dimensionless velocity and temperature but raises the dimensionless angular velocity. Magnetic field suppresses the velocity but elevates the temperature and angular velocity. Results reported in this paper are in good agreement with the ones reported by the previous authors.

Unsteady flow of Maxwell fluid in the presence of nanoparticles toward a permeable shrinking surface with Navier slip

Abstract: A detailed study on the problem of unsteady boundary layer flow and heat transfer of an upper-convected Maxwell fluid in the presence of nanoparticles over a permeable shrinking sheet with wall mass transfer is presented. In contrast to the conventional no-slip condition at the surface, Navier’s slip condition is applied at the surface. By use of a similarity transformation, the partial differential equations are reduced to a system of ordinary differential equations which is then solved numerically with shooting technique. The numerical results pertaining to the present study indicate that dual solutions exist for negative values of the unsteadiness parameter (A). It results in from the stability analysis that the upper branch solutions are stable and physically realizable, while the lower branch solutions are not stable and, therefore, not physically realizable. It is also found that as the Maxwell parameter (β) and velocity slip parameter (δ) increase, the range of the unsteadiness parameter (A) for which the solution exists gradually increases. The local Nusselt number and the local Sherwood number increase with the increase in the values of Maxwell parameter (β) and velocity slip parameter (δ). Furthermore, the effects of different physical parameters on the flow, temperature and concentration profiles are shown graphically and discussed in details.

MHD viscous Casson fluid flow and heat transfer with second-order slip velocity and thermal slip over a permeable stretching sheet in the presence of internal heat generation/absorption and thermal radiation

Abstract: This article is devoted to describing the boundary layer flow and heat transfer for an electrically conducting Casson fluid over a permeable stretching surface with second-order slip velocity model and thermal slip conditions in the presence of internal heat generation/absorption and thermal radiation. The basic equations governing the flow and heat transfer are in the form of partial differential equations; the same have been reduced to a set of highly non-linear ordinary differential equations by applying suitable similarity transformations. Exact solution corresponding to momentum equation is obtained, and, in the case of no slip conditions, we get the exact solutions for both momentum and energy equation. The resulting similarity equations are solved numerically by shooting method. Comparisons with previously published work are performed and the results are found to be in excellent agreement. In the present work the effect of magnetic parameter, suction/injection parameter, Casson parameter, slip parameters, radiation parameter, internal heat generation/absorption parameter and the Prandtl number on flow and heat transfer characteristics have been discussed. Also, the local skin-friction coefficient and the local Nusselt number at the sheet are computed and discussed. It is found that the temperature rises to a higher value when the Casson parameter increases but the reverse is true for the velocity distribution. Finally, increasing the velocity and thermal slip parameters makes the rate of heat transfer decrease.