Effect Of Surface Waviness Research Articles

Modeling and analysis of 3D mixed lubrication in marine cam–tappet pair

During the operation of the marine cam–tappet pair, affected by periodic dynamic load, transient velocity, and micromorphology, it usually operates in a mixed lubrication state. Under extreme operational conditions, contact is likely to occur at the asperity of the interface, leading to problems such as stress concentration and dry contact. Considering the transient dynamics and three-dimensional roughness of cam–tappet pair, a mixed-elastohydrodynamic lubrication model is developed in this article, while the effects of surface waviness on the lubrication state are also investigated. The results show that the film thickness can be increased by 0.098 μm, and the coefficient of friction can be reduced by 10.6% when the wavelength ratio ranges from 1/6 to 6. However, when the amplitude exceeds 0.6 μm, the coefficient of friction may reach 0.10. Under conditions of low speed and high load, the film thickness decreases and contact load ratio increases. And about 30% reduction in film thickness is achieved on cam–tappet pair, potentially leading to increased wear or scuffing failure.

On the effects of surface waviness upon catalytic steam reforming of methane in micro-structured reactors - a computational study

The effects of wavy channels upon steam methane reforming in catalytic micro-structured reactors, using Nickle as the catalyst, are investigated numerically. Laminar, three-dimensional models of reacting flows, with heterogeneous chemistry, are developed and applied to micro-structured reactors with different wave patterns on their internal walls. It is observed that introduction of surface waves on the walls of reactor, can significantly alter production and consumption of H2 and CH4. This is shown to be due to large fluctuations in convective mass and heat transfer, induced by the surface waviness. In particular, it is shown that separation and reattachment of concentration and thermal boundary layers and the subsequent modifications in Sherwood and Nusselt number can significantly affect the catalytic processes over the walls of reactor. A major local intensification of catalytic processes is observed where Sherwood and Nusselt number are maximised. Similarly, the catalytic process becomes highly inefficient in places with minimal Sherwood (and Nusselt) number. The analyses further reveal that a strategic discrete coating of wavy walls with the catalyst can substantially improve the performance of microstructure. For example, by coating only 25% of the surface area of wavy walls, CH4 conversion rate and selectivity per coated surface area increase by 459% and 308% compared to those of an equivalent fully coated straight channel. This implies the possibility of developing highly efficient and cost-effective catalytic micro-reactors for production of hydrogen from methane.

Performance analysis of journal bearing having surface waviness operating under misaligned condition

In this present study, the effect of surface waviness on the performance of journal bearing operating in misaligned conditions has been investigated. The journal’s misaligned conditions in the present analysis are taken about the circumferential, the axial, and both axes. For computing the pressure of lubricant inside the bearing, the finite element method has been applied to solve the Reynolds equation and thus static parameters are obtained. The static parameters, that is, load carrying capacity and coefficient of friction are evaluated at different waviness variables and are compared with misaligned journal bearing without surface waviness. It is observed that misalignment considered in both axes has the most severe effect on static performance parameters as compared to misalignment only in the circumferential or axial axis. With the increase in circumferential waviness number up to n = 5, the load-carrying capacity increases, and the coefficient of friction decreases under high eccentricity ratios. Change in waviness amplitude also impacts the bearing performance. Axial waviness always deteriorates the bearing performance. Combined waviness increases the load carrying capacity and decreases the coefficient of friction when circumferential waviness number n = 5 and axial waviness number m = 2. The highest performance enhancement ratio is attained at an eccentricity ratio of 0.8 with a circumferential waviness number n of 5, axial waviness number m of 2, and dimensionless waviness amplitude [Formula: see text] of 0.075.

Impact of partial surface waviness on the tribological performance of hydrodynamic journal bearing

AbstractIn this paper, the static performance analysis of journal bearing having full and partial surface waviness has been presented. The surface waviness is to be considered in the full, first half, second half, and pressure‐increasing and decreasing regions of the bearing for analysis. The effect of surface waviness is considered by modifying the lubricant flow governing Reynolds equation with the film thickness equation and it is solved with the finite element method to get performance parameters like bearing load capacity, friction coefficient, and so forth operating under eccentricity ratios range of 0.2–0.8. The waviness geometrical parameters like waviness numbers and amplitudes are also considered in circumferential, axial, and both directions in the selected regions. The maximum performance has been found for waviness in the full and pressure‐increasing region in the circumferential direction at a high eccentricity ratio.

Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss—Part II: Experimental Assessments and Applications

AbstractPart II describes the experimental assessment and the application of the ideas in Part I concerning the mechanisms that determine the role of blade surface waviness on laminar-turbulent transition and their consequent effect on civil aircraft fan performance. A natural transition wind tunnel was designed and constructed to characterize the impact of surface waviness on transition, using both hotwire anemometry and infrared thermography. The experimental results support the new hypothesis presented in Part I, concerning the way in which blade surface waviness affects fan performance through motion of the transition onset location due to interaction between surface waviness and Tollmien–Schlichting (TS) boundary layer instability. In particular, the theoretical amplification of the TS waves, and the corresponding transition onset location movement due to surface waviness, was borne out over a range of variations in Reynolds number, nondimensional surface wavelength, nondimensional surface wave height, and location of surface wave initiation, relevant to composite fan blade parameters. Further, the increase of receptivity coefficient, and thus, the initial amplitude of disturbances due to geometric resonance between surface wavelength and TS wavelength was also confirmed by the experiments. Surface waviness was estimated, in some cases, to result in a nearly 1% decrease in fan efficiency compared to a nonwavy blade. Suggestions are given for mitigation of the effects of waviness, including the idea of blade curvature rescheduling as a method to delay transition and thus decrease loss.

Effect of Surface Waviness on the Performances of an Aerostatic Thrust Bearing with Orifice-Type Restrictor

Effect of Surface Waviness on the Performances of an Aerostatic Thrust Bearing with Orifice-Type Restrictor

Effect of surface waviness on MHD thermo-gravitational convection of Cu−Al2O3−water hybrid nanofluid in a porous oblique enclosure

This study investigates thermo-fluid phenomena of magnetohydrodynamic (MHD) free convection utilizing Cu-Al2O3/water hybrid nanofluid in a porous oblique enclosure consisting of a heated wavy vertical wall. The coupled transport equations are solved numerically by implementing the dimensionless governing equations and using an indigenous FORTRAN-based CFD code and the finite volume approach (FVM). The flow physics along with heat transfer characteristics are explored thoroughly by varying the number of peaks (n) of the wavy wall at different Darcy-Rayleigh numbers (Ram), Darcy numbers (Da), Hartmann numbers (Ha), and nanoparticle volumetric fractions (ϕ) for different inclinations (γ) of the enclosure. The study findings indicate that the wavy curved wall does not always guarantee heat transfer boosting even with the increase in the effective heating surface area. An increase in active length of the wavy heated wall by the undulations (which is ∼320% with 8 undulations) leads to the heat transfer enhancement of ∼20% compared to a no-undulated cavity. The average heat transfer rate is maximum when n = 4, beyond which heat transfer decreases. Depending upon the setting of the value of Ram, Da, Ha, ϕ and γ, the flow-structure and associated heat transfer characteristics are severely altered. Cavity inclination angle has a significant role in controlling the overall thermal performance.

Heat transfer enhancement by sinusoidal-shaped disk rotating in a forced flow

The geometric characteristics of the heat transferring surface and the outer flow conditions have a significant impact on heat transfer augmentation. Both, the surface roughness and the pressure gradient attribute to an enhanced heat transfer. These two effects are utilized in this study to enhance the convective heat transfer rate in a non-similar boundary-layer flow induced by the rotation of a sinusoidal-shaped disk in an external forced flow. The heat transfer coefficient is calculated numerically for the laminar boundary-layer flow with the help of the Keller-box method. The numerical solution of the governing system of equations is first validated by previous published (theoretical and experimental) results for a wavy rotating disk in the absence of an external flow field and also for a flat disk rotating in a forced flow. It is observed that the effect of surface waviness along with a relative fluid motion on heat transfer rate, shear stresses, and shaft torque is quite pronounced. Specifically, enhancement of moment coefficient due to waviness of the disk leads to increase the power of a wavy disk pump in comparison to a smooth one. Furthermore, 119%, 174%, 86%, and 86% enhancement in the heat transfer rate, the radial shear stress, the tangential shear stress, and the moment coefficient, respectively, is observed for a rotating wavy disk subjected to a forced flow (at fixed a/? = ? and a0/? = 0.125) in comparison to a free rotating flat disk.

Effect of Surface Waviness on Stability of Hydrodynamic Journal Bearing Systems

Effect of Surface Waviness on Stability of Hydrodynamic Journal Bearing Systems

Effect of Surface Waviness on Aerostatic Bearing with Speed

In this paper, the Reynolds equation is solved by the different finite methods. On the basis of the ideal circle, the effect of surface ripple on the static pressure bearing is considered, and the performance parameters of the gas bearing are obtained by using the Newton iteration method. Considering the influence of different rotational speeds on the gas bearing, the influence of the bearing capacity, the air consumption and the friction coefficient on the static pressure bearing are analyzed, and the effect of the axial and circumferential waviness on the aerostatic bearing is analyzed. The results show that with the increase of the rotational speed and the error value, the bearing capacity becomes smaller and the friction coefficient becomes larger. In the specific error value, as the film thickness increases, the bearing capacity increases first and then becomes smaller.At the same time, the circumferential ripple error has a greater influence on the gas bearing than the axial direction.

Effect of surface waviness on the static performance of aerostatic journal bearings

A numerical study of the effect of the bearing surface waviness on the performance of aerostatic journal bearings is presented. The finite difference method (FDM) and an iterative procedure are proposed to solve Reynolds equation and derive the air film pressure distribution. The calculated results indicate that the surface waviness can influence the bearing characteristics obviously. The effect of the wave's spatial wavelength on the bearing performance is not in order, whereas the effect of the waviness amplitude is ordinal. With the growth of the circumferential or axial waviness amplitude from 1.0µm to 3.0µm, the load capacity, stiffness and mass inflow rate can be decreased, whereas the circumferential or axial friction coefficient can be increased.

Effects of surface waviness on heat and fluid flow in a nanofluid filled closed space with partial heating

The current computational study focused on the effects of surface waviness on heat and fluid flow in a partially heated cavity filled with a nanofluid. The cavity has a partial heater and a wavy wall which is kept cooled isothermally. The current study investigated the effects of the heat and fluid flow in the cavity due to the cooled wall waviness. The study covered a wide range of Rayleigh numbers (103–105), nanofluid volume fraction (0–9 %), surface waviness ratio, non-dimensional length of the heater (0.25–0.75) and non-dimensional location of the heater (0.25–0.75). It is found that the location and the length of the heater are significant parameters on heat and fluid flow. However, the cooled wall surface waviness does not influence the heat transfer substantially.

617 Effect of Surface Waviness on Thermal Contact Resistance under Low Contact Pressure

617 Effect of Surface Waviness on Thermal Contact Resistance under Low Contact Pressure

Enhancement of phase change material (PCM) based latent heat storage system with nano fluid and wavy surface

Abstract A numerical study is performed on the effects of surface waviness and nanoparticle dispersion on solidification of Cu–water nanofluid inside a vertical enclosure for different Grashof numbers. A geometry with sinusoidally curved wavy surface can be used to enhance heat transfer performance if it is carried out in an appropriate way. Therefore, the enclosure has wavy surfaces on right side with higher temperature and left side with lower temperature, while the top and bottom walls are both flats with insulated condition. Computations are conducted for the surface waviness ranging from 0 to 0.4, Grashof number from 104 to 106 and nanoparticle dispersion from 0 to 0.1. An enthalpy porosity technique is used to trace the solid and liquid interface inside the enclosure. To validate the results, the numerical solutions for special cases in a rectangular cavity were compared with previously published works which are in good overall agreement with those results. The numerical results show that for surface waviness of 0.25 and 0.4, a maximum of 60% decrease in solidification time for Gr = 106 is observed in comparison with Gr = 105 which indicates the increasing effects of natural convection on solidification due to distortion on surface. Therefore, surface waviness can be used to control the solidification time based on enhancing different mechanism of solidification.

Solidification of nano-enhanced phase change material (NEPCM) in a wavy cavity

The effects of surface waviness (λ = 0, 0.125, 0.25, 0.5) and nanoparticle dispersion (ϕ = 0, 0.05, 0.1) on solidification of Cu-water nanofluid inside a vertical enclosure are investigated numerically for different Grashof number (Gr = 105, 106, 107). An enthalpy porosity technique is used to trace the solid and liquid interface. Comparisons with previously published works show the accuracy of the obtained results. A maximum of 25.9% relative variation of freezing time with surface waviness was observed for λ = 0.5, while the relative variation of freezing time with nanoparticles in comparison with surface waviness was negative for high values of λ. It was observed that surface waviness can be used to control the solidification time based on enhancing different mechanism of solidification.

Prediction of boundary layer transition on a flat plate subject to surface waviness

The current understanding of the boundary layer transition is reviewed briefly. The effects of leading edge geometry, inlet turbulence, and surface waviness, on boundary layer transition on a flat plate are predicted using a commercial computational fluid dynamics (CFD) code, STAR-CCM+ which incorporates the γ − R θ correlation model. The investigations on surface waviness were focused on sinusoidal waves with the ratios of wave amplitude to wavelength h/ Lw and wave amplitude to boundary layer displacement thickness h/ δ* in the range 0.0025–0.015 and 0.3–2.8, respectively. It is recommended that in wind tunnel testing/CFD analysis of boundary layer transition, a leading edge aspect ratio of 12 is maintained to avoid significant effect of leading edge geometry. The predictions for the effect of surface waviness on transition for multiple waves, using γ − R θ model, agree well with those using the stability theory. New correlations for the effect of waviness on transition Reynolds number are proposed. The correlations combine the effects of upstream boundary layer displacement thickness, wave height, and wavelength ( h* or h**). It is recommended that a value of h* < 2 or h** < 0.03 is maintained on aircraft surfaces to avoid any significant effect of waviness on drag. The variation of transition Reynolds number with h* for a surface with waviness is of the same order to that on a surface with a forward facing step, but significantly smaller when compared with a surface with a backward facing step (BFS). A value of h* < 0.5 is recommended for a BFS to avoid significant effect on transition.

J0601-1-4 固体表面間の接触熱抵抗に関する理論的研究 : 熱流の縮流に及ぼすうねりの影響([J0601-1]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(1))

To minimize the volume and weight of electronic systems like spacecraft, aircraft and computers, the systems are packed with high-density electronic devices. In addition to this situation, the heat dissipation density of microprocessors has been increased at a rapid pace. Under such a high heat dissipation density, thermal contact conductance plays an important role in cooling of electronic equipment. In this paper, the effect of surface waviness on the heat flow field near the contact interface has been studied analytically. In the analysis, a contact surface model with waviness and roughness is introduced, and two-dimensional cylindrical heat conduction equation has solved numerically. From a series of numerical calculations, the effect of surface waviness on the heat flow field has been clarified.

The Effects of Surface Waviness and Length on Electrokinetic Transport in Wavy Capillary

An electrokinetic model for a wavy capillary has been developed. Poisson-Nernst-Planck and Navier-Stokes equations constitute the model that governs fluid and ionic fluxes and electric potential distribution inside the capillary. In the present paper, a finite wavy cylindrical capillary with a large reservoir at both capillary ends is analyzed using finite element method. The model is used primarily to examine the influence of capillary surface waviness on the electrokinetic transport behaviours. Different frequencies and amplitudes of the wavy surface are considered to investigate the influence of surface waviness on electrokinetic transport. Fluctuations in potential and ionic concentration distribution increase with the increase in either amplitude or frequency of the capillary surface waviness. However, for higher frequencies the fluctuation diminishes for all surface waviness amplitudes. It is observed that for any irregularity in the capillary surface results in higher salt rejection. Salt rejection is found to be dependent on capillary axial length as well as flow velocity. A critical Peclet number, beyond which salt rejection attains a constant steady value, dictates maximum salt rejection.

Rolling Bearing Vibrations—The Effects of Surface Waviness and Radial Internal Clearance

This paper presents the nonlinear dynamic analysis of a balanced rotor supported by roller bearings. The mathematical formulation accounted for tangential motions of rolling elements as well as inner and outer races with the sources of non-linearity such as Hertzian contact force and radial internal clearance resulting transition from no-contact to contact state between rolling elements and the races. In the formulation the contacts between the rolling elements and the races are considered as nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The implicit type numerical integration technique Newmark-β with Newton-Raphson method is used to solve the nonlinear differential equations iteratively. The results show the appearance of instability and chaos in the dynamic response as the speed of the rotor-bearing system is changed. Period doubling and mechanism of intermittency have been observed, which lead to chaos. The appearance of regions of periodic, subharmonic and chaotic behavior is seen to be strongly dependent on these imperfections. Poincarè maps, phase plots and frequency spectra are used to elucidate and to illustrate the diversity of the system behavior.

Stability analysis of a rotor bearing system due to surface waviness and number of balls

In the paper, the stability analysis of a rigid rotor supported by ball bearings has been studied. In the analytical formulation, the contacts between balls and races are considered as nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The implicit type numerical integration technique Newmark-β with Newton–Raphson method is used to solve the nonlinear differential equations iteratively. The effects of surface waviness and the varying number of balls on stability of rotor bearing system are observed. All results presented in form of fast fourier transformations show that the vibration characteristics of the rotor and its bearings change, when the bearings operate in different regions of their nonlinear load deflection characteristics. From the analysis, it is implied that the number of balls and number of waves in the ball bearing are two important governing parameters affecting its dynamic behavior.