Magnitude Of Roughness Research Articles

Influence of Surface Roughness on a Highly Loaded Axial Compressor Stage Performance at Low Reynolds Number

In the present study, a numerical simulation was conducted to investigate the influence of surface roughness on the aerodynamic performance of a 1.5-stage highly loaded axial compressor at low Reynolds number. It was especially considered how the roughness Reynolds number ( k + ) affected the change of the inlet and outlet conditions, the growth of the separation bubble (LSB), the status of the limiting streamline, and the patterns of the wake. Regarding the roughness settings, five roughness magnitudes and four roughness locations were mainly studied. The results showed that at low Re, surface roughness mainly improved the stage performance by reducing the length and width of the LSB as well as the rotor tip vorticity, delaying the occurrence of three-dimensional flow separation and increasing the turbulence level near the wall. However, it also aggravated the incoordination between the subsequent stages to a certain extent, which limited further improvement of the overall aerodynamic performance. Generally, with k + increasing, the compressor aerodynamic performance improved and achieved the best at k + = 137.8 . The maximum increases in the total pressure ratio, peak efficiency, and chocked mass flow were approximately 4.01%, 5.34%, and 2.24%, respectively. In addition, for all the four roughness locations, the roughness covering from the leading edge to 50% of the axial chord length on the suction surface had a relatively evident advantage in improving the compressor peak efficiency because of the better control of the LSB and wall shear stress.

Effect of nonvertical ion bombardment due to edge effects on polymer surface morphology evolution and etching uniformity

Maintaining uniform sample etching during a plasma process is a critical requirement for applications in large-scale wafer processing. The interface between the plasma and the sample surface is defined by the plasma sheath, which accelerates ions toward the sample surface. In areas where the plasma sheath is not parallel to the sample surface, such as near the sample edges, the incident ions arrive at shallower, off-normal angles that can result in a greater etch yield relative to other areas of the sample. This phenomenon leads to nonuniform etching, along with characteristic surface morphology evolution. In this work, we utilized a combination of spatial ellipsometry for etching behavior, atomic force microscopy (AFM) for surface morphology evolution, and power spectral density (PSD) analysis to quantify the extent and spatial dependence of the nonuniform etching near the sample edges. The spatial ellipsometry indicated that a region extending for about 1000 μm from the sample edge experiences approximately 10%–15% more thickness loss (∼10–15 nm) relative to areas near the center of the sample under the tested processing conditions. Within this area, the greatest rate of change in the sample thickness occurs within 5 Debye lengths or ∼300 μm from the sample edge. Via AFM analysis, we detected the presence of ripple features that are consistent with directional ion impacts caused by deflection of ions from normal incidence on the surface morphology [Merkulov et al., Appl. Phys. Lett. 80, 4816 (2002)] AFM scans performed in two different sample orientations confirmed that the ripple features are oriented perpendicular to the direction of incident ions and propagate along the direction of the incident ions. Correspondingly, the magnitude of surface roughness decreases as the distance from the sample edge increases. The ripple features were quantified via PSD analysis, which found the presence of a greater population of long-wavelength roughness closer to the sample edge. The findings of this study provide insight into the influence of the plasma sheath distortions near sample edges on the extent of nonuniform sample etching and characteristic surface morphology evolution in plasma etching applications.

Uncertainty quantification of heat transfer in a microchannel heat sink with random surface roughness

To numerically investigate the stochastic heat transfer performance of a microchannel heat sink, a randomly generated, rough surface profile with a prespecified autocorrelation function is applied to its bottom surface. The magnitude of the maximum relative roughness of the surface is treated as a Gaussian random input with specified uncertainty, and uncertainty in the output is modeled via polynomial chaos expansions. According to deterministic analysis of the simulation results, an increase in surface roughness enhances the heat transfer. As found through stochastic analysis of the joint probability density functions of the local surface height and local Nusselt number, the local surface height alone is insufficient to explain changes in the local Nusselt number, and the sensitivity of the local Nusselt number to other factors increases with the absolute value of the local surface height. Polynomial chaos expansions are used to identify the peaks and ridges of the surface as regions where the Nusselt number and velocity magnitude are more sensitive to the local surface roughness than in valleys. Probability density functions are estimated from the polynomial chaos expansions of the local Nusselt number, spanwise-averaged Nusselt number, and three global outputs: the average Nusselt number over the rough bottom surface, the pressure drop over the channel, and the performance factor of the bottom surface. Because of nonlinear propagation of the Gaussian random input, the distributions of the local and spanwise-averaged Nusselt numbers can not generally be assumed to have a Gaussian shape. In contrast, the global outputs can be treated as Gaussian as a good approximation.

Investigating the geometrical effects of cutting tool on the surface roughness of titanium alloy (Ti6Al4V) during milling operation

The quality and performance of a product in service is partly a function of its surface integrity and dimensional accuracies. The cutting tool employed for machining operation plays significant role in the determination of the surface finish of the final product. This study considers the use of the Computer aided modelling and simulation tool (ANSYS 2019) for the determination of the geometrical effects of the cutting tool on the surface roughness of titanium alloy using an indexable double sided round carbide insert milling cutter during milling operation. The cutting tool geometry namely the helix angle (β), number of flutes (n), and cutting edge angle (α) were modelled and simulated iteratively with the corresponding strain and displacement taken as the response of the designed experiment. In order to validate the numerical analysis, the physical experiments were carried out on test pieces of titanium alloy on a DMC 635 V DMG ECOLINE, Deckel Maho Germany, Siemens 810D, 3- Axis, CNC vertical milling machine and the values of the surface roughness were measured using the Mitutoyo SJ – 201, surface roughness machine. The results obtained produced the most feasible combinations of the cutting tool geometry and cutting parameters that gave the least surface roughness. Hence, the successful completion of this work provides a numerical approach which is validated experimentally. It is envisaged that the findings in this study will assist manufacturers in predicting and minimizing the magnitude of surface roughness during cutting operations.

Sensitivity of material failure to surface roughness: A study on titanium alloys Ti64 and Ti407

The relationship between material failure and surface roughness has been investigated using two titanium alloys: Ti64 and the more ductile Ti407. Three surface types were created (polished, sandblasted and scratched) with instances spanning a wide range of average roughness. The surfaces were tested in three-point bending with the imparted roughness on the tensile under-surface of a rectangular beam specimen. Results showed failure of Ti64 to be highly sensitive to both magnitude and orientation of roughness. High roughness in the maximum tensile stress direction (and scratch like features perpendicular to this direction) were most detrimental. Thus, strain-to-failure (and work-to-failure) in Ti64 dropped off significantly with increasing surface roughness in the tensile direction. Finite element modelling of the test indicated that cracks initiate at zones of high plastic strain at the tips of roughness valleys due to high local surface curvature. Thus, roughness can be considered as a series of blunt crack-like features where larger crack tip curvature induces greater likelihood of crack propagation. Contrastingly, the mechanical response of Ti407 was insensitive to surface roughness owing to its significantly greater ductility. Thus, designers need to be aware of the sensitivity of failure of particular materials to surface roughness. The insensitivity of Ti407 is advantageous, but the sensitivity of failure to surface roughness in a material like Ti64 is potentially serious if not properly accounted for.

Nanoscale Surface Roughness Influences Candida albicans Biofilm Formation.

The microbial contamination of surfaces presents a significant challenge due to the adverse effects associated with biofilm formation, particularly on implantable devices. Here, the attachment and biofilm formation of the opportunistic human pathogen, Candida albicans ATCC 10231, were studied on surfaces with decreasing magnitudes of nanoscale roughness. The nanoscale surface roughness of nonpolished titanium, polished titanium, and glass was characterized according to average surface roughness, skewness, and kurtosis. Nonpolished titanium, polished titanium, and glass possessed average surface roughness (Sa) values of 350, 20, and 2.5 nm; skewness (Sskw) values of 1.0, 4.0, and 1.0; and (Skur) values of 3.5, 16, and 4, respectively. These unique characteristics of the surface nanoarchitecture were found to play a key role in limiting C. albicans attachment and modulating the functional phenotypic changes associated with biofilm formation. Our results suggest that surfaces with a specific combination of surface topographical parameters could prevent the attachment and biofilm formation of C. albicans. After 7 days, the density of attached C. albicans cells was recorded to be 230, 70, and 220 cells mm-2 on nonpolished titanium, polished titanium, and glass surfaces, respectively. Despite achieving a very low attachment density, C. albicanscells were only observed to produce hyphae associated with biofilm formation on nonpolished titanium surfaces, possessing the highest degree of surface roughness (Sa = 350 nm). This study provides a more comprehensive picture of the impact of surface architectures on C. albicans attachment, which is beneficial for the design of antifungal surfaces.

Effects of water jet peening on residual stresses, roughness, and fatigue

ABSTRACT Water jet peening is a surface modification technique which can introduce compressive residual stresses beneath the surface of the engineering components. In this paper, the effects of water jet peening process, in the absence of abrasive materials on residual stresses, surface roughness, and fatigue life of the aluminium alloy 7020 samples were numerically and experimentally investigated. Therefore, two nozzles with respective exit angles of 0° (round nozzle) and 20° (orifice nozzle) were used and residual stresses were measured through centre-hole drilling technique. Furthermore, fatigue tests were performed on the water peened samples. Results indicated that in contrast to the horizontal speed of the nozzle, pressure of source and stand-off distance exerted a profound influence on the magnitude of residual stresses and surface roughness. Moreover, in cases which the pressure of the source exceeded a certain limit, fatigue life of the workpiece declined due to the surface crack formations.

On the influence of a surface roughness on propagation of anti-plane short-length localized waves in a medium with surface coating

We discuss the propagation of localized surface waves in the framework of the linear Gurtin–Murdoch surface elasticity and taking into account a roughness of a free boundary. We derive a boundary-value problem for anti-plane motions with curvilinear boundary and surface stresses. Using the asymptotic technique developed earlier, we obtain the form of a localized wave and analyze its amplitude evolution. As the main result we present the dependence of the wave amplitude on the roughness magnitude. The presented results could be used for non-destructive evaluation of the surface microstructure using surface waves-based devices. In particular, measuring the decay rate with the depth one can estimate roughness of a surface and appearance of new surface defects.

The Effect of Fracture Roughness on the Onset of Nonlinear Flow

AbstractIn fractures where surface fluctuations are large compared to their aperture (narrow fractures), the flow is forced to move in tortuous paths that produce additional viscous friction and are subject to inertia effects. We consider the relation between the magnitude of surface roughness and the onset of inertial effects in the pressure driving the flow through a single open fracture. We performed experiments systematically varying the average aperture of the open fracture and covering a wide range of Reynolds numbers. For each aperture, we analyze the data in terms of the Forchheimer equation and show that the critical Reynolds number, defined as the Reynolds number at which inertial effects contribute 10% of the total pressure losses, is highly correlated with the roughness of the surface. In particular, we show that significant inertial effects appear earlier as the relative importance of surface roughness increases. Finally, we present results showing that the magnitude of the deviations in the pressure field compared to a linear profile, taken at different points in the fracture along the flow direction, is directly related to the relative surface roughness of the fracture.

FEATURES OF HIGH-SPEED THE SUPER-FINISHING DISCS CERAMIC

The possibility of providing high performance of super-finishing of ceramics based on the analysis of the processes of super-finishing of metal products is proved. For conducting experimental studies, a special installation has been developed, including a sharpening machine and a device for superfinishing. For such processing conditions, the necessity of using a low-rigidity technological system is justified. Discs made of ceramic materials of various machinability with diamond bars were super-finished at a cutting speed of up to 9.1 m/s and a clamping force of up to 90 N. Experimental data on the change in the value of cut allowance on the duration of treatment, the impact speed super-finishing of ceramic disks and grit sizes of diamond bars on the magnitude and rate of stock removal, roughness and waviness of machined surfaces and consumption of the tool. The results of super finishing of ceramic materials with processing of metal products are compared.

Effects of surface roughness on the aerodynamic performance of a high subsonic compressor airfoil at low Reynolds number

The aerodynamic performance of compressor airfoil is significantly affected by the surface roughness at low Reynolds number (Re). In the present study, numerical simulations have been conducted to investigate the impact of surface roughness on the profile loss of a high subsonic compressor airfoil at Re = 1.5 × 105. Four roughness locations, covering 10%, 30%, 50% and 100% of the suction surface from the leading edge and seven roughness magnitudes (Ra) ranging from 52 to 525 μm were selected. Results showed that the surface roughness mainly determined the loss generation process by influencing the structure of the Laminar Separation Bubble (LSB) and the turbulence level near the wall. For all the roughness locations, the variation trend for the profile loss with the roughness magnitude was similar. In the transitionally rough region, the negative displacement effect of the LSB was suppressed with the increase of roughness magnitude, leading to a maximum decrease of 14.6%, 16.04%, 16.45% and 10.20% in the profile loss at Ra = 157 μm for the four roughness locations, respectively. However, with a further increase of the roughness magnitude in the fully rough region, the stronger turbulent dissipation enhanced the growth rate of the turbulent boundary layer and increased the profile loss instead. By comparison, the leading edge roughness played a dominant role in the boundary layer development and performance variation. To take fully advantage of the surface roughness reducing profile loss at low Re, the effects of roughness on suppressing LSB and inducing strong turbulent dissipation should be balanced effectively.

Visual motion information modulates tactile roughness perception

We perceive the roughness of an object through our eyes and hands. Many crossmodal studies have reported that there is no clear visuo-tactile interaction in roughness perception using static visual cues. One exception is that the visual observation of task-irrelevant hand movements, not the texture of task-relevant objects, can enhance the performance of tactile roughness discrimination. Our study investigated whether task-irrelevant visual motion without either object roughness or bodily cues can influence tactile roughness perception. Participants were asked to touch abrasive papers while moving their hand laterally and viewing moving or static sine wave gratings without being able to see their hand, and to estimate the roughness magnitude of the tactile stimuli. Moving gratings with a low spatial frequency induced smoother roughness perceptions than static visual stimuli when the visual grating moved in the direction opposite the hand movements. The effects of visual motion did not appear when the visual stimuli had a high spatial frequency or when the participants touched the tactile stimuli passively. These results indicate that simple task-irrelevant visual movement without object roughness or bodily cues can modulate tactile roughness perception with active body movements in a spatial-frequency-selective manner.

Investigation of the roughness variation along the length of LPBF manufactured straight channels

ABSTRACT Conformal cooling channels, made by the laser powder bed fusion process, are a promising design strategy for optimising cooling and process control of manufacturing tools and injections moulds. The addition of internal features such as corrugations and ribs are becoming an interesting addition to the cooling channel designs. Internal surfaces of laser powder bed fusion components have an inherent process-induced roughness. The roughness may affect the flow in the channels and may affect the addition of internal features by changing the actual geometry of the channels. This work seeks to characterise the variation of the internal surface roughness along the length of seven straight channels, manufactured using the laser powder bed fusion process, by utilising X-ray CT and image analysis. The characterisation showed that the surface roughness varied discontinuously along the length of the channels and that the roughness magnitudes and roughness variations along the channel lengths were dependent on the orientation of the channels with respect to the build direction. Therefore, the actual geometries of multiple, nominally equal, embedded internal features would vary differently from nominal design, dependent on the location of the feature along the channel length and orientation in the channel.

Tailoring Surface Roughness Using Additive Manufacturing to Improve Internal Cooling

Abstract Surface roughness present on internal cooling channels produced with additive manufacturing has been previously shown to augment heat transfer and pressure loss to levels similar to traditionally cast turbulators. Given the ability of the surface roughness to improve the cooling performance of small cooling channels, the question arises on whether there is an optimal combination of random roughness features to maximize internal cooling performance. To investigate this question, test coupons with different surface roughness morphologies and magnitudes were manufactured by manipulating the parameters in the laser powder bed fusion additive manufacturing process. The coupons were tested to characterize the friction factor and Nusselt number of the cooling channels over a range of Reynolds numbers. Results showed that certain roughness combinations outperformed others, increasing the internal cooling performance of the channels. Additionally, manipulation of the performance using the process parameters allowed for reductions in build time, which could be useful for controlling component cost.

Optical transmission spectra study in visible and near-infrared spectral range for identification of rough transparent plastics in aquatic environments

Erosion of microplastics due to residence time in aquatic environments causes roughening of the microplastic. Unfortunately, currently used measurement methods do not provide information on the surface roughness of the microplastic embedded in water. In this study we propose a novel method by using transmittance to get information on the magnitude of the surface roughness of microplastics and to rank microplastics by thickness.For such a purpose, we studied optical properties such as dispersion, absorption of both plastics and water in the partial spectral range of visible light (Vis), transmission and scattering of light by plastic sheets, as well as, the calculated sample thickness in the Vis region. These were explored for the detection of both smooth and roughened plastic sheets immersed in water. Moreover, by using the transmission spectrum and refractive index of both plastic and water it is possible to estimate the average surface roughness of plastic samples. Our results suggest that the optical properties in the Vis region offer an interesting way for the detection of both rough and smooth plastic sheets and for ranking the type of plastics in an aquatic environment.

Effect of particle roughness on the rheology of suspensions of hollow glass microsphere particles

The rheology of high volume fraction (30–40%) suspensions with hollow glass microspheres (radius r = 15 µm) in a matrix of silicone oil has been studied experimentally. The surface of the hollow glass microspheres was roughened by wet chemical processing, using hydrochloric (HCl) acid and also sodium hydroxide etching. We obtained particles of various roughnesses in the range of Ra = 62–655 nm. The effect of particle roughness on the overall rheology is investigated, demonstrating its clear impact. The effect depends on the volume fraction, the magnitude of roughness and shear rate. At a 30% volume fraction, increasing the roughness ratio (Ra/r) from 0.42% to 4.44% does not result in a measurable change in viscosity. At a higher volume fraction of 40%, even a modest increase of the roughness ratio to 1.5% causes a significant increase in the viscosity of 117%, 97%, 50% and 39%, respectively at shear rates of 0.47, 1, 10 and 100 s−1. Increasing the roughness to 4.44% results in an increase of 272%, 105%, 41%, 23% in viscosity over the same range of shear rates. In all cases, we show that the effect of roughness diminished by increasing the shear rate. Some estimates of the average interparticle coefficient of friction are given- showing roughness increases friction. The friction coefficient is shown to increase with the volume fraction. Friction coefficient shows a power-law dependence on shear rate and decreases with the shear rate. The rate of decrease with shear rate is smaller for higher volume fraction of 40%.

Impact on Sea-Surface Electromagnetic Scattering and Emission Modeling of Recent Progress on the Parameterization of Ocean Surface Roughness, Drag Coefficient, and Whitecap Coverage in High Wind Conditions

Ocean surface wind stress is the force generating ocean surface roughness and whitecaps. The surface wind stress is related to the surface wind speed by the drag coefficient. Consequently, the magnitude of roughness and whitecaps calculated from wind speed input depends on the applied drag coefficient formula, which remains uncertain especially for high wind conditions. Because roughness and whitecaps are two major components of the ocean surface response in microwave remote sensing, a clear understanding of the drag coefficient, ocean surface roughness, and whitecap coverage is critical to interpreting the microwave signals emitted or scattered from the ocean surface. In reverse, the microwave signals represent precious data sources of these ocean surface properties [surface wind stress (or equivalently the drag coefficient), surface roughness, and whitecaps] that are difficult to measure with traditional oceanographic instruments, especially in severe weather conditions. This article describes the improvement of ocean surface properties achieved by incorporating microwave remote sensing measurements. In essence, the global data of microwave monostatic and bistatic radar cross sections contribute to the revision of ocean surface roughness spectrum model, and microwave radiometer measurements in tropical cyclones provide clarification regarding the dependence on wind speed of the drag coefficient and whitecap coverage. In return, the calculated excess emissivities and scattering radar cross sections are improved from implementing the updated results of drag coefficient, whitecap coverage, and surface roughness in microwave emission and scattering models.

Relationship Between Spatial Variations in Static Skin Deformation and Perceived Roughness of Macroscopic Surfaces.

The perceived roughness of macroscopic surface features is related to finger skin deformation. For example, skin indentation into surface grooves and the spatial variation in slowly adapting type 1 (SAI) mechanoreceptor activities are linked to the magnitude of subjective roughness. However, the perception of macroscopic roughness has not been directly linked to the spatial variations in skin deformation; therefore, this article investigated the relationship between the subjective roughness magnitude and the spatial spectrum of skin deformation through contact with roughened macroscopic surfaces. Experiments were performed to measure deformation of a finger pad when it statically touched different shaped grating scales. Then, the spatial spectra of skin deformation were computed by applying the Gabor filter with varying spatial selectivity. Some spectral components, particularly those for the spatial period ranging from 2.45-4.00mm, exhibited a good correlation with the perceived roughness magnitude. When the optimal spatial periods were determined for individual subjects, the spectral components and perceived roughness exhibited a strong linear relationship with an average correlation coefficient of 0.94. Therefore, the amount of spatial variation in finger skin deformation can be linked to the subjective roughness intensities of macroscopic surface features.

Pore-Scale Modeling of Fluid-Fluid Interfacial Area in Variably Saturated Porous Media Containing Microscale Surface Roughness.

A pore-scale model is developed to simulate fluid-fluid interfacial area in variably saturated porous media, with a specific focus on incorporating the effects of solid-surface roughness. The model is designed to quantify total (film and meniscus) fluid-fluid interfacial area (Anw ) over the full range of wetting-phase fluid saturation (Sw ) based on the inherent properties of the porous medium. The model employs a triangular pore space bundle of cylindrical capillaries (BCC) framework, modified with three surface roughness-related parameters. The first parameter (surface roughness factor) represents the overall magnitude of surface roughness, whereas the other two parameters (interface growth factor and critical adsorptive film thickness) reflect the micro-scale structure of surface roughness. A series of sensitivity analyses was conducted for the controlling variables, and the efficacy of the model was tested using air-water interfacial area data measured for three natural porous media. The model produced good simulations of the measured Anw data over the full range of saturation. The results demonstrate that total interfacial areas for natural media are typically much larger than those for ideal media comprising smooth surfaces due to the substantial contribution of surface roughness to wetting-film interfacial area. The degree to which fluid-fluid interfacial area is influenced by roughness is a function of fluid-retention characteristics and the nature of the rough surfaces. The full impact of roughness may be masked to some degree due to the formation of thick wetting films, which is explicitly quantified by the model. Application of the model provides insight into the importance of the interplay between pore-scale distribution and configuration of wetting fluid and the surface properties of solids.

The influence of fuel surface roughness on ignition in the mining industry – an exploratory analysis

The environment in mining industries is distinguished by heavy tear and rough fuel surfaces. The surface roughness magnitude of the gauges, dents etc. could be substantial, where the roughness depth would range from less than a millimeter up to several millimeters. Surface structures on vehicle tyres could include treads that are several centimeters in depth. Performing fire experiments and testing the ignition characteristics of the fuel surface, the influence of surface roughness and surface structures should be investigated and accounted for. Ignition would occur first at any part exposed by heat transfer from several directions and we are facing a two/three-dimensional ignition scenario. In this paper the gauge depth, angle and distance were varied to depict roughness. In five out of thirteen experimental cases the average ignition time showed significant difference when compared to the flat surface case, but no clear pattern was detected. No clear patterns were found when studying the two-dimensional analysis results at the time of ignition. In both experiments and the two-dimensional analysis, most of the temperatures were within the one standard deviation variation and did not show any significant difference compared with the flat case, except when comparing the gauge bottom temperatures and upper surface temperatures of the two-dimensional analysis where significant difference was found in all cases.