Presence Of Roughness Research Articles

Passive Control of the Flow Around a Rectangular Cylinder with a Custom Rough Surface

Motivated by existing techniques for implementing roughness on cylinders to control flow disturbances, we performed delayed detached eddy simulations (DDES) at Re = 6×106 that generated unsteady turbulent flow around a rectangular cylinder with a controlled wrinkled surface and a 1:4 aspect ratio. A systematic study of the roughness effect was carried out by implementing different configurations of equally spaced grooves and bumps on the top-surface of the cylinder. Our results suggest that groove geometries reduce energy dissipation at higher rates than the smooth reference case, whereas bumped cylinders produce relative pressures characterized by a sawtooth pattern along the middle-upper part of the cylinder. Moreover, cylinders with triangular bumps increase mean drag and lift forces by up to 8% and 0.08 units, respectively, while circular bumps increase vorticity and pressure disturbances on the wrinkled surface. All of these effects impact energy dissipation, vorticity, pressure coefficients, and flow velocity along the wrinkled surface. Both the surface-manufactured cylinders and the proposed visualization techniques could be replicated in a variety of engineering developments involving flow characterization in the presence of roughness.

Multiple current reversals in driven inertial coupled Brownian particles under rough symmetric periodic potential

Multiple current reversals, where the direction of the net current changes multiple times with the external load, is an anomalous transport property of a driven inertial Brownian particle under periodic potential. Here, we investigated inertial coupled Brownian particles under rough symmetric periodic potential driven by external periodic force to uncover that small microscopic spatial heterogeneity leads to multiple current reversals under weak inter particle coupling. We showed that the current reversals do not exist without the roughness in the potential and coupling of the particles. Although the multiple current reversals persists in a wide range of noise strengths, however, it is sensitive to dissipation constant and parameters of the external driving force. The collective dynamics of the coupled particles becomes asynchronous in presence of roughness and may be responsible for the anomalous behavior. Our calculations underscore a nontrivial role of microscopic spatial heterogeneity of the periodic potential in the transport properties of coupled Brownian particles.

A CFD Analysis of Oscillating Airfoil with Leading Edge Roughness: Comparing Correlations for Equivalent Sand Grain Roughness

Numerical simulations express surface roughness as equivalent sand grain roughness values, so the correlation is required to convert realistic roughness into equivalent sand grain roughness values. The correlations were designed to match the wall velocity distributions for static cases with roughness, and they accurately predicted roughness effects when applied to URANS simulations. Several studies have examined the roughness effect on dynamic pitching airfoils. Still, they have only considered the presence of roughness, neglecting the process of converting the actual roughness to equivalent sand-grain roughness. Thus, in the present study, we apply a static case-based equivalent sand-grain roughness correlation to dynamic pitching analysis to validate the suitability of each correlation and verify the significance of correlation parameters. It was observed from a comparison study between numerical aerodynamic coefficients and experimental data from Ohio State University that physical parameters such as skewness and roughness height were important parameters to predict the dynamic stall behaviour more accurately. It was also observed that dynamic stall prediction accuracy is affected by the frequency and type of airfoil, and through this, it was confirmed that there are additional factors to consider when using an equivalent sand grain roughness correlation on pitching airfoils.

Why soft contacts are stickier when breaking than when making them.

Soft solids are sticky. They attract each other and spontaneously form a large area of contact. Their force of attraction is higher when separating than when forming contact, a phenomenon known as adhesion hysteresis. The common explanation for this hysteresis is viscoelastic energy dissipation or contact aging. Here, we use experiments and simulations to show that it emerges even for perfectly elastic solids. Pinning by surface roughness triggers the stick-slip motion of the contact line, dissipating energy. We derive a simple and general parameter-free equation that quantitatively describes contact formation in the presence of roughness. Our results highlight the crucial role of surface roughness and present a fundamental shift in our understanding of soft adhesion.

Surface Roughness in RANS Applied to Aircraft Ice Accretion Simulation: A Review

Experimental and numerical fluid dynamics studies highlight a change of flow structure in the presence of surface roughness. The changes involve both wall heat transfer and skin friction, and are mainly restricted to the inner region of the boundary layer. Aircraft in-flight icing is a typical application where rough surfaces play an important role in the airflow structure and the subsequent ice growth. The objective of this work is to investigate how surface roughness is tackled in RANS with wall resolved boundary layers for aeronautics applications, with a focus on ice-induced roughness. The literature review shows that semi-empirical correlations were calibrated on experimental data to model flow changes in the presence of roughness. The correlations for RANS do not explicitly resolve the individual roughness. They principally involve turbulence model modifications to account for changes in the velocity and temperature profiles in the near-wall region. The equivalent sand grain roughness (ESGR) approach emerges as a popular metric to characterize roughness and is employed as a length scale for the RANS model. For in-flight icing, correlations were developed, accounting for both surface geometry and atmospheric conditions. Despite these research efforts, uncertainties are present in some specific conditions, where space and time roughness variations make the simulations difficult to calibrate. Research that addresses this gap could help improve ice accretion predictions.

Role of Surface Roughness in Surface Energy Calculation of Aggregate Minerals

Surface energy is a key material property and can work as a crucial parameter in various mechanical models to predict the moisture sensitivity and fatigue damage of asphalt mixtures. The calculated surface energy values of the aggregate minerals strongly depend on their surface roughness. Therefore, it is very relevant for accurate calculation of surface energy to study the relationship between roughness and surface energy. This study aims to investigate the relationship between surface roughness and surface energy of aggregate minerals. Two minerals—quartz and calcite—were used for this study. The surfaces of the mineral specimens were treated to achieve four levels of roughness. Their surface roughness was described by three roughness parameters. Based on the sessile drop method, an optical tensiometer with a 3D topography module was employed to measure the contact angle and the surface energy of the minerals with different roughness. The influences of surface roughness on the contact angle and the surface energy were then analyzed. The results showed that the contact angle for both quartz and calcite decreases with the increasing surface roughness when it is less than 90° and increases when it is greater than 90°. The Wenzel equation can remove the effect of surface roughness on the contact angles of the minerals. The surface energy of quartz and calcite in the presence of roughness at the microscale would be underestimated when using the measured (apparent) contact angle. The corrected surface energy based on the Wenzel equation must be applied to represent the real surface energy of the minerals.

Effects of freestream turbulence on the secondary instability of the roughness-induced crossflow vortex in swept flat plate boundary layers

In a three-dimensional boundary layer with spanwise constant flow and chordwise acceleration, which is unique to the vicinity of the leading edge of a swept wing, an inviscid instability induces the crossflow vortex (CFV), around which a secondary instability further occurs to yield a turbulent transition. It is well known that surface roughness induces stationary CFVs and that CFVs are receptive to freestream turbulence (FST), but the interference of both effects remains unclear. To determine the transition mechanisms in mixed roughness and FST environments, we performed direct numerical simulations of a Falkner–Skan–Cooke boundary layer under various conditions considering the presence of cylindrical roughness and the peak FST wavelength. Without roughness, the FST with a long wavelength comparable to the most unstable mode promotes CFV induction, resulting in an earlier transition. Conversely, the short-wavelength FST interacts with a wake vortex induced by the presence of roughness, yielding a hairpin vortex as a secondary instability. We discuss the main production terms of the disturbance energy associated with each of the type-1 and -2 secondary instabilities, which are accompanied by finger and hairpin vortices, respectively. The rapid turbulent transition via the type-1 secondary instability is due to the spanwise velocity gradient of the developed CFV, whereas that via the type-2 is due to a wall-normal gradient and is similar to the fully developed wall turbulence. The wavelength of FST played a key role in inducing a high-frequency secondary instability on the CFV or the CFV itself, and the receptivity to FST differed between the CFV and wake vortex.

Secondary motions and wall-attached structures in a turbulent flow over a random rough surface

Large-eddy simulations (LESs) are performed to explore the effects of roughness on the secondary motions (SMs) and wall-attached structures in a turbulent open-channel flow over a random rough surface at a friction Reynolds number of Reτ≈1000. Turbulent flow over two groups of rough walls – a homogeneous random arrangement and a clustered arrangement – is considered, and the results are compared with the turbulence over a smooth wall. The results show that the two roughness arrangements exhibit minor differences in the variation of mean streamwise velocity. The rough surfaces of a clustered arrangement can generate large-scale SMs, resulting in spanwise-alternating high-momentum pathways (HMPs) and low-momentum pathways (LMPs) in the time-averaged velocity. Because of SMs, the streamwise turbulence intensity is enhanced in the outer region and a larger-scale spectral peak occurs in the turbulence energy spectra. On the other hand, the outer-layer similarity is still satisfied for the homogeneous random arrangement. The wall-attached structures of streamwise velocity fluctuations in the presence of roughness are extracted through a three-dimensional clustering identification approach. The wall-attached structures retain their geometric self-similarity for both rough surfaces, whereas the length and width of these structures decreases and increases, respectively. The population density scales inversely with the height, reflecting the hierarchical nature of the structures. In addition, when the streamwise velocity fluctuations within the wall-attached structures are conditionally averaged, the profile exhibits logarithmic behavior in the logarithmic region for the homogeneous random arrangement; in the case of the clustered arrangement, the reconstructed profile is affected by the SMs. A new identification approach is applied to decompose the secondary flow structures into wall-detached structures, and the logarithmic behavior of the streamwise turbulence intensity is reconstructed on the basis of the new wall-attached structures. The present results provide evidence of the presence of the wall-attached structures in instantaneous flow fields of rough-wall turbulence, for both homogeneous and heterogeneous roughness arrangements.

Influence of Gutta-Percha Surface on Enterococcus faecalis Initial Adhesion In Vitro: An Atomic Force Microscopy Study.

The aim of this study was to evaluate the influence of surface topography of gutta-percha (GP) cones and plasticized disks of GP on the initial adhesion of Enterococcus faecalis (E. faecalis). The GP cones (Tanari and Dentsply brands) were cut 3 mm from the apical portion and fixed on a glass slide. To make the disks, the cones were thermoplasticized in standardized molds. The specimens were divided into groups according to the shape of the GP and the presence or absence of the bacteria. For contamination, the strain of E. faecalis (ATCC 29212) was used. The surface topography was analyzed using an atomic force microscope (AFM). The surface, roughness, and waviness parameters were evaluated by the Kruskal-Wallis and Dunn test. The comparison between disks and cones showed significant differences, where the cones were rougher, with a higher value attributed to the Dentsply cone (DC group). The same was observed for the waviness. After contamination, there was greater bacterial accumulation in cones, especially in their valleys, but both the surface and the topography became more homogeneous and smoother, with no differences between disks and cones of both brands. The topographic surface of the GP, at the micro and nanoscale, influences the initial adhesion of E. faecalis, with a greater tendency for contamination in regions associated with the presence of roughness and waviness. In this context, plasticization of GP is indicated, as it reduces surface irregularities compared to cones, contributing to less retention of bacteria.

Simulation of turbulent flow over roughness strips

Heterogeneous roughness in the form of streamwise aligned strips is known to generate large scale secondary motions under turbulent flow conditions that can induce the intriguing feature of larger flow rates above rough than smooth surface parts. The hydrodynamical definition of a surface roughness includes a large scale separation between the roughness height and the boundary layer thickness which is directly related to the fact that the drag of a laminar flow is not altered by the presence of roughness. Existing simplified approaches for direct numerical simulation of roughness strips do not fulfil this requirement of an unmodified laminar base flow compared with a smooth wall reference. It is shown that disturbances induced in a modified laminar base flow can trigger large-scale motions with resemblance to turbulent secondary flow. We propose a simple roughness model that allows us to capture the particular features of turbulent secondary flow without impacting the laminar base flow. The roughness model is based on the prescription of a spanwise slip length, a quantity that can directly be translated into the Hama roughness function for a homogeneous rough surface. The heterogeneous application of the slip-length boundary condition results in very good agreement with existing experimental data in terms of the secondary flow topology. In addition, the proposed modelling approach allows us to quantitatively evaluate the drag increasing contribution of the secondary flow. Both the secondary flow itself and the related drag increase reveal a very small dependence on the gradient of the transition between rough and smooth surface parts only. Interestingly, the observed drag increase due to secondary flows above the modelled roughness is significantly smaller than the one previously reported for roughness resolving simulations. We hypothesise that this difference arises from the fact that roughness resolving simulations cannot truly fulfil the requirement of large scale separation.

A Closer Look at the Contact Conditions of a Block-on-Flat Wear Experiment

Specific wear rates of tribosystems always rely on the data obtained from wear experiments. Nonetheless, the events taking place during an experiment may often lead to wide variations and low repeatability of the results. In this work, the authors attempt to take a closer look into the dynamic contact conditions of a dry linearly reciprocating block-on-flat wear experiment. The finite element method and Archard’s wear model are used through COMSOL Multiphysics® 5.2a and LiveLink™ for MATLAB® software to model the wear and study the influence of different conditions of the block surface and alignment of the sample. Changes of the geometry of the block and the contact pressure are quantified for several back and forth motions, using an extrapolation scheme in the wear modelling methodology. The tracking of such changes allow a dynamic overview of how the block contact area and the contact pressure distribution change throughout time. The results show how the assumption of a constant contact area and use of a nominal contact pressure in calculating the wear rate in such experiments can be inappropriate, especially in the presence of roughness and misalignments of the block.

A Cross-Sectional Study of Acoustic and Perceptual Changes in Voice During Pregnancy

Introduction: Voice is one of the many systems which may show deviancies during pregnancy. The present study aimed to profile the acoustic and perceptual characteristics of voice during pregnancy. Methods: Pregnant women in the age range of 18-30 years were divided into seven groups starting from the third month of pregnancy to the ninth month of pregnancy, with 30 participants in each group. Praat software was used to collect the phonation and narration sample from each participant at their most comfortable pitch and loudness. The acoustic and perceptual analyses were performed on recorded voice samples. Results: Results revealed that fundamental frequency (F0) is affected by the 6th month of pregnancy until the 9th month of pregnancy. However, jitter and shimmer abnormalities are evident from the 3rd month of pregnancy. The results of the perceptual analysis indicated the presence of roughness and breathiness from the third month of pregnancy until the 9th month of pregnancy. Discussion: The results indicated that fundamental frequency (F0) was affected by the 6th month of pregnancy and continued until the 9th month of pregnancy. The jitter and shimmer abnormalities were evident from the 3rd month of pregnancy. These findings were further supported by perceptual deviations on the Grade Roughness Breathiness Asthenia Strain (GRBAS) scale. Conclusions: These findings are of value for a pregnant woman who is sensitive to the vocal deviations and also for a professional voice user as they are more prone to voice changes or disorders due to their extensive voice usage.

A new finite element paradigm to solve contact problems with roughness

This article’s main scope is the presentation of a computational method for the simulation of contact problems within the finite element method involving complex and rough surfaces. The approach relies on the MPJR (eMbedded Profile for Joint Roughness) interface finite element proposed in [Paggi, M., Reinoso, J., 2020. Mech. Adv. Mater. Struct. 27:1731–1747], which is nominally flat but can embed at the nodal level any arbitrary height to reconstruct the displacement field due to contact in the presence of roughness. Here, the formulation is generalized to handle 3D surface height fields and any arbitrary nonlinear interface constitutive relation, including friction and adhesion. The methodology is herein validated with BEM solutions for linear elastic contact problems. Then, a selection of nonlinear contact problems prohibitive to be simulated by BEM and by standard contact algorithms in FEM are detailed, to highlight the promising aspects of the proposed method for tribology.

Medidas perceptivo-auditivas e acústicas de mulheres com e sem nódulos vocais

ABSTRACT Purpose To compare the acoustic and auditory-perceptual measures of the voice of women with and without vocal nodules. Methods Twelve women with vocal nodules (MNV group) and 12 without vocal nodules (MSNV group) participated in the study. They were submitted to the recording of their sustained /a/ vowel, in order to extract the mean of the fundamental frequency (f0), standard deviation of f0 (SD f0), jitter, shimmer, GNE, cepstral measure of CPPS, and spectral measures of differences of the first and second harmonics (H1-H2); and recording of the carrier phrases: “I say papa baixinho”, “I say pipa baixinho” and “I say pupa baixinho”, to extract the first (F1) and second formant (F2) of the vowel segments /a, i, u/. For auditory-perceptual assessment, the visual-analog scale (VAS) was used. Results The comparative analysis between the groups shows higher values for the MNV in the parameters general degree, roughness and breathiness, and for the shimmer acoustic measure. The F1 values for the vowels /a/ and /u/, and the F2 values for the vowel /a/ were higher in the same group. Conclusion According to the data observed in the investigated sample, women with nodules have more deviated voices, with the presence of roughness and breathiness, and changes in vocal tract adjustments, with a possible reduction in the amplitude of the articulators, when compared to women without vocal nodules.

Automatic Extraction of Rock Discontinuities from the Point Cloud Using Dynamic DBSCAN Algorithm

Detection and mapping of rock discontinuities are important during excavation. The terrestrial laser scanning (TSL) technology is widely used to acquire accurate quantitative. However, there is rarely study about the influence of discontinuities parameters on the detection. Through the 3D printing technology, we have built discontinuity models with different roughness and connectors with different angles. Therefore, we can control the variables in the scanning. Several open‐source packages were applied to derive the information from the point cloud acquired by TSL. The result shows that the recognition effect decreases with the angle between discontinuities. Moreover, the presence of roughness of discontinuity makes it prone to lead to lousy classification in the detection process. The proposed method has successfully extracted discontinuity dip, dip direction, and roughness automatically from the point cloud. The application on the two datasets showed great adaptability and accuracy. Consequently, the method could meet realistic engineering needs.

A method to determine wall shear stress from mean profiles in turbulent boundary layers

The direct measurement of wall shear stress in turbulent boundary layers (TBL) is challenging, therefore requiring it to be indirectly determined from mean profile measurements. Most popular methods assume the mean streamwise velocity to satisfy either a logarithmic law in the inner layer or a composite velocity profile with many tuned constants for the entire TBL, both of which require reliable data from the inner layer. The presence of roughness and pressure gradient brings additional complications where most existing methods either fail or require significant modification. A novel method is proposed to determine the wall shear stress in zero pressure gradient TBL from measured mean profiles, without requiring near-wall data. The method is based on the stress model of Kumar and Mahesh [Phys. Rev. Fluids 6, 024603 (2021)], who developed accurate models for mean stress and wall-normal velocity in zero pressure gradient TBL. The proposed method requires a single point measurement of mean streamwise velocity and mean shear stress in the outer layer, preferably between $20$ to $50 \%$ of the TBL, and an estimate of boundary layer thickness and shape factor. The method can handle wall roughness without modification and is shown to predict friction velocities to within $3 \%$ over a range of Reynolds number for both smooth and rough wall zero pressure gradient TBL. In order to include the pressure gradients effects, the work of Kumar and Mahesh [Phys. Rev. Fluids 6, 024603 (2021)] is revisited to derive a novel model for both mean stress and wall-normal velocity in pressure gradient TBL, which is then used to formulate a method to obtain the wall shear stress from the profile data. Overall, the proposed method is shown to be robust and accurate for a variety of pressure gradient TBL.

Acoustic and phase portrait analysis of leading-edge roughness element on laminar separation bubbles at low Reynolds number flow

Since laminar separation bubbles are neutrally shaped on the suction side of full-span wings in low Reynolds number flows, a roughness element can be used to improve the performance of micro aerial vehicles. The purpose of this article was to investigate the leading-edge roughness element’s effect and its location on upstream of the laminar separation bubble from phase portrait point of view. Therefore, passive control might have an acoustic side effect, especially when the bubble might burst and increase noise. Consequently, the effect of the leading-edge roughness element features on the bubble’s behavior is considered on the acoustic pressure field and the vortices behind the NASA-LS0417 cross-section. The consequences express that the distribution of roughness in the appropriate dimensions and location could contribute to increasing the performance of the airfoil and the interaction of vortices produced by roughness elements with shear layers on the suction side has increased the sound frequency in the relevant sound pressure level (SPL). The results have demonstrated that vortex shedding frequency was increased in the presence of roughness compared to the smooth airfoil. Also, more complexity of the phase portrait circuits was found, retrieved from velocity gradient limitation. Likewise, the highest SPL is related to the state where the separation bubble phenomenon is on the surface versus placing roughness elements on the leading edge leads to a negative amount of SPL.

Effect of Shearing on Non-Darcian Fluid Flow Characteristics through Rough-Walled Fracture

The heterogeneous fracture geometry induced by the presence of roughness and shearing complicates the fracture flow. This paper presents a numerical investigation of the non-Darcian flow characteristics of rough-walled fractures during shear processes. A series of fracture flow simulations were performed on four types of fractures with different joint roughness coefficients (JRCs), and the different shear displacements were imitated by degrees of mismatch on two fracture surfaces. The results show that the disorder of fracture geometries and the increase in flow rate are the main causes for the emergence of an eddy flow region, which can significantly reduce the fracture conductivity and change the fracture flow from linear to nonlinear. The Forchheimer equation provides a good model for the nonlinear relationship between the hydraulic gradient and the flow rate in the fracture flow. When the shear displacement or JRC increased, the linear permeability coefficient kv decreased, while the nonlinear coefficient β increased. A three-parameter equation of β was used to examine the inertial effect induced by the fracture roughness JRC and the variation coefficient of aperture distribution σs/em. The critical Reynolds number was a combined effect of aperture, viscous permeability, and inertial resistance, assuming the flow becomes non-Darcian when the inertial part is greater than 10%.

A Cellular Potts energy-based approach to analyse the influence of the surface topography on single cell motility

The surface shape is an important aspect to take into account to ensure the success of an implant. At the cellular scale level, the cell behaviour, especially its migration, is affected by the specificities of the surface of the substrate, such as the stiffness of the surface and its roughness topography. The latter has been shown to have a great impact on various cell mechanisms, such as the cell adhesion, migration, or proliferation. In fact, the mere presence of micro roughness leads to an improvement of those mechanisms, with a better integration of the implants. However, the phenomena behind those improvements are still not clear.In this paper, we propose a three-dimensional (3D) model of a single cell migration using a Cellular Potts (CP) model to study the influence of the surface topography on cell motility. To do so, various configurations were tested, such as: (i) a substrate with a random roughness, (ii) a substrate with a rectangular groove pattern (parallel and perpendicular to the direction of motion), (ii) a substrate with a sinusoidal groove pattern. To evaluate the influence of the surface topography on cell motility, for each configuration, the cell speed and shape as well as the contact surface between the cell and the substrate have been quantified.Our numerical results demonstrate that, in agreement with the experimental observations of the literature, the substrate topography has an influence on the cell efficiency (i.e. cell speed), orientation and shape. Besides, we also show that the increase of the contact surface alone in presence of roughness is not enough to explain the improvement of cell migration on the various rough surfaces. Finally, we highlight the importance of the roughness dimension on cell motility. This could be a critical aspect to consider for further analyses and applications, such as surface treatments for medical applications.

Swallowing, voice and quality of life of patients submitted to extended supratracheal laryngectomy.

ABSTRACTObjective To describe functional and quality of life results after extended supratracheal laryngectomy.Methods In the period from September 2009 to January 2018, 11 male subjects were submitted to extended supratracheal laryngectomy. Swallowing abilities were assessed through videofluoroscopy and the clinical scale Functional Communication Measures of Swallowing. The voices were classified by means of the perceptual-auditory analysis Consensus Auditory-Perceptual Evaluation of Voice. All subjects completed a self-assessment questionnaire for voice and swallowing.Results Aspiration was found in four patients and all presented stasis in different structures. All subjects in this study were exclusively orally fed and hydrated. In the evaluation of quality of life in swallowing, patients had mean >80 in all areas (83.47 mean of scores). The general degree and the presence of roughness were the highest means present in Consensus Auditory-Perceptual Evaluation of Voice (37.81 and 49.36, respectively). The mean of 33.36 (±22.56) had little impact on quality of life under the perspective of vocal aspects.Conclusion After supratracheal laryngectomy, swallowing was sufficiently restored and the quality of life was satisfactory. The voice presents severely impaired quality and preserved oral communication, with low impact on the activities of daily living. All individuals who maintained two cricoarytenoid units presented better functional results in swallowing and voice.