Surface Shear Stress Research Articles

Experimental and numerical analysis of laminated carbon fibre-reinforced polymer gears with implicit model for coefficient-of-friction evaluation

Abstract Laminated composites have so far received little attention as a potential material for gear drive applications. In the presented study, the thermomechanical performance of a newly developed type of epoxy impregnated, autoclave-cured carbon fibre-reinforced polymer gear—running in pair with a steel pinion—was analysed, using a combination of experimental and numerical approaches. The employed methods enabled the identification of the composite’s mechanical, thermal, and tribological characteristics, as related to the studied gear pair application. A newly proposed, finite-element-analysis-based iterative procedure enabled an implicit evaluation of the analysed material pair’s coefficient of friction (COF), which is a key parameter in determining the gear pair’s thermomechanical characteristics. For the considered material pair, a value of 0.34 was identified for the coefficient in the quasi-steady region. As the coefficient is strongly correlated with frictional heat generation and significantly affects the surface shear stress, it can consequently have a meaningful influence on the composite’s wear rate. The developed COF identification procedure was validated using a reciprocating cylinder-on-flat tribological test method. The composite gear’s service life was additionally tested at various running loads, resulting in pitch contact pressures ranging between 400 and 540 MPa. Lifetime gear test results showed a markedly superior performance compared to the high-temperature thermoplastic polyether ether ketone, which is typically employed in the most demanding polymer gear applications. Several methods are additionally proposed that could further improve the developed composite gears’ performance.

3D printed nanofiltration composite membranes with reduced concentration polarisation

3D printed nanofiltration (NF) composite membranes with surface patterns minimising the impact of concentration polarisation (CP) are presented here for the first time. The membranes consist of a NF polydopamine‐coated polyvinylidene fluoride (PVDF/PDA) selective layer on a 3D printed asymmetric wavy (patterned) support. The result is a wavy composite membrane with pure water permeance of 14 ± 2 LMH bar − 1 and molecular weight cut-off of ∼550 Da, measured using a crossflow NF setup at a transmembrane pressure of 2 bar for Reynold number ( Re ) of 700, using a range of dyes (mass balance >97% for all tests). The CP behaviour of the composite membranes was assessed by filtration of Congo red (CR) dye solution (0.01 g L − 1 ) , showing that the wavy pattern significantly reduced the impact of CP compared to the flat membranes, with a nearly tripling of the mass transfer coefficient and a 57% decline of the CP factor. Computational fluid dynamics showed that these significant performance improvements were due to improved hydrodynamics, with the maximum surface shear stress induced by the wavy structure (1.35 Pa) an order of magnitude higher than that of the flat membranes (0.18 Pa) at Re = 700. These results demonstrate that 3D printing is a viable technology route to reducing concentration polarisation in membrane nanofiltration applications. • Fabrication via 3D printing of NF composite membranes with surface wavy patterns. • Wavy composite membranes had a PWP of 14 ± 2 LMH bar − 1 and a MWCO of ∼550 Da. • Concentration polarisation was assessed by filtration of a Congo red solution. • The wavy structure led to a 57% lower CP and triple mass transfer coefficient. • Shear stress over the wavy structure is an order of magnitude higher than the flat one.

Investigating Neutral and Stable Atmospheric Surface Layers Using Computational Fluid Dynamics

Computational fluid dynamics (CFD) is an effective technique for investigating atmospheric processes at a local scale. For example, in near-source atmospheric dispersion applications, the effects of meteorology, air-pollutant sources, and buildings can be included. A prerequisite is to establish realistic atmospheric conditions throughout the computational domain. This work investigates the modeling of the atmospheric surface layer under neutral and stable boundary-layer conditions, respectively. Steady-state numerical solutions of the Reynolds averaged Navier–Stokes equations were used, including the k-ε turbulence model. Atmospheric profiles derived from the Cooperative Atmosphere–Surface Exchange Study-99 (Kansas, USA) were used as reference data. The results indicate that the observed profiles of velocity and potential temperature can be reproduced with CFD, while turbulent kinetic energy showed less agreement with the observations. For the stable boundary layer, reasonable agreement of the numerical results with the observations was also obtained for surface layer depth, shear stress, and heat-flux profiles, respectively. The results are discussed in relation to the boundary conditions and sources, and the observation data.

Thermal Radiation and Viscous Dissipation Impacts of Water and Kerosene‐Based Carbon Nanotubes over a Heated Riga Sheet

This research communication explains the flow of water/kerosene‐based CNTs (carbon nanotubes) over a Riga sheet. The energy analysis is debated with the availability of radiation, viscous dissipation, and convective heating conditions. Two divisions of CNTs, like, SWCNTs (single‐wall carbon nanotubes) and MWCNTs (multiwall carbon nanotubes), are considered. The pertinent variables are applied to overhaul the governing mathematical models into ODE expressions. The overhaul expressions are analytically solved by HAM (homotopy analysis method) and numerically solved by MATLAB bvp4c scheme. The repercussions of relevant parameters on nanoliquid velocity, nanoliquid temperature, skin friction coefficient, and local Nusselt number are inspected via graphs, tables, and charts. Our computational results are compared with the previous researcher results and have the most acceptable agreement. Our outcomes are used to understand the flow attributes, behavior, and how to predict it for those working in the design of thermal equipment in thermal industry. It is noticed that the nanoliquid velocity decayed in counter to the unsteady parameter, and it enhances for larger values of Hartmann number. The nanoliquid temperature enriches when raising the Biot number and radiation parameter. The change in unsteady parameter decays the surface shear stress, while reverse results are found in the local Nusselt number.

Low maintenance gravity-driven membrane filtration using hollow fibers: Effect of reducing space for biofilm growth and control strategies on permeate flux

The implementation of centralized drinking water treatment systems necessitates lower operational costs and improved biopolymer removal during ultrafiltration (UF), which can be afforded by gravity-driven membrane (GDM) filtration. However, prior to implementing GDM filtration in centralized systems, biofilm growth in compacted membrane configurations, such as inside-out hollow fiber (HF), and its impact on permeate flux need to be investigated. To this end, we operated modules with distinct limits on available space for biofilm growth: (1) outside-in 1.5 mm 7-capillary HF (non-limited), (2) inside-out 1.5 mm 7-capillary HF (limited), and (3) inside-out 0.9 mm 7-capillary HF (very limited). Here, we observed that the lower the space available for biofilm growth, the lower the permeate flux. To improve GDM performance with inside-out HF, we applied daily shear stress to the biofilm surface with forward flush (FF) or combined relaxation and forward flush (R+FF). We showed that applying shear stress to the biofilm surface was insufficient for controlling flux loss due to low available space for biofilm growth. At the experimental endpoint, we backwashed with a stepwise transmembrane pressure (TMP) increase or a single TMP on all inside-out HF modules, which removed the biofilm from its base. Afterwards, higher fluxes were yielded. We also showed that all modules exhibited a gradual increase in biopolymer removal followed by stabilization between 70 and 90%. Additionally, control of biofilm growth with surface shear stress did not affect biopolymer removal. In summary, the implementation of inside-out HF with GDM filtration is challenged by low available space for biofilm growth, but may be remedied with a regular backwash to remove biofilm from its base. We showed that a wider range of GDM applications are available; making GDM potentially compatible with implementation in centralized systems, if space limitation is taken into consideration for operation optimization.

Laboratory-scale investigation of a periodically forced stratified basin with inclined endwalls

We present results of numerical simulations of a stratified reservoir with a three-layer stratification, subject to an oscillating surface shear stress. We investigate the effect of sloped endwalls on mixing and internal wave adjustment to forcing within the basin, for three different periods of forcing. The simulations are carried out at a laboratory scale, using large-eddy simulation. We solve the three-dimensional Navier–Stokes equations under the Boussinesq approximation using a second-order-accurate finite-volume solver. The model was validated by reproducing experimental results for the response of a reservoir to surface shear stress and resonant frequencies of internal waves. We find interesting combinations of wave modes and mixing under variation of the forcing frequencies and of the inclination of the endwalls. When the frequency of the forcing is close to the fundamental mode-one wave frequency, a resonant internal seiche occurs and the response is characterized by the first vertical mode. For forcing periods twice and three times the fundamental period, the dominant response is in terms of the second vertical mode. Adjustment to forcing via the second vertical mode is accompanied by the cancellation of the fundamental wave and energy transfer to higher-frequency waves. The study shows that the slope of the endwalls dramatically affects the location of mixing, which has a feedback on the wave field by promoting the generation of higher vertical modes.

Heat transfer performance and thermal energy storage in nano-enhanced phase change materials driven by thermocapillarity

We study the influence of metallic nanoparticles on heat transfer and thermal energy storage in a phase change material driven by thermocapillarity. Thermocapillary flows break the symmetry of the transport coefficients in the Prandtl number, weighting more strongly the viscosity. The metallic nanoparticles generate competitive effects on the heat transfer rate: (i) higher conductive heat transfer by raising the effective conductivity of the solid and liquid phases of the PCM, and simultaneously (ii) slower convective heat transfer by raising the viscosity of the melted phase and reducing the surface shear stress responsible for the Marangoni effect. We find that metallic nanoparticles with higher diameters support higher convective flows since they exhibit lower decay of the Marangoni number and have lower Prandtl numbers for high concentrations. High aspect ratio geometries with long free surfaces extend the regions governed by thermocapillary flows enhancing the heat transfer performance for most nanoparticle configurations with respect to the base PCM, also leading to reduced thermal energy required for the complete melting of the PCM. We also find that the melting front at the free surface advances following a power-law ∼tα whose exponent grows with the Prandtl number.

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

Probing thermocapillary convection and multisolute dilution in laser welding of dissimilar miscible metals

Coupled with convection flow, multisolute dilution was investigated by an improved numerical model during laser dissimilar welding of 304 stainless steel and nickel. Thermal behavior was firstly studied and solidification characteristics were also analyzed. Then, dimensional analysis of driving force was carried out, and the evolution of surface tension and surface shear stress were quantitatively analyzed for a better understanding of driving mechanism. Finally, species dilution was investigated based on multisolute model, and then compared with binary model for a clear illustration. Cooling rate was found much larger at SS side, but the morphology parameter changed little between different sides. Both the surface tension and surface shear stress were relatively larger at SS side, but this difference decreased with time. Surface shear stress reached 3390 Pa and 2000 Pa at SS side and Ni side, respectively, and results in a centrally outward Marangoni flow. Multisolute effect was considered, and the distribution of all main elements was obtained one time with high efficiency. Simulated dilution result from multisolute model showed great correspondence with EDS observation. The fundamental conclusions in this work provided a valuable insight into the heat and mass transfer process during welding and additive manufacturing.

Computational Analysis of Heat Transfer Intensification of Fractional Viscoelastic Hybrid Nanofluids

In the current article, we have performed computational analysis on convection heat transfer of a hybrid nanofluid in occurrences where porous media and the effect of magnetic force are involved. In order to assess the time-fractional derivatives, Caputo’s notion is utilized while the Darcy–Forchheimer model is applied due to the involvement of the porous medium. Moreover, the boundary conditions are assumed to be nonuniform through the equilibrium between the surface tension and shear stress over a semi-infinite permeable flat surface. Keeping in view the complexity of the fractional derivative model and nonuniform boundary conditions, the problem in question is a complicated one. Accordingly, the coupled momentum and energy equation is linearized and the finite difference scheme is then applied and implemented in MATLAB Code R2020b. Furthermore, we have also offered a comprehensive analysis regarding error and convergence of the proposed numerical method. The newly introduced numerical technique to determine the numerical solutions and some unique and interesting deductions are established. From the computational results, one can conclude that the fluid motion in both hybrid and single nanofluids slows down due to magnetic field, porosity, and inertia coefficient as the magnetic and electric fields are synchronized due to the formation of the Lorentz force and viscous interference. We believe that our proposed numerical technique regarding employment of the fractional model for heat transfer application to the hybrid nanofluid over a semi-infinite nonuniform permeable surface along with variable heat flux is not found in the literature so far. Furthermore, the obtained results will be a valuable addition to fractional calculus from an engineering point of view.

Effect of the tire – Pavement contact at the surface layer when the tire is tilted in bend

Tire-pavement interaction is a rolling contact problem that depends on tire and pavement factors, such as vehicle speed and weight, material and type of tire, tire pressure inflation, camber and texture of the surface layer. In this paper, the problem of tire-pavement contact is studied using a realistic description in normal section and bend. The study focuses on the shape of the contact patch and the stress distribution at the tire-pavement interface and the surface shear stresses rather than internal stresses in the structure of the pavement. The numerical approach introduced requires precise tire geometry (estimated by a photogrammetry method) and an equivalent Young's modulus (function of the inflation pressure resulting from the press load tests). Vertical contact stress at the tire-pavement interface predicted by a Semi-Analytical model were compared to experimental measurements with a press system under different loads and angles of inclination. Finally, we discuss the effect of the tire inclination on the calculated shear stresses (origins of damage in turns). The model shows that the increase of the angle of inclination in a turn has a direct influence on the distribution of the tire-pavement contact stresses and the shear stresses. These results will provide indications for the evaluation of the performance of the surface layer with respect to rutting and downward cracking.

CAD Based Analysis for Feasibility of Design of an Amphibious Vehicle for Recreation

An amphibious vehicle is the vehicle that allows occupants to travel on both land and water. Since an amphibious vehicle must inherently possess both land and water capabilities, design of the vehicle should not compromise the requirements for a good boat as well as a good land vehicle. Although, amphibious vehicles were used for different purposes, still there is no mention of application of amphibious vehicle in recreational purposes such as beach riding, surfing on water and travel within Science Parks. Further, with depletion of fossil fuel and for all the negative effect on marine life. Hence, an attempt is made to design an electric amphibious vehicle for recreational purpose and utilize for travel within Science & Technology Park. A conceptual design was worked out and it is matched with visual aspects of amphibian animal like duck. A CAD model was prepared with structural details. Structural strength was analyzed using ANSYS software. CFD analysis was conducted for calculating drag and surface shear stress and buoyancy was calculated. Thus it gives a practical approach to construction of an amphibious vehicle for recreational purpose. The results of the CAD analysis shows that the stress on the Frame was within acceptable limit and the buoyancy conditions are fulfilled. It also suggest for a maximum speed of 40kmph on water. As look and feel of the vehicle inspired from duck beak, it gives expression of amphibian characteristics along with sporty look. Thus, the conceptual vehicle is suitable for use on land and on water inside Science & Technology park.

The effect of frictional coefficients and sock material on plantar surface shear stress measurement

At present, there are no viable systems that can acquire in-shoe measurement of distributed shear forces. Foot-shoe interactions are such that skin shear is a notoriously difficult quantity to measure under the best of conditions. This is further complicated by the presence of forces normal to the skin surface that are large compared to the shear forces, which often results in crosstalk between pressure and shear signals. The present study used multibody dynamic simulations to investigate the combined effects of (i) coefficient of friction (COF) at skin-sock and sock-sensor interfaces, as well as (ii) sock stiffness on the accuracy of measured shear against the skin. These factors were systematically altered within a wide range (COF: 0.04, 0.34, 0.54, and 0.9; sock stiffness: 100, 250, 500, 1000, 1500 and 2000 N/m) to simulate a total of 96 scenarios. The correlation between the shear at the skin and at the sensor was used to compare each set of conditions. The results indicated that a high COF at the sock-sensor interface and a low sock stiffness would individually result in a significantly higher accuracy of shear measurements (p < 0.001). A low COF at the skin-sock interface was observed to reduce the occurred shear against the skin up to a factor of five, with very minimal effect on the accuracy of shear measurements (p = 0.98). These findings allow researchers to understand the potential effects of (i) sock stiffness, and (ii) coefficients of friction, on skin shear, and potentially correct for the effects of interface materials when trying to determine shear at the skin-sock interface.

Sutterby fluid flow past a stretching sheet embedded in a porous media with viscous dissipation

This article mainly concerns investigating the fluid flow, heat, and mass transfer of a Sutterby fluid (Biofluid) towards a stretching sheet saturated with a porous medium with considering viscous dissipation. The solution to the transformed similarity equations is derived using the Spectral Relaxation Method (SRM). The SRM is established with modest iterations. This scheme is initiated with the diminution of the order of the momentum equation and regrouping the derived governing equations. The precision and convergence of the results are also presented. Graphs, tabular forms of the individual parameters associated with the current perusal were exhibited, correspondingly. Besides, the local Sherwood number, Nusselt number, and surface shear stress were also computed. It is found that strengthening the porous media values improves the shear stress of the surface. Shear-thinning fluids have a higher velocity than that of shear thickening fluids and opposite behaviour was observed in temperature and concentration fields.

Unsteady MHD Mixed Convection Flow of Non-Newtonian Casson Hybrid Nanofluid in the Stagnation Zone of Sphere Spinning Impulsively

In the present analysis, an unsteady MHD mixed convection flow is scrutinized for a non-Newtonian Casson hybrid nanofluid in the stagnation zone of a rotating sphere, resulting from the impulsive motion of the angular velocity of the sphere and the velocity of the free stream. A set of linearized equations is derived from the governing ones, and these differential equations are solved numerically using the hybrid linearization–differential quadrature method. The surface shear stresses in the x- and y-directions and the surface heat transfer rate are improved due to the Casson βo, mixed convection α, rotation γ and magnetic field M parameters. In addition, as nanoparticles, the solid volume fraction (parameter ϕ) increases, and the surface shear stresses and the rate of heat transfer are raised. A comparison between earlier published data and the present numerical computations is presented for the limiting cases, which are noted to be in very good agreement.

Mathematical analysis of MHD stagnation point flow of Cu-blood nanofluid past an exponential stretchable surface

Two dimensional, steady, incompressible magnetohydrodynamic flow near a stagnation region toward an exponentially stretching plate is numerically investigated in present illustration. Base fluid– blood, along with copper (Cu) is taken to compose the nanofluid and different shapes of nanoparticles such as sphere, hexahedron, tetrahedron, column and lamina are taken into considerations. By using the suitable similarity transformations, the consequent equations are converted to a set of nonlinear ordinary differential equations. The spectral relaxation method is applied to compute the solution of the system. Several parameters like stretching parameter, nanoparticle volume fraction, magnetic parameter, Brinkman number and empirical shape factor are emerging in the governing equations, which affects the fluid flow veocity and temperature. These changes are given in the graphical form. Furthermore, impacts of specified parameters on surface shear stress and surface heat flux are also enlisted in form of tables. To ensure the validation of the results, the present results are compared with already existing data.

An Enhanced Treatment of Boundary Conditions for 2D RANS Streamwise Velocity Models in Open Channel Flow

A 2D streamwise velocity model based on the Reynolds Averaged Navier–Stokes (RANS) is a useful approach to predict the boundary shear stress and the streamwise velocity in a free surface stream where secondary flows are not relevant. Boundary conditions treatment is a key aspect implementing these models. A low computational cost and fully predictive numerical model with a novel treatment of boundary conditions is presented. The main features of the modified model are the employment of a modified law of the wall valid for any roughness condition, the estimation of the boundary shear stress is done only focusing on the near-contour region, the use of a full-predictive physical based model for the eddy viscosity distribution and the incorporation of the free surface shear stress due to water–air interface. The validation of the proposed changes was performed with a substantial number of experimental cases available in the literature using different cross-section shapes (circular, rectangular, trapezoidal and compound section) and roughness condition with quite good agreement. Preliminary results suggest that the influence of the free surface boundary layer has a significant impact on the results for both the streamwise velocity and boundary shear stress in windy conditions. The proposed approach allows its considerations in practical applications.

Role of solution reconstruction in hypersonic viscous computations using a sharp interface immersed boundary method.

This work discusses the development of a sharp interface immersed boundary (IB) method for viscous compressible flows and its assessment for accurate computations of wall shear and heat fluxes in hypersonic flows. The IB method is implemented in an unstructured Cartesian finite-volume (FV) framework and resolves the geometric interface sharply on the nonconformal mesh through direct imposition of boundary conditions employing a local reconstruction approach. The efficacy of the IB-FV solver is investigated for canonical high-speed viscous flows over a range of Mach numbers. The numerical results indicate that the surface pressure and shear stress distributions are computed with reasonable accuracy, whereas surface heat fluxes for aerodynamically blunt configurations are underpredicted. Employing a set of carefully designed experiments and simple diagnostic tools, we probe the possible causes for the underprediction in heat flux. We show that there exist two sources of error-one due to grid resolution and the other due to solution reconstruction, with the latter being more prominent and responsible for the observed underprediction in heat fluxes. Studies reveal that the heat flux estimates are sensitive to the choice of temperature reconstruction and linear interpolations could lead to poor estimates of heat flux. Our investigations conclusively point out the fact that existing polynomial-based reconstruction approaches for sharp interface IB techniques are not necessarily adequate for heat transfer predictions in high Reynolds number hypersonic flows.

Intra-articular injection of phospholipid-based lubricant reduces shear-responsive inflammatory genes in the superficial layer of cartilage post murine joint destabilisation

Purpose: The synovial joint exhibits extraordinary biotribological properties allowing the articular cartilage layers to slide past each other at very low friction even under local pressures of up to 18 MPa (∼180 atm). Articular cartilage is exquisitely mechanical sensitive. Compressive mechanical load contributes to articular cartilage homeostasis; however, overuse or destabilizing the joint increases surface shear stress, which promotes cartilage degradation. Our previous Results show that shear stress, induced by joint destabilization, regulates a number of inflammatory genes 6h post surgery, including Mmp3, Il1b, Arg1, Ccl2, and Il6.

Evolution of wall flow structure and measurement of shear stress issuing from supersonic jet with extended shelf

This paper reports an experimental study on the supersonic jet surface flow structure visualization and shear stress field measurement issuing from a rectangular nozzle with extended shelf. The evolution of the near-field surface flow structures with an increased Nozzle Pressure Ratio (NPR) is successfully captured by the surface oil flow, infrared detection technology, and the Shear-Sensitive Liquid Crystal Coating (SSLCC) technique. Results reveal that under smaller NPR, the wall flow structure is similar to that of a jet without the extended shelf i.e., clean jets, and this is caused by insufficient effect on the boundary layer. However, at higher amplitudes of NPR, there exists a significant effect of the boundary layer, as a near triangular separation forms on the trailing edge of the Mach stem due to the adverse pressure gradient, which is visualized for the very first time in this paper. Furthermore, the vector field of shear stress is measured quantitatively by SSLCC technique. Results shows that the magnitude of shear stress heightened with NPR increasing, and the directions of shear stress changes across the shock wave and expansion fans. In addition, surface streamlines measured by SSLCC is significantly consistent with the streamlines visualized using the oil flow technique.