Wall Roughness Research Articles

Evaluation of spatial resolution effects in rough wall-bounded turbulence

This study investigates the impact of insufficient spanwise spatial resolution on the measurement accuracy of streamwise velocity fluctuations over rough walls. We use a direct numerical simulation (DNS) database of turbulent open-channel flow over three-dimensional sinusoidal roughness with varied wavelengths and roughness heights. Employing a triple decomposition, we investigate both the attenuation of the turbulent fluctuations (about the local mean), u′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$u^\\prime$$\\end{document} and the dispersive stresses (roughness-induced fluctuations of the time-averaged mean about the global mean), U~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ilde{U}}$$\\end{document}. A boxcar filter on DNS data is applied to investigate the effects of spanwise spatial filtering on these quantities. Our analysis reveals the significance of two key length-scale ratios for velocity measurements over rough walls: the wire length relative to the spatially and temporally plane-averaged Kolmogorov scale at the roughness crest (l/⟨η⟩k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l/\\langle \\eta \\rangle _k$$\\end{document}), and the wire length relative to the roughness spanwise wavelength (l/Λy\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l/\\Lambda _y$$\\end{document}). We observe that maintaining l/⟨η⟩k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l/\\langle \\eta \\rangle _k$$\\end{document} constant while increasing l/Λy\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l/\\Lambda _y$$\\end{document} attenuates the variance of U~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ilde{U}}$$\\end{document} and u′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$u^\\prime$$\\end{document} within the roughness sublayer. When fixing l/Λy\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l/\\Lambda _y$$\\end{document}, an increase in l/⟨η⟩k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l/\\langle \\eta \\rangle _k$$\\end{document} influences the turbulent fluctuations across all wall-normal locations. These findings highlight the necessity of considering both length scales when evaluating spanwise spatial resolution in turbulence measurements over rough walls.

The Effect of Fracture Wall Surface Roughness on Proppant Transport

Summary Proppant transport into created fractures is crucial in maximizing hydrocarbon recovery in unconventional reservoirs. Injected proppants keep the created fractures open, enhancing final fracture conductivity and propped and effective fracture length. The roughness and width of the created fracture are also important in proppant transport and distribution within induced fractures, affecting fracture conductivity. This study investigates the effect of fracture width on proppant transport into a complex slot system with 3D-printed rough wall surfaces. This study builds upon previous experimental work (Tatman et al. 2022), exploring different fracture roughness profiles and varying fracture widths. The effects of proppant densities, sizes, and concentrations on proppant transport within rough fracture surfaces were also investigated. A laboratory-scaled slot apparatus was used to examine the effects of various parameters. The slot consisted of a 4-ft-long primary fracture intersecting with a secondary fracture at a 90o angle. The wall surface roughness was printed using 3D printing technology and average fracture widths were set at 0.1 in. and 0.2 in. Fresh water (1 cp) with proppant concentrations of 1 ppg and 2 ppg and proppant sizes of 100-mesh sand [2.65 specific gravity (SG)], 40/70-mesh sand (2.65 SG), and 35/45-mesh ultralightweight (ULW) proppant (1.07 SG) were tested. The results show that fracture wall roughness impacts proppant transport behavior. The rough wall surface formed irregular proppant dune shapes and trapped some of the injected proppant at different locations within the slot, which is distinct from smooth wall surfaces. Decreasing the fracture width of a rough wall surface had a significant impact on proppant transport. The majority of the injected proppant was transported away from the injection point due to the increased slurry velocity. This led to improved proppant transport due to redirected flow direction and associated decreased proppant settling velocities, and a decrease in the proppant-dune-building rate near the inlet point, which carried more proppant deep into the secondary slot. Increasing the proppant concentration had a positive impact on proppant transport within both tested fracture widths by increasing the proppant-dune-buildup rate along the fracture slot and increasing the proppant-covered area inside fractures. The slurry injection rate had a great impact on low-density proppant transport. Decreasing the injection rate for lighter proppant (1.07 SG) helped to build a proppant dune near the injection point, increasing the proppant-covered area. Conversely, the higher injection rate carried the majority of the lighter proppant farther and out of the slots. Larger proppant sizes, (i.e., 40/70-mesh sand) resulted in a large proppant-covered area for both tested fracture widths, due to more particle-to-wall interaction, particle-to-particle interaction, and high density, which increased the settling velocity. However, injecting lighter and larger proppant sizes, such as 35/45-mesh ULW proppant, resulted in less settling and more particles suspended during injection due to lower density.

Exploring building materials: human skin as a sensory reference in the absence of visual cues

Material texture significantly influences how people perceive built environments, yet empirical evidence supporting its impact on spaciousness perception is limited. This study aimed to explore how people perceive building materials through sense in the absence of visual attention and how texture meanings affect indoor spaciousness perception. Conducted with 160 participants (90 males, 70 females, mean age ±SD: 22 ± 5 years), the study comprised three phases: baseline tactile assessment, blindfolded navigation in a lab and exposure to real-world environments. Findings revealed the skin’s ability to discern textural quality without visual cues, with slightly rough wall surfaces consistently perceived as more spacious. Moreover, the association between wall texture and perceived space varied, with subjective aspects influencing spaciousness in relatively spacious rooms, while objective factors played a larger role in less spacious settings. This study provides insights into sensory referral processes, warranting further investigation into the potential psychological impacts of textures.

The failure and re-initiation of quasi-detonations in stoichiometric acetylene-oxygen mixtures diluted by nitrogen

In this study, the failure and re-initiation of quasi-detonations are investigated systematically in stoichiometric acetylene-oxygen mixtures diluted by nitrogen, and the nitrogen dilution range of 10–45 % is considered. Photodiodes are introduced to obtain the average velocity by recording the detonation time-of-arrival. The smoked foil technique is performed to register the detonation cellular structures, and a high-speed schlieren system is used to observe the propagation processes. Three propagation modes are defined based on nine repeated experiments, i.e., Go, No-go and Critical regimes. For the “go” regime, the exiting detonation all successfully evolves into a spherical detonation in nine repetitions of the experiments. For the “no-go” case, the detonation all fails upon exit and becomes a deflagration. The case between the Go and No-go is called as the critical mode. Near the limits, the critical pressure of successful evolution into a spherical detonation is obtained, and the data indicates that the critical pressure is approximately independent of the wall roughness. But the critical pressure can increase obviously by introducing the nitrogen dilution. The cell sizes for quasi-detonations are measured, and the ratio of the critical tube diameter (dc) to the cell size (λ) is considered to quantify the critical criterion of detonation re-initiation. Note that the previous criterion of dc/λ ≥ 13 about normal detonation re-initiation cannot be applied to the quasi-detonation, and the re-initiation condition for quasi-detonations can be nearly quantified as dc/λ ≥ 8. The results are consistent with those obtained in our previous study (Xuxu Sun et al., Combustion and Flame, 112280). Corresponding to the normal detonation in a smooth tube, the critical value of dc/λ is always lower for quasi-detonations, which indicates a favorable effect on the detonation transmission is verified.

Passive earth pressure on vertical rigid walls with negative wall friction coupling statically admissible stress field and soft computing

It is well known that the roughness of a wall plays a crucial role in determining the passive earth pressure that is exerted on a rigid wall. While the effects of positive wall roughness have been extensively studied in the past few decades, the study of passive earth pressure with negative wall friction is rarely found in the literature. This study aims to provide a precise solution for negative friction walls under passive wall conditions. The research is initiated by adopting a radial stress field for the cohesionless backfill and employs the concept of stress self-similarity. The problem is then formulated in a way that a statically admissible stress field be developed throughout an analyzed domain using a two-step numerical framework. The framework involves the successful execution of numerical integration, which leads to the exploration of the statically admissible stress field in cohesionless backfills under negative wall friction. This, in turn, helps to shed light on the mechanism of load transfer in such situations so that reliable design charts and tables be provided for practical uses. The study continues with a soft computing model that leads to more robust and effective designs for earth-retaining structures under various negative wall frictions and sloping backfills.

EDM-Grinding composite machining and drilling of polycrystalline diamond tool

ABSTRACT Polycrystalline diamond (PCD) is widely used for micro tools due to its high hardness and wear resistance. However, micro PCD tools face challenges in machining with high accuracy and efficiency. Therefore, electrical discharge machining grinding (EDM-grinding) composite machining was proposed. The effects of pulse discharge parameters on surface quality and microhole drilling performance of PCD tool were investigated. The results show that the surface roughness of helix flute and flank face of the fabricated PCD tool were 0.125 µm and 0.158 µm, respectively, as well as the inner wall roughness achieved 0.331 µm after drilling of microhole. The average current displayed a greater effect on the machining quality of PCD tools, with tool breakage in excessive average current. The preferred pulse discharge parameters were determined as an open-circuit voltage of 95 V, an average current of 1400 mA, a pulse width of 400 ns, and a pulse interval of 2000 ns.

Effects of Liquid Film Instability on Spray Features of Liquid–Liquid Pintle Injectors

As one of the crucial structural parameters for the pintle injectors, the design of the skip distance ratio is still heavily empirical-dependent in engineering, and the intrinsic correlations between the skip distance ratio and spray characteristics of liquid–liquid pintle injectors are also unclear. Inspired by the observations that the instability of axial liquid film exerts significant influence on the downstream spray behaviors of a liquid–liquid pintle injector, the influence of the skip distance ratio on the instability of the axial liquid film and the subsequent spray characteristics of the pintle injector was experimentally investigated. The spray steadiness of the pintle injector was evaluated based on the instantaneous images using the proper orthogonal decomposition technique, and the effects of the skip distance ratio and the momentum ratio on the spray features were analyzed. Furthermore, a proactive strategy was proposed to adjust the liquid film instability by modifying the outer wall morphology of the pintle post, and the verification experiments were carried out based on three different wall morphologies. It was discovered that the rough wall enhances the axial liquid film instability and promotes the liquid sheet breakup and atomization of the pintle injector. These results provide new insights and valuable references for the optimization design of pintle injectors.

Numerical Calculation of Electric Field Enhancement in Neutron Traps with Rough Walls Coated with Superfluid Helium

Numerical Calculation of Electric Field Enhancement in Neutron Traps with Rough Walls Coated with Superfluid Helium

A Josephson–Anderson relation for drag in classical channel flows with streamwise periodicity: Effects of wall roughness

The detailed Josephson–Anderson relation equates the instantaneous work by pressure drop over any streamwise segment of a general channel and the wall-normal flux of spanwise vorticity spatially integrated over that section. This relation was first derived by Huggins for quantum superfluids, but it holds also for internal flows of classical fluids and for external flows around solid bodies, corresponding there to relations of Burgers, Lighthill, Kambe, Howe, and others. All of these prior results employ a background potential Euler flow with the same inflow/outflow as the physical flow, just as in Kelvin's minimum energy theorem, so that the reference potential incorporates information about flow geometry. We here generalize the detailed Josephson–Anderson relation to streamwise periodic channels appropriate for numerical simulation of classical fluid turbulence. We show that the original Neumann b.c. used by Huggins for the background potential creates an unphysical vortex sheet in a periodic channel, so that we substitute instead Dirichlet b.c. We show that the minimum energy theorem still holds and our new Josephson–Anderson relation again equates work by pressure drop instantaneously to integrated flux of spanwise vorticity. The result holds for both Newtonian and non-Newtonian fluids and for general curvilinear walls. We illustrate our new formula with numerical results in a periodic channel flow with a single smooth bump, which reveals how vortex separation from the roughness element creates drag at each time instant. Drag and dissipation are thus related to vorticity structure and dynamics locally in space and time, with important applications to drag-reduction and to explanation of anomalous dissipation at high Reynolds numbers.

Investigation on the heat transfer characteristics of rotor-stator cavity with different disk roughness

In this study, we numerically investigated the rotor-stator cavity for different disk surface roughness (rough rotor-RR, rough stator-RS, and rough rotor & stator-RRS) with the aim of determining the effect of surface roughness on the heat transfer characteristics of the disk cavity over a range of parameters. First, we experimentally verified that the numerical simulation has high accuracy. Next, the third-generation vortex identification method-Ω vortex identification method is used to preliminarily analyze the effect of different disk cavity roughness on the heat transfer in the rotor-stator cavity. The results indicate that the roughness of the rotor surface plays a dominant role in influencing the flow in the disk cavity. Third, we qualitatively and quantitatively analyzed the temperature field in the disk cavity. Interestingly, we discovered that the roughness of the stator decreases the temperature in the disk cavity to some extent. Thus, we judged the effect of stator surface roughness on the flow in the disk cavity based on the pressure variation in the rotor-stator cavity and gave an optimal roughness range for the stator. This will help to improve the cooling effect in the disk cavity. Finally, we investigated the effect of roughness on the rotor-stator heat transfer capacity. The effect of roughness on overall heat transfer in disc cavities is quantified based on average local heat transfer coefficient. It was concluded that the local heat transfer coefficient of the disk cavity is sensitive to the wall roughness, even for small wall roughness. We then added a roughness term to our previous work on average Nusselt number predictions for disk cavities. This provides a more accurate prediction of the heat transfer capacity of the disk cavity. On the basis of our results, it can provide some assistance to the relevant designers to quickly and accurately predict the heat transfer capacity of the rotor-stator cavity.

NST3 induces ectopic transdifferentiation, forming secondary walls with diverse patterns and composition in Arabidopsis thaliana.

The master transcription factor NAC SECONDARY WALL THICKENING PROMOTING FACTOR3 (NST3), also known as SND1, plays a pivotal role in regulating secondary cell wall (SCW) development in interfascicular and xylary fibers in Arabidopsis thaliana. Despite progress in understanding SCW assembly in xylem vessel-like cells, the mechanisms behind its assembly across different cell types remain unclear. Overexpressing NST3 or its homolog NST1 leads to reduced fertility, posing challenges for studying their impact on secondary wall formation. This study aimed at developing a tightly regulated dexamethasone (DEX)-inducible expression system for NST3 and NST1 to elucidate the structure and assembly of diverse SCWs. Using the DEX-inducible system, we characterized ectopically formed SCWs for their diverse patterns, mesoscale organization, cellulose microfibril orientation, and molecular composition using spinning disk confocal microscopy, field emission scanning electron microscopy (FESEM), vibrational sum-frequency generation (SFG) spectroscopy and, histochemical staining and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. Upon DEX treatment, NST3 and NST1 transgenic hypocotyls underwent time-dependent transdifferentiation, progressing from protoxylem-like to metaxylem-like cells. NST3-induced plants exhibited normal growth but had rough secondary wall surfaces with delaminating S2 and S3 layers. Mesoscale examination of induced SCWs in epidermal cells revealed that macrofibril thickness and orientation were comparable to xylem vessels, while wall thickness resembled that of interfascicular fibers. Additionally, induced epidermal cells formed SCWs with altered cellulose and lignin contents. These findings suggest NST3 and/or NST1 induce SCWs with shared characteristics of both xylem and fiber-like cells forming loosely arranged cell wall layers and cellulose organized at multiple angles relative to the cell growth axis and with varied cellulose and lignin abundance. This inducible system opens avenues to explore ectopic SCWs for bioenergy and bioproducts, offering valuable insights into SCW patterning across diverse cell types and developmental stages.

Effect of surface roughness on methane adsorption in shale organic nanopores from the perspective of molecular simulations

Understanding the shale gas adsorption behavior within organic nanopores is crucial for its development. The pore surfaces commonly exhibit random inherent roughness, which can significantly impact gas adsorption, while it’s still in debate about whether the roughness could enhance the gas adsorption or not. To clarify the underlying mechanisms of the effect of surface roughness, in this study, the Grand Canonical Monte Carlo and Molecular Dynamic simulations are used to investigate the methane adsorption in wrinkled graphene nanochannels with various roughness. The heterogeneity of the adsorption layer along the rough topology is described in detail. The adsorption is enhanced near the concave region and weakened near the convex region. Additionally, increased surface roughness shifts the gas molecules’ aggregation modes in the concave region from a gradual gradient to oscillatory “adsorption points”. We observe that wall roughness due to the wrinkle can enhance the adsorption amount overall, attributed to the increased surface area and the increased unit adsorption capacity due to potential energy overlap. However, the contributions of both factors differ under various pressure and roughness conditions. Then a new mathematical method to estimate the gas adsorption amounts is provided and aligns well with molecular simulation results for a wide range of pressure and roughness conditions. And a potential answer the current debate about the positive or negative impact of adsorption due to roughness is promoted. The key may lie in the dominant role of the co-existed roughness caused by the fragment basal or edge surface. Our work could shed light on the underlying effect of surface roughness on the gas adsorption in shale, and have significant implications for the reserve estimation of shale gas formations.

Modeling and verification of cortical bone drilling forces based on tissue structure heterogeneity

Bone drilling mechanism study is the basis for the optimization of cortical bone drilling process and drill geometry. In this paper, a drilling force model for modified drills with thinned chisel edge is established considering the heterogeneous structure of cortical bone. The bone mineral density is embedded into the established model, the model can predict the axial thrust force change along the drilling depth direction, and the model is verified through cortical bone drilling experiments. The thrust force and torque predicted by the model are in good agreement with the drilling experimental results of cortical bone drilling. Then, the drilling performance of the modified drill and the common drill is compared through cortical bone drilling experiments. Compared with common drill bits, the maximum reduction in average thrust force of the modified drill bit during stable drilling is 21.21 % (n = 2500 rpm, Vf=60 mm/min). The maximum reduction in average roughness of the hole wall is 21.87 % (n = 500 rpm, Vf=10 mm/min). The drill chisel edge thinning design reduces the negative impact of the negative normal rake angle on the cutting lip of common drill on drilling force and stability. Therefore, the drill bit chisel edge thinning design can effectively improve the drilling performance.

Effects of steepness on turbulent heat transfer over sinusoidal rough surfaces

We conducted a direct numerical simulation (DNS) study to investigate the impact of surface undulation steepness on rough wall turbulent heat transfer. The flow geometry was turbulent open-channel flow over three-dimensional sinusoidal rough surfaces. To examine the effects of steepness, we systematically varied the streamwise and spanwise wavelengths of the sinusoidal roughness while keeping the roughness height constant. The friction Reynolds number ranged from 180 to 600, and we considered a passive scalar with the fluid Prandtl number was 0.7, assuming air flow conditions. In the fully rough regime, the velocity roughness function is expressed as a function of the inner-scaled equivalent sand grain roughness ks+ independent of steepness, whereas the steeper surfaces with shorter wavelengths result in larger temperature roughness functions at the same ks+ value. Analysis of the physical mechanisms that increases the roughness function shows that the pressure drag primarily contributes to the increase in the velocity roughness function, while the temperature roughness function is mainly augmented by the roughness-induced wall heat transfer term, correlating with the steepness of the surface undulations. It is also suggested that the effective slope, which quantifies the steepness of rough surfaces, could improve the predictive accuracy of existing correlations for the temperature roughness function.

Precisely regulating thermal deformation behavior of wire electrical discharge machining thin-wall fin via pulsed laser-induced shockwave

The thermal deformation in the process of thin-walled metal fin processed by wire electrical discharge machine (WEDM) is almost unavoidable, which restricts the application of wire electrical discharge machining in the precision machining of thin-walled parts. In this study, a new process of thermal bending deformation regulation by laser-induced shockwave of wire electrical discharge machining thin-wall fin was proposed to obtain low/no deformation thin-wall parts. The thermal deformation of thin-wall In718 metal processed with different wire electrical discharge machining parameters was calibrated, and the law between the thermal bending and the process parameters was obtained. The thermal ablation and laser shock thermal deformation regulation model was established to accurately describe the stress distribution and deformation behavior of thin walls. For In718 thin-wall fin with different thicknesses, the thermal bending deformation could be regulated by laser-induced shockwave. After adjustment, the warpage of all thin walls was only −0.174μm at the lowest, and the thermal deformation could be reduced by 98.35 % at the highest. Laser shock improved the surface integrity of thin walls, increased the surface hardness to 433.9HV, increased by 46.84 %; laser shock also reduced the surface roughness of thin walls to a maximum of 2.67μm, a decrease of 33.58 %. In addition, laser shock could reduce the number of large-size grains, increase the number of twins, refine the impact surface grains to a certain extent, and the particle size was reduced to 7.64μm, which was reduced by 45.62 %.

Large eddy simulations of flow over additively manufactured surfaces: Impact of roughness and skewness on turbulent heat transfer

Additive manufacturing creates surfaces with random roughness, impacting heat transfer and pressure loss differently than traditional sand–grain roughness. Further research is needed to understand these effects. We conducted high-fidelity heat transfer simulations over three-dimensional additive manufactured surfaces with varying roughness heights and skewness. Based on an additive manufactured Inconel 939 sample from Siemens Energy, we created six surfaces with different normalized roughness heights, Ra/D=0.001,0.006,0.012,0.015,0.020, and 0.028, and a fixed skewness, sk=0.424. Each surface was also flipped to obtain negatively skewed counterparts (sk=−0.424). Simulations were conducted at a constant Reynolds number of 8000 and with temperature treated as a passive scalar (Prandtl number of 0.71). We analyzed temperature, velocity profiles, and heat fluxes to understand the impact of roughness height and skewness on heat and momentum transfer. The inner-scaled mean temperature profiles are of larger magnitude than the mean velocity profiles both inside and outside the roughness layer. This means, the temperature wall roughness function, ΔΘ+, differs from the momentum wall roughness function, ΔU+. Surfaces with positive and negative skewness yielded different estimates of equivalent sand–grain roughness for the same Ra/D values, suggesting a strong influence of slope and skewness on the relationship between roughness function and equivalent sand–grain roughness. Analysis of the heat and momentum transfer mechanisms indicated an increased effective Prandtl number within the rough surface in which the momentum diffusivity is larger than the corresponding thermal diffusivity due to the combined effects of turbulence and dispersion. Results consistently indicated improved heat transfer with increasing roughness height and positively skewed surfaces performing better beyond a certain roughness threshold than negatively skewed ones.

Study on hole wall morphology and defects in burst mode of femtosecond laser drilling

Through-hole drilling experiments are conducted on nickel-based superalloys GH3536 using femtosecond laser and burst modes of femtosecond laser. The morphology and roughness of the hole wall are studied. Indentation experiments show an increase in microhardness to 10 GPa in the recast layer at the edges of holes at GHz mode and MHz-200 μJ. EDS finds that the increase is attributed to oxidation and the formation of Cr2O3. EBSD and kernel average misorientation (KAM) reveal the laser induced heat-affected-zone (HAZ) at Single-Pulse-200 μJ and GHz-200 μJ. The removal characteristics under four burst modes are compared in single pulse/burst percussion experiment, indicating that the efficient removal of molten material in BiBurst mode accounts for its superior hole wall quality. The BiBurst mode offers significant advantages in terms of enhancing machining efficiency while minimizing material damage, which can extend to various metal materials.

Experimental investigation on the crystallization mechanism and mitigation strategies for gas injection and brine discharge pipes in salt caverns

Salt cavern gas storage (SCGS) not only holds promise for CO2 storage but also helps combat climate change by providing a reliable and adaptable solution for storing natural gas. Herein, this capability facilitates the integration of renewable energy sources and helps decrease greenhouse gas emissions from fossil fuel-based power generation. Firstly, a physical simulation platform for gas injection and brine discharge was developed to investigate the crystallization mechanism and devise preventive measures for constructing SCGS. Secondly, the study involved analyzing the mechanism of brine crystallization and determining experimental parameters using similarity theory. Furthermore, the effects of gas/water injection temperature, brine temperature in the salt cavern, flow rate, and pipe wall roughness on brine crystallization were examined. Finally, preventive measures were suggested to address issues related to crystallization and blockage. Results indicate that a 10℃ increase in gas/ water injection temperature leads to an average decrease of 26.56 % in the crystallization rate, while a corresponding increase of 186.16 % occurs for brine temperature. Heating the injected gas/water and opting for shallow strata for SCGS construction can alleviate crystallization. The crystallization rate initially increases and then decreases with flow rate, with a preferable flow rate exceeding 96 m3/h to prevent crystal adhesion and enhance scouring effects. Therefore, crystallization in the middle of the brine discharge pipe warrants special attention. Significantly reducing pipe wall roughness can effec- tively minimize crystallization, highlighting the importance of developing erosion-resistant coatings. Moreover, a proposed small U-shaped pipe backflushing method aims to solve blockages, along with preliminary application suggestions.

Unsteady flow of nanofluid over a sheet of variable thickness with nonlinear kinematics

The transport of heat in an unsteady flow of nanofluid has been discussed in this paper. The flow is maintained over a non-flat, variably porous, and moving sheet in the present simulation. Moreover, the sheet has both constant temperature and nanoparticle concentration at its surface. Unsteadiness in all field variables (i.e. the flow, temperature, and nanoparticles concentration) has been produced by the time-dependent quantities, specified at the surface of the sheet (i.e. kinematics of sheet). The well-known Buongiorno model of nanofluid has been undertaken in the present studies. Furthermore, the simulation includes the particular cases of uniform and linear (polynomial & algebraic functions) stretching/shrinking and injection/suction velocities. Besides that observations of the same nature have been recorded for the non-flat sheet. The boundary layer form of the governing PDEs has been utilized to evaluate the exact status of field variables in the flow domain. Appropriate conditions are imposed by considering the geometry of the flow problem. The problem at hand is simplified by introducing a new set of functions for the field variables because of boundary inputs. After this treatment, the system of boundary value ODEs, which contains several dimensionless numbers (parameters), has appeared, and the problem is solved numerically for various values of parameters, involved in it. More precisely, effects of unsteadiness, wall roughness, surface deformation parameters, Prandtl, Schmidt, thermophoretic, and Brownian motion numbers have been seen on profiles of four field variables. Besides that, the numerical results are also obtained for the skin friction coefficient, Nusselt, and Sherwood numbers. The present modelled problem and its solution are compared with classical models of that particular nature and with their solutions.

Spreading dynamics of a microgel particle-laden thermosensitive polymer drop along smooth and nanofiber surfaces

The research focuses on the influence of 300-μm microgel particles in an aqueous solution of a thermosensitive biopolymer on the spreading and deformation of 3.7-mm drops. The drops impact a smooth hydrophilic and a rough hydrophobic surface. A mass fraction of microgel particles varies in a range of 0–0.2. A universal physical model of the spreading of thermosensitive polymer drops laden with microgel particles along surfaces with significantly different roughness is proposed. It explains the strong inhomogeneity of the contact line stretching due to the deceleration of the continuous phase flow by microgel particles and the increased flow vorticity because of the addition of the surface roughness factor. The validity of the proposed physical model is proven by qualitative and quantitative assessments of the contact line deformation when spreading. An empirical expression for the maximum spreading factor is derived, taking into account the properties of liquids, wall roughness, and microgel particle concentration; it reliably predicts when Re≈110−3100, the surface roughness is 0.5–125 nm, Ca=4.5×10−7, and the number of microgel particles in drops is up to 100. The expression was successfully tested during the modeling of arbitrary surface roughness and the increased concentration of microgel particles relative to those considered in experiments during the formation of a biopolymer layer. When developing the method of additive manufacturing of a functional layer, a practical correlation was established between the volume content of microgel particles, acting as potential containers for living cells, in a drop and the area of the biopolymer layer.