Wall Surface Roughness Research Articles

Stokes flow in a rough curved channel

A two-dimensional viscous flow in a rough curved channel is investigated. The roughness are considered to be sinusoidal corrugations. The asymptotic solution is obtained using boundary perturbation technique for small amplitude of the corrugations. It is found that, for any radius of curvature, the flow rate is invariably decreased by the corrugations. The effect of corrugations on the flow rate increases with the corrugation wavenumber, as well as the phase difference between the corrugated curved walls. For sufficiently large corrugation wavenumbers, the phase difference between the corrugated walls becomes insignificant. The findings of this study indicate that a smooth curved channel with no corrugations, will give more flow rate than a corrugated curved channel, comparatively, for the same radius of curvature, as the flow resistance is relatively higher for the latter, due to the effects of the wall-surface roughness.

Research on ultrasonic-assisted drilling in micro-hole machining of the DD6 superalloy

The DD6 nickel-based superalloy exhibits remarkably high temperature properties; therefore, it is employed as a crucial structural material in the aviation industry. Nevertheless, this material is difficult to process. Ultrasonic-assisted drilling (UAD) combines the characteristics of vibration processing technology and conventional drilling technology, significantly improving the machinability of difficult-to-machine materials. Thus, UAD experiments were performed on micro-hole machining of DD6 superalloy in this study. The effects of amplitude, frequency, spindle speed, and feed rate on thrust force, machining quality, and drill bit wear were studied; thereafter, a comparison was drawn between these effects and those of conventional drilling (CD). The experimental results reveal that the thrust force decreases with an increase in spindle speed or a decrease in feed rate for both UAD and CD. UAD can significantly reduce the thrust force. With the same processing parameters, the greater the amplitude, the greater the reduction of the thrust force. The surface roughness of the hole wall produced by UAD is lower than that of CD. Compared with CD, UAD reduces the burr height, improves machining accuracy, and reduces drill bit wear.

Multiple performance characteristics optimization in end milling of thin-walled parts using desirability function

With the development of high-performance CNC machine tools, milling has been established as one of the main means of machining thin-walled parts. Thus, the selection of process parameters for milling operations is an important issue in end milling of thin-walled parts to assure product quality and increase productivity. The current study explores three machining parameters, namely wall thickness, feed, and machining strategies, that influence dimensional and form errors, surface roughness, and machining time milling of 7075-T6 aluminum alloy thin-walled parts. The effects of machining parameters on each of the response variables were analyzed using graphs of the main effects and three-dimensional surface plots. Analysis of the results show that the most influential factor for wall thickness deviation, dimensions deviation, perpendicularity deviation, flatness deviation, surface roughness of inner walls, surface roughness of outer walls, and surface roughness of reference plane was machining strategy, while feed is the most influential parameter affecting the machined time, followed by the machining strategy. The desirability concept has been used for simultaneous optimization in terms of machining parameters of the thin-walled parts machining process. Finally, a confirmation test with the optimal parameter settings was carried out to validate the results.

Characterization of a Capillary Flow Controller for Electric Propulsion

A low-cost and reliable propellant flow controller is necessary to offer competitive electric propulsion systems. This paper first reviews xenon flow control methods for Hall thrusters and ion engines. Through a trade study, a simple and low-cost xenon flow controller applying a heated capillary is proposed. The test article is fabricated based on a developed theory and tested with xenon. The estimation based on laminar flow shows slightly different characteristics from those of the experiment, although the Reynolds number indicates a laminar condition. The turbulent flow assumption is in good agreement with the experiment at a high mass flow rate while the flow characteristics are between laminar and turbulent at a low mass flow rate. That implies that the surface roughness and tube curvature induce the laminar–turbulent transition even in the low mass flow rate case. To obtain a wider flow rate range, maintaining laminar flow in the capillary is desirable because of the high sensitivity of the friction coefficient with temperature in the laminar flow. Component improvements achievable through miniaturization and reduction of the inner wall surface roughness and capillary curvature are considered to be necessary to prevent the turbulent transition.

The Impact of Single- and Multicomponent Liquid Drops on a Heated Wall: Child Droplets

This paper presents the experimental research into the impingement of single- and multicomponent liquid drops on a solid wall. We focus on studying the conditions and characteristics of two impact scenarios: rebound and breakup. We performed a comprehensive analysis of the effect of a group of factors on the drop transformation and fragmentation characteristics. These factors include the drop velocity and size, Weber number, impinging angle, wall temperature, thermophysical properties of the wall material, surface roughness, hydrophilic and hydrophobic behavior of the surface, homogeneity and inhomogeneity of the drop composition, as well as viscosity and surface tension of the liquid. We compared the outcomes of one, two, and three drops with the same total volume on a wall. Histograms were plotted of the number and size distribution of the emerging secondary droplets. The results include the critical conditions for the intense breakup of drops. Such factors as wall heating, its roughness, impinging angle, drop size and velocity affected the breakup conditions most notably. The variation of a group of these factors could provide a 2–25-fold increase in the liquid surface area as a result of the impact.

Characterization and Parametric Optimization of Micro-hole Surfaces in Micro-EDM Drilling on Inconel 718 Superalloy Using Genetic Algorithm

Drilling of cooling holes in turbine blades on difficult to machine materials like Inconel 718 has been one of the significant applications of micro-EDM. Owing to the difficulties in the contact measurement techniques, the actual side wall characteristics of micro-holes were not explored in detail. In this study, optical non-contact 3D profilometry is used to characterize the side wall surface. The 3D roughness parameter, Sa, has been introduced to measure the side wall surface quality of the holes drilled using micro-EDM. Along with side wall roughness, all the significant responses in the micro-hole manufacturing like material removal rate, overcut, and taper angle were also taken as the responses. The voltage, feed rate, and electrode rotation speed were chosen as the factors. The Box–Behnken design for three factors was used as the experimental design to conduct the study. The analysis showed that voltage was the most significant factor influencing all the responses within the design space. Multi-objective optimization of the process parameters was carried out by the method of sum of weighted objectives using genetic algorithm. A machining strategy was proposed combining both response surface methodology and genetic algorithm to formulate an optimum cutting condition which was able to reduce the inner side wall surface roughness to 1.3587 $$\upmu $$ m. The predicted responses were validated experimentally and the maximum relative error obtained was less than 10%.

过渡Reynolds数下Stokes层的间歇湍流特性

The characteristics of intermittent turbulence induced by wall surface roughness in a finite Stokes layer were investigated numerically, including the velocity gradient at the wall, the velocity profile and the Reynolds stress, etc.， with a transitional Reynolds number Re=495.The results show that, the velocity profile does not follow the logarithmic law in most phases, but does only in some rare phases during the decelerating stage. The comparison between the Reynolds stress and the result in the case of the incompressible boundary layer indicates that, the Reynolds stress distribution in the turbulence stage is similar to that in the case of the incompressible boundary layer, including the peak amplitude and the peak position, but there is significant discrepancy in the turbulence core region between the 2 cases. Above characteristics reveal the strong nonequilibrium behaviors of intermittent turbulence in the Stokes layer.

Effect of Process Parameters and Preheating Temperature on Surface Roughness and Thickness Distribution in Hole Flanging using Incremental Sheet Metal Forming

Incremental Sheet metal forming is a die less method of forming which offers high formability. In this research work; effect of step depth, tool rotation speed and preheating temperature on surface roughness and thinning of flange wall is investigated in hole flanging using incremental forming. The parameter optimization is carried out by Taguchi method. Grey relational analysis is carried out to obtain best parameter combination.

Effect of process parameters and preheating temperature on surface roughness and thickness distribution in hole flanging using Incremental Sheet metal Forming

Incremental Sheet metal forming is a die less method of forming which offers high formability. In this research work; effect of step depth, tool rotation speed and preheating temperature on surface roughness and thinning of flange wall is investigated in hole flanging using incremental forming. The parameter optimization is carried out by Taguchi method. Grey relational analysis is carried out to obtain best parameter combination.

The Influence of Loading Force on Ultrasonic Drilling Garnet Ferrite

In order to achieve high precision microholes of garnet ferrite, the rotary ultrasonic assisted machining and the tool load matching system were employed. An ultrasonic precise microholes technology experiment platform was built to machine garnet ferrite materials. A series of drilling experiments to machine garnet ferrite were presented in this paper, which were used to explore the influence of cutting force on tool wear. And the holes’ exit aperture and wall surface roughness were applied to be evaluation parameters to explore the effect of loading force on machining quality. As a result, tool wear is aggravates as cutting force increases. And loading force shows different influence tendency on exit aperture size precision and wall surface roughness, the selection of proper loading force does good to control exit aperture size and hole wall surface roughness effictively.

On thermal performance of serpentine silicon microchannels

In the present study, three different serpentine microchannels (Rectangular, U and V) of rectangular cross-section with a channel span 24 mm were fabricated on a 0.525 mm thick (100) silicon substrate using micro-ultrasonic machining (micro-USM) technique. Thermal performance of the microchannels was experimentally investigated by making the working fluid (water) to flow through them at different Reynolds numbers (100–400) and at different heat fluxes (10 kW/m2, 20 kW/m2 and 30 kW/m2). Similar microchannels were modeled and analysed numerically simulating the experimental conditions. The performances of the microchannels obtained with the experimental as well as numerical results were compared in terms of pressure drop, substrate and fluid temperatures and heat transfer coefficient. The results indicate that the overall thermal performance of the microchannel heat sink mostly depends on the type of pattern as the fluid-substrate interaction area, defined by the Sink Area Factor (SAF), changes appreciably with the pattern. It was found that the U-serpentine microchannel exhibited the best thermal performance while compared to the other two serpentine microchannels. The sharp bends of the microchannel patterns and the surface roughness of the microchannel walls adversely affect the overall thermal performance of the microchannels. The study also outlines the need for a compromise in the Reynolds number, as higher Reynolds number tends to lower the overall thermal performance of the microchannels.

Rotating detonation engines with two fuel orifice schemes

Hollow combustors without centerbodies are becoming popular for rotating detonation engines. The present experimental study compares detonation and pressure gain performances of hollow combustors with two fuel orifice schemes to choose a better one. Hydrogen and air sources at room temperatures of 280–285 K are used as propellants. The combustors are optically accessible by embedding a piece of quartz glass in the outerbody. The hollow combustor channel here has an outer diameter of 100 mm. Fuel is injected into the combustor from 150 cylindrical orifices in a diameter of 0.8 mm or 90 orifices in a diameter of 2 mm, and air is injected through a circular channel with a throat width of 1 mm. Results show that the hollow combustor with 150 cylindrical orifices in a diameter of 0.8 mm has a better detonation performance and a higher pressure gain performance than the other one. High-speed images show the wall surface roughness affects the RDW strength greatly.

Flow Characteristics Considering the Temperature Viscosity of Oils in the Gap based on Micro Geometric Roughness Fractal Surface

Due to the limitation of manufacturing conditions in China, the valve core will always exhibit random, disordered and multi-scale micro geometric characteristics in recent years. Based on the fractal features of the micro-scale surfaces of the cores and the chambers of a multi-way valve, this research establishes3-danisotropic models for the surface shapes of the valve cores and chambers using the Weierstrass-Mandelbrot (W-M) function. Then, the boundary conditions of the Navier slip model and computational fluid dynamics (CFD) are used to analyse the flow characteristics of the hydraulic oil in the gap and the wall slip. The research results demonstrate that the surface roughness of the solid walls exerts a significant influence on the flow characteristics of the hydraulic oil as it flows in the gaps: the greater the surface roughness, the higher the probability of occurrence of slip between the surfaces of the solid walls. With varying surface roughness of the solid walls, the greater the slip coefficient b is, the larger the slip velocity on the walls, and the greater the flow velocity of the hydraulic oil in the whole gap; meanwhile, this phenomenon occurs when the temperature difference between the upper and lower walls increases as well, and the flow velocity of the hydraulic oil increases significantly.

Study on Wall Heights and Surface Roughness of Spun Cups Produced of Metal Blanks by Multipass CNC Spinning Technology

This research paper deals with the influence analysis of the conventional metal spinning parameters (tool path profile tpp, tool feed f and mandrel rotational speed n) on the wall heights and the surface roughness Ra of the cylindrical-shaped spun parts measured in various directions with respect to the material rolling direction. Experimental research was carried out according to the 3-level full factorial design of experiment (DoE). Experimental study was also statistically analyzed by the ANOVA method. It was observed that tool path profile is a process parameter which has the most significant impact on the spun cup height and the surface finish, as well.

Effect of surface characteristics on cleaning performance for CIP system in food processing

In food processing, insufficient cleaning can result in reduced efficiency, contamination in final product, and energy losses. To optimise widely implemented clean-in-place (CIP) systems, it is critical to understand the influence of the interactions between surfaces, foulant, and chemical agents on the efficiency of the cleaning process. The present work investigates the effect of wall temperature and surface roughness on the surface free energy of stainless steel 316L coupons. Equilibrium contact angles (ECA) of four commonly used liquids, namely ethylene glycol, 1-bromonaphathalene, water, and diiodomethane were measured on the surfaces of interest. Finally, ECAs of liquids were used to quantify surface free energy (SFE) of the solid substrate. Our results show that surface energy is proportional to the roughness and well-prediction of liquids wettability as a function of roughness and temperature. It demonstrates the importance of surface characteristics in determining interfacial energy, and consequently the efficiency of CIP for food engineering.

Influence of Surface Roughness on the Pump Performance Based on Computational Fluid Dynamics

The influence of surface roughness on the pump performance was deeply analyzed based on computational fluid dynamics (CFD). A series of numerical calculations with different grid numbers, turbulence models, and surface roughness were made for a typical multistage centrifugal pump. Moreover, the external characteristic experiments were also conducted to verify the numerical calculations. The results show that the surface roughness has enormous influences on the pump performance. With the increase of the surface roughness, the head and the efficiency of the pump decreases continuously, but the decreasing rate slows down gradually, and the surface roughness has a greater influence on the efficiency than that on the head. Moreover, the influence of surface roughness on the disk friction loss power is much greater than that on the hydraulic power. Besides, the total efficiency of the pump reduces mainly by decreasing the hydraulic efficiency and the mechanical efficiency, due to the negative effect of surface roughness. In addition, the surface roughness of the impeller and the diffuser mainly affects the hydraulic efficiency, the surface roughness of the shroud's outer wall mainly influences the mechanical efficiency, and the surface roughness of the inner wall of the pump cavity mainly affects the volume efficiency, but the influence of surface roughness on the pump performance is interconnected. Therefore, due to that, it's very difficult to make the precision-machine inside the impeller and diffuser, polishing the impeller shroud and pump cavity is beneficial to improve the pump efficiency and reduce the pump shaft power.

Surface roughness analysis and optimization during drilling on chemically treated natural fiber composite

Abstract A new composite is prepared using vetiveria zizanioides as reinforcement and polyester as the matrix. The composite is subjected to drilling based on central composite design. Spindle speed, feed rate and point angle are taken as the input factors and wall surface roughness is taken as output factor. The study includes analysis of relationship between the input and output factors and a mathematical model to predict the response. The output is optimized using a minimization approach and optimum conditions are obtained. Confirmatory experiment is made and compared with the optimum condition. The comparison showed that the optimization is highly consummate.

Proposal for a method of measurement and control of surface quality in the course of abrasive waterjet cutting of material

The paper deals with the automation of the hydroabrasive production process, which leads to higher productivity and production optimization. In the submitted work, the basis of control design is a topography function of surface roughness of abrasive waterjet cut walls, and its functional relations to the controlled speed and to the measured mean values of sound pressure level, including a design of a suitable diagram of connections of controlling elements and equipment. The controlled parameter is the final roughness of a cut wall; in the design, the roughness is program-regulated according to the continuously measured root mean square of sound pressure level by means of continuous control of the traverse speed of cutting head.

Research on drilling for cooling hole of die and mold

In die casting mold and plastic mold，the cooling holes are designed for increasing cooling efficiency by cooling water． Recently, as purpose of high cycle of molding，the position of cooling holes has been closer to the mold surface，and the number of cooling holes has been increasing．If cooling and heating are repeated in mold，stress corrosion cracking and fatigue corrosion cracking are likely to occur at the cooling hole wall, then this phenomenon might be cause of short mold life．In order to solve this problem，mold manufacturer designs sphere radius(SR) at the hole bottom to avoid thermal stress. Therefore, we developed drill for SR machining，and we researched cutting method for SR machining for improving mold life．As a result，the cutting method of " Finishing the hole wall and hole bottom SR " can eliminate the slight step difference between them．The cutting method improve the surface roughness of the hole wall，and improve the mold life.

Study of micromilling parameters and processes for thin wall fabrications

Thin wall fabrication is a long lasting hot research topic in the precision manufacturing fields. There is still a lack of studies in key machining parameters and qualities for thin wall fabrications. In this paper, micromilling parameters and processes are comprehensively studied for thin walls fabrications considering the dimensional errors and surface quality. First, the influences of key process parameters in micromilling as the feed engagement fz, radial depth of cut ae and axial depth of cut ap on milling forces, surface roughness and dimensional errors of thin walls are analyzed by single-factor finite element simulations and experiments. The reasonable micromilling parameters are identified by the single-factor studies. Second, contrast experiments have been conducted to evaluate the effects of multi-axial feed engagement on dimensional errors. It turns out that there exists the appropriate feed times for achieving smaller dimensional errors of thin walls with the same height. Then, thin wall fabrication experiments have been conducted. The suitable feed times identified by the study are 2 and 3 for thin walls made of the material brass H59 with the width of 50 μm, height of 300 μm and 900 μm, respectively. The correspondingly dimensional errors are 0.73 μm and 5.95 μm, respectively. The study indicates that both micromilling parameters and feed times need to be separately optimized for the fabrication of thin walls with good dimensional accuracies.