Groove Width Ratio Research Articles

Shear Adhesion of Ice on Large-Sized Grooved Aluminum Surfaces.

Ice adhesion is important when designing aircraft anti-icing/de-icing systems. Major and minor grooves are common in the skin of aircraft. However, the effects of millimeter-scale grooves on ice adhesive strength have not been given due attention. Specimens with varying depths, widths, and numbers of grooves were fabricated by machining to investigate the ice adhesive characteristics of large-sized grooved aluminum surfaces. After the ice cube was frozen on the surface using a silicon mold, the adhesive force was measured using a self-assembled shear adhesive force setup. A correlation between groove size and apparent adhesive strength in the perpendicular loading direction was established based on the experimental results. Every 1% increase in the groove width ratio was associated with an 18.7 kPa increase in apparent adhesive strength. The increasing speed of the adhesion rapidly decayed as the groove depth increased. The increase in adhesion reached 99% of the maximum increase when the groove depth reached 0.8 times the width. The number of grooves had little effect on the adhesion when the total width of the grooves was kept constant. Stress distribution analysis was conducted using the finite element method, and the results were in accordance with the cracking phenomena in the experiments. The adhesive strength in the parallel loading direction was 30% lower than that in the perpendicular loading direction for all six chosen surfaces. This study is the first to propose a quantitative relationship between the surface textures of millimeter-sized grooves and ice adhesive strength. The loading orientation also had a substantial influence on adhesion. The results will serve as a valuable reference for future studies on ice adhesion on textured surfaces and for improving the performance of anti-icing/de-icing systems.

Lubrication structure design of water lubricated rubber thrust bearing with spiral groove for shaftless rim driven thruster

The existing design methodologies generally rely on experience and the design-test-modify process to fulfill the urgent requirements of shaftless rim-driven thrusters for low and medium speed, high load capacity, and wear-resistant water-lubricated bearings. In order to innovate current design methods and improve the design capabilities of such bearings, this paper conducts research on the lubrication structure design of water-lubricated spiral groove rubber thrust bearings (SGRTBs). Furthermore, the model developed in this paper takes the effect of surface roughness into account, proposes a mixed lubrication analysis technique for water-lubricated SGRTBs, achieves the optimization design of the spiral groove structure parameters (spiral angle, groove width ratio, number of spiral grooves, and tilt angle), and addresses the mixed lubrication issue of typical spiral surface contact.

Effect of herringbone groove structure parameters on the static performance of gas foil herringbone groove thrust bearings

The application of foil bearings technology into high speed and heavy load turbine machinery with high axial force is limited because of the insufficient load capacity of gas foil thrust bearings. This paper presents a new type gas foil thrust bearing, engraving the herringbone groove on the top foil surface of gas thrust foil bearing, relying on the pumping effect of herringbone grooves, so that the bearing load capacity of gas foil thrust bearings can be further improved by using the secondary pressure boosting effect of herringbone grooves on the basis of taper dynamic pressure effect. The physical models of non-groove gas foil thrust bearing and gas foil herringbone groove thrust bearings are established. The Reynolds equation, gas film thickness equation and foil deformation equation are coupling solved by finite difference method to obtain gas film thickness distribution and gas film pressure distribution for non-groove and herringbone grooves gas foil thrust bearing. The effects of the number of grooves, groove depth, groove width ratio, groove angle of the herringbone groove and the Taper inlet height on the friction torque, bearing load capacity and ultimate load capacity of the herringbone grooves gas foil thrust bearing are researched. Furthermore, when compared to the traditional non-groove gas foil thrust bearing, the optimal herringbone groove structure parameters are obtained, and a feasible method for optimizing the performance of gas foil thrust bearings is proposed.

Flow Mechanisms and Lubrication Performance of Water-Lubricated Thrust Bearings with Herringbone Grooves

Due to their excellent stability and zero leakage capability, thrust bearings with herringbone spiral grooves are frequently used in transmission mechanisms. However, the lubrication mechanism of thrust bearings has not been clearly understood and explained, preventing the optimization of the bearing performance. Thus, this paper is devoted to solving this problem by building a three-dimensional finite element flow model. In this model, the change in viscosity temperature is considered using Roelands equation, and the turbulence and cavitation are taken into consideration. Using the established model, the influence of parameters such as spiral angle, groove width ratio, and rotational speed on the cavitation area of the thrust bearing are analyzed. The pressure contour and speed distribution are obtained inside the clearance, as well as the volume fraction of the gas phase at the end face. Finally, according to the analysis results, the optimum structural parameter for the herringbone spiral groove structure is proposed, which enables higher bearing stability and provides a reference for engineering practice.

Spiral Groove Parametric Study of Solid Particles Deposition Characteristics in Sealing Lubrication Film

In order to study the effect of groove parameters on solid particles’ deposition in mechanical face seal lubrication film, a multi-phase flow calculation model for the sealing micro-gap lubricating film was established based on the Laminar model, mixture multi-phase flow model, Zwart–Gerber–Belamri cavitation model, and DPM model in Fluent, and a numerical simulation of the effect of groove parameters is presented. The results show that, with the increase of groove depth, the circumferential sedimentary zone in the dam area decreases or even disappears, and the groove area becomes the main sedimentary part; the particle deposition rate decreases first and then increases with the increase of groove depth and spiral angle. The influence of groove depth on the deposition rate at low speed is more significant than that at high speed. The increase of deposition rate caused by a spiral angle that is too large is greater than that caused by a spiral angle that is too small. The optimal groove depth and spiral angle are around 6 µm and 18°, respectively; when the rotating speed is 1000 rpm, the deposition rate increases obviously with the increase of the groove diameter ratio; meanwhile, when the rotating speed increases to more than 2000 rpm, the deposition rate increases first and then decreases with the increase of the groove diameter ratio. When the groove diameter ratio is about 0.5, the deposition rate is the largest. For example, when the rotating speed is 2000 rpm, the deposition rate of the groove diameter ratio, 0.5, is about 200% higher than that of groove diameter ratio, 0.2. The lower the speed, the more sensitive the deposition rate is to the groove diameter ratio. The sensitivity at 1000 rpm is 14 times that at 5000 rpm. The deposition rate increases with the increase of the groove width ratio. The higher the rotating speed, the smaller the rate of deposition rate increase. However, when the rotating speed is 5000 rpm and the groove width ratio is higher than 0.7, the deposition rate increases sharply.

Experimental study of different structural parameters on gas lubricated spiral groove thrust bearing for cryogenic turbo expander

With the development of high speed and miniaturization of turbo expander, the gas-lubricated spiral groove dynamic pressure gas bearing plays an important role. An experimental study on the gas-lubricated spiral groove gas thrust bearing is carried out to research the relationship between the bearing loading capacity and the structural parameters such as the spiral angle, the groove length ratio, the groove width ratio and the rotating speed. The contrast experiment of spiral groove structure on thrust disc and bearing end face was also carried out. The experimental results show that the optimum spiral angle is 20°, the optimum groove length ratio is 0.61∼0.68, the optimum groove width ratio is 0.5∼0.55, and the new structure of the spiral groove on the thrust disc will increase the bearing loading capacity by 7.6% than the traditional structure.

A comprehensive multi-objective, multi-parameter and multi-condition optimization of a spiral groove in dry gas seals

Dry gas seals are widely used in rotating equipment for fluid leakage control and operating efficiency enhancement, while the geometric parameters of the spiral groove affect its sealing performance significantly. Groove width ratio δ, groove length ratio α, and spiral angle β are the selected optimization geometric parameters for different objectives, including opening force Fo, film stiffness kz, and stiffness–leakage ratio Γ. The genetic algorithm and loop iteration optimization method are used to solve the multi-dimensional optimization problems under different working conditions, which are reflected in a new dimensionless number λ in the range 1 to 1000. Moreover, a concept of optimum spectrum is developed to obtain the global optimal geometric parameters. The performance comparison of two dry gas seals with different geometric parameters is conducted experimentally to verify the effectiveness of numerical results. Results show that both genetic algorithm and loop iteration optimization method can provide optimal geometric parameters for better sealing performance than single factor optimization, and the global optimal results were significantly influenced by working conditions and objectives. The multi-dimensional optimization methods and results presented in this paper provide a theoretical and experimental reference for designing dry gas seals in different working conditions to meet various sealing performance requirements.

Optimization of slanted grooved micromixer with a serpentine channel at a lower Reynolds number

Abstract In Lab-On-Chip (LOC) applications, micromixing is the most important step to obtain fast analytical response in many biochemical and biological detections. Design and realization of smaller and shorter mixers with higher efficiency has become a necessity more than a recommendation. In this work, a numerical optimization of a passive mixer with a serpentine-shaped channel is proposed. By considering a laminar flow regime, the continuity and momentum equations, along with the advection-diffusion equation, are solved to evaluate the mixing performance. The optimization of the slanted grooves micromixer with a serpentine channel is achieved using computational fluid dynamics (CFD) and response surface methodology (RSM) based on Box-Behnken design. This method is used to find a second-order polynomial regression model and to obtain the optimal groove design. The considered objective function is the mixing index, while the four design variables are: the number of grooves per half cycle (N), the groove angle (θ), the groove depth to channel height ratio (d/h) and the ratio of groove width to channel width (Wd/W). The optimization results indicate that the highest values of each selected interval of the groove depth to channel height ratio (d/h) and the angle between the radius and the groove (θ), on the other hand, the ratio of groove width to channel width (Wd/W) of about 0.45 are desirable to promote faster mixing. The Flow behaviour in optimized “slanted grooves mixer (SGM) with serpentine channel was tested for low Reynolds number Re ranging between 0.3 and 5, and the results have shown that in the range of Re from 0.3 to 0.7 the mixing index is greater than 85%, for large range of Re from 1 to 4.5, the mixing index reaches the value of 93% in the first cycle of the channel and it approaches 100% for channel length of 1.25 mm from the inlet of the channel. Thus the most important result of this work shows that higher efficiency is obtained for short distance and the required pressure drops decreases. This micromixer can be selected as a good candidate in applications that require a high degree of mixing with relatively small length mixing as polymerase chain reaction (PCR) in the analysis and extraction of DNA.

Research on structure characteristics of the helium-lubricated spiral grooved thrust bearing for helium turbine expander

The helium-lubricated spiral grooved thrust bearing of helium turbo expander was studied by numerically simulating the steady-state non-linear Reynolds equation, the Reynolds equation of the pressure was solved by finite difference method (FDM), the film pressure distribution is calculated iteratively by MATLAB program, the structural parameters including the spiral angle, the groove length ratio, the groove width ratio influenced on the static characteristics were analyzed. The results show that: The bearing loading capacity of helium lubricated spiral grooved thrust gas bearing is lower than that of air lubricated bearing under the same conditions; The viscosity of the lubricant only affects the gas carrying capacity of the thrust disc when the spiral groove is on the bearing, while the density of the lubricant has a greater influence on the bearing loading capacity; When the spiral groove is designed on the rotor thrust disc, the bearing loading capacity of the spiral grooved thrust bearing increases by 6% on average compared with that of the spiral groove on the bearing.

Leakage analysis of helical grooved pump seal using CFD

The helical grooved seal, which is a non-contact sealing device using the viscosity of the fluid, prevents leakage by reducing fluid pressure according to the shapes of the rotor and stator. It has been widely adopted to turbomachinery because no wear deliveries high efficiency, unlike to the existing contact sealing device. In this study, parametric study was performed by CFD analysis, considering helical grooved seal shape: ratio of groove width and land width (Wratio), helical angle (β) and groove depth (d). Based on the leakage characteristics analyzed through CFD results, improved seal shape of the helical grooved seal to reduce leakage was suggested.

Effect of the Lapping Platen Groove Density on the Characteristics of Microabrasive-Based Lapping.

Microabrasive-based lapping is widely used in the manufacturing of single-crystal substrates such as sapphire, SiC, and GaN. Although many studies have been conducted to improve the lapping process characteristics, most of them focused on process conditions or consumables. In this study, the effect of the lapping platen groove density on the lapping characteristics was studied using a sapphire substrate. Groove density was defined as the ratio of groove width to groove pitch, and the displacement of the lapping head was measured to calculate the oil film thickness. It was confirmed that, for groove densities below 0.30, hydroplaning occurs when the oil film thickness increases. When the oil film thickness is larger than the abrasive particle size, the material removal rate is low because the abrasive does not participate in the lapping process. When the oil film was developed, the experimental results showed a high surface roughness and poor flatness of the substrate, as only large abrasive particles participated in the lapping process. Therefore, to improve the lapping characteristics, it is important to reduce the groove density by reducing the groove pitch, which prevents the development of the oil film.

Analysis of Cracking Development and Mechanical Characteristics of High-Filled Cut-and-Cover Tunnel

The cut-and-cover tunnel (CCT) construction scheme has led to the popularity of high-filled cut-and-cover tunnel (HFCCT). HFCCT possesses a backfilling height of 30–50 m. However, such a high soil column produces a large force on the structure and the structure is prone to crack, causing structural damage and difficulty in normal use. In order to provide a reference for the structural safety assessment of HFCCT, we conducted a similarity model test to study the variation law of the development of crack, displacement, and internal force of HFCCT with a coefficient of λ (the ratio of the backfilling height to the height of the cut-and-cover tunnel). In the test, a 1:20 similar scale CCT model with slope angle 70° and groove width ratio 1 was built using data from the HFCCT on the Lanyu Line. The backfilling process on site was simulated in a simulation box (360 cm long, 120 cm wide and 209 cm high). A numerical model was also built using PFC2D to verify the accuracy of the model test and further explain the crack formation mechanism of the HFCCT from a microscopic perspective. The results show that with the increase of the coefficient of λ, the bearing stage of the CCT can be roughly divided into three stages: steady growth stage, rapid growth stage, and accelerated growth stage. Furthermore, the development of cracks is closely related to the displacement and internal force of the CCT. The larger the displacement of the CCT, the greater the instability of the structure and the larger the ratio of the bending moment to the internal force, which causes the crack to develop faster.

Performance of novel air foil thrust bearings with taper-groove on surface of top foil

To improve the load capacity of air foil thrust bearing, the micro taper-grooves on the surface of top foil was introduced and studied. A modified Reynolds equation considering the gas rarefaction effect was established, in which the Knudsen number was affected by the film thickness and pressure. A new bump stiffness model was built with the consideration of bump rounding, friction, and bending stiffness of foil. By considering the variation of gas film thickness, the load capacity, friction torque, and power loss of novel bearing with grooves were calculated by the finite difference method. Moreover, the effect law of groove parameters, groove shape and grooves number on the novel bearing performance was studied systematically. The results show that the predicted axial load capacity considering gas rarefaction effect is decreased slightly in smaller clearance and more consistent with the actual test data. The novel air foil thrust bearing with taper-groove can weaken the air end leakage and enhance the local dynamic pressure efficiently in the parallel portion of top foil, thus improving the static characteristics of bearing. For the novel air foil thrust bearing with taper-groove depth of 10 µm, the load capacity can be increased by about 13.33%, compared with traditional bearing. With the increments of taper-groove depth and length on top foil, the load capacity can be increased. However, the friction torque is decreased when there is a longer taper-groove in the circumferential direction. Meanwhile, the optimal groove width ratio is about 0.5, and the structure of multi-grooves is beneficial to the decreased friction torque. The validity of presented theoretical model has been verified by the literature data, and the results are expected to be helpful to bearing designers, researchers, and academicians concerned.

Theoretical and Experimental Study of Transient Behavior of Spiral-Groove Thrust Bearings during Start-Up

In this study, a transient mixed lubrication model that considers mass-conserving cavitation and deterministic asperity contacts is established to study the evolution of the tribological behavior of spiral-groove thrust bearings during start-up. To overcome oil film thickness discontinuity at the edges and the complicated boundary shape of spiral grooves, a boundary-fitted coordinate system transformation is adopted. The evolution of the tribological behavior, including the asperity contact force, load-carrying capacity, minimum oil film thickness, and friction torque during start-up, is presented using the current model. To illustrate more clearly, the evolution of hydrodynamic pressure and cavitation fraction is also displayed. Experiments are performed to verify the proposed theoretical model. The results demonstrate that this model is able to capture the evolution of the tribological behavior of spiral-groove thrust bearings during start-up. To improve start-up performance, a parametric analysis is conducted to identify the effects of the main design parameters (groove depth, groove width ratio, and spiral angle) on the lift-off speed.

Predictions of the effective slip length and drag reduction with a lubricated micro-groove surface in a turbulent channel flow

We perform direct numerical simulations of a turbulent channel flow with a lubricated micro-grooved surface to investigate the effects of this surface on the slip characteristics at the interface and the friction drag. The interface between water and lubricant is assumed to be flat, i.e. the surface-tension effect is neglected. The solid substrate, where a lubricant is infused, is composed of straight longitudinal grooves. The flow rate of water inside the channel is maintained constant, and a lubricant layer under the interface is shear driven by the turbulent water flow above. A turbulent channel flow with a superhydrophobic (i.e. air-lubricated) surface having the same solid substrate configuration is also simulated for comparison. The results show that the drag reduction with the liquid-infused surface highly depends on the lubricant viscosity as well as the groove width and aspect ratio. The amounts of drag reduction with the liquid-infused surfaces are not as good as those with superhydrophobic surfaces, but are still meaningfully large. For instance, the maximum drag reduction by the heptane-infused surface is approximately 13 % for a rectangular groove whose spanwise width and depth in wall units are 12 and 14.4, respectively, whereas a superhydrophobic surface with the same geometry results in a drag reduction of 21 %. The mean slip length normalized by the viscosity ratio and groove depth depends on the groove aspect ratio. The ratio of fluctuating spanwise slip length to the streamwise one is between 0.25 (ideal surface without groove structures) and 1 (i.e. isotropic slip), indicating that the slip is anisotropic. Using the Stokes flow assumption, the effective streamwise and spanwise slip lengths are expressed as a function of groove geometric parameters and lubricant viscosity. We also suggest a predictive model for drag reduction with the heptane-lubricated surface by combining the predicted effective slip lengths with the drag reduction formula used for riblets (Luchini et al., J. Fluid Mech., vol. 228, 1991, pp. 87–109). The predicted drag reductions are in good agreements with those from the present and previous direct numerical simulations.

On hydrodynamic lubrication characteristics of ferrofluid film in a spiral groove mechanical seal

PurposeThe purpose of this study is to investigate the hydrodynamic lubrication characteristics of ferrofluid film for spiral groove mechanical seal in external electromagnetic field and to analyze the effects of the volume fraction of ferrofluid, parameters of the electromagnetic field, operating parameters and geometrical parameters of mechanical seal on the characteristics of ferrofluid film.Design/methodology/approachThe relationship between the ferrofluid viscosity and the intensity of external electromagnetic field was established. Based on the Muijderman narrow groove theory, the pressure distribution was calculated with the trial method by trapezoid formula.FindingsIt was found that pressure, average viscosity, average density and opening force of ferrofluid between end faces increase with the increase in intensity of current, volume fraction of ferrofluid, rotating speed, pressure differential and spiral angle; decrease with the increase in temperature; and increase at first and then decrease with the increase in the ratio of groove width to weir and the groove length. All of them reach the maximum value when the ratio of width of groove to weir is 0.7 and the ratio of groove length is 0.6. Leakage of ferrofluid increases with an increase in intensity of current, volume fraction of ferrofluid, rotating speed, pressure differential, spiral angle and ratio of groove length; decreases with an increase in temperature; and increases at first and then decreases with the increase in the ratio of groove width to weir. The tendencies of characteristics of silicone oil are consistent with those of ferrofluid, and the characteristics of silicone oil are smaller than those of ferrofluid under the same condition.Originality/valueThe volume fraction of ferrofluid, rotating speed, spiral angle, ratio of groove width to weir, groove length and temperature have a significant influence on the characteristics of ferrofluid film; however, intensity of current and the pressure differential have slight influence on the characteristics of ferrofluid film. An analytical method for analyzing hydrodynamic lubrication characteristics of ferrofluid film in a spiral groove mechanical seal was proposed based on the Muijderman narrow groove theory.

Numerical analysis of water-lubricated thrust bearing with groove texture considering turbulence and cavitation

PurposeThis paper aims to establish the mathematical models for the water-lubricated thrust bearing with groove texture considering turbulence and cavitation and numerically analyze the influence of rotary speed, texture depth, groove number and groove width on the static performance of the bearing.Design/methodology/approachThe turbulent Reynolds equation and the Jakobsson–Floberg–Olsson cavitation model are adopted for the analysis. The Payvar–Salant algorithm and Finite difference schemes are used to discretize the governing equations. To illustrate the influence of turbulence, the performance of the bearing predicted by the turbulent and laminar models are compared.FindingsAccording to the results, the load capacity and the friction force calculated by the turbulent model are greater than those obtained by laminar model, and the deviation between them gradually increases with the increased rotary speed. So, the turbulent effect should be fully considered for high-speed water-lubricated bearing with surface texture. There exists a peak value for the load capacity of the water-lubricated thrust bearing in respect to the texture depth, the number of grooves and the groove width ratio, while the friction force varies slowly with those parameters. Well-designed groove texture can improve the performance of the water-lubricated thrust bearing.Originality/valueThis paper proposes a mathematical model considering turbulent and cavitation effect for water-lubricated thrust bearing with surface texture. This model can be complementary to conventional laminar model which is used to analyze the performance of textured bearing at low rotary speed.

Enhancement of Forced Convection Heat Transfer for SiO2 flow through Channel with Ribs at Constant Heat Flux

Numerical investigation of forced convective flow in a 2-dimensional microchannel. This investigation is analyzed with nanoparticles SiO2 and water as a base fluid studying the influence of turbulence model inside multi geometrical channel (Triangular, Trapezoidal, Semi-circular, and Rectangular) by using "Finite Volume Method (FVM)". The heat flux is applied on the lower wall of channel and the upper is insulated. The diameter of nanoparticles is 20 nm. The Reynolds number ranges are from 10000 to 30000 for ratio of groove width (B) to channel height (H) was used 0.75. The volume fractions range is between 1-4%. Triangular channel score higher Nusselt number and lower friction factor than other cases against Reynolds number. When the volume fraction was increase, the Nusselt number increased and friction factor decreased, this gives 4% has the optimal properties.

Numerical and experimental study on the separation characteristics of microgroove rotary seals

The microgroove rotary seals used in the wet clutches of a vehicle operate in a mixed-lubrication state at low rotational speeds. When the speed increases to a certain value, the full-film hydrodynamic-lubrication state occurs in the sealing end face. The transition characteristics of the microgroove rotary seal in this operating state are called the separation characteristics and the critical speed is called the separation speed. In this paper, the separation characteristics of microgroove rotary seals are studied. First, a theoretical model considering the asperity contacts, the fluid lubrication with microgrooves and the axial motion dynamic characteristics of the seal is established. Then, the variation in the separation characteristics is studied systematically using the microgroove parameters, such as the number Ng of microgrooves, the groove width ratio δθ, the extent δr of the radial seal dam and the spiral angle β. The optimum ranges of the microgroove parameters are determined: Ng = 40–50, δθ = 0.65–0.75 and δr = 0.7–0.8 for radial grooves and Ng = 30–40, δθ = 0.5–0.7, δr = 0.7–0.8 and β = 12–17° for spiral grooves. Finally, the variations in the microgroove parameters of the separation characteristics are verified by several experiments. The experimental results are in good agreement with the simulation results.

Investigating Effects of Groove Dimensions on Microstructure and Mechanical Properties of AA6063/SiC Surface Composites Produced by Friction Stir Processing

Friction stir processing forms an innovative and promising technology for surface composite fabrication where their fabrication is accomplished in solid state. In the current research, AA6063/SiC surface composites were fabricated and effect of ratio of groove width (w) to tool pin diameter (d) on dispersion of reinforcement particles and mechanical properties were investigated. Five varying groove widths were chosen at constant levels of tool dimensions and process parameters to observe the exclusive effect of variation of groove width on area of developed SCs. Results reflected that groove width have strong impact on the area of surface composites and a ratio of w/d of 0.5 was found optimum for developing high volume percentage of 40% of SiC reinforced surface composites. The results were supported by macro and microstructural images.