Wrap Angle Research Articles

Fabric friction behavior: study using capstan equation and introduction into a fabric transport simulator

All thin materials, such as textiles, papers, polymers, or metals, are handled on rollers during manufacture and subsequent use. This requires several unwinding and winding processes. The goal of this study was to investigate the friction behavior of fabrics relative to sliding velocity and to introduce friction coefficient evolution in a fabric transport model. For the experimental part, a specific fabric/roll friction bench is presented. The friction coefficient was calculated from the capstan equation. The evolution of the friction coefficient was quantified relative to the sliding velocity for different textile fabrics and also for a polymer and a paper web. The influence of some measurement process parameters was studied: web tension, roll diameter, and wrap angle. The friction coefficient initially increased with sliding velocity and then became constant. This phenomenon can be explained by the deformation of the fabric due to friction, thereby inducing an increase in web tension with the sliding velocity. The relationship between tension and rolling friction behavior of the fabric was investigated. The variability of the friction coefficient was introduced to web/roll simulator, and improvements to the simulator are shown.

Influence of blade wrap angle on centrifugal pump performance by numerical and experimental study

The existing research on improving the hydraulic performance of centrifugal pumps mainly focuses on the design method and the parameter optimization. The traditional design method for centrifugal impellers relies more on experience of engineers that typically only satisfies the continuity equation of the fluid. In this study, on the basis of the direct and inverse iteration design method which simultaneously solves the continuity and motion equations of the fluid and shapes the blade geometry by controlling the wrap angle, three centrifugal pump impellers are designed by altering blade wrap angles while keeping other parameters constant. The three-dimensional flow fields in three centrifugal pumps are numerically simulated, and the simulation results illustrate that the blade with larger wrap angle has more powerful control ability on the flow pattern in impeller. The three pumps have nearly the same pressure distributions at the small flow rate, but the pressure gradient increase in the pump with the largest wrap angle is smoother than the other two pumps at the design and large flow rates. The pump head and efficiency are also influenced by the blade wrap angle. The highest head and efficiency are also observed for the largest angle. An experiment rig is designed and built to test the performance of the pump with the largest wrap angle. The test results show that the wide space of its efficiency area and the stability of its operation ensure the excellent performance of the design method and verify the numerical analysis. The analysis on influence of the blade wrap angle for centrifugal pump performance in this paper can be beneficial to the optimization design of the centrifugal pump.

Dynamic Pressure Gradient Model of Axial Piston Pump and Parameters Optimization

The unsteady pressure gradient can cause flow noise in prepressure rising of piston pump, and the fluid shock comes up due to the large pressure difference of the piston chamber and discharge port in valve plate. The flow fluctuation control is the optimization objective in previous study, which cannot ensure the steady pressure gradient. Our study is to stabilize the pressure gradient in prepressure rising and control the pressure of piston chamber approaching to the pressure in discharge port after prepressure rising. The models for nonoil shock and dynamic pressure of piston chamber in prepressure rising are established. The parameters of prepressure rising angle, cross angle, wrap angle of V-groove, vertex angle of V-groove, and opening angle of V-groove were optimized, based on which the pressure of the piston chamber approached the pressure in discharge port after prepressure rising, and the pressure gradient is more steady compared to the original parameters. The max pressure gradient decreased by 70.8% and the flow fluctuation declined by 21.4%, which showed the effectivness of optimization.

Application of two-fluid model in the unsteady flow simulation for a multiphase rotodynamic pump

Based on the assumption of tiny bubbly flow, the gas-liquid two-phase unsteady flow in a multiphase rotodynamic pump was numerically simulated with two-fluid model. The two-phase transport process and the evolution characteristic of the pump head were analyzed. In the working conditions, the liquid flow rate was constant, and the IGVF (inlet gas volume fraction) was 0.05, 0.15 and 0.25, respectively. The k ω− based SST model was used for turbulence; the drag force and the added mass force were accounted for in the interfacial momentum transfer terms. Because the wrap angle of the blade was large, the hybrid mesh was adopted to guarantee high mesh quality. The simulation results demonstrate that two-fluid model can more reasonably capture the transport process than the homogeneous model; and the drag law should be corrected based on the mixture viscosity in high gas volume fraction conditions. If the liquid flow rate is constant, the increase of IGVF can raise the pressure in the inlet extended region, while the pressure in the outlet extended region will not be affected much, thus the pump head will go down. In addition, due to the fluctuation of gas volume fraction field, the pump head will also fluctuate around a stable value in the transport process.

Effects of Structural Parameters and Performance on Poisson's Ratio of Auxetic Yarn

Auxetic yarn is designed by ourselves by wrap-core structure, which has special physical properties and geometrical structure different from traditional yarn. The wrap-core auxetic yarn will expand transversely under tension. Therefore, the tensile tests were conducted to analyze effects of structural parameters and performance on lateral deformation of yarn. The experimental results show that yarn with negative Poissons ratio as low as-4.31 is produced successfully. Moreover, effects of structure and performance, including the wrap angle, the diameter ratio, the tension modulus of the wrap yarn and the twist of the core yarn, on poissons ratio of yarn are analyzed. It is found that the negative Poissons ratio effect becomes more observable with the higher diameter ratio or lower wrap angle, and it becomes much more observable when the twist degree of the core yarn is higher or the wrap yarns modulus is lower.

Smart textiles: evaluation of optical fibres as embedded sensors for structure health monitoring of fibre reinforced composites

Silica optical fibres (SOF) are established for the use of communicating digital data and numerous applications including structure health monitoring. However, SOFs exhibit drawbacks such as brittleness, low strain and signal attenuation due to bending. These drawbacks limit the use of SOF as embedded sensors for monitoring composite structures’ internal health. Unlike SOFs, the relatively newly developed polymer optical fibres (POF) do not possess such drawbacks and they are able to monitor the health of fibre-based composite structures. Bending in optical fibres is a major concern since this causes signal attenuation at bending points. Integrating optical fibres into a woven preform requires bending because of the crimping that occurs as a result of weave interlacing. The main objective of this research was to evaluate the effect of the macrobending of optical fibres on signal power integrity. The goal is to design optical fibre sensors embedded in woven preforms that have high sensitivity for monitoring the health of composite structures. Newly developed Graded Index Perfluorinated POF (GI-PF-POF) and two types of SOFs were evaluated in a three-point macrobending test bed using a laser light source. A systematic experimental design was executed to evaluate the optical fibres’ signal loss as a result of the bending radius, bending deflection and wrap angle of optical fibre around the middle rod of the test bed. The results showed that POF provides higher signal sensitivity and greater robustness against signal attenuation under bending when compared to SOF. The work also unveiled the bending radius of optical fibres at which minimum or no signal loss occurred. This finding is essential for designing embedded optical fibre sensors with high sensitivity.

Three-dimensional design method for mixed-flow pump blades with controllable blade wrap angle

In this article, a direct and inverse iteration design method for mixed-flow pumps was introduced, and a three-dimensional design platform for mixed-flow pumps was established. Through iteration calculation of two kinds of stream surfaces to solve both the continuity equation and motion equation of the fluid at the same time, and therefore obtaining the quasi-three-dimensional flow field inside the mixed-flow pump, the accuracy of the flow field calculation was improved. By repeating iteration of the direct calculation and inverse design, influence of blade shape on flow field calculation was fully considered, thus assuring that the final design of blade camber line complies with actual flow pattern. After comparing and analyzing the meridional velocity distribution, as well as the relative circulation distribution and expelling coefficient in the blade zone, it was proved that compared with others designed by conventional methods, the impeller designed with three-dimensional design platform has a better hydraulic performance, especially the blade energy conversion capacity that witnessed a significant improvement. With this three-dimensional design platform, a parametrization was applied to velocity moment distribution and blade leading and trailing edges positions. The influence of velocity moment distribution parameters P and a0, and the blade leading and trailing edges positions parameters θh and θt on blade wrap angle and the internal flow of the impeller were analyzed. By curve fitting, the functional relationship between blade wrap angle ϕ and parameters θt, P and a0 was obtained. The blade wrap angle control strategy during the process of mixed-flow pump impeller design was then put forward, thus realizing three-dimensional design of mixed-flow pump blades with controllable blade wrap angle. The performance test for the mixed-flow pump model suggested that the three-dimensional design method with controllable blade wrap angle, by controlling blade wrap angle size and adopting direct and inverse iteration design method, ensures a better hydraulic and cavitation performance for the mixed-flow pump impeller designed with three-dimensional design platform.

Parametrization of blade leading and trailing edge positions and its influence on mixed-flow pump performance

Based on the three-dimensional design platform, this article conducted parametrization of blade leading and trailing edge positions, and analyzed the influence of different position parameters on mixed-flow pump hydraulic performance and internal flow with model test and numerical simulation. The results showed that the hydraulic efficiency η of a mixed-flow pump increased slightly when the position parameter θh of the blade leading edge on the hub increased, and η increased significantly when the position parameter θt of the blade leading and trailing edge positions on the shroud increased. However, with θt increasing, the growth rate of η decreased. Numerical simulation has shown that by selecting a proper value of θt, the impeller energy conversion capacity can be effectively improved, and the distributions of static pressure and total energy can be more uniform in the flow passage. Meanwhile, with θt increasing, blade angle on the blade trailing edge decreased. Correspondingly, the absolute velocity in the outlet zone decreased, and the hydraulic loss in the outlet zone also decreased, which is beneficial to improving hydraulic efficiency of the mixed-flow pump. Within the value range of 7–9°, with different combinations of position parameter θt1 of the blade leading edge on the shroud and position parameter θt2 of the blade trailing edge on the shroud, the mixed-flow pump hydraulic efficiency η and blade wrap angle ϕ show a linear positive correlation, suggesting that an increase in ϕ could significantly improve impeller energy conversion capacity. Compared to θt1, θt2 has a more significant influence on ϕ and η. Thus, the value of θt2 should be carefully attended to during design process.

Modeling and Validation of Rotational Vibration Responses for Accessory Drive Systems—Part I: Experiments and Belt Modeling

Experimental and modeling techniques for belt longitudinal static stiffness, longitudinal dynamic stiffness and damping coefficient, bending stiffness, and friction coefficient between a pulley and a belt are presented. Two methods for measuring longitudinal dynamic stiffness and damping coefficient of a belt are used, and the experimental results are compared. Experimental results show that the longitudinal dynamic stiffness of a belt is dependent on belt length, pretension, excitation amplitude and excitation frequency, and the damping coefficient of a belt is dependent on excitation frequency. Two models are presented to model the dependence of longitudinal dynamic stiffness and damping coefficient of a belt on belt length, pretension, excitation amplitude and excitation frequency. The proposed model is validated by comparing the estimated dynamic stiffness and damping with the experiment data. Also, the measurements of belt bending stiffness are carried out and the influences of the belt length on the belt bending stiffness are investigated. One test rig for measuring friction coefficient between a pulley and a belt are designed and fabricated, and the friction coefficient between the groove side belt with the groove side pulley, and the flat side belt with a flat pulley is measured with the test rig. The influences of wrap angle between pulley and belt, pretension of belt and rotational speed of the pulley on the friction coefficient are measured and analyzed. Taking an engine front end accessory drive system (FEAD) as the research example for the accessory drive system, experimental methods and the static and dynamic characteristics for the FEAD with seven pulleys, a tensioner, and a serpentine belt are presented.

Study on Design Criteria and Methods for the Valve Train of the Compressed-Air Engine

The Compressed-air (CA) engine car is receiving increasingly worldwide attention because it takes advantages of renewable energy and has zero exhaust emissions. However it is limited by its low efficiency. This paper focuses on a systematic study on valve timing for optimizing its efficiency and performance. The requirements for the valve train were presented and an optimized polynomial cam profile was applied. Using the programme of Matlab, the influences of the half wrap angle and the maximum valve lift to the fullness coefficient were studied. The article proves that the designed cam profile should use the minimum maximum valve lift to receive the maximum fullness coefficient.

Research on Wrapping Angle Compensation Technology of Cold Strip and its Industrial Application

In the paper, the cold strip online dynamic wrapping angle compensation model is established based on the latest intelligent shape meter developed by Yanshan university. It could improving recisions of the shape detection and the shape closed-loop control under specific working conditions effectively. The model was successfully applied to Angang HC 6-high reversible cold rolling mill, meeting bad working conditions on site. The remarkable results were obtained in industrial application. The error between calculated values and measured values of total tensions is within 3%.

Hydraulic design of a low-specific speed Francis runner for a hydraulic cooling tower

The air blower in a cooling tower is normally driven by an electromotor, and the electric energy consumed by the electromotor is tremendous. The remaining energy at the outlet of the cooling cycle is considerable. This energy can be utilized to drive a hydraulic turbine and consequently to rotate the air blower. The purpose of this project is to recycle energy, lower energy consumption and reduce pollutant discharge. Firstly, a two-order polynomial is proposed to describe the blade setting angle distribution law along the meridional streamline in the streamline equation. The runner is designed by the point-to-point integration method with a specific blade setting angle distribution. Three different ultra-low-specificspeed Francis runners with different wrap angles are obtained in this method. Secondly, based on CFD numerical simulations, the effects of blade setting angle distribution on pressure coefficient distribution and relative efficiency have been analyzed. Finally, blade angles of inlet and outlet and control coefficients of blade setting angle distribution law are optimal variables, efficiency and minimum pressure are objective functions, adopting NSGA-II algorithm, a multi-objective optimization for ultra-low-specific speed Francis runner is carried out. The obtained results show that the optimal runner has higher efficiency and better cavitation performance.

Friction characteristics between paper and steel roller under mixed lubrication

This article describes the new theoretical modeling of friction coefficient between uncoated paper-web (newsprint; for example) and steel roller. In the modeling, the paper base is approximated by the linear spring and the surface asperities are treated as rigid body based on the observation of web surface structure. Introducing the contact mechanics, the mixed friction coefficient is formulated theoretically for a wide range of roller surface velocity, in which the air film thickness between the web and roller is estimated based on the foil bearing model. In the experiments, the newsprint is used as uncoated paper-web. Euler’s belt formula is applied to calculate the friction coefficient from the measured data of tension increase. The measurements are carried out by changing five design parameters such as web width, wrap angle, tension, roller diameter, and roller surface velocity. The measured results are compared with the predicted results to verify the applicability of the present theoretical model. Good agreements can be seen between the predicted and measured results.

Computational Studies of Nucleotide Selectivity in DNA–Carbon Nanotube Hybrids

Using classical molecular mechanical techniques, we have investigated the morphological properties and interaction mechanisms of single-walled carbon nanotubes (SWNT) functionalized by DNA. Our simulations evidence sequence preference trends for the homogeneous single-strand DNA on the (6,5) vs the (9,1) SWNTs. The DNA–SWNT interaction strength is ordered as G ≳ A > C > T for (9,1) and A > C > G > T for (6,5) hybrids. This preference in a DNA sequence versus tube chiralities is accompanied by variations in wrapping geometries, demonstrating large wrapping angles (40–60°) for the (6,5) and two ranges of wrapping angles (10–30° and 45–60°) for the (9,1) systems. In addition, we found correlations between the most stable wrapping angles of SWNT–DNA hybrids and the most preferential DNA orientations on the graphene with respect to its lattice vectors, which could elucidate the sensitivity of SWNT–DNA structures to the DNA sequence.

Effects of impeller trimming influencing pump as turbine

Pump manufactures normally do not provide performance curves of their pumps working as turbines, especially performance curves of trimmed impellers. Impeller trimming is necessary to adapt to a certain operating condition. Therefore, establishing the correlation of PAT’s performance curve and impeller trims is essential. In this paper, a laboratory model of a pump as turbine (PAT) open test rig was set up. Experimental research was carried out on a single stage centrifugal PAT, performance curves of original impeller, impeller after once and twice trims were acquired. Numerical simulation and analysis were performed on the PAT. The accuracy of CFD was validated through comparison between numerical and experimental data. As impeller diameter is cut down, its geometrical parameters of impeller diameter, blade wrap angle, impeller inlet width and blade inlet angle are changed. So, research on effects of the above four parameters to the performance influence of PAT were carried out using CFD. Through analysis of the predicted performance curves, the reasons for the variation of performance curves after impeller trimming were explored.

Effects of Blade Wrap Angle Influencing a Pump as Turbine

A pump is not ideally designed to operate as a turbine. To improve the efficiency of a pump as turbine (PAT), the redesign of the PAT, according to the flow of the turbine, is required. The blade wrap angle is one of the main geometric parameters in impeller design. Therefore, an investigation into the blade wrap angle to the PAT’s influence can be useful. In order to understand blade wrap angle to the influence of the PAT, this paper numerically investigated three different specific speeds of PATs with different blade wrap angles. The validity of numerical simulation was first confirmed through a comparison between numerical and experimental results. The performance change of the PATs with the blade wrap angle was acquired. A detailed hydraulic loss distribution and a theoretical analysis were performed to investigate the reasons for performance changes caused by the blade wrap angle. The results show that there is an optimal blade wrap angle for a PAT to achieve the highest efficiency and the optimal blade wrap angle decreases with an increasing specific speed. A performance analysis shows the PAT’s flow versus pressure head (Q-H) and flow versus generated shaft power (Q-P) curves are lowered with the decrease of the blade wrap angle. The hydraulic loss distribution and theoretical analysis illustrate that it is the decrease of hydraulic loss within the impeller, together with the decrease of the theoretical head, that results in the performance decrease. The decrease of hydraulic loss within the impeller is attributed to the shortened impeller blade passage and the reduced velocity gradient within the impeller flow channel. With the decrease of the blade wrap angle, the slip factor of the PAT’s impeller is decreased; therefore, its theoretical head is also decreased.

Process simulation and optimization of laser tube bending

A 3D thermomechanical finite element analysis model for laser tube bending is developed based on the software MSC/Marc. The processes of single- and multi-scan are analyzed numerically. The gradient and development of the temperature between the laser scanning side and the nonscanning side leads to the changing complexity of the stress and strain. Consequently, the length of the laser scanning side becomes shorter than that of nonscanning side after cooling. The length difference between both sides makes the tube produce the bending angle. The relationship between the number of scans and the bending angle is about in direct ratio. The bending angle induced by the first irradiated time is largest. Meanwhile, the finite element simulation is integrated with the genetic algorithm. Aiming at different process demands, corresponding objective functions are established. Laser power, beam diameter, scanning velocity, and scanning wrap angle are regarded as design variables. Process optimizations of maximum angle bending and fixed angle bending after single laser scan are realized. Groups of optimized process parameters can be obtained according to different optimization objectives. The bending angle can approach to the maximum when the laser power, spot diameter, scanning velocity, and scanning wrap angle are 381.24 W, 3.37 mm, 16.34 mm/s, and 123.1°, respectively. When the laser power, spot diameter and scanning velocity are 426.12 W, 4.9 mm, 14.31 mm/s respectively, a fixed angle bending can be achieved.

소형 냉장고에 대한 스크롤 압축기 적용성에 관한 연구

To study the applicability of a scroll type compressor to small capacity refrigerators, a R600a scroll compressor with algebraic scroll wrap has been designed. Its size and performance have been compared to a reciprocating type of the same displacement volume. By employing scroll wrap based on algebraic curve, high compression ratio can be accomplished without increasing the wrap angle much so that compact scroll may be obtained. Compared to a reciprocating one, the designed scroll compressor has diameter and height reduced by about 50% and 80%, respectively. By numerical simulation, it has been estimated that the scroll compressor provides 38.6% more cooling capacity than reciprocating type with 8.9% more power consumption, resulting in 27.3% increase in COP for ASHRAE low back pressure condition. With increasing the operating pressure ratio from 9.5 to 15.3, the overall compressor efficiency of the scroll compressor decreases from 72.6% to 65.2%, while that of the reciprocating compressor increases from 55.7% to 59.8%.

Effect of blade wrap angle on efficiency and noise of small radial fan impellers—A computational and experimental study

Radial impellers have several technical applications. Regarding their aerodynamic performance, they are well optimized nowadays, but this is in general not true regarding acoustics. This work was therefore concerned with analyzing the flow structures inside isolated radial impellers together with the far-field sound radiated from them in order to optimize the aerodynamic and acoustic performance. Both numerical and experimental techniques were applied in order to study the effect of varying wrap angle and otherwise identical geometric configuration on aerodynamics and acoustics of the radial impellers. The results give a detailed insight into the processes leading to sound generation in radial impellers. Measurements were performed using laser Doppler anemometry for the flow field and microphone measurements to analyze the radiated noise. In addition, unsteady aerodynamic simulations were carried out to calculate the compressible flow field. An acoustic analogy was employed to compute far-field noise. Finally, the phenomena responsible for tonal noise and the role of the wrap angle could be identified. Using this knowledge, design guidelines are given to optimize the impeller with respect to the radiated noise. This work shows that improved aerodynamic efficiency for isolated impellers does not automatically lead to a smaller flow-induced sound radiation.

Analysis on Effects of the Blade Wrap Angle and Outlet Angle on the Performance of the Low-Specific Speed Centrifugal Pump

In order to research the effect of the blade wrap angle and outlet angle on the hydraulic performance of the low-specific speed sewage pump, the Reynolds time-averaged Navier-Stokes equations was discretized based on the finite volume method, and the modified k-ε turbulence model were chosen in FLUENT. Numerical simulation of the internal flow within the centrifugal pump with the specific speed of 60 at different blade wrap angle and outlet angle is carried out. The analysis of the velocity and the turbulent kinetic energy distribution in different cases, and predicts the external characteristics of the several cases based on the loss analysis method. The study results show that the efficiency of pumps increase with decreasing the outlet angle and increasing the wrapping angle at the design of sewage pumps. According to the analysis, changing the blade outlet Angle has much more influence on the performance of the pump than changing the wrap angle.