Length Of Straight Section Research Articles

On the corrugation effect on thermo-fluids characteristics and entropy generation in channels equipped with wavy and straight sections

A numerical simulation was performed to investigate the characteristics of thermo-fluids and the irreversibility generation of laminar forced convection through three different channel designs. This article first presents a comprehensive study of combination of straight and wavy sections in order to create a balance between improved thermal performance from the wavy design and optimized flow properties from the straight section, leading to an overall enhancement in cooling efficiency. A novel design has been considered using a channel configuration that consists of different lengths of wavy and straight sections and is named (cases I, II, and III). The outcomes are shown in terms of average Nu, enhancement ratio (ER), performance factor, total irreversibility generation, as well as the contours of streamlines, isothermal, and Bejan numbers for different values of the Reynolds number range of 5≤Re≤400 and dimensionless wave amplitude 0.3≤α≤0.6. The results were compared of the three cases with the plane channel, revealing an augmentation in HTR of 73.7%, 64.9%, and 43.3% for cases III, II, and I, respectively. On the other hand, with both Re and α, the total irreversibility generation increases continuously.

Analysis of energy loss in the helical hedge flow channel of fruit tree root emitter

This paper proposes the design of a helical hedge flow channel with a high energy loss, which shows promising potential for application in fruit tree root emitters. The aim is to investigate the relationship between the energy loss form in the channel and its influencing factors. The hydraulic performance testing method is employed to analyze the factors that affect energy loss. The main influencing factors are determined using the response surface methodology (RSM) for experimental design. Based on the obtained experimental results, the energy loss form and influencing factors are analyzed, and a prediction model for the energy loss coefficient (ξ) is established. The results indicate that the ξ exhibits a decreasing trend with an increase in the diversion angle (α), a trend of first increasing and then decreasing with an increase in the channel width (b), and an increasing trend with an increase in the number of channel units (n). The effects of the straight section length (l1), convergence section length (l2), and bend radius (r) on the ξ can be neglected. The ranking of the geometric parameters' influence on the ξ is as follows: n > b > α > l1 > r > l2. The experimental results reveal that the ξ ranges from 19.2 to 234.3. Furthermore, the head loss along the flow channel constitutes merely 0.06–0.47% of the local head loss, The main form of energy loss in the spiral counter flow channel is local head loss. There is a significant linear relationship between α, b, n and the ξ, The established prediction model (R2 = 0.9691) can accurately predict the ξ of the channel.

Research on hysteretic performance of a semi-rigid energy dissipation connection for precast cladding panels

A novel semi-rigid energy dissipation connection (SEDC), capable of transitioning the precast cladding panel from a rigid connection to a flexible connection with the primary structure as the seismic action increases, is proposed in the present study. The combination of the bending part and friction part endows the connection with the ability to provide adjustable sliding force and sufficient energy dissipation for the precast cladding panel. The design methods of SEDC, including the elastic stiffness, the yield force, the yield displacement, and the bear capacity, are proposed, followed by a coordinated design method between the precast cladding panels and the primary structure based on SEDC. Fourteen SEDC specimens are designed and tested under monotonic and cyclic loading tests to investigate the semi-rigid workability of SEDC and to evaluate the influence of design parameters of the bending and friction parts. Two working processes, which are the static friction process and the sliding friction process, are clearly reflected by the monotonic test results. The cyclic test results indicate that the SEDC specimens demonstrate satisfactory plastic development with full hysteretic curves, stable load capacity, reliable deformation ability, and favorable energy dissipation ability. The U-shaped bending plates exhibited a track-like deformation pattern without any observed tears or cracks. The NAO friction pads demonstrated a fragmented damage pattern, while the Brass friction pads demonstrated a linear scratch damage pattern. SEDC specimens equipped with Brass friction pads exhibited better low-cycle fatigue performance, which can be attributed to the favorable wear resistance of the Brass material. In addition, finite models of SEDCs are established and validated based on Abaqus. The combined working mechanism of SEDC, including the contribution ratio of load capacity and dissipated energy from the bending part and the friction part, is clearly revealed. Furthermore, the influence of parameters including the thickness (t), width (B), straight section length (l), radius (R), and height (h) of the bending part, as well as the pre-tightening force (pc) and the friction coefficient (f) of the friction part, are also summarized based on both the experimental and numerical analyses. Further discussions, including the calculation of the seismic behavior factor and the measurements for accurate construction, are conducted.

Seismic mitigation of continuous girder bridges equipped with U-shaped stainless steel dampers under near-fault earthquake excitations

Bridges that are close to seismic faults may suffer from severe damages under earthquake excitations. To enhance the seismic performance of continuous girder bridges, this paper presents a combined energy dissipation system (CEDS), incorporating isolation bearings and U-shaped stainless steel dampers. The U-shaped stainless steel dampers are equipped between every two bearings, and the top and bottom ends of dampers are fully fixed with the girders and the bent caps, respectively. Considering the strained conditions under seismic loadings, the mechanical property of U-shaped stainless steel dampers is numerically investigated with the loading directions of 0, 45, and 90 degrees. The hysteretic behavior of U-shaped stainless steel elements affected by the geometric parameters, i.e., the width, the thickness, the radius of arc segment, and the length of straight section, are further investigated. After that, a continuous girder bridge is adopted to verify the feasibility of the combined energy dissipation system, and two groups of U-shaped stainless steel dampers are designed for continuous piers and transition piers, respectively. The results turn out that the U-shaped stainless steel element shows excellent energy dissipation capacity. The maximum relative displacement between the girders and bent caps of piers can be effectively reduced by adopting the CEDS, which prevents the girders falling from supporting seats, and it is more effective in the longitudinal direction of bridges with the seismic reduction rate of 20–70%. Though the installation of U-shaped stainless steel dampers enhances the constrict of the top of piers, the maximum drift ratio increases in an acceptable range.

Enhanced Levitation Performance of Magnetic Levitation System Using HTS Racetrack Coil

We have studied a magnetic levitation system including an HTS bulk as magnetic shield. This system consists of a ferromagnetic rail, HTS bulks, and HTS coil. In this paper, the vertical attractive force was discussed in two types of the analytical models. First, the model with the racetrack coil was proposed. We analyzed the vertical attractive force depending on the length of the coil's straight section. As a results, the maximum vertical attractive force became large with increasing a straight section, and the force reached approximately 20 kg when the straight section was 1 m. Next, we proposed a scaled-up model which was a 10-fold scaled-up of the HTS racetrack coil, HTS bulk, and ferromagnetic rail assuming an actual train size. Here we considered that one vehicle body, whose weight was 25 t, was levitated by four racetrack coils. Hence the vertical attractive force of each racetrack coil needed to be about 6.25 t. According to the analysis, the maximum vertical attractive force was about 16 t. The force was generated by one racetrack coil. Therefore, the vertical attractive force was enough larger than the weight of the actual vehicle body.

Flow Conditioner Design and Analysis Based on Computational Fluid Dynamics

To address the issue of uneven gas flow velocity distribution upstream of natural gas pipeline flow meters, a wave-type fin flow conditioner was designed. The Computational Fluid Dynamics (CFD) numerical simulation method was used to analyze the velocity distribution inside the pipe, and the rectification effect of the flow conditioner was measured by using the offset degree and the minimum length of the straight pipe section. The offset degree at a specific downstream section was calculated when the fluid passed through a 90 degrees elbow spoiler component without a flow conditioner with an Etoile conditioner and wave-type flow conditioner. The results show that the wave-type flow conditioner has a better rectification effect, and the minimum straight pipe section length is shortened by 72% compared to without a flow conditioner, greatly reducing the pipeline design cost and improving the accuracy of measurement of the Ultrasonic flowmeter.

Development of superconducting model dipole magnets beyond 12 T with a combined common-coil configuration

The superconducting magnet group at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences, China) has been engaging in the R&D of high field accelerator magnets since 2014 for the pre-study of the next-generation high energy particle accelerators like CEPC-SPPC (Circular Electron Positron Collider-Super Proton Proton Collider), FCC (Future Circular Collider), etc. A superconducting model dipole magnet named LPF1 was first fabricated with NbTi and Nb3Sn in a combined common-coil configuration in 2017 and tested in 2018, a main field of 10.23 T was reached within two 10 mm apertures. The magnet was reassembled with higher pre-stress in 2019 to investigate the influence of the pre-stress loading level on the performance of common-coil dipole magnets. The main field of this upgraded magnet named LPF1-S was increased to 10.71 T within two 12 mm apertures. By improving the key processing technologies in Rutherford cable fabrication, coil winding, Nb3Sn & NbTi splices soldering and coil impregnation, the recently fabricated model dipole magnet named LPF1-U attained a 12.47 T main field in two 14 mm apertures in 2021. To fully take advantage of Nb3Sn and NbTi superconductors in different field regions, LPF1-U was still designed and developed with a combined coil configuration with Nb3Sn for the inner two coils and NbTi for the outer four coils. Additionally, graded coil topology and different coil LSS (length of straight section) settings were adopted in the optimization of LPF1-U layouts. Bladder and key technology was used for the support structure, and fiber optic sensors based on FBG (fiber Bragg grating) were utilized to monitor the stress distribution and variation in the structures and coils through the whole process from magnet assembly to cool-down and excitation. During the performance test, a relatively large number of trainings were carried out and LPF1-U became more stable after the thermal cycle. A peak field of 12.7 T in the coils (12.47 T main field in apertures) corresponds to an operating current of 6865 A and a load line ratio of 90% was finally attained. It is worth mentioning that LPF1-U is the first hybrid—Nb3Sn, NbTi—common coil dipole magnet that has achieved a main field of more than 12 T in two apertures. The design, fabrication and performance analysis of the LPF series dipole magnets are presented in this paper.

Design and Experiment of Hydraulic Scouring System of Wide-Width Lotus Root Digging Machine

In response to the problems of small working width and low operating efficiency of existing hydraulic scouring lotus root harvesters, a wide-width hydraulic scouring system was designed based on a wide-width self-propelled lotus root harvester. The main parameters of the key components were determined through theoretical analysis of the water flow energy of the hydraulic scouring system pipelines. An experimental study was also carried out on the main factors affecting the working performance of this hydraulic scouring system. Through hydrodynamic simulation tests, the effect of nozzle type and constriction section structure on the turbulence intensity at the nozzle outlet and the pressure loss per unit mass of fluid between the nozzle inlet and outlet sections were compared and analysed. The test yielded conical-cylindrical nozzle geometry parameters for nozzle inlet diameter of 40 mm, shrinkage angle of 30°, nozzle outlet straight section length of 20 mm, nozzle outlet diameter of 16 mm, the nozzle had better flushing performance. Single-factor tests were carried out with nozzle outlet pressure, scouring angle and nozzle height from the mud surface as influencing factors. Based on the optimum effective scour depth, a three-factor, three-level Box–Behnken central combination design test was completed. The primary and secondary factors affecting the effective scouring depth were obtained in the following order: nozzle height from the mud surface, nozzle outlet pressure, and scouring angle. Finally, the performance test of the hydraulic scouring system was completed. Results showed that when the nozzle outlet pressure of 0.30 MPa, the scouring angle of 60° and the nozzle height from the mud surface of 0 mm, the effective scouring depth was 395 mm, the lotus root floating rate was 90% and the damage rate was 5%, which meet the requirements of lotus root harvesting operations.

Buckling analysis of thin-walled metal liner of cylindrical composite overwrapped pressure vessels with depressions after autofrettage processing

Abstract The cylindrical filament wound composite overwrapped pressure vessels (COPV) with metal liner has been widely used in spaceflight due to their high strength and low weight. After the autofrettage process, the plastic deformation of the metal liner is constrained by composite winding layers, which introduce depressions to the metal liner that causes local buckling. To predict the local buckling of the inner liner with depressions of the pressure vessel after the autofrettage process, a local buckling analysis method for the metal liner of COPV was developed in this article. The finite element method is used to calculate the overall stress distribution in the pressure vessel before and after the autofrettage process, and the influence of local depressions on the buckling is evaluated. The axial buckling of the pressure vessel under external pressure is analyzed. The control equation of the metal liner with depressions is developed, considering the changes in the pressure and the bending moment of the liner depressions and its vicinity during the loading and unloading process. Taking the cylindrical COPV (38 L) with aluminum alloy liner as an example, the effects of liner thickness, liner radius, the thickness-to-diameter ratio, autofrettage pressure, and the length of straight section on the autofrettage process are discussed. The results show that the thickness of the inner liner has the most significant influence on the buckling of the liner, followed by the length of the straight section and the radius of the inner liner, while the autofrettage pressure has the least influence.

Symmetric and asymmetric shocked gas jets for laser-plasma experiments.

Shocks in supersonic flows offer both high density and sharp density gradients that are used, for instance, for gradient injection in laser-plasma accelerators. We report on a parametric study of oblique shocks created by inserting a straight axisymmetric section at the end of a supersonic "de Laval" nozzle. The effect of different parameters, such as the throat diameter and straight section length on the shock position and density, is studied through computational fluid dynamics (CFD) simulations. Experimental characterizations of a shocked nozzle are compared to CFD simulations and found to be in good agreement. We then introduce a newly designed asymmetric shocked gas jet, where the straight section is only present on one lateral side of the nozzle, thus providing a gas profile well adapted for density transition injection. In this case, full-3D fluid simulations and experimental measurements are compared and show excellent agreement.

Analysis of the Mechanical Properties and Parameter Sensitivity of a U-Shaped Steel Damper

To clarify the mechanical properties of the U-shaped steel damper under tension and compression along the opening direction and the energy dissipation mechanism in the energy dissipation system, a mechanical model was established to describe the plastic failure response of the damper, and the formula for theoretical calculation of its mechanical properties was derived. Using the straight line segment length, radius of circular arc, and opening direction as parameters for testing four specimens, through the design of reasonable pulling and pressing fixture, four specimens were tested for tension and compression. The initial stiffness and yield load test results and theoretical analysis were good and verified that the opening direction of the U-shaped steel damper affected its mechanical performance. Further analysis of the U-shaped steel damper’s mechanical properties using numerical finite element analysis of the arc radius and the straight line segment length, width and thickness in relation to the initial stiffness shows that increasing the straight section length and end arc radius can reduce initial stiffness, and increase the thickness and width can increase initial stiffness.

Influence of Butterfly and Gate Valves Upstream Large Water Meters

The research presented was conducted to quantify the effects of butterfly and gate valves located upstream water meters with diameters larger than 50 mm. Errors caused by these valves can have an enormous financial impact taking into consideration that a small percentage of variation in the error of a large meter is typically related to a significant volume of water. The uncertainty on the economic impact that a valve installed upstream of a medium size water meter leads to many water utilities to oversize the meter chambers in order to mitigate the potential negative errors. Most manufacturers approve their meters for a specific flow disturbance sensitivity class according to the standard ISO 4064-1:2018. Under this classification, a correct operation of the meters requires a certain length of straight section of pipe upstream the meter. However, this classification of the meters cannot consider all types of flow perturbances. For this study, two types of valves, butterfly and gate, were tested upstream ten brand-new water meters from six different manufacturers constructed in four different metering technologies: single-jet, Woltmann, electromagnetic and ultrasonic. In each meter unit was tested at five flow rates, from minimum to the overload flow rates. The tests were conducted with valves set in different orientations, closing degrees, and upstream distances from the water meters under study. The research shows that the valves used can produce significant deviations in the measuring errors with respect the errors found for undistorted working conditions.

Numerical Studies on Mechanical Behavior of Dry-Wound HTS Racetrack Coil

This paper presents numerical studies on the mechanical behavior of dry-wound high-temperature superconducting (HTS) racetrack coil. After calculating the Lorentz force induced from the self-field of the racetrack coil based on the 3D finite element method (FEM), the 2D mechanical stress analysis is performed based on the plane-stress assumptions to mitigate computational loads, and the mechanical behavior including displacement and stress are investigated. Based on analysis model, two following case studies are conducted: 1) analysis of mechanical behavior on various-shaped of racetrack coils having a different ratio of straight section length and semicircular section radius, and 2) analysis of stress reduction effect according to the degree of curvature when slight curvature is included in the straight section. In each case study, the factors affecting the mechanical behavior of racetrack coils are numerically analyzed and their trends are presented. The results obtained in this paper would be useful for the design of dry-wound racetrack coil, including no-insulation coil, applied in a large-scale and high-field application.

Geometric Effects Analysis and Verification of V-Shaped Support Interference on Blended Wing Body Aircraft

A special V-shaped support for blended wing body aircraft was designed and applied in high-speed wind tunnel tests. In order to reduce the support interference and explore the design criteria of the V-shaped support, interference characteristics and geometric parameter effects of V-shaped support on blended wing body aircraft were numerically studied. According to the numerical results, the corresponding dummy V-shaped supports were designed and manufactured, and verification tests was conducted in a 2.4 m × 2.4 m transonic wind tunnel. The test results were in good agreement with the numerical simulation. Results indicated that pitching moment of blended wing body aircraft is quite sensitive to the V-shaped support geometric parameters, and the influence of the inflection angle is the most serious. To minimize the pitching moment interference, the straight-section diameter and inflection angle should be increased while the straight-section length should be shortened. The results could be used to design special V-shaped support for blended wing body aircraft in wind tunnel tests, reduce support interference, and improve the accuracy of test results.

Mixing and heat release characteristics in the combustor of solid-fuel rocket scramjet based on DES

Based on the previous experimental results, in order to improve the understanding of the mixing and heat release process of the internal flow field in the solid-fuel scramjet combustor, and to provide theoretical reference for the layout of the combustor configuration in the next step, the numerical simulation method of DES combined with the gas mixing degree, mixing layer thickness and mixing fraction was used to analyze quantitatively the microscopic structures and the mixing combustion enhancement mechanism in the combustor at different lobe sweep angles based on the influence of the change of lobe sweep angle on engine performance, and then the influence law was explained from the microscopic point of view. Results demonstrate that 1) based on the engine configuration in this paper, in the design process of staggered support plate structure, the lobe sweep angle should be based on the width and the straight section length of the support plate. And the engine performance improves with the decrease of the lobe sweep angle. 2) The growth of the reaction mixture layer is in four typical stages: the initial growth zone, the rapid growth zone, the saturated growth zone and the full development zone. 3) The downstream part of combustor is in the full development zone of the reaction mixing layer. The full development zone as the main area determining the heat release performance of the engine, the mixing degree increases with the decrease of the lobe sweep angle in the behind part of the combustor. Therefore, the pressure in the downstream flow passage of the combustor and the space of combustor occupied by the high pressure area increase with the decrease of the lobe sweep angle.

Determination of Rational Profile of Fine-Module Internal Ratchet Teeth When Using Cutter

The article discusses the method for determining the length of straight sections of the working surfaces of internal fine-module ratchet teeth. A design scheme is proposed and the analysis of mathematical expressions describing the process of shaping the working edges of the ratchet teeth when cutting with a cutter by the generating method is performed. Mathematical dependences for calculation of the straight section length of the front and back edges of the ratchet teeth are obtained, allowing to determine rational profile at the design stage. It is established that the straight section on the front edge of the internal ratchet teeth can exist only at a certain value of its angle of inclination. The use of fine-module ratchet teeth of rational profile can improve the kinematic characteristics and increase the load capacity of ratchet engagement.

Influence of lobe geometry on mixing and heat release characteristics of solid fuel rocket scramjet combustor

The highly efficient and organized combustion of combustors should be achieved to improve the performance of solid fuel rocket scramjets. This study investigated the influence of changes in lobe sweep angle and height on the mixing and heat release characteristics of a solid fuel scramjet combustor on the basis of a staggered support plate structure introduced in a previous experimental study. The goal was to determine the optimal parameters of lobe sweep angle and height for subsequent engine design. Numerical simulation was conducted to quantitatively analyze the mixing and heat release characteristics of the combustor at different lobe sweep angles and heights in terms of combustion efficiency, gas mixing degree, and oxygen–fuel ratio. Results demonstrate that 1) the lobe sweep angle should be based on the width and straight section length of the staggered support plate structure. Engine performance improves with the decrease of the lobe sweep angle. 2) There is an optimum lobe height in the range of 0–24 mm, and the optimum value point is approximately 14 mm according to the proposed engine configuration.

Numerical study of heat transfer in square millimetric zigzag channels in the laminar flow regime

The present work deals with the simulation of heat transfer in zigzag millimetric channels with square cross-section of 2 mm width in the laminar flow regime. They consist of periodic zigzag units composed of straight sections and 90° bends with a curvature radius of 1.5 mm. The influences of fluid velocity and straight section length on the thermo-hydraulic performances are investigated. The results showed that by increasing the flow velocity or decreasing the straight section length between two bends, a transition from periodic flow to non-periodic flow can be observed. A thermo-hydraulic performance factor based on heat transfer enhancement and pressure drop penalty compared with a straight channel is then discussed. It is observed that the ratio of the Nusselt number in the zigzag channels to that in the straight channel is always higher than one. This ratio increases with increasing Reynolds number and values up to 6.4 are reached in the cases studied (Pr = 6.13). When the pressure drop penalty is considered in the performance factor, an enhancement is still observed with a factor up to 2.5. It is shown that non-periodic flow is not particularly interesting in terms of thermo-hydraulic performance compared with periodic flow.

INFLUENCES OF LOCAL RESISTANCES OF TECHNOLOGICAL CHANNELS OF PULP AND PAPER PRODUCTION ON THE OPERATION OF VORTEX FLOW METERS OF WATER AND WATER SUSPENSIONS OF LOW CONCEN-TRATIONS

The question of the features of operation of submersible vortex flowmeters of water and water suspensions of low concentrations in pulp and paper production, which are installed in process pipelines with local hydraulic resistance, is considered.
 It is shown that with an insufficient straight section after local resistance, an additional error appears, which appears due to the influence of local resistance (transition or retraction) on the symmetry of the velocity diagram in front of the device. This error arises due to a change in the Strouhal number (Sh) and is related to the measurement method. The Strouhal number begins to depend on both the distance to the local resistance and the fluid flow rate.
 Identify this relationship and is dedicated to this work. Recommendations on the length of straight pipeline sections in front of the flow meter have been developed, which can be significantly reduced by limiting the range of operating flow rates.
 The studies were carried out by the method of numerical simulation of hydrodynamic processes with subsequent processing of the results by the method of experiment planning.
 The dependence of the number Sh on the length of the relative diameter of the pipeline L/ for hydrodynamic resistance in the form of a transition is presented. This error shows that the measurement error is within 2% already with a straight section in front of the flowmeter equal to 5–7 diameters.
 The response surface for pipe bends (rotations) is considered at 90º from which it follows that while maintaining the length of the straight section within 5–7 pipe diameters, it is necessary to narrow the measurement range of the instruments 2.5 times.

Рекомендуемые способы предотвращения попадания речных наносов и шуги в водоводы деривационных гидроэлектростанций

The article discusses methods for preventing river drift from getting into the diversion canals of hydroelectric power plants (HPPs). The considered methods imply the use of a curvilinear intake channel, within which longitudinal-transverse circulation occurs, during the high-water period, and the use of drift protection thresholds for setting up artificial circulation during the period of low water level. The river flow hydromorphometric characteristics in the river bed curvilinear part were analyzed, as a result of which empirical dependencies for determining the water intake location and for calculating the intake stream canal straight section length have been obtained. A system of discharge balance equations in the section of the river hydroelectric power plant’s dike structure is given. Based on experimental investigation results, three water intake layout arrangements for mountain rivers are recommended. A method for protecting the diversion canal from sludge ice is suggested. According to this method, in the winter season water is taken from the stream lower layers, and sludge and ice are dumped into the hydroelectric complex tail race by means of special sludge dumping devices. The problem of modeling spatial turbulent fluid flow within the water intake structure head race for diversion power plants (DPP WIS) is solved using the FLOW 3D software package. The velocity distribution patterns along the flushing path axis for favorable and unfavorable sludge passage conditions are given. The diagram of water intake structure flushing path regimes for diversion power plants has been drawn. The obtained investigation results can be used in the design, construction, and operation of the water intake structures of diversion power plants in mountain and piedmont areas.