Contraction Section Research Articles

Numerical Simulation on the Hydrodynamic Flow Performance and an Improve Design of a Circulating Water Channel

A Circulating Water Channel (CWC) is an important piece of equipment for hydrodynamic tests in ocean engineering, the quality of the flow field produced by the CWC directly affects the accuracy of the experimental results. Optimizing the key parts of the CWC device can efficiently improve the velocity uniformity and helps to achieve a high-level flow performance. In this paper, a CWC flume is set up numerically, and a series of hydrodynamic tests were carried out to evaluate the flow uniformity by optimizing the turning vane and contraction section. The numerical model is solved based on the RANS equation by using the RNG model to simulate turbulence. The improved design of the CWC includes the investigations of the flow guiding vane at the turning corners and the contraction section in the flow acceleration zone. The turning vane cross-sectional shape, the straight-edged length of the wing, and the layout of the contraction transition section design were considered and verified. The obtained results show that the wing-type turning vane with appropriate straight-edged length can help to improve the velocity uniformity of the flow field. The Witozinsky transition curve could achieve better pressure gradient effects for CWC contraction section design, and the flow uniformity improved by increasing the contraction transition length. Based on the optimal design, the internal flow characteristics of the circulating water channel have been greatly improved, laying a solid foundation for wind-wave-current multifunction CWC equipment applications for future experiments.

Evaluating and selecting the supplier in prefabricated megaprojects using extended fuzzy TOPSIS under hesitant environment: a case study from China

PurposePrefabricated components sustainable supplier (PCSS) selection is critical to the success of prefabricated projects. However, limited studies have addressed the uncertainty and complexities during the selection process, particularly in multi-criterion group decision-making (MCGDM) circumstances. Hence, the research aims to develop a group decision-making model using a modified fuzzy MCGDM approach for PCSS selection under uncertain situation.Design/methodology/approachThe proposed study develops a framework for sorting decisions in PCSS selection by using the hesitant fuzzy technique for order preference by similarity to ideal solution (HF-TOPSIS) method. The maximum consistency (MC) model is used to calculate the weights of decision makers (DMs) based on the cardinality and sequence of decision data.FindingsThe proposed framework has been successfully applied and illustrated in the case example of CB01 contract section in Hong Kong-Zhuhai-Macao Bridge (HZMB) megaproject. The results show various complicated decision-making scenarios can be addressed through the proposed approach. The MC model is able to calculate the weights of DMs based on the cardinality and sequence of decision data.Originality/valueThe research contributes to improving accuracy and reliability decision-making processes for PCSS selection, especially under hesitant and fuzzy situations in prefabricated megaprojects.

Finite-Element Modelling of Double-Roller Clamping Spinning of Wind Concentrator

In order to improve the unit-power of a wind-driven generator, a wind concentrator with complex shape is installed in front of the impeller, which makes the airflow integrated and accelerated. It is important to manufacture the wind concentrator with high precision. The double-roller clamping spinning (DRCS) is a dieless, flexible spinning process that is very suitable for forming a wind concentrator with complex shape. The profile of a wind concentrator is divided into two parts: the contraction section and the expanding section. The process routes of both the contraction section and the expanding section are determined, and roller path equations are derived. Then the finite element (FE) analysis model that can describe the plastic deformation behavior of the DRCS forming for a wind concentrator is established, and the DRCS process of the flange is simulated. Furthermore, the wall-thickness distribution on the expanding section during the forming process is obtained. Finally, the reliability of the FE model is verified using the experimental results.

Characterization, Design Testing and Numerical Modeling of a Subsonic-Low Speed Wind Tunnel

Context: Wind tunnels are essential devices in the study of flow properties through objects and scaled prototypes. This work presents a numerical study to characterize an existing wind tunnel, proposing modifications with the aim to improve the quality of the flow in the test chamber. Method: Experimental measurements of the inlet velocity and pressure distribution of a wind tunnel are nperformed. These empirical values are used as parameters to define boundary conditions in simulations. The Finite Element Method (FEM) at low speeds is implemented to determine the stream function by using a standard Galerkin method. Polynomial interpolations are employed to modify the contraction section design, and numerical simulations are performed in order to compare the numerical results of the flow for the existing and the modified wind tunnels. Results: Experimental measurements of the flow at the wind tunnel entrance are presented. The velocity field and distribution of thermodynamic variables inside the tunnel are numerically determined. This computations are useful since it is experimentally difficult to make measurements inside the channel. Additionally, numerical calculations of these variables are presented under modifications in the tunnel geometry. Conclusions: A comparison between these simulations show that laminar flow at low velocities can be modeled as incompressible and irrotational fluid under a bidimensional approximation along its longitudinal section. It is observed that modifications in the geometry of the tunnel can improve the flow in the test section of the wind tunnel in the laminar regime.

Numerical simulation and experiment of grain motion in the conveying system of ratooning rice harvesting machine

The mixtures, grains, and residues in the ratooning rice harvesting machine need to be conveyed forward, backward, upward, and downward. Due to such operations, often accumulation and blockage take place at the intersection of a horizontal-vertical screw conveyor, resulting in low efficiency, high power consumption, and even grain damage. In this study, a CFD-DEM approach was applied to address the above problems. Firstly, a pneumatic conveying device was designed for ratooning rice, and then the motion of the rice grains and airflow field was analyzed in detail. The effects of different cross-sectional heights and lengths of the contraction section related to the mixing cavity were examined. Finally, the three-factor quadratic regression orthogonal rotational combination method was adopted in the experiment, and the fan velocity, filling coefficient, and speed of the horizontal screw conveyor were taken as test factors. The results showed that with the increasing cross-sectional height of the contraction section in the mixing cavity, the grain velocity decreased and the dispersity increased. With increasing length of the contraction section in the mixing cavity, the area of the high-speed airflow zone increased and the diffusion effect was enhanced. At the fan velocity of 2700 r/min, the filling coefficient was 0.41, the speed of the horizontal screw conveyor was 1173 r/min, and the outlet flow optimization index was the highest, which was 45.9% higher than that obtained without airflow. Keywords: ratooning rice, screw conveyor, grain motion, harvesting machine, CFD-DEM DOI: 10.25165/j.ijabe.20221503.6681 Citation: Liu W J, Luo X W, Zeng S, Zang Y, Wen Z Q, Zeng L, et al. Numerical simulation and experiment of grain motion in the conveying system of ratooning rice harvesting machine. Int J Agric & Biol Eng, 2022; 15(3): 103–115.

Research on the Arbitrary Right of Revocation of Gift Contract

As a typical kind of gratuitous contract, gift contract is an important part of the contract section of our civil code. The right of revocation in the gift contract is an important part of the gift system, and it also gives the donor a certain right of estoppel in law. However, due to the imperfect provisions of our laws on the right of arbitrary revocation, and the different legislations of various countries on whether to establish the right of arbitrary revocation in the gift contract, it is necessary to discuss the necessity of our country on the right of arbitrary revocation in the gift contract and study the improvement methods of this system.

Investigation of the Perfect Hydraulic Jump in Horizontal Rectangular Channel

Accelerating the process of transition from supercritical to subcritical flow, by formation a forced hydraulic jump at the contract section (Forced perfect hydraulic jump), is one of the most important measures, in decreasing flow velocity, water energy dissipation and alleviation the scouring problem, leading to lessening the required protection length against the erosion issues in the bed of downstream of the channel. In the current study, physical model was prepared precisely at fluid mechanics laboratory in the faculty of Engineering/Alkhums at Elmergib University. Comprehensive experiments were conducted to evaluate measured and calculated characteristics of the perfect free jump, and consequently, the existence of the perfect hydraulic jump is investigated. Eventually, equation was derived that might be used to guarantee the existence of a free perfect jump, which is the limiting condition between both repelled and drowned jumps as well as, the limiting condition between both repelled and drowned jumps was graphically found.

ABOUT SELECTING THE VORTEX FLOWMETER OPTIMAL BLUFF BODY SHAPE

Vortex flow meters are becoming more widespread in many industries. This is due to the simplicity and reliability of the flow transducer, the scale linearity, the frequency measuring signal presence, low requirements for alignment and ensuring the straight sections length at the installation site, etc. Among the vortex measuring instruments, the most common are instruments with a bluff body. Such flow meters operation principle is based on measuring the vortex stripping frequency behind a streamlined body installed in the flow.
 In this case, the metrological characteristics are determined by the bluff body shape. Therefore, the search for the optimal sensing element shape and the hydraulic channel configuration of the flow meter as a whole remains an actual issue.
 The paper proposes an algorithm for solving this issue according to the criteria of the measured flow rates maximum range and the interaction efficiency of the bluff body with the measured medium flow. The first criterion value is determined from the condition that the Strouhal’s number remains unchanged; the second criterion is based on the estimation of the measured medium pressure drop and the measurement error.
 To realize the algorithm, simulation modeling is used in the Ansys Fluent fluid simulation software, which uses computational fluid dynamics methods. Modeling carried out for three shapes of the bluff body: a cylinder, a prism with a triangular section, a prism with a trapezoidal section, which made it possible to choose a sensitive element for further solving the multi-parameter optimization problem.
 Geometric features of the selected sensitive element shape, the limits of their change and boundary values are grounded.
 The simulation made it possible to estimate the measured flow rates range and pressure losses, as well as to determine the vortex stripping frequency, measurement error and efficiency factor for the investigated geometric model.
 To further improve the instrument metrological parameters, the authors proposed to supplement the primary transducer geometric model with gradual contraction and diffuser sections. These sections parameters are selected from the conditions of a continuous flow and the maximum measured flow rates range with a minimum pressure loss.
 The obtained results confirmed the strategy proposed by the authors. The further research prospect is to carry out simulation studies of the flow meter hydraulic channel proposed configuration for different measured media.

Simulation and Optimization of the Nozzle Section Geometry for a Suspension Abrasive Water Jet

In order to improve the life cycle and cutting ability of a suspension abrasive water jet nozzle at the same time, hydrodynamics technology, an enumeration method and multiparameter orthogonal optimization are used to optimize the nozzle section geometry, taking the inlet diameter coefficient of the nozzle, the axial length coefficient of the contraction section and the contraction section curve as optimization variables, and selecting the peak velocity and the unit flow erosion rate as the indicators, it is concluded that the optimal contraction section curve is a Widosinski curve, the optimal inlet diameter coefficient of the nozzle is 0.333 and the optimal axial length coefficient of the contraction section is 2.857. Compared with the commercial product single cone nozzle, the performance of the optimal section nozzle improves by 5.64% and the life cycle increases by 43.2%. On this basis, the effects of operating parameters, including inlet pressure, abrasive particle flow rate and abrasive particle size, are further studied. It is determined that the optimal section nozzle has the best performance under the above operating parameters. It is demonstrated that by optimizing the nozzle section geometry, the cutting capacity and life cycle of the nozzle are improved, the performance of the nozzle can be significantly improved and the optimization of the performance of the nozzle is realized.

Design and analysis of smoke flow visualization apparatus for wind tunnel

In the present study, the design and analysis of smoke generator are done for the low-speed wind tunnel. The wind tunnel fan is fitted with the Variable Frequency Drive to produce the wind speed in the range of 3 to 32 m/s with fan speed of 150 to 1500 rpm. The design of smoke generator was done according to Preston Sweeting mist generator principle corresponding to the free stream velocity of 3 m/s. A controlled smoke generator consisting of kerosene reservoir, controlled heater, blower, liquid column height adjustment mechanism, valves etc. was designed and fabricated. The smoke generator produced the smoke at the rate of 154 cm3/s which was close to the design flow rate of 149 cm3/s. To supply the required quantity of smoke in the wind tunnel, the smoke rake of NACA 0010 profile was developed and installed in the rapid contraction section of the wind tunnel to achieve the streamlined flow. The parametric studies were done on the smoke generator at different power inputs and its effects were studied on smoke temperature, smoke discharge and boiling time of the kerosene. The flow visualization was carried out on NACA 0015 airfoil model and the images were captured to examine the flow physics around them under different operating conditions.

Impacts of structural parameters of baffle plate on jetting pigging robot in the underwater oil and gas pipeline

During the operation of oil and gas transportation pipeline, condensate forms on the inner wall of the pipeline can lead to reduced transportation efficiency and potential safety hazards. Pigging is a widely used technology to remove deposition in pipelines. From the studies, it is found that the effect of pigging largely depends on the structure of the pig. The jetting pig is a new type of pigging device designed to prevent the blocking in the pigging process, and its baffles play an important role in guiding the jet fluid. In this paper, the impact of the structure of the baffle plate on the downstream flow field of the jetting pig is simulated and analyzed. The surface of the baffle plate is changed by using the curve of the contraction section of the water tunnel. It is found that the baffle plate structure has a great influence on the flow field at the outlet of the jet pig: (1) The increase of buffle area leads to the increase of turbulent kinetic energy and the decrease of velocity; (2) The rise of edge angle lead to the regular change of turbulent kinetic energy; (3) Different curved surfaces make the change of turbulent kinetic energy and velocity. The results in this study are helpful for a better understanding of mechanism of jetting pig and improved design of mechanical structure for improved pigging performance.

Flame characteristics of a high-pressure LOX/H2 rocket combustor with large optical access

Hot fire tests were performed with a newly developed single-injector research combustor featuring a large optical access (255 × 38 mm) for flame imaging. Within these tests the propellant combination of liquid oxygen and cold gaseous hydrogen (LOX/H2) has been used at chamber pressures up to 70 bar and ratios of oxidizer to fuel (ROF) at the main injector of 3.4–6. The large optical access enabled synchronized flame imaging using OH* and blue radiation wavelengths covering an area of the combustion chamber from the injection plane to shortly before the contraction section of the nozzle. High-speed flame imaging was realized for three different operating conditions. Combined with data from temperature, pressure and unsteady pressure sensors high-quality validation data for numerical modeling has been gained. Several key dimensions of the flame topology were extracted from the imaging. The change in flame topology in response to different operating conditions is consistent with expectations from the literature, in particular the dependence of flame opening angle on injection momentum flux ratio. Using OH* imaging for such topology measurements was found to have less uncertainty than with blue radiation imaging.

Experimental and numerical investigation on a supersonic inlet with large bleed window

AbstractThe design of a two-dimensional supersonic inlet with large bleed window at low Mach number was developed. Numerical simulation and wind tunnel experiments were carried out to investigate the aerodynamic performance and variable geometric rules of the inlet. The result indicates that the single-degree-of-freedom variable geometry scheme adopted in this paper guarantees the steady work of the inlet over a wide speed range. The large bleed window caused by rotation of the compression ramp appears near the throat at low Mach number. Low-pressure airflow near the bleed window neutralises the original high-pressure airflow behind the shock train, which decreases the overall pressure of the downstream region of the internal contraction section. To match the lower pressure, the structure of the shock train changes from strong $\lambda$-type to weak $\lambda$-type, and finally to a normal shock wave as backpressure increases at Mach number 2.5. Herein, the total pressure recovery coefficient of the inlet near the critical condition improves by 8.5% as the backpressure ratio (Pe/P0) adds from 13 to 14.6 at Mach number 2.5. It proves that the scheme is effective on terminal shock wave control and inlet performance improvement. In addition, due to the background wave and the bleed window, two kinds of shock wave oscillation occur when the backpressure ratio is 13.1.

Wet gas measurements of long-throat Venturi Tube based on forced annular flow

A wet gas dual-parameter measuring device composed of a cyclone and a long-throated Venturi tube is proposed to overcome the difficulty of measuring the liquid content of wet gases and reduce the error caused by the wet gas flow pattern. The flow pattern is transformed into an annular flow by a cyclone. In this study, the proposed device was compared with a traditional non-cyclone long-throat Venturi tube; furthermore, the pressure difference ratio W between the contraction and expansion sections of the long-throat Venturi tube was introduced as a parameter. Through numerical simulations, the relationship between W, the gas Froude number, over-reading, and liquid-gas mass flow ratio was analyzed, and a new wet gas flow measurement model was established. The reliability of the measurement model was verified through indoor experiments. The experimental results showed that the traditional wet gas measurement device had gas phase and liquid phase errors of ±4.5% and ±10%, respectively; on the other hand, the cyclone-based wet gas measurement device had gas phase and liquid phase errors of ±3% and ±8%, respectively. Thus, the performance of the wet gas measurement device with the cyclone was higher than that of the traditional wet gas measurement device.

Hydrologic and hydraulic assessment of scour problems at bridge sites in Tigray region, northern Ethiopia

This study was conducted to assess scour problems at three selected bridge sites in the Tigray region, northern Ethiopia, namely the Ilala, upper Geba, and Tankwa bridges. Smart-GIS, ArcGIS, Hydrologic Engineering Centre Hydrologic Modeling System (HEC-HMS), and Hydrologic Engineering Centre River Analysis System (HEC-RAS) were used for the river morphology, hydrologic, and hydraulic analysis. The riverbanks were subjected to higher degradation and instability problems. The estimated 100-year flows were 272.5, 940.4, and 249.9 m3/s for Ilala, upper Geba, and Tankwa bridges, respectively. Flow depth calibration were resulted in model performance with Nash Sutcliffe Efficiencies of 0.90, 0.88, and 0.87 for Ilala, upper Geba, and Tankwa bridge sites, respectively. Scour depths were 1.3, 1.6, and 0.8 m at contracted sections; 3.2, 3.0, and 2.2 m at the piers; 2.6, 3.6, and 2.2 m at the left abutment; and 1.6, 3.0, and 2.1 m at the right abutment of Ilala, upper Geba, and Tankwa bridges, respectively. The use of riprap at the bridges resulted in the reduction of scour depths by 60–100%. Overall, the hydrologic and hydraulic models performed well.

PIV investigation of cavitating flows around circular cylinders with hydrophobic coatings

The treatment of the hydrophobic properties of solid surfaces is considered as a passive method to reduce the drag in water flows (Rothstein, 2010) and to potentially affect the flow separation and vortex shedding (Sooraj et al., 2020). The manufacturing of surfaces with micro- and nano-scale roughness allows to extend the hydrophobicity towards superhydrophobicity with the contact angle close to 180°. In such conditions the solid surface is not wetted completely and the air-water interphase partially remains on the surface texture. This results in so-called flow slip effect. Therefore, a local phase transition during the flow cavitation or gas effervescence in near-wall low-pressure regions may additionally affect the slip effect for hydrophobic surfaces. The present work is focused on the comparison between cavitating and noncavitating flows around circular cylinders with lateral sectors with hydrophobic and non-hydrophobic coatings. The experiments are performed in a water tunnel, which consists of a water outgassing and cooling/heating section, honeycomb, contraction section, test section and diffuser. The water flow is driven by an electric pump, providing a bulk velocity up to 10 m/s in the transparent test section with 1 m length and 80×150 mm2 rectangular cross-section. The facility is equipped with an ultrasonic flowmeter, temperature and pressure sensors. Besides, the static pressure inside the water tunnel can be varied by using a special shaft section. The measurements are performed by using high-repetition and low-repetition PIV systems. The former is used for the analysis of large-scale flow dynamics in the wake region, whereas the latter one is used for high-resolution measurements in near-wall regions by using a long-distance microscope. The Reynolds number based on the bulk velocity of the flow, diameter of the cylinders (D = 26 mm) and kinematic viscosity of the water is varied up to 2×105..

Parameterization and optimization design of a two-dimensional axisymmetric hypersonic inlet

Optimization method, as a promising way to improve inlet aerodynamic performance, has received increasing attention. The present research is undertaken to design a two-dimensional axisymmetric hypersonic inlet using parametric optimization. The inlet configuration is parameterized and optimized in consideration of total pressure recovery and starting performance. A Pareto front is obtained by solving the multi-objective optimization problem. Then, the flow structures of the optimized inlets are analyzed and the starting performances are evaluated. Results show that the total pressure loss mainly occurs in the internal contraction section, especially near the inlet entrance, and therefore the total pressure recovery coefficient can be greatly improved by decreasing external compression. As a result, the guidance for designing high-performance inlets is concluded. Besides, it is found that as the internal contraction ratio increases, the inlet starting ability becomes worse, which attributes to the larger separation bubble at the inlet entrance. Finally, the total pressure recovery coefficient and the starting Mach number of the optimized inlets are obtained, which can be a reference for engineering design.

Investigation of amplification process of heavy oil viscosity reduction device based on jet cavitation using lab experimental and numerical simulation method

ABSTRACT With the increasing requirement of global energy resources, researchers seek for new ways to deal with unconventional crude oil resources. Using the Computational Fluid Dynamics numerical simulation method, the standard k-ɛ turbulence model and the cavitation dynamics model are used to simulate the internal flow field of the 105t/a heavy oil viscosity reduction spray nozzle device which is designed by the jet cavitation theory. The jet cavitation intensity is evaluated by cavitation number and gas content. The influence of spray nozzle structural parameters such as inlet diameter, contraction length, expansion cone angle and expansion length on the cavitation effect of the spray nozzle are studied. The results show that the cavitation effect is the best when the inlet diameter, contraction section length, expansion section cone angle, and expansion section length of the large capacity device are 120 mm, 110 mm, 10°, and 150 mm, respectively. A laboratory test device with a processing capacity of 2000 t/a is built to conduct jet cavitation test on a batch of Saudi crude oil to obtain the change rate of crude oil viscosity, density and molecular weight. The numerical results are consistent with the outcome of laboratory experiments, and it is concluded that this spray nozzle can meet the needs of large processing capacity while ensuring a high cavitation rate.

Experimental and theoretical modeling of a quarter-circular gate flow

Gates are important hydraulic structures and used for flow measurement, water delivery, and water level regulation in open channels and irrigation networks. In this study, the quarter-circular gate is introduced and investigated. The cross section of this gate consists of a quarter circular arc and the lip angle of the gate equals to zero. Discharge coefficient, variation of downstream flow depth, and velocity distribution at opening section of gate were experimentally measured. Using potential flow theory supported by dimensional analysis, equations for discharge coefficient and velocity distribution at gate opening section of quarter-circular gate were derived and then validated using experimental data. The mean percentage error (MPE) of obtained equation for discharge coefficient of quarter-circular gate was calculated as 2.24%, indicating the high precision of the proposed theory. Based on obtained results, downstream flow depth of quarter-circular gate is uniform. Also, velocity distribution at gate opening section is nearly uniform. Discharge coefficient of quarter-circular gate was averagely obtained 55% larger than that of sluice gate. It was also obtained larger than that of radial gate. Elimination of contraction section at downstream of gate opening, which is the main source for energy loss and therefore discharge capacity reduction, is the main reason for larger discharge coefficient of quarter-circular gate.

Logistics of deep tunnel construction sites without portal access – SBT2.1 Semmering Base Tunnel

AbstractThe 27.3 km long Semmering Base Tunnel is a major component of the Baltic‐Adriatic Corridor trans‐European rail link. The SBT2.1 Fröschnitzgraben Tunnel section involves more construction work than any other contract section of the Semmering Base Tunnel project. First, two shafts over 400 m deep had to be sunk down to tunnel level in order to create the emergency station. From here, the tunnels are being driven towards Gloggnitz and Mürzzuschlag. The falling drives towards Gloggnitz, each approx. 8.5 km long, are being excavated with two tunnel boring machines (TBM), while conventional tunnelling methods (drill and blast) are being used to drive the 4.3 km long rising section towards Mürzzuschlag. Another major component of the contract is the creation and management of the Longsgraben landfill site.With a complex construction project of this nature, the local conditions, changing construction phases, different tunnelling methods, geological conditions, safety and contractual aspects, and the long duration of the construction, must all be given careful consideration when planning the logistics. The overall scope of logistics is broken down into individual areas; this enables several logistical concepts to be developed which do not necessarily have to correlate with one another. Through the involvement of the client, it has been possible to develop efficient and, for the most part, straightforward organisational measures and solutions for this construction project.