Secondary Flow in Smooth and Rough Turbulent Circular Pipes: Turbulence Kinetic Energy Budgets

Direct Numerical Simulations have been performed for turbulent flow in circular pipes with smooth and corrugated walls. The numerical method, based on second-order finite discretization together with the immersed boundary technique, was validated and applied to various types of flows. The analysis is focused on the turbulence kinetic energy and its budget. Large differences have been found in the near-wall region at low Reynolds number. The change in the near-wall turbulent structures is responsible for increase of drag and turbulence kinetic energy. To investigatselinae the effects of wall corrugations, the velocity fields have been decomposed so as to isolate coherent and incoherent motions. For corrugated walls, we find that coherent motions are strongest for walls covered with square bars aligned with the flow direction. In particular, the coherent contribution is substantial when the bars are spaced apart by a distance larger than their height. Detailed analysis of the turbulence kinetic energy budget shows for this set-up a very different behavior than for the other types of corrugations.

Multiphase Flow in Circular and Triangular Pipes: Examining Flow Characteristics, Sand Erosion and Heat Transfer Via CFD and Experimental Work

Air-water two-phase flow in circular pipes has been studied by many investigators. However, investigations of multiphase flow in non-circular pipes are still very rare. Triangular pipes have found a number of applications, such as multiphase flow conditioning, erosion mitigation in elbows, compact heat exchanges, solar heat collectors, and electronic cooling systems. This work presents a survey of air-water and air-water-sand flow through circular and triangular pipes. The main objective of this investigation is to study the potential effects of triangular pipe geometry on flow patterns, slug frequency, sand erosion in elbows, and heat transfer in multiphase flow. Firstly, twenty-three experiments were performed for horizontal air-water flow. Detailed videos and slug frequency measurements were collected through circular and triangular clear pipes to identify flow patterns and create a database for these pipe configurations. The effect of corners of the triangular pipe on the liquid distribution was investigated using two different orientations of triangular pipe: apex upward and downward and results of triangular pipes were compared to round tubes. Secondly, ultrasonic wall thickness erosion measurements, paint removal studies, and CFD simulations were carried out to investigate the erosion patterns and magnitudes for liquid-sand and liquid-gas-sand flows in circular and triangular elbows with the same radius of curvature and cross-sectional area. Thirdly, heat transfer rates for liquid flows were also simulated for both circular and triangular pipe cross-sections. Although similar flow patterns are observed in circular and triangular pipe configurations, the orientation of the triangular pipes seems to have an effect on the liquid distribution and slug frequency. For higher liquid rates, slug frequencies are consistently lower in the triangular pipe as compared to the circular pipe. Similarly, the triangular elbow offers better flow behavior as compared to circular elbows when investigated numerically with similar flow rates for erosion patterns for both liquid-sand flow and liquid-gas-sand flows. Experimental and CFD results show that erosion in the circular elbow is about three times larger than in the triangular elbow. Paint studies results validated erosion patterns and their relations with particle impacts. Finally, heat transfer to/from triangular pipes is shown to be more efficient than in circular pipes, making them attractive for compact heat exchangers and heat collectors. This paper represents a novel experimental work and CFD simulations to examine the effects of pipe geometries on multiphase flow in pipes with several practical applications. The present results will help to determine the efficiency of utilizing triangular pipes as compared to circular pipes for several important applications and field operations such as reducing slug frequencies of multiphase flow in pipes, and reducing solid particle erosion of elbows, and also increasing the efficiency of heat exchangers.

VERIFICATION OF ELECTRICALLY CONDUCTIVE FLUID FLOW CALCULATION IN CIRCULAR PIPES

Magnetohydrodynamics (MHD) treats the phenomena that arise in fluid dynamicsfrom the interaction of an electrically conducting fluid with the electromagnetic field. Thedevelopment of computational hydrodynamics has significantly improved the accuracy ofcalculations on mathematical models, but it is still difficult to choose the optimal turbulence models,mesh quality, model parameters to solve a particular problem. The aim of the work is to verify thecalculation of the conducting fluid flow in circular pipes and to determine the optimal error of theturbulence model calculation and the parameters of its use. The study was conducted on the basis ofa comparison of experimental studies by the PIV-method of velocimetry with the results of numericalcalculations. The liquid is considered viscous, incompressible, and electrically conducting. Controlnonlinear momentum equations are solved numerically using the method of control volumes.Comparison of velocity profiles showed that almost all models show a fairly good match with theresults of the experiment. Analysis of the sum of squares residuals of calculation points fromexperimental shows that the BSL Reynolds Stress turbulence model is the best for the flow withoutthe influence of the magnetic field, and the k-ɛ model is the best in the presence of a magnetic field.The SST k-ω model has quite enough results regardless of the Hartmann number. The number ofmesh elements has little effect on the ac-curacy of the pressure drop calculation. For simplegeometries it is enough to use meshes with the number of elements that does not exceed the 500000elements. According to all criteria, it is rational to choose the k-ɛ turbulence model for furthercalculations. This model has some shortcomings in the calculation of wall layers, but allows to obtainhigh-quality and adequate results for the flow of conducting fluid with a limit on the mesh elementsnumber.

Drag Reduction Using Additives in Smooth Circular Pipes Based on Experimental Approach

Reduction of fluid resistance using the rheological characteristics of a polymer-surfactant solvent is research that contains many aspects, such as the theory of the drag reduction process, historical journey, and ongoing current research development. Many studies have been conducted, but it is challenging to know all existing and new research threads. The present investigation was conducted using literature studies regarding drag reducing agents. This research will also discuss the characteristics of flowing fluids and their effects on the velocity profile with friction factor of flowing fluids in smooth circular straight pipe geometries based on experimental, theoretical approaches. It concludes with aspects of research conducted around reducing drag using drag reducing agents, ideas about innovations, structuring overlook in testing, and modification of the fluid flow state.

The effect of the roller profile oncave-in defect in reshaping processby considering nonlinear combine strain hardening

The reshaping process of pipes is an important method in producing non-circular pipes. Desired profile products are produced by passing round pipe through the rotating rollers. Cave-in defect is one of the common defects in the reshaping process. Roller design issues can decrease this kind of defect. In this paper, a method based on the slab method and the incremental plasticity has been presented to the numerical study of a 2D reshaping process. For investigating the Cave-in defect, the contact model has been developed. The concept of element elongation has been introduced to increase the accuracy of the contact model. Based on the presented method, numerical software has been developed to simulate the 2D reshaping process. Elastic-plastic equations for this subject have been driven based on the incremental method, J yielding criterion, and non-linear combined hardening. The effects of the radius of the roller profile on cave-in defects have been investigated by using the presented software (DARF). A set of experiments has been conducted in a forming station to verify the results. Results show that the presented model has higher accuracy than the Abaqus commercial software in predicting the cave-in defect. Based on the results of the model, the local increase of yielding stress directly affects the cave-in defect. Also, a meaningful relationship between the radius of the roller and the amount of the cave-in has been observed.

The Dynamic and Strength Analysis of an Articulated Covered Wagon with the Circular Pipe Design

An articulated covered wagon design was developed. The wagon feature is that the body-bearing elements are made of circular pipes. This technical solution made it possible to reduce the tare weight of the wagon while ensuring the strength conditions. Mathematical simulation of the dynamic loading of the developed articulated covered wagon design was carried out under the main operating conditions. In the calculations of the observed quantities, an application of symmetry with regard to the longitudinal axis of the wagon was used. The accelerations, as the components of the dynamic load acting on the wagon, were determined. The dynamic loading computer simulation results of the developed wagon design are also presented. The strength analysis of the articulated covered wagon supporting structure made it possible to conclude that the strength indexes were within the allowed limits. The wagon bearing structure was analyzed for fatigue strength. The weld strength analysis results of the most loaded part of the wagon-bearing structure are presented. The results obtained for the desired quantities revealed their symmetrical distribution in the wagon structure. This research will contribute to improving the efficiency of railway transport operation.

Design of Collection System Parameters Using Known Reference Pipe Method (KRPM)

The storm water drainage network is generally calculated based on the Manning equation, where the slope, roughness of the pipe wall, and flow are known, while conversely the velocity, diameter, and hydraulic radius are unknown characteristics, although they are very important for the work done by a hydraulic engineer who needs these parameters to find their values, including the students taking coursework relating to waste-water engineering. The computation of these parameters in partially full pipes and based on the Manning equation is implicit and needs to be computed using iterative and laborious methods. In this paper, a new, simple and easy method is presented based on a reference pipe with known characteristics (Known Reference Pipe Method: KRPM), as well as the effect of the up-pipe parameters on the down-pipes according to each case that is possible through the watershed drainage system arrangement, for both full and partially filled circular pipes.

Analysis of the Loading on an Articulated Flat Wagon of Circular Pipes Loaded with Tank Containers

This research is concerned with the use of double walls filled with foam aluminum for an open wagon to decrease loading during operational modes. The research presents the strength calculation for the frame of a wagon with a consideration of the engineering solutions proposed. It was found that the maximum equivalent stresses appeared in the bottom section of the center sill behind the back support; they amounted to about 290 МPа and did not exceed the allowable values. The maximum displacements were in the middle parts of the main longitudinal beams of a section, and they amounted to 8.8 mm. The research also presents the strength calculation for a weld joint in the maximum loaded zones of the frame of a wagon and reports the results of the modal analysis of the frame of the improved wagon. It was found that the oscillation frequencies did not exceed the allowable values. The results of the research may be useful for those who are concerned about designing innovative rolling stock units and improving the operational efficiency of railway transport.