Development of Two-Dimensional Bubble Movement and Development Benchmark Dataset for Numerical Validation

2012 ◽  
Author(s):  
Gholamreza Keshavarzi ◽  
Tracie J. Barber ◽  
Guan Yeoh
Keyword(s):  
High Speed ◽  
Numerical Models ◽  
Experimental Studies ◽  
Fluid Flows ◽  
Full Time ◽  
Two Phase ◽  
Point Of Interest ◽  
Time Shape ◽  
Computational Resources ◽  
Bubble Movement

The motion and transport of bubbles in fluid flows have many engineering applications. The rise of a bubble has been a point of interest for both numerical and experimental studies. Various tracking methodologies have been developed, including markers, level sets and volume tracking. In order to validate numerical models of bubble flow, detailed experimental data describing the transient bubble shape is needed. This is best found from a 2D comparison rather than 3D experiment because computational resources for determining an accurate shape can be maximized. No real full time shape and subsequent deformation of this 2D bubble has yet been demonstrated. In this paper 2D bubble experiments have been conducted, in which a single bubble has been injected inside a close-walled tank and the rising of the bubble has been captured through a high speed camera. This data is now being used as a benchmark for numerical interface capturing and two phase flow methodology validations.

scholarly journals Numerical and Experimental Study of Phase Transformations in Welding Processes / Badania Numeryczne I Doświadczalne Przemian Fazowych W Procesach Spawania

2015 ◽  
Vol 60 (4) ◽  
pp. 2559-2568 ◽  
Author(s):  
W. Piekarska
Keyword(s):  
Solid State ◽  
Heat Source ◽  
Phase Transformations ◽  
High Speed ◽  
Numerical Models ◽  
Experimental Studies ◽  
Butt Joint ◽  
Heat Of Fusion ◽  
Large Temperature ◽  
Welding Processes

The paper concerns the mathematical and numerical modeling of phase transformations in solid state occurring during welding. The analysis of the influence of heating rate, cooling rate and maximum temperatures of thermal cycles on the kinetics of phase transformations is presented. On the basis of literature data and experimental studies the evaluation of classic mathematical and numerical models of phase transformation is presented with respect to the advanced methods of welding by using a high speed and a high power heat source. The prediction of the structure composition in laser welded butt-joint made of S460 steel is performed, where phase transformations are calculated on the basis of modified numerical models. Temperature distributions are determined as well as the shape and size of fusion zone and heat affected zone (HAZ). Temperature field is obtained by the solution of transient heat transfer equation with convective term and external volumetric heat source taken into account. Latent heat of fusion, evaporation and heats generated during phase transformations in solid state are considered in the numerical algorithm due to the large temperature range present in analyzed process. Results of the numerical prediction of structure composition in HAZ are presented in this work. Obtained results of computer simulations are compared to experimental research performered on the laser welded joint.

Investigation of Material Deformation by the High-Speed Water Slugs

2002 ◽  
Author(s):  
O. Petrenko ◽  
E. S. Geskin ◽  
G. A. Atanov ◽  
B. Goldenberg ◽  
A. Semko
Keyword(s):  
Shock Waves ◽  
Nozzle Exit ◽  
High Speed ◽  
Numerical Models ◽  
Water Pressure ◽  
Experimental Studies ◽  
Surface Cleaning ◽  
Water Velocity ◽  
Material Deformation ◽  
The Impact

Water constitutes an attractive manufacturing tool It is readily available and clean. The waterjets are conventionally used for surface cleaning, material removal, and surface modification. The intrinsic shortcomings of such an application are the need in the use of expensive and heavy pumping facilities and, what are more important, peculiarities of the waterjet-substrate interaction which limit material deformation by the incoming jet. These shortcomings are eliminated if the workpiece is impacted by the array of the water slugs, generated by the direct injection of high-intensity energy pulses into the water vessel (barrel) and ejection the portion of the water via the nozzle attached into the barrel. Such a device (barrel-nozzle combination) will constitute an effective and versatile manufacturing tool. Understanding of the phenomena that occur in the course of the energy injection into the water is necessary for the design of the desired device. The phenomena in question are determined by the ratio between the speed of the water in the barrel in the course of the energy injection and the speed of the shock waves in the water. If this ratio is much less than unity, the exit velocity is determined by the ratio between the cross section areas of the nozzle exit and the barrel. If the ratio in question approaches the unity, the water velocity at the nozzle exit is determined by the impact pressure. The device utilizing this principle is termed the water extruder. If however, the ratio is much more than unity the exit water velocity is determined by the superposition of shock waves developed in the fluid. This device termed the water cannon is able to accelerate the water slug to the speed far exceeding 1,000 m/sec. The numerical and experimental studies of water extruder were carried out. The numerical models were constructed and the variation of the water velocity and the water pressure in the barrel were investigated. Experimental setup for the study of the water extruder was constructed by the modification of Remington power tool. The experiments involved the piercing of metal strips. The effect of operational conditions on the maximal depth of the piecing was determined. Another series of experiments involved the study of the slug impact on plastic (lead) and brittle (concrete) materials. The effect of the stand off distance on the removal of both kinds of material was investigated. As the result the suggestions about the way of construction of the water extruders and their practical applications were made.

scholarly journals Electromagnetic reducers in electromechanical systems

2021 ◽  
pp. 42-46
Author(s):  
Igor Tkachuk ◽  
Mykhailo Kovalenko
Keyword(s):  
Wind Turbines ◽  
High Speed ◽  
Numerical Models ◽  
Mechanical Energy ◽  
Experimental Studies ◽  
Total Weight ◽  
Electromechanical Systems ◽  
Low Speed ◽  
Electric Generator ◽  
Additional Noise

      Currently, due to the rising cost of electricity, low-power wind turbines (1-5 kW) are often used to supply consumers with electricity. In this case, wind turbines are used with both horizontal and vertical axes of rotation, the speed of which at an average wind speed V = 5 ÷ 10 m / s and is quite low, and is approximately n = 100 - 300 rpm. A low-speed electric generator for a wind generator with such a speed of rotation with a direct connection of the wind rotor shaft and the electric generator has a large number of poles and reaches a fairly large size. Therefore, magnifying gears (multiplexers) are often used and can increase the speed of the electric generator several times and, thus, reduce the mass of its active part, because the electromagnetic moment is proportional to the volume of the electric machine. However, manual transmissions are a source of additional noise, require frequent maintenance and reduce the durability of the wind turbine. This article will use permanent magnet reducers for wind turbines, which, unlike mechanical reducers, do not create additional noise, do not require lubrication, their durability is higher, operating costs are also significantly reduced, while the magnetic reducer can be integrated with an electric generator. at a wind rotor power P = 4 kW and speed n = 100-300 rpm, high-speed electric generator and magnetic reducer have approximately 2 times less total weight of magnets and 1.7 times less total weight of active materials (magnetic reducer + electric generator) than a low-speed multipole external generator. The aim of the study is to develop and implement an electromagnetic reducer in electromechanical systems. The basis of such systems are high-coercive magnets. To achieve this goal, the following tasks are set: - literary-patent search on the research topic; - selection of a prototype of a magnetic reducer and calculation of its main parameters; - development of graphical and numerical models to evaluate the effectiveness of the developed prototype; - optimization of the design of the magnetic reducer; - development of a system for converting mechanical energy with low potential into electricity; - prototyping and experimental studies of the system of conversion of mechanical energy with low potential into electrical energy

Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part II — The Development of Prediction Criteria

2020 ◽  
Author(s):  
Carlo Cravero ◽  
Davide Marsano
Keyword(s):  
High Speed ◽  
Numerical Models ◽  
Fluid Dynamic ◽  
Stability Limit ◽  
Design Phase ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Vaned Diffuser ◽  
The Stability ◽  
Computational Resources

Abstract The challenge to be able to predict the stability limit in high speed centrifugal compressor is particularly strategic in an initial design phase. Furthermore, to be able to predict the limit massflow rate through the use of simplified numerical models (which does not require excessive computational resources) is very important. In the literature there are several methods to predict the chocking condition, while there is a lack as regards the surge condition. The authors have already presented a criterion to predict the surge line valid for centrifugal compressors with vaned diffuser. Instead those with vaneless diffuser have a very different behavior. For this reason, in the first paper an in-depth fluid dynamic analysis has been carried out, in order to identify the main phenomena linked to the trigger of instability in this type of compressors. This analysis has allowed understanding that the rotational speed is a discriminating factor in the phenomenology. In this second part, using the previous information, different criteria to predict the limit massflow rate for centrifugal compressors with vaneless diffuser are described. All the criteria are based on different simplified CFD approaches that can be routinely used during the design phase.

Flow Boiling in Microgaps for Thermal Management of High Heat Flux Microsystems

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Xuefei Han ◽  
Andrei Fedorov ◽  
Yogendra Joshi
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Flow Boiling ◽  
Experimental Studies ◽  
High Heat ◽  
Bubble Nucleation ◽  
Inlet Temperature ◽  
High Heat Flux ◽  
Two Phase ◽  
Outlet Pressure

In the first part of this paper, a review of fundamental experimental studies on flow boiling in plain and surface enhanced microgaps is presented. In the second part, complimentary to the literature review, new results of subcooled flow boiling of water through a micropin-fin array heat sink with outlet pressure below atmospheric are presented. A 200 μm high microgap device design was tested, with a longitudinal pin pitch of 225 μm, a transverse pitch of 135 μm, and a diameter of 90 μm, respectively. Tested mass fluxes ranged from 1351 to 1784  kg/m2s, and effective heat flux ranged from 198 to 444 W/cm2 based on the footprint surface area. The inlet temperature varied from 6 to 12 °C, and outlet pressure ranged from 24 to 36 kPa. The two-phase heat transfer coefficient showed a decreasing trend with increasing heat flux. High-speed visualizations of flow patterns revealed a triangular wake after bubble nucleation. Flow oscillations were seen and discussed.

Experimental Characterization of the Flow Instabilities of a Mixed-Flow Multiphase Pump Operating Air and Water Through Local Visualization and Analysis of Dynamic Measurements

2015 ◽  
Author(s):  
Alberto Serena ◽  
Lars E. Bakken
Keyword(s):  
High Speed ◽  
Numerical Models ◽  
Operating Conditions ◽  
Test Facility ◽  
Two Phase ◽  
Flow Mechanisms ◽  
Local Measurements ◽  
Specific Geometry ◽  
Promising Development

Part load operation of pumps generates flow and machine instabilities, which are not desirable and should be avoided as they result in premature wear and mechanical problems. Two-phase flow introduces additional challenges, both at the design and operational stages, due to the different phase behavior and mutual interaction. The phenomena involved present an intermittent character and are strongly dependent on the specific geometry and operating conditions. Despite the recent promising development of numerical simulations capabilities, an accurate characterization of the flow mechanisms still relies on real tests, which are needed to validate the numerical models too. An advanced laboratory test facility built at the Norwegian University of Science and Technology provides the required optical access to the pump channels, and high-speed recordings, along with local measurements of the pressure pulsations, allow to describe the flow structures in terms of location, length and time scales, and relate them to overall machine measurements, such as flow, pressure and torque. This provides a wide collection of test data of great value for a further understanding of the surging phenomenon, the development of a surging onset prediction model and a control strategy. Tests are performed covering the whole range of flow rates; a characteristic surging condition is identified and described in the article.

The Oscillation Behaviour of Liquid Metal in Arc Welding

2007 ◽  
Vol 539-543 ◽  
pp. 3877-3882 ◽  
Author(s):  
M.J.M. Hermans ◽  
B.Y.B. Yudodibroto ◽  
Yoshinori Hirata ◽  
G. den Ouden ◽  
I.M. Richardson
Keyword(s):  
Liquid Metal ◽  
Weld Pool ◽  
Arc Welding ◽  
High Speed ◽  
Numerical Models ◽  
Experimental Studies ◽  
Intermediate Step ◽  
Filler Wire ◽  
Research Activities ◽  
Penetration Control

This paper gives an historic overview and new developments of research activities in the field of the oscillatory behaviour of liquid metal in arc welding. Early work focused on the oscillation behaviour of the weld pool in Gas Tungsten Arc Welding (GTAW). Agitated weld pools exhibit specific modes of oscillation, the frequency of which can be measured from the arc voltage data and is conditioned by the geometry of the weld pool and the properties of the liquid metal. Of technological interest is the alteration of the oscillation behaviour for partially and fully penetrated situations, which can be used for penetration control during welding. A logical extension of the research activities was related to the influence of filler wire addition on the oscillation behaviour. An intermediate step towards the description of Gas Metal Arc Welding (GMAW), is the situation of GTAW with cold filler wire supply. It was found that both the liquid weld pool and the pendant liquid droplet at the tip of the filler wire experience an oscillation, which obscures the influence of the individual contributions of both liquid masses on the voltage data. It was shown that online penetration control is still possible, provided that the metal is transferred in an uninterrupted way, i.e. the filler wire flows smoothly into the weld pool. For GMAW, in which detached droplets collide with the weld pool surface, the difficulties are even more prominent. Recent work is related to this issue. Monitoring of the phenomena occurring at the weld pool and the pendant droplet become problematic by means of the voltage data. Observations by means of high-speed video imaging will be discussed. Apart from the experimental studies, efforts are undertaken in numerical simulations of the processes. A good correlation is obtained between experimental data and the results of the numerical models.

scholarly journals Dynamics of dry spots in the liquid film moved by the gas flow in the mini-channel under intensive local heating

2018 ◽  
Vol 194 ◽  
pp. 01059
Author(s):  
Egor Tkachenko
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Gas Flow ◽  
Local Heating ◽  
Experimental Studies ◽  
Heater Surface ◽  
Two Phase ◽  
Heat Transfer Crisis ◽  
Typical Size ◽  
Dry Spot

Experimental studies of hydrodynamics and the heat transfer crisis were carried out for a two-phase stratified flow in a mini-channel with intensive heating from a heat source of 1x1 cm2. It has been established that as the heat flow increases, the total area of dry spots on the heater increases, but when a certain temperature of the heater surface reaches ≈100 °C, the area of dry spots begins to decrease. With the help of high-speed visualization (shooting speed 100000 frames per second), several stages of formation of a dry spot (a typical size of the order of 100 microns) were isolated. It was found that at a heat flux of 450 W/cm2 about 1 million dry spots per 1 second are formed and washed on the surface of the heater (1 cm2). The speed of the contact line when dry spot is forming reaches 10 m/s.

scholarly journals The Thermal—Flow Processes and Flow Pattern in a Pulsating Heat Pipe—Numerical Modelling and Experimental Validation

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5952
Author(s):  
Przemysław Błasiak ◽  
Marcin Opalski ◽  
Parthkumar Parmar ◽  
Cezary Czajkowski ◽  
Sławomir Pietrowicz
Keyword(s):  
Heat Pipe ◽  
High Speed ◽  
Numerical Models ◽  
Input Parameter ◽  
Experimental Studies ◽  
Internal Flow ◽  
Numerical Analyses ◽  
Flow Structures ◽  
Pulsating Heat Pipe ◽  
Fixed Temperature

The aim of the article is to numerically model a two-dimensional multiphase flow based on the volume of fluid method (VOF) in a pulsating heat pipe (PHP). The current state of knowledge regarding the modeling of these devices was studied and summarised. The proposed model is developed within open source software, OpenFOAM, based on the predefined solver called interPhaseChangeFoam. The analyses were carried out in terms of the influence of four different mass transfer models between the phases, proposed by Tanasawa, Lee, Kafeel and Turan, and Xu et al. on the shape and dynamics of the internal flow structures. The numerical models were validated against data obtained from a specially designed experimental setup, consisting of three bends of pulsating heat pipes. The numerical calculations were carried out with ethanol being treated as a working medium and the initial and boundary conditions taken directly from the measurement procedures. The variable input parameter for the model was the heat flux implemented in the evaporation section and a fixed temperature applied to the condensation section. The flow structures obtained from the numerical analyses were compared and discussed with the flow structures gained from experimental studies by employing a high speed camera. In addition, to verify the quantitative results obtained from the numerical analyses with the experimental data, a technique called particle image velocimetry (PIV) was used for the velocity vector field. For the analysed velocity ranges, the relative error obtained was reached at the level of 10%.

scholarly journals A New Method of Selecting the Airlift Pump Optimum Efficiency at Low Submergence Ratios with the Use of Image Analysis

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 735 ◽  
Author(s):  
Grzegorz Ligus ◽  
Daniel Zając ◽  
Maciej Masiukiewicz ◽  
Stanisław Anweiler
Keyword(s):  
High Speed ◽  
Two Phase Flow ◽  
Experimental Studies ◽  
New Method ◽  
Optimum Operating ◽  
Phase Flow ◽  
Two Phase ◽  
Gas Flux ◽  
Riser Pipe ◽  
Airlift Pump

This paper presents experimental studies on the optimization of two-phase fluid flow in an airlift pump. Airlift pumps, also known as mammoth pumps, are devices applied for vertical transport of liquids with the use of gas. Their operating principle involves the existence of a density gradient. This paper reports the results of experimental studies into the hydrodynamic effects of the airlift pump. The studies involved optical imaging of two-phase gas-liquid flow in a riser pipe. The visualization was performed with high-speed visualization techniques. The studies used a transparent model of airlift pump with a rectangular cross-section of the riser. The assessment of the airlift pump operation is based on the image grey-level analysis to provide the identification of two-phase flow regimes. The scope of the study also involved the determination of void fraction and pressure drops. The tests were carried out in a channel with dimensions 35 × 20 × 2045 mm with the gas flux range 0.2–15.0 m3/h. For the assessment of the two-phase flow pattern Probability Density Function (PDF) was applied. On the basis of the obtained results, a new method for selecting the optimum operating regime of airlift pump was derived. This method provides the finding of stability and efficiency of liquid transport. It can also be applied to determine the correlation between the total lifting efficiency and the required gas flux for proper operation of the airlift pump.

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