bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Analysis of Droplet Impact on a Smooth Slippery Surface
Authors: Yeganehdoust F. , Karimfazli I. , Dolatabadi A. 
Published: October 2018

Spontaneous bouncing of a droplet that impacts a surface is a mechanism that occurs for the moderate range of droplet impact velocities and is caused by the formation of a stable air layer (cushion) between the droplet and the surface. This bouncing behavior is more pronounced on Lubricant Impregnated Surfaces (LISs) inspired by the natural non-wetting surface of the pitcher plant, which relies on the stable formation of a thin lubricant film across its surface.
In this study, we performed modeling of the water-oil–air interfacial surfaces using the volume of fluid (VOF) methodology to simulate the impact of a water droplet onto a lubricant smooth surface with an oil as the lubricant. To resolve the effects of the air surrounding the droplet, computational cells were extensively small to capture the presence of the sub-micron layer of air trapped underneath the droplet during the impact.
The model was able to capture the initiation and subsequent effect of the air cushion on the droplet hydrodynamics. We found that the stability of the air cushion and the impact dynamics are independent of the oil viscosity for specific thicknesses of lubricant layers, whereas the impact conditions such as velocity and droplet properties played a significant role on the outcome of droplet impact. Hence, the dynamics of a droplet falling on a specific thickness of oil film was influenced by the squeezed air trapped between the two immiscible fluid (water and oil). In addition, the formation of high pressure dimple region was evident, which in some cases lead to entrapment of the air bubble. Finally, we validated the results with the existing experimental data in the literature.
A Wall Film Model for Membrane Fouling
Authors: Mamouri Sina Jahangiri , Tarabara Volodymyr V. , Bénard André 
Published: October 2018

Deoiling of produced or impaired waters associated with oil and gas production represents a significant challenge for many companies. Centrifugation, air flotation, and hydrocyclone separation are the current methods of oil removal from produced water [1], however the efficiency of these methods decreases dramatically for droplets smaller than approximately 15–20 μm. More effective separation of oil-water mixtures into water and oil phases has the potential to both decrease the environmental footprint of the oil and gas industry and improve human well-being in regions such as the Gulf of Mexico.
New membrane separation processes and design of systems with advanced flow management offer tremendous potential for improving oil-water separation efficacy. However, fouling is a major challenge in membrane separation [2]. In this study, the behavior of oil droplets and their interaction with crossflow filtration (CFF) membranes (including membrane fouling) is studied using computational fluid dynamics (CFD) simulations. A model for film formation on a membrane surface is proposed for the first time to simulate film formation on membrane surfaces. The bulk multiphase flow is modeled using an Eulerian-Eulerian multiphase flow model. A wall film is developed from mass and momentum balances [3] and implemented to model droplet deposition and membrane surface blockage. The model is used to predict film formation and subsequent membrane fouling, and allow to estimate the actual permeate flux. The results are validated using available experimental data.
Effects of the Forcing Frequency on Pulsating Impinging Jet Behavior and the Boundary Layer on the Target Curved Wall
Authors: Kharoua N. , Khezzar L. , Nemouchi Z. 
Published: October 2018

In the present work, time-dependent responses of Nusselt number, friction coefficient and pressure profiles to the passage of groups of coherent structures along a curved impingement wall, is considered. It is meant to replicate a more realistic picture of the flow. The jet considered belongs to heating applications where the jet flow temperature is higher than that of the impingement wall.
The flow was simulated using Large Eddy Simulation with the Dynamic Smagorinsky sub-grid-scale model. The plane jet was forced at frequencies increasing gradually to a maximum of 2200 Hz with an amplitude equal to 30% of the mean jet velocity. The computational domain was divided into 16.5 million hexahedral computational cells whose resolution was assessed based on the turbulence scales.
It was found that for low forcing frequencies (e.g., 200Hz), coherent forced primary vortices induced by the pulsations are separated by less organized vortices naturally induced similar to those of the unforced jet. It could be seen that the natural vortices have moderate effects on the boundary layer development on the impingement surface starting at relatively short distances from the stagnation point compared to the forced vortices. Increasing the forcing frequency to 1000Hz reduces the distance separating successive forced vortices causing the pairing phenomenon to occur at a certain distance along the target wall. Increasing the forcing frequency further to 2200Hz makes the pairing phenomenon followed by vortex breakdown to occur at shorter distances along the target wall.
The smaller forcing frequencies yield large and strong distant vortices which affect the dynamical field noticeably in conjunction with an important deterioration of heat transfer due to their strong mixing effect and entrainment of cold air from the surroundings. On the other hand, high frequencies generate smaller vortices which are relatively close to each other. Thus, they have a weaker effect allowing the growth of the boundary layer on the target wall up to a distance equal to four times the jet-exit width where the minimum heat transfer is observed. In fact, the small successive vortices form a sort of shield preventing the cold air from the surroundings to reach the target wall until their breakdown.
CFD Characterization of a Wet Foam Flow Rheological Behavior
Authors: Dallagi Heni , Gheith Ramla , Al Saabi Ahmad , Faille Christine , Augustin Wolfgang , Benezech Thierry , Aloui Fethi 
Published: October 2018

In some industrial processes, aqueous foams flow presents an important phase of the process, whereas, they cause pressure drop when designing and dimensioning systems. Identifying the different rheological parameters of foam flow is an interest key to understanding the interfacial phenomena. Actually, the difficulty to model the rheological parameters of foam flow is a major challenge.
In this study, we present a robust model to describe the foam fluid inside horizontal channels by the reverse approach of a numerical simulation (Computational Fluid Dynamics: CFD), based on the behavior laws of the Herschel-Bulkley type, for the non-Newtonian fluids. This reverse method starts from experimental (deduced from Particle Image Velocimetry (PIV) technique) results of the previous experimental work of Chovet (2015). The pressure losses measurements near-wall velocity fields, velocity profiles and the wall shear stress evolution including the void fraction from 55% to 85%, are considered in order to identify the different parameters of the developed model to determine the nature of the flow, the foams rheological behavior and the foam flow regime along the length of the channel.
The numerical study (CFD) is applied for two conditions: the first one for a wet foam flow with a void fraction of 70% and a foam flow velocity of 2cm/s (one-dimensional regime) and the second one, for a foam quality of 55% and a flow rate of 6cm/s. The numerical evolutions are identical to experimental ones for these same conditions. Therefore, we can conclude that the Herschel-Bulkley rheological model can correctly describe the aqueous foams fix behavior.
Particle Image Velocimetry Measurements of Flow Inside a Hydrocyclone With an Air Core
Authors: Shingote Chinmay , Furlan John , Kadambi Jaikrishnan , Visintainer Robert , Ke Renjie , Garman Mohamed 
Published: October 2018

Hydrocyclone separators are widely used in the oil and mining industries to sort, classify and separate solid particles or liquid droplets within liquid suspensions. In this study, the liquid-air flow inside a mining hydrocyclone is investigated using particle image velocimetry (PIV). Previous work completed by Ke (2016), using the same technique and experimental setup as the current study, mainly focused on the flow velocities in the radial-tangential plane within a hydrocyclone running with an air core. Due to optical limitations, the velocity measurements in the radial-tangential plane were limited to the inlet head. Previous work by Chinmay et al (FEDSM 2017) was also performed which concentrated mainly on the dimensions of the air core.
The study revealed several physical phenomena and flow patterns of the multi-phase flow in a hydrocyclone. An air core is generated along the central axis of the hydrocyclone, as the underflow is open to atmosphere. In this study, the flow field in the radial-axial (r-z) plane has been investigated, and measurements have been obtained in the conical regions outside of the inlet head including the center (axially) of the cyclone.
Particle Imaging Velocimetry (PIV) method was used with a laser as the light source in order to obtain experimental data for the purpose of developing and validating computational models of hydrocyclone flows. Refractive index matching technique was used, with the hydrocyclone model being made of clear acrylic material. The test liquid used in the experiments was sodium iodide aqueous solution (63.3% NaI by weight), in order to achieve a refractive index match between the curved inner cyclone walls and test fluid. The seed particles used in the experiments were 10 μm silver coated hollow glass spheres which were introduced into the flow by global seeding. Three fields of view (FOV) were investigated in the r-z plane of the hydrocyclone. Two dimensional velocity vector maps were obtained in each of the fields of view. Additionally, a SONARtrac unit was installed in the overflow piping in order to measure the % air content of the cyclone overflow. The PIV and % air content measurements will be presented and discussed.
Void Fraction Measurements for Air-Water Pipe Flows Using Quick-Closing Valves and Wire-Mesh Sensors
Authors: Lessard Étienne , Yang Jun 
Published: October 2018

In support of a header/feeder phenomena study, an adiabatic, near-atmospheric, air-water flow loop was commissioned simulating a single feeder of a Pressurized Heavy Water Reactor’s primary heat transport system under a postulated Loss of Coolant Accident scenario. An extensive database in representative two-phase flow conditions was collected, 750 tests in total, in order to create a two-phase flow map to be used in the more complex geometries such as header/feeder systems. The flow loop consists of two vertical test sections, for upwards and downwards flow, and one horizontal test section, each with an inner diameter of 32 mm and at least 120 diameters in length. Superficial velocities extended up to 6 m/s for the water and 10 m/s for the air. Void fraction was measured by means of quick-closing valves and a pair of wire-mesh sensors (WMS) in each test section.
Two-phase repeatability tests showed that the liquid and gas superficial velocities varied by 1.1% and 0.6% at reference conditions of 2.0 and 2.8 m/s, respectively. The corresponding void fraction measurements varied for the quick-closing valves by at most 6.8%, which indicates a low sensitivity to the closure time of the valves and an appropriate axial distance between them, and 2.3% for the WMS. For both measurement techniques, the largest variations occurred in the vertical downwards test section.
For the formal two-phase tests, over 600 distinct flow conditions were performed. The results showed that the two measurement techniques agreed within 5% at high void fractions and low liquid flow rates in vertical flow. For all other cases corresponding to the transitional or dispersed bubbly flow regime, the WMS over-estimated the void fraction by a consistent bias. An empirical correction is proposed, with a root-mean-square error of 6.6% across all tests. The void fraction map resulting from this database provides validation for the WMS measurements, a quantitative assessment of its uncertainty and range of applicability, and will be used as a reference in future tests under similar scale and flow conditions.
Effect of Pipe Inclination on Settling Slurry Flow Near Deposition Velocity
Authors: Matoušek Václav , Kesely Mikoláš , Konfršt Jiři , Vlasák Pavel 
Published: October 2018

Inclined slurry flows occur often in industrial applications such as mining and dredging. Pipelines transporting slurries contain inclined sections of various lengths and slopes. If the transported slurry is settling slurry then pipe inclination considerably affects flow structure and behavior.
We discuss settling slurry flow near and at the deposition limit at which stationary deposit starts to be formed at the bottom of the pipe. In particular, we focus on the effect of the pipe slope on the deposition velocity, and on the solids distribution and manometric hydraulic gradient in flow round the deposition limit. We introduce our new layered model for inclined settling slurry flows and demonstrate its predictive capabilities. Model predictions are verified by our experiment in a laboratory loop. We also introduce our new experimental approach to a detection of the deposition velocity based on radiometric sensing of the change of local concentration of solids at the bottom of a pipe.
Our experiments cover a broad range of flow slopes and contain measurements of solids distribution in a pipe cross section. Experimental results show that the degree of flow stratification and frictional pressure drop decrease with the increasing angle of inclination in the ascending pipe while the opposite applies in the descending pipe, which affects the deposition velocity and other related flow parameters.
A comparison with model predictions demonstrates that experimentally observed effects of pipe inclination are reproduced well by the layered model. Predicted deposition velocities, pressure drops and solids distributions are in a good agreement with the experimental results and indicate suitability of the model for engineering practice.
CFD Analysis of Natural Gas Cooling System Through a Conventional Aircooler Improved by a Fogging System
Authors: Pérez Jhon , Asuaje Tovar Miguel 
Published: October 2018

Nowadays, under unstable prices scenarios, the oil and gas industry is looking for improvement in its production processes, either by increasing the production and/or lowering the operational costs. Aircoolers, particularly, are key equipments in the natural gas industry, and are frequently the bottleneck of gas conditioning processes.
To improve air cooling efficiency and increase their gas volume capacity, several solutions are commonly implemented such as: fan blade angle change, air inlet section modification, fogging cooling system, among others.
The present study shows the CFD (Computational Fluid Dynamics) analysis of an air cooler, under an air flow with an evaporative cooling system, in order to quantify the effect of this cooling process on its overall equipment performance.
Simulations were carried out using sing the ANSYS CFX v-14® software, in a simplified multidomain which consider fluid and solid blocks:
1.- External two-phase flow (air + water droplets) with heat and mass transfer
2.- Heat transfer through the pipe wall
3.- Single phase natural gas flow inside the tubes
In order to stablish an operational range of the fogging system, the influence of parameters like: inlet temperature and relative humidity of the air, water flow rate, water droplets mean diameter, water injection position, were studied [9, 10].
The results show a good agreement (around 5%) respect to the reported values on the literature. The best performance for the equipment was reported with a droplet diameter of 20 μm and for low relative humidity (less than 65%), which guarantees the complete evaporation of the droplets within the studied domain. For the analyzed operating conditions, a reduction of the gas outlet temperature of up to 1.5°C can be achieved.
Flow Control Around a SUV Simplified Vehicle
Authors: Edwige Stéphie , Gilotte Philippe , Mortazavi Iraj , Eulalie Yoann , Holst David , Nayeri Christian N. , Aider Jean-Luc , Varon Eliott 
Published: October 2018

The research on the external aerodynamics of ground vehicles can nowadays be related to sustainable development strategies, confirmed by the worldwide CO2 regulation target. Automotive manufacturers estimate that a drag reduction of 30% contributes to 10g/km of CO2 reduction.
However, this drag reduction should be obtained without constraints on the design, the safety, comfort and habitability of the passengers.
Thus, it is interesting to find flow control solutions, which will remove or remote recirculation zones due to separation edges with appropriate control techniques. In automotive sales, the SUV, 4x4 and compact cars represent a large part of the market share and the study of control approaches for this geometry is practically useful.
In this work, appropriate control techniques are designed to decrease the drag forces around a reduced scale SUV car benchmark called POSUV. The control techniques are based on the DMD (Dynamic Mode Decomposition) algorithms generating an optimized drag reduction procedure. It involves independent transient inflow boundary conditions for flow control actuation in the vicinity of the separation zones and time resolved pressure sensor output signals on the rear end surface of the mockup. This study, that exploits dominant flow features behind the tailgate and the rear bumper, is performed using Large Eddy Simulations on a sufficient run time scale, in order to minimize a cost function dealing with the time and space average pressure coefficient. The resulting dynamic modal decomposition obtained by these LES simulations and by wind tunnel measurements has been compared for the reference case, in order to select the most appropriate run time scale. Analysis of the numerical results shows a significant pressure increase on the tailgate, for independent flow control frequencies. Similar decomposition performed in the wake with and without numerical flow control help understanding the flow modifications in the detachment zones.
Vibration Characteristics of a 50MW Francis Type Hydro Power Plant
Authors: Cho Y. , Oh Y. R. , Choi J. W. , Kim Y. J. , Novotny J. , Loub R. 
Published: October 2018

Vibration characteristics of the rotating machinery has been usually managed to facilitate the deterioration of the equipment and to prevent accident in advance. In a hydropower turbine, pressure pulsation characteristics to induce vibration is investigated during the model testing with a small scale model turbine for various operating conditions, and a prototype turbine is constructed to operate stably on the site. However, the model test has limitation that can’t be considered together with the vibration characteristics of a generator itself and of civil engineering structures for the building that support a turbine and a generator. Therefore, field tests of vibration for a hydroelectric power plant are carried out periodically, thereby maintaining reliability for safe operation of power generation facilities.
In the study, the vibration of a Francis type hydroelectric power plant operated over 30 years and overhauled a year and a half ago was measured and its characteristics has been investigated. Displacement and velocity sensors were installed at appropriate positions to measure the vibration of the rotating shaft and bearing support of a turbine and a generator, and the vibration characteristics of a typical hydroelectric power plant have confirmed by analyzing the measurement results. The vibration characteristics of rotating shaft and non-rotating parts of the hydroelectric turbine have been analyzed to confirm the degree of aging of the plant. Vibration in the power plant building depending on the operating conditions was also measured to be large enough to sense, and its frequency characteristics were analyzed.
Remarks on the Recirculation at the Outlet of a Radial Impeller Near Shut-Off
Authors: Palamarchuk Evgenii , Mengdehl Tino , Thamsen Paul Uwe 
Published: October 2018

Centrifugal pumps are characterized by the performance curves, showing the dependency between its main operating parameters for a range of external conditions. One of the most important curves is the head curve, which shows the dependency between the volume flow rate and the pressure head, induced by the pump. Stable operating conditions occur when the pump curve has a negative slope for the point of intersection with the system resistance curve (dH/dQ < 0). Most of the pump curves have a “stable” negative slope of the head curve for the most part of the possible operating range. Nevertheless, centrifugal pumps of low specific speed display a tendency to generate an unstable pump performance curve, especially if designed with a high head coefficient at the best efficiency point [1]. These curves are characterized by lowering the pressure head near the shut-off area (drooping curves). Operating range of such pumps could be significantly limited in the case of high static head component for the system resistance curve (firefighting applications) or parallel operation.
The flow pattern for the part load conditions differs from the one by the optimum conditions. There are two recirculation zones, occurring at the inlet and at the outlet of the impeller [2]. This paper concentrates on the investigation of the pressureside recirculation and its influence on the curve slope. The pressure-side recirculation may have various position and intensity in the case of a radial impeller with an axis-parallel trailing edge [3, 4]. There are a few measures that influence positively the stability of the performance curve [3, 5].
The tests contain an experimental setup with comparison of experimental data to numerical simulations. Subject of the experimental investigations is a single volute radial centrifugal pump with a specific speed nq = 35 min−1. The casing was modified in order to provide optical access to the impeller outlet area. Radial velocity components are measured by using the Particle Image Velocimetry (hereafter: PIV) methods in order to define the backflow zones for the part load regimes. Measured operating points are then compared to numerical simulations carried out by Computational Fluid Dynamics (hereafter: CFD). The flow pattern gained by CFD allows analyzing the phenomena of the pressure side recirculation in detail, also in areas, where the access with measuring instruments is limited.
The investigation is performed on two modifications of the pump impeller — applying the slots opening in the back shroud [2] and diagonal trimming of the impeller [5], as well as for the original (unmodified) case. The combination of the described methods gives a clear vision on the 3D recirculating structures for the cases of stable and unstable behavior of the curve.