bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of Axial Thrust Balancing Swirl Breakers in a Centrifugal Pump Using Stochastic Methods
Authors: Lefor Dominik , Kowalski Jan , Kutschelis Boris , Herbers Thomas , Mailach Ronald 
Published: December 2014

Hydraulic axial thrust balancing in single-stage radial pumps is a frequently applied procedure to reduce the bearing load to a reasonable level. It leads to considerable efficiency loss, which gives reason to investigate the optimization potential of the common balancing methods. This paper’s focus is on so-called casing ribs, which are used in the default design of an examined industrial pump. Radial vanes on the casing wall of the front impeller side chamber work as swirl breakers by decreasing rotating flow whereby the static pressure at the shroud increases and counteracts the resulting axial thrust. The objective is to retain the reduction of axial thrust and to improve the internal efficiency simultaneously.
Therefore a CFD model of the industrial radial pump is created with Ansys CFX. Sufficient numerical quality is ensured whereby consistency is verified by a mesh study. The model is validated by integral values of the characteristic curve and axial thrust measurements as well as by experimental transient static pressure measurement at different locations of the pump flow. Probes are placed in the suction port, the volute and the impeller side chambers, where most balancing methods are implemented.
Since the side chamber contains a complex flow, the effect of geometry changes is hard to predict. For this reason a stochastically based sensitivity analysis using a comprehensively parameterized geometry of the front side chamber domain with the included casing ribs is carried out. For this purpose 110 design points are calculated and evaluated with support of the software Optislang. Correlations of parameters are suggested and important parameters regarding the objective are identified. Some reasonable model simplifications are conducted to reduce the computational time. According to the acquired findings a local optimization is executed using the best sample of the sensitivity analysis as start design. An evolutionary algorithm method determines a best design with an efficiency improvement of 0.26 percentage points. It is discussed in detail conclusively.
Experimental Study of Reynolds Number Effects on Three-Dimensional Offset Jets
Authors: Durand Zacharie M. J. , Clark Shawn P. , Tachie Mark F. , Malenchak Jarrod , Muluye Getnet 
Published: December 2014

The effect of Reynolds number on three-dimensional offset jets was investigated in this study. An acoustic Doppler velocimeter simultaneously measured all three components of velocity, U, V and W, and turbulence intensity, urms, vrms, and wrms, and all three Reynolds shear stresses, uv, uw, and vw. Turbulent kinetic energy, k, was calculated with all three values of turbulence intensities. Flow measurements were performed at Reynolds numbers of 34,000, 53,000 and 86,000.
Results of this experimental study indicate the wall-normal location of maximum mean velocity and jet spread to be independent of Reynolds number. The effects on maximum mean velocity decay are reduced with increasing Reynolds number. Profiles of mean velocities, U, V and W, turbulence intensities, urms, vrms, and wrms, and turbulent kinetic energy, k, show independence of Reynolds number. Reynolds shear stress uv was independent of Reynolds number while the magnitude of uw was reduced at higher Reynolds number.
Parametric Study of Churn Flow in Large Diameter Pipes
Authors: Hewakandamby Buddhika N. , Kanu Aime U. , Azzopardi Barry J. , Kouba Gene 
Published: December 2014

Two phase flow in vertical risers are common place in oil and gas industry and many other process industries. Depending on the flow rates of the phases, there could be several flow patterns could exist inside the riser. These could vary from bubbly flow to annular flow with slug and churn flow in between. When the liquid phase flow rate is higher the bubbly flow exists while the annular flow is dominated by higher gas flow rate that forms a distinct gas core in the middle of the vertical riser. Of these flow regimes, churn flow is of particular interest as it is not well understood. The paper will report findings of an experimental campaign investigating the development of churn flow.
Experiments were carried out in a closed loop flow facility with a 127 mm ID, 11 m long vertical test section. The maximum flow rates achievable in the system were 17 and 1.2 m/s for gas and liquid phases respectively. Compressed air was used as the gas phase while water and water/glycerol mixtures were used as the liquid phase. The mixtures of water and glycerol were used to investigate the influence of the viscosity on the flow regime investigated. The flow was investigated using a Wire Mesh Sensor (WMS), an intrusive measurement device that can map the cross sectional distribution of phases. Void fraction measurements were made at several axial locations for a number of flow rate combinations from onset of churn flow until it turns into annular flow.
A region in flow rates where large liquid ligaments (wisps) suspended in the gas core was found and the breakup mechanism has been observed. Furthermore, huge waves were observed in this region. Analysis of results shows that the frequency of both huge waves and the wisps entrained in the gas core increase along the axial distance. The changes to the flow behaviour with the increase of viscosity and other findings will be presented in detail in the paper.
Effect of Liquid Properties on Thermal Mixing in a T-Junction
Authors: Kashinsky O. N. , Lobanov P. D. , Kurdyumov A. S. , Pribaturin N. A. 
Published: December 2014

Results of experimental study of mixing of liquids with different temperatures in a T-junction are presented. Experiments were performed with liquids which have significantly different physical properties. The liquid with higher temperature was injected through the branch of the T-junction. The test section was made of thin wall stainless tubes. The distribution of wall temperature over the surface was measured using a high speed infrared camera. Both time averaged and fluctuational characteristics of the temperature field were obtained from infrared image processing.
The structure of temperature field inside the channel was measured by a microthermocouple. It was mounted on the traversing unit which allowed its translation along the channel diameter. Measurements were made over different diameters in the same cross section. This allowed to construct the three-dimensional structure of the temperature field.
Results obtained provide experimental data necessary for validation of thermo hydraulic codes for the design of power equipment.
Experimental Study of Confined Turbulent Vortical Flow in a Narrow Annulus
Authors: Perelstein Yuri , Gancedo Matthieu , Farbos de Luzan Charles , Gutmark Ephraim , Frosell Thomas 
Published: December 2014

An experimental study was carried out to investigate the turbulent flow field of confined vortical flow in a narrow annulus. The test section consists of two concentric annuli that are separated by a tube with four equally spaced rectangular apertures. Water is passing from the inner annulus to the outer annulus and the main region of interest is near aforementioned rectangular holes.
Flow velocity was measured using a stereoscopic particle image velocimetry (PIV) system. The small size of the outer annulus required development of multiple improvements to the PIV system. Stereoscopic calibration within the curved and narrow annulus required development of a calibration method that ensured accurate alignment of the laser sheet to provide an accurate polynomial mapping of the physical coordinates to the pixel location on the ICCD chips of the cameras. Macro lenses were used to provide the desired field of view. Test section dimensions required accurate vertical repositioning of the cameras and the laser within the measurement plane. This was implemented using a two-axis positioning system. Reflections within the outer annulus required development of a polyurethane based paint that reflected the laser light with a shifted wavelength. The paint survived high shear stresses and pressure gradients during testing.
Three dimensional flow field was assembled based on measurements taken, providing insight into the behavior of the flow as it exits the aperture and mixes in the outer annulus. A vortex core was identified.
The results of measurements are compared to CFD results and serve as a tool validating the CFD model. Both the CFD and the measured results predict similar trends in flow behavior, showing strong radial and tangential components of velocity at the plane coincident with the edge of the hole.
Nonlinear Multi-Modal Panel Flutter Oscillations at Low Supersonic Speeds
Authors: Vedeneev Vasily , Shishaeva Anastasia , Kuznetsov Konstantin , Aksenov Andrey 
Published: December 2014

In this paper aeroelastic instability of a plate in a gas flow is investigated by direct time-domain numerical simulation. Plate deformation and gas flow are simulated in solid and fluid codes, respectively, with direct coupling between these codes. A series of simulations under different parameters has been conducted.
Three types of the plate response have been observed: stability, static divergence and flutter. Depending on Mach number, two types of flutter were detected: single mode flutter and coupled mode flutter. At M = 1.8, a good correlation between the present study and the piston theory for coupled mode flutter has been obtained. At lower M, from 1 to 1.6, single mode flutter in 1st, 2nd and higher modes has been observed. Amplitudes and frequencies of flutter limit cycle oscillations have been studied. It is shown that limit cycle oscillations can occur in form of pure one-mode oscillations, or include 1:2 internal resonance, when fluttering mode excites another mode. In the region of Mach numbers from 1.3 to 1.5, where several plate modes are simultaneously unstable, transition from periodic to quasi-chaotic flutter oscillations occurs.
CFD Computations Using Preconditioned Krylov Solver on GPUs
Authors: Amritkar Amit , Tafti Danesh 
Published: December 2014

GPU computation in recent years has seen extensive growth due to advancement in both hardware and software stack. This has led to increase in the use of GPUs as accelerators across a broad spectrum of applications. This work deals with the use of general purpose GPUs for performing CFD computations.
The paper discusses strategies and findings on porting a large multi-functional CFD code to the GPU architecture. Within this framework, the most compute intensive segment of the software, the BiCGSTAB linear solver using additive Schwarz block pre-conditioners with point Jacobi iterative smoothing is optimized for the GPU platform using various techniques in CUDA Fortran. Representative turbulent channel and pipe flow are investigated for validation and benchmarking purposes. Both single and double precision calculations are highlighted.
It is found that the precision has a negligible effect on the accuracy of predicted turbulent statistics. However, it was found that single precision calculations led to instabilities in the initial convergence of the pressure equation if the convergence criterion was set at too low a value. This was remedied by limiting the number of iterations during the initial stages of the calculation. For a modest single block grid of 64×64×64, the turbulent channel flow computations showed a speedup of about 8 fold in double precision whereas it was more than 13 fold for single precision on the NVIDIA Tesla GPU. For the pipe flow consisting of 1.78 million grid cells distributed over 36 blocks, the gains were more modest at 4.5 and 6.5 for double and single precision respectively.
Shock-Induced Mixing With Chemical Reactions Using the FLASH Code
Authors: Varshochi H. , Attal N. , Ramaprabhu P. 
Published: December 2014

FLASH is a massively parallel, multi-physics, open source code developed by the University of Chicago [1] for investigating astrophysical phenomena. FLASH was modified [2] to handle detailed chemical kinetics for hydrogen and methane combustion and heat release, in order to enable the code to be used for combustion applications. These capabilities have been tested and validated [2, 3] through an extensive suite of simulations. These modifications include the addition of detailed H2-air and CH4-air chemistry along with temperature dependent thermodynamic and transport properties.
The aim of this work is to apply the modified version of FLASH to three cases of highly compressible supersonic flows, involving chemical reactions. The first problem is a reacting shock-bubble interaction, in which the shock triggers combustion in a fuel bubble. In the second problem, a two-dimensional, Richtmyer-Meshkov Instability leading to combustion of the fuel at a non-premixed, single mode perturbed interface has been studied numerically. In these cases, the relationship between the integral heat release rate, the integral H2O production rate and total circulation is investigated. In the third example, a multimode perturbed interface has been implemented into a 3D simulation. Time evolution of the interface undergoing reacting RMI is studied. By defining a reflecting endwall for RMI simulations, the effect of a second reflected shock on the mixing behavior and combustion on an already shocked interface has been studied.
Numerical simulations of the interaction of a shock (Mach number 2) in air with H2 bubble was performed [2]. The misalignment between the pressure gradient across the shock front and the density gradient at the site of H2-Air interface generates baroclinc vorticity. This phenomenon generates counter-rotating vortices that breakdown the H2 bubble (fuel). The rapid breakdown of the H2 bubble transitions to turbulent mixing, intensifying the heat release rate. In two more general configurations, chemically reacting, single-mode and multimode Richtmyer-Meshkov Instability has been studied. RMI is the driving mechanism for growth of small interfacial perturbations. Initially single-mode perturbations of small amplitude grow linearly due to impulsive acceleration by shock. This is followed by non-linear growth at late times due to the formation of secondary Kelvin-Helmholtz instability. Heat release and product formation in the vicinity of interface will affect perturbation growth rates which will affect the mixing behavior and therefore the combustion efficiency [4].
Thermal and Dissolved Gas Effects on Cavitation in a 2-D Convergent-Divergent Nozzle Flow
Authors: Watanabe Satoshi , Enomoto Keisuke , Yamamoto Yuya , Hara Yoshinori 
Published: December 2014

It is well known that the thermal effect of cavitation suppresses the development of cavity with the decreased local temperature due to the latent heat of evaporation. In the present study, to obtain the fundamental knowledge of thermal effect of cavitation, an experimental study of cavitation in a simple convergent-divergent nozzle was carried out using hydro-fluoro-ether (HFE) as a working fluid. HFE was expected to reveal the thermal effect at room temperature, which enabled us to simply neglect the heat flux between the test section and outside, and to roughly keep adiabatic conditions on nozzle wall surfaces.
It was found that the cavitation in HFE was a foam-like sheet cavity, which was different from a film like cavity in cold water. The temperature depression, near the leading edge of cavitation, was confirmed especially in more developed cavitation cases, revealing the existence of thermal effect of cavitation. However, in lower velocity cases, the measured cavity length was apparently longer in HFE despite of the expected thermal effect. The measured pressures inside the cavity were found to be apparently larger than the vapor pressure, indicating the possible separation of dissolved air into the cavity. Then, the cavitation number based on the measured cavity pressure instead of vapor pressure was proposed, and by using the proposed cavitation number, the thermal effect was clearly confirmed in terms of the cavity development. Frequency characteristics of measured pressure fluctuations were qualitatively similar regardless of the species of working fluid.
Novel Atomization Process for Large Scale Nanoparticle Production by Flame Spray Pyrolysis
Authors: Achelis Lydia , Meierhofer Florian , Hodapp Maximilian J. , Buss Lizoel , Noriler Dirceu , Meier Henry F. , Fritsching Udo 
Published: December 2014

An advanced atomizer concept to obtain larger production rates of nano-particles by the Flame Spray Pyrolysis process (FSP) is investigated. In the conventional FSP process (external mixing gas/liquid nozzle) production rates may be varied by increasing the precursor feed rate and/or the precursor concentration. However, both measures typically result in the formation of larger nanoparticles. These effects may be avoided by the development and integration of advanced atomizer concepts. The aim is to address the spray structure in a way that keeps the flame height constant and modifies the flame width. Therefore, the time scales and the residence time-temperature histories of droplets and nanoparticles are expected to be similar while the production rate is increased. The atomizer concept for creation of a modified spray and flame combines a swirling liquid film generation that is atomized with an external swirling gas flow.
In the first step a hollow cone of liquid ligaments and primary droplets is generated through a conventional pressure-swirl nozzle. The liquid phase is atomized in the second step, by the expanding gas of a circular ring nozzle. To study the main characteristics of the combined atomizer in model experiments, water and water/glycerol mixtures are used as the liquid phase and air as the gas phase. For investigation of the atomizer and spray properties, the relation between liquid outlet angle, inlet angle of the gas, the gas/liquid flow rates, the spray cone geometry and droplet size distribution are investigated. The spray structure and the breakup of the film are analyzed by high speed images. Laser diffraction is used to measure the droplet size distribution in the spray.
A numerical model is developed and used to simulate the cold gas flow and spray distribution as in the adapted atomizer concept. The Eulerian-Lagranian approach is solved by means of a computational fluid dynamics (CFD) code. The process parameters such as liquid composition, liquid and gas flow rates are varied to meet the specific requirements of the nanoparticle production in the FSP process. The experimental and numerical investigation showed that an enlarged and steady spray resulted from an increased outlet angle of the liquid and gas swirl. Increased tangential velocities increase the entrainment of surrounding gas, widening and providing a more uniform velocity profile to the spray. Spray droplet mean diameters resulted in the desired range of ≤ 20 μm.
Oscillation of Mixing Jets in a Long Horizontal Tank
Authors: Yu Zhao , Kar Kishore , Storrs Tyrone , Jian Christopher , Cope Richard , Feng Jinli , Aglave Ravindra 
Published: December 2014

In contrast to mixing in vertical tanks, jet mixing in long horizontal tanks is scarcely investigated in the literature. It is known that jet mixing in long horizontal tanks is more difficult when compared to short tanks, as more liquid volume must be recirculated through the jets.
In this study, computational fluid dynamics (CFD) simulations are conducted for the flow in a horizontal cylindrical tank with a length-to-diameter ratio of 3:1 and a nominal volume of 112,560 L (liquid volume of 75,708 L, i.e. 20,000 gallons). A pair of back-to-back Coldrey nozzles is placed near the center of the tank bottom, and each nozzle directs its jet towards the corresponding vessel end. An intriguing phenomenon is observed in the transient simulations, where the turbulent jets oscillate in both horizontal and vertical directions with a low frequency. In order to determine the source of such oscillation, a number of simulations are conducted to explore the effects of mesh type and size, boundary condition on the free surface, turbulence model, and time step. Oscillation persists in all cases, indicating that it is unlikely the result of some numerical instability. The oscillation also appears to be insensitive to the Reynolds number or symmetry in the nozzle or tank geometry. Another simulation with a single jet also shows the oscillatory flow behavior, and thus the oscillation is more likely to be caused by interaction between the jet and the recirculating flow in the tank, rather than interaction between the two jets. Further analysis of the jet velocity profile suggests that the secondary flow on the cross section of the jets might also contribute to the oscillation.
While similar confined jet oscillations due to Coanda effect and blind cavity effect have been previously observed in small cavities by both 2D numerical simulations and laboratory scale experiments, this study shows that such oscillation also exists in industrial scale horizontal tanks. The oscillatory motion of the liquid may lead to improved mixing in the tank.
A review of the legged mealybugs on bamboo (Hemiptera: Coccoidea: Pseudococcidae) occurring in China
Authors: LI WEN-CHAO , TSAI MING-YU , WU SAN-AN 
Published: December 2014

Twenty-two species of legged mealybugs occur on bamboo (Poaceae: Bambusoideae) in China. These species are reviewed and two of them are described for the first time: Dysmicoccus luoyangensis Li & Wu, sp. nov. and Trionymus indocalamus Li & Wu, sp. nov. Two new combinations are established: Pseudococcus bambusicola Takahashi and Kaicoccus bambusus Wu are transferred to genus Formicococcus Takahashi as F. bambusicola (Takahashi) comb. nov. and F. bambusus (Wu) comb. nov., respectively. Formicococcus bambusicola, Heliococcus bambusae (Takahashi), Neoripersia miscanthicola Takahashi and Trionymus formosanus Takahashi are redescribed and reillustrated based on type specimens. Brief notes are provided for Balanococcus kwoni Pellizari & Danzig, B. zhejiangensis Li & Wu, Dysmicoccus dengwuensis Ferris, D. indocalamus Wu, Eumyrmococcus smithii Silvestri, Ferrisicoccus angustus Ezzat & McConnell, Heliococcus lingnaniae Wang, H. takae (Kuwana), Heterococcus abludens Borchsenius, Miscanthicoccus miscanthi (Takahashi), Palmicultor lumpurensis (Takahashi), Paraporisaccus guizhouensis Lu & Wu, Paraserrolecanium fargesii Wu, Pseudantonina magnotubulata Borchsenius and Trionymus bambusae (Green). A key to the species of legged mealybugs on bamboo occurring in China is given. A list of bamboo mealybugs worldwide is also provided.
Grasshoppers of the Mascarene Islands: new species and new records (Orthoptera, Caelifera)
Authors: HUGEL SYLVAIN 
Published: December 2014

The grasshopper fauna of Mascarene Islands (Mauritius, Rodrigues and La Réunion), in South Western Indian ocean is examined. Numerous field surveys and examination of museum specimens recorded twenty species of Grasshoppers on the archipelago. Five of them are new records, including a new species: Odontomelus ancestrus n. sp. restricted to Round Island, a 2 km² islet North to Mauritius. Despite intensive searching, five of the non endemic species once recorded on the archipelago have not been recorded again and might correspond to temporary settlements/introductions. A key to Mascarene grasshoppers is given.