bluuebunny/crossref_metadata_2025 huggingface dataset:
The Optimum Meridian Profile of Various Annular Surface Roughness and Impeller Blade Number
Authors: Tsugawa Takuji
Published: October 2017

In the previous study, the optimum meridian profile of impeller and guidevane in two kinds of typical specific speed (very high and very low). The two kinds of optimum meridian profile were obtained by one initial meridian profile obtained by no restriction optimum process. As a result, the design parameters of almost all kinds of specific speed were obtained in above optimum process. In no restriction optimum process, the all of design parameters and specification are variable optimum parameters. In the optimum process, loss calculation consists of blade-to-blade diffusion loss and axial-symmetrical annular wall friction loss. In the calculation of axial-symmetrical annular wall friction loss, the wall friction factor is the function of Reynolds number because tip and hub annular walls were smooth surfaces. One of important merit of this optimum method is to obtain the best flow condition in inlet and outlet of impeller and guidevane without detailed impeller and guidevane shape design. This optimum method is executed on the assumption that the impeller and guidevane was designed to satisfy inlet and outlet flow conditions from hub to tip. In the present case study, the influence of the annular rough surface friction loss was studied in above two kinds of specific speed. In large Reynolds number, the relative roughness influences the wall friction factor but Reynolds number does not influence the wall friction factor. It is assumed that the annular surface is rough and Reynolds number is sufficiently high. Then, the annular wall friction factor is constant value decided by surface roughness. In the result, the optimum meridian profile was obtained in case of the rough annular surfaces. In the next case study, the impeller blade number of the previous optimum meridian profile is small. So, the restriction of impeller blade number was calculated to obtain the large blade number impeller. When one design parameter was changed gradually as restriction for goal value, the other design parameters were variable optimum design parameters or constant design parameters. In case study, the specific speed NS, mixed flow angle of impeller inlet N1 or impeller blade number Nimp were three design parameters as restriction. It is important that the only one parameter of three design parameters was changed gradually as restriction at the same time. In the optimum process, the restriction parameter was changed gradually as restriction. In the result, the optimum meridian profile of the large impeller blade number was obtained. It was difficult to obtain the initial design parameters of traditional impeller and guidevane using in this method up to now. In the future, the traditional impeller and guidevane will be able to modify by means of the design parameters restriction of this optimum method to agree with the primary design parameters of traditional impeller and guidevane.
A Numerical Study on Flow Characteristics Through Orifice Flowmeter and Measurement Accuracy Depending on Upstream Straight Length
Authors: Lee Jang Il , Cheong Ae Ju , Min Bok Ki
Published: October 2017

In this numerical study, Commercial CFD (Computational Fluid Dynamics) code, ANSYS CFX ver. 17.1, is used to analyze the 3-Dimensional flow characteristics through orifice plate (β = 0.6) with two 90 degree bends in different planes. The purpose of this numerical study is to evaluate measurement accuracy and flow characteristics of orifice flowmeter depending on upstream straight length from 12D to 56D.

Thus, numerical calculations of pressure drop caused by swirling flow and distortion of axial velocity profile on orifice plate are performed by using numerical analysis. In addition, numerical analysis results are compared with recommended upstream straight length of ASME Performance Test Codes 19.5 for orifice plates and nozzles.

The results show that if upstream straight length of orifice flowmeter is more than 40D, there is a little deviation of differential pressure. Moreover, it is found that up-down asymmetry of recirculation zones is relatively attenuated as the upstream straight length increases.
Measured Static and Rotordynamic Characteristics of a Smooth-Stator/Grooved-Rotor Liquid Annular Seal
Authors: Moreland J. Alex , Childs Dara W. , Bullock Joshua T.
Published: October 2017

Electric submersible pumps utilize grooved-rotor seals to reduce leakage and break up contaminants within the pumped fluid. Additionally, due to their decreased surface area (when compared to a smooth seal), grooved seals decrease the chance of seizure in the case of rotor-stator rubs. Despite their use in industry, the literature does not contain measurements for smooth-stator/circumferentially-grooved-rotor liquid annular seals.

This paper presents test results consisting of leakage measurements and rotordynamic coefficients for a smooth-stator/circumferentially-grooved-rotor liquid annular seal. Both static and dynamic performance for the grooved seal are investigated for various imposed pre-swirl ratios, static eccentricities, axial pressure drops, and running speeds. The grooved seals′ static and dynamic performance are compared to those of a smooth seal with identical length, diameter, and radial clearance.

Results show that adding grooves reduces leakage at lower speeds (less than 5 krpm) and higher axial pressure drops, but does little at higher speeds. The grooved seal’s direct stiffness is generally negative, which would be detrimental to pump rotordynamics. Furthermore, increasing pre-swirl increases the magnitude of cross-coupled stiffness and increases the whirl frequency ratio. When compared to the smooth seal, the grooved seal has smaller effective damping coefficients, indicative of worse stability characteristics.
Experimental Investigation of the Wake Decay Process in an Axial Pump With Varied Rotor-Stator Axial Spacings
Authors: Xu Han , Wang Mengyu , Jin Donghai , Sun Dakun , Gui Xingmin , Sun Xiaofeng
Published: October 2017

For a compressor stage, the mechanism of wake recovery leads the rotor wakes to decay in a reversible process through the stator passage. Based on this theory, the rotor-stator axial spacing is believed to be a significant factor bound up with the wake mixing loss. In this paper, the wake decay processes in a tiny axial pump with varied rotor-stator axial spacings are studied using particle image velocimetry (PIV) measurement. PIV results indicate that the rotor wakes interact with the stator blade and generate flow regions with elevated turbulence. This interaction is enhanced when the axial spacing is close. The attenuation process of the disturbance kinetic energy (DKE) and the relative wake depth demonstrate that the axial spacing significantly affects the proportion of the wakes that decay in the stator passage. Close rotor-stator axial spacing is proposed to increase the recovery rate of the rotor wakes. Supplementary CFD computation is conducted to certify that the experimental results are universal for pumps with and without splitters.
Three-Dimensional Computational Hydrodynamics Modeling for Algae Transport and Growth
Authors: Liu Haidong , Zheng Zhongquan Charlie , Young Bryan
Published: October 2017

In this study, a three-dimensional model coupling hydrodynamics with algae transport dynamics is investigated. The hydrodynamic model solves the three-dimensional Navier-Stokes equations by a semi-implicit, fractional step method, where the hydrostatic components are determined first and the non-hydrostatic pressure and other components are determined in a subsequent step. Wind velocity on the water surface is accounted for the effect of wind stress on the flow velocities in the hydrodynamic model. Then, the model is coupled with an algae transport model, which enables simulation of algae transport and algal blooms. As an example, the model is implemented to analyze the transition of blue-green algae in Milford Lake, which is the largest man-made lake in Kansas suffering from blue-green algae blooms. The three-dimensional model provides a robust and efficient way for hydrodynamic and algae modeling and can be implemented to studies on different types of rivers and reservoirs easily. The simulated results can be very useful for algae control and prediction in both short and long terms.
Data Mining of Experimental Data on Separation Control of the Flows Over NACA0015 and Ishii Airfoils Using Dielectric Barrier Discharge Plasma Actuator
Authors: Asada Kengo , Sekimoto Satoshi , Tatsukawa Tomoaki , Shimizu Tomoyasu , Yabu Masaya , Fujii Kozo
Published: October 2017

Analysis of the experimental results of separation control with a dielectric barrier discharge plasma actuator over a NACA0015 airfoil and an Ishii airfoil, which is practical airfoil and gains better aerodynamic performance than NACA0015 airfoil at low Reynolds number, is conducted to investigate the relationship between the parameters (i.e. nondimensional burst frequency: F+, input voltage: Vpp, angle of attack: AoA) and the improvement of the aerodynamic performance. Time-averaged pressure distributions are measured at Reynolds number of 62,000 around the airfoils. In this study, scatter plot matrix (SPM) is used as the data mining technique to extract the correlation between parameters. Results indicate that for both NACA0015 and Ishii airfoils, F+ = 6 and 1 are effective for low and high AoA, respectively. Also SPM plots show that the pressure coefficient at the trailing edge and lift-to-drag ratio (L/D) are well related each other.
Leak Rate Uncertainty Parametric Study
Authors: Magradey John W. , Daniels Christopher C. , Oravec Heather A.
Published: October 2017

The desire of humans to explore beyond low-Earth orbit has provided motivation for technology development to reliably confine gases. The new technologies have driven the need to accurately quantify the mass flow rate past gas pressure seals. While the classic method of helium leak detection is widely accepted and reliable, the method has weaknesses when applied to determining air leak rates. The newest advance in air leak rate quantification acts as an extension of the pressure decay method. In this enhanced method, the downstream pressure is controlled and a constant pressure differential is maintained across the seal under test. The effect of the enhancement is improved measurement uncertainty of the leak rate over the basic pressure decay method which may chase a valid measurement as the differential pressure changes with uncontrolled downstream pressure. Theoretically, each measurement system should produce the same value for a given leak rate; however, the measurement uncertainty is dependent upon the instruments used. As this enhanced method can be accomplished using off-the-shelf equipment and instrumentation, the measurement uncertainty strongly depends upon each unique test set-up. A parametric study of the leak rate uncertainty equation was completed, and the effect of changing the quality and quantity of the pressure and temperature measurement instruments was observed. The study quantified the differences in measurement uncertainty at different test conditions depending upon the instrument choices, as well as, the differences made in uncertainty by modifying the test conditions alone. The calculated measurement uncertainty was beneficially lower when using a single high-quality pressure measurement device when compared to utilizing multiple low-quality pressure transducers. Similar results were shown for temperature measurement devices. The data acquisition sampling rate, initial pressure, and mass flow rate also affected the uncertainty values in some cases, but may not be variable parameters.
Multi-Scale Transport Modeling: Asbestos and Nano Fibers in Inhalation Risk Assessments
Authors: Tian L. , Ahmadi G. , Tu J. Y.
Published: October 2017

Recent rapid development of the carbon nanotubes (CNTs) industry has raised health concerns as these engineered particles have the appearance of asbestos, which is a well-known inhalation hazard. Compared to asbestos, CNTs have similar elongated rod shaped structure, while they are in nano-scale where the particle motion is markedly affected by Brownian diffusion. However, limited studies on Brownian dynamics of CNTs are available in the literature and the details of motions of these elongate ultrafine particles, and in particular, their transport and deposition processes are largely unknown. In this study, multi-scale analysis of transport and deposition of elongated particles in micro and nano-scales were performed. Particular attention was given to the differences and similarities of the physical mechanisms governing the particle/fiber motions at different length scales. The study was focused on revealing the details of the interaction between elongated particles at different scales and the fluid motions. Such information is very useful in understanding the transport processes of asbestos and nano-fibers in human airways for inhalation risk assessment studies.
New Method of Flow Maldistribution Mitigation in Parallel Microchannel Heat Sink
Authors: Yadav Vikas , Kumar Ritunesh
Published: October 2017

Microchannel heat sinks (MCHS) are explored as integrated cooling option in diversified applications ranging from microelectronic devices to nuclear reactors. Parallel channel MCHS suffers from the problem of flow maldistribution in channels. The phenomenon of flow maldistribution causes undesired effects such as non-uniform temperature distribution, increase in base maximum temperature and drop in MCHS performance. In the present single phase numerical study; flow maldistribution in vertical supply MCHS has been estimated by taking entire heat sink as computational domain. Three-dimensional governing equations for both fluid flow and energy transfer are solved by finite volume method. A novel heat sink design by splitting the inlet flow in two equal parts has been proposed to effectively reduce flow maldistribution problem in MCHS. Results of velocity distribution, temperature distribution of fluid and overall thermal performance of proposed MCHS are compared with the conventional MCHS design. Proposed scheme helps in reducing flow maldistribution problem significantly (∼55%) as compared to conventional MCHS.
First Attempt on Numerical Prediction of Cavitation Damage on a Centrifugal Pump
Authors: Leclercq Christophe , Fortes-Patella Regiane , Archer Antoine , Cerru Fabien
Published: October 2017

The cavitation erosion remains an industrial issue for many applications, mainly for hydraulic machines. This paper deals with the cavitation intensity, which can be described as the fluid mechanical loading causing cavitation damage. The estimation of this intensity is a challenging problem both in terms of modeling the cavitating flow and predicting the erosion due to cavitation. For this purpose, a numerical methodology was proposed to estimate cavitation intensity from 3D unsteady cavitating flow simulations. CFD calculations were carried out using Code_Saturne, which solves U-RANS equations for a homogeneous fluid using the Merkle’s model [1], coupled to a k-ε turbulence model with the Reboud’s correction.

A cavitation intensity prediction model was developped based on pressure and void fraction derivatives obtained through CFD calculations. It was previously applied to study cavitation damage [2] on a NACA65012 hydrofoil.

The article briefly presents this validation case as well as the prediction of the cavitation intensity on the blades of a centrifugal pump called “SHF pump” and tested at EDF R&D laboratory [3]. The numerical predictions of cavitation damage are in good agreement with experimental results obtained by pitting.
Research on Flow Field of a Fixed Duct in a Rotary Energy Recovery Device
Authors: Liu K. , Deng J. Q. , Yang B.
Published: October 2017

An experimental study was carried out to investigate flow structures in the duct of a rotary energy recovery device (RERD). In order to visualize the flow field, a new type structure of the RERD was proposed in this experiment, which had a fixed duct and two rotating ports. A two-dimensional particle image velocimetry (PIV) measurement was performed to visualize the flow structure in the duct of the RERD. The turbulent flow structure in the duct was analyzed. The instantaneous vorticity contours and associated vectors showed the generation of vorticities in the duct. Moreover, the formation of the small-scale-vortex would significantly increase the flow instability and the fluid mixing rate. These results may be beneficial to researchers in better understanding the flow dynamic in the duct of a RERD and optimize the operating conditions and structural parameters of it.
Visualizing Near-Field Spray Characteristics With Broadband X-Rays
Authors: Li Danyu , Morgan Timothy B. , Pulfer Luke D. , Heindel Theodore J.
Published: October 2017

Liquid sprays play a key role in many engineering processes (e.g., food processing, coating and painting, 3D printing, fire suppression, agricultural production, combustion systems, etc.). Spray characteristics can easily be assessed in the mid- and far-field regions, well after liquid sheet breakup and droplet formation, using various optical/laser diagnostic techniques. The conditions in the near-field region, near the spray nozzle exit, can influence mid- and far-field characteristics; however, near-field measurements are extremely challenging because the spray in this region is typically optically dense and optical/laser diagnostics are ineffective in this region. This study presents the advantages and challenges of using broadband X-rays to characterize the near-field region of a spray. A generic spiral jet hollow cone spray nozzle is used to demonstrate near-field spray imaging for three different flow conditions. Radiographic movies of the spray show a very dynamic near-field region. X-ray computed tomography (CT) reconstructions of the spray display a 3D map of the time-average spray distribution. The two X-ray imaging modes provide qualitative information of the near-field spray region. A discussion of the quantitative measures that can be acquired from X-ray radiographs and CT images is provided.
A Generalized Model for Dynamic Contact Angle
Authors: Thalakkottor Joseph J. , Mohseni Kamran
Published: October 2017

Contact angle is an important parameter that characterizes the degree of wetting of a material. While for a static case, estimation and measurement of contact angle has been well established, same can not be said for the dynamic case. There is still a lack of understanding and consensus as to the fundamental factors governing the microscopic dynamic contact angle. With the aim of understanding the physics and identifying the parameters that govern the actual or microscopic dynamic contact angle, we derive a model based on first principles, by performing a force balance around the region containing the contact line. It is found that in addition to the surface tension, the microscopic dynamic contact angle is also a function of surface tension gradient and the jump in normal stress across the interface. In addition to having a significant contribution in determining the microscopic dynamic contact angle, surface tension gradient is also a key cause for contact angle hysteresis.
Influence of Gas-Liquid Multiphase-Flow on Acoustic Behavior and Performance of Side Channel Pumps
Authors: Fleder Sebastian , Hassert Frank , Böhle Martin , Zientek-Strietz Beate
Published: October 2017

Side-channel pumps (SCP) are a niche product, able to deliver relatively high heads at low flow rates, which corresponds in a low specific speed. They are closing the gap between classical radial centrifugal pumps and positive displacement pumps, combining the advantages of both without having all the negative effects. The hydraulic efficiency of SCP seems low at first sight. But classical centrifugal pumps are often working under part load conditions, when working at this volume flow and specific speed range, which means they are not able to perform at their BEP. This reduces the efficiency of centrifugal pumps and creates a major benefit of SCP, which are able to work in their BEP.

The acoustic behavior and the characteristic pulsations and vibrations of a side channel pump are measured with various measurement methods, such as vibrometry, sound level measurement and sound cartography using an acoustic camera. The characteristic vibrations are shown and compared to the characteristic pressure-pulsations of the working fluid.

The two-phase liquid-gas flow has, beside the effects on the characteristic curves such as head drop and efficiency reduction, many side effects on the behavior of the pump. This could be acoustical and vibrational effects. When gas is present in the working fluid, the emitted noise from the pump reduces significantly. This effect is shown by sound intensity measurements as well as measurements with an acoustic camera and laser vibrometry and compared to the results for single-phase flow.

The maximum amount of gas for the test pump is measured at different rotational speeds. Some theories to improve the maximum amount of gas in the working fluid are presented and the modifications are tested on a test rig. These modifications consist of the idea that a pump without NPSH-impeller could process higher amounts of gas in multiphase-flow conditions. An additional gas outlet hole is added to the pump to allow a phase separation and therefore a better two-phase flow handling of the pump. The effect of these changes on the maximum amount of gas are presented and evaluated.
Investigation of Dust Separator Design and Risk Mitigation
Authors: Strasser Wayne , Strasser Alex
Published: October 2017

A computational study was carried out to investigate the effects of internal geometry changes on the likelihood of solids buildup within, and the efficiency of, an industrial dust collector. Combustible solids held up in the unit pose a safety risk. The dust collector serves multiple functions, so the design requires a delicate balance. Particles should be separated from the incoming mixture and collected in the bottom of the unit. This particulate material should freely flow into a high-speed ejector (Mach 0.4) underneath. Gas must also flow freely to the top outlet, but sufficient gas must flow down to the ejector so that its motive gas augments the transport of particles back to the reactor (“recirculation”). Computational design evaluations included 1) rod spacing, 2) ledge removal, and 3) rod cover plates. Testing on particle size distribution and density were carried out in-house to provide inputs to the CFD model. Rod spacing reduction had a mixed effect on flow distribution. Plates were found to induce a negative effect on recirculation and a mixed effect on combustible solids accumulation. Removal of the ledge, however, offered slightly more recirculation along with completely alleviating stagnant solids accumulation. It is shown that, without consideration of detailed fluid physics, general separator design principals might be misguiding.
High-Speed Microdroplet Impact on a Textured Rough Surface: A Numerical Investigation
Authors: Tan Hua
Published: October 2017

In this paper, the investigation on dynamics of high-speed micron-sized droplet impact on textured surfaces is carried out through computational fluid dynamics (CFD) simulations. An open-source code Gerris has been adapted to address the challenging issues facing simulations of high-speed impact of microdroplets on the rough surface, such as thin spreading lamella, secondary droplet breakup, and small features of rough surfaces. Validation is first presented to evaluate the accuracy of the simulation code for modeling high-speed droplet impact on the microstructured surface. Then, we carry out 3D simulations of a 10 μm diameter water droplet impact on different textured surfaces with different impact velocities. We find that a large portion of the thin lamella actually surfs over the top of pillars during spreading with only center area of impact saturated with liquid. Our simulations indicate that both impact velocity and surface morphology play an important role in the splashing phenomenon. Increasing pillar spacing makes droplet impact more prone to splashing. Splashing on surfaces of larger pillar spacing is characterized by the breakup of high-speed jets. Larger impact velocity results in more intensified splashing. For a given impact velocity, densely packed pillars (i.e., smaller pillar spacing) can reduce or even suppress the splashing due to viscous drag effect from pillars in wetted region. The existing splashing threshold models that depend only on surface roughness fail in the prediction of the critical speed for splashing on textured surfaces.
Study on the Methods for Adjusting the Vacuum Degree of Jet Vacuum Device
Authors: Feng Xusong , Xiang Qingjiang , Xu Zhengdian , Sun Tao
Published: October 2017

Vacuum preloading technique was used to deal with the dredged sludge and the jet vacuum device was adopted. The adjustable vacuum degree device has the advantage for the dredged sludge treatment process. By using the test rig of jet pump, the vacuum adjustable ways and methods were experimentally studied. The results are as follow: when changing the parameter m, which represent the area ratio of throat and nozzle, different gas suction ability and vacuum degree will be obtained. According to vacuum preloading technique construction stage, nozzles with different diameter can be replaced in jet pump to meet different needs. Distance between nozzle outlet and throat inlet L has an optimized value, during the process of adjusting the distance L toward the optimal value, the vacuum degree in jet pump was changed, but the changing range was limited. There is a small influence on the adjustable vacuum degree when changing the length of throat. The highest vacuum value can be achieved with a vertical installation of the jet pump and with long length of throat. The vacuum value appears a logarithmic growth with the nozzle jet intensity, thus changing the working pressure in front of nozzle is a suitable way for vacuum adjustable. There is a good prospect in other applications when the vacuum degree can be adjusted accurately.
Numerical Analysis of a Centrifugal Fan for a Road Sweeper
Authors: Chen Xiaoxuan , Yang Mingyang , Deng Kangyao , Bai Yunlong
Published: October 2017

Road sweeper is the widely-employed machine to clear up garbage and dust on streets. Its performance has profound influence on the reduction of fuel consumption and hence CO2 emission. The key component of a road sweeper is a centrifugal fan which produces suction force for clearing. Therefore, the performance of this device has direct impact on fuel economy of the machine. This paper targets at the performance analysis of a centrifugal fan in a commercial road sweeper. Firstly, the performance and flow field of the centrifugal fan are analyzed by computational fluid dynamics (CFD) method. The breakdown of the flow loss in the fan shows that the volute and the impeller are major components contributing to flow loss in the fan. The flow at the inlet of the impeller is highly distorted due the interaction among the asymmetrical inlet duct, the leakage and the volute tongue. Because of the interaction, flow passages near the tongue are the ones with the highest flow loss. Moreover, the flow velocity entering the volute is considerably high which thus results in high flow loss in the volute. Finally, based on the flow field analysis, an inlet duct with round shape is designed preliminarily and simulated together with the centrifugal fan. The results show that the efficiency can be improved by more than 4% compared with the original configuration due to the alleviation of the interaction.
Design Study of a Pyrolysis Plant Compressor With Heavy Wall Erosion From Metal Particle Impact
Authors: Omri Riadh , Semel Matthias , Delgado Antonio , Russwurm Hans J.
Published: October 2017

In a pyrolysis plant, a mounted centrifugal compressor takes heavy damage because of erosion originating from metal particle mixed with the inlet air flow impacting its blades and volute walls. In a first step, the original impeller design as well as other centrifugal compressor designs are studied to identify the design parameters which influence the erosion distribution, shape and magnitude. It has been concluded that the first impact plays an important role in defining the particles trajectories and the erosion on the walls.

A novel impeller design method based on particle trajectories after a controlled first impact is introduced.

The new setup is simulated via CFD coupled with Finnie erosion model to assess the damage. This design is improved in a further step. Adequate simulation setups such as interfaces, boundary conditions and particle coupling methods with carrier fluid are introduced.

This study focuses on predicting the particle trajectory within the impeller to reduce the impacts on blade walls and thus reducing the erosion rate. For all designs, the analysis is conducted in the same stage operating point, this point is defined at a predefined volume flow VF [kg/m3] and total-to-static pressure Δp[Pa] as is recommended for the pyrolysis facility including the compressor. Simulations are conducted in a steady state with compressible air at high static temperature going to 530°C. For CFD calculations the software in use is CFX of the ANSYS Group. All mesh used is structured and produced by TurboGrid for the blade rows and with Icem for inlet, outlet and volute.

The final compressor design contain the design recommendation for hub form and outlet flow angle.
Separation Kinetics of Oil/Water Emulsions Stabilized by Nanoparticles
Authors: Gavrielatos Ilias , Dabirian Ramin , Mohan Ram S. , Shoham Ovadia
Published: October 2017

A state-of-the-art, Portable Dispersion Characterization Rig (P-DCR) is used to investigate the effect of nanoparticles on oil-water emulsion formation and stabilization. Mineral oil and distilled water are used as the test fluids and separation profiles are obtained from the experiments using a sophisticated software. Spherical silica nanoparticles of average primary particle size of 20 nm were selected as the emulsifying agent, since silica is commonly found in the produced fluids. Nanoparticles of different wettabilities were used to investigate their effect on separation kinetics of solid stabilized emulsions in terms of solid particle concentration, wettability, initial dispersion phase, water-cut, and shearing time.

In one series of experiments the emulsions were prepared with intermediate-wet nanoparticles. Both simple water-in-oil (W/O), as well as multiple oil-in-water-in-oil (O/W/O) emulsions were observed. Faster separation occurred when the particles were initially dispersed in oil. Increased nanoparticle concentration, as well as shearing time typically resulted in slower emulsion separation rates.

Another series of experiments was performed with hydrophobic and hydrophilic nanoparticles. Very fast separation rates were observed when using hydrophilic silica nanoparticles and 25% water-cut regardless of solid concentration. However, when the water-cut was increased to 50% and 75% very stable emulsions were produced. Emulsions prepared using hydrophobic particles were the most stable across all water-cuts. For the case of 25% water-cut, no water coalescence was observed for a wide range of oil-wet nanoparticle concentrations. Oil creaming was promoted as the concentration of solids decreased, and the emulsions remained oil continuous and highly resistant to water coalescence even for very low solid concentration (100 ppm), resulting in a dispersed phase volume fraction as high as 93%. The effect of nanoparticles on the properties of pure fluids, namely, density, viscosity and surface/interfacial tension is also reported.

The main findings of the study include the following: Nanoparticles, even at low concentrations, can significantly decrease separation rates of oil and water emulsions. The Portable Dispersion Characterization Rig (P-DCR) is recommended as an effective way to measure emulsion stability in the field.
Investigating the Effects of Using Synthetic Jet on Wing Tip Vortex at Low Reynolds Number
Authors: Kamari Djavad , Tadjfar Mehran
Published: October 2017

Evolution of wing tip vortex has been widely studied by many researchers. Winglet, jet, and suction devices have been implemented close to the wing tip to passively or actively mitigate the tip vortex effects. This study aims to investigate the effects of employing a synthetic jet at the tip of a half wing model. The flow was assumed to be incompressible, low speed and the Reynolds number based on chord length with aspect ratio equal to two for half wing was 1.8 × 105. Different reduced frequencies and momentum coefficients were applied. A Detached Eddy Simulation by considering Spalart-Allmaras as the turbulence model for subgrid scale zone and near the walls was employed to simulate the flow field study. Results showed large diffusivity in vortex core. Also, a reduction in longitudinal and total velocity magnitude has observed at vortex core region in the near wake.
Numerical and Experimental Investigation of Trailing Edge Modifications of Centrifugal Wastewater Pump Impellers
Authors: Litfin Oliver , Delgado Antonio , Haddad Kais , Klein Horst
Published: October 2017

Centrifugal pump impellers for wastewater applications have to be designed to meet additional requirements compared to clearwater pumps. Therefore these impellers usually have only one to three relatively thick blades and large width to diameter ratios. The presented study deals with the effect of trailing edge modifications, especially under-filing, to this class of impellers. Two wastewater pump impellers with different specific speeds have been investigated numerically and a detailed loss analysis has been made for the impellers with default and modified trailing edge configurations. In case of the impeller with lower specific speed the head but not the efficiency could be increased by trailing edge under-filing. For the impeller with higher specific speed, under-filing resulted in an significant increase in head and efficiency. The analysis of the losses showed how the losses in different sections of the impeller are affected by the trailing edge modifications and how and under what circumstances the efficiency can be increased in this way. Experiments on the test rig confirmed the numerical results and stated an increase in head of 7.7 percent at no increase in efficiency for the impeller with the lower specific speed and an increase in head of 11.7 percent at an efficiency gain of 1.7 percent at the design flow-rate and even 4.4 percent increase in maximum efficiency for the impeller with higher specific speed.
Vortex-Induced Vibration of a Circular Cylinder With Low Mass Ratio Near a Plane Wall
Authors: Daneshvar Sina , Morton Chris
Published: October 2017

Vortex induced vibration of a circular cylinder with low mass ratio in vicinity of a wall boundary is investigated experimentally in a water tunnel facility. Simultaneous measurements of the flow field via planar Particle Image Velocimetry and amplitude response have been carried out across a wide range of reduced velocities and cylinder-wall gap ratios (S* = S/D). For S* ≥ 3, both the amplitude response and the wake development are not significantly affected by the presence of the wall boundary. As S* is decreased below 3, the amplitude response decreases until S* ≈ 0.5, where the cylinder begins to periodically impact the wall. For all S* ≤ 0.5, the cylinder continues to impact the wall in a periodic fashion, and the reduced velocity range over which this occurs increases. Mean field and RMS field statistics revealed strong asymmetric wake development for S* < 3. Proper Orthogonal Decomposition of the velocity data was used to investigate the energy distribution in the coherent wake structures, and to filter the incoherent fluctuations via construction of a Reduced Order Model. Reconstructions of instantaneous vorticity fields obtained from the ROM illustrate the changes in vortex shedding patterns with the cylinder response.
Distribution of Air Flow Through a Green Wall Module
Authors: Abdo Peter , Huynh B. P. , Avakian Vahik
Published: October 2017

Green or living walls are active bio-filters developed to enhance air quality. Often, these walls form the base from which plants are grown; and the plant-wall system helps to remove both gaseous and particulate air pollutants. A green wall can be found indoors as well as outdoors, and could be assembled from modules in an arrangement similar to tiling. The module is a rectangular plastic box (dimensions about 500 mm × 500 mm × 130 mm) that holds a permeable bag containing a plant-growing medium (replacement for soil). The front face of the module has multiple openings for plants to protrude out from the bag inside. Plant roots are imbedded in the medium. A fan positioned at a central opening on the module’s back face drives air through the medium-plant-roots mix and then onward through the plants′ canopy; and these would help remove both gaseous and particulate pollutants from the air. Volatile Organic compounds (VOCs) and particulate matters PMs are both reduced by passing through the plant-growing medium, thus reducing the percentage of air flow that passes through the open top face of the module is essential to maximize the capacity of bio-filtration. Drip-irrigation water is dispensed from a tube running along the open top-face of the module. The module has also a small drainage hole on its bottom face. Pressure drop across the module as well as air-flow rate through it have been obtained in a previous work [1], air-flow distribution through the module and the effect of introducing a cover to the module’s open top face are investigated in this work to improve the design of the module and achieve more appropriate flow rate and flow distribution. The top cover essentially includes small holes of 10 mm diameter to allow the necessary irrigation. The measurements help to determine the pattern of flow resistances which in turn will be used in a future CFD (Computational Fluid Dynamics) analysis.
A Molecular Dynamics-Based Model for Knudsen Number and Slip Velocity
Authors: Cheikh Mohamad I. , Schinstock Emma A. , Ferland Grant P. , Chen James
Published: October 2017

Much research has been devoted to incestigating the relationship between Knudsen number and slip velocity using different lattice Boltzmann methods. However, these models are complex to implement for simulations in continuum regime, and have shown to diverge when compared with Direct Simulation Monte Carlo (DSMC) simulations at high Knudsen numbers. In this study, a molecular dynamics (MD)-based Knudsen number is presented, and the relationship between Knudsen number and slip velocity is presented. The proposed slip model directly correlates the Knudsen number with the slip velocity. The model is implemented on a shear-driven MD simulation of a Couette flow, and curve fitting is used to get an exponential solution for the slip velocity. The solution obtained from the proposed model as well as the solutions from the literature are compared with a DSMC simulation. The results show that the proposed exponential solution agrees well with DSMC simulations in comparison with the models from the literature. The exponential solution can serve as boundary conditions for simulating flows at different Knudsen numbers in continuum regime.
Compact and Thermosensitive Micropump Inspired by Plant Leaf
Authors: Kim Hyejeong , Kim Kiwoong , Lee Sang Joon
Published: October 2017

Liquid transportation without employing a bulky power source, often observed in nature, has been an essential prerequisite for smart applications of microfluidic devices. In this report, a leaf-inspired micropump (LIM) which is composed of thermo-responsive stomata inspired membrane (SIM) and mesophyll-inspired agarose cryogel (MAC) is proposed. The LIM provides a durable flow rate of 30 μl/ḣcm2 for more than 30 h at room temperature without external mechanical power source. By adapting a thermo-responsive polymer, the LIM can smartly adjust the delivery rate of a therapeutic liquid in response to temperature changes. In addition, as the LIM is compact, portable, and easily integrated into any liquid, it might be utilized as an essential component in advanced hand-held drug delivery devices.
Part-Load Cavitation Instability Investigation of a High Specific Speed Pump
Authors: Shen Zhenhua , Pedersen Nicholas , Li Hong , Jacobsen Christian Brix , Ma Xiaofen
Published: October 2017

Cavitation instability in pump part-load condition is an ongoing subject of research due to erosion and noise. For some high specific speed (nq) pumps, NPSH3%-peak at part-load represents one of the cavitation instabilities. This paper describes the recent investigations and results on performance and cavitation instabilities of a high nq pump. An nq 99 impeller that shows a NPSH3%-peak at 70% of nominal flow rate is investigated by using numerical calculations and experiments. Both experimental and numerical results show that the head curves also have instability phenomenon near 70–80% of nominal flow rate. By analyzing simulation results, part-load recirculation near the shroud is found both under non-cavitating and cavitating conditions. With the pressure decreasing, the recirculation zone become larger and cavitation bubbles influence the flow pattern near the trailing edge at the suction side.
Calculation Model Based Design-Point Gas Generator Performance Adaptation Method
Authors: Li Shiyao , Li Zhenlin , Huang Ning
Published: October 2017

Accurate performance simulation can provide operating parameters and performance parameters for the gas turbine’s optimization, maintenance, and fault diagnosis. However, the components maps necessary for performance simulation are not publically available. In addition, the same type of gas turbine has slightly different component operating characteristics due to components′ variations in status and assembly tolerance. These causes bring real difficulties to the research of performance simulation.

In order to obtain accurate components characteristics and performance simulation results, the original or generic components maps should be modified by the scaling factors. In the process of calculating scaling factors, the simulation model is applied repeatedly to determine the engine’s actual performance parameters until the simulated gas path thermal parameters are compatible with the actual measureable data.

This paper introduces a new adaptation method and substitutes the calculation model with the simulation model in the adaptation process. It directly calculates the mass flow rate, isentropic efficiency, and pressure ratio of compressor and turbine based on measureable parameters such as gas path temperature, pressure, fuel component and mass flow rate. Moreover, this paper introduces the virtual gas generator model that enhances the applicability of calculation model based performance adaptation method on gas generators with different structures.

This method has been applied to GE PGT25+ gas generator (single-spool) and RR RB211-24G gas generator (double-spool). Compared with the simulation model used in adaptation process, performance calculation model is much simpler and less time consuming.
Numerical Study on the Characteristics of Natural Supercavitation by Planar Symmetric Cavitators With Streamlined Headforms
Authors: Zheng Zhi-Ying , Wang Lu , Li Qian , Wang Yue , Cai Wei-Hua , Li Feng-Chen
Published: October 2017

A novel supercavitation-based device named Rotational Supercavitating Evaporator (RSCE) was recently designed for desalination. In order to improve the blade shape of rotational cavitator in RSCE for performance optimization and then design three-dimensional blades, two-dimensional numerical simulations are conducted on the supercavitating flows (with cavitation number ranging from 0.055 to 0.315) around six planar symmetric cavitators with different streamlined headforms utilizing k – ε – v′2 – f turbulence model and Schnerr-Sauer cavitation model. We obtain the characteristics of natural supercavitation for each cavitator, including the shape and resistance characteristics and the mass transfer rate from liquid phase to vapor phase. The effects of the shape of the headform on these characteristics are analyzed. The results show that the supercavity sizes for most cavitators with streamlined headforms are smaller than that for wedge-shaped cavitator, except for the one with the profile of the forebody concaving to the inside of the cavitator. Cavitation initially occurs on the surface of the forebody for the cavitators with small curvature of the front end. Even though the pressure drag of the cavitator with streamlined headform is dramatically reduced compared with that of wedge-shaped cavitator, the pressure drag still accounts for most of the total drag. Both the drag and the mass transfer rate from liquid phase to vapor phase are in positive correlation with the supercavity size, indicating that the cavitators with the elliptic and hyperbolic cosine-type forebodies could be utilized for the optimal design of three-dimensional blade shape of RSCE.
A Detailed Experimental and Numerical Investigation of Flow Structures in a Turbine Tip Gap With Passive Injection
Authors: Passmann Maximilian , aus der Wiesche Stefan
Published: October 2017

An experimental and numerical study of the flow in the tip gap of a linear turbine blade cascade has been performed. Besides the plain tip gap flow, a passive injection with a single injection hole at the blade tip near the pressure side has been considered. Detailed measurements of the static pressure distribution on the cascade end wall and on the blade surface are conducted. The pressure measurements are supported by surface oil flow visualizations of the blade tip and suction side surface to get qualitative insights into the underlying flow structures. The experimental data is compared to highly resolved unsteady RANS simulations. Previous investigations on the same cascade have shown, that flow separation phenomena on the suction side surface play an important role on this blade profile, hence the transition model by Menter was used for all simulations. It was found, that the influence of a single passive injection hole is limited to a narrow region downstream. The additional injection jet leads to a changed pressure distribution, indicating a lower velocity level and a weakened tip gap vortex.
Numerical Study on Two-Phase Flow Patterns in Vortex Dropshaft
Authors: Wang Xichen , Zhang Jian , Yu Xiaodong , Chen Sheng
Published: October 2017

As one of the main types of dropshaft structure, vortex dropshaft is commonly used in hydropower stations, urban drainage systems and other water conservancy projects. Many scholars have conducted researches into hydraulic characteristics of this type of dropshaft. However, its flow patterns and mechanisms are still not clear. Consequently, a 3-D, steady, two-phase numerical model of vortex dropshaft is developed through FLUENT software, using volume of fluid (VOF) method to track the interface of air and liquid water. Four cases sharing the same geometry domain and boundary conditions with different inlet velocities have been studied. The specific flow patterns and formation mechanisms in the four cases are discussed in this study, and the influences of inlet velocity are investigated as well. The results show two negative pressure zones appearing at inlet and outlet connections threatening the structural safety, and it is important to optimize the structure design and control the inlet flow.