bluuebunny/crossref_metadata_2025 huggingface dataset:
Brownian Diffusion of Nano-Fibers: Application to Mobility Characterizations
Authors: Tian L. , Ahmadi G. , Tu J. Y.
Published: November 2019

In this study, the Brownian diffusion of elongated nano-fibers was investigated numerically. Motions of nano-fibers of different sizes and aspect ratios were resolved by solving the corresponding system of equations governing their coupled translational and rotational motions. The study allowed a close examination of the Brownian diffusion of nano-fibers with respect to the coupling of their translational and rotational motions and how the rotation affects the fibrous particle macroscopic diffusion properties. Particular attention was given to the rotational relaxation time in determining the isotropic and anisotropic diffusive properties of elongated particles. Theoretical and semi-empirical equations were developed to quantify the diffusion coefficients of nano-fibers. Orientation averaged mobility of the nanofiber, nanorod and non-spherical nano-agglomerates was examined by the newly developed Brownian diffusion model. The result was compared with the particle mobility by collision limited reaction rate theory, empirical models and the experimental measurements. The study led to the discovery of a surface dominated mobility for nanoparticles with Knudsen number greater than 5 (Kn > 5). For particles in this range, all morphologies can be viewed as point collision and therefore the use of the equivalent surface mobility diameter was reasonably justified. Beyond this range when Kn < 0.1, however, the study showed that the particle morphology starts to play an important role, and accuracy of the surface mobility approximation reduces as the Knudsen number decreases. The study opened up new approaches for studying fundamental diffusive processes of nano-particles of complex shapes which are numerous in natural environment.
Two Types of Nonlinear Pressure Waves in Bubbly Liquids Incorporating Viscosity and Thermal Conductivity
Authors: Kamei Takafumi , Kanagawa Tetsuya
Published: November 2019

The present study theoretically elucidates an effect of the viscosity and the thermal conductivity on the propagation process of finite amplitude disturbance in bubbly liquids by deriving two types of weakly nonlinear wave equations. Appropriate choices of a set of scaling relations of physical parameters characterizing waves, that is, the wavelength, incident wave frequency, propagation speed, yield the derivation systematically. From the combination of appropriate scaling relations and the method of multiple scales, we can derive the Korteweg–de Vries–Burgers equation for the low frequency long wave and the nonlinear Schrödinger equation for slowly varying envelope wave of the quasi-monochromatic short carrier wave. As a result, the incorporation of conservation equation of energy affects nonlinear, dispersion, and dissipation terms for both long and short waves. Especially, the viscosity and the thermal conductivity lead to change considerably the form of coefficient of dissipation term.
A Dynamic Time Filtering Technique for Hybrid RANS-LES Simulation of Non-Stationary Turbulent Flow
Authors: Jamal Tausif , Walters D. Keith
Published: November 2019

Unsteady turbulent wall bounded flows can produce complex flow physics including temporally varying mean pressure gradients, intermittent regions of high turbulence intensity, and interaction of different scales of motion. As a representative example, pulsating channel flow presents significant challenges for newly developed and existing turbulence models in computational fluid dynamics (CFD) simulations. The present study investigates the performance of the Dynamic Hybrid RANS-LES (DHRL) model with a newly proposed dynamic time filtering (DTF) technique, compared against an industry standard Reynolds-Averaged Navier-Stokes (RANS) model, Monotonically Integrated Large Eddy Simulation (MILES), and two conventional Hybrid RANS-LES (HRL) models. Model performance is evaluated based on comparison to previously documented Large Eddy Simulation (LES) results. Simulations are performed for a fully developed flow in a channel with time-periodic driving pressure gradient. Results highlight the relative merits of each model type and indicate that the use of a dynamic time filtering technique improves the accuracy of the DHRL model when compared to a static time filtering technique. A comprehensive evaluation of the results suggests that the DHRL-DTF method provides the most consistently accurate reproduction of the time-dependent mean flow characteristics for all models investigated.
Numerical Simulation and Vorticity Analysis of Cavitating Flow Around a Marine Propeller Behind the Hull
Authors: Long Yun , Han Chengzao , Ji Bin , Long Xinping , Zhang Zhirong
Published: November 2019

In this paper, the unsteady cavitating turbulent flow around a marine propeller behind the hull is simulated by the k-ω SST turbulence model coupled with the Zwart cavitation model. Three systematic refined structured meshes around the hull and propeller have been generated to study the predicted cavitation patterns and pressure fluctuations. Numerical results indicate that the predicted transient cavitating flow behind the hull wake, including sheet cavitation and tip vortex cavitation, shows quasi-periodic feature and agrees fairly well with the available experimental data. The deviations of pressure fluctuations between experimental data and numerical results are much small. With mesh refining, the cavitation region and the magnitudes of the calculated pressure fluctuations increase, while the differences between two adjacent sets of grids become smaller. In addition, the uncertainty of the thrust coefficient obtained by Factor of Safety method is significantly small. Further, the interaction between the cavitation and the vortex by the relative vorticity transport equation is illustrated. Results show that the magnitude of stretching term is obviously larger than the other three terms, and the dilatation term and the baroclinic term both have an important influence on the generation of vortices.
A Model for a Gas Column Oscillation Inside a Hole by Irradiating an Acoustic Wave
Authors: Furuya Yuki , Sanada Toshiyuki , Watanabe Masao
Published: November 2019

Wet cleaning methods using fluid are widely applied in many industrial fields. For a cleaning inside closed-end holes, it is first necessary to fill the holes to be cleaned with the liquid. However, in structures with small holes, it is difficult to discharge inside the gas due to surface tension. In our early studies, we have found that the discharging a gas inside a closed-end hole was promoted by an impingement of droplet train. And the pressure fluctuation near the gas-liquid interface due to droplet impingement was important.

In this study, we attempted the gas discharge from closed-end holes due to acoustic wave irradiation. First, we theoretically estimated the oscillation of the gas column inside the hole during acoustic wave irradiation. We modeled the natural frequency of the gas column using a spring-mass system. Then we experimentally measured the fluctuation of the gas-liquid interface for the evaluation of the model. In addition, we compared the gas discharge ratio with different frequency and pressure level. The fluctuation of gas-liquid interface and discharging the gas were observed with a high-speed video camera.

As results, the natural frequencies of a gas column were depending on the length of the gas column and the diameter of the hole. From the experiments, we confirmed that the acoustic wave certainly propagated into the hole, and the frequency of the irradiated acoustic wave and the experimentally obtained natural frequency were in good agreement except for extremely low gas discharge ratio condition. Moreover, we observed gas discharge process and found that the high gas discharge ratio were achieved using the acoustic wave close to natural frequency. From these results, we concluded that the assumption based on a spring-mass system is valid.
Numerical Study on the Flow Field Analysis and Optimization of Turbine in Supercritical Compressed Air Energy Storage
Authors: Wang Meng , Deng Jianqiang , He Yang , Chen Haisheng , Xu Yujie
Published: November 2019

Supercritical compressed air energy storage system requires high turbine efficiency over a wide working range at both the design-point and off-design point. The operating range of the turbine is often limited by the occurrence of flow instability, such as distinct vortex and load deterioration. In specific situations, the development of aerodynamic instabilities at low inlet pressure operating conditions can lead to lower turbine efficiency, even lead to turbine choke, limiting the wide operating range of the turbine. Specifically, the high-pressure stage turbine of the expander, namely the first stage turbine, will not only bears a sharp change of inlet pressure but also experiences the maximum and variable pressure drop. In this paper, Real Gas Property (RGP) file for supercritical air is used for simulations. The CFD method and RGP file are validated by the turbine in the NASA report. A detailed 3D CFD analysis is performed for the preliminary designed first stage turbine under variable inlet pressure. With the purpose of improving the aerodynamic performance of the first stage turbine under extreme working conditions, a series of simulations are conducted to examine the effects of the IGV parameters (i.e. different types of IGVs, the nozzle-impeller radial gap distance and the nozzle blade installation angle) and blade thickness, which led to the optimization in overall turbine stability. The results show that IGV TC-2P have good aerodynamic performance, and the matched rotor can achieve an isentropic efficiency of 80% under off-design working conditions. The optimal blade installation angle blade is 35°. And there exists an optimal nozzle-impeller radial gap distance Δr. The turbine efficiency obtains a maximum value at Δr = 5 mm. In all cases for blade thickness, the different configurations have a significant change in inlet total pressure of 4.5 MPa compared to the design pressure of 7 MPa. The maximum efficiency is reached at the ellipse ratio is 1:1 for Case-2. The results of the optimal IGV TC-2P performance optimization is essential to improve the isentropic efficiency at low inlet pressure.
Accuracy of the CRW Models for Prediction of the Deposition and Dispersion of Particles in Inhomogeneous Turbulent Channel Flows
Authors: Mofakham Amir A. , Ahmadi Goodarz
Published: November 2019

The accuracy of the continuous random walk (CRW) stochastic model for prediction of dispersion and deposition of suspended particles in inhomogeneous turbulent channel flows was explored. The Reynolds-averaged Navier-Stokes (RANS) equations in conjunction with the Reynolds Stress Transport model was used to evaluate the mean flow and RMS velocity fluctuation characteristics of a fully developed turbulent channel flow at shear Reynolds number of 219. Then, spherical particles with diameters ranging from 10 nm to 30 μm and dimensionless relaxation times of 10−4 to 50 (in wall units) were uniformly introduced into the channel and their trajectories were evaluated by using the equation of particle motion including the Stokes drag and Brownian excitation. The particle laden flow was assumed to be sufficiently dilute so that the particle-particle collisions and the effects of particles on the flow could be ignored. To incorporate the effects of turbulence velocity fluctuations on particle motions, first, the Conventional-CRW stochastic model, which was originally proposed for homogenous turbulent flows, was used. The particles were tracked for the duration of 10,000 wall units of time and the deposition of particles on the walls was evaluated. By conducting ensemble averaging, the steady-state concentration profiles and deposition velocity of the particles were calculated. Comparison of the predicted results with the direct numerical simulation (DNS) and experimental data suggests that the deposition velocity was overestimated. In addition, unrealistic accumulation of fluid-point particles in the near-wall regions, and overestimation of the turbophoresis effects on finite-size particles were also observed. The poor agreement of the concentration profiles and deposition velocities resulting from the conventional (homogenous flow) CRW model with the experimental and the DNS data pointed to the lack of accuracy of the Conventional-CRW model in generating instantaneous fluid velocity fluctuations seen by ultrafine and finite-size particles in inhomogeneous turbulent flows. Then, the normalized Langevin equation with a drift correction term that was suggested by Bocksell and Loth [1] was used as an improved CRW model for applications to inhomogeneous flows. The simulations for the same range of particle sizes were repeated and the corresponding concentration profiles and the deposition velocity were evaluated. It was shown that the improved CRW model led to a reasonable uniform concentration profile for the ultrafine particles and the predicted concentration profiles of finite-size particles quantitatively matched with the DNS data. In addition, the evaluated deposition velocities from the improved CRW model were also in a good agreement with the experimental data and empirical model predictions.
Effects of Splitter Vanes on the Performance and Pressure Pulsation in a Centrifugal Pump
Authors: Li Chao , Gao Bo , Zhang Ning , Ni Dan
Published: November 2019

Two types of arrangement of splitter vanes at the outlet of a centrifugal impeller is proposed in this paper, that is, staggered vanes and splitter vanes. By means of CFD, the effects of different vanes arrangement schemes on the performance and pressure fluctuation characteristics of the centrifugal pump are compared. The influence mechanism of different schemes is explored based on the fluid flow field analysis. The results show that, compared with ordinary impellers, when the short vanes are 10 degree offset to the suction side of the main vanes, staggered vanes impellers cause the pump head and efficiency to decrease, while the amplitude of pressure pulsation at blade passing frequency (BPF) is reduced by 28% compared with that of the ordinary impeller under the design condition. In the splitter vanes scheme, the pump head and efficiency increased, however the efficiency increased more significantly under the large flow rate condition. The amplitude of pressure fluctuation at BPF is decreased by 14% compared with that of the ordinary impeller under the design condition. The existence of short vanes in both schemes changes the wake flow structure downstream the impeller vanes and tends to weaken the pressure pulsation induced by the rotor-stator interaction (RSI) phenomenon. The results can provide a reference for optimized design of the low vibration and less noisy pumps.
Computational Study of the Downpull Force on High-Head Slide Gates
Authors: Arango Escobar Juan C. , Calderon Villegas David , Benavides Moran Aldo , Molina Ochoa Alejandro
Published: November 2019

This paper presents CFD simulations of the flow through a real bottom outlet equipped with high-head slide gates. The operating head of the gates and the maximum flow rate are 70 m and 650 m3/s, respectively. The numerical simulations were performed in ANSYS-FLUENT version 19.2. VOF method was used to model the free surface flow downstream the slide gates. Hydrodynamic forces were calculated at nine gate openings for a standard 45° lip gate; the downpull coefficients obtained from the simulations were compared with estimates from Naudascher’s analytical method. According to the CFD results, the downpull force acting on the 45° lip gate is 5%–10% lower than the one estimated analytically for the analyzed gate positions. Additionally, the flow through an inverted 30° lip gate was simulated to estimate the downpull coefficient at various gate openings. These coefficients cannot be determined analytically. The methodology here described can easily be applied to different gate geometries for which design coefficients are not available.
Effect of Moisture Content on Mixing Air With Water-Liquid Flowing Through Inverted U-Tube for Power Plant Condenser Applications
Authors: Yousef Khaled , Hegazy Ahmed , Engeda Abraham
Published: November 2019

Computational Fluid Dynamics (CFD) for air/water-vapor and water-liquid two-phase flow mixing with condensation in a vertical inverted U-tube is presented in this paper. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in air/water-vapor and water-liquid mixing flow when condensation is considered. Water-liquid flows upward-downward through the inverted U-tube while the air/water-vapor mixture is extracted from a side-tube just after the flow oriented downward. The CFD simulation is carried out for a side air/water-vapor mixture volume fraction (αm) of 0.2–0.7, water-vapor mass fraction (Xv) of 0.1–0.5 in the side air/water-vapor mixture and water-liquid mass flowrate (mw) of 2,4,6, and 8 kg/s. The present results reveal that, at lower air mass flow rate, no significant effect of Xv on the generated static pressure at the inverted U-tube higher part. However, by increasing the air mass flow rates, ma ≥ 0.001 at mw = 2 kg/s, and ma ≥ 0.00125 at mw = 4 kg/s, we can infer that the lowest static pressure can be attained at Xv = 0.1. This may be attributed to the increased vapor and air mass flow rates from the side tube which results in shifting the condensation from the tube highest part due to air accumulation. This leads to increasing the flow pressure and decelerating the water-liquid flow. Raising mw from 2 to 4 kg/s at the same vapor mass ratio results in a lower static pressure due to more condensation of water vapor. The turbulent intensity and kinetic energy starts to drop approximately at ma = 0.002 kg/s, and αm = 0.55–0.76 at mw = 2 kg/s for all Xv values but no noticeable change at mw = 4 kg/s occurs. These findings estimate the operational values of air and water mass flow rates for stable air entrainment from the side-tube. Increasing the air and vapor mass ratio over these values may block the evacuation process and fails the system continuance. Likewise more air entrainment from the side-tube will decelerate the water flow through the inverted U-tube and hence the flow velocity will decrease thereafter. Moreover, this study reveals that the inverted U-tube is able to generate a vacuum pressure down to 55.104 kPa for the present model when vapor condensation is considered. This generated low-pressure helps to vent an engineering system from the non-condensable gases and water vapor that fail its function if these are accumulated with time. Moreover, the water-liquid mass flow rate in the inverted U-tube can be used to sustain the required operating pressure for this system and extract the non-condensable gases with a less energy consuming system. The present CFD model provides a good physical understanding of the flow behavior for air/water-vapor and water-liquid flow for possible future application in the steam power plant.
Development of High-Efficiency Half-Ducted Propeller Fan for Air-Conditioners by Blade Tip Shape Modification
Authors: Yoshikawa Masashi , Toyoda Hiroyuki , Daisaka Hisashi
Published: November 2019

We developed a high-efficiency half-ducted propeller fan to reduce the electric power consumption of the outdoor unit of air conditioner by using computational fluid dynamics (CFD). Total pressure loss coefficient on the cylindrical surface of blade tip started increasing at the middle of the blade, and the region of high total pressure loss coefficient was formed after trailing edge. Therefore, we assumed that decreasing this region helped increasing static pressure efficiency. Limiting stream lines on the pressure surface showed that the flow from leading edge leaked at the middle of the blade tip, so it was assumed that the region of the high total pressure loss coefficient arose from the leakage at the middle of the blade tip. We confirmed that static pressure at the middle of blade tip, which was the leakage point, was low. We assumed that low inward force to the flow caused the leakage. On the other hand, static pressure at trailing edge of the blade tip was high. Therefore, it was found that the inward force could be increased by making the static pressure higher at the meddle of the blade tip. In order to make the static pressure higher at the middle of the blade tip, we attempted to move the maximum camber position of the blade tip from trailing edge side to leading edge side. Calculation results showed leakage at the blade tip decreased and the static pressure efficiency increased by 0.5%. Experimental results showed that the static pressure efficiency increased by 1.7 % and sound pressure level was almost the same. For the above reasons, we found leakage of flow from leading edge could be decreased by adjusting the maximum camber position of the blade tip. Decreasing leakage contributed to increasing static pressure efficiency and decreasing electric power consumption.
Pressure Fluctuation Reduction in Side Channel Pumps Using a Modified Impeller Blade
Authors: Wei Xueyuan , Zhang Fan , Appiah Desmond , Chen Ke , Yuan Shouqi , Böhle Martin
Published: November 2019

For the unique performance advantages of side channel pump delivering flows at high heads, it has been applied in many fields such as petrochemical, pharmaceutical, food processing, automobile fuel pumping etc. However, the operation of the pump is strongly affected by the intensity of the pressure fluctuation, thus the pressure fluctuation exiting within the pump cannot be neglected because of its direct influence on the noise and vibration performance. Therefore, reducing the pressure fluctuation intensity is a key point for research. The side channel pump studied in this paper is a prototype with an axial channel and a 24-blade impeller. The pressure fluctuation intensity of the pump is studied using numerical simulations at best efficiency point. The Reynolds-averaged Navier-Stokes equations (URANS) are solved with the Shear Stress Transport (SST) k-ω turbulence model using commercial CFX codes. The time and frequency plots of the pressure fluctuation coefficient, Cp of the original impeller scheme at different monitoring points revealed high pressure fluctuation intensities affecting the pump’s operating reliability. For the purpose of reducing the pressure fluctuation intensity in the pump, the impeller geometry is modified with a small blade at the outer radius. The study showed that the pressure fluctuation within the pump is reduced significantly at the monitoring points. Moreover, it is found out that the pressure fluctuation in both impeller schemes are mainly caused by the flow exchange between the impeller and side channel. The results of this paper can provide reference for pressure fluctuation reduction and Noise-Vibration-Harshness (NVH) study in turbomachinery.
Physicochemical Characterization of Mammalian Mucus and Mucin Solutions in Response to pH and [Ca2+]
Authors: Curnutt Austin , Smith Kaylee , Darrow Emily , Walters Keisha B. , Vasquez Erick S. , Kundu Santanu
Published: November 2019

Mucus is a complex fluid that maintains moisture and simultaneously acts as a barrier and facilitates transport of select materials between the body and adjacent fluids. While mucus is comprised primarily of water, it is highly heterogeneous containing the biopolymer mucin along with lipids, salts, DNA, proteins, and cells. Complex mechanisms control the reversible network formation observed in mucus and mucin solutions. Some isolated relationships between biopolymer network structure, pH and ionic strength, and rheology have been identified; however, a complete understanding of the interplay in these mechanisms is lacking. In this effort, rheology of native mucus and mucin solutions was examined as a function of pH and salt concentration. Bulk rheology of native and artificial lung mucus confirmed that native mucus displays a solid-like behavior at low strain values. Mucus displays this solid-like gel behavior at pH values ca. 4 and below, and displays solution behavior at higher pH values. Ion concentration also plays an important role with divalent cations (Ca2+) reducing the viscosity of gelled mucin and increasing the viscosity of solution-state mucin. In addition to rheological characterization, mucin-mucin and mucin-solute interactions and resultant changes in microstructure were also studied. Morphological and chemical changes at the nano-scale were correlated to the micro-structural changes observed with rheology. Dynamic light scattering showed mucin polymer particle size heterogeneity as well as a significant increase in particle size at pH values ca. 4 and below — where the solutions display a gel behavior. Using zeta potential a decrease in dispersive forces was observed that allows for polymer-polymer interaction and particle aggregation at low pH values. Atomic force micrography showed spheroid-like aggregates between adjacent mucin particles under acidic conditions. The ability to understand and control the reversible association of network structures in polymer and biopolymer systems, such as mucin, through supramolecular interactions has fundamental impacts in the field of polymer science and engineering. There is also significant potential to advance applications involving novel hydrogel materials, such as disease treatments and drug delivery.
Flow Past Two Cylinders Arranged in Tandem Within a Microbubble Plume
Authors: Uchiyama Tomomi , Kano Ryota , Degawa Tomohiro , Takamure Kotaro
Published: November 2019

This study investigates the flow past two cylinders arranged in tandem within a microbubble plume inside a tank. Microbubbles with a mean diameter of 0.055 mm are released by water electrolysis from electrodes placed at the bottom of the tank. Upon rising, these microbubbles induce an upward water flow around them due to buoyancy. Orthogonally to the axis of this microbubble plume, two cylinders with a diameter D of 30 mm are arranged in tandem. The distance between the cylinders, L, ranges between 1.5D and 3D. The bubbles and the water flow around the cylinders are visualized, and the bubble velocity distribution is measured. The experiments reveal the water and bubble shear layers originating at the sides of the lower cylinder, and allow the elucidation of their behavior around the upper cylinder. Furthermore, this study makes clear the effects of L on the flow around the two cylinders, such as the stagnant bubbly flow and the bubbly wake.
Design and Development of a Small Multistage Flash Desalination System Using Aspen HYSYS
Authors: Islam Md. , Banat F. , Baba A. , Abuyahya S.
Published: November 2019

Fresh water demands are increasing day by day because of growing population, industrialization, and increased living standards. Desalination technology has become a significant solution of fresh drinking water for many parts of the world. Lack of fresh water resources in dry environments has encouraged the establishment of desalination processes and developed technology to compensate for water scarcity. The MSF (multistage flash) desalination technique has received wide spread acceptance due to low temperature heat source (waste heat/inexpensive energy), simple construction high process reliability and simple maintenance. MSF typically has the highest water production cost among available desalination technologies, which can be reduced with using solar energy/co-generation. Since Abu Dhabi is in the solar belt region and is blessed with huge solar energy, MSF desalination can be powered by solar power in addition to industrial waste/fossil fuel energy, which will significantly reduce the cost as well as carbon, footprint. In this research, multistage flash desalination is modelled using ASPEN HYSYS package V8. We have designed each components of the system, mostly heating source, vacuum/flash chambers, heat exchangers and developed the whole system. Some parametric study, i.e. feed rate, top brine temperature, heat input, pressure, productivity etc. of multistage flash desalination system has been conducted in this research. Two case studies have been conducted and found a relation between feed flow rate and water production rate as well as chamber pressure with vapor formation. This design will help to build the pilot plant, do experimental test and validate the model.
Experimental, Numerical and Analytical Evaluation of a Helical-Turbine Performance
Authors: Kang Donghyuk , Tsutsumi Hiromasa , Hirahara Hiroyuki
Published: November 2019

A helical wind turbine has been analyzed experimentally and numerically and a novel design protocol has been proposed by means of blade element and momentum theory. The subject of the present analysis is to discuss the effect of low tip speed ratio and high one, respectively. In the low tip speed ratio, the turbine is driven by the torque generated from the flow turning radially after colliding with the runner. On the other hand, in the high tip speed ratio, the turbine is operated by the torque generated from the flow passing through axially the turbine.
Experimental Investigation on the Electrokinetic Motions of Colloidal Particles at an Interfacial Boundary Between Solid and Liquid
Authors: Shirai Katsuaki , Kaji Shoichiro , Hosokawa Shigeo , Kawanami Tsuyoshi , Hirasawa Shigeki
Published: November 2019

We investigate electrokinetic behavior of colloidal particles in the vicinity of a solid-liquid interface. Colloidal liquids are expected to be used as thermal transport media for heat transfer applications such as nanofluids and phase change emulsions. They contain submicrometer-sized particles in liquid, and electrokinetic behavior of the solute particles should play an important role in the heat transfer between solid-liquid interfacing boundaries. However, experimental investigation of the behavior remains difficult due to the required spatial resolution beyond diffraction limit. We developed a measurement system based on laser Doppler principle using an interference of evanescent waves generated at total internal reflections of incident lasers at a solid wall. The system was developed for the measurement of velocities of colloidal particles at an interfacing boundary of colloidal liquid and a solid wall. The system has a unique advantage of a high spatial resolution in the direction perpendicular to the boundary due to the short penetration depth of an evanescent wave in the range of a few hundred nanometers. The principle and performance of the measurement system were investigated using a scanning probe in the measurement volume. We experimentally confirmed the validity of the measurement and characterized the uncertainty of velocity measurement. The system was further applied in a series of measurements of alumina particles dispersed in water in a square-shaped cell under induced electric fields. The measured velocities are proportional to the field strengths at different particle concentrations. The linear relationship is consistent with theoretical predictions, which demonstrates the feasibility of the system for the measurement of velocities of colloidal particles in the near wall region.
A Multi-Relaxation-Time Finite Volume Discrete Boltzmann Method for Viscous Flows
Authors: Chen Leitao , Sadat Hamid , Schaefer Laura
Published: November 2019

Conventional constitutive law-based fluid dynamic models solve the conservation equations of mass and momentum, while kinetic models, such as the well-known lattice Boltzmann method (LBM), solve the propagation and collision processes of the Boltzmann equation-governed particle distribution function (PDF). Such models can provide an a priori modeling platform on a more fundamental level while easily reconstructing macroscopic variables such as velocity and pressure from the PDF. While the LBM requires a rigid and uniform grid for spatial discretization, another similar unique kinetic model known as the finite volume discrete Boltzmann method (FVDBM) has the ability to solve the discrete Boltzmann equation (DBE) on unstructured grids. The FVDBM can easily and accurately capture curved and more complicated fluid flow boundaries (usually solid boundaries), which cannot be satisfactorily realized in the LBM framework. As a result, the FVDBM preserves the physical advantages of the LBM over the constitutive law-based model approach, but also incorporates a better boundary treatment. However, the FVDBM suffers larger diffusion errors compared to the LBM approach. Building on our previous work, the FVDBM is further developed by integrating the multi-relaxation-time (MRT) collision model into the existing framework. Compared to the existing FVDBM approach that uses the Bhatnagar–Gross–Krook (BGK) collision model, which is also known as the single-relaxation-time (SRT) model, the new model can significantly reduce diffusion error or numerical viscosity, which is essential in the simulation of viscous flows. After testing the new model, the MRT-FVDBM, and the old model, the BGK-FVDBM, on Taylor-Green vortex flow, which can quantify the diffusion error of the applied model, it is found that the MRT-FVDBM can reduce the diffusion error at a faster rate as the mesh resolution increases, which renders the MRT-FVDBM a higher-order model than the BGK-FVDBM. At the highest mesh resolution tested in this paper, the reduction of the diffusion error by the MRT-FVDBM can be up to 30%.
Dissipation of Injected Slug in Enlarged Impacting Tee in Single Branch Blocking Configuration
Authors: Cole Tanner , Dabirian Ramin , Mohammadikharkeshi Mobina , Mohan Ram , Shoham Ovadia
Published: November 2019

A novel Enlarged Impacting Tee-Junction (EIT), which introduces longer slugs to be dissipated utilizing “Single-Branch-Blocking” is studied experimentally and theoretically under stationary slug-injection conditions to further understand the dissipation mechanism through observation of longer slugs.

The EIT test section is designed and constructed, which consists of one inlet pipe connected to a larger, perpendicular pipe allowing flow in both directions. The inlet is 4.6 m of 0.05 m diameter pipe, while the perpendicular “manifold” is 0.074 m in diameter and 5.5 m in length. In order to observe the dissipation of longer slugs, a modification is made to the Normal EIT configuration. The longer slugs in the EIT are generated by blocking one of the EIT branches, allowing flow in only the unblocked branch of the EIT. Thus, the entire injected slug (rather than half in the case of no blocking configuration) dissipates in the branch. For this configuration, stationary slugs are injected into the EIT with lengths of 40d, 50d, 60d, and 70d (with d being the inlet diameter). A total of 64 slug injection tests are conducted utilizing both air-water and air-oil flow.

The experimental data show that slug dissipation has a nonlinear increasing relationship with mixture velocity. Furthermore, the data show that higher dissipation length is observed with air-water flow as compared to air-oil flow in the slug injection experiments due to higher shed slug volume of oil. Also, the acquired data are used to validate the EIT slug dissipation model developed by Mohammadikharkeshi (2018). For the Single-Branch-Blocking investigation, comparison between the acquired experimental data and the modified Mohammadikharkeshi (2018) Normal EIT model predictions reveals excellent comparison, with an average discrepancy of 12%.
Numerical Investigation of an Intake Duct for a Waterjet Propulsion System Using Modified Partially Averaged Navier-Stokes Method
Authors: Huang Renfang , Luo Xianwu
Published: November 2019

When the marine vessels exceed the speed of 30 knots, it is preferred to adopt the waterjet propulsion method due to its high propulsive efficiency, good maneuverability, less vibration and good anti-cavitation performance. The efficiency of the waterjet pump is up to 90% with advanced modern design methods while 7∼9% of total power is lost in the intake duct. In this paper, the flow simulation in an intake duct has been conducted using the modified partially averaged Navier-Stokes method for better understanding of flow features inside the intake duct and instructing how to reduce the power loss at various ship speeds and inlet velocity ratio (IVR) with considering the hull boundary layer. The nonuniformity and perpendicularity at the impeller plane is applied to analyze the flow quality at the outlet plane of intake duct. The results indicate that the nonuniformity decreases while the perpendicularity increases with increasing IVR. Thus a large IVR together with a high ship speed would cause better outflows. Further analyses of the pressure along the ramp and cutwater depict that cavitation easily occurs at the upper side of the cutwater with a larger IVR. The hydraulic efficiency is seen to firstly increase and then decrease with an increase in IVR. The hydraulic efficiency of the intake duct is over 80% during IVR = 0.4∼1.2 with the maximum value of 92.19% at IVR = 0.6.
Investigation of Pressure Pulsation in the Stages of an Electric Submersible Pump at Best Efficiency Point Under Various Speeds
Authors: Arumugam Dhanasekaran , Sivasailam Kumaraswamy
Published: November 2019

Fluctuating pressures can induce vibration in the Electric Submersible Pump (ESP) and severely affect the pump components. The installation depths of ESP systems are varying from a few meters to several hundred meters. Once installed ESPs are not accessible for diagnostic measurement and maintenance activity, so it becomes necessary to obtain detailed information of mean and fluctuating pressures to attain an optimal pressure distribution inside the pump. In this paper the results obtained from an experimental investigation of stage-wise pressure pulsation at Best Efficiency Points at various speeds are presented. Tests were conducted on a five stage ESP having impellers of 121 mm diameter and 14 mm width at outlet with impeller of 8 vanes and a diffuser-return channel of 6 vanes which delivers 7 lps (litres per second) and develop 60 m total head at various speeds. Unsteady pressure signals were captured by mounting piezoresistive transducers at each stage of ESP. Captured pressure signals were converted into frequency domain to analyze the characteristics of pressure pulsation. The results have indicated that the maximum amplitude of pressure pulsation was obtained at the highest operating speed setting of 60 Hz at stage 4. The normalized frequency at which this amplitude was maximum was highest at stage 2 at all the speeds.
Large Eddy Simulation of Turbulent Combustion Flows in a Methane-Hydrogen Gasturbine Combustor and NOx Prediction by its Database
Authors: Oshima Nobuyuki , Kishine Ryosuke , Oda Takeo
Published: November 2019

In this research, the LES with the multiple-scalar flamelet approach is performed for an industrial gasturbine combustor, L30A, produced by Kawasaki Heavy Industries, which can appropriately simulate a partial premixed combustion by methane-hydrogen mixed fuel operation. Its instantaneous and time-averaged data by LES result are analyzed for predict NO production in thermal and prompt regime under different operation conditions. PDF statistical analysis is also applied to evaluate the effects from turbulent fluctuations of flame propagation and mixture fraction. These analyses reveal different mechanisms of turbulent fluctuations to increase or decrease NO productions.
Methane Production Strategies for Oceanic Gas Hydrate Reservoirs
Authors: Choudhary Neelam , Phirani Jyoti
Published: November 2019

Gas hydrates can be an efficient replacement for the conventional fossil fuels, as the large amount of methane gas is trapped in the gas hydrate reservoirs that can be used as a potential source of energy. In this study, we investigate the impact of a combination of horizontal and vertical wells on the gas production from oceanic Class-2, unconfined gas hydrate reservoirs. An In-house multicomponent, multiphase, thermal, 3-D finite volume simulator is used. Different locations of horizontal and vertical wells as warm water injectors and methane gas producers are investigated. For unconfined reservoirs, depressurization is found to be ineffective with horizontal and vertical wells. Horizontal warm water injectors are more effective for gas production. The gas production increases from 22% of original gas in place (OIGP) when vertical injector is used to 48% of OGIP when horizontal injector is used.
The Effect of Suction Pressure and Flow Rate on the Dynamic Characteristics of a Cavitating Inducer
Authors: Morimoto Yuta , Sugiura Takafumi , Horiguchi Hironori , Sugiyama Kazuyasu
Published: November 2019

This paper presents an experimental work on dynamic characteristics of a cavitating inducer. In the present study, the focus is placed on the cavitation compliance K and the mass flow gain factor M, which are necessary for stability analysis of a propulsion system of liquid propellant rockets. Our experiment revealed that the magnitude of K and M increased as the inlet pressure and the flow rate decreased: the volume of the cavity increased. It also clarified that K had no significant phase delay and M had the phase delay of about 90 degrees, regardless of the inlet pressure and the flow rate.
Secondary Flow Loss Reduction Method by Use of 3D-Fence in a Gas Turbine Cascade
Authors: Uehara Ryota , Mizuguchi Syohei , Kusano Kakeru , Miyabe Masahiro , Kawata Yutaka
Published: November 2019

The aerodynamic loss accounted to the secondary flow, or secondary loss is one of the most prominent causes of the internal losses in turbine cascades. The secondary flow losses are mostly due to the interaction between horseshoe vortex and endwall crossflow. The authors have developed a so-called endwall fence experimentally to reduce the secondary loss in a gas turbine cascade. However, it is very difficult to handle many design parameters simultaneously in experiment.

The objective of this research work is to optimize the shape of the 3D-fence with considering many design parameters and clarify the flow mechanism of loss reduction. In addition, one of the most important objectives of this paper is to show this optimization method is effective for the designer of the turbine. In this study, the optimization framework and CFD were applied to the endwall fence (3D-fence) and the effect of it on the crossflow was investigated. As a result, the optimized shape, installation position, and the setting angle of the 3D-fence to mitigate the interaction between the horseshoe vortex and endwall crossflow was specified. In order to validate the effectiveness of the optimization method, total pressure was measured and loss analysis was implemented and flow visualization using oil-film and smoke were implemented. Then, the good agreement can be seen qualitatively between the experimental results and CFD results. It is clarified the 3D-fence delays the confluence between suction side leg and pressure side leg of the horseshoe vortex. Based on both calculation and experiment, it is revealed that the 3D-fence has good effect to reduce the secondary flow loss.
Improvement of Film Cooling Effectiveness in the Gas Turbine Endwall by Use of Optimization Framework
Authors: Hata Daisuke , Kakio Kazuto , Kawata Yutaka , Miyabe Masahiro
Published: November 2019

Recently, the number of gas turbine combined cycle plants is rapidly increasing in substitution of nuclear power plants. The turbine inlet temperature (TIT) is constantly being increased in order to achieve higher effectiveness. Therefore, the improvement of the cooling technology for high temperature gas turbine blades is one of the most important issue to be solved.

In a gas turbine, the main flow impinging at the leading edge of the turbine blade generates a so called horseshoe vortex by the interaction of its boundary layer and generated pressure gradient at the leading edge. The pressure surface leg of this horseshoe vortex crosses the passage and reaches the blade suction surface, driven by the pressure gradient existing between two consecutive blades. In addition, this pressure gradient generates a cross-flow along the endwall. This all results into a very complex flow field in proximity of the endwall. For this reason, burnouts tend to occur at a specific position in the vicinity of the leading edge. In this research, a methodology to cool the endwall of the turbine blade by means of film cooling jets from the blade surface and the endwall is proposed. The cooling performance is investigated using the transient thermography method. CFD analysis is also conducted to investigate the phenomena occurring at the endwall and calculate the film cooling effectiveness.
Numerical Investigation of the Influence of Impeller-Diffuser Gap (A- and B-Gaps) on Unsteady Flow in a Centrifugal Pump at Part Flows
Authors: Takamine Taiki , Watanabe Satoshi
Published: November 2019

Because of the high energy density of multi-stage centrifugal pump, it is really important to ensure the reliability of the pumps thus the stability of rotor system in the wide flow rate range. Rotating stall is a well-known unsteady flow phenomenon in which one or several stall cell structures propagate circumferentially in impeller and/or diffuser. Rotating stall alters the peripheral pressure distribution of rotors, and therefore it is often regarded as one of the primary trigger of unstable fluid force acting on the rotor system. One possible factor which could affect the rotating stall is a geometrical relationship between the rotor and the stator. In the present study, unsteady RANS simulations of internal flow in a centrifugal pump are carried out. The pump is the partial model of the final stage of the three-stage centrifugal pump used in our previous study. In order to investigate the effect of the gap between impeller trailing edge and diffuser leading edge on the unsteady flow of the pump, three cases of impeller-diffuser gap is simulated; one is the smaller gap case with original impeller. The other cases are two larger gap cases with only cutting the impeller blades and with cutting the both impeller blades and impeller shroud walls. For all gap cases, the computations are conducted for the nominal flow rate and the low flor rate with 10% of the nominal flow rate.

As a result, the rotating stall is observed only in the larger gap case with the cut shroud walls, indicating that the key phenomenon for the stable formation of the stall cell is not only the weakened rotor-stator interaction, but also the other phenomenon attributed to the enlarged gap between the impeller shroud walls and the diffuser walls. In the shroud cut case, a part of the main flow blocked by the stalled region and the secondary flow on the diffuser walls tend to flow into the side gaps more easily than other cases. They might be the important phenomenon associated with the diffuser rotating stall in the enlarged wall gap condition.