bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Analysis of the Hemodynamic Functionality of Human Coronary Stenosis Under Different Physiologic Conditions and Boundary Condition Formulations
Authors: Fayssal Iyad , Moukalled Fadl
Published: November 2019

Coronary artery disease (CAD) is among the foremost causes for human death worldwide. This study aims at investigating the performance of different boundary condition model types to characterize CAD functional significance. In addition, alternate models to estimate FFR using any different combination of boundary conditions at inlet and outlet were analyzed. In the first type of boundary condition, an outflow resistance model is used combined with a fixed pressure at inlet. In the second model of boundary conditions, constant pressure values are imposed at the domain inlet and outlet/s sections. In the third model, a zero diffusion flux is applied at outlet with a pre-specified flow rate at inlet. Numerical simulations performed on healthy and stenosed idealized and physiological arterial models revealed the superiority of the first type of boundary condition to directly capture the level of ischemia in diseased arteries. However, in this model, special numerical treatment at the outflow boundary is needed to dampen pseudo numerical reflections entering the computational domain. Alternative simple methods are developed to tackle the problem incurred in the second and third types of boundary condition types. The alternate models are effective for carrying extensive parametric studies with minimal computational effort. The new developed methods allow results generated via generic simulations under any specified boundary condition type to correctly estimate CAD functional significance. The obtained surrogate models account for the effects of the patient-specific physiologic parameters and can be easily incorporated without modifying existing CFD codes. Moreover, where it is unfeasible to experimentally incorporate the downstream effects of a given diseased arterial segment, an important aspect the alternative models provide is that they can be easily adopted by experimentalists through building in-vitro arterial models to assess the functional significance of the obstruction caused by the disease and its relation to any given patient specific physiologic parameter.
Heat Transfer and Fluid Flow in Arc-Based Additive Manufacturing
Authors: Zhou Jun
Published: November 2019

Additive manufacturing (AM) is gaining rapid popularity in many industries like automotive, medical, electronics and aerospace due to its flexibility to build parts with complex geometry. Nowadays, laser/electron-beam/arc melting or deposition are commonly used for AM of metallic parts. Melting-solidification and melt flow repeatedly occur in the AM process, which are critical in determining the final shape, precision, and quality of the AM products. In this study, melt flow and heat transfer in arc-based metallic additive manufacturing process are discussed. The key parameters affecting the fluid flow; heat transfer; defect formation; and surface topology of the AM parts are investigated.
Fluid-Structure Interaction Simulation of Lactating Human Breast
Authors: Azarnoosh Jamasp , Hassanipour Fatemeh
Published: November 2019

Extracting milk during breastfeeding is not only caused by intra-oral vacuum pressure by the infant suckling but also is the periodic motion of the infant’s jaw, which is the focus of this study. A Fluid-structure interaction simulation provides a better understanding of the milk flow behavior in the human breast ductal system as the breast interacts with the infant’s oral cavity and jaws. Simulations were performed from the instance of latching and continued for two cycles of periodic tongue motion. The negative vacuum pressure profile was measured from the clinical data and applied in the simulation. The nipple dimensions were obtained using ultrasound images and used as boundary conditions in the simulation. The effect of vacuum pressure and the peripheral pressure on the milk flow behavior in breast ductal system were studied individually. It was observed that the deformation of the ductal system has a critical impact on milk flow behavior and the amount of expressed milk.
On the Low and High Speed Flow of Gases Through Pillow Plate Channels
Authors: Passmann Maximilian , aus der Wiesche Stefan , Kenig Eugeny Y.
Published: November 2019

Low speed and high speed flow phenomena in pillow plate channels are considered. High speed flows were investigated by means of analytical methods and fully three-dimensional computational fluid dynamics (CFD) simulations. The theoretical analysis indicated that a Fanno-type flow model described high speed flow behavior in pillow plate channels reasonably well. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was applied in order to derive similarity laws for the high speed flows. The detailed CFD analysis was used to support the assumption of a Fanno-type flow. The effects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated in detail. The present analysis demonstrates that pillow plate heat exchangers represent promising candidates for high speed turbo machinery applications.
On the Influence of Gas Content on the Rotordynamic Force Coefficients of a Three-Wave (Air in Oil) Annular Seal for Multiple Phase Pumps
Authors: San Andrés Luis , Lu Xueliang , Wu Tingcheng
Published: November 2019

The subsea oil & gas industry efficiently uses multiphase pumps and wet gas compressors to eliminate upstream oil and gas separation stations, hence saving up to 30% in capital expenditures. Subsea multiphase process facilities must operate reliably for extended lengths of time while the wells, as they deplete, produce a process fluid varying from a pure liquid, to a mixture of gas and liquid, and to eventually just gas. The variation of gas volume fraction (GVF), by affecting the leakage and dynamic forced performance of sealing elements, alters turbomachinery performance to produce both an increase in synchronous speed rotor vibrations and a reduction in rotor dynamic stability. Prior laboratory work shows that plain cylindrical surface annular seals operating with a fluid flow in the laminar flow regime produce no direct (centering) stiffness and a large added mass, in particular for the liquid only condition. The early work also advanced a simple three-wave shape seal (akin to lobes) that generates a significant direct stiffness, impervious to GVF as large as 90%, and hence aids to increase the natural frequency of a vertical pump. Dynamic load tests for this wavy-seal configuration operating with a gas in liquid mixture [air in light ISO VG 10 oil] are the subject of this paper that presents dynamic force coefficients vs. excitation frequency (ω) while the shaft turns at a speed (Ω) equal to 3.5 krpm (23.3 m/s surface speed), a typical operating speed for multiphase pumps. The test seal has length L = 43 mm, diameter D = 127 mm, and a mean radial clearance cm = 0.191 mm. For operation with a pure liquid (GVF = 0), the seal force coefficients are frequency independent, thus a stiffness (K) - damping (C) − Mass (M) model fully characterizes the test article. On the other hand, for operation with an air in oil mixture, the test seal dynamic stiffness coefficients vary greatly with excitation frequency; the direct dynamic stiffness hardens while the cross coupled stiffness decreases as the frequency approaches running speed (ω < Ω) and then increases for super synchronous frequency excitations (ω > Ω). For operation with GVF from 0.1 to 0.8, the wavy seal produces a positive centering dynamic stiffness with large magnitude; a most desirable feature for a vertically installed pump. Notably, the seal direct damping coefficient (C) does not depend on the excitation frequency though reduces continuously as the inlet GVF increases from 0 to 1. For operation with either a pure liquid or a pure air conditions, a computational fluid dynamics (CFD) analysis accurately captures the seal leakage and force coefficients. The current research product adds relevant test data to better the design selection of seals in multiphase pumps.
Effect of Interstage Injection on Compressor Flow Characteristic
Authors: Von Deschwanden Inez , Braun Stefan , Brillert Dieter
Published: November 2019

Wet compression is a widely used approach to enhance the compressor performance of gas turbine units. For wet compression, a water-spray consisting of tiny droplets is injected into the air inlet duct of the compressor. A multi-phase flow of humid air and water droplets enters the compressor. The continued water evaporation inside the compressor stages causes further cooling during the compression process.

Water injection between the compressor stages is called interstage injection. An advantage of interstage injection compared to wet compression is the optimized injection of water at specific positions inside the compressor. The amount of injected water can be adopted to the specific operating conditions of the different injection positions with the ideal of isothermal compression.

Interstage injection can be realized by several techniques. This paper focuses on interstage injection of water from the trailing edge of stator blades. The water spray is generated in the complex wake flow of the airfoil. This leads to strong interaction between the water spray and the carrier gas flow.

In this paper, especially the impact of water injection on the air flow and the spread of the spray is investigated. Phase Doppler Anemometry (PDA) measurements enable two dimensional velocity measurements linked with the droplet size. The comparison of PDA measurements and Computational Fluid Dynamic (CFD) calculations of the dry gas flow allows for the identification of flow instabilities due to interstage injection. Within this publication, a significant influence of the water injection from the trailing edge on the carrier flow is identified. Furthermore, the ability of the spray to spread widely into the flow demonstrates that water injection from the trailing edge is a promising technique for interstage injection.
Validation and Development of DNS Database for Low Prandtl Numbers in Rod Bundle
Authors: Lai Jonathan K. , Merzari Elia , Hassan Yassin A. , Obabko Aleksandr
Published: November 2019

Difficulty in capturing heat transfer characteristics for liquid metals is commonplace because of their low molecular Prandtl number (Pr). Since these fluids have very high thermal diffusivity, the Reynolds analogy is not valid and creates modeling difficulties when assuming a turbulent Prandtl number (Prt) of near unity. Baseline problems have used direct numerical simulations (DNS) for the channel flow and backward facing step to aid in developing a correlation for Prt. More complex physics need to be considered, however, since correlation accuracy is limited. A tight lattice square rod bundle has been chosen for DNS benchmarking because of its presence of flow oscillations and coherent structures even with a relatively simple geometry.

Calculations of the Kolmogorov length and time scales have been made to ensure that the spatial-temporal discretization is sufficient for DNS. In order to validate the results, Hooper and Wood’s 1984 experiment has been modeled with a pitch-to-diameter (P/D) ratio of 1.107. The present work aims at validating first- and second-order statistics for the velocity field, and then analyzing the heat transfer behavior at different molecular Pr. The effects of low Pr flow are presented to demonstrate how the normalized mean and fluctuating heat transfer characteristics vary with different thermal diffusivity. Progress and future work toward creating a full DNS database for liquid metals are discussed.
Numerical Simulation and Experiment of the Fire Protecting System of the Manipulator in High Temperature Environment
Authors: Kim Byeong Cheon , Chang Kyoungsik
Published: November 2019

In the present work, the strategy for cooling the manipulator in high temperature environment is studied using both numerical and experimental methods. Since the manipulator is designed to operate in the environment with the maximum 250 °C temperature, fire protection system and the cooling system should be installed for normal operation of the manipulator. The para-aramid-filament with the thickness of 0.5 mm and Graphite felt with the thickness of 5.5mm is considered for fire protection suit and air blowing technique is applied for cooling the electronic circuit and hydraulic pressure cylinders. For numerical simulation, ANSYS Fluent V18.2 is adopted to simulate the convective heat transfer flows and the radiation with the model, S2S (Surface to surface). Two types of blowing techniques are considered, global blowing and local one. Even though the global blowing at the inlet is most effective for cooling system, so much amount of compressed air is required, which means that extra big compression system should be added in the system. The local blowing is applied to the component with small holes of the flexible pipe and the magnitude of the local blowing mass flow rate is 0.0166kg/s. The technique of local blowing is more effective than the global blowing for cooling the system. To validate numerical simulation, the model is tested within the hot temperature chamber whose mean temperature is approximately 250 °C.
Flying Spiders: Effects of the Dragline Length and the Spider Mass in Free-Fall
Authors: Stevens Tessa , Zhao Longhua , Courtney Ryan , Zhang Wei , Miller Laura
Published: November 2019

Many species of spiders move from one location to another using a remarkable aerial dispersal “ballooning”. By ballooning, spiders can reach distances as far as 3200 km and heights of up to 5 km. Though a large number of observations of spider ballooning have been reported, it remains a mysterious phenomenon due to the limited scientific observation of spider ballooning in the field, high uncertainties of the meteorological conditions and insufficient controlled laboratory experiments. Most of the ballooning spiders are spiderlings and spiders under 3 mm in length and 0.2 to 2 mg in mass with a few exceptions of large spiders (over 3 mm in length, over 5 mg in mass). What physical mechanism dominates the three stages of spider ballooning — take-off, flight, and settling? Many factors have been identified to influence the physical mechanism, including a spider’s mass, morphology, posture, the silken dragline properties, and local meteorological conditions (e.g., turbulence level, temperature and humidity). A thorough understanding of the roles of key parameters is not only of ecological significance but also critical to advanced bio-inspired technologies of airborne robotic devices.

This work aims to determine how the dragline length and spider mass affect the interaction of the spider-dragline system in the free-fall scenario. Experiments using a thread of different lengths and a sphere of different masses to mimic the spider-dragline were carried out. The first sets of tests focused on the spider-dragline system, rather than the fluid flow. High-speed images of a spider-dragline falling in a closed container of air were recorded with 1500 frames per second at Reynolds numbers of several thousand, based on the spider dragline and the local relative velocity. Image data allow for tracking the vertical velocities and acceleration of the spider-dragline, as well as the drag force acting on the spider-dragline. Terminal velocities in the settling stage are compared with estimates using various fluid dynamics models in previous work. Such results under controlled laboratory conditions are expected to shed lights on the intriguing flow physics of spider ballooning at the settling stage and to inform future experiments and numerical models.
Effect of Bionic Groove Surface Blade on Cavitation Characteristics of Centrifugal Pump
Authors: Zhang Zicheng , Dai Yun , Gu Yunqing , Shi Zhengzan , Mou Jiegang
Published: November 2019

In order to improve the cavitation resistance of centrifugal pump, bionic groove surface structure was arranged on the suction surface of centrifugal pump blade which is the most prone to cavitation. Numerical simulation method was used to study the influence of different-shape groove blade on cavitation performance of centrifugal pump. The results showed that the head and efficiency of the centrifugal pump with circular grooved surface blades were close to the smooth surface blade centrifugal pump and higher than those with triangular grooved surface blades and rectangular grooved surface blades. The low pressure area of the circular groove blade was the smallest and the cavitation resistance was the best. At the critical cavitation margin point, circular groove blade can effectively reduce the probability of negative incidence, and the cavitation inhibition effect was the most obvious.
Robustness of Turbulent Stripes in Particle-Laden Channel Flows
Authors: Hanabusa Masaki , Tsukahara Takahiro
Published: November 2019

It is known that intermittent localized turbulence, so-called turbulent stripes, sustains in the form of oblique bands in subcritical transitional regime of channel flows. The pattern is formed and accompanied by secondary flows along the localized turbulence. In particle-laden turbulent flows, turbulent intensity can be enhanced or suppressed by particles. However, the effect of the particles on the turbulent stripes in subcritical transitional regime is still unknown. In this paper, we investigated the particle distributions with respect to the turbulent stripes in one-way coupling simulations and studied the effect of particle-fluid interactions on the robustness of the stripes in two-way coupling simulations. In one-way coupling, the turbulent stripe provides a cluster of heavier, or large-Stokes-number, particles in a form of oblique band similar to the stripe, in the wall-parallel direction. Furthermore, heavier particles accumulate near the wall even without gravity. In two-way coupling, the stripes tend to be broken for heavier particles. The stability of the pattern also depends on the particle volume fraction. For higher volume fraction of particle, particles have a significant effect on the sustenance of the stripes. In such a case, the particle-fluid interactions exhibit the force that accelerates the fluid near the wall. The turbulent kinetic energies of large-scale flow and fine-scale eddies are attenuated by heavier particles. Different wave-number scaled structures were generated and disappeared as a laminarization process.
Similarity of the Output Characteristics of the Small Vertical Axis Wind Turbine
Authors: Sekiya Naoki
Published: November 2019

Several models have been proposed to predict the shaft output characteristics of the vertical axis wind turbine from the aerodynamic characteristics of the blade. However, it has not predicted the output characteristics of the small wind turbine, turbine diameter less than 1 m, even the multiple stream tube model included effect of the momentum reduction. A solidity of the small wind turbine become higher than large, i.e. blades interval of small wind turbine becomes short. Therefore, it expects that the wake of preceding blade influence strongly aerodynamic character of following blade. Thus, we have investigated the relation between wake of rotating turbine and its shaft output characteristics. From result obtain, we had cleared the shaft output character agree with variation of momentum loss of the wake of turbine. Moreover, the relevance between the shaft output characteristics and velocity fluctuation in the wake had been found. In the low tip speed ratio region increasing the shaft output, the periodical component synchronized with motion of the blade remarkably appear in velocity fluctuation, and it disappear near the peak of shaft output. Meanwhile, in the high tip speed ratio region decreasing the shaft output, the turbulent component is dominant in velocity fluctuation. It indicates that the blade-wake interference was affected on shaft output of the small wind turbine. Therefore, the purpose of this study was to find out a similarity parameter of the shaft output characteristics based on blade-wake interference. The larger the scale of blade wake or slower the advection velocity of it, the higher the possibility that blade wake generated from previous blade interfere to following blade become. For blade-wake interaction, these two parameters which the scale and the advection velocity of blade wake, are important. Thus, I estimated these parameter in this study using the wind turbine model with single blade. From measurement of the blade wake, I found that the scale of the blade wake depends on the ratio of the rotational speed of the turbine to the free stream velocity, and the advection velocity of blade wake depends on the free stream velocity. From these characteristics of blade wake, I suggest a new parameter based on the blade-wake interaction using tip speed ratio, solidity, number of blade, and turbine diameter. The shaft output characteristics of the small wind turbine indicates good similarity for the new parameter.
Numerical Simulation of Intermittent-Controlled Multiple Jets
Authors: Tsujimoto Koichi , Kitahara Kango , Shakouchi Toshihiko , Ando Toshitake
Published: November 2019

Multiple jets are used in industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. Unlike single jet, since the jets issuing from nozzles will coalescence, merge or combine with each other, it is necessary to reduce mixing performance such as entrainment from surroundings and spreading into surroundings. It is well known that the characteristics such as mixing and diffusion of the jet are strongly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, an appropriate inflow condition at a nozzle is capable of controlling the large vortex structures near field around the nozzle and improves the mixing performance. In this study, we examine an intermittent control of jets varying the control frequency and the jet spacing so as to reduce the interaction between each jet. We conduct the DNS (direct numerical simulation) of intermittently-controlled two round jets. In order to quantify the mixing efficiency of the intermittent control, statistical entropy and entrainment are examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the intermittent control can be expected to be useful for the improvement of mixing performance of multiple jets.
Temperature Compensation for Measurement of Low-Speed Internal Flow Fields Using Fast-Response Pressure Sensitive Paint
Authors: Mori Hideo , Imazeki Tomohiro , Moon Kil-Ju
Published: November 2019

Because most fast-response pressure sensitive paints (PSP) suffer from temperature sensitivity, causing large error in pressure measurement when spatial non-uniformity of pressure distribution is large. In this study, the two methods of composite measurement of temperature and pressure by using the segment painting of PSP and TSP, and Dual-layer PSP/TSP (DL-PTSP), are applied to measurement of pressure distribution on inner surface of casing of test axial compressor, by using transparent method. We apply a paintable fast-response PSP composed of PtTFPP and silica nanoparticles and polymer-based TSP composed of Ru-phen and PMMA, with opaque, oxygen permeable overcoat, in order to enhance the luminescence intensity of PSP and TSP and avoid overlaying image of rotors inside the casing. When segmented-painting method of PSP and TSP is applied, pitch-wise symmetry is assumed. Therefore, asymmetric temperature distribution causes error in temperature compensation. On the other hand, DL-PTSP method can be used for asymmetric conditions, but sequential measurement of pressure and temperature may cause error in temperature compensation, when temperature distribution on the surface is nonstationary.
Is Radioactive Tank Waste a Bingham Fluid?
Authors: Pease Leonard F. , Fuher Arich J. , Bamberger Judith A. , Burns Carolyn A. , Daniel Richard C. , Minette Michael J.
Published: November 2019

Slurries and sludges across the United States Department of Energy (DOE) complex rank among the most rheologically interesting. Their composition is heterogeneous, spanning a very broad range of particle sizes, densities, and interparticle forces. All exhibit shear thinning, some have yield stresses, and many are thixotropic. Despite the variety, these complex fluids are often represented using the historic Bingham fluid model, which fits higher shear rate data to a simple straight line. The intercept provides a yield stress, which has been a key design parameter in construction of large-scale waste processing facilities. However, many radioactive wastes are simply not Bingham fluids, and this representation extrapolates poorly across low to intermediate shear rates that are characteristic of typical processing conditions. Indeed, processing shear rates as high as 200 1/s, which has been a typical minimum shear rate used in fitting the Bingham fluid model, are seldom encountered in nuclear waste processing. Therefore, more realistic rheological models are necessary to accurately predict waste processing performance.

Pacific Northwest National Laboratory (PNNL) recently re-evaluated the rheology of reconstituted Hanford REDOX (reduction-oxidation) process sludge waste against a wide variety of rheological models including the Bingham, Cross, Cross with yield stress, Carreau, biviscous, Herschel-Bulkley (which includes a power law dependence), Casson, and Gay models. They found that all of the models provided a closer fit than the Bingham model and that the biviscous model and Cross with yield stress model were convincing. However, reconstituted Hanford REDOX sludge waste is but one type of DOE waste and a direct contrast, and comparison of these three models against undiluted, unmixed tank waste (actual not simulant) has not been performed previously. Therefore, the purpose of this paper is to evaluate the rheology of actual tank waste with these more accurate rheological models.

In this paper, we evaluate select rheological data for slurry samples from Hanford’s AZ-101, AZ-102, and SY-101 waste tanks. In each of these cases, we find that Cross’ model with yield stress and the biviscous model significantly outperform the Bingham fluid model. Furthermore, the AZ-101 data also shows that the shear stress peak at startup significantly exceeds the Bingham yield stress, which is commonly observed in the initial moments of rheological measurements on simulants. Remarkably, Cross’ model may empirically accommodate an initial spike in shear stress at modest shear rates. These are important observations because computational and analytical fluid dynamics simulations rely on rheological constitutive models for accurately and conservatively predicting waste processing performance. These findings suggest the need for better rheological modeling of and validation against radioactive waste.
Contribution of Fluctuating Large-Scale Motions in Turbulent Fluid Flow Through a Channel
Authors: Mito Yoichi
Published: November 2019

The key mechanism that sustains fluid turbulence flowing through a channel is examined using the Lagrangian experiment, done in a direct numerical simulation (DNS) of the turbulent fluid flow and that being damped by addition of a small amount of small particles. The results indicate large contribution of the fluctuations of large-scale fluid motions, which are seen as their multi-directionality and multi-dimensionality, to sustenance of wall turbulence. Small-scale fluid turbulence structures, such as vortices and packets of them, are seen to induce the fluctuations of large-scale fluid motions.
Influence of Nozzle Aspect Ratio and Orientation on Flow Characteristics of Multiple Elliptic Jets
Authors: Teramoto Hiroshi , Kiwata Takahiro , Yajima Kako
Published: November 2019

An experimental study is conducted to investigate the flow characteristics of multiple elliptic jets issuing from a 6 × 6 nozzle array at a relatively low-Reynolds number (Re = 4.3 × 103). Two aspect ratios of the multiple elliptic nozzles (equivalent diameter, de, of a nozzle was 6 mm), namely a/b = 2.25 and 6.25, where a and b are the radii of the major and minor axes of an elliptic nozzle, respectively, and two nozzle azimuthal orientations, namely the same and alternate azimuthal orientation arrangements, were used. The mean and fluctuating velocities were measured using a constant-temperature hot-wire anemometer. The multiple jets located at the side of the ambient fluid were stretched due to interactions between the self-induced flow of an elliptic vortex ring and the secondary flow caused by the entrainment of the ambient fluid. For a/b = 2.25, axis switching occurred only once in the range of 1 < x/de ≤ 3 for both nozzle azimuthal orientations. For a/b = 6.25 and the same azimuthal orientation arrangement, axis switching occurred only once at 3 < x/de ≤ 5; axis switching did not occur for the alternate azimuthal orientation arrangement. Thus, the flow characteristics of multiple elliptic jets are influenced by the azimuthal orientation of adjoining nozzles.
Predictability Study of Viscoelastic Turbulent Channel Flow Using Deep Learning
Authors: Nagamachi Atsushi , Tsukahara Takahiro
Published: November 2019

We tested Artificial Neural Networks (ANNs) to predict a fully-developed turbulent channel flow of a viscoelastic fluid in preparation for elucidating flow phenomenon and solving the difficulty in DNS (Direct Numerical Simulation) due to numerical instability of the viscoelastic fluid. Two kinds of ANNs (multi-layer perceptron (MLP) and U-Net) were trained using DNS data to predict conformation stress from given instantaneous field. The MLP showed accurate predictions and predictions got better with z-score normalization. ANN predicted accurately in near-wall region having coherent structures. In addition, we demonstrated that ANN get the nonlinear relationship between velocity gradient and viscoelastic stress partially.
Void Waves Developing in Gas-Liquid Two-Phase Turbulent Boundary Layers Beneath a Flat Bottom Model Ship
Authors: Tanaka Taiji , Park Hyun Jin , Tasaka Yuji , Murai Yuichi
Published: November 2019

To investigate the development process of a void wave, spatio-temporal fluctuation of void fraction, we examined experimentally a turbulent boundary layer with bubble injections. The experiments performed on a flat bottom of 4-mlong transparent model ship towed in a tank of 100 m length with the speed of up to 3.00 m/s. In bubbles injection with constant air flow rate, void fluctuations with 4 Hz or 8 Hz appeared dependent on the towing speed. With periodically fluctuated air flow rate, artificial void waves were provided into the turbulent boundary layer and their frequency was maintained during the downstream propagation. The attenuation rate of the fluctuation evaluated using Fourier analysis of the wave took the minimum value at specific injection frequency conditions.
Effect of Splitter Configurations on the Performance of a Sludge Pump
Authors: Jin Jeong-Min , Ji Hyo-Geun , Kim Youn-Jea
Published: November 2019

Sludge pump, a type of centrifugal pump, is widely used to transport high-density sludge. The pump uses the impeller to generate a pressure difference for transporting the working fluid. The impeller is a crucial component of the pump. The internal pressure becomes higher with an increasing number of impeller blades, and this in turn results in an increased head. However, the increase in the number of blades interferes with the pump inlet flow, resulting in an efficiency loss due to an increase of surface friction. Therefore, in this study, numerical analysis was performed using ANSYS CFX ver. 17.1 to elucidate the effect of splitter configurations on the performance of sludge pump. The numerical results were compared with the efficiency and head according to the change of the splitter length, as 35%, 60%, and 80% of the reference blade shape.
Direct Numerical Simulation of Supersonic Flow Over a Counter-Rotating Vane-Type Vortex Generator Implemented on Slip Wall
Authors: Nagata T. , Daspit T. , Nonomura T. , Loth E.
Published: November 2019

In this study, flow over a pair of vane-type vortex generator is investigated by solving the Navier–Stokes equation. A pair of the vane-type vortex generator implemented on a slip wall in laminar flow is considered so that the problem setting could be simple. The Reynolds number based on freestream quantities and the height of the vanes is set to be 500. The effect of the arrangement and geometry of vanes on the circulation coefficients, induced flow velocities, and aerodynamic force coefficients of VGs are investigated. In addition, a new non-dimensional circulation coefficient, normalized by freestream velocity and the height of the vortex core was introduced and its effectiveness is examined. This new parameter, CΓ’, include the height of the vortex core, so that appears to be a better measure of VG effectiveness on momentum exchange. From the computational results, the wider arrangement can introduce the effective vortices with small drag. Also, the longer vanes can introduce strong and effective vortices with smaller drag coefficient.
Simultaneous Optimization of Impeller Blade Loading Distribution and Meridional Geometry for Aerodynamic Design of Centrifugal Compressor
Authors: Manabe Kaito , Ito Sasuga , Furukawa Masato , Yamada Kazutoyo , Oka Nobuhito , Tomita Isao , Hayashi Yoshihiro
Published: November 2019

The present optimum design method has been advanced for simultaneous optimization of impeller blade loading distribution and meridional geometry. This is based on an aerodynamic design method and a genetic algorithm. The aerodynamic design method consists of two parts: a meridional viscous flow analysis and a two-dimensional inverse blade design procedure. In the meridional viscous flow analysis, an axisymmetric viscous flow is numerically analyzed on a two-dimensional grid to determine the flow distribution around the impeller and diffuser. Effects of blades onto the axisymmetric flow field are considered by a blade force modeling. In the inverse blade design procedure, 3-D impeller geometry can be obtained from the result of meridional viscous flow analysis and the predetermined blade loading distribution. In the optimization procedure, the total pressure ratio and adiabatic efficiency obtained from the meridional viscous flow analysis are employed as objective functions. As a constraint of the optimization, mass flux distribution at the impeller trailing edge is introduced in the evaluation procedure, in order to suppress the boundary layer development near the shroud, especially under low flow rate condition.

Total performances and three-dimensional flow fields of centrifugal compressors have been analyzed by 3D-RANS simulations to certify effectiveness of the present design method. The 3D-RANS simulations and the flow visualization have been applied to a conventional centrifugal compressor and optimized design cases. From the analysis results, the performance enhancement of optimized designs is confirmed under low flow rate condition including design point. In addition to that, it is revealed that the constraint works effectively on the performance improvement. As a result, construction of the simultaneous optimization using the aerodynamic design method and the genetic algorithm is successfully achieved.
Delta Winglet Pairs in the Core of a Pipe and its Effect on Heat Transfer and Flow
Authors: Islam Md. , Chong Z. , Alam Md.
Published: November 2019

Vortex generators/turbulent promoters generate the longitudinal vortices which introduce the better mixing of the fluid with fluid circulation and enhance heat transfer. In this research, experimental investigations have been carried out to study the effect of delta winglet vortex generator (DWVG) in the core of the pipe on heat transfer and flow behavior. In this experiment, two pairs of delta winglet vortex generators (DWVG) were printed on the upside and downside of the thin plate using 3D printing technology in a ring and then placed in the core of the pipe to generate longitudinal vortices. Middle plate was very thin. The effect of heights (H = 5mm, 10mm, 15mm and 20mm) of DWVG for 10° angle of attack and 15mm spacing between leading edges of VG pairs on heat transfer and pressure drop was studied. The experiments were conducted for a fully developed turbulent flow of air in the range of Reynolds numbers (Re) 5000–25000. The influence of the DWVGs on heat transfer and pressure drop was investigated in terms of the Nusselt number (Nu) and friction factor (f). The experimental results indicate that DWVG in the core of the tube results in a considerable increase in Nu with some pressure penalty. It is found that DWVG increase Nu considerably only when H is over 10mm. Nu increases with Re and H. Friction factor decreases with Re but increase with H. The thermal performance enhancement (TPE) was noticed decreasing with Re. TPE could be obtain up to 1 only when the height is over 10mm for Re ≤ 7500. The experimental results show that the DWVG in the core of the pipe is not a good option to enhance the heat transfer at a higher Re.
Numerical Investigation on the Effect of Blade Loading on Unsteady Sheet Cavitation Patterns
Authors: Nahon Jeremy , Zangeneh Mehrdad , Nohmi Motohiko , Watanabe Hiroyoshi
Published: November 2019

Cavitation commonly manifests itself as vapour structures attached to the suction surfaces of impeller, runner or propeller blades. The numerical study carried out here seeks to correlate the changes in the behaviour of sheet cavitation to variations in blade geometry. The analysis is run for a two-dimensional stationary cascade. The streamwise loading distribution is the metric used to characterise the geometry. It determines the rate and amount of work generated across the channel and is directly connected to blade surface pressure.

In this study, the test sample consists of a set of varying blade profiles characterised by specific loading configurations: foreloaded, aft-loaded or bespoke distributions. Time-resolved simulations of the cavitating flow are generated to study cavity behaviour. Computations are run through Fluent using the SST URANS formulation. The Zwart-Gerber-Belamri homogeneous cavitation model is used to treat cavitation. A range of behaviours are observed for the cavitation patterns. Variations are found in inception conditions, shape and sheet stability. For the latter, two dynamic regimes are identified with a transition point that varies according to the loading profile. A pair of tradeoff relations are also observed: hydrodynamic efficiency versus suction performance and suction performance versus cavity stability. The results demonstrate the capacity of the loading distribution to affect cavitation dynamics.
Wake Flow Visualization of a Simplified Vehicle Model During Flow State Change
Authors: Nakashima Takuji , Moriuchi Takashi , Chao Yan , Kohri Itsuhei
Published: November 2019

A flow around a three-dimensional bluff body such as an automobile sometimes exhibits a bi-stable state wherein two stable flow states exist for a single condition. Better aerodynamic characteristics can be obtained if we suppress or promote the flow state change between such bi-stable states. Hence, it is necessary to understand the trigger conditions and process of the flow state change. In this study, we investigated the transient aerodynamics of the Ahmed model with the slant angle of 32°, exceeding the critical angle of 30°, known to exhibit bi-stable state under crosswind conditions. Changing the Yaw angle by rotating the model, produced change in the flow state, accompanied by time delay. While continuously measuring fluid force, we performed PIV measurement triggered by a sudden change in fluid dynamic force corresponding to the flow state change. Using these methods, we realized the synchronous measurement of the fluid force and wake flow during the flow state change. At the beginning of the flow state change, flow velocity changed around the trailing edge of the slant surface. Subsequently, the separated flow above the slant surface increased. A gradual decrease of drag coefficient was observed before the flow state change though flow behavior associated with the drag change was not observed in the velocity field of PIV measurement.
Experimental and Numerical Analysis of an Axial Piston Pump: A Comparison Between Lumped Parameter and 3D CFD Approaches
Authors: Frosina Emma , Marinaro Gianluca , Senatore Adolfo
Published: November 2019

In this paper an axial piston pump is studied using numerical and experimental approaches. The pump, manufactured by the company Continental Hydraulic Inc., has a maximum operating pressure limit of 280 bar and a displacement of 65.9 cm3/rev; it is a variable swashplate design with nine-piston, suitable for open circuit application, medium to high pressure.

Two numerical approaches have been compared to simulate the pump units. First of all, an accurate 3D -CFD model has been built up putting emphasis on the description of the detailed features of the flow through the unit. Specific attention has been reserved to the flow losses due to cavitation. Then a fast-lumped parameter approach has been built up focusing the attention on the valve plate geometry. Using the proposed numerical approaches, it is possible to fully understand the unit operation with, obviously, different assumptions and level of result details.

Numerical models have been validated with an experimental data performed by the pump manufactured on their test ring with high agreement.

As results, the proposed analysis permit to gain a high level of understanding of the operation of the unit finding the critical aspects and giving important information to the designer in order to improve the pump performance.

By the end a new valve plate has been designed to improve the pump volumetric efficiency and to reduce the flow ripples and the reverse flow.
Investigation of Turbulent Flow Behavior in a Heated Boundary Layer
Authors: Dennis Kadeem , Siddiqui Kamran
Published: November 2019

The boundary layers are known to play key roles in many engineering systems. The hydrodynamic boundary layer found in these systems is often turbulent in nature and heat transfer is involved which further increases flow complexity due to the influence of buoyancy. One of the constituent layers of the turbulent boundary layer, the inner layer, has been established as home to key dynamical turbulent phenomena which can be influenced by the buoyant force. In the mixed convection flow regime, flow inertia and buoyant force are on the same order of magnitude. In this regime, buoyant thermals rising from the wall interact with the inertia-driven turbulent flow field resulting in highly complex three-dimensional flow dynamics. Past research studies conducted in this flow regime have been mostly computational in nature with little experimental work. The current knowledge on the impact of the relative contributions by the buoyant force and flow inertia on turbulent phenomena in the mixed convection flow regime is very limited.

This study reports on an investigation into the turbulent flow phenomena present in mixed convection turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop wind tunnel where the turbulent boundary layer was heated from below. The multi-plane particle image velocimetry (PIV) technique was used to capture two-dimensional velocity fields over two planes with respect to the flow direction. Experiments were conducted over a range of Richardson numbers (Ri) between 0.0 and 2.0 to control the relative contribution of the buoyant force with respect to flow inertia. The measured velocity fields are used to describe the influence of buoyancy on the three-dimensional turbulent boundary layer flow.
Experimental Investigation of Nozzle Orientation Effects on Mixing Characteristics of Elliptic Triple Free Jets
Authors: Morris Ella M. , Aleyasin Seyed S. , Biswas Neelakash , Tachie Mark F.
Published: November 2019

An experimental investigation of nozzle orientation effects on turbulent characteristics of elliptic triple free jets was carried out for three nozzle configurations. The first configuration had all three nozzles oriented along the minor plane (3_Minor), the next had two nozzles oriented along the minor plane and one along the major plane (2_Minor_1_Major) and the last configuration had one nozzle oriented along the minor plane and two along the major plane (1_Minor_2_Major). The experiments were conducted using modified contoured nozzles with a sharp linear contraction for a nozzle-to-nozzle distance of 4.1, a nozzle equivalent diameter of 9 mm and a Reynolds number of 10,000. The effects of nozzle orientation on the mean velocity, turbulence intensity and Reynolds shear stress were discussed. The velocity decay, jet spread, merging point, combined point and potential core length were used to characterize the effects of nozzle orientation on the mixing performance. The results show that the 3_Minor configuration had shorter potential core length and closer merging point location which are indicative of a faster mixing in the converging region. Two-point correlation, skewness and flatness factors were used to provide insight into the effects of nozzle orientation on turbulence structure and higher order turbulence statistics.
Open-Source Computational Fluid Dynamics in Engineering Education
Authors: Nedyalkov Ivaylo
Published: November 2019

Computational Fluid Dynamics (CFD) is widely used in industry but is not discussed sufficiently in undergraduate engineering education. In some cases, CFD is studied only from a mathematical perspective, focusing on computational partial differential equations, and in some cases it is introduced as a black-box tool. A hybrid CFD class was developed for undergraduate and graduate students at the University of New Hampshire, which combines the two approaches. The students are exposed to the mathematics and physics behind CFD, and they also utilize OpenFOAM — an open source CFD package — to work on practical problems. Since the code is open-source, the students are able to see and modify it. Although OpenFOAM is challenging due to the minimum graphical user interface, the code-base environment forces the students to learn what the code is doing. Sample assignments and project submissions from the students are presented in the paper.
Validation of Numerical Simulation of Drop Motion on Surfaces With Micro Patterns
Authors: Onishi Junya , Shikazono Naoki
Published: November 2019

Numerical simulation of drop motion on surfaces with micro patterns is conducted. The results are compared with existing experimental and analytical studies to validate the reliability of the numerical simulations. In the comparison of the liquid phase morphology on a surface with straight grooves, it is confirmed that a variety of liquid shapes, including droplets, filaments with positive/negative Laplace pressure and so on are successfully reproduced by the numerical simulation. Moreover, the numerically observed transition between these morphologies in a broad range of the groove aspect ratio and the static contact angle agrees with the morphology diagram which is obtained by a semi-analytic approach based on the surface free energy minimization. Furthermore, in the comparison of the spreading behaviors of a liquid drop on a surface with square pillars, it is shown that the numerical simulations can predict the time-dependent drop deformation during the spreading process. The comparison of the length of two spreading modes shows a quantitative agreement with the experimental results.