bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Twin Unidirectional Impulse Turbine With Fluidic Diode for Wave Energy Conversion
Authors: Sato Hideki , Takao Manabu , Okuhura Shinya , Ahsraful Alam Miah Md. , Setoguchi Toshiaki 
Published: July 2018

As an air turbine equipped with oscillating water column (OWC) based wave energy plant, a rectification-valve system has been invented to date. However, this turbine system has problems with the durability of the valves and the complex mechanism. Moreover, it has a major fault in that the valves must be large for high output. Therefore, a twin unidirectional impulse turbine topology has been suggested in previous studies in order to use conventional unidirectional turbines without valves [1, 2]. The topology is composed of two unidirectional impulse turbines. However, the past study indicated that the mean efficiency of the topology was shown to be low, when the performance prediction of the topology in oscillating airflow was carried out by means of quasi-steady analysis [2]. Further, the cause of the low efficiency is because part of the air flow gets through the unidirectional impulse turbine in the direction of low efficiency [2].
In this study, a fluidic diode [3, 4] is adopted in order to suppress the air flow rate into the inefficient turbine in a twin unidirectional impulse turbine topology for wave energy plant, and the effect of the fluidic diodes on the performance of twin unidirectional impulse turbine topology is investigated by a wind tunnel test and computational fluid dynamics (CFD). Further, its usefulness is discussed from a view point of the turbine mean efficiency under unsteady flow condition.
Relationship Between Diffusing-Material Lumps and Organized Structures in Turbulent Flow
Authors: Endo Masaya , Tsukahara Takahiro , Kawaguchi Yasuo 
Published: July 2018

When a material spreads in the turbulent flow, its instantaneous concentration distribution becomes not homogenous in space, and areas with high concentration containing sudden change of the concentration are formed by the local intense turbulence. In this study, we extracted such localized high-concentration areas by a conditional sampling technique, and observed the behavior of the areas.
In order to realize the scalar diffusion in quasi homogeneous isotropic turbulent flow, a model experiment was performed in a water channel flow. Fluorescent dye was introduced from a nozzle located at the center of the channel, and the concentration images of the dye were obtained at several downstream positions by PLIF measurement. To extract areas of high concentration containing a sudden change of the concentration, three types of analysis techniques including the conditional sampling technique were applied to PLIF images.
By the conditional sampling technique, we can extract areas of high concentration, which cannot be identified by the other two kind methods, and the effectiveness of this technique was proved. It was found that the areas extracted by the conditional sampling technique appear as lumps. The spanwise numerical probability distribution of the lumps roughly follows the Gaussian distribution, and the peak of the distribution decreases while its standard variation increases as streamwise distance increases. This result implies that performing extraction of areas with high concentration appropriately would enable to realize the material diffusing process as a Lagrange particle and provide a prediction method about the material diffusion source and the damage of the pollutant.
Experimental and Computational Investigation on Gyromill Wind Turbines Focusing on Wing Camber
Authors: Ejiri Eiji , Iwadate Tomoya 
Published: July 2018

Gyromill wind turbines with three different blade profiles were investigated experimentally and numerically in order to verify the effect of the direction of camber on aerodynamic performance.
Experiments were carried out using a model turbine impeller with an axial length of 200 mm and a diameter of 200 mm. The results showed that the maximum power coefficient was higher for blades with negative camber than for ones with positive camber. On the other hand, the operating range of the tip speed ratio tended to be narrower for the blades with negative camber than for the ones with positive camber.
An unsteady numerical flow analysis around the wind turbines was conducted using a commercial code employing the finite volume method. The results showed that the power coefficient of one blade had a maximum value in the second quadrant and that the blades with negative camber were advantageous for obtaining high rotational force in the position, compared with the blades with positive camber and a symmetrical blade.
The Effects of Bubble Interface Contamination on Bubble Motion, Bubble-Induced Surrounding Liquid Motion and Mass Transfer
Authors: Iburi Yuki , Huang Jie , Saito Takayuki 
Published: July 2018

Mass transfer from a bubble to the surrounding liquid plays an important role in chemical engineering processes. To improve the efficiency and safety of the processes, a deep understanding of the mass transfer mechanism from bubbles to the surrounding liquid is essential. In the present study, we examined a CO2 single bubble of 2∼3 mm in equivalent diameter that ascended zigzag in purified water and contaminated water (500ppm 1-pentanol solution). We used a high speed video camera systems with high spatial and temporal resolution, for visualization of the bubble wake and bubble-induced surrounding liquid motion.
The dissolution process of CO2 from the bubble to the surrounding liquid was visualized via LIF/HPTS (Laser Induced Fluorescence) method. HPTS, which is a fluorescent substance, was excited by Ar ion laser with a wavelength of 458 nm, then emitted with a wavelength of 513 nm. A pH level of CO2 solution decreased with increase in CO2 concentration; hence the emission intensity of HPTS was reduced. As a result, dark regions observed below the bubble rear accorded with the bubble wakes; from visualization of this bubble wakes through the high speed video cameras, dynamic CO2 dissolution process was obtained. In the purified water, the bubble shape was oblate ellipsoid, and horse-shoe-like vortices were formed in the rear of the bubble. On the other hand, in the contaminated water, the bubble was nearly spherical. Furthermore, behavior of the vortices changed. These different results in two conditions were caused by the decrease in the surface tension owing to the bubble surface contamination. While the bubble was rising, the non-uniform distribution of the surfactant on the bubble surface occurred. Hence, a gradient of the surface tension was formed on the bubble surface, furthermore, it caused the Marangoni convection.
Meanwhile, in order to consider the relationship between dissolution process and the surrounding liquid motion, we measured the liquid phase velocities via PIV.
Cavitation Flow Structure and Unsteady Pressure Pulsation Around a Hydrofoil
Authors: Ni Dan , Yang Minguan , Li Zhong , Zhang Ning , Gao Bo 
Published: July 2018

The present work is an original study of the flow induced vibration, cavitation structures and cavitation induced pressure pulsation characteristics around a typical hydrofoil named 791, which is widely applied in the axial flow pump.
From the vibration experiment of the hydrofoil at various operating conditions, it is clear that at low frequency band, with Reynolds number increasing, vibration energy first experiences a stable slightly increasing tendency, and then decreases rapidly, finally rises steeply again. Besides, according to the results of several positive incidence angles, it is observed that vibration energy usually achieves a local minimum level at a certain positive incidence angle falling into the range of 2° to 4°.
Based on results obtained from the detached eddy simulation (DES) turbulent model, full developing process of cavitation stages including, incipient cavitation, sheet cavitation and cloud cavitation could be captured and easily identified. It is found that pressure spectra in accordance with different cavitation stages show great discrepancy. In the stage of incipient cavitation and cloud cavitation, predominant components in pressure spectra are caused by the cyclical evolution of the main cavity and the periodic variation of the small vacuoles shedding at the span-wise outer edge of the hydrofoil. However, in sheet cavitation stage, the pronounced excitation frequencies are generated by cyclical evolution of the main cavity and cavity shedding from both sides of the U-shaped cavitation structure. Pressure pulsation amplitude is pretty small at the cavity stable adhesion region. But the amplitude of vacuoles shedding from the hydrofoil is much larger than main cavity adhesion region at these three stages.
Optimal Sensor Placement Using Chaotic Monkey Search Algorithm
Authors: Zhang Fuli , Brezhneva Olga , Shukla Amit 
Published: July 2018

The optimal sensor placement (OSP) problem is integral to modern large scale structures for their health monitoring. Evolutionary algorithms for the OSP problem are attractive as they can result in global optima without gradient information. In this paper, a modification of the Monkey Algorithm with a chaotic search strategy and adaptive parameters is proposed. It includes chaotic initialization, variable search step length, and adaptive watching time.
The performance of the proposed chaotic Monkey Algorithm (cMA) is compared with the original Monkey Algorithm. Convergence property of cMA is established. The proposed method is applied to an optimal sensor placement problem for structural health monitoring. The OSP problem is solved for a mass-spring-damper system and then for a model of the I-40 bridge developed by the Los Alamos National Laboratory. Numerical results demonstrate that the proposed Chaotic Monkey Algorithm has capability of solving mixed-variable optimization problems and that it performs better than the originally proposed Monkey algorithm. Finally, nonparametric uncertainty modeling is used to evaluate variability in a model and its effect on the optimal sensor placement.
Generation and Optimization of Traveling Vibrating Waves in Self-Assembling Swimming Smart Boxes
Authors: Bani-Hani Muath , Borazjani Iman , Esfahani Ehsan T. , Krovi Venkat , Karami M. Amin 
Published: July 2018

This paper presents vibration analysis and structural optimization of a self-assembled structure for swimming. The third mode shape of the structure in the longitudinal direction resembles the body waveform of a swimming eel fish. At the final destination, the box self-assembles using shape memory alloys. MFCs (Piezoelectric Micro Fiber Composites) are actuated at the fundamental natural frequency of the structure. This excites the primary mode of resonance. We optimize the thickness of the panels and the stiffness of the joints to most efficiently generate the swimming waveforms that resembles the body waveform of eel. Traveling wave is generated using two piezoelectric batches actuators bonded on the first and fourth segments of the beams in the longitudinal direction. Excitation of the piezoelectrics results in coupled system dynamics equations that can be translated into generation of waves. Theoretical analysis based on the distributed parameter model was conducted in this paper.
A scalar measure of the traveling to standing wave ratio was created using 2-dimensional Fourier Transform of the wave form. The results then were compared to common method in the literature for assessment of standing to traveling wave ratio.
Discrete Time Finite Element Transfer Matrix Method Development for Modeling and Decentralized Control
Authors: Cramer Nick , Swei Sean , Cheung Kenny , Teodorescu M. 
Published: July 2018

The current emphasis on increasing aeronautical efficiency is leading the way to a new class of lighter more flexible airplane materials and structures, which unfortunately can result in aeroelastic instabilities.
To effectively control the wings deformation and shape, appropriate modeling is necessary. Wings are often modeled as cantilever beams using finite element analysis. The drawback of this approach is that large aeroelastic models cannot be used for embedded controllers. Therefore, to effectively control wings shape, a simple, stable and fast equivalent predictive model that can capture the physical problem and could be used for in-flight control is required.
The current paper proposes a Discrete Time Finite Element Transfer Matrix (DT-FETMM) model beam deformation and use it to design a regulator. The advantage of the proposed approach over existing methods is that the proposed controller could be designed to suppress a larger number of vibration modes within the fidelity of the selected time step. We will extend the discrete time transfer matrix method to finite element models and present the decentralized models and controllers for structural control.
A Device for Improving Oxygenation in Patients With Acute Respiratory Distress Syndrome
Authors: Gordon Alex , Ai Xin Jue Luo Kevin , Saab Rami , Engelberts Doreen , Kavanagh Brian , Yoshida Takeshi , Looi Thomas 
Published: July 2018

In this paper we present a device for improving blood oxygenation in patients with Acute Respiratory Distress Syndrome (ARDS). ARDS is caused by lung-related illness or injury, and can occur in mechanically ventilated ICU patients due to volutrauma or barotrauma. In ARDS, the lower lung is closed resulting in impaired gas exchange, and the upper lung is easily overstretched resulting in injury. The application of continuous negative abdominal pressure (CNAP) assists in opening the lower lung by pulling the diaphragm towards the abdomen. The device, consisting of a rigid arch, a compliant patient interface, and a pressure sensor module, allows for the application of CNAP to a patient suffering from ARDS.
An initial pig trial using the prototype device showed significant improvement in the ratio of oxygen in the blood to the fraction of inspired oxygen, PaO2/FiO2, after five minutes of −5 cmH2O pressure application. Furthermore, preliminary testing on healthy humans indicated the device was comfortable, easy to apply, and formed a consistent airtight seal. Future prototypes will focus on ease of application, rigidity, and adjustability.
Development of Cavity Shapes of Labyrinth Seals Through CFD Analysis
Authors: Ramanadham Mohana Rao , Gaja Balakrishna , Kanchanapally Sravan Kumar 
Published: July 2018

Axial flow compressors of Gas turbines use labyrinth seals to prevent the backflow of the working fluid. However some fluid will leak through the seals due to the clearance provided between the stationery and rotating components and due to the pressure difference across the seals, which affects the efficiency. The geometric shape of the seal plays an important role in influencing the fluid flow through the seals and the leakage rate.
The flow through the seals consists of the primary flow and the secondary flow. The secondary flow is the flow through the cavity which is associated with vortex currents and tends to obstruct the primary flow. The geometric shape of the cavity is varied to study its effect on the vortex and resultant leakage flow through the seals.
The curvatures of the seal and the distance of the seal tip to the end of the seal are the main parameters considered to arrive at the desired cavity which helps to create the required whirling action and to reduce the velocity of the leakage flow.
Gambit software is used for modeling the geometry and Fluent software is used for the analysis. Axi-symmetric pressure based analysis is carried out using the standard κ-ε turbulence. The results of the standard cavity are compared with different variants.
The flow velocity and mass flow is studied at different locations of the seal. The results indicate that by optimizing the shape of the seal cavity, the leakage through the labyrinth seal can be reduced.
An Assessment of Turbulence Models for S-Duct Diffusers With Flow Control
Authors: Bhat S. P. , Sullerey R. K. 
Published: July 2018

The selection of a turbulence model for a problem is not trivial and has to be done systematically after comparison of various models with experimental data. It is a well known fact that there is no such turbulence model which fits all problems ([3], [13]). The flow in S-duct diffuser is a very complex one where both separation and secondary flow coexist. Previous work by the author on CFD analysis of S-duct diffuser was done using k-ε-Standard model [1], however it has been seen that choosing other turbulence model may result in better capturing of the physics in such a problem. Also flow control, to reduce energy losses, is achieved using a technique called Zero Net Mass Flow (ZNMF), in which suction and vortex generation jets (VGJ) are combined and positioned at optimum location. A proper turbulence model has to be chosen for capturing these phenomena effectively. Extensive experimental data is available on this problem and ZNMF technique from previous work done by one of the authors which is used for validating the CFD results. Here the focus is on choosing the best turbulence model for the S-duct diffuser.
Numerical (CFD) analysis is carried out using Ansys Fluent 13.0 with six turbulence models for the geometry with (ZNMF) and without (Bare duct) flow control and then compared with the experimental results. The turbulence models used are Spalart-Allmaras, three variants of k-ε – Standard, RNG and Realizable and two variants of k-ω – Standard and SST model. All the parameters of comparison are non-dimensionalized using the free stream properties, so that the results are applicable to a wider range of problems. This work is limited to incompressible flow analysis, as the experimental data is only available for low Mach number flows. Comparison of all these models clearly shows that results obtained using k-ω-SST model are very comparable to the experimental results for the bare duct (without flow control) and flow controlled duct both in terms of distribution of properties and aggregate results. Compressible flow analysis can be attempted to achieve reliable results in future with ZNMF using the best turbulence model based on this study.
Steady State Thermal Analysis of an Afterburner Liner
Authors: Batchu Suresh , Kishore Kumar S. 
Published: July 2018

Military aero engines employ afterburner system for increasing the reheat thrust required during combat and takeoff. During reheat the gas temperature in the afterburner is of the order of 2100K.The afterburner liner has to be cooled with the available bypass air to maintain metal temperature within allowable limits. The liner has cooling rings at the rear to cool the liner with tangential film cooling.
This paper discusses the methodology of afterburner liner metal temperature prediction and comparison with measured metal temperature during aero engine testing at reheat condition. All the modes of heat transfer are considered for thermal analysis, radiation due to higher level of gas temperature during reheat, conduction due to presence of low conductivity thermal barrier coating and convection due to higher gas velocities are considered.
At different steady state reheat conditions metal temperature are predicted and compared with measured data during aero engine testing. The predicted skin temperatures and measured temperatures are in good agreement. Empirical correlations are used for estimating the heat loads coming on the liner and adiabatic film temperature near screech holes and cooling rings. Metal temperature and thermal loads coming onto the liner are predicted with 1D code. The estimated thermal loads are applied on 3D FE model to obtain nodal temperature distribution. The thermal Analysis is carried using ANSYS software in which thermal barrier coating is also modeled.
The parameters like gas temperature, thermal barrier coating thickness, coating conductivity, and coolant mass flow distribution are considered for carrying out a sensitivity analysis of liner metal temperature.
Finite Element Analysis for Prediction of Permanent Growth of Rotating Disc of Aero Engine During Over-Speed and Burst-Speed Conditions and Validation of Results Through Experiment
Authors: Rudra Goud M. , Manjunatha C. , Venkateshwarlu M. , Patnaik B. V. A. 
Published: July 2018

The service life of critical aerospace components is governed by the modes of degradation and failure such as: yielding, fatigue, fracture, creep, corrosion, wear, etc. A single disc is used for over-speed and burst-speed tests to know the growths (plastic deformation). In this paper, a cyclic symmetry sector of disc model with non linear elastic-plastic material is considered. A non-linear finite element method is utilized to determine the stress and strain state of the disc under over-speed and burst-speed conditions using material stress strain curves.
Permanent growths and strains obtained from the over-speed analysis are incorporated in the burst-speed Finite element Model. The original stress strain curve used in over-speed analysis is modified with plastic strain and used in burst-speed analysis of same disc.
Elastic strains obtained from the over-speed and burst-speed analysis are utilized in stress strain relationship equations to calculate the permanent growths at critical locations of disc.
Growths predicted from Analysis are comparable with the experimental results of disc where a maximum variation of 11% at bore and rim of disc is observed.
A Numerical Model for Unsteady Oil Film Motion in Aero-Engine Bearing Chambers and Experimental Verification
Authors: Liu Zhenxia , Zhao Jingyu , Hu Jianping , Lu Yaguo 
Published: July 2018

The work presented here focusing on the motion of oil film heat and mass transfer. A complete mathematical model based on theoretical study to solve three-dimensional unsteady oil film motion was established. Numerical simulation for different test rigs (bearing chamber test rig of Karlsruhe Institute of Technology (KIT) and rotating cylinder test rig of Northwestern Polytechnical University (NPU)) and different working conditions was carried out by using CFD commercial software. Particle tracks, oil film thickness change history and film stripping were studied, and the numerical results of oil film thickness were obtained.
The numerical results show that the motion of the oil film will reach the state of basic stability for unsteady oil flow, and a development process from the oil film formation to basic stability in this paper is less than 1.5 seconds. Moreover, comparison between the numerical results and the experimental values shows that the maximum error of oil film thickness is less than 7% at the measurement points under the calculation conditions, which indicates the proposed computational model to solve unsteady oil film motion is a valuable technical means for the study of oil film movement mechanism and oil film heat and mass transfer.