bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Enhanced Damping Figure of Merit in Biomimetic Hierarchical Staggered Composites
Authors: Zhang Pu , To Albert C.
Published: December 2013

Most composites exhibit a damping figure of merit, a crucial index of a material's dynamic behavior, lower than the value predicted by the Hashin–Shtrikman bound. This work found that the biomimetic hierarchical staggered composites inspired by bone structure can have a damping figure of merit tens of times higher than the Hashin–Shtrikman composite. The optimum state is achieved when the hard and soft phases contribute equally to the overall stiffness of the composite in the direction parallel to the platelets. At this optimal point, the model predicts that the overall stiffness is half the Voigt bound while the damping loss factor is half that of the soft phase. This behavior stems from a deformation mechanism transition from soft-phase-dominant to hard-phase-dominant as the platelet's aspect ratio increases. The findings from this study may have important implications in the future design of composites to mitigate vibration and absorb shock in load-bearing structures.
Choked-Flow Inlet Orifice Bubbler for Creating Small Bubbles in Mercury
Authors: Wendel Mark , Abdou Ashraf , Riemer Bernard
Published: December 2013

Pressure waves created in liquid mercury pulsed spallation targets like the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, induce cavitation damage on the target container. The cavitation damage is thought to limit the lifetime of the target for power levels at and above 1 MW. One way to mitigate the damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating a bubble size distribution that is sufficiently large and disperse in mercury is challenging due to the high surface tension. Also, measuring the population is complicated by the opacity and the high level of turbulent mixing.

Recent advances in bubble diagnostics by batch sampling the mercury made it possible to compare bubble populations for different techniques in a SNS-1/20th scale test loop. More than 10 bubblers were tested and the most productive bubblers were taken for in-beam testing at the Los Alamos Neutron Science Center (LANSCE) WNR user facility. One bubbler design, referred to as the inlet-orifice bubbler, that showed moderate success in creating populations also has an added advantage that it could easily be included in the existing SNS full-scale mercury target configuration. Improvements to the bubbler were planned including a reduction of the nozzle size to choke the gas injection, thus steadying the injected mass flow and allowing multiple nozzles to work off of a common plenum. For the first time, reliable bubble population data are available in the prototypical target geometry and can be compared with populations that mitigated cavitation damage. This paper presents those experimental results.
Flow Structure of Tandem Cascades in the Region of the Sidewalls
Authors: Frey Thomas , Böhle Martin
Published: December 2013

Numerical and experimental investigations about tandem blades have often been performed for the 2D flow of tandem cascades. The open literature suggests that tandem blades may be superior to single blades, especially for large turning angles. However, the investigations up to now never involved the losses, arising at the sidewall. Less information about the flow structure near the sidewall are available. This raises the question whether the geometry that generates minimal losses for the 2D flow also generates minimal losses near the sidewall for large turning angles. This paper deals with the 3D flow in the region of the sidewall of a high turning tandem cascade with low aspect ratio. For the numerical and experimental investigation two tandem cascades were designed using empirical correlations of Lieblein and Lei. Starting with these tandem cascades the configuration of the individual profiles is determined that generates minimal loss at the wall. Based on the flow topology the loss generation is identified and explained. The images of the flow topology are created on the basis of numerical and experimental oil pictures. The procedure and results are discussed in detail. In particular the occurrence of flow phenomena like corner stall of the 3D boundary layer is discussed. Finally design rules for the spacing ratio of the forward and afterward blades as well as the percent pitch of the blades are given. The examinations are performed with tandem cascades turning the flow from approximately 50° at a Reynolds number of 8 · 105. In every cascade the load split is constant (50%). The profiles are NACA65 with circular camber lines.
Numerical Investigation on Periodic Flow Unsteadiness in a Centrifugal Pump With Volute
Authors: Pei Ji , Yuan Shouqi , Li Xiaojun , Yuan Jianping , Wang Wenjie
Published: December 2013

In this paper, the CFD simulation and flow unsteadiness analysis for a centrifugal pump with volute were carried out in whole flow passage including impeller, volute and side chamber. The periodic flow unsteadiness based on URANS equations has been quantitatively investigated in detail by defining unsteady velocity intensity, and turbulence intensity under design condition was also studied. Meanwhile, three-dimensional effect has been considered for the twisted blade channels. The time-averaged unsteady velocity intensity and time-averaged turbulence intensity were calculated by averaging the results of each grid node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively. The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the centrifugal pump optimum design procedure for obtaining more stable inner flow of the pump and cutting down certain components of flow-induced vibration and noise.
Interaction Between a Pair of Drops Ascending in a Linearly Stratified Fluid
Authors: Bayareh M. , Dabiri S. , Ardekani A. M.
Published: December 2013

In this paper, we provide fully resolved three-dimensional direct numerical simulations of ascending motion of a pair of drops in a linearly stratified fluid using a finite-volume/front-tracking method. We study the density stratification effects on the rise velocity of drops and their stable position for different initial alignments. Due to the formation of a jet in the lee of a single drop rising in a stratified fluid, a decrease in rise velocity (or an increase in drag) is observed compared to the homogeneous case. The hydrodynamic interaction between two drops in a linearly stratified fluid depends on the properties of both fluids and initial orientation of the two drops. For the case of drops rising side by side, the lateral separation of drops is suppressed due to stratification effects. In contrast to homogeneous case, two nearly spherical drops collide with each other at low Froude numbers and oscillate around their neutrally buoyant density level. Two spherical drops rising in tandem in a linearly stratified fluid at finite Reynolds number regime undergo drafting, kissing, and tumbling unlike their counterpart in a homogenous fluid.
Numerical and Experimental Investigation of Tip Leakage Vortex Trajectory in an Axial Flow Pump
Authors: Zhang Desheng , Shi Weidong , Wu Suqing , Pan Dazhi , Shao Peipei , Wang Haiyu
Published: December 2013

In this paper, the tip leakage vortex (TLV) structures in an axial flow pump were investigated by numerical and experimental methods. Based on the comparisons of different blade tip clearance size (i.e., 0.5 mm, 1mm and 1.5mm) and different flow rate conditions, TLV trajectories were obtained by Swirling Strength method, and simulated by modified SST k-ω turbulence model with refined high-quality structured grids. A high-speed photography test was carried out to capture the tip leakage vortex cavitation in an axial flow pump with transparent casing. Numerical results were compared with the experimental leakage vortex trajectories, and a good agreement is presented. The detailed trajectories show that the start point of tip leakage vortex appears near the leading edge at small flow rate, and it moves from trailing edge to about 30% chord span at rated flow rate. At the larger flow rate condition, the starting point of TLV shifts to the middle of chord, and the direction of TLV moves parallel to the blade hydrofoil. As the increasing of the tip size, the start point of TLV trajectories moves to the central of chord and the minimum pressure in vortex core is gradually reduced.
Geometrical Consideration of Permeation in Elastomers
Authors: Garafolo Nicholas G. , Daniels Christopher C.
Published: December 2013

Elastomer seals for space applications are integral for the success of manned space flight. These seals inhibit the loss of habitable cabin air to the vacuum of Space. The loss of breathable atmosphere due to leaks of a seal must be replaced through the use of a costly make-up air system. A cost-effective sealing solution for long-duration manned space flight is thereby enabled by seal leak mitigation, while maintaining acceptable behavior in other requirements (e.g., closure force, reusability). Thus, there is a need for optimization from a multitude of geometric possibilities. To facilitate the selection of space seals mechanisms, designers and researchers have relied heavily on engineering judgment and intuition in the design phase of equipment. The main geometric hypothesis utilized in past design is that the leak rate depends on two aspects: (1) the permeation path length, and (2) the wetted gas-elastomer contact area. The research detailed herein highlights the necessity for computational prediction methods in the preliminary phase of space seal design. To this end, a series of computational analyses were performed utilizing a compressible permeation approach to elastomeric space seals. Utilizing a simple rectangular domain, the hypotheses were confirmed and are reflected in an analysis of the model equations, however, for one-dimensional flow. Unique to this analysis, additional domains were studied incorporating a periodic perturbation in the sidewalls. The analysis simulated the leak rate of each seal design domain, as manufactured from silicone elastomer S0383-70. Foremost, results highlight the significance of the leak rate prediction methodology, as mere engineering intuition does not always lead to true design optimization. A study in the boundary conditions is also presented, whereas the elastomeric nature of space seal materials can be utilized for a strategic gain in leak rate performance. As an additional benefit, the analysis proved its merit as a cost reduction technique. Whereas by undergoing design iterations in a virtual environment, the cost associated with manufacturing faulty designs are eliminated.
Transport Phenomena in Passively Manipulated Chaotic Flows: Split-and-Recombine Reactors
Authors: Ghanem Akram , Lemenand Thierry , Della Valle Dominique , Peerhossaini Hassan
Published: December 2013

Static mixers and multifunctional heat exchangers/reactors are being used increasingly in process industries. In the inertial or turbulent regime, mixers often incorporate inserts or corrugated walls whose primary function is to create embedded flow vorticity. On the other hand, in low-Reynolds-number flows, for viscosity or residence time purposes, it is necessary to provide solutions based on kinematic mixing, i.e. the topology of the primary flow, such as split-and-recombine reactors (SAR). The concept is based on passive liquid stream division, then rotation in bends of opposite chiralities, and finally recombination, achieving stretching/folding following the baker’s transform. Mixing is efficiently ensured by diffusion without generating prohibitive pressure drops. In this work, a chemical probe is used to study mixing and mass transfer in two different split-and-recombine square duct geometries, SAR-1 and SAR-2 of 3 mm side. Results show that effective mass transfer and mixing can be achieved with a short reactor length and moderate pressure losses; the SAR-1 geometry being more efficient. The chaotic configurations are a good compromise even for higher Reynolds numbers compared to static mixers operating in the transitional regime: they produce moderate pressure losses while enhancing mass transfer.
Development of a Novel Pressure-Based Coupled CFD Solver for Turbulent Compressible Flows in Turbomachinery Applications
Authors: Mangani Luca , Darwish Marwan , Moukalled Fadl
Published: December 2013

This paper reports on a newly developed fully coupled pressure-based algorithm for the solution of turbulent all-speed compressible flows implemented within the framework of the open-source OpenFOAM® library.

In the algorithm the velocity and pressure fields are assembled into one extended system of equations that is diagonally dominant and then resolved simultaneously using a robust algebraic multigrid solver. At the heart of this algorithm is a re-derived fully coupled pressure equation that is very similar in form to the rhie-chow segregated pressure equation. After presenting the details of the coupled approach its performance is compared to that of a pressure-based SIMPLE compressible solver again implemented in OpenFOAM. A number of tests including laminar and turbulent flow problems are thus solved using both methodologies with their convergence history and computational cost compared.
Evaluation of a Laser Diode for DGV Application
Authors: Morrison Gerald L. , Karabacak Mustafa
Published: December 2013

This paper will present the evaluation of a 300 mw, continuous wave, laser diode system which appears to be suitable for DGV use. The laser frequency range is sufficiently narrow and the lasing frequency can be adjusted across the range of the iodine reference cell (absorption line filter). A spectrum analyzer is used to document the frequency content of the laser across the frequency range of the iodine reference cell. The response of the iodine reference cell to the laser across its spectrum is measured at several iodine reference cell temperatures. The beam profile is also measured. This set of data determined the applicability of this laser for DGV use.
Drag Reduction by Boundary Layer Control With Passively Moving Wall
Authors: Koch Helge , Kozulovic Dragan
Published: December 2013

There exists a wide range of approaches to reduce the skin friction drag. One of the approaches is to attenuate the no-slip condition by moving the wall in flow direction. This reduces the velocity difference between the mean flow and the wall and thereby the wall shear stress. Actively moving walls are used for nearly all known investigations on this topic. This paper presents a concept for a passive moving wall. The motion of the wall is driven by the wall shear stress itself. For this investigation the moving wall is designed as a rotating disc which is embedded in the surface of a flat plate. One half of the disc is covered, whereas the other part is exposed to the flow. The interaction between the rotating disc and the flow is investigated experimentally by means of flatted Pitot probe measurements and rotation speed measurements.
Transition Criteria for Laminar to Turbulent Flow for Yield Power Law (YPL) Fluids Based on Stability Analysis
Authors: Kalayci Goktug , Ozbayoglu Evren M. , Miska Stefan Z. , Yu Mengjiao , Takach Nicholas , Saasen Arild , May Roland
Published: December 2013

It is well known that a Newtonian fluid with the presence of solid particles in suspension behaves non-Newtonian. Higher the solid content, more significant the yield stress of the fluid. Determination of the hydraulic behavior of fluids having a significant yield stress is a challenging task. For engineering purposes, pressure drop within the system, during pipeline transportation, has to be estimated carefully and accurately. Flow regime plays a vital role during hydraulic calculations. The inaccurate determination of flow regime can lead us to large errors in frictional pressure drop calculations and ultimately leads to error in designing and flow assurance point of view, since hydraulic calculations are including a friction factor term, which is a direct function of flow regime. In general, Reynolds number is the main parameter used by the industry for determining the flow regime, and the friction factor. This approach works reasonably accurate for Newtonian fluids. However, as the yield stress of the fluid increases, this conventional technique for determining the flow regime is not as accurate. Although many approaches have been introduced for estimating the flow regime for non-Newtonian fluids, there exists a lack of information and confidence of such predictions for fluids having high yield stress, such as Yield Power Law (YPL) fluids (i.e., Herchel-Bulkley). (1)τ=τy+Kγm

This study presents an analytical solution for predicting the transition from laminar to non-laminar flow regime based on Ryan & Johnson’s approach using the stability analysis and equation of motion for YPL fluids. Comparing with the experimental results for YPL fluids under different flow conditions, including laminar and non-laminar flow regimes, show that presented approach gives a better estimation of the transition from laminar to non-laminar flow regime than conventional Reynolds number approach. In some cases, it is observed that although the Reynolds number is high, flow is still laminar, which is predicted accurately using the presented model. This study provides a higher accuracy in estimating the flow regime, which leads to a higher confidence in hydraulic designs and determining limitations of the system in concern.
Development of a Low Cost Particle Image Velocimetry System for Fluids Engineering Research and Education
Authors: Ring Brock P. , Atkinson Daniel K. , Henderson Andrew W. , Lemley Evan C.
Published: December 2013

Particle image velocimetry (PIV) has transformed fluid mechanics research in recent years. PIV also holds the possibility to transform fluids engineering undergraduate education with the ability of students to get hands-on experience in visualization of real flow fields. One barrier to use of PIV is the cost of a system. Research grade systems are often over $100,000 and inaccessible to many undergraduate students. Recent availability of low-cost high-frame-rate digital cameras, lasers, and public domain software offer potential accessibility for PIV for many labs at academic institutions.

In this paper we describe the development of a PIV system for under $1000 including specific components and their costs. In our lab this system is currently being used for several liquid flow experiments including obtaining the flow field in and near small bifurcations. Although we are using the system for liquid flows, it may be used for gas flows as well. One issue that is addressed is the cost of flow seeding — this has been solved by using pulverized green algae as seed particles with a strong reflection by a 532 nm green laser.

The system is small and portable and is useful for observing flow in locations that are not of direct interest for experiments, but may have a bearing on flow conditions in experimental measurements; such as upstream of test sections. We describe some examples of how we have used the lost-cost PIV system in our lab and how it can be used for fluids engineering education and research. The current research application of this system is performing loss coefficient calculations in a test section using the energy dissipation.
Teaching Heat Exchanger Design in Mechanical Engineering With CFD
Authors: Teixeira José C. , Teixeira Senhorinha F. C. , Oliveira António
Published: December 2013

Technologies for energy recovery and conversion are at the forefront of any mechanical engineering curricula. Heat exchangers are often found in various industries and, therefore, deserve a special dedication to the effort in under and post graduate education.

The Integrated Masters degree in Mechanical Engineering at the University of Minho includes a semester (out of 10) dedicated to the thermal analysis of heat exchangers. Traditionally such subject would follow the route of application of the NTU charts and the efficiency method. Although this approach is still of great relevance both as a calculation methodology and as a method to develop the physical insight into the subject, the application of advanced computation tools has been introduced into the course with great acceptance by the students. In brief, the course provides an excellent opportunity to integrate various subjects.

This paper details the rationale for the application of CFD techniques in heat exchanger design and calculations. It frames this approach within the overall education in mechanical engineering, and integrates the methodology with traditional design methodologies. Various test cases are detailed (constant wall temperature heat exchanger, double pipe and shell and tube) and the results are compared with integral methods. The local heat transfer coefficients are discussed with regard to the empirical correlations.
Performance Characteristics and Flow Conditions of High Pressure and Large Flow Rate Cooling Fan
Authors: Shigemitsu Toru , Fukutomi Junichiro , Agawa Takuya
Published: December 2013

Data center has been built with spread of cloud computing. Further, electric power consumption of it is growing rapidly. High pressure and large flow rates small-sized cooling fans are used for servers in the data center and there is a strong demand to increase pressure and flow rate of it because of increase of quantity of heat from the servers. Contra-rotating rotors have been adopted for some of the high pressure and large flow rate cooling fans to meet the demand of it. There is limitation of space for servers and geometrical restriction for cooling fan because spokes to support the fan motor, electrical power cables and so on should be installed in the cooling fan. It is important to clarify performance of each front and rear rotor of contra-rotating small-sized cooling fan and internal flow condition to achieve the high performance cooling fans.

In the present paper, detailed performance and the flow condition around the rotor of the high pressure and large flow rate contra-rotating small-sized axial fan with 40mm square casing are investigated. Pressure, shaft power and efficiency curves of each front and rear rotor are clarified by the experimental and the numerical results. Furthermore, the internal flow condition of the rear rotor is clarified by the numerical analysis results and design guideline to improve the performance is discussed by these results.
Large Eddy Simulation of a Forced Turbulent Jet Impacting on a Semi-Cylinder
Authors: Li Z. , Khezzar L. , Kharoua N.
Published: December 2013

This study is devoted to a forced turbulent plane jet emerging from a slot rectangular nozzle impinging on a semi-cylindrical surface using large eddy simulation. Both forced and unforced cases are considered. The Reynolds number, based on the slot velocity and width, was 5600. The LES simulations were validated using published experimental results and contrasted against RANS models. The study is performed for a slot-to-surface distance equal to twice the nozzle width and considers two forcing frequencies equal to 400 and 800 Hz. The jet was excited using a sinusoidal inlet velocity profile at several harmonics of the preferred mode and the flow and heat transfer characteristics were analyzed. The phase averaged Nusselt number exhibited several peaks along the semi-circular target plane. Increases above the steady unforced jet values of heat transfer rates were obtained in the stagnation region and decreases were observed in the wall jet region. The fluctuations in the phase averaged surface Nusselt number are explained in terms of the interaction of organized shear layer structures with induced target wall structures.
Plasma Flow Control Simulation of an Airfoil of Wind Turbine at an Intermediate Reynolds Number
Authors: Aono Hikaru , Nonomura Taku , Yakeno Aiko , Fujii Kozo , Okada Koichi
Published: December 2013

The flow over a National Renewable Energy Laboratory S825 airfoil was simulated for a chord Reynolds number of 7.5×105 and an angle of attack of 22.1 deg. These conditions approximately matched a blade element condition of 75% radius of 42-m-diameter wind turbine operating 2.5 rpm under a free-stream of 10 m/s. Computed flow of the uncontrolled case characterized massive separation from near the leading edge due to high angle of attack. With the active flow control by a dielectric barrier discharge plasma actuator, separation was reduced and the lift-to-drag ratio increased from 2.25 to 6.52. Impacts of the plasma actuator on the shear layer near the leading edge were discussed. Direct momentum addition provided by the case setup of plasma actuator considered in current study seemed to be a dominant factor to prevent the separation of shear layer near the leading edge rather than influence of small disturbances induced by the plasma actuator operated in a burst modulation. However, due to the high angle of attack and the thick airfoil, the control authority of the plasma actuator with the setup (i.e. the operating condition and number of plasma actuators installed on the wing surface) considered was insufficient to completely suppress the separation over the NREL S825 airfoil.
Lattice Boltzmann Simulation of the Flow Field in Pump Intakes: A New Approach
Authors: Schneider Andreas , Conrad Daniel , Böhle Martin
Published: December 2013

In recent years Lattice Boltzmann Methods have become popular for solving fluid flow problems of engineering interest. Reasons for this popularity are due to the advantages of this method which are for example the simplicity to handle complex geometries and the high efficiency in calculating transient flows.

For the operational reliability and efficiency of pumps and pump systems the incoming flow conditions are crucial. Since the efficiency and reliability requirements of pumps are rising and must be guaranteed by the pump and plant manufacturer, the flow conditions in pump intakes need to be evaluated during plant planning. Recent trends show that pump intakes are built more and more compact which makes the flow in the intake even more complex and holds a higher risk for unacceptable pump inflow conditions. If the inflow conditions of the pump are not according to the demand of the pump manufacturer or to international standards, optimization needs to be done.

In this contribution a numerical scheme for the simulation of pump intakes based on a Lattice Boltzmann-LES approach is presented and the ability to capture the flow phenomena of the intake flow is analyzed.
Experimental Investigation on Unstable Flow in Multi-Stage Centrifugal Blower With Inlet Guide Vane
Authors: Hiradate Kiyotaka , Sakamoto Kiyohide , Kanno Toshio , Shinkawa Yasushi , Joukou Satoshi , Suzuki Katsunari
Published: December 2013

This study experimentally examines unstable flow phenomena occur in a five-stage centrifugal blower equipped with inlet guide vanes (IGVs) before the first stage.

High response pressure transducers were mounted on a suction nozzle, an U-turn bend between a diffuser and return channel in the second stage, and a discharge nozzle to detect surge. Moreover, at a vaneless space between an impeller and a vaned diffuser in the second stage, three pressure transducers were located thirty degrees apart in the circumferential direction to distinguish rotating stall in the diffuser from surge. Measurements were performed at several flowrates changing the IGVs from fully opening condition to partially opening conditions.

We confirmed three types of pressure fluctuation in low flowrate region. The first is the fluctuation showing the largest amplitude and the lowest frequency (about 7–9 percent of impeller rotation frequency) and observed at all the sensors. This appears in the positive slope region of the total system head curve. The second is the spike-like fluctuation intermittently observed only in the vaneless space. This occurs at the IGVs partially opening conditions and shows observed time lag among the three sensors. The last is the fluctuation with smaller amplitude and higher frequency (about 14–23 percent of impeller rotation frequency) than that of the first and observed at all the sensors. This occurs at the IGVs partially opening conditions. At 4.5 percent IGVs opening, this fluctuation is observed in the steep negative slope region of the total system head curve, where the whole compression system is supposed to be stable. Moreover, this fluctuation is measured at the same phase in the vaneless space.

We concluded that the first-mentioned fluctuation is deep surge and the second-mentioned fluctuation is rotating stall in the diffuser. On the other hand, we have considered the last-mentioned fluctuation to be mild surge and the reason why this occurs in the negative slope region to be as follows. At 4.5 percent IGVs opening, slope of the first stage head curve becomes steeply negative by prewhirl and this negative slope stabilizes the system. By contrast, at the second to the last stage, the slope of the head curve becomes positive in low flowrate region and this positive slope destabilizes the system. Therefore, even if the total system head curve maintains a steep negative slope, the system operating point oscillates slightly (mild surge situation) due to a balance of these stabilization and destabilization effects.
The Effect of the Incidence Angle on the Flow Over a Rotating Disk Subjected to Forced Air Streams
Authors: Helcig Christian , aus der Wiesche Stefan
Published: December 2013

The flow over a stationary and a rotating disk subjected to an outer forced air stream was investigated particular with a look to the effect of incidence angle β. The experiments were carried out with an electrically heated disk placed in a wind tunnel. The measurement of the mean and the local convective heat transfer coefficient enabled a clear study of the flow behavior. The incidence angle β was scanned with high resolution over the entire range, and a large number of crossflow and rotational Reynolds numbers were covered. It was found that a well defined transition incidence angle β existed leading to a symmetry breaking of the flow. The resulting mean heat transfer was in agreement with the phenomenological Landau-de Gennes model in case of small rotational Reynolds numbers. In case of large rotational effects, a different type of transition occurred. Based on the experimental and theoretical results, a discussion of the different phenomena due to the involved flow parameters is given in the paper.
A Numerical Analysis on the Behaviors of Polymer Film and Resin in an In-Mold Decoration Process
Authors: Yoon Jonghyuk , Hur Nahmkeon , Bae Ah-Hyun , Lee Taehee
Published: December 2013

In various manufacturing industries, an in-mold decoration (IMD) process for plastic objects is widely utilized because a film forming and an injection molding process run simultaneously. In the present study, the deformation of polymer film and resin in the IMD process were numerically investigated to evaluate the quality of the plastic object formed by the IMD process, which consists of vacuum suction and injection molding. To obtain the initial shape of the polymer film during the injection molding process, the deformation of the polymer film in the vacuum suction process was pre-formed using the operating conditions needed to attach the film to a cavity. Since the properties and deformation of polymer film are greatly affected by the behavior of polymer resin being injected into a cavity, numerical simulations for the injection molding and film forming were performed with one-way coupling method. The results showed that the resin being injected could lead to the tearing of the polymer film in local regions near the corners. In order to verify the proposed numerical methodology, the numerical results of the deformation patters printed on the initial polymer film were compared with the experimental data.
Numerical Simulation of Fluid Flow in Deterministic Lateral Displacement Devices
Authors: Feng Haidong , Miskovic Sanja
Published: December 2013

Deterministic lateral displacement (DLD) is a continuous, flow-based micro-particle separation method. DLD takes advantage of the laminar nature of the fluid flow in microchannels by directing the small particles along the main streamline of the fluid flow, while laterally displacing larger particles along the axis of the micropillar array. When optimally designed, this simple and energy-efficient method allows a high-resolution separation of particle mixtures carried along by the liquid at high velocity. In this paper, a numerical modeling of fluid flow inside of different DLD devices at different Re numbers is performed. A parametric study is conducted to assess the variation of theoretical critical particle size for various DLD devices. Parameters that affect flow velocity distribution, such as shift fraction and tilt angle are studied. Simulation results show that both micropillar shift fraction and the tilt angle significantly affect the velocity profile within the DLD device. A model is presented to describe the critical diameter for a wide range of pillar-diameter-to-gap-size ratios. The possibility of achieving greater throughput, while preserving flow characteristics and therefore particle separation efficiency, is demonstrated.
Numerical Study and Optimization of Air Flow and Thermal Behavior Inside a Typical Cold Room Loaded With Agricultural Produce
Authors: Balakrishna Abhijith , Lawrence Wilson
Published: December 2013

This work is part of a research activity aiming to improve and optimize air flow and temperature distribution inside a refrigerated cold room. An improved flexible air duct design inside the cold room is studied for uniform air flow and minimum temperature gradient inside the cold room. The present study investigates on various flexible air duct designs inside the cold room to provide better thermal management to improve the shelf life of the produce. In this study, the most commonly used refrigerated cold room is considered with inlet and outlet sections placed in the front wall of the room. The numerical modeling of airflow was performed using the computational fluid dynamics (CFD) code Fluent and turbulence modeling with standard k–ε model.
An Improved Direct-Forcing Immersed Boundary Method for Fluid-Structure Interaction Simulations
Authors: Zhang Xing , Zhu Xiaojue , He Guowei
Published: December 2013

Simulation of fluid-structure interaction (FSI) of flexible bodies are challenging due to complex geometries and freely moving boundaries. Immersed boundary method has found to be an efficient technique for dealing with FSI problems because of the use of non-body-fitted mesh and simple implementation. In the present work, we developed a FSI solver by coupling a direct forcing immersed boundary method for the fluid with a finite difference method of the structure. Several flow problems are simulated to validate our method. The testing cases include flow over a stationary cylinder and flat plate, two-dimensional flow past an inextensible flexible filament and three-dimensional flow past a flag. The results obtained agree well with those from previously published literatures.
Correlation of Near Field Pressure With Coherent Structures in an Excited Mach 1.3 Jet
Authors: Speth Rachelle L. , Gaitonde Datta V.
Published: December 2013

Large Eddy Simulations (LES) were performed of a Mach 1.3 cold jet excited by plasma actuators arranged on the periphery of a round nozzle exit to understand the effect of excitation on the near field sound and shear layer structures. The flow is excited with the axisymmetric (m = 0) mode at 0.525% duty cycle. The time period between pulses was varied from a very low value, where the response is expected to be similar to that due to an impulse, to a value near the preferred column mode value where the response is highly non-linear. Simulation data was collected at points on three arrays radiating 8.6° to the horizontal, originating at radial distances of 1.126D, 2.126D and 5.76D respectively. Detailed auto and two-point correlations of measurements on these rakes have been examined. In the first set of observations, different points were considered on Array 1. The auto-correlations clearly show the existence and growth of structures with excitation. At the lowest frequency, the effect of individual pulses is distinct, confirming that at this value, the response is similar to that of an impulse. At the highest frequency, the interaction between structures yields an almost sinusoidal value. In the second set of observations, two point correlations of each point on the innermost array were obtained with the downstream point of the outer-most array where the signal is purely acoustic. The analysis indicate that the highest correlation occurs with the region immediately downstream of the potential core collapse as well as with the point immediately beneath (sideline). The features observed in the statistical analysis are connected to the phase averaged flow structure which includes a series of rollers and ribs and associated dilatational field.
Study on Similarity of Pump Blade Adjusting Performances
Authors: Yao Yuan , Chao Liu
Published: December 2013

Through analyzing the change in velocity triangles at the inlet and exit of pump impeller with blade adjusting, and the flow behaviors in the pump passage the pump blade adjusting formulae were derived which reflect the similarity of flow and pumping head with the blade angles adjusted. Based on the experimental data of pump performances a mathematical model was developed to calculate the flow index and head index of the formulae. The objective function is a minimized the least square sum of the errors of the formulae’s calculation and the test data. The formulae were applied to three model pumps. The results show that the errors between calculated and measured data are 0.0228, 0.0116%, 0.0123 respectively, and all the head-flow curves (H-Q) and the power-flow curves (P-Q) agree well with the measured data from model test. Therefore, the derived formulae are featured with good similarity in pump performances for change blade angle, which can be applicable to the performances conversion and prediction of pump with blade adjusting.
Cross-Wind Influence on Low Aspect Ratio Wings at Low Reynolds Numbers
Authors: Noughabi Amir Karimi , Tadjfar Mehran
Published: December 2013

The aerodynamics of the low aspect ratio (LAR) wings is of outmost importance in the performance of the fixed-wing micro air vehicles (MAVs). The flow around these wings is widely influenced by three dimensional (3D) phenomena: including wing-tip vortices, formation of laminar bubble, flow separation and reattachment, laminar to turbulent transition or any combination of these phenomena. All the recent studies consider the aerodynamic characteristics of the LAR wings under the effect of the direct wind. Here we focus on the numerical study of the influence of cross-wind on flow over the inverse Zimmerman wings with the aspect ratios (AR) between 1 and 2 at Reynolds numbers between 6×104 and 105. We have considered cross-wind’s angles from 0° to 40° and angle of attack from 0° to 12°. The results show that lift and drag coefficient generally decrease when the angle of the cross-wind is increased.
Flow and Heat Transfer Enhancement of Nanofluids in Microchannel With Blocks and Grooves
Authors: Li Ping , Chen Jianhui , Qu Huancheng , Xie Yonghui , Zhang Di
Published: December 2013

A code based on the lattice-Boltzmann method was programmed. At various Reynolds numbers, simulations of the Cu/water nanofluid flow structure and heat transfer performance in a two dimensional microchannel with blocks (Re = 10–100) and grooves (Re = 50–200) were conducted, and the factors affecting the flow and heat transfer were explored. The flow and heat transfer of nanofluids with nanoparticle volume concentration of 0.5%, 1.0%, 1.5% and 2.0% were simulated, obtaining the velocity and temperature distributions to compare with the results of base fluid. Flow analysis showed that recirculation zones formed behind the blocks and in the grooves when nanofluids flowed in the microchannel, and the size of recirculation zone increased with the increase of Reynolds number and nanoparticle volume concentration. The core of the recirculation zone in the groove gradually moved to the right wall as Reynolds number increased at the same nanoparticle volume concentration, and the direction of the main flow was getting horizontal. Heat transfer results indicated that the addition of nanoparticles could promote fluid flow and energy transport, so that the thermal boundary layer thickness decreased and the heat transfer was enhanced. The heat transfer enhancement increased with the increase of Reynolds number and nanoparticle volume concentration. It was also shown that the heat transfer enhancement by increasing the Reynolds number was limited. The results could give a fundamental understanding for designing highly efficient heat exchangers.
Numerical Study on Flow Separation Control for High-Lift Low-Pressure Turbine Split Blade
Authors: Chen Jianhui , Qu Huancheng , Li Ping , Li Yage , Xie Yonghui , Zhang Di
Published: December 2013

The low-pressure high-lift blade aims to reduce blades number for reducing manufacturing cost, but the flow separation is easy to appear on the boundary layer of low-pressure turbine cascade under operating condition with low Reynolds number, which will significantly decreases the efficiency and safety of turbine blade and even the whole engine. Flow control on boundary layer of the cascade can reduce flow separation and improve the aerodynamic performance of low-pressure high-loaded turbine. In this study, a new flow control approach called split blade is applied on the LPT (low pressure turbine) PakB. This technology is a passive flow control method by using the jet created by different pressure of two points on the blade surface to control the boundary layer separation on the suction surface. Different operating conditions were investigated including flow separation on PakB cascade without control and cascade with slot at four kinds of Reynolds number (Re = 25000, Re = 50000, Re = 75000, Re = 100000) (based on the chord length in axial direction). The outlet of the slot is located upstream of the separation point on the boundary layer which is 0.68Cax (chord length in axial direction) on the suction surface, the inclination angle of slot is 30°, the diameter of slot is 2mm. Detailed flow characteristics, separation and reattachment locations are presented at the different Reynolds numbers were presented in this paper. The results show that without control the separation location on the boundary layer of the cascade moves downstream with the increase of Reynolds number while the reattachment location moves up. The results also show that at Reynolds number is 25000, as different pressure of slots two ends is low, the jets velocity is low and the control effect is not obvious. At other three kinds of Reynolds number, the reattachment location moves up separation zones decreases due to the flow control.
Design and Optimization of a Thermal Knudsen Force Actuated Microbeam System
Authors: Wada Mizuki , Sun Lin , Alexeenko Alina
Published: December 2013

Thermal Knudsen forces arise in microsystem in presence of a thermal gradient and a rarefied gas environment due to the non-equilibrium energy exchange between gas molecules and solid surfaces. Knudsen force can be used as an alternative actuation mechanism for microactuators. The purpose of this work is to design and optimize a Knudsen force actuated microbeam using modeling and simulation. The microbeam is heated by an external heat source that causes a thermal gradient between the beam and substrate. The characteristic domain size is small enough so that the rarefied gap effect is present. The study focuses on three major components that influence the Knudsen force significantly, including geometry of microbeam, external heat input to the system, and the radiometric effects generated by Peltier thermoelectric device. A Boltzmann-ESBGK model is implemented to simulate the rarefied gas flow and a continuous Fourier heat transfer model is used to solve the beam temperature field generated by the external heat source, and the fluid and solid regions are coupled using an effective heat convection interface condition.
Development and Validation of Fluid-Solid Interaction Analysis for Crashworthiness Studies
Authors: Satterwhite Matthew , Bayandor Javid
Published: December 2013

Improved numerical analysis of fluid-solid interaction of rigid wedge water entry with multiple deadrise angles was conducted. This involved the coupling of fluid flow and structural mechanics, normally analyzed through separate numerical platforms. To capture the subtleties of water behavior in detail using finite elements, an advanced gradient meshing technique involving meshed and meshless Lagrangian elements was developed. The gradients varied particle spacing to maximize the resolution at the area of impact while reducing computation time. The properties of water, incorporating compressibility, were simulated and used in small and full scale analysis models. Results of multiple converging gradient schemes were compared to existing models, physical experiments, and analytical representations. The advanced gradient mesh schemes were able to capture the qualitative and quantitative essences of the event. Further experimental trials are needed to establish the predicting capabilities of the developed model when examining large scale fluid-solid interactive systems.
Uncertainty Quantification of the Hybrid Method for Particle Field Measurement Using Digital In-Line Holography
Authors: Gao Jian , Chen Jun , Guildenbecher Daniel R. , Reu Phillip L.
Published: December 2013

Digital in-line holography has been applied extensively to particle field measurement, where the particles can be the tracer particles for flow measurements, droplets in spray diagnostics, or aquatic microorganisms. The particle detection algorithm plays a key role in accurate detection of particle 3D locations and sizes. A hybrid method has recently been proposed for particle field measurement in digital in-line holography. It features automatic determination of the threshold for segmentation of the particle field and the capability to measure particles of arbitrary shapes. Using the hybrid method, the particle 3D location, size and shape information can be extracted. The uncertainty of the hybrid method is characterized using both synthetic and experimental holograms at different particle field conditions. The depth measurement uncertainty is within 2 times the particle diameter for a wide range of particle field conditions.