bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi Objective Optimization of a Multiphase Pump for Offshore Plants
Authors: Kim Joon-Hyung , Lee Him-Chan , Yoon Joon-Yong , Lee Kyoung-Yong , Lee Yong-Kab , Choi Young-Seok
Published: December 2014

The crude oil produced from well contains a mixture of oil, gas and water. The existing pump system that uses a single phase pump requires a separator to separate the crude oil. Changing from a single phase pump to a multiphase pump significantly reduces costs because a multiphase pump does not require a separator. Therefore, most wells currently being developed apply the multiphase pump system. In this study, a multiphase pump was designed using a multi objective optimization technique. To conduct research, a base model was chosen and its performance was evaluated through numerical analysis. The design variables and variable ranges were set for the impeller and the diffuser. Based on the selected variables, experiment sets were produced. The experiment sets were also evaluated for their performance using numerical analysis. Based on the performance evaluation results of each experiment set, the optimization model for a multiphase pump was derived using Response Surface Method (RSM). In addition, each model’s performance for multiphase flow was also evaluated according to changes in Gas Volume Fraction (GVF) using multiphase numerical analysis. Furthermore, the internal flow characteristics of each model were analyzed.
Experimental Investigation of Liquid Phase Breakup in Solid Fuel Rockets
Authors: Amano Ryo S. , Yen Yi-Hsin , Hamman Michael , Rockey Kristopher , Stangel Joshua
Published: December 2014

Solid rocket motors (SRM)s commonly use aluminized composite propellants. The combustion of aluminum composite propellants in SRM chambers lead to high temperature and pressure conditions resulting in the liquid alumina as a combustion product. The presence of liquid alumina in the flow presents problems such as; chemical erosion of propellant, and mechanical erosion of nozzle. One method of solving the problem of liquid alumina in flow is to change the SRM geometry to induce liquid breakup and suspend the alumina in the flow thus avoiding erosive behavior. To validate numerical simulation methods for geometric breakup induction simulation models of alumina flow can be compared to air and liquid water flows, and the air-liquid water flow models then compared to water-air experimental results. This study investigates experimental geometric induced liquid breakup behavior for the implementation of the alumina flow and nozzle geometry simulation in SRM design. A rectangular chamber was considered for experimental and simulation to explore the air-water flow behavior. The suspension of water was induced with a triangular shaped jump. The resulting two phase flow was examined using photography technique. Significant incitement in the air-water behavior was observed due to geometry modification. Replication of experimental results was simulated with some accuracy.
A Feasibility Study to Identify Ice Types by Measuring Attenuation of Ultrasonic Waves for Aircraft Icing Detection
Authors: Liu Yang , Chen Wenli , Bond Leonard J. , Hu Hui
Published: December 2014

Aircraft icing has been recognized as the most significant weather hazard that impacts aviation safety. A thin sheet of ice on lifting or control surfaces of an aircraft can adversely affect its flight performance by increasing drag and decreasing lift and thrust. The uncontrolled shedding of ice built up on surfaces may severely damage critical components. The occurrence of ice accretion is also a big challenge in terms of economic impact. The presence of ice can not only cause flight delays, but also reduce flight profits by increasing fuel consumptions and additional cost for de-icing operations. A better understanding of the physical mechanisms of water movement and the ice formation process on aircraft surfaces is very important and critical in ensuring safe and efficient operation of aircraft in cold weather. Generally there are two types of ice that can be deposited during flight: glaze ice and rime ice, which occur is dependent on weather conditions. Glaze ice is formed with high liquid water content (LWC) and large droplet size at temperatures just below the freezing point, and it has a smooth, clear and dense appearance. Rime ice forms with lower LWC and smaller droplet size at temperatures around or below −12 C°. It is a mixture of tiny ice particles, containing many micro bubbles and cracks, and it has a white rough appearance. These two types of ice may have significantly different effects on flight performance. However, most of the current de-icing approaches and practices do not consider this and operators potentially perform a lot of unnecessary actions. In this study, attenuation measurement of ultrasonic waves is performed to investigate the feasibility of characterization of ice types. Analysis investigates frequency dependent attenuation properties that are potentially closely related to ice acoustic properties and hence the micro-structure.
Measurement Uncertainties Analysis in the Determination of Adiabatic Film Cooling Effectiveness by Using Pressure Sensitive Paint (PSP) Technique
Authors: Johnson Blake Everett , Hu Hui
Published: December 2014

Pressure sensitive paint (PSP) is useful for measurements of wall pressure in high speed flows, but can be used in an alternative manner in low-speed flows as a gas species concentration detector. Film cooling technology studies have been greatly aided by this use of PSP through use of a mass transfer analogy to determine the adiabatic film cooling effectiveness. The PSP technique allows measurements that have high spatial resolution at high enough sampling rate that a good statistical mean can be determined rapidly. Due to the potential of this technique to deliver high quality adiabatic effectiveness measurements, a detailed analysis of its associated uncertainty is presented herein. In this study, an ambient temperature low speed wind tunnel drives air as the main flow while carbon dioxide (CO2, DR=1.5) is used as the “coolant” gas, though the experiments are done under isothermal conditions. A detailed analysis of the technique is performed here with focus on the measurement uncertainty and process uncertainty for a film cooling study using an array of five cylindrical holes spaced across the span of a flat test plate at a spacing of three diameters center-to-center. The final analysis indicates that the total uncertainty depends strongly on the local behavior of the coolant, with near-field uncertainty as high as 5% at isolated points. In the far-field, the total uncertainty is more uniform throughout the measurement domain and generally lower, at about 3%.
Fault Diagnosis Technique for a Squirrel Cage Fan Using Vibration Analysis Signals
Authors: Delgado Laura , Gonzalez Perez Jose , Fernandez Oro Jesus M. , Velarde-Suárez Sandra , Rodríguez David , Argüelles Diaz Katia
Published: December 2014

An experimental vibration study for a small centrifugal fan unit is presented in this work. The flow features in this kind of units are always of unsteady nature due to the geometrical constraints. As a consequence of such unsteady features, the vibrations and noise become often a serious design problem and may cause the unit bad functioning. With the use of fast response accelerometers, a fault diagnosis protocol is introduced in order to measure the extent of signal variations for different and expected failures.

The study is based on the experimental measurements of two perpendicularly placed sensors which capture the acceleration signals for three different flow rates and three different operations, namely, the normal (or no failure) operation, the obstructed channel operation and the unbalance shaft operation. A squirrel cage or Sirocco fan is used for the study. It is a kind of centrifugal turbomachine with forward curved blades, often characterized by their small size. Its low cost and size make them be ideal for residential heating and cooling of vehicles. One of the important characteristics, the small chord of the rotor blades and the high number of them often used has been previously reported in the bibliography. Typically, most common damages or faults come from the moving blades, bearings, fixed blades, rotor and sealing. In general, the vibration signals indicate malfunction symptoms, one symptom may be due to two different faults, and the same fault can produce two different symptoms.

The main goal of the study is the application of a fault diagnosis technique as the purified orbit diagram (POD) to reveal the limit range values for some standard failures. The finding of such limits is determinant to implement a fault diagnosis protocol that will decrease the maintenance costs and increase the operation efficiency of the unit. Such protocol would become straightforward from the presented data. The Purified Orbit Diagram is obtained by harmonic reconstructing corresponding harmonic components of two perpendicular directions in time domain. Three different flow rates, namely nominal and two off-design conditions are tested to be able to compare the different POD components as a function of the flow rate.
Break-Up of Threads From Laminar Open Channel Flow Influenced by Cross-Wind Gas Flow
Authors: Kamplade Jens , Mack Tobias , Küsters Andre , Walzel Peter
Published: December 2014

The breakup process of threads from laminar operating rotary atomizer (LamRot) is in the scope of this investigation. A similarity trail is used to investigate the influence of the thread deformation within a cross-wind flow on the thread breakup process. The threads emerge from laminar open channel flow while the liquid viscosity, the flow rate, the pipe inclination towards the gravity as well as the cross-wind velocity is varied.

The breakup length and drop size distribution are analyzed by a back-light photography setup. The results thus obtained are compared with results of previous examination by Schröder [1] and Mescher [2].

It is found that the breakup length decreases and that the drop size grows with rising cross-wind intensity, while the width of the drop size distribution increases. At the same operating conditions, the breakup length for laminar open channel flow is smaller compared to completely filled capillaries. In contrast to this observation, the drop size distribution remains nearly unchanged. The critical velocity for the transition from axisymmetric to wind-induced thread breakup was found to be smaller than for completely filled capillaries.
A Smoothed Void Fraction Approach for the Detection of Bubble Clusters
Authors: Santarelli Claudio , Hashimoto Kazutaka , Fukagata Koji , Fröhlich Jochen
Published: December 2014

A new method is proposed for the detection and characterization of bubble clusters in the framework of Euler-Lagrange simulations. It is based on the definition of the smoothed void fraction which depends only on geometrical information, i.e. on the bubble positions. Two variants are proposed, one in an Eulerian fashion and a more efficient one in a Lagrangian style. Both techniques are applied to a vertical channel flow laden with monodispersed bubbles.
Influence of an Upstream Obstacle on the Flow Characteristics of Axial-Flow Fans
Authors: Nakamura Shinsaku , Takahashi Masayuki , Sato Kotaro , Yokota Kazuhiko
Published: December 2014

System environments vary for axial-flow fans, which are often used under unsuitable operating conditions. In the recent high density design of such equipment, obstacles are being more frequently distributed upstream of the fan to determine a smaller fan size. In this study, an attempt is made to clarify the influence of an obstacle on the flow characteristics of axial-flow fans. In our experiment, blockage disks with various diameters were placed upstream of a typical cooling axial-flow fan. The performance curves of the axial-flow fan with the blockage disks were measured. In addition, the flow instabilities and their cell structures were investigated under typical conditions. The main objectives of the present study are as follows: (1) to evaluate the performance degradation when obstacles are placed upstream of the test fan, (2) to elucidate the causes of a positive slope and reverse flow, and (3) to clarify the generation mechanism of flow instabilities when the blockage disks, which have a larger diameter than the test fan, are used.
Experimental Investigation of Air Vortex Interaction With Porous Screen
Authors: An Xudong , Fultz Howard , Iyengar Srinath , Hassanipour Fatemeh
Published: December 2014

This study presents the experimental analysis of air flow vortex propagation through porous screens. Our research was conducted with a new and unique experimental setup for measuring and visualizing air vortex flow through porous media. A custom-made, high-precision vortex generator provided a variety of velocity profiles for vortex generation with an unprecedented level of precision. The flow field was captured with the use of a fog generator and a high-speed CCD camera. The porous screens were constructed out of acrylic rods with various orientations, thickness, and porosities from rod separation. The results presented in this paper show the effect of porosity and air injection velocity on the behavior of air flow (separation, accumulation), and the transport phenomena of vortex flow through porous screens.
A Comparative Study of the Wind Loads and Wake Characteristics of a Single-Rotor Wind Turbine and Dual-Rotor Wind Turbines
Authors: Ozbay Ahmet , Tian Wei , Hu Hui
Published: December 2014

An experimental study was carried out to investigate the aeromechanics and wake characteristics of dual-rotor wind turbines (DRWTs) with co- and counter-rotating configurations, in comparison to those of a conventional singlerotor wind turbine (SRWT), in order to elucidate the underlying physics to explore/optimize design of wind turbines for higher power yield and better durability. The experiments were performed in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) wind tunnel under neutral stability conditions. In addition to measuring the power output performance of DRWT and SRWT systems, static and dynamic wind loads acting on those systems were also investigated. Furthermore, a high resolution PIV system was used for detailed near wake flow field measurements (free-run and phase-locked) so as to quantify the near wake turbulent flow structures and observe the transient behavior of the unsteady vortex structures in the wake of DRWT and SRWT systems. In the light of the promising experimental results on DRWTs, this study can be extended further to investigate the turbulent flow in the far wake of DRWTs and utilize multiple DRWTs in different wind farm operations.
Numerical Simulations of Near-Nozzle Exit Characteristics for an Effervescent Atomizer at Low Gas to Liquid Mass Flow Ratio
Authors: Law Deify , Shepard Thomas , Strykowski Paul
Published: December 2014

Effervescent atomization is a process in which a bulk liquid is transformed into a spray of droplets by injecting a small amount of gas into the liquid before it is ejected from the atomizer. Advantages of using effervescent atomization method include larger exit orifices to reduce clogging issues, reduced injection pressures, and lower gas to liquid mass flow ratios (GLR) as compared to pressure or air-blast atomizers [1]. Effervescent atomization has been used in a number of applications including agricultural sprays, paint sprays, combustion for lowering pollutant emissions, spray cooling for gas turbine and medical applications, waste incineration, and process industry applications. In the present work, the near-nozzle exit characteristics of an air-water effervescent atomizer at gas to liquid mass flow ratio such as 0.25% are investigated numerically through two-fluid Eulerian-Eulerian ensemble-averaged modeling. The two-fluid model is solved through the finite volume method. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. The effects of effective (average) air bubble diameter size inside the atomizer, exit nozzle diameter, and injection pressures on the average liquid water jet width are presented. An optimal bubble size is observed for increasing the average liquid jet width which leads to enhanced jet breakup at downstream of the nozzle. The water volume fraction profiles within the sprays are also reported. The numerical results are compared with experimental visualizations and jet-width measurements to further the understanding of the spray characteristics of effervescent atomization for atomizer design.
Three-Dimensional Vortex Structure Around a Free Flight Butterfly
Authors: Fuchiwaki Masaki , Kuroki Taichi , Tanaka Kazuhiro , Tabata Takahide
Published: December 2014

Micro-air-vehicles (MAVs) and micro-flight robots that mimic the flight mechanisms of insects have attracted significant attention. From this reason, the flight mechanism of the butterflies and their flow fields also has attracted attention. A number of studies on the mechanism of butterfly flight have been carried out. Moreover, a number of recent studies have examined the flow field around insect wings. The present authors conducted a particle image velocimetry (PIV) measurement around the flapping wings of Cynthia cardui and Idea leuconoe and investigated the vortex structure and dynamic behavior produced. However, these results are for a flow field under a fixed condition. The vortex flow structure and the dynamic behavior generated by the wings of a butterfly in free flight are expected to be important for generating the aerodynamic forces required for flight. In the present study, we attempt to clarify the three-dimensional vortex structure around a butterfly in free flight by a scanning PIV measurement. The vortex ring formed by the front wings during the flapping downward grows without attenuation toward the wake. Moreover, during the flapping upward of the wings, a vortex rolls up from the wing, eventually forming a single vortex ring. This vortex ring forms in the vertical direction in contrast to vortex ring formed during the flapping downward, and we may anticipate that the two vortex rings interfere with each other as they advance toward the wake.
Design of a Novel Bidirectional Valveless Piezoelectric Micropump With Three Chambers Using Coanda Effect Based on Numerical Simulation
Authors: He Xiuhua , Yang Song , Yuan Shouqi , Zhu Jiawei , Zhang Xitong
Published: December 2014

A novel bidirectional valveless piezoelectric micropump with three chambers using the Coanda effect has been developed. The volume efficiency of the micropump is able to reach 50% which is much higher than that of the traditional diffuser/nozzle valveless micropump and its transport direction is easy to change. The chambers are covered by three piezoelectric actuators, respectively. There are three channels connected with each chamber, respectively. And the other ends of the channels join together and connect with a diffuser. One of the channels has the same centerline with the diffuser. The centerline is perpendicular to the other two channels which situate on the two sides of the diffuser symmetrically. Inlet and outlet channels are connected with the other end of the diffuser. Three piezoelectric actuators are driven by the synchronous voltages with different magnitude. When the fluid is discharged from the pump chambers, the flowrate of one channel situated on the side of the diffuser is smaller than that of the two others. Due to the Coanda effect, the jet flow in the diffuser attaches the wall and all fluid enters the outlet channel. And some fluid is sucked from inlet channel because of the vortex induced by the jet flow. When the fluid is sucked into the pump chambers, the flowrate of fluid sucked into the inlet and outlet channels are same. So the fluid transports from the inlet channel to outlet channel in a cycle. And the micropump could change the transport direction by changing the flowrate of the two channels situated on the two sides of the diffuser. CFX is applied to simulate the flow field of the micropump and the dynamic mesh method is used for the simulation of the piezoelectric actuator. The sinusoidal vibration is applied to the piezoelectric actuator and the frequency is 10Hz. The narrowest width and height of the diffuser is 200μm. The Reynolds number is between 1000 and 1800 in the simulation and the SST model is chosen. Hexahedral mesh is used and the number of elements is about 1.2 million. The result shows that when the amplitude of two actuators is same and the amplitude of the third one is 20% of the former (the maximum Reynolds number of the diffuser is about 1200), the maximum flowrate of the micropump is 2.43 ml/min and the volume efficiency reaches 58%.
Analysis of Pressure Pulsations in the Intake Duct of a Single Cylinder Diesel Engine
Authors: Rajagopal Manjunath C. , Dwarshala Siva Krishna Reddy , Rehan Shaik , Ramadandi Padmavathi
Published: December 2014

The inlet air flow rates of a naturally aspirated engine can be enhanced by proper synchronization of the pressure fluctuations to obtain maximum air flow rate. Single cylinder diesel engine is considered as a test case for this study. 1-D simulation software AVL-BOOST is used for predicting the air flow rates in intake duct. Using this validated simulation model, theoretical correlations from wave theories are used to explain the arrival of pressure pulses at the intake valve. The pressure pulsations at the port for different lengths of the intake duct are analyzed. It is found that, a weighted combination of one or more effects results in a peak in volumetric efficiency and it cannot always be determined from a single correlation. The effects of diameter of the intake duct on the air flow rates are also studied. The air flow rates for each crank angle are calculated based on gas dynamic relations and these numerical calculations are validated against the simulation model. The calculations are then extended, to analyze the choking effects based on a non-dimensional number. Its predominance during the early stage of intake is identified and it increased with decreasing diameter of intake duct.
Controlling the Intensity of a Bathtub Vortex by Acting on the Upstream Flow
Authors: Recoquillon Yann , Andrès Emmanuelle , Kourta Azeddine
Published: December 2014

In a motor vehicle, the cowl box is a volume located at the bottom of the windshield. It collects rainwater and drains it to provide clean and dry air to the passenger compartment through the ventilation system. When rainwater is accumulated into the box, a bathtub vortex appears above the drain pipe. This vortex sucks up air into the pipe and creates an air core responsible of the decreased water drain rate in the pipe. It leads to an increased water level in the box and can cause a water overflow into the ventilation system.

The behavior of this bathtub vortex has been experimentally studied using a simplified geometry representative of a real cowl box. The inlet water flow rate is controlled and a capacitive probe measures water level in the box. The flow has been studied using Particle Image Velocimetry to measure velocity field around the vortex.

The flow pattern is described using these data. Due to geometry and inlet conditions, the upstream flow forces the vortex counter-clockwise. It is also responsible for a shift of the vortex axis from the drain axis. In this configuration, the upstream flow is strongly asymmetric and feeds the vortex using less than half the width of the box.

Based on these observations, a device has been tested in order to reduce the vortex intensity and consequently the water level. Resulting velocity fields show a better distribution of the upstream flow. The vortex intensity is decreased up to 55% and the water level up to 53%. Despite there is still a vortex with an air core, the water level is therefore significantly reduced.

These results are particularly interesting for the cowl box design: if this device can guarantee a lower water level, the cowl box depth can be reduced and space can be saved.
LES of Contrails With Ice Habit Treatment Using the Fickian-Distribution Model
Authors: Inamdar Aniket R. , Lele Sanjiva K. , Jacobson Mark Z.
Published: December 2014

This study uses a Fickian-Distribution parameterization [Chen & Lamb, 1994] to model the effects of ice habits on contrail formation within a large eddy simulation (LES). Box model cases were first performed at various ambient temperatures and relative humidities over ice (RHi) and results compared with available laboratory data of ice crystal growth and habit distribution [Bailey & Hallett, 2004]. The model was then used in a full 3-D LES of contrails and results were compared with in-situ observations [Febvre et. al., 2009]. Comparisons are also made with results from simulations that used a probabilistic ice habit model [Inamdar et. al., 2013].
Leakage Detection Techniques Using Nearfield Acoustic Holography
Authors: Chelliah Kanthasamy , Raman Ganesh , Muehleisen Ralph T.
Published: December 2014

This paper attempts to explore the possibilities of using various methods of nearfield acoustic holography (NAH) to detect the air/sound leakages from a container by locating the noise sources. The detection capabilities of three different NAH methods are compared. An acoustic source is placed inside the container and the hologram measurement is performed near the surface of the container. The NAH methods are applied on the hologram data to detect and quantify the leakage locations. Reconstructed acoustic pressure and particle velocity results are presented. NAH algorithms are found to work better for the higher input frequency cases. Tikhonov regularization is used to alleviate the singularity in the transformation matrices. However, generalized cross validation over-predicts the Tikhonov parameter for the present geometry. The resolution limitations of the NAH methods with respect to the hologram distance are addressed.
Reynolds-Averaged Simulation on Turbulent Drag-Reducing Flows of Viscoelastic Fluid Based on User-Defined Function in FLUENT Package
Authors: Zheng Zhi-Ying , Li Feng-Chen , Li Qian
Published: December 2014

A new numerical simulation methodology for turbulent flows of viscoelastic fluid was developed for engineering application purpose based on commercial computational fluid dynamics code FLUENT package. An in-house subroutine was established and embedded into FLUENT code through userdefined function functionalization. In order to benchmark this methodology, numerical simulations on turbulent channel flows of viscoelastic fluid are conducted under different cases with drag reduction rates varied from low level to high level. FENE-P (finitely extensive nonlinear elastic-Peterlin) constitutive model is used to describe the viscoelastic effect of viscoelastic fluid flow. The turbulent model is developed in the framework of k–ε–ν′2¯–f model, for which the elliptic relaxation model is modified to account for the Reynolds stress equilibrium established by the presence of elasticity in the fluid. The numerical simulation results, including velocity profiles, turbulent flow characteristics, elastic stress and conformation field, show good agreements with published DNS results, which validates the newly established method on turbulent flows of viscoelastic fluid based on FLUENT software platform for engineering applications.
Concurrent Droplet Coalescence and Solidification on Surfaces With Various Wettabilities
Authors: Moghtadernejad Sara , Jadidi Mehdi , Tembely Moussa , Esmail Nabil , Dolatabadi Ali
Published: December 2014

Experimental study is performed to analyze the shear driven droplet shedding on cold substrates with different shear flow speeds typical of those in the flight conditions. Understanding the mechanism of simultaneous droplet shedding, coalescence and solidification is crucial to devise solutions for mitigating aircraft in-flight icing. To mimic this scenario experimental set up is designed to generate shear flow as high as 90 m/s. The droplet shedding at high speed is investigated on a cold surface (0 and −5 °C) of different wettabilities ranging from hydrophilic to superhydrophobic. Result analyses indicate that on a hydrophilic substrate, the droplets form a rivulet which then freezes on the cold plate. In contrast, on the superhydrophobic surface, there is no rivulet formation. Instead, droplets roll over the substrate and detach from it under the effect of high shear flow.
Experimental and Numerical Investigation on the Erosion Wear of an Impact Sprinkler
Authors: Xu Yuncheng , Lin Guan , Yan Haijun
Published: December 2014

In the middle and western China, agricultural irrigation water often contains a high sediment concentration. In order to save the cost, no filtration devices are required for sprinkler irrigation, which results in the wear of sprinkling irrigation equipment, especially on the nozzle. In this study, experiments on the erosion wear of an impact sprinkler (PY1-20sh with aluminum alloy nozzles) were conducted under different conditions of sediment concentration and erosion time. Using the experimental data as boundary conditions, numerical simulations based on the discrete phase model (DPM) were conducted to analyze the wear of the internal surface of the sprinkler’s full flow passage. Based on both experimental and numerical results, the erosion wear mechanism of the internal flow surface was revealed, and prediction model of the nozzle’s wear rate was established, providing the technical guidance for design and operation of the impact sprinkler.
Effect of Forebody Strake on Directional Aerodynamic Characteristics of Typical Configuration and Its Mechanism
Authors: Wang Yankui , Fu Bingrui , Ou Shuai
Published: December 2014

Nowadays many research works have been conducted on improving the directional instability of aircraft by adopting forebody strake, but there is lack of deep understanding about the flow mechanism. The purpose of this paper is to investigate the directional characteristics of one typical configuration and promote improved method by forebody strakes. Furthermore, the flow mechanism will also be studied in detail. All the studies are finished by the CFD method at free-stream Reynold number 4.6e+5 and 4° side slip.
Diffuser Influence on the Mixing of Coaxial Swirling Jets
Authors: Parra-Santos Teresa , Perez-Dominguez Ruben , Esteban Gonzalo Lorenzo , Szasz Robert Z. , Gutkowski Artur N. , Castro-Ruiz Francisco
Published: December 2014

Numerical results depicting the effects of diffusers on confined isothermal high-swirl jets are presented. The aim is analyze the mixing between a non-swirling inner jet (natural gas) and a swirling annular jet (primary air). This simple setup is widely used in burners to promote stabilized flames of lean mixtures.

Flow patterns for sudden-expansion and diffusers are contrasted for swirl number of 1 and expansion area ratio of 4 in a transitional turbulence regime. Diffusers have important influence on size and location of recirculation zones. Hence knowledge of flow characteristics is a prerequisite in the design process. The criteria to establish the optimum diffuser would be better mixing as well as minimum residence time in the recirculation zones to prevent the formation of NOx in the future burner. The dissipated mechanical energy is not important in burner applications.
The Structure of Forward Facing Step Flows in Adverse Pressure Gradient
Authors: Shao Weijie , Agelin-Chaab Martin
Published: December 2014

This paper reports an investigation of the effects of adverse pressure gradient on turbulent flows over forward facing step. Three adverse pressure gradients were created for this study using diverging channels. A particle image velocimetry technique was used to conduct measurements in the streamwise-wall-normal (x-y) planes at the mid-plane of test section at several locations downstream to 68 step heights. A Reynolds number of Reh = 4800 and δ/h = 4.7 were employed, where h is the mean step height and δ is the approach boundary layer thickness. The results include the mean flow and turbulence quantities as well as proper orthogonal decomposition analysis. The mean reattachment length obtained indicates that the adverse pressure gradient created in this study does not have significant effects on the reattachment length. The triple velocity correlations imply that there is negative transport of turbulence kinetic energy close to the wall and positive transport away from the wall. In addition to the physical insight, the high quality data reported are useful for assessing the ability of turbulence models to reproduce the behaviour of complex flows.
Mixing Enhancement in a Chaotic Micromixer Using Pulsating Flow
Authors: Karami Mohammad , Jarrahi Mojtaba , Shirani Ebrahim , Peerhossaini Hassan
Published: December 2014

This study determines the simultaneous effects of spatial disturbance and flow pulsation on micromixing by using three different metrics: concentration distribution, Lyapunov exponent and axial vorticity. Numerical simulations are performed for both steady and pulsating flows through a microchannel made up of C-curved repeating units. Moreover, a straight microchannel is analyzed to compare the effects of chaotic advection and molecular diffusion, the main mechanisms of transverse mixing in the chaotic and straight mixer respectively. Simulations are carried out in the steady flow for the Reynolds number range 1≤Re≤50 and in the pulsating flow for velocity amplitude ratios 1≤β≤2.5, and the ratio of the peak oscillatory velocity component to the mean flow velocity, Strouhal numbers 0.1≤St≤0.5. It was found that chaotic advection improves mixing without significant increase in pressure drop. The analysis of concentration distribution implied that full mixing occurs after Reynolds number 50 in the steady flow. When the flow is pulsatile, small and moderate values of the Strouhal number (0.1≤St≤0.3) and high values of velocity amplitude ratio (β ≥ 2) are favorable conditions for mixing enhancement. Moreover, mixing has an oscillating trend along the microchannel due to the coexistence of regular and chaotic zones in the fluid. These results correlate closely with those obtained using two other metrics, analysis of the Lyapunov exponent and axial vorticity.
Numerical Simulation of the Effect of Rheological Parameters on Shear-Thinning Droplet Formation
Authors: Wong Voon-Loong , Loizou Katerina , Lau Phei-Li , Graham Richard S. , Hewakandamby Buddhika N.
Published: December 2014

Immiscible non-Newtonian-Newtonian fluid systems in microfluidics constitute an essential study as non-Newtonian fluids consistently met in medical and biological systems. Although a large number of experimental investigations have been reported in this area, attempts to develop predictive models appear to be limited. This paper is an attempt to incorporate a non-Newtonian stress model together with front-tracking scheme used in computational fluid dynamics. A conservative two-phase level set method (LSM) was applied for capturing the droplet breakup dynamics and relevant hydrodynamics of shear-thinning carboxymethylcellulose (CMC) droplets. Our droplets comprise of 0.02wt% to 1.2wt% CMC solutions in a Newtonian continuous fluids system (olive oil) employed in a T-shaped microfluidic cell. A Carreau-Yasuda viscosity model for shear-thinning CMC droplets has been implemented. This shear-dependent constitutive model fitted well to our steady state non-linear shear measurements for polymeric CMC solutions, with asymptotic viscosities at zero and infinite shear rates, and with different degrees of shear thinning (η0/η∞) in steady state. The particular focus of this study was to systematically undergo parametric studies on the influence of rheological parameters of the specified model such as zero (η0) and infinite shear viscosity (η∞), and relaxation time (λ) on the droplet formation processes. The level set simulation predicted that the droplet diameter increases with increasing η0/η∞. The effect of η0/η∞ has been found to have more prominent impact on droplet diameter for higher CMC concentrations. The variation in droplet diameter becomes less significant at the higher degrees of shear-thinning for all concentrations of CMC dispersed solutions. In the limit of zero shear-thinning effect, the droplet diameter increases when the dispersed phase viscosity decreases. Additionally, the effect of λ on the droplet diameter is also discussed. The reciprocal of the characteristic relaxation time (1/λ) corresponds to a critical shear rate that indicates the onset shear rate for shear-thinning. As λ increases, the numerical studies clearly reveal that the droplet diameter is increasing until it reaches a plateau for larger values of λ. The influence of λ leads to a more significant impact on droplet diameter for higher CMC concentration. These findings will ultimately help in understanding the sensitivity of rheological parameters to the microdroplet formation.
Investigation of a Dynamic Power Line Rating Concept for Improved Wind Energy Integration Over Complex Terrain
Authors: Phillips Tyler B. , Senocak Inanc , Gentle Jake P. , Myers Kurt S. , Anderson Phil
Published: December 2014

Dynamic Line Rating (DLR) is a smart grid technology that allows the rating of power line conductor to be based on its real-time temperature. Currently, conductors are generally given a conservative static rating based on near worst case weather conditions. Using historical weather data collected over a test bed area in Idaho, we demonstrate there is often additional transmission capacity not being utilized under the current static rating practice. We investigate a DLR method that employs computational fluid dynamics (CFD) to determine wind conditions along transmission lines in dense intervals. Simulated wind conditions are then used to calculate real-time conductor temperature under changing weather conditions. In calculating the conductor temperature and then inferring the ampacity, we use both a steady-state and transient calculation procedure. Under low wind conditions, the steady-state assumption predicts higher conductor temperatures which could lead to unnecessary curtailments, whereas the transient calculations produce temperatures that can be significantly lower, implying the availability of additional transmission capacity. Equally important, we demonstrate that capturing the wind direction variability in the simulations is critical in estimating conductor temperatures accurately.
Low Frequency Acoustic Streaming in a Hele-Shaw Cell
Authors: Costalonga Maxime , Peerhossaini Hassan , Brunet Philippe
Published: December 2014

When an acoustic wave propagates in a fluid, it can generate a second order flow which characteristic time is much longer than the period of the wave. Within a range of frequency between 1 and several hundred Hz, a relatively simple and versatile way to generate streaming flow is to put a vibrating object in the fluid. The flow develops vortices in the viscous boundary layer located in the vicinity of the source of vibrations, which in turns leads to an outer irrotational streaming denoted as Rayleigh streaming. Due to that the flow originates from non-linear time-irreversible terms of the Navier-Stokes equation, this phenomenon can be used to move fluids and even to generate efficient mixing at low Reynolds number, for instances in confined geometries. Here we report an experimental study of such streaming flow in a Hele-Shaw cell of 2 millimeters span using long exposure flow visualization and PIV measurements. Our study is especially focused on the effects of acoustic frequency and amplitude on flow dynamics. It is shown that some features of this flow can be predicted by simple scaling arguments, invoking a balance between viscous dissipation in the boundary layer and inertia term, and that acoustic streaming facilitates the generation of vortices.
Flow Control of a Bluff Body Wake by Means of Self-Adaptive Flaps
Authors: Feuvrier Audrey , Mazellier Nicolas , Kourta Azeddine
Published: December 2014

The performance of two self-adaptive flaps designed with a biomimetic approach is investigated. Each flap comprised a rigid plastic frame covered with a porous material (characterized by its solidity, σ) and is installed on the side of a square cylinder. In order to investigate the effect of the flap dynamics, the flaps are either positioned at a given angle (passive control) or hinged on their leading edges and left free to adapt to the flow changes (self-adaptive control). For the optimum position of 20° and σ=100%, a significant drag reduction of 30% is obtained over a large range of Reynolds numbers (Re 20,000 to 60,000). The investigation of the flow in the close wake of the model for both fixed and moving flaps reveals a modification of the flow topology and a possible change in the mode of vortex formation.
Results and Analysis of Implicit Large Eddy Simulations of Equilibrium Spatially Developing Turbulent Boundary Layers at Multiple Mach Numbers
Authors: Waindim Mbu , Gaitonde Datta V.
Published: December 2014

Equilibrium turbulent flat plate boundary layers with time invariant statistics were obtained at Mach numbers 1.7, 2.3, and 2.9. These are to be used as the initial condition for Large Eddy Simulations (LES) or Direct Numerical Simulations (DNS) of shock wave/turbulent boundary layer interactions utilizing a body force-based method. The results obtained are supplemented by an analysis of the mean and statistical properties of the respective boundary layers. The spanwise extent of the domain required to allow adequate decorrelation between the centerline and the boundaries is investigated by extensively probing the flowfields obtained. This is done to quantify the coherent structures of the turbulent flow. Specifically, two point correlations and integral length scales are used to investigate spanwise decorrelation distances in an attempt to pick a computational domain which is large enough to permit decorrelation downstream but small enough to minimize computational costs. It is shown that by examining the precursor events in the upstream region, namely the generalized stability criterion, it is possible to provide estimates for the force field parameters necessary for transition for a given flow, with only a small portion of the domain in the neighborhood of the trip. The technique is made even more efficient by investigating the possibility of determining these parameters using a two-dimensional simulation. Additionally, the three flow fields obtained are surveyed to confirm that they are suitable for subsequent SBLI simulations. We check that (i)they possess the expected turbulent characteristics and (ii)there is no signature of the tripping mechanism.
Numerical Analysis of Flare Gas Recovery Ejector
Authors: Sonawat Arihant , Samad Abdus , Goharzadeh Afshin
Published: December 2014

Flaring and venting contributes significantly to greenhouse gas emissions and environmental pollution in the upstream oil and gas industry. Present work focuses on a horizontal flow, multiphase ejector used for recovery of these flared gases. The ejector typically handles these gases being entrained by high pressure well head fluid and a comprehensive understanding is necessary to design and operate such recovery system. A CFD based analysis of the flow through the ejector has been reported in this paper. The flow domain was meshed and the mass and momentum equations for fluid flow were solved using commercial software CFX (v14.5). Euler-Euler multiphase approach was used to model different phases. The entrainment behavior of the ejector was investigated and compared for different fluid flow conditions. It was observed that for a fixed primary fluid flow rate, the entrained or secondary flow rate decreased linearly with an increase in pressure difference between exit and suction pressure. The higher was primary flow rate, the greater was the suction created ahead of the primary nozzle and greater was the amount of energy added to the entrained fluid.
Numerical Simulation of Transient Conjugate Heat Transfer in Liquid Jet Impingement
Authors: Lee Jaewon , Son Gihun
Published: December 2014

Numerical simulation is performed for a quenching process in liquid jet impingement, which is applicable to thermal control in metal manufacturing and emergency cooling of nuclear reactors. The flow and cooling characteristics of jet impingement are investigated by solving the conservation equations of mass, momentum and energy in the liquid and gas phases. The liquid-vapor and liquid-air interfaces are tracked by a sharp-interface level-set method which is modified to include the effect of phase change at the liquid-vapor interface. The temporal and spatial variation of solid temperature is analyzed by solving a conjugate problem with the conduction in the solid as well as the convection in the liquid and gas phases. The numerical results demonstrate that the temporal variations of the temperature and heat flux near the fluid-solid interface are very steep compared to those inside the solid. The heat flux variations at the fluid-solid interface are observed to be much larger in the convection mode than in the film boiling mode. The solid temperatures and heat fluxes obtained from the present study are compared with the experimental data reported in the literature.
Impact of the Collision Model for Fully Resolved Particles Interacting in a Fluid
Authors: Abdelsamie Abouelmagd , Eshghinejad Fard Amir , Oster Timo , Thévenin Dominique
Published: December 2014

The impact of the collision model employed when simulating fully resolved particles interacting in a fluid is investigated in the present study. We are using for this purpose a p seudo-spectral in compressib le Direct Numerical Simulation (DNS) code based on the Navier-Stokes equation as well as a Lattice-Boltzmann Method (LBM), developed in our group and coupled with the direct-forcing Immersed Boundary Method (IBM) to describe the particles.

Most of the corresponding literature assumes that the collision model does not have a significant impact on the flow field. Additionally, the impact of the collision model on the particle trajectories has not been analyzed in a systematic manner. Thus, by using the DNS solver, four different collision models (velocity barrier, repulsive potential force, lubrication barrier and hard-sphere model) have been employed in order to examine consequences for particle behavior and turbulence structure. It was found that the particle motion and turbulence statistics are qualitatively similar for all models. However, noticeable quantitative differences appear concerning the turbulent dissipation rate.

In the LBM section two different types of repulsive-force collision model are selected and their effect on a 2D fluid-particle interaction is investigated. Furthermore, other factors affecting performance of the LB-IBM solver, like the forcing scheme will be discussed.
Localization of Incipient Propeller Cavitation in a Cavitation Tunnel Using Inversion Method
Authors: Kim Dongho , Lee Keunhwa , Lee Jeunghoon , Seong Woojae
Published: December 2014

An algorithm for the source localization of incipient vortex cavitation is suggested. Model scale experiment is performed in the Samsung cavitation tunnel to analyze the acoustic characteristics of propeller incipient vortex cavitation and desired target frequencies are determined for the localization based on the experiment. Incipient cavitation is modeled with monopole type sound sources and the source location is set as unknown. Incoherent matched-field inversion signal processing technique is applied to find the optimum source position by comparing the spatial correlation between received pressure fields and numerically computed replica pressure fields at the same position of receiver array. The replica pressure fields are obtained by direct-path ray method within an area in which the source is expected to be. Hybrid optimization algorithm is applied for an efficient search of source position. For the validation of suggested localization algorithm, localization is performed with synthetic data and virtual source. Consequently, it is found that this suggested localization method enables efficient localization of incipient cavitation using a few pressure data measured on the outer hull above the propeller.