bluuebunny/crossref_metadata_2025 huggingface dataset:
Wind Energy and Compressed Air Energy Storage Potential for New York City
Authors: Waite Michael , Modi Vijay
Published: July 2013

The energy potential from wind is significant in many locations in the U.S., including in some areas of New York State. The intermittent availability of wind — specifically, higher wind potential at night and in the winter in New York — would require extensive storage to make use of that energy during times of peak electricity demand — during the day and in the summer. Although the total energy available from wind may be sufficient and available at a low cost, the cost of implementing traditional storage techniques (e.g. batteries) would be expensive and require large amounts of space to address the offset supply and demand profiles. As such, base electricity loads are likely to continue to be served by a combination of less expensive energy conversion technologies, particularly given the current low cost of wholesale natural gas for gas-fueled power plants. Compressed air energy storage (CAES) has been evaluated — and implemented or proposed at a small number of facilities — as a potential energy storage technology that could be used to reduce the amount natural gas required to operate compressors at natural gas-fueled power plants serving base electricity demands. The result of this strategy is, effectively, an increase in thermal efficiency of the power plant.

This paper presents an evaluation of wind energy available at a site in New York State, its potential to meet the electricity demand in New York City, the expected capital and recurring costs of the overall system, and a comparison to electricity provided by natural gas, a likely alternative large-scale fuel source. Annual wind data for the site and annual New York City electricity usage were analyzed. Available wind energy was first assumed to serve any electricity demand above the New York City base load. Additional available wind energy operates compressors, storing compressed air in underground caverns. The cavern sizes required and associated capital costs was calculated. The expected reduction in natural gas requirements were calculated for gas-fuelled power plants designed to accept compressed air from the caverns, with additional electricity demand met by gas turbine power plants. The recurrent cost reductions associated with reduced natural gas volumes were calculated based on a range of natural gas prices to evaluate the feasibility of the system described above under different market conditions. The potential usage of CAES systems for peak electricity demands was also evaluated.
Macroencapsulation of Sodium Nitrate for Thermal Energy Storage in Solar Thermal Power
Authors: Pendyala Swetha , Sridharan Prashanth , Kuravi Sarada , Jotshi Chand K. , Ram Manoj K. , Rahman Muhammad , Stefanakos Elias , Goswami D. Yogi
Published: July 2013

Storage systems based on latent heat storage have high-energy storage density, which reduces the footprint of the system and the cost. However, phase change materials (PCMs) have very low thermal conductivities making them unsuitable for large-scale use without enhancing the effective thermal conductivity. In order to address the low thermal conductivity of the PCMs, macroencapsulation of PCMs is adopted as an effective technique. The macro encapsulation not only provides a self-supporting structure but also enhances the heat transfer rate.

In this research, Sodium nitrate (NaNO3), a low cost PCM, was selected for thermal storage in a temperature range of 300–500°C. The PCM was encapsulated in a metal oxide cell using self-assembly reactions, hydrolysis, and simultaneous chemical oxidation at various temperatures. The metal oxide encapsulated PCM capsule was characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The cyclic stability and thermal performance of the capsules were also studied.
Potential for Distributed Combined Heat and Power in an Urban Environment
Authors: Howard Bianca N. , Modi Vijay
Published: July 2013

Combined heat and power (CHP) has the potential to decrease greenhouse gas emissions by utilizing waste heat that is typically rejected to the environment. CHP systems have been used to satisfy loads on university and corporate campuses but there may be other clusters of mixed used buildings that are viable for a CHP system. In an urban environment, such as New York City, high electricity loads and space heating loads are located in close proximity to each other, whether in a single building or in a neighborhood. This indicates a potential for clusters of buildings demand that could be satisfied by CHP. The analysis presented attempts to determine the potential for CHP systems for the 28,840 blocks of New York City many of which incorporate buildings of mix use. The systems are sized to meet the electrical base load and are considered viable if the CHP efficiency (useful electrical and thermal energy divided by the fuel input) is greater than 60% and the system size is larger than 30kW. The analysis determined that of the 28,840 blocks in New York City, 3,205 could be considered for a CHP system.
Sensitivities in Fitting a Parabolic Trough Facet
Authors: Gray Allison , Lewandowski Allan
Published: July 2013

The collector accuracy requirements for parabolic trough systems are a function of the concentrator and receiver geometry. As the current trend is to use larger trough designs the need for higher accuracy is generally more important. Concentrating solar power (CSP) companies developing and deploying collectors need to meet stringent optical performance requirements and thus require accurate surface characterization instruments to validate that performance. All reflective characterization processes are sensitive to the instrument resolution, experimental setup, data fitting process, and analysis. Small changes in any of these factors can impact the estimated optical performance. It is desirable to have total local surface measurement uncertainties less than 0.5 milliradians (mrad) for a parabolic trough reflector and many instruments are capable of achieving this. Most surface characterization instruments perform a fitting process on measured data that yields a best fit description of the collector surface using some sort of polynomial. Because of this relationship it is desirable to have a robust fitting process. The type and order of the fitted polynomial and fitting process are the two major contributors to describing a facet’s surface based on the measured data. The order of the polynomial can increase or decrease the accuracy of surface description relative to the true surface. This is a function of the existing aberrations in the facet and the surface naturally described by the polynomial. An accurate description of a surface is typically obtained by performing a least squares fit on measured surface data relative to the polynomial. The best analytical description of the surface is achieved when residual errors relative to the polynomial are minimized. The difference between measured data and the best fit description is completed using an iterative process. However, not all surface imperfections on a single reflector can be accurately described with a polynomial as an exact mathematical description of the surface can never be truly achieved. Local positional errors exist in isolated areas of a facet cannot always be fit accurately. The sensitivity in the best fit description of the surface and the surface resulting from the fitting process using higher order polynomials will be discussed in this paper. The change in calculated facet location and surface slope are compared to determine the sensitivity of the process. The results are then used to calculate the intercept factor using ray tracing and estimate the sensitivity in this calculated performance metric.
Next Generation Parabolic Trough Solar Collectors for CSP
Authors: Chen Daniel T. , Reynolds Glenn , Gray Allison , Ihas Ben , Curtis Gary , Molnar Attila , Hackbarth Dean , Vezzuto Robert
Published: July 2013

In order for Concentrating Solar Power (CSP) to become a significant contributor to utility scale baseload power, dramatic reductions in cost and increases in performance must be achieved. 3M Company and Gossamer Space Frames have developed advanced collectors that are centered on a step-change in solar technology aimed at transforming the economics and industrialization of CSP. In particular, we focus on mirror film based reflective materials, stiff and shape accurate panel constructions, and lightweight and accurate space frames. These technology elements have been combined into a new parabolic collector design with an aperture of 7.3 m and length of 12 m. The geometric concentration ratio of the design is 103, far exceeding current designs. The National Renewable Energy Laboratory (NREL) has measured an intercept factor exceeding 99% on the subject collector fielded at SEGS II (Daggett, CA). The successful implementation of this technology platform has implications for new solar collector designs for both point and line focus systems.
The Manufacture and Performance Test of a Mini-Type Single Screw Compressor
Authors: Lu Yuanwei , Wu Yuting , Ma Chongfang , Mu Xiaoying
Published: July 2013

With the development of very large scale integration, the chip heat dissipation is a problem that needs to be solved urgently. Vapor compression refrigeration system is a valid method to cool the electric chip. However, a particular challenge is to make a small and efficient gas compressor. In this paper, a mini-type single screw compressor was manufactured in Beijing University of Technology and a corresponding performance test system was set up. Experimental results show that the heat created by the single screw compressor is higher, which led to an extreme high exhaust temperature. An effective solution is to introduce the low temperature refrigerant from the condenser to the compressor directly to cool down the compressor. Based on this procedure, the compressor performance was measured experimentally. It was found that the condensing temperature, compressor rotation speed and refrigerant charge can affect the compressor performance noticeably and every affective factor has an optimal value. According to the optimal results, the compressor refrigerating capacity of 2.03 kW and system coefficient of performance (COP) of 2.24 was achieved at the evaporating temperature of 5 °C and condensing temperature of 32 °C. Those results can be a baseline for the further performance enhancement of the single screw compressor and can be a valid method for the cooling of large scale integration.
Simulation and Comparison of Particle Injection in an Indoor Environment Using the Species Transport and Discrete Phase Models
Authors: Zheng Z. C. , Wei Z. , Bennett J. S. , Yang X.
Published: July 2013

In simulating fluid/solid-particle multiphase -flows, various methods are available. One approach is the combined Euler-Lagrange method, which simulates the fluid phase flow in the Eulerian framework and the discrete phase (particle) motion in the Lagrangian framework simultaneously. The Lagrangian approach, where particle motion is determined by the current state of the fluid phase flow, is also called the discrete phase model (DPM), in the context of numerical flow simulation. In this method, the influence of the particle motions on the fluid flow can be included (two-way interactions) but are more commonly excluded (one-way interactions, when the discrete phase concentration is dilute. The other approach is to treat the particle number concentration as a continuous species, a necessarily passive quantity determined by the fluid flow, with no influences from the particles on the fluid flow (one-way interactions only), except to the extent the discrete phase “continuum” alters the overall fluid properties, such as density. In this paper, we compare these two methods with experimental data for an indoor environmental chamber. The effects of injection particle numbers and the related boundary conditions are investigated. In the Euler-Lagrange interaction or DPM model for incompressible flow, the Eulerian continuous phase is governed by the Reynolds-averaged N-S (RANS) equations. The motions of particles are governed by Newton’s second law. The effects of particle motions are communicated to the continuous phase through a force term in the RANS equations. The second formulation is a pure Eulerian type, where only the particle-number concentration is addressed, rather than the motion of each individual particle. The fluid flow is governed by the same RANS equations without the particle force term. The particle-number concentration is simulated by a species transport equation. Comparisons among the models and with experimental and literature data are presented. Particularly, results with different numbers of released particles in the DPM will be investigated.
Numerical Simulation of Inner Flow in a Double Blades Pump Based on OpenFOAM and its PIV Verification
Authors: Ren Yun , Liu Houlin , Wang Kai , Tan Minggao , Wu Denghao , Yang Hongbin
Published: July 2013

The presence of unstable flow phenomena may significantly alter the flow pattern and characteristics of centrifugal pumps; that is, the unstable flows may seriously deteriorate the pumps performance. In this paper, considering the high cost of running license fees and not available with all the computing resources, a high quality Open Source CFD simulation platform like OpenFOAM instead of commercial software packages is adopted. Furthermore, the required capability such as GGI is added and boundary conditions are specialized to better simulate complex flow behavior through rotor-stator components in a double blades pump, whose specific speed is 115.6. In order to disclose the characteristics completely, six research schemes are developed and are now presented in this paper. The ratios (Q/Qd) of the flow rate are 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, respectively. The task mainly focuses on the comparison of energy performance under different operating conditions between numerical calculations and experiments, the analysis of the inner flow in the impeller and the comparison of the velocity field in the impeller mid-height between simulation data and the Particle Imaging Velocimetry (PIV) experimental data. The results show that good agreements are found both in terms of the energy performance with experimental results and computed velocities with the PIV data, but improvements can be made.
Modeling EHL of Rough Piston Skirts Using Different Viscosity-Grade Lubricants in Initial Engine Startup
Authors: Qasim Syed Adnan , Gulzar Mubashir , Mufti Riaz A. , Malik M. Afzaal
Published: July 2013

An engine lubricant plays a significant role in preventing adhesive wear of the rough interacting surfaces of the piston skirts and the cylinder liner. A fully established elastohydrodynamic lubricating (EHL) film, appropriate viscosity oil and the fairly rough interacting surfaces prevent wear during normal engine operation. The absence of an EHL film and inappropriate viscosity lubricant fail to minimize wear in the initial engine startup. This work considers a fairly viscous Newtonian engine lubricant to model the rough piston skirts hydrodynamic and EHL in the initial engine start up. The isotropic surfaces of the skirts and the cylinder liner having different roughness amplitudes are considered in the basic lubrication models. The flow factors are introduced in the 2-D average Reynolds equation, which is solved numerically to generate the hydrodynamic pressures. The inverse solution technique is used to develop the basic EHL model of the rough surfaces. The secondary piston dynamics and the contact geometry of interacting surfaces are incorporated in the basic lubrication models. The profiles of the piston eccentricities, secondary velocities, film thicknesses and pressures are generated as the function of 720 degrees crank rotation cycle. The study is extended to develop the lubrication models for the low and high viscosity grade engine lubricants separately. The simulation results are analyzed and compared with those of the basic lubrication model. The results show that the different lubricant viscosities alter the secondary displacements of the sliding piston and affect the lubrication of the rough interacting surfaces. The comparative analysis leads to optimize the use of appropriate viscosity-grade engine lubricant for a few low speed initial engine startup cycles.
High Reynolds Number Airfoil Simulations Using the Immersed Boundary Method
Authors: Johnson James P. , Iaccarino Gianluca , Chen Kuo-Huey , Khalighi Bahram
Published: July 2013

The Immersed-Boundary Method is coupled to an incompressible-flow RANS solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0×105 and 1.8×106. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to show the need for locally refined grids to capture the thin boundary layers close to the airfoil leading edges. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The Immersed-Boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.
Swirl Induced Flow Through a Venturi-Ejector
Authors: Samad Abdus , Omar Rajab , Hewakandamby Buddhika , Lowndes Ian , Short Garry
Published: July 2013

A swirl body inserted into the entry of the primary fluid to a venturi-ejector influences the subsequent mixing of the two fluids and increases the suction rate of the ejector. An experimental facility has been developed to study the influence that a variation in the swirl angle has on the operational performance of a model venturi-ejector. Water and air were the primary and secondary fluids employed. Three swirl body configurations representing three different swirl angles were inserted upstream of the entry nozzle and the resultant downstream flow mixing characteristics were studied. The performance of the venturi-ejector with and without the use of the swirl body inserts was compared. The paper presents a description of the experiments performed and an analysis and discussion of the results obtained from this initial experimental study.
Effects of Splitter Blades on the Unsteady Flow of a Centrifugal Pump
Authors: Ye Liting , Yuan Shouqi , Zhang Jinfeng , Yuan Ye
Published: July 2013

Numerical simulations and performance tests were conducted to analyze the effects of splitter blades on the performance and whole unsteady flow field of a centrifugal pump. The studied pump is a single stage pump with a shrouded impeller (diameter = 160mm, 4 blades, specific speed = 47). Based on the original impeller, we designed 5 impellers with different splitter blades parameters. All the numerical simulations were carried out by using the commercial software ANSYS CFX 12.1 based on standard k-ε turbulence model and standard boundary function. The results showed that, the head of the impellers with splitter blades was approximately 2%∼12% higher than that without splitter blades. When adding splitter blades, the pressure fluctuations at the impeller inlet, volute outlet and the interface of impeller and volute are reduced, this can improve the “jet-wake” flow structure. Different design parameters of splitter blades have a certain effect on the pressure fluctuations at the interface of impeller and volute. When the splitter blades deviated 5° to the suction side of the long blade and the splitter blade inlet diameter is 106 mm, the head is highest and the pressure fluctuations are lowest. The work will provide a basis for the further study on the internal flow field, reducing vibration and noise of a centrifugal pump.
The Interaction of Porous Metal Coating With the Near Wake of Bluff Body
Authors: Liu Hanru , Wei Jinjia , Qu Zhiguo
Published: July 2013

The flow around a circular cylinder with porous metal coating (PMC) is numerically investigated based on an approach of unsteady Reynolds Averaged Navier-Stokes (URANS) at subcritical Reynolds number. The model validation is carried out through comparison with some available experimental results in the literatures. It is found that the simulated results in the present work coincide well with the experimental data. The interaction of PMC with the near wake of circular cylinder such as streamline, vorticity and shear stress are studied in detail. The result reveals that PMC has capability of manipulating the wake flow so that the near wake of PMC cylinder is substantially different from that of smooth one. In addition, the fluctuations of aerodynamic forces are mitigated effectively. Varying the thickness of porous metal coating causes various velocity distributions and aerodynamic performance of bluff body. When the thickness is appropriate, the drag forces can be reduced to a certain extent. It is expected that the modification of flow characteristic and aerodynamic forces also produces the suppression of flow-induced noise generated by bluff body. These studies on wake flow and analysis of its relationship to flow-induced noise will be useful to understand the mechanism of controlling bluff body flow-induced noise by using PMC and to optimize the PMC for controlling flow and flow-induced noise.
Transition Prediction on NACA0012 Airfoil Using Parabolized Stability Equations Approach
Authors: Fang Yihong , Tong Chuanchen , Zhou Yi
Published: July 2013

Accurate prediction of laminar-to-turbulent transition in boundary-layer flows is a key issue in fluid dynamics and design of aerospace vehicles. Existing transition prediction methods vary in their approaches from purely empirical transition criteria to direct numerical simulation (DNS). The most significant problem of the eN method exists in the determination of N factor, while, the DNS is too costly for some problems. The objective of present study is to develop an approach base on parabolized stability equations (PSE) for exactly predicting laminar-turbulent transition. The study is focused on natural transition of flow around NACA0012. The effects of on-flow characteristics and the properties of instability waves are investigated. A good agreement is found, comparing with experiments and numerical simulations. The result highlights the reliability and accuracy of PSE approach.
Pressure and Velocity Fluctuations in the Diffuser for Rotating Stall Period
Authors: Shin Youhwan , Yoon Ji-In , Lee Yoon Pyo
Published: July 2013

This study describes details on local reverse flow patterns in a vaneless diffuser by experiments through PIV measurement technique in the water bath during the unstable operation of a compressor with radial impeller. In order to do these measurements, the pressure transducers were installed on the hub wall with several diffuser radius ratios and they were synchronized with the velocity images of CCD camera. Especially we tried to make them synchronize with time during rotating stall period. For relatively high and low pressure instants, we observed and discussed how the radial and tangential velocity components fluctuated.
Yaw- and Trailer Dependence for Rear-Mounted Cooling Installations for Heavy Vehicles
Authors: Larsson Lisa , Wiklund Torbjörn , Dahl Erik , Löfdahl Lennart
Published: July 2013

Due to stricter emissions legislation and increasing fuel prices vehicle efficiency must be improved. A trend that has been seen in recent years is increased engine power for heavy vehicles. Different exhaust gas after-treatment systems have also been introduced to be able to meet the emission demands. Though, these implementations do not only affect the engine power and the emission levels, they also tend to increase the cooling demand. Therefore, the cooling performance for vehicles has to be increased. At the same time the cooling installation in the front of the vehicle accounts for a substantial part of the total aerodynamic resistance of the vehicle. To reduce the fuel consumption the grill in the front could be covered and the cooling module could be relocated elsewhere. This would decrease the aerodynamic resistance; but a more frequent fan operation would most likely be needed to achieve the same cooling performance in different driving conditions.

This paper presents a comparative study of front-mounted and rear-mounted cooling package installations, using three different configurations for the rear installation on a rigid truck. For each case the cooling performance, fan demand and aerodynamic resistance were compared for different operating conditions at both lower and higher vehicle speeds and engine loads. The study was based on Computational Fluid Dynamics (CFD), where the simulations were performed in zero and five-degree yaw conditions, with and without a trailer added behind the truck.

It was seen that a relocation of the cooling module has a potential for fuel savings at higher vehicle speeds, due to the reduction in power to overcome the aerodynamic resistance. At lower vehicle speeds the cooling performance was increased since a lower system restriction was observed for the rear-mounted configurations. Results also showed that both the cooling performance and the aerodynamic drag was affected by the yawed air condition and when adding a trailer behind the truck. The mass airflow was increased when the air was directed towards the air intake, while it was decreased when the air intake was positioned at the leeward side of the vehicle. When the trailer was added behind the vehicle less air entered the cooling module at a higher vehicle speed. But for the critical cooling situation the trailer did not affect the amount of air entering the cooling module.
Stability of an Evaporating Liquid Film Under Nonequilibrium Conditions With Variable Gravity
Authors: Narendranath Aneet D. , Hermanson James C. , Struthers Allan A. , Kolkka Robert W. , Allen Jeffrey S.
Published: July 2013

An evolution equation describing the dynamics of an evaporating liquid film has previously been developed from the governing equations of fluid dynamics after the application of the lubrication approximation and the choice of a viscous time scale.

The authors have solved the evaporating liquid film evolution equation with a validated numeric program. Different mechanical boundary conditions were successfully applied and their effect on the film dynamics was examined. The evolution equation has also been modified to include buoyancy driven instabilities.

This paper outlines a linear stability analysis that was performed on the time dependent, evaporating liquid film evolution equation. The effect of the evaporation rate, departure from equilibrium at the interface and variable gravity is examined by solving the equation as an initial value problem.
Generation and Transport of Bubbles in Intense Ultrasonic Fields
Authors: Lu Yuan , Katz Joseph , Prosperetti Andrea
Published: July 2013

This paper examines cavitation phenomena generated by a 500 kHz, high-intensity focused ultrasonic (HIFU) beam, with pressure amplitude in the focal zone of up to 19 atm, in quiescent water and at the exit of a jet. The pressure field and cavitation are visualized using high-speed digital in-line holography. The spatial distribution of the acoustic pressure is determined form the variations in the water density and refractive index. A partial standing wave is generated by the reflection of the sound from the wall of the test chamber. Several cavitation phenomena are observed. At low to moderate sound levels, bubbly layers form in the pressure nodes of the standing wave, in the periphery of the focal zone. At high sound levels, clouds of vapor bubbles are generated in the antinodes, and migrate in the direction of the acoustic beam at speeds in the 1–4 m/s range. Both the cloud size and velocity oscillate, with the size peaking in the nodes and the velocity in the antinodes. A model for the cloud dynamics shows that the periodic velocity variation is dominated by the balance between the primary Bjerknes force and the drag. The secondary Bjerknes force involving interactions among the bubbles within the cloud is a likely cause for the size oscillations.
Performance and Emissions of Diesel Engine Using Bio-Fuel Derived From Waste Fish Oil
Authors: Mrad Nadia , Aloui Fethi , Tazerout Mohand
Published: July 2013

In the present work, waste fish fat from fish processing industry is considered as an energy source for diesel engines. In this regard, catalytic cracking process is considered for this present study. The physical and chemical properties of biofuel are very close to diesel fuel. The experiments were conducted in a single cylinder diesel engine to study the performance, emission and combustion characteristics of biofuel. As a result, fuel undergoes good combustion and hence there is significant improvement in performance and reduction in emissions. Experimental results indicate a marginal increase in brake thermal efficiency at all loads compared to diesel fuel. The results show that despite of high NOx and CO2, the engine has lesser UHC, CO and PM than standard diesel fuel. The premixed and diffusion combustion duration is decreased with biofuel compared to diesel fuel. The engine was running smooth at all load conditions with biofuel. It is concluded that the biofuel derived from waste fish fat can be consider as a substitute for diesel fuel.
Multi-Phase CFD Modeling of a Solid Sorbent Carbon Capture System
Authors: Ryan Emily M. , Xu Wei , DeCroix David , Saha Kringan , Huckaby E. David , Dartevelle Sebastian , Sun Xin
Published: July 2013

Post-combustion solid sorbent carbon capture systems are being studied via computational modeling as part of the U.S. Department of Energy’s Carbon Capture Simulation Initiative (CCSI). The work focuses on computational modeling of device-scale multi-phase computational fluid dynamics (CFD) simulations for given carbon capture reactor configurations to predict flow properties, outlet compositions, temperature and pressure. The detailed outputs of the device-scale models provide valuable insight into the operation of new carbon capture devices and will help in the design and optimization of carbon capture systems. As a first step in this project we have focused on modeling a 1 kWe solid sorbent carbon capture system using the commercial CFD software ANSYS FLUENT®. Using the multi-phase models available in ANSYS FLUENT®, we are investigating the use of Eulerian-Eulerian and Eulerian-Lagrangian methods for modeling a fluidized bed carbon capture design. The applicability of the dense discrete phase method (DDPM) is being considered along with the more traditional Eulerian-Eulerian multi-phase model. In this paper we will discuss the operation of the 1 kWe solid sorbent system and the setup of the DDPM and Eulerian-Eulerian models used to simulate the system. The results of the hydrodynamics in the system will be discussed and the predictions of the DDPM and Eulerian-Eulerian simulations will be compared. A discussion of the sensitivity of the model to boundary and initial conditions, computational meshing, granular pressure, and drag sub-models will also be presented.
Simulations and Analysis of Shock Accelerated Inhomogenous Flows With and Without Reshock
Authors: McFarland Jacob A. , Ranjan Devesh , Greenough Jeffery A.
Published: July 2013

A computational study of the Richtmyer-Meshkov instability is presented for an inclined interface perturbation in support of experiments being performed at the Texas A&M shock tube facility. The study is comprised of simulations performed using the Arbitrary Lagrange Eulerian (ALE) code called ARES. These simulations were performed to late times after reshock with varying parameters including inclination angle, and incident shock Mach number. The inclination angle was varied over a wide range which provided initial interface perturbations in both the linear and non-linear regimes. Recent work have shown a distinct difference between the linear and nonlinear interface perturbations growth using a newly developed inclined interface scaling model. This work is extended here by examining the vorticity distribution for these two cases and focusing on the conditions before and after reshock. One linear and one non-linear interface perturbation case are examined qualitatively through plots of the vorticity, and density fields. The total circulation and circulation production rates for these cases are plotted as a function of time. The circulation is shown to double after reshock for the non-linear case, while for the linear case it increases by approximately the same amount as the non-linear case but from near zero just before reshock. The mixing width, and mix mass growth rates are also examined for each case both before and after reshock.
The Effect of Nozzle Shape and Configuration on Bubble Formation in a Liquid Cross Flow
Authors: Hassanzadeh Jobehdar Mona , Gadallah Aly H. , Siddiqui Kamran , Chishty Wajid A.
Published: July 2013

Gas injection into a liquid cross flow from a nozzle causes bubble formations which have potential applications in industry such as chemical plants, waste water treatment and bio- and nuclear-reactors. The purpose of this study is to experimentally investigate the effects of nozzle shape and configuration with respect to the liquid cross-flow direction, on the bubbly flow characteristics such as bubble formation, detached bubble size and frequency at different gas and liquid flow rates. The experiments were conducted in a Plexiglas two-dimensional rig using a high speed camera. High speed imaging and an image processing algorithm were used to track each individual bubble and to quantify the bubble growth as well as the detachment frequency and the bubble velocity. Back light shadowgraphy which utilizes a low intensity diffuse light source to illuminate the background was used to image bubbles. Nozzles were mounted in the test section which was designed such that the flow in this section has a two-dimensional profile.

The results showed that the bubble size increases with an increase in GLR (gas to liquid flow rates ratio). Furthermore, the bubble formations and detached bubble size were strongly influenced by the nozzle shape and configuration.
Simulation of the Tilted Rig Experiment
Authors: Rollin Bertrand , Andrews Malcolm J.
Published: July 2013

The tilted rig experiment is a derivative of the rocket rig experiment designed to study mixing of fluids by the Rayleigh-Taylor instability. In the latter experiment, a tank containing two fluids of different densities is accelerated downwards between two parallel guide rods by a rocket motor. Misalignment between density and pressure gradients trigger the instability leading turbulence and mixing of the fluids. In the tilted rig experiment, the rocket rig is inclined by few degrees off the vertical before firing, creating a slanted initial perturbation interface. The purpose of the tilted rig experiment was to help with calibration of mixing models, as it is a unique two-dimensional Rayleigh-Taylor instability flow. We reproduce conditions similar to this experiment using a Monotone Integrated Large Eddy Simulation (MILES) technique, and for the first time look at statistics of turbulence quantities that appears in “RANS-type” variable density turbulence model. Our statistics show that for the most part, the turbulence quantities in this two-dimensional Rayleigh-Taylor instability configuration behave in a similar fashion as in the planar Rayleigh-Taylor instability configuration when looking in a direction perpendicular to the mixing layer centerline.
Experimental Investigation of Boundary Layer Instabilities on the Free Surface of Non-Turbulent Jet
Authors: Andre Matthieu A. , Bardet Philippe M.
Published: July 2013

Shear instabilities induced by the relaxation of laminar boundary layer at the free surface of a high speed liquid jet are investigated experimentally. Physical insights into these instabilities and the resulting capillary wave growth are gained by performing non-intrusive measurements of flow structure in the direct vicinity of the surface. The experimental results are a combination of surface visualization, planar laser induced fluorescence (PLIF), particle image velocimetry (PIV), and particle tracking velocimetry (PTV). They suggest that 2D spanwise vortices in the shear layer play a major role in these instabilities by triggering 2D waves on the free surface as predicted by linear stability analysis. These vortices, however, are found to travel at a different speed than the capillary waves they initially created resulting in interference with the waves and wave growth. A new experimental facility was built; it consists of a 20.3 × 146.mm rectangular water wall jet with Reynolds number based on channel depth between 3.13 × 104 to 1.65 × 105 and 115. to 264. based on boundary layer momentum thickness.
Detailed Wake Structure Around Moving Elastic Airfoils and Their Characteristics of Dynamic Thrust
Authors: Fuchiwaki Masaki , Kurinami Tomoki , Tanaka Kazuhiro , Tabata Takahide
Published: July 2013

The unsteady flow field around a moving airfoil has attracted significant attention in bio-hydrodynamics, micro-air-vehicles and micro flight robots. Recently, a number of studies have been performed on the flow field around airfoils with unsteady motion in low Reynolds number regions using both experiment and numerical analysis. On the other hand, it is well known that insects and aquatic animals fly or swim by skillfully controlling their wings or fins, which deform elastically, and vortices are generated around their bodies. The flow around an elastic body is treated as a coupled problem between the fluid and structure. There have been only a few reports on the experimental evaluation of vortex flow structures around an elastic moving airfoil and their fluid dynamical properties. In this study, we investigate the wake structures behind the moving elastic airfoils and the characteristics of the dynamic thrusts acting on them. The thrust producing vortex streets are clearly formed behind the combination airfoils for all phase differences. The dynamic thrust acting on the moving elastic airfoil depends strongly on the Strouhal number based on the maximum trailing edge deformation and is independent of the moving motion and phase difference. The maximum thrust efficiency of the combination airfoil is higher than that for the pure pitching and heaving airfoils and become about 0.5 at φ = 90 deg. around St = 0.3.
Modelling Concentrated Slurry Pipeline Flows
Authors: Antaya Charlene L. , Adane Kofi Freeman K. , Sanders R. Sean
Published: July 2013

A numerical investigation of two-phase solid-liquid (slurry) flow in horizontal pipes has been carried out. Simulations of concentrated slurry flows in pipes 0.0515 m and 0.15 m in diameter were performed using the two-fluid approach implemented in the commercial CFD code, ANSYS CFX. Mixtures of monosized and bimodal particle sizes were tested. Several test cases were investigated to predict particle velocity- and concentration-distributions and frictional pressure gradients. The effects of turbulence model selection, dispersed phase wall boundary conditions, and interphase force terms on model performance were evaluated. The selection of turbulence model had a significant impact on the dispersed phase velocity and concentration distributions. Comparison of simulations with benchmark experimental data shows clearly that for the relatively small particle sizes (∼100 microns), poor solids concentration profile predictions are obtained if the turbulent dispersion force is not included. In general, very good agreement between numerical and experimental results was observed.
RANS Predictions of Turbulent Scalar Transport in Dead Zones of Natural Streams
Authors: Drost Kevin , Jackson Tracie , Apte Sourabh V. , Haggerty Roy
Published: July 2013

Natural stream systems contain a variety of flow geometries which contain flow separation, turbulent shear layers, and recirculation zones. This work focuses on stream dead zones. Characterized by slower flow and recirculation, dead zones are naturally occurring cutouts in stream banks. These dead zones play an important role in stream nutrient retention and solute transport studies. Previous experimental work has focused on idealized dead zone geometries studied in laboratory flumes. This work studies the capabilities of computational fluid dynamics (CFD) to investigate the scaling relationships between flow parameters of an idealized geometry and the passive scalar exchange rate. The stream geometry can be split into two main regions, the main stream flow and the dead zone. For the base case simulation, the depth-based Reynolds number is 16,000 and the dead zone is 0.5 depths in the flow direction and 7.5 depths in the transverse direction. Dead zone lengths and the main stream velocity were varied. These flow geometries are simulated using RANS turbulence model and the standard k–ω closure. Scalar transport in dead zones is typically modeled as a continuously stirred tank with an exchange coefficient for the interface across the shear layer. This first order model produces an exponential decay of scalar in the dead zone. A two region model is also developed and applied to the RANS results. Various time scales are found to characterize the exchange process. The volumetric time scale varies linearly with the aspect ratio. The simulations showed significant spatial variation in concentration leading to many different time scales. An optimized two region model was found to model these different time scales extremely well.
Optimal Disturbances in Three-Dimensional Natural Convection Flows
Authors: Merzari Elia , Fischer Paul , Pointer W. David
Published: July 2013

Buoyancy-driven systems are subject to several types of flow instabilities. To evaluate the performance of such systems it is becoming increasingly crucial to be able to predict the stability of a given base flow configuration. Traditional Modal Linear stability Analysis requires the solution of very large eigenvalue systems for three-dimensional flows, which make this problem difficult to tackle.

An alternative to modal Linear stability Analysis is the use of adjoint solvers [1] in combination with a power iteration [2]. Such methodology allows for the identification of an optimal disturbance or forcing and has been recently used to evaluate the stability of several isothermal flow systems [2]. In this paper we examine the extension of the methodology to non-isothermal flows driven by buoyancy. The contribution of buoyancy in the momentum equation is modeled through the Boussinesq approximation.

The method is implemented in the spectral element code Nek5000. The test case is the flow is a two-dimensional cavity with differential heating and conductive walls and the natural circulation flow in a toroidal thermosiphon.
Unsteady Modeling of Powdered Activated Carbon Deposition on Collection Electrode of a Lab-Scale Electrostatic Precipitator (ESP)
Authors: Khakpour Yasmin , Clack Herek L.
Published: July 2013

Particulate sampling in the flue gas at the Electrostatic Precipitator (ESP) outlet during injection of powdered activated carbons (PACs) has provided strong anecdotal evidence indicating that injected PACs can penetrate the ESP in significant concentrations. The low resistivity of PAC is consistent with poor collection efficiency in an ESP and lab-scale testing has revealed significantly different collection behavior of PAC in an ESP as compared to fly ash. The present study illustrates the use of a commercial CFD package — FLUENT — to investigate precipitation of powdered activated carbon (PAC) in the presence and absence of electric field. The computational domain is designed to represent a 2-D wire-plate ESP channel. The governing equations include those covering continuous phase transport, electric potential, air ionization, and particle charging. The particles are tracked using a Lagrangian Discrete Phase Model (DPM). In addition, a custom user-defined function (UDF) uses a deforming boundary condition and a prescribed critical particle velocity to account for particle deposition and dust-cake growth on the electrodes. The effect of Electrohydrodynamics (EHD) induced flow on the ESP collection efficiency under various flow and particle characteristics as well as different ESP configurations are illustrated.
Super-Hydrophobic Effect in Single Phase Fluids
Authors: Floryan Jerzy M. , Mohammadi A.
Published: July 2013

Super-hydrophobic effect involves capture of gas bubbles in pores of a solid wall, which separates liquid from the solid, resulting in the reduction of the shear drag experienced by the liquid. This effect occurs in the presence of two phases. A similar effect might be produced by creating separation bubbles made of the same fluid through proper shaping of the surface. Use of transverse grooves with a sufficiently short wavelength creates the required flow topology. The shear drag decreases by up to 50% compared with the smooth wall but the interaction pressure drag increases, resulting in only minor reduction in the overall drag. Proper shaping of the grooves may reduce the interaction pressure drag.
Aluminum Particle Ignition Studies
Authors: Cornelius Michael S. , Donaldson Burl
Published: July 2013

Experiments have been performed to study the combustion criteria of aluminum particles at atmospheric pressure. The primary goal is to quantify the outcome for a particle into which thermal energy has been deposited. Experiments utilized instantaneous joule heating of an aluminum wire. Once the particle was generated, it fell under gravity and the flight was recorded by video; in some cases, the ignited particle quenched or fragmented, and the residue was collected for SEM and EDS imaging. This provided information related to the aluminum oxide shell which was formed when combustion occurred. These experiments produced particles of approximately 150450 microns in the arc heating tests. In a second set of experiments, particles were produced under more observable time scales. This provided observation of the oxide skin, which is known to influence the ignition process. This experiment utilized a pressure pulse to eject a small droplet of molten aluminum through a small orifice. From this experiment, particle sizes ranging 2–3 mm were produced.
Effect of Synthetic-Jet Actuation on Airfoil Acoustic Radiation
Authors: Golubev Vladimir , Sewell Cody , Nguyen Lap , Mankbadi Reda
Published: July 2013

Synthetic jet actuators (SJAs) have been primarily investigated as means of unsteady flow control on aircraft wing. The current work for the first time explores the effectiveness of SJAs for control of a low-speed airfoil acoustic radiation both with the uniform upstream flow conditions (with noise dominated by the trailing-edge sources) and in the presence of an upstream flow disturbance (with noise dominated by the leading-edge sources or stall-related phenomena depending on the disturbance character and amplitude). In the high-fidelity numerical study, the effect of the selected SJA location and other parameters characterizing SJA performance are determined. In the adopted numerical procedure, the actuator is modeled without its resonator cavity through imposing a simple fluctuating-velocity boundary condition at the bottom of the actuator’s orifice. The orifice cavity with the properly defined boundary condition is then embedded into the airfoil surface for conducting high-accuracy viscous analysis of SJA-based active noise control. The effects of the actuation on sound radiated by the airfoil both in presence and absence of the upstream flow disturbance are examined for a benchmark problem of time-harmonic gust interaction with a symmetric Joukowski airfoil.