bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Numerical Simulation of Drops in Three Dimensional Viscoelastic Simple Shear Flows
Authors: Pillapakkam Shriram B. , Singh Pushpendra 
Published: November 2021

Abstract
A three dimensional finite element scheme for Direct Numerical Simulation (DNS) of viscoelastic two phase flows is implemented. The scheme uses the Level Set Method to track the interface and the Marchuk-Yanenko operator splitting technique to decouple the difficulties associated with the governing equations. Using this numerical scheme, the shape of Newtonian drops in a simple shear flow of viscoelastic fluid and vice versa are analyzed as a function of Capillary number, Deborah number and polymer concentration. The viscoelastic fluid is modeled via the Oldroyd-B model. The role of viscoelastic stresses in deformation of a drop subjected to simple shear flow and its effect on the steady state shape is analyzed. Our results compare favorably with existing experimental data and also help in understanding the role of viscoelastic stresses in drop deformation.
Experimental Visualization of Lagrangian Coherent Structures in Aperiodic Free Surface Flow
Authors: Chrisohoides Antonis , Sotiropoulos Fotis 
Published: November 2021

Abstract
We propose a simple experimental technique for visualizing Lagrangian coherent structures (LCS) in turbulent free-surface flows. The technique employs digital photography to record the transport of passive tracers (small paper pieces) introduced manually at the free surface. Coherent eddies are detected by time-averaging the instantaneous light intensity fields on finite-size temporal windows. We demonstrate the potential of the method by applying it to visualize the flow in the vicinity of a surface-piercing rectangular block mounted at one corner of a rectangular open channel. We show that by appropriately selecting the time averaging window, the technique can reveal the presence of organized patterns in the chaotic instantaneous flow and elucidate their complex interactions.
Calculation of Transient Flow in Circulating Fluidized Beds With Straight and Double Abrupt Outlet Configuration: Relation With the Inelasticity of the Particle-Particle Collisions
Authors: De Wilde Juray , Vierendeels Jan , Heynderickx Geraldine J. , Dick Erik , Marin Guy B. 
Published: November 2021

Abstract
Gas-solid flow in industrial scale Circulating Fluidized Beds (CFB’s) is calculated in 3D using the Eulerian-Eulerian approach and the Kinetic Theory of Granular Flow (KTGF). Two outlet configurations are used: a straight top outlet and a double abrupt T-outlet. The effect of the value of the restitution coefficient for particle-particle collisions on the stability of the flow is investigated. Oscillations appearing in CFB’s, are shown to be gravity waves.
An E/H Displacement and Power Control Design for Hydraulic Variable Displacement Pumps
Authors: Du Hongliu 
Published: November 2021

Abstract
In this paper, a novel E/H control design is proposed for displacement and power control of hydraulic variable displacement pumps. The displacement control is treated as tracking the desired swashplate angle time history αd(t) with the consideration of system uncertainties. The robust stability of the control system is achieved by a very rugged control design. The resulting error dynamics is of first order, which guarantees no overshoot for step response. An adaptive term is added to further improve the system performance. The smooth transfers between the displacement control and power control modes are achieved. The provided control design significantly simplifies the hydro-mechanical design for variable displacement pumps and results in a cost reduced pump with a better performance. Experimental results validate the theoretical development.
Investigation of the Ageing Behaviour of Ecologically Acceptable Hydraulic Fluids and Their Interaction With Surface Coatings
Authors: Murrenhoff Hubertus , Schmidt Martin 
Published: November 2021

Abstract
Environmental aspects have a major impact on the application of technical products and decide about their success. Especially, with regard to hydraulic systems, these aspects can be fulfilled by the use of environmentally friendly fluids, based on synthetic esters. But the fluid’s properties strongly differ from the ones of the well-known mineral oil based fluids. Therefore, a profound knowledge of the fluid’s properties and their interaction with hydraulic components is essential for a successful usage of these fluids in hydraulic systems and moreover the basis of the development of a new generation of fluids which is going to take place within a research program at the University of Aachen. There, new environmentally friendly fluids are developed and tested in tribosystems applying new surface coated materials. Aim is to transfer important tribological features from fluids onto these base materials. Taking this route certain additives are no longer required and the missing characteristics have to be taken on by specially coated materials.
Therefore, analysis of the properties of synthetic esters, their change due to usage and the interaction with specially coated materials have been carried out. Moreover, a test facility will be presented which is able to do both ageing the fluid to analyze its ageing behavior and testing the fluid’s tribological properties. Besides the presentation of results with respect to the subject ageing of esters also results with respect to the influence of ageing on the tribological fluid properties will be shown.
Production of Diffusion Flames in the Near Extinction Limit Regime Using a Hele-Shaw Apparatus in a Simulated Low Gravity Environment
Authors: Oravecz-Simpkins Lisa M. , Wichman Indrek S. 
Published: November 2021

Abstract
A Hele-Shaw apparatus that produced spreading diffusion flames in the near extinction limit was designed and constructed. A scaling analysis was used to determine the maximum test section height for which effects of gravity could be neglected. Preliminary results showed that this apparatus could be used to produce flame instabilities which resemble drop tower test results from NASA [1,2] and other diffusion flame instability studies [3,4,5,6]. Therefore, the Hele-Shaw apparatus is useful for studying flames in a simulated low gravity environment. Additional unstable behaviors seen in the device, such as flame pulsing and spreading blue cusps, not in the NASA testing further supported the need for investigations during longer microgravity times on the International Space Station. The initial testing was only used to gain an observable region of unstable flames. Further studies will be directed at explaining and quantifying specific behaviors with test conditions.
A New LES Pool Fire Simulation Tool
Authors: Rawat Rajesh , Spinti Jennifer P. , Yee Wing , Smith Philip J. 
Published: November 2021

Abstract
In a large-scale pool fire simulation, the processes that must be modeled are complex and coupled. The flow is often highly turbulent, dynamic vortical structures are present, the chemical reactions involve several thousand elementary steps and hundreds of species/intermediates, and radiation, the dominant mode of heat transfer, is strongly affected by the presence of soot. The range of length and time scales associated with all these processes cannot be simulated on even the most powerful supercomputers available today. Our approach to making this intractable problem tractable has been twofold: one, to improve the models used at all levels in the simulation (i.e., transport models and subgrid scale models) and two, to parallelize the simulation tool to run on massively parallel machines. We have employed Large Eddy Simulation (LES) to model the fluid dynamics and the convection-diffusion scalar transport. LES successfully captures the transient nature of the coherent vortical structures present in a pool fire. We have integrated these improved models into a computational framework that provides support for parallelization. Preliminary validation results show the capability of the fire simulation tool to capture the puffing nature of pool fires. In addition, scalability studies of the simulation tool reveal close to linear scalability up to 500 processors.
Thermocapillary Convection With Undeformable Curved Surfaces in Open Cylinders
Authors: Sim Bok-Cheol , Zebib Abdelfattah 
Published: November 2021

Abstract
Thermocapillary convection driven by a uniform heat flux in an open cylindrical container of unit aspect ratio is investigated by two- and three-dimensional numerical simulations. The undeformable free surface is either flat or curved as determined by the fluid volume (V ≤ 1) and the Young-Laplace equation. Convection is steady and axisymmetric at sufficiently low values of the Reynolds number (Re) with either flat or curved interfaces. Only steady convection is possible in strictly axisymmetric computations. Transition to oscillatory three-dimensional motions occurs as Re increases beyond a critical value dependent on Pr and V. With a flat free surface (V = 1), two-lobed pulsating waves are found on the free surface and prevail with increasing Re. While the critical Re increases with increasing Pr, the critical frequency decreases. In the case of a concave surface, four azimuthal waves are found rotating clockwise on the surface. The critical Re decreases with increasing fluid volume, and the critical frequency is found to increase. The numerical results with either flat or curved free surfaces are in good quantitative agreement with space experiments.
Effective Flux Temperature Formulation for Energy Conversion Using Microscale Thermal Radiation
Authors: Whale MacMurray D. 
Published: November 2021

Abstract
The non-Planckian spectrum of microscale thermal radiation is interpreted using a formulation for non-thermal radiation. The non-thermal aspects of the energy spectrum that results when radiating bodies are in close proximity are examined using the fluctuational electrodynamic approach to microscale thermal radiation. A definition of the effective flux temperature for microscale thermal radiation is presented. A technique to determine the entropy flux in a microscale field is obtained and used to calculate the effective flux temperature for chromium surfaces. The effective flux temperature of microscale radiation permits an assessment of the limits of the performance of proposed devices for the exploitation the spacing effect for energy conversion. The performance of a microscale thermophotovoltaic device is examined in terms of this flux temperature.
An Evaluation of a NN-Based Model for the Prediction of Foundation Heat Transfer From Basements
Authors: Salehi Mustafa , Krarti Moncef 
Published: November 2021

Abstract
In this paper, a feed-forward artificial neural network module is presented to predict seasonal variations of foundation heat transfer from conditioned basements. The training data for the NN-based module were obtained from a detailed solution of the ground-coupled problem. Input variables for the NN module include foundation geometric dimensions, insulation configuration, indoor and outdoor temperatures, and soil thermal properties. The paper discusses the network architecture and the training and testing procedures. The predictions of the NN-based module are compared to a correlation-based method for a set of basement configurations. The main conclusion of the paper is that NNs can predict seasonal variation of building foundation heat transfer with high accuracy and little effort for model development.
Thermal Analyses and Frequency Shift Design Studies for the Spallation Neutron Source Drift Tube Linac
Authors: Parietti Lucie 
Published: November 2021

Abstract
Los Alamos National Laboratory is responsible for the design of the room-temperature linac for the Spallation Neutron Source (SNS). This linac consists of a Coupled-Cavity Linac (CCL) and a Drift Tube Linac (DTL). During normal operation, about 80% of the Radio Frequency (RF) power is dissipated in the DTL cavity walls. This waste heat causes the cavities to expand, causing shifts in their RF resonant frequency. The DTL relies on the water cooling system to compensate for the frequency shift caused by RF heating. To guide the design of the cooling system and the frequency control scheme, thermal expansion and frequency shift studies for several DTL cells are performed via numerical simulations. Temperature distributions and thermal deformations resulting from RF heating are evaluated separately for the tanks and 22 drift tubes using finite element models. The frequency shift of these cells are then computed based on the calculated deformations. Size and locations of the cooling channels are designed accordingly to provide adequate cooling and minimize frequency shift. The tank finite element model used to predict the tank temperature profile is benchmarked against experiment data.
Implementation of the Compressible Flow Solution Methodology for Solving 2D Shallow-Water Flow Problems
Authors: Moran Joaquin E. , Rincon Jose A. 
Published: November 2021

Abstract
This paper concerns with the implementation of the compressible flow solution methodology for solving 2D shallow water flow problems. It is well known that in both cases, the continuity and momentum conservation equations look quite similar, but depth replaces density of compressible flow, and the Froude number will replace the Mach number. Thus, any mass imbalance produces a change in depth equivalent to the density change for compressible flow. It is possible to combine momentum and continuity equations to obtain a predictor-corrector algorithm for establishing the depth field. However, as the Froude number increases, the governing equations change their character from elliptic to hyperbolic, with a parabolic transition at a Froude number of unity and this change is not reflected in the equivalent classical pressure-correction equation, which keeps its elliptic character. The extension of incompressible (SIMPLE-based methods) to compressible flows, incorporates a convection-like term (wave velocity related) to the pressure-correction equation. The drawback of the extension of the pressure-correction to compressible flows was the poor shock-capturing capability, which is due mainly to the treatment of the convective terms in the conservation equations. In this work, a high order bounded treatment of the convective terms along with the depth-correction for all Froude numbers is implemented. A numerical solution is presented for all Froude numbers, and it is compared with benchmark problems.
Geometric Optimization of Radiative Enclosures Through Nonlinear Programming
Authors: Daun K. J. , Howell J. R. , Morton D. P. 
Published: November 2021

Abstract
Optimization routines have become a popular tool in the design of thermal systems. These routines dramatically reduce the time and computational effort needed to find the optimal design by reducing the number of iterations required by the forward design procedure. Also, these methods often find solutions that are not intuitive to the designer. Although these routines have been applied to solve conduction and convection problems, they have not been used to design radiant enclosures.
This paper introduces a methodology for applying nonlinear programming to design 2-D radiant enclosures. The process is facilitated by representing the enclosure surface parametrically with B-spline curves, and an infinitesimal-area analysis technique is then used to solve the radiosity distribution within the enclosure. The enclosure geometry is repeatedly adjusted with a gradient-based minimization algorithm, until the optimum solution is found.
This technique is demonstrated by optimizing the geometry of a 2-D radiant enclosure, with the objective to obtain a specified radiosity distribution over a portion of the enclosure surface. The steepest descent, Newton’s method, and quasi-Newton’s method are used to find the optimum enclosure geometry, and the performance of these methods is compared.
A Reliable Procedure for Testing the Accuracy of Numerical Algorithms in CFD and Heat Transfer
Authors: Murty V. Dakshina 
Published: November 2021

Abstract
A reliable procedure for benchmarking of computer solutions in the fields of computational mechanics including computational fluid mechanics, heat transfer, and k-ε turbulence models is presented. The procedure consists of using assumed solutions to calculate the required source terms (which could be in the form of body forces for momentum equations) and use the resulting source terms as inputs to back calculate the displacements, velocities, temperature, etc. The procedure works especially well for nonlinear problems. Several examples are provided from fluid mechanics and heat transfer.
Numerical Modelling of Air Temperature and Velocity in a Forced and Free Ventilation Piggery
Authors: Mossad Ruth 
Published: November 2021

Abstract
Pigs are subjected to intensive environment control and management for higher productivity due to their sensitivity to climatic variation, which affects their growth. The aim of the current work is to numerically model the air speed and temperature in forced and free ventilation piggeries to achieve optimum environmental control. A steady two-dimensional numerical model including the effect of buoyancy, turbulence and heat generated by the pigs was solved using the computational fluid dynamics software Fluent, which is based on the integral volume method. In the forced ventilation case, air speed and temperature inside the piggery and at the pigs’ level were predicted for three different locations of ventilation opening, variable air inlet velocities (in the range 0.3 m/s – 7 m/s), and insulated or non insulated external walls, for ambient temperatures of 5 °C and 32 °C. In the free ventilation case, temperature and air speed at the pig’s level were predicted for a particular wind speed and direction, and some variations in the design. These variations were adding louvers in the air opening, lowering the outer wall of the piggery and changing the type of pen fence used. These results helped to identify problems in the design and offer suggestions for improvements.
Direct Chill Casting of Aluminum Alloys: Modeling and Experiments on Industrial Scale Ingots
Authors: Vreeman Christopher J. , Schloz J. David , Krane Matthew John M. 
Published: November 2021

Abstract
A continuum mixture model of the direct chill casting process is compared to experimental results from industrial scale aluminum billets. The model, which includes the transport of free-floating solid particles, can simulate the effect of a grain refiner on macrosegregation and fluid flow. It is applied to an Al - 6 wt% Cu alloy and the effect of grain refiner on macrosegregation, sump profile, and temperature fields are presented. Two 45 cm diameter billets were cast under production conditions with and without grain refiner. Temperature and composition measurements and sump profiles are compared to the numerical results. The comparison shows excellent agreement for the grain refined case. It is believed that an incorrect assumption about the grain structure prevents good agreement in the non-grain refined billet.
Heat Transfer Associated With Air-Water Spray Cooling of Forgings From High Temperatures
Authors: Ward J. , de Oliveira M. , Garwood D. R. , Wallis R. A. 
Published: November 2021

Abstract
The desired mechanical properties of the nickel-based or titanium forgings used in gas turbines for aircraft and power generation applications can be controlled by varying the rate of cooling from the so-called solution temperature during an initial heat treatment process. The use of dilute air-water spray cooling of these forgings is a technique which can provide heat transfer rates lying between those associated with conventional oil quenching or convective air-cooling. Air assisted atomisation can result in fine sprays over a wide range of water flow rates and it has a further advantage in that the air “sweeps” the surface and hence helps to prevent the build up of deleterious vapour films at high surface temperatures. The paper presents experimental data for the heat transfer rates associated with the use of these sprays to cool surfaces from temperatures of approximately 800°C. Many forgings contain surface recesses, which can lead to build up or “pooling” of the water so that the effect of variations in surface geometry is also reported. Periodic interruption of the water flow is a technique which can be employed to provide additional control of the heat transfer rate, particularly at temperatures below 500°C so that data is also presented for pulsed sprays.
Analysis of Measuring Techniques of Superlattices Thermal Conductivity
Authors: Travkin V. S. , Catton I. 
Published: November 2021

Abstract
It has been reported in a number of publications that measured values of superlattice thermal conductivities, for example, GaAs/AlAs, Si/Ge, InAs/AlSb, etc., do not compare well with expected or modeled values. There are questions about measurement techniques that are used and some improvements are being made. One of the used techniques is the 3 (omega) measurement of thermal conductivity of superlattices. Some of these issues will be addressed in our work. The full two-scale heat transport and electrodynamics governing equations are used to achieve understanding of the possible mechanisms that play a role in shaping the effective (measured) coefficients of thermal and electrical conductivities in superlattices. It is shown that the issues of simulation or measurement of the effective coefficients at the upper scale are essentially the same as simulation of the complete two-scale problem in its complexity. Some of these concerns have been dealt with elsewhere. Here we will contribute to understanding of surficial transport and its inclusion into simulation procedures on the upper scale, and the problem of interaction of charge carriers transport and heat transport on both scales. Possible improvements of techniques for measuring superlattices conductivities will be suggested.
A Study of the Transport of Nanopowders in a Solidifying Solder Melt and its Influence on Microstructural Development
Authors: Lin D. C. , Liu S. , Guo T. M. , Wang G.-X. , Srivatsan T. S. 
Published: November 2021

Abstract
Recent experiments have clearly demonstrated an innate capability to judiciously use nanopowders to increase the strength of engineering materials. This can be achieved even for low weight percentages of the nanopowders, as low as a few percent. This research finding has provided the much desired impetus of producing high-strength materials by adding small amounts of nanopowders into a solidifying molten metal with the objective of forming nano-particle reinforced metallic composites. A practical application of such a composite is in microelectronic and/or opto-electronic devices and assemblies, which necessitate the need for high strength solders. This paper presents preliminary results of experiments aimed at understanding the kinetics governing the solidification of solders blended with nanopowders. Composite solder paste was prepared by mechanically mixing nanopowders of either copper or TiO2 with tin-lead powders (tens of microns in size). Solidification experiments of the composite solders were performed in an aluminum crucible and temperature variations during cooling and solidification were measured. For the TiO2 nanopowder reinforced composite solders, the data show a strong melt undercooling followed by recalescence to an increased melting temperature, while for the Cu nanopowder reinforced composite solders, one sees a reduced melting temperature with two-stages of solidification. Metallographic observations of the solidified composite solders find a significant reduction in both the grain size and spacing of eutectic lamellae, leading to an increase in microhardness.