bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Measurement of the Internal Geometry of a CFD Validation Experiment
Authors: Jones Kyle L. , Nani David , Smith Barton L. 
Published: July 2013

Computational Fluid Dynamics (CFD) validation experiments require careful documentation of the boundary conditions. Many validation experiments contain complex geometries or facilities that are not accesible for meaurement using calipers. This paper describes a method for providing accurate optical measurement of physical geometries using an Nd:YAG laser, a CCD camera, and two 1-dimensional traverses. The facility used is a cylinder array test section. The laser sheet is aligned perpendicular to the cylinder span and the camera is aligned parallel to the cylinders.
After images were acquired, a code was written to analyze the images based on the Gaussian-like intensity profiles of the illuminated cylinder edges and walls in the facility. The peaks were extracted and a least squares fit applied to the peaks resulting in the center coordinates and diameter of the cross-sections. These were then reconstructed into a surface which can be imported into a CFD simulation package. This study shows that the cylinder diameters and x- and y-coordinates can be determined accurately.
The effects of various surface finishes are also compared. Three finishes were used: transparent, painted flat black, and a rhodamine painted surface with an appropriate band pass filter. The intensity profiles were compared using a single laser power setting.
Numerical Optimal Design of a Non-Overload Centrifugal Pump
Authors: Hu Bo , Yuan Shouqi , Lu Weigang , Li Tong , Guo Chenxu 
Published: July 2013

Shaft power characteristics of centrifugal pumps attract extensive attentions in order to improve the operating reliability of pumps. TS-50-32-250 type low specific speed centrifugal pumps are selected as the research subjects. Three parameters of impeller including blade outlet angle β2, outlet width b2 and wrapping angle of blade θ are selected for the impeller shape optimization. Maximum flow design method and non-overload design method are adopted to design 7 impellers. Numerical simulation with CFX 12.1 is used to reduce the cost and shorten the design period. The time-averaged Navier-Stokes equations of 3D steady flow in the pump are calculated by CFX 12.1 based on the standard k-ε turbulence model together with standard wall function. The structured grids of different qualities are used in unmodified impeller for comparison to confirm that the results are not influenced by the quality of mesh.
The optimal impeller is obtained when β2, b2, θ are 18°, 7mm, 175°, respectively. The performances of NCPs at other working conditions satisfy the requirements of heads and efficiencies obtained from China National Standard. The shaft power reaches to 15 kW which is the power rating of the matched motor, at 1.45QR (35m3/h), showing that the non-overload performance of the pump is also significantly improved after modifying impeller geometries. Impeller 6 is considered as the optimal one and produced for experiments. Experiment results prove that it is effective and reliable to improve a non-overload pump’s performance by maximum flow design method and non-overload pump design method. The results provide a reference for increasing the efficiencies and heads of non-overload pumps at multiple operating conditions.
Passive Control of Flow in an A-Pillar Region in the Presence of Uniform or Turbulent Upstream Flow
Authors: de Moraes Luis F. G. , Sicot Christophe , Paille François , Borée Jacques 
Published: July 2013

The flow at the level of A-pillar region is characterized by complex and unsteady three-dimensional separated areas. They are mainly responsible for pressure fluctuations which are the source aerodynamic noises radiated outward or transmitted in the passenger compartment. This noise can make the driver tired and stress the passengers in the cabin. Therefore, one of the technological challenges for ground vehicles is the reduction of noise generated by these aerodynamic sources. At the present time, active control devices are wanted to control the vortex and its interaction with the wall (lateral windows). However, fixed devices can also be installed to a form of passive control which will play on the relative position of the vortex and its dynamics. In the present work, simple geometric devices were installed on the A-pillar strut of a model body to modify the development of the conical vortex and its fluctuating pressure footprint. Two strategies were tested. The first consisted in a narrow plate running along the A-pillar, expected to modify the A-pillar strength and its position relative to the side wall. The second consisted in generating a secondary vortex, intense enough to interact with the main structure. The efficiency of these devices has been tested in the presence of a uniform upstream flow and a turbulent upstream flow. The isotropic and homogeneous turbulent flow was generated using a grid placed in the entry of test section, generating an intensity of 4% and an integral length scale of the magnitude of the A-pillar vortex diameter.
For a uniform upstream flow, it was observed that the simple geometric devices used made the vortex core more energetic and coherent. Moreover, the group of devices acting as a vortex generator was able to very significantly reduce the coefficient of fluctuating pressure. Such an improvement was however not obtained in the presence of upstream turbulence.
Thermodynamic Parameter on Cavitation in Space Inducer
Authors: Yoshida Yoshiki , Kikuta Kengo , Niiyama Kazuki , Watanabe Satoshi 
Published: July 2013

Cavitation is physically “a vaporization of liquid” which needs latent heat for phase change. A cavity grows in the liquid, so the latent heat of vaporization can only be supplied by the liquid surrounding the cavity. Thus, the liquid close to the interface region of the cavity is cooled down.
In general, cryogenic liquids are very thermosensitive. For liquid hydrogen and oxygen used in rocket propulsion, the temperature in the cavity, i.e., the vapor pressure in the cavity, is lower than those of the liquid bulk. Thanks to this thermal effect, cavitation in cryogenic liquids is less developed than that in water at room temperature. This thermal effect on cavitation is beneficial in that it improves cavitation performance and alleviates cavitation instability in space inducers.
In previous works, we investigated the relationship between the thermodynamic effect and the cavitation instabilities, e.g., rotating cavitation and cavitation surge, with a focus on the cavity length as an indication of cavitation. In the present work, first, aspects of cavitation in the inducer were observed by direct optical visualization in liquid nitrogen. Second, joint experiments in liquid nitrogen and cold water were conducted on a cavitaing inducer. In nitrogen experiments, operating conditions, i.e., rotational speed and liquid temperature, were varied to determine the cavitation scaling law. Through these experimental results, characteristic times, namely, the transit time for bubble growth and the characteristic thermal time introduced from the thermal property, were investigated as a cavitation thermodynamic parameter. It was found out that the adjustment of cavitation number has a good correlation with the ratio of the transit time and the characteristic thermal time.
Modification of Turbulence in Boundary Layers by Mean and Fluctuating Pressure Gradients
Authors: Joshi Pranav , Liu Xiaofeng , Katz Joseph 
Published: July 2013

In this study we focus on the effect of mean and fluctuating pressure gradients on the structure of boundary layer turbulence. Two dimensional, time-resolved PIV measurements have been performed upstream of and inside an accelerating sink flow for inlet Reynolds number of Reθ = 3071, and acceleration parameter of K=1.1×10−6. The time-resolved data enables us to calculate the planer projection of pressure gradient by integrating the in-plane components of the material acceleration of the fluid (neglecting out-of-plane contribution). We use it to study the effect of boundary layer scale fluctuating pressure gradients ∂p′~/∂x, which are expected to be mostly two-dimensional, on the flow structure. Due to the imposed mean favorable pressure gradient (FPG) within the sink flow, the Reynolds stresses normalized by the local freestream velocity decrease over the entire boundary layer. However, when scaled by the inlet freestream velocity, the stresses increase close to the wall and decrease in the outer part of the boundary layer. This trend is caused by the confinement of the newly generated vortical structures in the near-wall region of the accelerating flow due to combined effects of downward mean flow, and stretching by velocity gradients.
Within both the zero pressure gradient (ZPG) and FPG boundary layers, sweeping motions mostly occur during positive fluctuating pressure gradients ∂p′~/∂x>0 as the fluid moving towards the wall is decelerated by the presence of the wall. Vorticity is depleted in the near-wall region, as the wall absorbs −ω′ from the flow by viscous diffusion. On the other hand, ejections occur mostly during periods of favorable fluctuating pressure gradients ∂p′~/∂x<0. During these periods, there is more viscous flux of vorticity −ω′ into the flow, since ∂−ω′/∂y<0 at the wall. Large scale ejection motions associated with ∂p′~/∂x<0 are more likely to transport smaller scale turbulence to the outer region of the boundary layer, while turbulence remains largely confined close to the wall due to the sweeping motions accompanying ∂p′~/∂x>0. During periods of ∂p′~/∂x>0 in the ZPG boundary layer, sweeps tend to increase the momentum in the near-wall region, whereas the adverse pressure gradient decelerates the fluid. These competing effects result in an unstable ω′<0 shear layer which rolls up into coherent vortical structures and increases ω′ω′ near the wall as compared to periods of ∂p′~/∂x<0. Due to the strong mean acceleration of the flow and weaker sweeps in the FPG boundary layer, the formation of an unstable shear layer, and hence vortical structures, is suppressed, decreasing the enstrophy close to the wall as compared to periods of ∂p′~/∂x<0.
Flow Experiments in Microjunction Networks
Authors: Henderson Andrew W. , Yasar Ozlem , Muvadgah Ane Joan , Lemley Evan C. 
Published: July 2013

Laminar flow dominates microscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been focused on turbulent flow conditions that exist in larger scale piping systems. There is a need for laminar flow studies of energy losses in junctions and networks of junctions so that engineers can better predict, design, and analyze flow in microscale systems. Unlike in the turbulent regime, Reynolds number plays a dominant role in energy losses for laminar flow. Studies focused on Reynolds number dependence are needed.
This paper documents laminar flow experiments in networks constructed from microscale junctions (microjunctions). This work builds on previous experience of the authors in computational fluids dynamics simulations of junctions and networks of junctions. The planar junctions studied consist of circular tubes with two outlets and one inlet. A general technique has been developed to produce computer and physical models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. There have been several techniques used to create the experimental microjunction networks: a “lost wax” method that creates the network in Polydimethylsiloxane (PDMS), stereolithography-based junctions connected by tubing, and photopolymer cured by ultraviolet radiation. Results are presented for pressure losses in various microjunction networks as a function of Reynolds number.
Modeling of Falling Film in Vertical Downward Two-Phase Pipe Flow
Authors: Lopez Jose M. , Mohan Ram , Shoham Ovadia , Gomez Luis , Kouba Gene 
Published: July 2013

Falling liquid films in vertical pipes are found in a variety of different industrial applications and industrial equipment, such as downcomers, caisson separators and reactors. The hydrodynamics of the falling film in vertical two-phase pipe flow can affect droplet entrainment, gas entrainment, and pressure drop. Therefore, a mechanistic model for prediction of falling liquid film thickness, falling liquid film velocity and a correlation for liquid droplet entrainment fraction in vertical downward liquid-gas systems has been proposed.
The falling film model developed is based on applying momentum balance on the liquid film. The liquid film is assumed to be in steady-state, incompressible and free of entrained gas. The mechanistic model includes both the developing and the developed regions. The shear effect between the gas core and the falling liquid film is considered. The liquid droplet entrainment fraction traveling in the gas core is considered and a new correlation for its prediction is proposed. Detailed uncertainty analysis is performed for liquid film thickness and liquid film velocity model predictions, including Monte Carlo simulation. Predicted liquid film thickness, liquid film velocity and liquid droplet entrainment fraction are validated against experimental data for different liquid fluid properties, such as water, Conosol mineral oil (light oil) and Drake mineral oil (heavy oil).
Application of Deterministic Correlations in the Analysis of Rotor-Stator Interactions in Axial Flow Fans
Authors: Galdo Vega Mónica , Rodriguez Lastra María , Argüelles Diaz Katia María , Fernández Oro Jesús Manuel 
Published: July 2013

Deterministic stresses account for the time-averaged contribution of the periodic unsteadiness in single-stage turbomachinery. An accurate modelling of these stresses allows for the development of steady simulations with full contribution of deterministic unsteady sources. Moreover, introducing both relative and absolute reference frames, the deterministic tensor can be split into a set of correlations which addresses the influence of the stator and rotor non-uniformities separately. As a consequence, a pure unsteady term showing rotor-stator interaction is rediscovered and can be established as an essential indicator of the strength of viscous, non-linear effects in multistage turbomachinery environments.
This work provides a comprehensive description of these correlations in the interrow region of a single stage axial flow fan. Two configurations are analyzed here: the upstream stator acting as a non-uniform inflow for the rotor and the complementary stator placed downstream of the rotor for pressure recovery at the exit. To illustrate the driven mechanisms in the tensor, a three-dimensional numerical simulation at the midspan section of a low-speed axial fan is employed in the present investigation. A deep analysis of the interaction between the rows using the deterministic framework is shown as a useful tool to devise deterministic models for steady computations.
The commercial code FLUENT is used to resolve the full unsteady 3-D Navier-Stokes equations using LES schemes. Nominal and off-design flow conditions have been considered to observe the relevance of the different deterministic correlations in the establishment of the unsteady sources.
The final objective pursues a deep understanding of the correlations behavior under variable flow conditions and different stage configurations. Thus, physical insight will be gained and more efficient and reliable deterministic models could be proposed, available for researchers and experts in the field.
Optimization of the Porosity Distribution in Transonic Wind Tunnel
Authors: Marino Antonello , Bonfiglioli Aldo 
Published: July 2013

During past years, to improve the quality of wind tunnel data in transonic configurations, researchers first designed new wind tunnel geometries (as porous and/or slotted wind tunnels), then developed more accurate correction laws giving acceptable results in certain conditions but absolutely not sufficient to satisfy the increasing aeronautical requirements. Recent studies showed that the quality of wind tunnel data can be improved by using test sections provided with variable streamwise porosity distributions instead of the typical uniform ones. Some authors identified this new concept of variable porosity distribution as the third generation of porous wind tunnels.
In order to improve knowledge about effects of the porosity distribution on the wall interference in subsonic/transonic conditions, an experimental investigation was carried out in the PT-1 CIRA transonic wind tunnel in the Mach range between 0.3 and 0.9 (over 400 test points were measured on different models and wall porosity configurations). At this aim, a dedicated experimental setup consisting in five plates positioned on the top and bottom walls of the PT-1 porous test section, has been designed and realized. Setting independently each plate, it is possible to obtain practically unlimited combinations of porosity distributions along the streamwise direction.
The final purpose of the present activity was to evaluate the optimal porosity distribution able to minimize wind tunnel wall interferences in the considered Mach range. The huge number of factors (Mach number and the positions of the five plates setting the porosity distribution) made practically impossible to study the porosity distribution effects by using a traditional One Factor At a Time (OFAT) approach. Therefore, the optimum porosity distribution has been achieved through an experiment designed with a Modern Design of Experiment (MDOE) approach. Within the MDOE approach, the RSM (Response Surface Modeling) has been selected. The objective of the experiment, designed with the RSM approach, is to acquire a sufficient number of data to create one or more response surface models to be used to predict the response variable of interest (within a specified uncertainty) as function of the factors which can affect the selected response variables.
The best porosity distribution able to improve the quality of wind tunnel data has been found for the PT-1 Wind Tunnel (but results and/or the procedure are applicable to all similar Wind Tunnels).
In the present paper, to contextualize the activity, after a short summary of the historical wind tunnel development, the stat of art of the variable streamwise porosity distribution is discussed. Then, the experimental setup to simulate in wind tunnel several streamwise variable porosity distribution and the design of Experiment are described. Finally, the main experimental results are reported and critically analyzed.
SOFC Modeling at the Cell Scale Including Hydrogen and Carbon Monoxide as Electrochemically Active Fuels
Authors: Andersson Martin , Navasa Maria , Yuan Jinliang , Sundén Bengt 
Published: July 2013

Fuel cells are promising for future energy systems, because they are energy efficient and able to use renewable fuels. A fully coupled computational fluid dynamics (CFD) approach based on the finite element method (with the software COMSOL Multiphysics) in two-dimensions is developed to describe an intermediate temperature solid oxide fuel cell (SOFC) single cell. Governing equations covering heat, gas-phase species, momentum, ion and electron transport are implemented and coupled to kinetics describing internal reforming and electrochemical reactions. Both hydrogen and carbon monoxide are considered as electrochemically active fuels within the anode.
The activation polarization in the electrodes and the ohmic polarization due to ion transport in the YSZ material are found to be the major part of the potential losses. The activation polarization is the most significant and it is smaller within the cathode compared to the anode for this study. The ion current density and the activation polarization are the highest at the electrolyte-electrode interface and decrease rapidly within the electrodes as the distance from the interface increases. However, the ohmic polarization by ion transfer increases for the positions away from the interface. The addition of the electrochemical reaction with CO as fuel increases the current density. It is concluded that the temperature and current density are strongly integrated and when any of them is changed, the other follows, and the change is accelerated.
Manufacturing Process Modeling of 100-400 kWe Combined Heat and Power Stationary Fuel Cell Systems
Authors: Warren Joshua , Das Sujit , Zhang Wei 
Published: July 2013

Despite significant cost reductions and reliability improvements in recent decades, combined heat and power (CHP) stationary fuel cells are expected to remain relatively limited in their commercial acceptance until additional advancements are realized.
In the present study, three stationary CHP fuel cell technologies — phosphoric acid (PAFC), molten carbonate (MCFC), and solid oxide (SOFC) — operating in the 100–400 kWe range were examined with process based cost models to estimate manufacturing costs and to highlight high cost steps where alternative production methods may have the greatest potential for high impact cost reduction. PAFC manufacturing costs, estimated to be $3049/kWe for a baseline manufacturing volume of 20 MWe/yr, may benefit most from reduced catalyst loading, lower cost substrates, reduced fuel processing balance of plant (BOP) costs, and near net shape bipolar plate manufacturing. MCFC manufacturing costs, while not reported in detail due to the proprietary nature of inputs employed in the model, may be reduced through advances in fuel desulfurization and stainless steel stack component manufacturing. SOFC manufacturing costs, estimated to be $1242/kWe, approach a commercially acceptable level, but significant advancements in seal and bipolar plate reliability are likely required before a commercially acceptable stack life of 40,000 hours is realized.