Academic literature on the topic 'COMSOL modul Thin-Film Flow'
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Journal articles on the topic "COMSOL modul Thin-Film Flow"
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Hingawe, Nilesh D., and Skylab P. Bhore. "Tribological performance of a surface textured meso scale air bearing." Industrial Lubrication and Tribology 72, no. 5 (October 26, 2019): 599–609. http://dx.doi.org/10.1108/ilt-04-2019-0146.
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Purpose The purpose of this study is to improve the tribological performance of meso scale air journal bearing by adopting texture on the bearing surface. Design/methodology/approach The present study is based on numerical analysis. The detailed numerical investigation is carried out using a fluid flow based thin-film model in COMSOL 5.2 software. Findings The influence of texture design parameters: geometry (shape, orientation and slender ratio), and position on the tribological performance of meso scale air journal bearing is investigated. It is found that texture shape has a strong influence on the tribological characteristics such as load capacity and friction coefficient of the bearing. Slender texture improves the load capacity, but it has a negligible effect on the reduction of friction coefficient. In contrast, texture orientation is found to be insignificant for both increasing load capacity and decreasing friction coefficient. Furthermore, the maximum improvement in load capacity is obtained for partially textured bearing, but the minimum friction coefficient is achieved for full texturing. Originality/value The present study investigates the influence of texture design parameters viz geometry (shape, orientation and slender ratio), and position on the tribological performance of meso scale air journal bearing.
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Folgerø, Kjetil, Kjetil Haukalid, Jan Kocbach, and Andreas Soto Peterson. "Combined Thickness and Permittivity Measurement of Thin Layers with Open-Ended Coaxial Probes." Sensors 19, no. 8 (April 12, 2019): 1765. http://dx.doi.org/10.3390/s19081765.
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This paper presents a method to simultaneously determine the thickness and permittivity of thin layers from multi-frequency reflection coefficient measurements using an open-ended coaxial probe. This is achieved by exploiting that the probe becomes radiating at frequencies higher than the probe’s typical operating range. Permittivity information is extracted from measurements in the typical frequency range, whereas thickness information is obtained from high frequency measurements by exploiting resonances that occur when the radiated waves are reflected at the layer boundary. A finite element model of the measurement set-up is made in COMSOL MultiphysicsTM, and a matrix of simulations spanning the relevant layer thicknesses and permittivity range is generated. The measured permittivity spectra of unknown samples are compared to the simulation matrix to estimate layer thickness and permittivity. The method is verified by measurements of water–ethanol mixtures. An application example where the water fraction and layer thickness of a gas hydrate deposition layer is estimated from permittivity measurements in a multiphase flow loop is also presented.
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Shinde, Anil B., and Prashant M. Pawar. "Effect of partial grooving on the performance of hydrodynamic journal bearing." Industrial Lubrication and Tribology 69, no. 4 (July 10, 2017): 574–84. http://dx.doi.org/10.1108/ilt-06-2016-0124.
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Purpose This study aims to improve the performance of hydrodynamic journal bearings through partial grooving on the bearing surface. Design/methodology/approach Bearing performance analysis is numerically carried out using the thin film flow physics of COMSOL Multiphysics 5.0 software. Initially, the static performance analysis is carried out for hydrodynamic journal bearing system with smooth surface, and the results of the same are validated with results from the literature. In the later part of the paper, the partial rectangular shape micro-textures are modeled on bearing surface. The effects of partial groove pattern on the bearing performance parameters, namely, fluid film pressure, load carrying capacity, frictional power loss and frictional torque, are studied in detail. Findings The numerical results show that the values of maximum fluid film pressure, load carrying capacity, frictional power loss and frictional torque are considerably improved due to deterministic micro-textures. Bearing surface with partial groove along 90°-180° region results in 81.9 per cent improvement in maximum fluid film pressure and 75.9 per cent improvement in load carrying capacity as compared with smooth surface of journal bearing, with no increase in frictional power loss and frictional torque. Maximum decrease in frictional power loss and frictional torque is observed for partially grooving along 90°-360° region. The simulations are supported by proof-of-concept experimentation. Originality/value This study is useful in the appropriate selection of groove parameters on bearing surface to the bearing performance characteristics.
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Caro, C. G., C. L. Dumoulin, J. M. R. Graham, K. H. Parker, and S. P. Souza. "Secondary Flow in the Human Common Carotid Artery Imaged by MR Angiography." Journal of Biomechanical Engineering 114, no. 1 (February 1, 1992): 147–49. http://dx.doi.org/10.1115/1.2895439.
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The blood flow in arteries affects both the biology of the vessels and the development of atherosclerosis. The flow is three dimensional, unsteady, and difficult to measure or to model computationally. We have used phase-shift-based magnetic resonance angiography to image and measure the flow in the common carotid arteries of a healthy human subject. There was curvature of the vessels and thin-slice dynamic flow imaging showed evidence of the presence of secondary motions. Flexing the cervical spine straightened the vessels and reduced the asymmetry of the flow.
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Shen, Xiaoyan, Jing Yu, Jianlong Yin, and Dongsheng Li. "Experimental Study of See-Saw Mode Nano-Vibration on Orifice-Type Restrictors." Applied Sciences 11, no. 11 (June 6, 2021): 5265. http://dx.doi.org/10.3390/app11115265.
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Slide stability is key to the aerostatic guide in ultra-precise machines; thus, it has garnered plenty of attention. Macro-scale studies are commonplace, but micro- and nano-vibration issues require more attention. Microscope vibration is mainly caused by tiny changes in the fluid parameters of lubricating gas film, which is complex and has no verdict. In this case, slide-gas interaction should be considered. In this study, the widely used orifice-type restrictor was investigated for its nano-vibration performance. A Comsol finite-element-method fluid–structure interaction model was used to simulate and analyze an orifice-type restrictor, and orifice-restrictor vibration characteristics at the nanometer scale were inspected using a high-performance laser vibrometer. The results demonstrate that see-saw mode vibrations occur in the restrictors, growing stronger with increased air-supply pressure. The see-saw vibration’s axis is speculatively determined based on orifice and restrictor structures, and the vibration type is related to the number of orifices. The results also show that the vibration is random with natural frequencies at the kilohertz level. The newly provided research results are beneficial for better understanding the nano-vibrations of orifice-type restrictors.
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Qi, Bo, and Zhang Yong. "Tribological study of piston–cylinder interface of radial piston pump in high-pressure common rail system considering surface topography effect." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, no. 9 (November 22, 2019): 1381–95. http://dx.doi.org/10.1177/1350650119887820.
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Based on the theory of thermal fluid dynamic lubrication, the Reynolds equation and energy equation of the average flow of a piston–cylinder interface of a radial piston pump in a high-pressure common rail system are established, considering the surface topography effect. The tribological properties of the piston–cylinder interface are calculated by solving the Reynolds equation and energy equation. A surface wear model is established and the wear distribution and trend of the piston–cylinder interface are studied. The wear characteristics of the piston–cylinder interface are verified through experiment, and the wear lubrication of the piston–cylinder interface is discussed. The surface topography effect has a considerable influence on the characteristics of the piston–cylinder interface film. Different surface morphologies change the film characteristics of the piston–cylinder interface, yielding different wear behaviors on the mating surface. The wear of the piston–cylinder interface first decreases along the film outlet to the inlet and then rises. The cylinder surface mainly exhibits abrasive, cavitation, and micro-convex scratch wear, whereas the piston surface mainly shows cavitation wear. The results obtained in this study are of considerable significance as they reveal the tribological properties of the piston–cylinder interface under the surface topography effect.
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Ghosh, Partha Sarathi, Abhishek Sen, Somnath Chattopadhyaya, Shubham Sharma, Jujhar Singh, Shashi Parkash Dwivedi, Ambuj Saxena, Aqib Mashood Khan, Danil Yurievich Pimenov, and Khaled Giasin. "Prediction of Transient Temperature Distributions for Laser Welding of Dissimilar Metals." Applied Sciences 11, no. 13 (June 23, 2021): 5829. http://dx.doi.org/10.3390/app11135829.
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Distribution of temperature during the welding process is essential for predicting and realizing some important welding features such as microstructure of the welds, heat-affected zone (HAZ), residual stresses, and their effects. In this paper, a numerical model was developed using COMSOL Multiphysics of dissimilar laser welding (butt joint) of AISI 316L and Ti6Al4V thin sheet of 2.5 mm thickness. A continuous mode (CW) fiber laser heat source of 300 W laser power was used for the present study. A time-dependent prediction of temperature distributions was attempted. The heat source was assumed as a Hermit–Gaussian analytical function with a moving velocity of 120 mm/min. Both convective and radiant heat loss and phase change of the materials were considered for the analysis. In addition, variation of temperature-dependent material properties was also considered. The maximum and minimum temperature for the two materials at different times and the temperature in the different penetration depths were also predicted. It was found that the average temperature that can be achieved in the bottom-most surface near the weld line was more than 2400 K, which justifies the penetration. Averages of maximum temperatures on the weld line at different times at the laser spot irradiation were identified near 3000 K.The temperature fluctuation near the weld line was minimal and decreased more in the traverse direction. Scanning with a displaced laser relative to the interface toward the Ti6Al4V side reduces the maximum temperature at the interface and the HAZ of the 316L side. All of these predictions agree well with the experimental results reported in current literature studies.
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Voznesensky, A. S., and L. K. Kidima-Mbombi. "Formation of synthetic structures and textures of rocks when simulating in COMSOL Multiphysics." Gornye nauki i tekhnologii = Mining Science and Technology (Russia) 6, no. 2 (July 14, 2021): 65–72. http://dx.doi.org/10.17073/2500-0632-2021-2-65-72.
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Rock texture and structure play an important role in the formation of the rock physical properties, and also carry information about their genesis. The paper deals with the simulation of geometric shapes of various structures and textures of rocks by the finite-element method (FEM). It is carried out by programmed detailing of the element properties and their spatial location in the simulated object. When programming structures, it is also possible to set the physical properties of various parts of the model, grids, initial and boundary conditions, which can be changed in accordance with the scenarios for numerical experiments. In this study, on the basis of FEM, simulation of various structures and textures of rocks with inclusions and disruptions was implemented in COMSOL Multiphysics in conjunction with Matlab. Such structures are used to conduct computer generated simulations to determine physical properties of geomaterials and study the effect on them of agents of various physical nature. The building of several models was considered: a rock specimen with inclusions in the form of ellipses of equal dimensions with different orientations; a sandstone specimen containing inclusions with high modulus of elasticity in cement matrix when deforming; a limestone specimen with fractures filled with oil and saline water when determining its specific electrical resistance. As an example of a fractured structure analysis, the influence of the filler on the electrical resistance of the limestone specimen containing a system of thin elliptical predominantly horizontal fractures was considered. The change in the lines of current flow at different ratios between the matrix and the fracture filler conductivities and their effect on the effective (averaged) conductivity of the rock specimen was clearly demonstrated. The lower conductivity of the fracture filler leads to increasing the length and decreasing the cross-section of the current flow lines that, in turn, leads to significant decrease in the conductivity of the fractured rock specimen. The higher filler conductivity results in a slight increase in the conductivity of the fractured specimen compared to that of the homogeneous isotropic specimen. The resulting structures can be used for numerical experiments to study physical properties of rocks.
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Fuhrmann, Jürgen, Hong Zhao, Ekkehard Holzbecher, and Hartmut Langmach. "Flow, Transport, and Reactions in a Thin Layer Flow Cell." Journal of Fuel Cell Science and Technology 5, no. 2 (April 11, 2008). http://dx.doi.org/10.1115/1.2821598.
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The performance of fuel cells depends on the rate parameters of the kinetic reactions between the involved species, among other conditions. The determination of these parameters is crucial for the understanding of the functionality of fuel cells. Differential electrochemical mass spectroscopy in thin layer flow cells is used as a tool to gain improved understanding of the heterogeneous catalytic reactions taking place in fuel cell catalytic layers. In this paper, we focus on the description of thin layer cells by numerical models based on partial differential equations and the extraction of kinetics parameters by inverse modeling. For the model setup, various software tools are used. The simulation of laminar free flow is performed by the commercial code COMSOL. A finite volume code is used for the simulation of the reactive transport. The latter is coupled with a Levenberg–Marquardt algorithm for the determination of kinetic constants. Two designs of thin layer flow cells are considered: a cylindrical and a rectangular design. A drawback of the cylindrical cell design is the highly inhomogeneous velocity field leading to spatial variations of the conditions for electrode reactions. In contrast, the rectangular cell design shows a homogeneous flow field in the vicinity of the catalyst. The rectangular cell design has the additional advantage that flow is essentially two dimensional and can be computed analytically, which simplifies the numerical approach. The inverse modeling procedure is demonstrated for a hydrogen-carbon monoxide system.
Dissertations / Theses on the topic "COMSOL modul Thin-Film Flow"
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Brhlík, Rostislav. "MKP simulace elastohydrodynamického kontaktu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231788.
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This diploma thesis deals with an application of the finite element method on elastohydrodynamic (EHD) lubrication simulations. Commercially available software COMSOL is used for the computation, while two different modules for modeling EHD lubrication are described in a detail. Firstly, a new approach using the module Thin-Film Flow is developed, considering and describing some limitations of this approach. This is the very first published work dealing complex with EHD simulation in Thin-Film Flow module. In the second part of the thesis, there was created a model of line contact using the module for the introduction of partial differential equations (PDE). The model is partially verified with available works for different values of the input parameters. Subsequently, the velocity effect of the contact surfaces on the pressure and the lubricant thickness in contact is analyzed. Finally, the last part is examines the influence of the values of some parameters on the final value of the contact pressure and the lubricant thickness, as well as on numerical stability of the entire model.
Conference papers on the topic "COMSOL modul Thin-Film Flow"
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Abyaneh, M. H. J., and M. H. Saidi. "Velocity Distributions in (r,θ) Directions for Laminar Flow of a Film Around Horizontal Circular Tube." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98087.
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Velocity distributions in (r,θ) directions are evaluated by solving simultaneous simplified Navier-Stokes equations (NSE) and continuity equation (CE) in polar coordinate. The analysis is based on steady state laminar flow of thin falling liquid film on a horizontal circular tube, for cases in which traction on the film surface is considered negligible. It is a common geometry for part of engineering problems such as evaporator, condenser, absorber, generator of absorption chillers and other similar units in mechanical and chemical engineering. Knowledge of the velocity profiles is usually needed for: 1- solving governing energy and species equations 2- estimating the average and film surface velocity, and 3- evaluating film thickness distribution and its gradient. Two models of velocity distributions are considered, namely actual model and simplified model. Models are compared not only with each other but also with semi actual model in (x,y) coordinate given in the literatures. The average and film surface velocity profiles and film thickness distribution for these models have been shown in various conditions. The results clearly show that the larger flow rates and/or smaller tube diameter increases the calculation error.
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Tichy, John, and Benyebka Bou-Sai¨d. "The PTT Model in Hip Joint Replacement: Shock Loading." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63979.
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The Phan-Thien Tanner (PTT) model is one of the most widely used rheological models. It can properly describe all the common characteristics of viscoelastic non-Newtonian fluids. Synovial fluid of human joints, which also lubricates artificial joints, is well known to be highly viscoelastic. Thus it is reasonable to attempt to describe such joint behavior using non-Newtonian flow models. Modeling the geometry of the total hip replacement, the PTT model is applied in spherical coordinates to a thin confined fluid film. As an illustrative problem, the case of a sudden impulsive start of simple squeezing motion is solved, similar to landing on one’s feet after a vertical jump. The phenomena of shear thinning, stress relaxation, and stress overshoot are all exhibited.
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Younes, Amen M., and Ibrahim Hassan. "An Analytical Model of Flow Boiling Heat Transfer for Slug Flow in a Single Circular Horizontal Micro-Channel." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-87468.
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Slug flow is one of the most common flow patterns that occur during flow boiling in horizontal micro-channels. In the present work, an analytical model of flow boiling heat transfer is developed for slug flow in a single circular horizontal micro-channel under a uniform heat flux. The heat transfer is affected mainly by the liquid film thickness confined between the vapor slug and the channel wall. For more physical and reliable flow boiling heat transfer model, the liquid film thickness variation and pressure gradient effects on the flow boiling heat transfer coefficient are considered. The influence of vapor quality on heat transfer coefficient, vapor velocity and liquid film velocity is studied. The model is constructed based on the conservation equations of the separated two phase flow. The interphase surface is assumed to be smooth and the flow is a laminar flow. The obtained model applied for flow boiling of R-134a refrigerant in the slug flow at a narrow vapor quality range (0.0 < x < 0.1). The heat transfer coefficient showed a high increase close to the low vapor quality while decreases gradually after the peak. Furthermore, the vapor velocity increases linearly by increasing the vapor quality while, the liquid film velocity decreases.
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Kefalas, Alexander, Friedrich-Karl Benra, Dieter Brillert, and Hans Josef Dohmen. "Comparison of Different Numerical Approaches for Determination of Compressible Fluid Flow in Narrow Gaps." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57898.
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The prediction of fluid flow through a narrow gap is a characteristic problem in fluid mechanics. In today’s turbomachinery, several applications in bearing and sealing technology are based on the phenomena of two surfaces being separated by a thin fluid film of only a few micrometers. The common method for analyzing the non-contact application’s performance usually applies the lubrication theory based on the Reynolds equation. This two-dimensional model is based on the assumption of a laminar viscous flow field, isothermal conditions and it takes aerostatic as well as aerodynamic effects into account. In cases of a complex geometry and challenging flow conditions this approach has its limitations. The usage of commercial state of the art computational fluid dynamics (CFD) software allows the circumvention of these restrictions. As a matter of fact CFD simulations take up high effort in terms of preparation and calculation time. The present contribution compares the numerical approaches with regard to the application’s performance accuracy and calculation effort, using the example of a dry gas seal. To extend the Reynolds equation’s applicability to a wide variety of geometries, a method for implementing the topography design with high fidelity is depicted. The numerical methods are performed for various dry gas seal designs at different operating conditions and are compared with reference data.
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Baldauf, Stefan, and Michael Scheurlen. "CFD Based Sensitivity Study of Flow Parameters for Engine Like Film Cooling Conditions." In ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-310.
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A standard CFD code with two-layer k-ε-model was used to calculate film cooling effectiveness of flat plate test cases. Experimental data from the literature were taken to perform extensive validation of the code for film cooling effectiveness prediction. Emphasis was put on injection of cooling gas through one row of cylindrical holes in the streamwise direction. Blowing ratio, density ratio, blowing angle, pitch, and hole length to diameter ratio were varied in a wide range. It was found that the code is well suited for the prediction of lateral averaged film cooling effectiveness for common film cooling conditions. A similarity analysis is presented for the prescribed film cooling problem to isolate the influence parameters of flow properties and geometry. A reduction of the parameters of influence was achieved using physical implications. The magnitude of the remaining parameters was compared for literature reported experimental results and gas turbine applications. It was found that experimental realized Reynolds and Eckert numbers are mostly far from turbine engine conditions. Therefore the validated CFD code was used to extrapolate the experimental configuration to engine like conditions. It was found that the examined Reynolds and Eckert numbers had no significant impact on lateral averaged film cooling effectiveness. It is hence possible to present a reduced but complete set of the governing influence parameters on the discussed film cooling problem.
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Bacci, Alessandro, and Bruno Facchini. "Turbulence Modeling for the Numerical Simulation of Film and Effusion Cooling Flows." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27182.
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RANS simulations are known to suffer from serious deficiencies in the prediction of jet in a crossflow (JCF) because of the high complexity of this kind of flow. Particularly, the coherent structures resulting from the interaction of the two flow streams are characterized by a highly unsteady and anisotropic behavior which hardly stresses the hypotheses underling common eddy viscosity models (EVMs). Direct numerical simulation (DNS) and large eddy simulation (LES) methodologies are still excessively computationally intensive to be used as ordinary design tools. Therefore, the development of reliable RANS turbulence models for film cooling flows deserved a great deal of attention from the gas turbine community. Computations presented in this work were carried out using a modified k-ε turbulence model specifically designed for film cooling flows. The model, due to Lakehal et al., is based on the usage of an anisotropic eddy viscosity. The model has been implemented in the framework of a CFD commercial package through the user subroutine features. Computational model is developed following the suggestions of Walters and Leylek concerning the correct representation of the problem geometry and the location of the boundary conditions. The predictive capabilities of the model concerning the ability to capture the main flow structures as well as heat transfer features are investigated. Comparison of computed adiabatic effectiveness profiles with experimental measurements is provided in order to quantitatively validate the model. Results obtained with standard EVMs, particularly a two layer standard k-ε model, are also shown in order to reveal the improvements in the predictive capabilities resulting from the modified models.
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Poitras, Ge´rard J., Laurent-E. Brizzi, and Yves Gagnon. "Flow Over Model Buildings With Sloped Roofs." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45518.
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The flow field around model buildings with different sloped roofs was investigated using Particle Image Velocimetry (PIV). The flow around model buildings having flat roofs was studied by many authors. Although buildings with sloped roofs are the most common type of low rise buildings, the flow around these buildings are not well known. Most of the studies for these types of buildings were made for the determination of surface pressures. The aim of this study is to highlight the fundamental differences between flat roofs and sloped roofs for three-dimensional obstacle flows. The experiments were performed in a wind tunnel having a cross section of 300 mm × 400 mm. All the models were 30 mm high (vertical wall) and were placed in a thin turbulent boundary layer. Three Reynolds numbers, based on the height of the obstacle, were used (12000, 22 000, 32 000). Furthermore, the quantitative data is analyzed and statistical results describing the mean and fluctuating velocity fields are presented. Finally, the surface pressures on the median plane were studied in order to correlate these pressures with the flow topology of different sloped roofs. It was found that upstream of the obstacle, the flow topology for the model having sloped roofs was similar to that of a flat roof apart from an increase in size of the well-known horseshoe vortex. However, the flow topology is not the same over different roofs, on the sides of the models and immediately downstream of the models. For the Reynolds number studied, there are no coherent flow structures over the upstream sloped roofs while an arch vortex is created on the sides of the models. This arch vortex is similar to the arch vortex that is created over a flat roof. An arch vortex is also present downstream of the models. The lower part of this vortex is similar to the one created for a flat roof. However, the upper part of the arch vortex starts from the tip of the roof and continues downstream and has an ellipse shape. This vortex also increases in size with the slope of the roof.
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Rutledge, James L., Marc D. Polanka, and Nathan J. Greiner. "CFD Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56760.
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The hostile turbine environment requires that film cooling designs are tested in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods is best suited to provide scaled film cooling performance. Furthermore, precise matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched. A computational simulation of an engine scale film cooled leading edge geometry at high temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low temperature experimental conditions with a 10x scale model. Matching was performed with three common coolant types used in low temperature film cooling experiments — room temperature air, CO2, and cold air to match density ratio. Results indicate that matched momentum flux ratio is the most appropriate for matching adiabatic effectiveness for the case of room temperature air coolant, but also matching density ratio through either CO2 or cold coolant has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches density ratio.
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Cable, Justin, and Kevin R. Anderson. "Fabrication and Multiphysics Modeling of MEMS Thermal Flow Sensor." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-4606.
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Abstract A micromachined thermal flow sensor is presented demonstrating sensing liquid flow rates as low as 2 microliters per minute capable of being used for biomedical applications. These flow sensors rely on the varying electrical resistance of sensors generated by forced convection at different flow rates. The sensor array presented was constructed using microelectromechanical systems (MEMS) techniques including micro-molding, wet etching and dry etching utilizing biocompatible materials. A numerical model was built using COMSOL multi-physics in order to predict and optimize the electrical, thermal and fluid behavior of the sensor, which was verified with experimental data. The construction allowed for multiple thermal flow sensing operational modes. Here, constant current hot film and constant current calorimetric were simulated and tested. A variety of flow sensor geometries were compared to investigate maximum heat transfer to the sensors, thermal insultation, size, sensitivity and range capabilities. The sensor design is such that it is capable of detecting different flow direction and various flow ranges for different fluids. In addition to the performance capabilities outlined, the sensor is relatively inexpensive and should have a long lifetime due to the lack of moving parts.
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Tabak, Ahmet Fatih, and Serhat Yes¸ilyurt. "Numerical Analysis of the 3D Flow Induced by Propagation of Plane-Wave Deformations on Thin Membranes Inside Microchannels." In ASME 2007 5th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2007. http://dx.doi.org/10.1115/icnmm2007-30135.
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Propulsion mechanisms of microorganisms are based on either beating or screw-like motion of thin elastic biopolymers. Arguably, this motion is optimal for propulsion at very low Reynolds numbers. Similar actuation mechanisms can be utilized in the design of an autonomous microswimmer or even a micropump. In principle, propagation of plane-wave deformations on a thin-membrane placed inside a channel can lead to a net flow in the direction of the wave propagation. In this study we present effects of the amplitude, frequency, and the width of the membrane on the time-averaged flow rate and the rate of work done on the fluid by the membrane by means of three-dimensional transient simulations of flows induced by plane-wave deformations on membranes. Navier-Stokes and continuity equations are used to model the flow on a time-varying domain, which is prescribed with respect to the motion of the membrane. Third party commercial software, COMSOL, is used in to solve the finite-element representation of the 3D time-dependent flow on moving mesh. Numerical simulations show that the flow inside the microchannel depends on the square of the amplitude and is proportional to the excitation frequency. Lastly, characteristic flow rate vs. pressure head curve and efficiency of a typical pump are obtained from 3D transient simulations, and presented here.