Volume 7: Fluids Engineering最新文献

{"title":"Jet Initiation After Drop Impact on Micropatterned Hydrophilic Surfaces","authors":"Anayet Ullah Siddique, F. Zhao, M. Weislogel, H. Tan","doi":"10.1115/imece2019-11500","DOIUrl":"https://doi.org/10.1115/imece2019-11500","url":null,"abstract":"\u0000 Droplet-wall impacts are well known to produce a wide variety of outcomes such as spreading, splashing, jetting, receding, and rebounding from hydrophobic and superhydrophobic surfaces. In this work, we focus on the growth of jets that form during the partial recoil of liquid droplets that impinge upon hydrophilic substrates composed of cylindrical micro-pillars of various dimensions and distributions (i.e., height, width, pillar spacing, etc.). Micro-pillars are fabricated on the hydrophilic silicon wafers by standard microfabrication processes, including metal etch mask patterning by photolithography, metal deposition, and lift-off to achieve the designed pillar shapes and spacing, and followed by dry etching for various pillar heights. Micrometer-sized drops of glycerol mixtures impacting micro-structured wafers are investigated using high-speed video photography. Impact velocities are varied to observe the influence of Weber number on the dynamic properties of the rebounding jet and jet initiation time, as well as whether or not the jet detaches ejecting satellite droplets normal to the substrate surface. The specific influence of the micro-patterned surfaces on maximum spreading, jet formation, jet tip velocity, and jet ejection is characterized. We find that the micro-patterned substrates have a significant effect on the behavior of the drop impact and jetting mechanism. From our experiments, we find that jet velocity is approximately 4 times that of the drop impact velocity. The jet formation time is shown to follow the capillary time scale as (ρDi3/σ)½ (where ρ, Di, and σ are density, initial droplet diameter, and surface tension, respectively).","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"59 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126959017","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Prediction of Transversal Flow in Non-Circular Tubes With a Higher Order Constitutive Equation","authors":"M. Letelier, D. Siginer, P. Merino, J. Stockle","doi":"10.1115/imece2019-12062","DOIUrl":"https://doi.org/10.1115/imece2019-12062","url":null,"abstract":"\u0000 In this paper we explore the potential of an explicit constitutive equation in predicting secondary flows in straight, non–circular tubes in steady and fully developed flow. We show that secondary flows appear at first order in k a constitutive parameter in the new constitutive structure when solving the field through an asymptotic approach. The structure of the transversal stream–function predicted by the new structure is the same as that obtained at third order in Weissenberg number with the Modified Phan–Thien–Tanner constitutive equation aside from constitutive constants. We present predictions of the velocity field and a comparison with the corresponding predictions of the MPTT model. These results are obtained using the analytical algorithm based on the shape factor concept coupled with asymptotic expansions developed and used previously by the authors to solve related problems.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125913760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Secondary Flows in Eccentric-Annular Tubes","authors":"M. Letelier, D. Siginer, Diego L. Almendra, J. Stockle","doi":"10.1115/imece2019-11548","DOIUrl":"https://doi.org/10.1115/imece2019-11548","url":null,"abstract":"\u0000 In this paper, transversal flow field of nonlinear viscoelastic fluids abiding by the modified-Phan-Thien-Tanner (MPTT) constitutive model in straight tubes of eccentric-annular cross-section is investigated. An analytical solution is developed based on an asymptotic expansion in terms of the Weissenberg number coupled with the shape factor method a one-to-one mapping taking the circular cross-section into the eccentric annular cross section. The analysis reveals the formation of transversal flows due to elasticity and to the eccentricity parameter. The number of vortices in the cross-section depends on the ratio of the diameters in addition to the eccentricity parameter. The effect of these parameters on the vortical structure is explored for different values of the material parameters.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126332396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Convergence of PIV Measurements at the Inlet of a Turbocharger Compressor","authors":"D. Banerjee, A. Selamet, R. Dehner, Keith Miazgowicz","doi":"10.1115/imece2019-10461","DOIUrl":"https://doi.org/10.1115/imece2019-10461","url":null,"abstract":"\u0000 Particle Image Velocimetry has become a desirable tool to investigate turbulent flow fields in different engineering applications, including flames, combustion engines, and turbomachinery. The convergence characteristics of turbulent statistics of these flow fields are of prime importance since they help with the number of images (temporally uncorrelated) to be captured in order for the results to converge to a certain tolerance or with the assessment of the uncertainty of the measurements for a given number of images. The present work employs Stereoscopic Particle Image Velocimetry to examine the turbulent flow field at the inlet of an automotive turbocharger compressor without any recirculating channel. Optical measurements were conducted at five different mass flow rates spanning from choke to surge at a corrected rotational speed of 80 krpm. The velocity fields thus obtained were used to analyze the convergence of the mean (first statistical moment) and variance (second statistical moment) at different operating conditions. The convergence of the mean at a particular location in the flow field depends on the local coefficient of variation (COV). The number of required images for the mean to converge to a particular tolerance was also found to follow roughly a linear trend with respect to COV. While the convergence of the variance, on the other hand, did not appear to show any direct dependence on the coefficient of variation, it takes significantly more images than the mean to converge to the same level of tolerance.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132647362","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Implications of Non-Bingham Rheology","authors":"L. Pease, J. Bamberger, M. Minette","doi":"10.1115/imece2019-11841","DOIUrl":"https://doi.org/10.1115/imece2019-11841","url":null,"abstract":"\u0000 One of the key challenges now facing the US Department of Energy (DOE) is the fate of radioactive waste remaining from World War II and the Cold War, which is stored underground in tanks some 75 feet in diameter and over 30 feet tall. Over time, the waste has segmented into multiple layers with sludges and slurries at the bottom with salt crust layers often at the top and liquid in between. DOE’s current official baseline plans call for remaining sludges and slurries to be removed from the tanks and converted into a stable glass waste form. Minimizing worker exposure to radiation drives DOE to use slurry processing techniques to suspend, mobilize, transport, mix, and process the waste. Therefore, a clear and quantitative understanding of Hanford waste rheology is essential for the success of the DOE mission.\u0000 Historically much of the waste has been characterized using Eugene Bingham’s century old model that provides a straight line fit to higher shear rate data with the intercept suggesting a yield stress and the slope providing the consistency. Yet, Bingham fits overestimate the shear stress at a given shear rate for low to intermediate shear rates, exactly the range of shear rates typically encountered in pipe flow, where shear rates peak along the pipe wall and vanish in the center. This model produces a fictitious yield stress for some of the wastes that do not exhibit yield phenomena. While overestimating the yield stress may be prudent, safe, and conservative for some applications (e.g., pump sizing to ensure that pumps can handle yield stresses), overestimating the rheology may be inaccurate and non-conservative for other applications (e.g., eroding settled particle beds). Therefore, this paper evaluates the slurry rheology of Hanford and Savannah River wastes using a more modern rheological model that fits the full range of experimental data.\u0000 Although a bias has been recognized and alternative models proposed, the magnitude of this bias and the implications for tank waste have only been qualitatively suggested. The purpose of this paper is to evaluate quantitatively implications of the poor quality of fit between a Bingham model for rheology and experimental data at modest shear rates. We first demonstrate the magnitude of the bias between the data and the Bingham extrapolation. We then evaluate quantitatively the velocity profile under laminar conditions. This analysis shows that the bias may be large (hundreds of percent or more) at modest shear rates and that modest shear rates dominate pipe velocity profiles.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132668305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Micro-Hydrokinetic Turbine Operating in the Vicinity of a Free Surface: Multiphase Large Eddy Simulations","authors":"Bashar Attiya, Muhannad Altimemy, Cosan Daskiran, I-Han Liu, A. Oztekin","doi":"10.1115/imece2019-10899","DOIUrl":"https://doi.org/10.1115/imece2019-10899","url":null,"abstract":"\u0000 Large Eddy Simulation (LES) turbulence and multiphase Volume of Fluid (VOF) model are employed to predict the spatial and temporal characteristics of the turbulent flow structures near micro-hydrokinetic turbine operating in the proximity of a free surface. The turbine power performance and the free surface dynamics, and its interaction with the turbine are characterized by examining the results of both single-phase and multiphase flow simulations. Simulations are conducted at the turbine’s best efficiency point at a tip speed ratio of 1.86 with the rotation rate of 150 rpm and the free stream water velocity of 2.25 m/s. The multiphase flow simulation is carried out at Froude number of 1.06. The results indicate slight interaction between the deformed free surface and the turbine wake structures. Acceleration in the flow velocity is observed near the free surface due to the physical confinement. The results indicate that turbine power generation is reduced by about 2.0%, and the thrust coefficient is reduced by 1.60%. It is demonstrated that the turbine performance at this Froude number is hardly influenced by the presence of the free surface.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125292633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of Lateral Restraint on Thermocapillary Migration of Wetting Droplets","authors":"K. S. Sagar, K. Dwaraknath, A. Pattamatta, T. Sundararajan","doi":"10.1115/imece2019-11270","DOIUrl":"https://doi.org/10.1115/imece2019-11270","url":null,"abstract":"\u0000 The present study aims at studying the characteristics of thermocapillary migration with varying levels of lateral restraints. A temperature gradient is created by heating and cooling either side of the substrate. When a droplet is placed near hot side it spreads as thin film and migrates towards the cold side. The advancing end assumes the shape of a parabolic rim while the receding end stays as a thin film. It is observed that the droplet decelerates to attain a steady state velocity and undergoes slight acceleration near the cold end of the substrate. The observed velocity trend follows the temperature gradient on the substrate. The velocity increases with the droplet volume and substrate temperature gradient. The liquid viscosity is observed to have a diminishing effect on migration velocity. The effect of lateral spread confinement is studied by performing experimental trails on substrates with different widths. It is found that reducing the substrate width increases the migration velocity due to increased footprint resulting in larger thermocapillary force. The results observed in the present study highlights the importance of thermocapillary flows in many academic and industrial applications.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115544387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Analysis of a Stokes Flow Past a Cube (Friction and Diffusion Coefficients for Brownian Dynamics Simulations)","authors":"K. Okada, A. Satoh","doi":"10.1115/imece2019-10549","DOIUrl":"https://doi.org/10.1115/imece2019-10549","url":null,"abstract":"\u0000 Magnetorheological properties significantly depend on the regime of aggregate structures. In the case of cubic particles, closely-packed clusters that are significantly different from those for the case of spherical or rod-like particles are formed in the system since magnetic cube-like particles prefer a face-to-face contact with the neighboring particles. Therefore, a cubic particle suspension is expected to exhibit a sufficiently strong magnetorheological effect, which may be investigated by means of Brownian dynamics simulations. However, the translational and rotational diffusion (or friction) coefficients of a cube are not known and indispensable in order to develop this simulation technique. From this background, in the present study, we have analyzed the flow field around a cube in a Stokes flow regime in order to estimate the diffusion (or friction) coefficients of cube-like particles that are required for performing Brownian dynamics simulations of a cubic particle suspension. In the situation of a uniform flow field with a Reynolds number sufficiently smaller than unity, the force acts on the cube only in the flow field direction, and the torque acting on the cube may be regarded as negligible. In the situation of a rotational flow field with a sufficiently low Reynolds number, the torque acts on the cube only in the direction of angular velocity of the rotational flow field, and the force negligibly act on the cube. These characteristics are in significantly similar to those for the case of spheres in a Stokes flow situation. From these results, we may conclude that the diffusion coefficients of cube-like particles can be expressed by introducing a correction factor to those of the spherical particles.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127965767","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Enhancing the Performance of Centrifugal Pump by Adding Cylindrical Disks at Inlet Suction","authors":"Linda Sadik, B. Jawad, Munther Y. Hermez, Liping Liu","doi":"10.1115/imece2019-11433","DOIUrl":"https://doi.org/10.1115/imece2019-11433","url":null,"abstract":"\u0000 Optimizing the high efficiency design of centrifugal pumps requires a detailed understanding of the internal flow. The prediction of the flow inside the pump can be acquired by understanding the rotatory motion and the three-dimensional shape of the impellers, as well as its fundamental unsteady behavior. The flow inside a centrifugal pump is three-dimensional, unsettled and always associated with secondary flow structures. When a centrifugal pump operates under low flow rates, a secondary flow, known as recirculation, starts to begin. Inside this, the separation of flow increases, which creates vortices and cause local pressure to decrease, which induces cavitation. This phenomenon of recirculation will increase the Net Positive Suction Head Required (NPSHR).\u0000 Improving the suction performance continues to remain a vital and continuous topic in the development and application of centrifugal pumps. In this research, the focal point is to enhance the pump suction performance under low flow rates by modifying the impeller design. This research entails a numerical simulation investigation on the addition of three different designs, each consisting of two cylindrical disks at the impeller inlet suction. It is hypothesized that these modifications will assist suppressing the recirculation phenomenon. The turbulent flow within the centrifugal pump was analyzed by applying the Reynolds-Averaged Navier-Stokes equations and the k–ϵ equations for turbulence modelling. The computational domain consists of the inlet, impeller, diffuser and outlet. Analysis of ΔP, torque data and pump efficiency was conducted. The application of CFD solvers to predict pump performance resulted in reduced prices for testing as well as pump development time.\u0000 The numerical simulation concluded that placing 3-D multi-cylindrical disks at the impeller inlet section improved the centrifugal pump performance under low flow rates. The model design 1 resulted in a pump efficiency improvement of about 5% at low flow rates by lowering the amount of flow leaking back (re-circulation) through the internal suction.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127987078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CFD Study of Particle and Compressible Flow Interaction for a Twin Wire Arc Spraying System","authors":"R. Faull, Nicole J. Wagner, K. Anderson","doi":"10.1115/imece2019-10101","DOIUrl":"https://doi.org/10.1115/imece2019-10101","url":null,"abstract":"\u0000 Plasma spraying is used in various industries for additive manufacturing applications to apply materials onto a workpiece. Such applications could be for the purpose of repair, protection against corrosion, wear-resistance, or enhancing surface properties. One plasma spraying method is the twin wire arc spraying (TWAS) process that utilizes two electrically conductive wires, across which an electric arc is generated at their meeting point. The molten droplets that are created are propelled by an atomizing gas towards a substrate on which the coating is deposited. The TWAS process offers low workpiece heating and high deposition rates at a lower cost compared to other plasma spraying techniques. As the spray angle for this technique is relatively large (15 degree half angle), particles are lost in the process, lowering the yield of deposited material. The motivation of this project was to constrict the particle flow and reduce the loss of particles that are ejected by the spraying torch. Torch nozzles were designed to help the particle trajectory match the axial flow direction of the atomizing gas flow. Simulations using ANSYS FLUENT Computational Fluid Dynamics (CFD) software was utilized to model both the atomizing gas flow and particle flow for a TWAS system. Various nozzle configurations with arc jet angles between 30–75 degrees showed only small effects on gas flow velocity and shape, with no significant variations in particle flow. These results indicate that nozzle configurations are only one factor in determining particle trajectory, and that phase changes and heat transfer need to be considered as well.","PeriodicalId":229616,"journal":{"name":"Volume 7: Fluids Engineering","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129955288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}