Central receiver of Concentrated Solar Power technology constitutes 15% of the total initial cost and plays an important role in achieving high operating temperatures. Central receiver systems are composed of tubes with heat transfer fluid flowing inside that transports heat from radiation on the outer wall of tubes. This work investigates radiation heat transfer to fluid in tubes of various geometries. Experimental and numerical analysis were conducted to observe the boundary layer temperatures, bulk fluid temperatures, and fluid mixing near the tube walls. Four different samples of corrugated tubes adopted from literature were compared to a circular tube and a generic tube designed to provide larger surface area exposed to radiation without corrugation. The circular tube had high temperature in the boundary layer but low bulk fluid temperature due to lack of fluid mixing at wall. A spirally corrugated tube was found to have the highest bulk fluid temperature due to turbulent mixing and low temperature at boundary layer. The generic tube had higher bulk temperature compared to circular tube and two other corrugated tubes.
{"title":"Experimental and Numerical Investigation of Various Tube Geometries for Improved Heat Transfer in Solar Central Receivers","authors":"S. M. Ismail, M. Rashwan, S. Ghani","doi":"10.1115/fedsm2020-20139","DOIUrl":"https://doi.org/10.1115/fedsm2020-20139","url":null,"abstract":"\u0000 Central receiver of Concentrated Solar Power technology constitutes 15% of the total initial cost and plays an important role in achieving high operating temperatures. Central receiver systems are composed of tubes with heat transfer fluid flowing inside that transports heat from radiation on the outer wall of tubes. This work investigates radiation heat transfer to fluid in tubes of various geometries. Experimental and numerical analysis were conducted to observe the boundary layer temperatures, bulk fluid temperatures, and fluid mixing near the tube walls. Four different samples of corrugated tubes adopted from literature were compared to a circular tube and a generic tube designed to provide larger surface area exposed to radiation without corrugation. The circular tube had high temperature in the boundary layer but low bulk fluid temperature due to lack of fluid mixing at wall. A spirally corrugated tube was found to have the highest bulk fluid temperature due to turbulent mixing and low temperature at boundary layer. The generic tube had higher bulk temperature compared to circular tube and two other corrugated tubes.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133745708","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}
This work concerns with numerical simulation of dense gas-particle two-phase flow in a fluidized bed in the framework of two-fluid model, where attention is given to the bubble formation in a single-jet and multi-jet fluidized beds. The kinetic theory is implemented in the model to avoid empirically determined model parameters. The validity of the approach is confirmed through the comparison between the computed results and the measurements in the literature. The results show that increasing the number of jets results in different behavior in bubble formation and the flow pattern in a multi-jet bed is much more complex than that in a single-jet bed.
{"title":"Bubbling Flow in a Multi-Jet Fluidized Bed","authors":"Liwu Wang, Sijun Zhang","doi":"10.1115/fedsm2020-20049","DOIUrl":"https://doi.org/10.1115/fedsm2020-20049","url":null,"abstract":"\u0000 This work concerns with numerical simulation of dense gas-particle two-phase flow in a fluidized bed in the framework of two-fluid model, where attention is given to the bubble formation in a single-jet and multi-jet fluidized beds. The kinetic theory is implemented in the model to avoid empirically determined model parameters. The validity of the approach is confirmed through the comparison between the computed results and the measurements in the literature. The results show that increasing the number of jets results in different behavior in bubble formation and the flow pattern in a multi-jet bed is much more complex than that in a single-jet bed.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134025874","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}
The Capstone design requirements have become an integral part of the most engineering curricula in the United States. They all share the goal of developing multidisciplinary designs for real-world problems/applications, often with industry sponsorship. In this paper, the three-capstone design options required by the aerospace engineering department at the University of Kansas are discussed. The aerospace engineering seniors have three design options based on their career interests. These are aircraft design, propulsion system design, and spacecraft system design options. In the aircraft design, our students may select individual or team design for their competitions. In the latter two, the propulsion and spacecraft system designs, the students are grouped in a number of teams, based on the class and team size requirements. The individuals and teams participate and compete in the respective American Institute of Aeronautics and Astronautics (AIAA) Design Competitions at the end of their senior year. Participation in the AIAA Design Competition is one of the course requirements. Written and oral communication is assessed throughout the semester. In this paper, the methodology used in the aerospace engineering propulsion system capstone design is presented.
{"title":"Capstone Design Sequence in Engineering Education","authors":"R. Taghavi, S. Farokhi","doi":"10.1115/fedsm2020-20298","DOIUrl":"https://doi.org/10.1115/fedsm2020-20298","url":null,"abstract":"\u0000 The Capstone design requirements have become an integral part of the most engineering curricula in the United States. They all share the goal of developing multidisciplinary designs for real-world problems/applications, often with industry sponsorship. In this paper, the three-capstone design options required by the aerospace engineering department at the University of Kansas are discussed. The aerospace engineering seniors have three design options based on their career interests. These are aircraft design, propulsion system design, and spacecraft system design options. In the aircraft design, our students may select individual or team design for their competitions. In the latter two, the propulsion and spacecraft system designs, the students are grouped in a number of teams, based on the class and team size requirements. The individuals and teams participate and compete in the respective American Institute of Aeronautics and Astronautics (AIAA) Design Competitions at the end of their senior year. Participation in the AIAA Design Competition is one of the course requirements. Written and oral communication is assessed throughout the semester. In this paper, the methodology used in the aerospace engineering propulsion system capstone design is presented.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126041456","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}
The concentration of the sand inside the flowlines can directly affect the magnitude of erosion in various pipelines and pipe fittings components. The erosion models available in the literature suggest that the relationship between erosion and sand concentration is linear. Furthermore, some authors believe that for a volume concentration of sand approximately below 0.75% by volume (corresponding to about 2% by mass in liquid), the effects of sand concentration on the rate of erosion are minimal. However, one could ask how this limitation on the amount of sand concentration varies in various geometries as the local concentration at the location where the sand particles are impacting can change within a flow geometry and how this can affect the maximum local erosion rates. Therefore, the sand concentration distributions inside a vertical pipe and two elbows in series for liquid-solid and liquid-gas-solid flows are examined in this investigation by CFD simulations and experimentally. Experiments are performed in a facility with two vertical pipe sections (101.6 mm reducing to a 50.8 mm inner pipe diameters) and immediately after the first and second elbows (50.8 mm inner pipe diameter) from the inner to the outer diameter of the elbows. The concentration distributions are associated with erosion measurement results in both the first and the second elbows. Finally, the CFD simulations of the corresponding experiments in liquid-sand and liquid-gas-sand flows are conducted and compared with the experimental erosion patterns and magnitude as well as various concentration distributions.
{"title":"Sand Particle Concentration Distribution Inside Vertical Pipes: A CFD and Experimental Analysis","authors":"T. Sedrez, S. Shirazi","doi":"10.1115/fedsm2020-20079","DOIUrl":"https://doi.org/10.1115/fedsm2020-20079","url":null,"abstract":"\u0000 The concentration of the sand inside the flowlines can directly affect the magnitude of erosion in various pipelines and pipe fittings components. The erosion models available in the literature suggest that the relationship between erosion and sand concentration is linear. Furthermore, some authors believe that for a volume concentration of sand approximately below 0.75% by volume (corresponding to about 2% by mass in liquid), the effects of sand concentration on the rate of erosion are minimal. However, one could ask how this limitation on the amount of sand concentration varies in various geometries as the local concentration at the location where the sand particles are impacting can change within a flow geometry and how this can affect the maximum local erosion rates. Therefore, the sand concentration distributions inside a vertical pipe and two elbows in series for liquid-solid and liquid-gas-solid flows are examined in this investigation by CFD simulations and experimentally. Experiments are performed in a facility with two vertical pipe sections (101.6 mm reducing to a 50.8 mm inner pipe diameters) and immediately after the first and second elbows (50.8 mm inner pipe diameter) from the inner to the outer diameter of the elbows. The concentration distributions are associated with erosion measurement results in both the first and the second elbows. Finally, the CFD simulations of the corresponding experiments in liquid-sand and liquid-gas-sand flows are conducted and compared with the experimental erosion patterns and magnitude as well as various concentration distributions.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122258741","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}
Piecewise Linear Interface Calculation (PLIC) schemes have been extensively employed in the Volume-of-Fluid (VOF) method for interface capturing in numerical simulations of multiphase flows. Dynamic overset meshes can be especially useful in applications involving component motions and complex geometric shapes. The basic idea of the overset mesh is the variable field interpolation within the overlapped region between the background and body meshes. The acceptor cell value is evaluated by a weighted average of its donors. The weighting factors are calculated by different algebraic methods, such as the averageValue, injection and inverseDistance schemes, which are implanted in the foam-extend library. A geometric interpolation scheme of the VOF field in overset meshes for the PLIC-VOF method has been proposed in the present study. The VOF value of an acceptor cell is evaluated geometrically with the reconstructed interfaces from the corresponding donor elements. Test cases of advecting liquid columns of different shapes inside a unit square/cube with a prescribed rotational velocity field have been performed to demonstrate the accuracy of the proposed overset interpolation scheme by comparing it with three algebraic ones. The proposed scheme has been shown to yield higher accuracy.
{"title":"A Comparative Study of Interpolation Schemes in Overset Meshes for the PLIC-VOF Method in Multiphase Flows","authors":"Ya-Yi Chang, Dezhi Dai, A. Y. Tong","doi":"10.1115/fedsm2020-20399","DOIUrl":"https://doi.org/10.1115/fedsm2020-20399","url":null,"abstract":"\u0000 Piecewise Linear Interface Calculation (PLIC) schemes have been extensively employed in the Volume-of-Fluid (VOF) method for interface capturing in numerical simulations of multiphase flows. Dynamic overset meshes can be especially useful in applications involving component motions and complex geometric shapes. The basic idea of the overset mesh is the variable field interpolation within the overlapped region between the background and body meshes. The acceptor cell value is evaluated by a weighted average of its donors. The weighting factors are calculated by different algebraic methods, such as the averageValue, injection and inverseDistance schemes, which are implanted in the foam-extend library. A geometric interpolation scheme of the VOF field in overset meshes for the PLIC-VOF method has been proposed in the present study. The VOF value of an acceptor cell is evaluated geometrically with the reconstructed interfaces from the corresponding donor elements. Test cases of advecting liquid columns of different shapes inside a unit square/cube with a prescribed rotational velocity field have been performed to demonstrate the accuracy of the proposed overset interpolation scheme by comparing it with three algebraic ones. The proposed scheme has been shown to yield higher accuracy.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122764168","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}
P. Gómez, Adolfo Esteban, C. Zanzi, Joaquín López, J. Hernández
We present a method based on a level set formulation to reproduce the behavior of the contact line on solid walls in the simulation of 3D unsteady interfacial flows characterized by large density ratios. The level set method poses a particular difficulty, related to the reinitialization procedure, when used in the simulation of interfacial flows in which the interface intersects a solid wall, due to the appearance of a blind zone where standard reinitialization procedures produce inconsistent results. The proposed method overcomes this difficulty by introducing a boundary condition for the level set function on the solid surface based on the normal extension of the contact angle from the interface along the solid wall. In order to reproduce the dynamics of the contact line we use a simplified model that imposes a boundary condition on the interface curvature based on the static contact angle, and define a thin slip zone at the solid wall around the contact line. To assess the accuracy and robustness of the proposed method, we conducted several preliminary numerical tests in three dimensions, whose results are compared with analytical solutions and other results available in the literature.
{"title":"On the Boundary Condition for the Level Set Function in the Numerical Simulation of Moving Contact Lines","authors":"P. Gómez, Adolfo Esteban, C. Zanzi, Joaquín López, J. Hernández","doi":"10.1115/fedsm2020-20396","DOIUrl":"https://doi.org/10.1115/fedsm2020-20396","url":null,"abstract":"\u0000 We present a method based on a level set formulation to reproduce the behavior of the contact line on solid walls in the simulation of 3D unsteady interfacial flows characterized by large density ratios. The level set method poses a particular difficulty, related to the reinitialization procedure, when used in the simulation of interfacial flows in which the interface intersects a solid wall, due to the appearance of a blind zone where standard reinitialization procedures produce inconsistent results. The proposed method overcomes this difficulty by introducing a boundary condition for the level set function on the solid surface based on the normal extension of the contact angle from the interface along the solid wall. In order to reproduce the dynamics of the contact line we use a simplified model that imposes a boundary condition on the interface curvature based on the static contact angle, and define a thin slip zone at the solid wall around the contact line. To assess the accuracy and robustness of the proposed method, we conducted several preliminary numerical tests in three dimensions, whose results are compared with analytical solutions and other results available in the literature.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115724092","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}
M. Pourghasemi, N. Fathi, P. Vorobieff, G. Ahmadi, K. Anderson
Here we present the results of the newly developed Eulerian-Lagrangian model to simulate both the primary and the secondary phases coupled in a transient analysis. A set of two a-dimensional, transient linear shear flow at low Reynolds numbers was considered, and the effect of shearing rate on a suspended buoyant spherical solid particle was analyzed. The rotation and displacement of the solid particle are considered in the model, and the effect of the secondary phase on the primary phase is also evaluated at each time step without any simplification. In order to overcome the existing discontinuity at the interface between secondary and primary phases in this Eulerian-Lagrangian approach, the interface between the solid particle and the fluid phase is replaced by a kernel function creating a smooth profile from the solid into the liquid with a predefined thickness. Several simulations were performed, and the reliability of the developed model was assessed. The global deviation grid convergence index (GCI) approach was employed to perform solution verification. The observed order of accuracy of the primary phase solver approaches 2, consistent with the formal order of accuracy of the applied discretization scheme. The obtained velocity profiles from the computational analyses show excellent agreement with the analytical solution confirming the reliability of the single-phase flow solver. To validate the computational results for the multiphase flow solver, we used the experimental data from our newly developed linear shear flow apparatus with suspended buoyant particles.
{"title":"Multiphase Flow Development on Single Particle Migration in Low Reynolds Number Fluid Domains","authors":"M. Pourghasemi, N. Fathi, P. Vorobieff, G. Ahmadi, K. Anderson","doi":"10.1115/fedsm2020-20477","DOIUrl":"https://doi.org/10.1115/fedsm2020-20477","url":null,"abstract":"\u0000 Here we present the results of the newly developed Eulerian-Lagrangian model to simulate both the primary and the secondary phases coupled in a transient analysis. A set of two a-dimensional, transient linear shear flow at low Reynolds numbers was considered, and the effect of shearing rate on a suspended buoyant spherical solid particle was analyzed. The rotation and displacement of the solid particle are considered in the model, and the effect of the secondary phase on the primary phase is also evaluated at each time step without any simplification. In order to overcome the existing discontinuity at the interface between secondary and primary phases in this Eulerian-Lagrangian approach, the interface between the solid particle and the fluid phase is replaced by a kernel function creating a smooth profile from the solid into the liquid with a predefined thickness. Several simulations were performed, and the reliability of the developed model was assessed. The global deviation grid convergence index (GCI) approach was employed to perform solution verification. The observed order of accuracy of the primary phase solver approaches 2, consistent with the formal order of accuracy of the applied discretization scheme. The obtained velocity profiles from the computational analyses show excellent agreement with the analytical solution confirming the reliability of the single-phase flow solver. To validate the computational results for the multiphase flow solver, we used the experimental data from our newly developed linear shear flow apparatus with suspended buoyant particles.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128202892","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}
In this study, the accuracy of the discrete random walk (DRW) stochastic model in generating the instantaneous velocity fluctuations as seen by micro- and nano-particles in inhomogeneous turbulent flows were examined. Particular attention was given to the effects of the non-uniform normal RMS velocity fluctuations and turbulence time scale on the DRW model predictions. The trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm in a duct were evaluated using an in-house Matlab particle tracking code. The particle equation of motion included the drag and Brownian forces. The fully developed mean velocity and RMS fluctuation velocity profiles were exported from the RANS (v2f) simulations and were used for the particle dispersion and transport analysis. It was assumed that the particle-laden flow is sufficiently dilute so that the particle-particle collisions and the two-way coupling effects of particles on the flow could be ignored. To incorporate the instantaneous turbulence velocity fluctuations effects on particle dispersion, the Conventional-DRW model (in the absence of drift corrections), which was originally developed for homogenous turbulent flows, was first used. It was shown that the Conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The Modified-DRW model with an appropriate velocity gradient drift correction term was also tested. It was found that the predicted concentration profiles of tracer particles still are not uniform. It was hypothesized that the reason for this erroneous prediction is due to the inhomogeneous turbulence time macroscale in the channel flow. A new drift correction term as a function of gradients of both RMS fluctuation velocity and the turbulence time macroscale was proposed. It was shown that the new Improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size particles. It was shown that the predicted deposition velocities of different size particles by the proposed Improved-DRW model are in good agreement with the available experimental data as well as the predictions of the empirical models and earlier DNS results.
{"title":"Improved DRW Model for Prediction of Deposition and Dispersion of Nano- and Micro-Particles in Turbulent Flows","authors":"Amir A. Mofakham, G. Ahmadi","doi":"10.1115/fedsm2020-20034","DOIUrl":"https://doi.org/10.1115/fedsm2020-20034","url":null,"abstract":"\u0000 In this study, the accuracy of the discrete random walk (DRW) stochastic model in generating the instantaneous velocity fluctuations as seen by micro- and nano-particles in inhomogeneous turbulent flows were examined. Particular attention was given to the effects of the non-uniform normal RMS velocity fluctuations and turbulence time scale on the DRW model predictions. The trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm in a duct were evaluated using an in-house Matlab particle tracking code. The particle equation of motion included the drag and Brownian forces. The fully developed mean velocity and RMS fluctuation velocity profiles were exported from the RANS (v2f) simulations and were used for the particle dispersion and transport analysis. It was assumed that the particle-laden flow is sufficiently dilute so that the particle-particle collisions and the two-way coupling effects of particles on the flow could be ignored.\u0000 To incorporate the instantaneous turbulence velocity fluctuations effects on particle dispersion, the Conventional-DRW model (in the absence of drift corrections), which was originally developed for homogenous turbulent flows, was first used. It was shown that the Conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The Modified-DRW model with an appropriate velocity gradient drift correction term was also tested. It was found that the predicted concentration profiles of tracer particles still are not uniform. It was hypothesized that the reason for this erroneous prediction is due to the inhomogeneous turbulence time macroscale in the channel flow. A new drift correction term as a function of gradients of both RMS fluctuation velocity and the turbulence time macroscale was proposed. It was shown that the new Improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size particles. It was shown that the predicted deposition velocities of different size particles by the proposed Improved-DRW model are in good agreement with the available experimental data as well as the predictions of the empirical models and earlier DNS results.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125317326","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}
The UAV industry is booming with investments in research and development on improving UAV systems. Current UAV machines are developed according to the quadcopter design which consists of a rotary propulsion system providing lift needed for flight. This design has some flaws; namely safety concerns and noise/vibration production both of which come stem from the rotary propulsion system. As such, a novel propulsion system using slip stream air passed through high performance slot jets is proposed and an analysis of the fluid characteristics is presented in this report. The test section for the experiment is developed using 3D printed ABS plastic airfoils modified with internal cavities where pressurized air is introduced and then expelled through slot jets on the pressure side of the airfoils. Entrainment processes develop in the system through high momentum fluid introduction into a sedentary secondary fluid. Entrainment is governed by pressure gradients and turbulent mixing and so turbulent quantities that measure these processes are extracted and analyzed according to the independent variable’s effects on these quantities. Pitot probe testing extracted one dimensional fluid information and PIV analysis is used to characterize the two-dimensional flow aspects. High slot jet velocities are seen to develop flows dominated by convection pushing momentum mixing downstream reducing the mixing in the system while low slot jet speeds exhibit higher mass fluxes and thrust development. Confinement spacing is seen to cause a decrease in flow velocity and thrust as the spacing is decreased for high speed runs. The most constricted cross sectional runs showed high momentum mixing and developed combined self-similar flow through higher boundary layer interactions and pressures, but this also hurts thrust development by minimizing secondary flows. The Angle of Attack of the assembly proved to be the most important variable. Outward angling showed the influence of coanda effects but also demonstrated the highest bulk fluid flow with turbulence driven momentum mixing. Inward angling created combined fluid flow downstream with high momentum mixing upstream driven by pressure. Minimal mixing is seen when the airfoils are not angled, and high recirculation zones occur along the boundaries. The optimal setup is seen when the airfoils are angled outwards where the highest thrust and bulk fluid movement is developed driven by the turbulent mixing induced by the increasing cross sectional area of the system.
{"title":"Fluid Flow Characteristics of a Co-Flow Fluidic Slot Jet Thrust Augmentation Propulsion System","authors":"B. Garrett","doi":"10.1115/fedsm2020-20006","DOIUrl":"https://doi.org/10.1115/fedsm2020-20006","url":null,"abstract":"\u0000 The UAV industry is booming with investments in research and development on improving UAV systems. Current UAV machines are developed according to the quadcopter design which consists of a rotary propulsion system providing lift needed for flight. This design has some flaws; namely safety concerns and noise/vibration production both of which come stem from the rotary propulsion system. As such, a novel propulsion system using slip stream air passed through high performance slot jets is proposed and an analysis of the fluid characteristics is presented in this report.\u0000 The test section for the experiment is developed using 3D printed ABS plastic airfoils modified with internal cavities where pressurized air is introduced and then expelled through slot jets on the pressure side of the airfoils. Entrainment processes develop in the system through high momentum fluid introduction into a sedentary secondary fluid. Entrainment is governed by pressure gradients and turbulent mixing and so turbulent quantities that measure these processes are extracted and analyzed according to the independent variable’s effects on these quantities. Pitot probe testing extracted one dimensional fluid information and PIV analysis is used to characterize the two-dimensional flow aspects.\u0000 High slot jet velocities are seen to develop flows dominated by convection pushing momentum mixing downstream reducing the mixing in the system while low slot jet speeds exhibit higher mass fluxes and thrust development. Confinement spacing is seen to cause a decrease in flow velocity and thrust as the spacing is decreased for high speed runs. The most constricted cross sectional runs showed high momentum mixing and developed combined self-similar flow through higher boundary layer interactions and pressures, but this also hurts thrust development by minimizing secondary flows. The Angle of Attack of the assembly proved to be the most important variable. Outward angling showed the influence of coanda effects but also demonstrated the highest bulk fluid flow with turbulence driven momentum mixing. Inward angling created combined fluid flow downstream with high momentum mixing upstream driven by pressure. Minimal mixing is seen when the airfoils are not angled, and high recirculation zones occur along the boundaries. The optimal setup is seen when the airfoils are angled outwards where the highest thrust and bulk fluid movement is developed driven by the turbulent mixing induced by the increasing cross sectional area of the system.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120993555","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}
Particle transport through Marangoni convection inside a sessile droplet can be controlled by the UV light distribution on the surface. The photosensitive solution changes the surface tension gradient on the droplet surface and can induce clockwise and counter-clockwise circulations depending on the incident light distribution. In this paper, the stream function in the sessile drop has been evaluated in toroidal coordinates by solving the biharmonic equation. Multiple primary clockwise and counter-clockwise circulations are observed in the droplet under various concentric UV light profiles. The downward dividing streamlines are expected to deposit the particles on the substrate, thus matching the number of deposited rings on the substrate with the number of UV light rings. Moffatt eddies appear near the contact line or centerline of the droplet either due to a sharp change in the UV light profile or because the illuminated region is away from them.
{"title":"Uniform and Gaussian UV Light Intensity Distribution on Droplet for Selective Area Deposition of Particles","authors":"Tianyi Li, A. Kar, Ranganathan Kumar","doi":"10.1115/fedsm2020-20464","DOIUrl":"https://doi.org/10.1115/fedsm2020-20464","url":null,"abstract":"\u0000 Particle transport through Marangoni convection inside a sessile droplet can be controlled by the UV light distribution on the surface. The photosensitive solution changes the surface tension gradient on the droplet surface and can induce clockwise and counter-clockwise circulations depending on the incident light distribution. In this paper, the stream function in the sessile drop has been evaluated in toroidal coordinates by solving the biharmonic equation. Multiple primary clockwise and counter-clockwise circulations are observed in the droplet under various concentric UV light profiles. The downward dividing streamlines are expected to deposit the particles on the substrate, thus matching the number of deposited rings on the substrate with the number of UV light rings. Moffatt eddies appear near the contact line or centerline of the droplet either due to a sharp change in the UV light profile or because the illuminated region is away from them.","PeriodicalId":333138,"journal":{"name":"Volume 2: Fluid Mechanics; Multiphase Flows","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2020-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126744949","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}
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