8 research outputs found
Large eddy simulations of ventilated micro-hydrokinetic turbine and pump-turbines
Large eddy simulations of ventilated hydrokinetic turbine and pump-turbine are conducted. The mathematical modeling of oxygen dissolution and the flow model employed were validated by comparing predicted dissolved oxygen concentration against reported experimental measurements. A parametric study is performed to investigate the influence of interfacial forces, surface tension and bubble breakage and coalescence terms. It is demonstrated that aeration via hydrokinetic turbines can be used to improve the dissolved oxygen level in rivers for better water quality. It is also shown that aeration can effectively be achieved via the pump-turbine system to provide the desired dissolved oxygen level for the microorganisms’ growth during the wastewater treatment process. Air injection is applied to the wake region of each unit. The influence of aeration on the turbine performance, flow induced vibration and oxygen dissolution characteristics are investigated. The numerical predictions reveal that the aeration can be utilized in both hydro systems without experiencing a significant penalty in power generations. Aeration significantly reduces the flow induced vibration in the pump turbine system. The pressure pulsation on the draft tube surface of the pump-turbine is reduced significantly with both central and peripheral aeration. In hydrokinetic turbine, the variation in the standard deviation of power, which is related to the vibration of the turbine unit, is strongly dependent on the turbine operating conditions. Draft tube aeration provided 30% greater amount of dissolved oxygen and 3.2 times higher dissolution efficiency inside the draft tube as compared to the central aeration. The mathematical approaches and the numerical methods employed here can be used to design and optimize the aeration process in these systems
Steady State and Transient Computational Study of Multiple Hydrokinetic Turbines
Computational fluid dynamics (CFD) simulations have been conducted for different configurations of pre-designed multiple hydrokinetic turbines. The turbines are modeled physically within the fluid domain instead of low fidelity actuator lines or actuator disk modeling approaches. The turbulence model, k-ω Shear Stress Transport (SST) was employed to resolve turbulent flow field. The primary focus of this study is to investigate transient behavior of multiple turbines and providing solutions to enhance downstream turbine performance in close proximity to the upstream turbine wake. The wake interaction behind the upstream turbine reduces downstream turbine performance with inline configurations being the most severe cases. One of the many suggested solutions is staggering downstream units beyond the wake region. Other solutions for an inline array: increasing the longitudinal distance between units and modifying downstream turbine rotation speed to move turbine operation point to the best efficiency point.The CFD simulations revealed that the upstream turbine power generation is nearly the same with the single unit power generation for each multiple turbine arrangement. The downstream turbine relative power obtained was 0.18 for the unit placed inline and 0.98 when it was placed outside the wake region. For inline configurations, increasing the stream-wise spacing between the units from 6Dt to 10Dt improved relative power from 0.16 to 0.60, while reducing the rotation speed from 150 rpm to 100 rpm resulted relative power increment from 0.24 to 0.55
Designing a Rear Wing for Binghamton\u27s Formula Race Car: From Small-Scale Simulations and Experiments to Full-Scale Manufacturing
Binghamton\u27s Formula Society of Automotive Engineers (FSAE) designed an aerodynamically efficient rear wing with three airfoils for their new electric vehicle (EV) to improve lap time. They used an integral model, JavaFoil, to determine the size and configuration of each airfoil. Over 4,000 simulations were conducted to determine the optimal spacing and angle of attack for each airfoil to achieve the best downforce. The results were confirmed through computational fluid dynamics (CFD) simulations and experiments at the AEROLAB Wind Tunnel. The final configuration was manufactured using a manual wet layup technique for epoxy resin and carbon fiber. The rear wing assembly will be installed on the 2023 FSAE EV vehicle, which will compete in June 2023 at the Michigan International Speedway. The findings and insights gained from this project will not only assist future aerodynamics teams at Binghamton Motorsports but will also benefit other FSAE teams.https://orb.binghamton.edu/research_days_posters_2023/1033/thumbnail.jp
Vortex Identification in Turbulent Flows Past Plates using Lagrangian Method
Vortex identifications in turbulent flows past arrays of tandem plates are performed by employing the velocity field obtained by high fidelity large eddy simulations (LES). Lagrangian coherent structures (LCSs) are extracted to examine the evolution and the nonlinear interaction of vortices and to characterize the spatial and temporal characteristics of the flow. LCSs identification method is based on the Finite-Time Lyapunov Exponent (FTLE) which is evaluated using the instantaneous velocity data. The simulations are performed in three-dimensional geometries to understand the physics of fluid motion and the vortex dynamics in the vicinity of plates and surfaces at Reynolds number of 50,000. The instantaneous vorticity fields, Eulerian Q-criterion and LCSs are presented to interpret and understand complex turbulent flow structures. The three-dimensional FTLE fields provide valuable information about the vortex generation, spatial location, evolution, shedding, decaying and dissipation of vortices. It is demonstrated here that FTLE can be used together with Eulerian vortex identifiers to characterize the turbulent flow field effectively.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Recommended from our members
Computational and experimental study of an oil jet in crossflow: coupling population balance model with multifluid large eddy simulation
Understanding the size of oil droplets released from a jet in crossflow is crucial for estimating the trajectory of hydrocarbons and the rates of oil biodegradation/dissolution in the water column. We present experimental results of an oil jet with a jet-to-crossflow velocity ratio of 9.3. The oil was released from a vertical pipe 25 mm in diameter with a Reynolds number of 25Â 000. We measured the size of oil droplets near the top and bottom boundaries of the plume using shadowgraph cameras and we also filmed the whole plume. In parallel, we developed a multifluid large eddy simulation model to simulate the plume and coupled it with our VDROP population balance model to compute the local droplet size. We accounted for the slip velocity of oil droplets in the momentum equation and in the volume fraction equation of oil through the local, mass-weighted average droplet rise velocity. The top and bottom boundaries of the plume were captured well in the simulation. Larger droplets shaped the upper boundary of the plume, and the mean droplet size increased with elevation across the plume, most likely due to the individual rise velocity of droplets. At the same elevation across the plume, the droplet size was smaller at the centre axis as compared with the side boundaries of the plume due to the formation of the counter-rotating vortex pair, which induced upward velocity at the centre axis and downward velocity near the sides of the plume
Recommended from our members
Hydrodynamics and dilution of an oil jet in crossflow: The role of small-scale motions from laboratory experiment and large eddy simulations
•Multiphase large eddy simulation of an oil jet in crossflow was conducted.•Oil trajectory and dilution rate were compared to experiments and integral model.•Multiphase model was modified to include the transport term due to the rise velocity of oil droplets.•Jet and crossflow interference created small-sized eddies near the upper edge of the plume.•Counter rotating vortex pair is likely to enhance the mixing of chemicals and droplets within the plume.
Experimental results were presented for the release of diesel oil from a one-inch (2.5Â cm) vertical pipe in a crossflow at 0.27Â m/s. The ratio of jet velocity to crossflow speed was 5.0 and the Reynolds number based on jet velocity and pipe diameter was 7.1Ă—103. In the experiments, the plume shape was photographed, and the oil droplets were measured at two vertical locations on the center axis of the plume. Acoustic Doppler velocimetry (ADV) data was also obtained and compared to numerical predictions. The plume was simulated using large eddy simulation (LES), and the mixture multiphase model. The impact of the oil buoyancy was captured by adding a transport term to the volume fraction equation. Using the rise velocity based on d50 (volume-median) droplet size in the lower part of the plume allowed us to capture the lower boundary of the plume, but the estimated upper boundary of the plume penetrated less into the crossflow as compared to the experimental findings. However, using the rise velocity of the d50 at the upper part of the plume allowed one to estimate the upper boundary of the plume. As the droplets are too small to be resolved by the LES, we could not use a systematic approach to allow the multiphase plume to spread to mimic the observations. Based on the simulation results, the interaction between the jet and crossflow yielded small-sized flow structures near the upper boundary of the plume. The wake vortices initiated from the leeward side of the plume showed an alternating vorticity pattern in the wake. The shear layer vortices were induced by Kevin-Helmholtz instabilities mostly on the windward side of the plume. The formation of counter rotating vortex pair (CVP) altered greatly the hydrodynamics of the jet from that of a vertical jet to manifest flow reversals in all directions. The formation of CVP is likely to enhance the mixing of chemicals and droplets within the plume
Recommended from our members
Transport of oil droplets from a jet in crossflow: Dispersion coefficients and Vortex trapping
Understanding the trajectory of oil droplets in crossflow jets is important to estimate the pathways of hydrocarbons and to plan countermeasures. We report experimental results of an oil jet with release velocity around 1.5 m/s in a crossflow of 0.3 m/s. The hydrodynamics of the jet obtained with the Large Eddy Simulation (LES) were used to predict the migration of the oil droplets. Two Lagrangian techniques were explored, one with the inertia of the droplet is considered and the other that treats the droplets as massless particles with rising velocities corresponding to their size. We did not note a large difference between the two approaches. The droplets showed stronger segregation in the vertical direction, which renders the usage of a Gaussian distribution approximation in the vertical inapplicable. The dispersion coefficient at each direction was computed for different-sized droplets. The eddy diffusivity computed based on Boussinesq gradient approximation using the LES data was compared with the dispersion coefficients obtained based on Lagrangian tracking. We also found that droplets 500 μm and larger escape the vortex while smaller ones get trapped within the vortex. A similar outcome was observed using a vortex trapping function based on inward–outward force balancing at the elevation of the vortex core. The counter-rotating vortex pair (CVP) altered the distribution of droplets of 1 mm and smaller significantly, and bimodal concentration distributions with peaks near the CVP vortex cores and minimum concentration near the center plane were obtained in the lateral–horizontal​ direction. Therefore, measurements of the oil droplet size distribution (DSD) in the center plane of crossflow jets could underestimate the number of small droplets in the whole plume.
•Oil droplet transport with Lagrangian techniques using the hydrodynamics obtained through large eddy simulation.•Larger droplets were observed near the top boundary of the plume in our experiments.•Eddy diffusivity based on Boussinesq approximation using LES and the dispersion coefficients based on Lagrangian tracking.•Trapping of 400μm and smaller droplets in the counter rotating vortex pair.•Droplet size distribution in the center plane of crossflow jets could underestimate the number of small droplets in the whole plume