Oscillatory momentum transport in cascade transitional boundary layer flows

The generation and early evolution of boundary layer transitional instabilities, named Tollmien-Schlichting (T-S) waves, in airfoil cascade flows are studied. The energy exchange between the mean flow and the flow instabilities is computed by performing Direct Numerical Simulation of the fluid flow governing equations and by calculating the fluctuating kinetic energy (FKE) budget within the separated boundary layer. The driving role of the FKE production in the wavelength modulation process associated to the receptivity phenomenon, i.e., the generation of T-S waves, is demonstrated. The FKE production largely hastens the wavelength modulation around the inflection point of the mean velocity profile across the boundary layer. Above the inflection point, the fluctuating pressure field favors the energy transport and provides the energy necessary to convect the instabilities out of the boundary layer. The evolution of the T-S waves depicts an asymmetric distribution of the production term in the transverse direction, i.e., in the lower half of the boundary layer the mean flow provides energy to the instabilities while the opposite occurs in the upper hal

Effects of external disturbances on the momentum transport in cascade transitional boundary layer flows

The effects on the boundary layer receptivity in airfoil cascade flow caused by superposed disturbances are studied using an energetic approach. The separated terms in the Fluctuating Kinetic Energy (FKE) budget are calculated. Monotonic time-harmonic disturbances are superposed to the inflow stream using forcing frequencies close to and far from the natural frequency of fluctuation found within the unsteady (supercritical) basic flow. For supercritical regimes, the receptivity is evaluated around the boundary layer separation point, where Tollmien-Schlichting (T-S) waves are naturally generated. For subcritical regimes, the receptivity is explored all over the suction-side of the airfoil since separation does not occur. Within subcritical flows, the superposed perturbation is seen to trigger the generation of T-S-like waves downstream the minimum pressure point only when the forcing frequency is close to n. Within supercritical flows, when the forcing frequency matches n, the FKE budget reflects the energetic interaction between the perturbation and the already existent boundary layer T-S wave

Modeling the Spread of COVID-19 Over Varied Contact Networks

When attempting to mitigate the spread of an epidemic without the use of a vaccine, many measures may be made to dampen the spread of the disease such as physically distancing and wearing masks. The implementation of an effective test and quarantine strategy on a population has the potential to make a large impact on the spread of the disease as well. Testing and quarantining strategies become difficult when a portion of the population are asymptomatic spreaders of the disease. Additionally, a study has shown that randomly testing a portion of a population for asymptomatic individuals makes a small impact on the spread of a disease. This thesis simulates the transmission of the virus that causes COVID-19, SARSCoV- 2, in contact networks gathered from real world interactions in five different environments. In these simulations, several testing and quarantining strategies are implemented with a varying number of tests per day. These strategies include a random testing strategy and several uniform testing strategies, based on knowledge of the underlying network. By modeling the population interactions as a graph, we are able to extract properties of the graph and test based on those metrics, namely the degree of the network. This thesis found many of the strategies had a similar performance to randomly testing the population, save for testing by degree and testing the cliques of the graph, which was found to consistently outperform other strategies, especially on networks that are more dense. Additionally, we found that any testing and quarantining of a population could significantly reduce the peak number of infections in a community

Numerical simulation of draft tube flow in off-design conditions

Draft tube flow fields are simulated with 3D unsteady Reynolds averaged Navier-Stokes equations.The purpose of this study is the modeling, simulation and characterization of a complex threedimensional unsteady flow inside a Francis turbine draft tube for two specific off-design conditions: A) Part load (0.88Q), frequently characterized by the occurrence of an unsteady rotating vortex rope linked to strong pressure fluctuations and, B) High load (1.21Q), where softer pressure surges taking place because the cavity volume at this condition has an axisymmetric shape. This work takes place after overhaul works on the actual turbine, which include new runner and wicket gates and modifications on stay vanes and other passageways; where power output, efficiency and stable operating range were increased. The computational domain consists of the draft tube alone. A relative poor mesh (430k nodes) and the k-ε turbulence model are implemented in order to get a quick, but clear explanation to understand how the flow in the existing draft tube responds in front of a new velocity distribution at runner outlet for off-design conditions. Numerical results are qualitative and quantitatively analyzed and compared with experimental data from model and prototype. The unsteady and complex nature of the flow field distribution inside the draft tube for both conditions is visualize

Torsional current - meter for channels

The main objective of this paper is to present the results of the experimental investigation of a Zarea-type torsional velocity-meter. For this, a torsional meter was designed, built and tested in the laboratory. The current meter consists of an axial rotor with blades fixed to a shaft which is in turn fixed to a rigid hub. The force of the water flow produces a torque which deforms the shaft. The current meter has been statically calibrated, thereby establishing the variational curve of the torsion angle as a function of the applied torque. A laboratory facility has been constructed in which tests were run for water speeds of up 3m/s. The torque measurements were taken by using strain gauges. The methodology and the equipment used for the experimental evaluation are shown. Additionally illustrated are the calibration curves, the analysis of obtained results, some advantages and disadvantages, and the range of application of the torsional current-meter are all discussed

Pinworms of the red howler monkey (Alouatta seniculus) in Colombia. Gathering the pieces of the pinworm-primate puzzle

Pinworms of primates are believed to be highly host specific parasites, forming co-evolutionary associations with their hosts. In order to assess the strength and reach of such evolutionary links, we need to have a broad understanding of the pinworm diversity associated with primates. Here, we employed an integrative taxonomic approach to assess pinworm diversity in red howler monkeys in Colombia. Molecular and morphological evidence validate the presence of at least four different species of Trypanoxyuris occurring in red howler monkeys: T. minutus, a widely distributed species, and three new species, T. seunimiii n. sp., T. kemuimae n. sp. and T. kotudoi n. sp. The mitochondrial COI gene and the 28S ribosomal gene were used for phylogenetic assessments through Bayesian inference. The three new species were morphologically distinct and formed reciprocally monophyletic lineages. Further molecular lineage subdivision in T. minutus and T. kotudoi n. sp. without morphological correspondence, suggests the potential scenario for the existence of cryptic species. Phylogenetic relationships imply that the different species of Trypanoxyuris occurring in each howler monkey species were acquired through independent colonization events. On-going efforts to uncover pinworm diversity will allow us to test the degree of host specificity and the co-phylogenetic hypothesis, as well as to further unravel the primate-pinworm evolutionary history puzzle

Prediction of blood damage within biomedical blood-wetted devices due to mechanical action

The goal of this project is to develop a CFD model of blood to predict hemolysis due to mechanical action in biomedical blood-wetted devices. Most of the current models approximate blood as a Newtonian fluid at high shear rates. Our work is based on numerical model developed in [1] that modeled blood as a multiphase fluid with constant viscosity. Although successful in capturing phase segregation (Fahraeus-Lindqvist effect), it still did not reach acceptable agreement with experimental data in terms of damage. Gijsen et al. [2] reported significant differences between flow fields obtained by Newtonian and non-Newtonian models of blood. The goal of this study is to introduce non-Newtonian blood rheology to the base model and validate it with existing experimental data

Fluid flow hydrodynamic modeling in the passage of an oil artificial lift pumping unit

The study of the two-phase flow through the standing and traveling valves used in an oil artificial-lift pumping unit is presented. The investigation aimed to determine the effects the gaseous phase may cause on the pump volumetric efficiency. Data obtained on a specially designed test facility is presented and analyzed as a first step before developing a semi-empirical model to predict the performance of the pump under two-phase flow conditions. Preliminary results, based on one-phase and two-phase runs, demonstrate important features introduced on the pump performance once the gas-phase is included in the proces

Two-dimensional numerical simulation of saltating particles using granular kinetic theory

Most granular flows at environmental conditions are unsteady and exhibit a complex physical behavior. Dune formation and migration in the desert are controlled not only by the flow of saltating particles over the sand bed, but also by turbulent atmospheric airflow. In fact, sediments are transported by the atmospheric airflow within a thin layer only a few centimeters above the sandy surface. These jumping particles reach a maximum sediment mass flux level at a certain delay time (known as the “saturation time”) after the initial movement by sliding and rolling begins. Unlike sediment transport in water where the particles are lifted by the turbulent suspension, the saltating particles are kept alive in the layer mainly due to particle-particle and particle-bed collisions. In order to model this Aeolian transport of sand, Jenkins and Pasini [1] proposed a two-fluid model (one-dimensional and steady state) using Granular Kinetic Theory (GKT) to describe the solid-phase stress. The present work extends the original idea of Jenkins and Pasini [1] by using a more robust model of GKT for the kinetic/collisional contributions to the solid-phase stress tensor, together with a friction model activated for sustained contacts between particles. In addition, a standard k-ε turbulence model for the air and a drag model for the interaction between the phases are employed. A rectangular 2D geometry was chosen with a logarithmic profile for the inlet air velocity, along with an initial amount of sand at rest in the lower part of the simulation domain, resembling the particle saltating flow commonly seen in the vertical middle plane within saltation wind tunnels. This model is validated with experimental data from Liu and Dong [2] and the results given by Pasini and Jenkins [1]. A good estimation for the particle erosion and mass flux in the saltation layer is predicted, even though the profiles of mass flux and concentration within the transport layer are very thin and lowe

Selection and validation of a turbulence model for the numerical simulation of the flow at hemodialysis cannulas

In recent years, CFD has become an increasingly used tool in the design of blood-based devices. Particularly, the estimation of red blood cell damage (hemolysis) becomes an important challenge to CFD scientists since the blood is a complex fluid present in turbulent regime in most pumping devices. Moreover, previous CFD studies on blood hemolysis lack of reliable relationships between hydraulic results and hematological responses. The objective of this work is to foresee a methodology for performing realistic CFD simulations that lead to reliable hydraulic and hematological correspondence. Cannulae geometries were studied to numerically assess a relatively simple flow with documented hematological data. For the turbulence modeling, a direct numerical simulation (DNS) for a coaxial jet array was used as a benchmark for the selection of an appropriate turbulence model, since the Cannulae approximates the coaxial jet features. Velocity and stress time-averaged profiles were compared between DNS results and the turbulence models. These results, pointed to the Shear Stress Transport with Gamma Theta correlation for transition model as the optimum turbulence model in that geometry. Accurate and reliable hydrodynamic CFD results were obtained for the Cannulae as a previous step to further hematological calculations with a minimum degree of uncertaint