Understanding the Role of Morphology and Kinematics in Bio-Inspired Locomotion

Inspired by the advanced capabilities of fish and other aquatic swimmers, in this thesis, a greater understanding of fish-like propulsion has been sought in terms of morphology and kinematics. Unsteady potential flow simulations on real cetacean flukes reveal that the effect of shape and gait on the swimming performance are not intertwined and are in fact independent. There is one fluke shape that maximizes the propulsive efficiency regardless of the gait and vice versa. It is also determined that the shape and the gait of the fluke have a considerable influence on the wake topology and in turn the Strouhal number. Evolutionary optimization is used to isolate the shape effects and study optimum conditions when the kinematic features of the animals are varied. Searching the optimum swimmer in terms of swimming gait is performed by considering the three main aspects of the swimming performance: swimming speed, swimming range, and efficiency. Optimum conditions are found when i) the swimmer keeps the duty cycle low and uses sinusoidal-like motion by maintaining higher pitching amplitudes to provide higher thrust and swimming range; ii) the swimmer uses square-like waveform shapes by increasing the duty cycle and using small pitching amplitudes which decrease the swimming range but increase the swimming speed. In all combinations, swimming efficiency is maintained at the maximum achievable level. Scaling laws are presented to predict thrust production and power consumption of the swimmers by accounting for three-dimensionality with shape and gait variations. The scaling laws presented here provide insight into the flow physics that drive thrust production, power consumption, and efficient swimming when the morphology and kinematics are varied

Parametrical and theoretical design of a Francis turbine runner with the help of computational fluid dynamics

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.A computational fluid dynamics based design system with the integration of blade modeler, mesh generator and Navier- Stokes based CFD codes makes the design optimization of turbine components quick and efficient. This design system is applied to a low head Francis turbine runner. The parameters of turbine runner affect the hydraulic performance of turbines. Its complex parameters cause direct effect on the global parameters which change the efficiency and the output power. The purpose of this study is the investigation of the effects of theoretical turbine runner parameters on the design. To determine the parameter effects on the turbine performance theoretical calculations and analyses of turbine runner were performed. A methodology was followed with the help of CFD to reach the best efficiency operating point of turbine. Starting from the preliminary design to the final design, theoretical calculations were performed and evaluated using the results of the CFD analyses. The CFD analyses were used to visualize the flow characteristics on runner blades induced by runner parameters. At the end, a new runner model is designed with a higher efficiency.dc201

Vortex dislocation in the near wake of a cylinder with span-wise variations in diameter

We examined the evolution of three-dimensional vortex shedding patterns induced by spanwise variations of the cylinder diameter. Two distinct types of shedding patterns have identified through flow vi sualization: continuous (in-phase) oblique shedding where vortices shed with lower frequency stay attached to the vortices with higher frequency without any discontinuity or splitting and discontinuous (out-of-phase) shedding where the lower frequency vortices have no attachment to higher frequency vortices and vortex dislocation occurs. The dislocation seen in the flow is strongly influenced by th e span wi se ir regularities. We ob served a clear and strong in-phase spanwise vortex shedding for the three smooth cylinder configurations tested in the study. The tapered, bumps and steps configurations showed sections of strong coherent spanwise vortex shedding, and we identified hardly any coherent structures for the rib, sinusoidal, and helical configurations. Depending on the geometry and number of span wise irregularities, incoherent structures make difficult to determine the occurrence and location of vortex dislocations in the cylinder wake without a method that enables a reduction in the complexity. Here, we introduce a numerical approach that obtains the dominant structures of vortex shedding patterns by reducing the complexity in noisy data. The method maps the variations in the oblique shedding angle over time and provide quantitative conclusions on the intermittent occurrence and location of vortex dislocations in the 15 000 snapshots taken for each of the different cylinder geometries regardless of turbulence

An Assessment of the State-of-the-Art from the 2019 ARO Dynamic Stall Workshop

Dynamic stall has been a limiting factor in design and operation on rotating systems within the rotorcraft, propulsion, and sustainable energy disciplines for more than forty years, impacting operational performance and component fatigue. In the last decade, significant advances have been accomplished in the understanding, prediction, modeling, and control of dynamic stall on both static and rotating wings. In September 2019, an Army Research Officefunded workshop was held at the Georgia Institute of Technology to evaluate the state of the art and future directions in the understanding and control of dynamic stall. Approximately forty attendees drawn from top experts in the field to graduate students convened to discuss experimental, computational, theoretical, and control research in the field over a two-day period. This workshop was designed to gather the details of these advances and to impart to the broader community the current state of the art in the understanding and prediction of dynamic stall for rotating systems. A summary of the discussions and findings from this workshop are presented here

Simulation-based design and optimization of Francis turbine runners by using multiple types of metamodels

In recent years, optimization started to become popular in several engineering disciplines such as aerospace, automotive and turbomachinery. Optimization is also a powerful tool in hydraulic turbine industry to find the best performance of turbines and their sub-elements. However, direct application of the optimization techniques in design of hydraulic turbines is impractical due to the requirement of performing computationally expensive analysis of turbines many times during optimization. Metamodels (or surrogate models) that can provide fast response predictions and mimic the behavior of nonlinear simulation models provide a remedy. In this study, simulation-based design of Francis type turbine runner is performed by following a metamodel-based optimization approach that uses multiple types of metamodels. A previously developed computational fluid dynamics-based methodology is integrated to the optimization process, and the results are compared to the results obtained from on-going computational fluid dynamics studies. The results show that, compared to the conventional methods such as computational fluid dynamics-based methods, metamodel-based optimization can shorten the design process time by a factor of 9.2. In addition, with the help of optimization, turbine performance is increased while cavitation on the turbine blades, which can be harmful for the turbine and reduce its lifespan, is reduced.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is financially supported by the Ministry of Development of Turkey. The computations are performed at TOBB ETU Center for Hydro Energy Research (ETU Hydro), CFD Laboratory