Conferences, Lectures, & Seminars
Events for January
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Simulation and Control of Three-Dimensional Separated Flows around Low-Aspect-Ratio Wings
Wed, Jan 14, 2009 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Kunihiko (Sam) Taira Postdoctoral Research AssociateDepartment of Mechanical and Aerospace EngineeringPrinceton UniversityPrinceton, NJ Micro air vehicles often fly with flow separation on their low-aspect-ratio wings due to the unique design and operational environment. However, three-dimensional flows around such vehicles have not been well understood compared to the classical high-Reynolds-number flows around conventional aircraft. To offer fundamental understanding of the flow field around small-scaled vehicles, a new formulation of the immersed boundary method is developed and used to perform three-dimensional flow simulations around low-aspect-ratio wings at low Reynolds numbers. The study highlights the unsteady nature of separated flows for various aspect ratios, angles of attack, and planform geometries. Following an impulsive start, the short and long time behavior of the wake and the corresponding forces exerted on the wing are examined. At high angles of attack, the leading-edge vortices are observed to detach in many cases, resulting in reduced lift. Inspired by how insects benefit from the added lift due to the leading-edge vortices, actuation is introduced to increase lift by modifying the three-dimensional dynamics of the wake vortices behind translating wings. Successful control setups that achieve lift enhancement by a factor of two in post-stall flows for low-aspect-ratio wings will be presented.
Location: Seaver Science Library (SSL) 150
Audiences: Everyone Is Invited
Contact: April Mundy
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Toward Numerical Simulations of Compressible Multiphase Flows with Applications to Shockwave Lithotr
Wed, Jan 21, 2009 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Eric Johnsen Postdoctoral FellowCenter for Turbulence ResearchStanford UniversityStanford, CA Multiphase flows are ubiquitous in nature and in engineering applications, and encompass a range of phenomena as diverse as the dynamics of bubble clouds, the ablation of human tissue by focused ultrasound, and the impact of ocean waves onto naval structures. Though numerical simulations have become common design and analysis tools in fluid dynamics, current multiphase flow algorithms are still in developmental stages, particularly when the flow is compressible. In the present talk, a compressible multicomponent flow method is presented and applied to study the non-spherical collapse of gas bubbles in the context of shockwave lithotripsy, a medical procedure in which focused shockwaves are used to pulverize kidney stones. The dynamics of non-spherical bubble collapse are characterized, and the damage potential of the shockwaves emitted upon collapse is evaluated by tabulating the wall pressure. In addition, various properties are compared to available experiments and theory, showing good agreement. Furthermore, by using the present results as boundary conditions for simulations of elastic wave propagation within a kidney stone, a new stone comminution mechanism is proposed. Finally, the application of the current method is discussed for simulations of the Richtmyer-Meshkov instability, in which a shock interacts with a perturbed interface.
Location: Staufer Science Library Rm 150
Audiences: Everyone Is Invited
Contact: April Mundy
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The Laminar Flame to Turbulent Flame to Detonation Transition: Studies of Non-Kolmogorov Turbulence
Thu, Jan 22, 2009 @ 03:00 PM - 05:00 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Elaine S. Oran Senior Research Scientist
Naval Research Laboratory Lecture Abstract "The transition from a propagating subsonic Laminar flame to a high-speed Turbulent flame and then to supersonic Detonation wave (the LTD transition) involves a series of often dramatic events involving changes in the nature of the reaction wave. Some of the events develop continuously whereas others appear suddenly and with little apparent warning. The LTD transition occurs in highly exothermic energetic materials, for example in hydrogen-air mixtures resulting from gas leaks at hydrogen production and storage facilities as well as in carbon-oxygen mixtures in white-dwarf stars which, after ignition, become thermonuclear supernovae. This presentation describes the properties of the LTD transition using videos made from numerical solutions of the multidimensional, unsteady, chemically reacting, Navier-Stokes equations. The discussion focuses on selected features of the flow, including: formation of a turbulent flame and the nature of the turbulence, creation of hot spots as the origins of detonations, effects of stochastic processes on our ability to make predictions, and comparisons between simulations and experimental data." Professor Oran, Gas Dynamics Laboratories, designs numerical methods for simulating complex fluid dynamic processes, and then uses these methods to solve complex fluid dynamic processes and a wide variety of other scientific and engineering problems. Her recent research interests include combustion and propulsion, rarefied gases and microfluidics, fluid turbulance, materials engineering, high-proformance computing and parallel architectures, computational science and numerical analysis, biophysical fluid dynamics, wave equations, and astrophysical phenomena such as supernova explosions and jets. Oran has authored over 200 refereed journal articles as well as many conference papers and presentatoins. She is also the co-author of the book Numerical Simulation of Reactive Flow (2nd edition, Cambridge Press, 2001).Location: Davidson Conference Center -Club Room 2nd Floor
Audiences: Everyone Is Invited
Contact: April Mundy
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Swimming and Flying Somewhere Between the Microscale and Macroscale: Curious Adaptations in Parasito
Fri, Jan 23, 2009 @ 12:00 PM - 01:00 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Laura Miller Assistant ProfessorDept. of Mathematics U. North Carolina at Chapel Hill Chapel Hill, NC Biologists, engineers, physicists, and mathematicians have long studied the fluid dynamics of animal swimming and flying. In most cases, methods of locomotion are divided neatly into high Reynolds number mechanisms (flapping wings and fins, gliding, jet propulsion) and low Reynolds number mechanisms (cilia and flagella). For the most part, mechanisms of locomotion for Reynolds numbers between 0.1 and 10 have not been explored. In these flows, both inertial and viscous effects are significant, and a number of interesting biological adaptations appear. For example, the wings of the smallest insects have a bristled structure. Similar structures are also observed on the appendages of aquatic invertebrates such as copepods and beetles. Some fairyflies use bristled wings to fly in the air and also to swim in the water. In this presentation, the fluid dynamics of locomotion at these Reynolds number is explored. We use computational fluid dynamics and particle image velocimetry (PIV) to characterize the flow around simplified models of flapping wings and fins. The immersed boundary method is used to solve the Navier-Stokes equations around a moving, flexible wing or fin. We then describe thrust and lift generation in air and water over a range of Reynolds numbers and relate the magnitude of these forces to the behavior of the wake behind the flapping appendages. The role of bristled wings in locomotion is also examined. Finally, we describe similar problems in moving and pumping fluids over the same Reynolds number range.
Location: Robert Glen Rapp Engineering Research Building (RRB) - 208 Laufer Library
Audiences: Everyone Is Invited
Contact: April Mundy
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Vortex Induced Vibrations
Wed, Jan 28, 2009 @ 03:00 PM - 05:00 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
A. Leonard Theodore von Kármán Professor of Aeronautics,
EmeritusGraduate Aeronautical LaboratoriesCalifornia Institute of TechnologyPasadena, CA Vortex shedding from a bluff body can impose significant, time-dependent forces on the body. If the body is freely oscillating, the amplitude of the resulting vibration can lead to disastrous consequences in some instances or, on the plus side, can be the essence of a proposed power generation scheme. The amplitude and frequency of the motion depends on the shape of the body and on four parameters: nondimensional mass, damping coefficient, spring constant or stiffness, and Reynolds number. In some cases, the expected resonant behavior occurs when the vortex shedding frequency is close to the natural vibration frequency of the mechanical system and the damping is low. But there are important ranges of these parameters that yield contrary results. Laboratory and computational experiments of flow past a freely oscillating circular cylinder will be discussed along with a new theoretical approach that requires only three parameters: effective stiffness, damping, and Reynolds number, and takes the mystery out of some of the mysterious results reported in the literature.
Location: Ronald Tutor Hall of Engineering (RTH) - 526
Audiences: Everyone Is Invited
Contact: April Mundy
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Computational analysis of droplet- and particle-laden, turbulent and separated high-speed flows
Thu, Jan 29, 2009 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Gustaaf B. JacobsDepartment of Aerospace Engineering & Engineering MechanicsSan Diego State UniversityThe optimization of fuel droplet/particle and fuel-air mixing improves performance of scramjets and pulse detonation engines and reduces environmental pollution. Understanding the impact of debris in explosions can save lives. The flows in dust explosions and in high-speed combustors are characterized by the intricate interaction between droplets, particles, separated shear layers, turbulence and/or shocks. The tremendous complexity of this interaction has left many questions unanswered. I will discuss our efforts to computationally analyze the droplet- and particle-laden flows. I will first discuss high-fidelity Eulerian-Lagrangian computational methods that model the gas flow equations in the Eulerian frame with high-order methods, while particles are traced along there path in the Lagrangian frame. I will discuss high-order coupling between the two frames and illustrate the performance of the method. I will secondly discuss flow separation, compressibility effects and the droplet dispersion of flows with relevance to the high-speed separated flows in simplified combustor geometries.
Location: James H. Zumberge Hall Of Science (ZHS) - 252
Audiences: Everyone Is Invited
Contact: April Mundy