Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session PL: General Fluid Mechanics II |
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Chair: Siva Thangam, Stevens Institute of Technology Room: 200A |
Tuesday, November 24, 2009 11:40AM - 11:53AM |
PL.00001: Hydrodynamic coupling of two cylinders in an inviscid fluid Andrew Tchieu, Anthony Leonard, Darren Crowdy A general treatment of computing the irrotational flow generated by two objects moving in a planar incompressible and inviscid fluid is studied. We apply the general treatment to a specific case where two circular cylinders are moving in an arbitrary configuration. Explicit equations for the force imposed on the cylinders are derived and are shown to be dependent on the time varying nature of the conformal map used in the problem. The equations can be coupled to the rigid body motion of the body to give a closed system of equations describing their dynamics. We take a closer look into the effects of the forced oscillatory motion of one cylinder on another and the dynamics of coupled near-collision scenarios. [Preview Abstract] |
Tuesday, November 24, 2009 11:53AM - 12:06PM |
PL.00002: Float height of a rectangular plate in planar stagnation flow Patrick Weidman Numerical integrations of the self-similar equations for steady planar fluid motion between infinite stationary parallel plates are reported for the case where the upper plate is impermeable and the lower plate has uniform transpiration. Such a reduction characterized by a single Reynolds number represents a new exact solution of the Navier-Stokes equations. High-Reynolds number asymptotics greatly facilitate numerical integration by a standard shooting technique. The results are applied to model the float height a rectangular plate under gravity when the plate separation distance is small. We use the results to compare the float heights of disks of fixed mass and surface area supported by axisymmetric and planar stagnation flows. [Preview Abstract] |
Tuesday, November 24, 2009 12:06PM - 12:19PM |
PL.00003: Modeling Gust in Model Reduction Framework Mehdi Ghommem, Imran Akhtar, Muhammad Hajj, Ishwar Puri Determining gust effects on fluid flows and fluid structure interactions is important in many applications. Direct numerical simulations of these effects may be very expensive. This is especially true in cases where gust parameters could vary. The overall goal of this effort is to develop tools and reduced-order models that are capable of assessing gust effects and that can be used for flow control or uncertainty quantification of flow parameters. As such, we simulate the flow past a circular cylinder with and without an incoming gust. Proper orthogonal decomposition (POD) is performed on the simulated flow data to compute the dominant basis functions (modes) using the method of snapshots. The results show that reduced-order models from steady flow cannot be readily used to develop reduced-order models for the same flow with incoming gust. Methodologies to incorporate gust effect within the reduced-order model are discussed. [Preview Abstract] |
Tuesday, November 24, 2009 12:19PM - 12:32PM |
PL.00004: A Novel Model Reduction Strategy Using Upper Bound Theory Greg Chini, Charles Doering We propose an original model reduction technique for driven, dissipative infinite-dimensional dynamical systems. Unlike popular -- but empirical -- POD-based methods, our approach does not require \emph{a priori} data sets from experiments or full PDE simulations and, thus, yields truly predictive reduced models. Instead, the basis functions are computed by solving a constrained, non-local eigenvalue problem drawn from energy stability and upper bound theory. In contrast to \emph{a priori} bases used in spectral expansions, the upper bound eigenfunctions appear to be well suited for the low-order description of strongly driven, spatiotemporally chaotic dynamics, as we demonstrate by applying our methodology to porous medium convection. [Preview Abstract] |
Tuesday, November 24, 2009 12:32PM - 12:45PM |
PL.00005: Laser front distortions due to flow field around a helicopter configuration on hover and forward motion Simha Dodbele Laser beam front distortions characterizing near field losses of energy from a turret mounted on a generic helicopter have been computed to support the modeling and simulation effort of a directed energy testing. The flow field has been computed using an unstructured computational fluid dynamics method with (a) Reynolds averaged Navier-Stokes method with Spalart-Almaras (SA) turbulence model and (b) time accurate Detached Eddy Simulation with SA turbulence model. The beam distortions have been computed using an aero-optics model developed at the University of Notre Dame. For study (a), the rotor surface is modeled by an actuator disk with a jump in the pressure at the disk plane with the laser passing through the flow field due to the fuselage and the rotor. In the case of study (b), the laser is passing through a time accurate flow field of an isolated rotor blade. The laser front distortions, computed through optical path differences for several azimuth and elevation angles for hover and forward flight conditions, are presented in this study. [Preview Abstract] |
Tuesday, November 24, 2009 12:45PM - 12:58PM |
PL.00006: Stabilities and transitions of vertical circulating flows induced by a small fan set on a lake surface Takashi Nakazawa, Hiroshi Suito The purpose for this research is to analyze flow patterns for the swirling upper-lid driven cavity flow in cylindrical coordinates. The swirling upper-lid driven cavity flow is very important for a water quality improvement in lakes. To survey aspects of such flows numerically and mathematically in a simple system, the flows induced by the top boundary condition which forces a horizontal rotating flow is investigated here. Simulations of flows created by the top boundary condition are carried out to obtain steady-state solutions with various Reynolds numbers and analyze stabilities and transitions. [Preview Abstract] |
Tuesday, November 24, 2009 12:58PM - 1:11PM |
PL.00007: Development of the Turbulent Flow in a Bent Pipe Phillip Wilson, Frank Smith The three-dimensional incompressible turbulent flow through a slender bent pipe of simple cross-section is analyzed, the pipe gradually bending the rapid flow through a substantial angle. The ratio of the relative radius of curvature to the magnitude of the turbulent fluctuations is a crucial factor: analysis of the entry region involving exact solutions of the governing equations shows three different downstream developments, depending on the magnitude of that ratio. The main velocity components are found in each case, and one downstream development studied in detail is when turbulence dominates the flow. The present physical situation arises commonly in industrial settings but has been little studied previously. The working applies for any two-tier mixing-length model, and, as a most surprising feature, the fully developed flow far downstream is not unique, being found to depend instead on the global flow behaviour (thus the centre-line velocity is not determined simply by the pressure drop, in contrast to the laminar case). [Preview Abstract] |
Tuesday, November 24, 2009 1:11PM - 1:24PM |
PL.00008: Fast chemical reactions in chaotic flows: predicting the product growth rate Yue-Kin Tsang We consider the fast irreversible bimolecular reaction in a two-dimensional chaotic flow. Simulations show that the reactant concentration decays exponentially with rate $\lambda$, and then crosses over to the algebraic law of chemical kinetics in the final stage of the reaction. We estimate the crossover time from the reaction rate constant and the flow parameters. The exponential decay phase of the reaction can be described in terms of an equivalent passive scalar problem, allowing us to predict $\lambda$ using the theory of passive scalar advection. Depending on the flow configuration, $\lambda$ is either related to the distribution of the finite-time Lyapunov exponent of the flow, or given in terms of an effective diffusivity. For the former case, we suggest an optimal choice of flow parameters at which $\lambda$ is maximum. [Preview Abstract] |
Tuesday, November 24, 2009 1:24PM - 1:37PM |
PL.00009: Giant Pumpkins David Hu, Alex Alexeev In this combined experimental and theoretical study, we investigate the growth of pumpkins from 1 to 1000 pounds in weight. Time-lapse photography is used to document the growth of pumpkins. Data is presented on the relation between the pumpkins' weights and aspect ratios (height divided by width). We observe pumpkins tend to become squashed (up to 50\%) as they increase in size. The lattice-spring method is used to numerically estimate the elasto-plastic forces resisting deformation of the pumpkin. Using levels of plasticity consistent with that of plant cell growth, we find pumpkins shapes consistent with those observed. [Preview Abstract] |
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