Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session E16: Computational and Theoretical Aerodynamics |
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Chair: Dietmar Rempfer, Illinois Institute of Technology Room: 319 |
Sunday, November 20, 2011 4:40PM - 4:53PM |
E16.00001: Numerical Study for Detailed Flow Fields and Performance of the Savonius-Type Rotor Tong Zhou, Dietmar Rempfer The Savonius-type rotor is simple in structure, has good starting characteristics, relatively low operating speeds, and an ability to accept wind from any direction, although it has a lower efficiency than other vertical axis wind turbines. So far a number of experimental investigations have been carried out to study the performance of the Savonius rotor, however, there is a lack of detailed descriptions of the flow field. The aim of this paper is to numerically explore the non-linear two- dimensional unsteady flow over a Savonius rotor and develop a simulation method for predicting its aerodynamic performance. The simulations are based on Star CCM+. The motion of the blades is solved by using a moving mesh. Different turbulence models are compared. Parameters such as mesh density, wall $y^+$, and boundary conditions will be discussed. Numerical simulation results are compared with experimental data. Separation of the flow at the blade tips is well modeled. The characteristics of flow fields details are studied, including boundary layer, moment coefficient, and pressure distribution. The wall shear on each surface of the blades is studied to look into the position of the separation point. Computational fluid dynamics is proven to be an effective approach for the investigation of the Savonius-type rotor, on the premise of proper theory and reasonable assumption. It also provides a basis for optimization of the Savonius wind turbine. [Preview Abstract] |
Sunday, November 20, 2011 4:53PM - 5:06PM |
E16.00002: The Kutta-Zhukovsky Lift Theorem revisited: Alteration due to the Viscous Wake Sven Schmitz The circulation theory of lift comprised in the classical Kutta-Zhukovsky Lift Theorem forms the foundation of modern aerodynamic wing theory. The theorem has been applied ever since in lifting-line models of aircraft and rotary wings. Reynolds numbers larger than one million support its validity, yet the effect of a viscous wake on a change in the functional relationship between lift and circulation is not taken into account in standard lifting-line analyses. A discrepancy in circulation of more than six percent in comparison to the classical Kutta-Zhukovsky Lift Theorem has been demonstrated by the author (Schmitz {\&} Chattot, \textit{Computers {\&} Fluids}, \textbf{36}) for moderately separated flow around a wind turbine airfoil by means of a control volume analysis governed by the Navier-Stokes equations. The present work extends the previous analysis to general three-dimensional flow around a lifting body. An analytical expression is presented that extends the classical Kutta-Zhukovsky Lift Theorem by adding terms to the theorem due to chord- and spanwise vorticity transport. An integrated solution for induced drag is given that has not been documented in previous literature on the subject. The generalized theorem will find future application and quantification in actuator-line methods used to predict wind farm wake interactions with Atmospheric Boundary Layer flow. [Preview Abstract] |
Sunday, November 20, 2011 5:06PM - 5:19PM |
E16.00003: A Computational Parametric Study of Drag Reducing Riblet Geometries Aaron Boomsma, Fotis Sotiropoulos Riblets are micro-grooved films that passively affect the skin friction of a turbulent boundary layer. Many researchers have shown that riblets can augment or decrease drag. This work utilizes high-resolution direct numerical simulations at low Reynolds numbers to conduct a parametric study of those riblets that decrease drag. Insights on drag reduction due to geometry are revealed for a variety of riblet heights, spacings, and shapes. Finally, this work discusses flow physics of the modified turbulent boundary layer and mechanisms of drag reduction. This work was supported by the Department of Energy (DE-EE0002980) and the University of Minnesota Initiative for Renewable Energy and the Environment. Computational resources were provided by the University of Minnesota Supercomputing Institute. [Preview Abstract] |
Sunday, November 20, 2011 5:19PM - 5:32PM |
E16.00004: Stability Analysis of a mortar cover ejected at various Mach numbers and angles of attack Jane Schwab, Maria-Isabel Carnasciali, Joe Andrejczyk, Mike Kandis This study utilized CFD software to predict the aerodynamic coefficient of a wedge-shaped mortar cover which is ejected from a spacecraft upon deployment of its Parachute Recovery System (PRS). Concern over recontact or collision between the mortar cover and spacecraft served as the impetus for this study in which drag and moment coefficients were determined at Mach numbers from 0.3 to 1.6 at 30-degree increments. These CFD predictions were then used as inputs to a two-dimensional, multi-body, three-DoF trajectory model to calculate the relative motion of the mortar cover and spacecraft. Based upon those simulations, the study concluded a minimal/zero risk of collision with either the spacecraft or PRS. [Preview Abstract] |
Sunday, November 20, 2011 5:32PM - 5:45PM |
E16.00005: Vorticity forces on an impulsively started finite plate Chin-Chou Chu, Cheng-Ta Hsieh, Jian-Jhih Lee, Chien Cheng Chang In this talk, various force contributions to an impulsively started finite plate with a high and low aspect ratio are investigated from the perspective of a diagnostic vorticity force theory. In contrasted to the traditional pressure force analysis (PFA), the vorticity force analysis (VFA) reveals new salient features in its applications to three-dimensional flow by examining section-wise force contributions along the spanwise direction. At a large aspect ratio (AR=3), the force distributions of PFA and VFA show close agreements with each other in middle sections, while at a lower aspect ratio (AR=1), the force distribution of PFA is substantially larger than that of VFA in most of the sections. The difference is compensated by the contributions partly by the edge sections and mainly by the outer tip vortices. The present force-element analysis provides a better perspective for flow control by relating the forces directly to the various sources of vorticity (or vortex structures) in the flow. [Preview Abstract] |
Sunday, November 20, 2011 5:45PM - 5:58PM |
E16.00006: Numerical simulation of Reynolds number effects on velocity shear flow around a circular cylinder Shuyang Cao Three-dimensional Direct Numerical Simulation and Large Eddy Simulation are performed to investigate the shear effects on flow around a circular cylinder at Reynolds numbers of Re=60--1000. The shear parameter, which is based on the velocity gradient, cylinder diameter and upstream mean velocity at the center plane of the cylinder, varies from 0 to 0.30. Variations of Strouhal number, drag and lift coefficients, and unsteady wake structures with shear parameter are studied, along with their dependence on Reynolds number. The presented simulation provides detailed information for the flow field around a circular cylinder in shear flow. This study shows that the Strouhal number exhibits no significant variation with shear parameter. The stagnation point moves to the high-velocity side almost linearly with shear parameter, and this result mainly influences the aerodynamic forces acting on a circular cylinder in shear flow. Both the Reynolds number and shear parameter influence the movement of the stagnation point and separation point. Mode A wake instability is suppressed into parallel vortex shedding mode at a certain shear parameter. The lift force increases with increasing shear parameter and acts from the high-velocity side to the low-velocity side. [Preview Abstract] |
Sunday, November 20, 2011 5:58PM - 6:11PM |
E16.00007: Large-Scale Numerical Simulation of Fluid Structure Interactions in Low Reynolds Number Flows Ali Eken, Mehmet Sahin A fully coupled numerical algorithm has been developed for the numerical simulation of large-scale fluid structure interaction problems. The incompressible Navier-Stokes equations are discretized using an Arbitrary Lagrangian-Eulerian (ALE) formulation based on the side-centered unstructured finite volume method. A special attention is given to satisfy the discrete continuity equation within each element at discrete level as well as the Geometric Conservation Law (GCL). The linear elasticity equations are discretized within the structure domain using the Galerkin finite element method. The resulting algebraic linear equations are solved in a fully coupled form using a monolitic multigrid method. The implementation of the fully coupled iterative solvers is based on the PETSc library for improving the efficiency of the parallel code. The present numerical algorithm is initially validated for a beam in cross flow and then it is used to simulate the fluid structure interaction of a membrane-wing micro aerial vehicle (MAV). [Preview Abstract] |
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