Fluid Dynamics Commons^™

Computational Solution Of Tail Buffet Response And Active Flow Control, Kaushik Laxmikant Joshi

Mechanical & Aerospace Engineering Theses & Dissertations

In this thesis, numerical simulation of the multidisciplinary method for prediction and control of vortex induced tail buffeting is studied using delta wing-single tail configuration. Flow conditions are chosen such that wing vortex cores experience vortex breakdown and the resulting wake flow impinges on the vertical tail. The aero/structure problem is solved sequentially using three sets of equations on a multi-block grid structure. To obtain aerodynamic loading on the tail, the fluid flow around the wing-tail assembly is computed by time-accurately solving unsteady, laminar, compressible Navier-Stokes equations using an implicit, upwind, flux-difference splitting finite volume scheme. Then the aeroelastic equations …

Modeling Redox-Based Magnetohydrodynamics In Three-Dimensional Microfluidic Channels, Hussameddine S. Kabbani, Aihua Wang, Xiaobing Luo, Shizhi Qian

Mechanical Engineering Faculty Research

RedOx-based magnetohydrodynamic MHD[1] flows in three-dimensional microfluidic channels are investigated theoretically with a coupled mathematical model consisting of the Nernst-Planck equations for the concentrations of ionic species, the local electroneutrality condition for the electric potential, and the Navier-Stokes equations for the flow field. A potential difference is externally applied across two planar electrodes positioned along the opposing walls of a microchannel that is filled with a dilute RedOx electrolyte solution, and a Faradaic current transmitted through the solution results. The entire device is positioned under a magnetic field which can be provided by either a permanent magnet or an electromagnet. …

Capillary-Driven Flows Along Rounded Interior Corners, Yongkang Chen, Mark M. Weislogel, Cory L. Nardin

Mechanical and Materials Engineering Faculty Publications and Presentations

The problem of low-gravity isothermal capillary flow along interior corners that are rounded is revisited analytically in this work. By careful selection of geometric length scales and through the introduction of a new geometric scaling parameter Tc, the Navier–Stokes equation is reduced to a convenient∼O(1) form for both analytic and numeric solutions for all values of corner half-angle α and corner roundedness ratio λ for perfectly wetting fluids. The scaling and analysis of the problem captures much of the intricate geometric dependence of the viscous resistance and significantly reduces the reliance on numerical data compared with several previous solution methods …

Flow Control Of Airfoil At Post-Stall Conditions By Multiple Frequency Applied Saado Jets, A. Şamil Demirsöz

Mechanical & Aerospace Engineering Theses & Dissertations

Flow separation over lifting aerodynamic components, such as airfoils and wings, occurs during stall conditions which are caused by adverse changes (i.e.; high angle of attack, inflow conditions, etc.) in the operating conditions of aerodynamic components. During stall conditions, the flow over airfoil loses its momentum, creating high pressure zones on the upper surface of the airfoil and even a small increase in pressure causes the fluid particles to stop and separate to a low pressure zone. In order to eliminate the flow separation, the low momentum flow should be removed in order to maintain the high momentum and low …

Response To "Comment On Variational Approach To The Volume Viscosity Of Fluids" [Phys. Fluids 18, 109101 (2006)], Allen J. Zuckerwar, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

We respond to the Comment of Markus Scholle and therewith revise our material entropy constraint to account for the production of entropy. (c) 2006 American Institute of Physics.

Variational Approach To The Volume Viscosity Of Fluids, Allan J. Zuckerwar, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

The variational principle of Hamilton is applied to develop an analytical formulation to describe the volume viscosity in fluids. The procedure described here differs from those used in the past in that a dissipative process is represented by the chemical affinity and progress variable (sometimes called "order parameter") of a reacting species. These state variables appear in the variational integral in two places: first, in the expression for the internal energy, and second, in a subsidiary condition accounting for the conservation of the reacting species. As a result of the variational procedure, two dissipative terms appear in the Navier-Stokes equation. …

Adaptive Harmonic Balance Method For Unsteady, Nonlinear, One-Dimensional Periodic Flows, Raymond C. Maple

Theses and Dissertations

A new adaptive split-domain harmonic balance computational fluid dynamics (CFD) method is developed to solve highly nonlinear time-periodic flows such as those found in turbomachinery. The basic harmonic balance CFD method transforms an unsteady time-periodic problem into a steady-state problem by assuming a solution in the form of a Fourier series in time. The new method employs a unique multi-domain split-operator solution technique to remove a large-series stability restriction present in previous harmonic balance CFD approaches. In addition, the new method adapts the frequency content to the flow, starting with a small number of Fourier frequencies and augmenting the frequency …

Computational Aerodynamic Analysis Of The Flow Field About A Hypervelocity Test Sled, Andrew J. Lofthouse

Theses and Dissertations

The flow field about the nose section of a hypervelocity test sled is computed using computational fluid dynamics. The numerical model of the test sled corresponds to the Nike O/U narrow gage sled used in the upgrade program at the High Speed Test Track facility, Holloman Air Force Base, New Mexico. The high temperatures and pressures resulting from the aerodynamic heating and loading affect the sled structure and the performance of the vehicle. The sled transitions from an air environment to a helium environment at a speed of approximately 3,300 feet per second (Mach 3 in air, Mach 1.02 in …

Reduced Order Modeling For High Speed Flows With Moving Shocks, David J. Lucia

Theses and Dissertations

The use of Proper Orthogonal Decomposition (POD) for reduced order modeling (ROM) of fluid problems is extended to high-speed compressible fluid flows. The challenge in using POD for high-speed flows is presented by the presence of moving discontinuities in the flow field. To overcome these difficulties, a domain decomposition approach is developed that isolates the region containing the moving shock wave for special treatment. The domain decomposition implementation produces internal boundaries between the various domain sections. The domains are linked using optimization-based solvers which employ constraints to ensure smoothness in overlapping portions of the internal boundary. This approach is applied …

Computational Fluid Dynamic Study Of A Nascar Winston Cup Series Race Car, Terry L. Meek Jr.

Mechanical & Aerospace Engineering Theses & Dissertations

Since the goal of NASCAR racing is to win and since drag is a force the vehicle must overcome, a thorough understanding of the drag generating airflow around and through the automobile is greatly desired. The external airflow contributes to most of the drag that a car experiences and most of the downforce the vehicle produces. Therefore, an estimate of the vehicle's performance may be evaluated using a computational aerodynamics model. This thesis presents a computational fluid dynamic (CFD) analysis of a NASCAR Winston Cup series race car to investigate the salient flow characteristics.

Before a computational analysis could be …

Efficient Dynamic Unstructured Methods And Applications For Transonic Flows And Hypersonic Stage Separation, Xiaobing Luo

Mechanical & Aerospace Engineering Theses & Dissertations

Relative-moving boundary problems have a wide variety of applications. They appear in staging during a launch process, store separation from a military aircraft, rotor-stator interaction in turbomachinery, and dynamic aeroelasticity.

The dynamic unstructured technology (DUT) is potentially a strong approach to simulate unsteady flows around relative-moving bodies, by solving time-dependent governing equations. The dual-time stepping scheme is implemented to improve its efficiency while not compromising the accuracy of solutions. The validation of the implicit scheme is performed on a pitching NACA0012 airfoil and a rectangular wing with low reduced frequencies in transonic flows. All the matured accelerating techniques, including the …

Vortex Wake And Exhaust Plume Interaction, Including Ground Effect, Ihab Gaber Adam

Mechanical & Aerospace Engineering Theses & Dissertations

Computational modeling and studies of the near-field wake-vortex turbulent flows, far-field turbulent wake-vortex/exhaust-plume interaction for subsonic and High Speed Civil Transport (HSCT) airplane, and wake-vortex/exhaust-plume interaction with the ground are carried out. The three-dimensional, compressible Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The turbulence models of Baldwin and Lomax, one-equation model of Spalart and Allmaras and two-equation shear stress transport model of Menter are implemented with the RANS solver for turbulent-flow modeling.

For the near-field study, computations are carried out on a fine grid for a rectangular wing with a NACA-0012 airfoil section and …

A Study Of The Numerical Implementation Of Multidisciplinary Design Optimization Strategies, Rodney A. Taylor

Mechanical & Aerospace Engineering Theses & Dissertations

Design optimization provides an organized, systematic, and efficient method for obtaining design improvements based upon a specified measure of design performance. In the multidisciplinary design optimization (MDO) environment efficient optimization techniques allow complex designs to be improved by managing conflicting disciplinary design goals so as to improve the global design. This thesis studies the implementation issues surrounding MDO techniques and strategies. To facilitate this investigation two testbed problems have been selected for study. These problems consider two approaches to the conceptual design of an aeroelastic wing. The first approach is based on an idealized, two-dimensional representation of an airfoil under …

Wing-Section Optimization For Supersonic Viscous Flow, Cem Cihan Item

Mechanical & Aerospace Engineering Theses & Dissertations

The recent interest in the High Speed Civil Transport (HSCT) has resulted in renewed research studies of optimized supersonic cruise transport configurations. Incorporation of flow viscosity effects in the design process of such a supersonic wing is currently under investigation. This may lead to more accurate problem formulations and, in tum, greater aerodynamic efficiency than can be obtained by the traditional, inviscid, linear theories. In this context, for a design code to be a candidate for a complex optimization problem, such as three-dimensional viscous supersonic wing design, it should be validated using simpler building-block shapes.

To optimize the shape of …

Simulation Of Vertical Tail Buffet In Internal Vortex Breakdown Flows, Mark William Flanagan

Mechanical & Aerospace Engineering Theses & Dissertations

Computational simulation of vertical tail buffet in an internal vortex breakdown flow is considered. The fiuid-flow problem is formulated using the full, compressible, unsteady Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite volume scheme. The fluid-flow problem is solved in a configured circular duct using quasi-axisymmetric assumptions to simplify the flow equations. A plate is placed transverse to the incoming flow. Solution of the flow in the duct is performed with and without a rigid plate, and with and without an elastic plate. The elastic response of the plate is calculated assuming that it is a cantilever …

Application Of Sensitivity Analysis To The Euler Equations, Vamshi Mohan Korivi

Mechanical & Aerospace Engineering Theses & Dissertations

An approximation method is presented for efficiently predicting the changes which occur in a steady-state numerical solution of the Euler equations as a consequence of a small change in the geometric shape of the domain. The method is extended to develop a general procedure for calculating aerodynamic sensitivity derivatives with respect to variations of geometric shape. The techniques are implemented using an upwind cell centered finite volume formulation, and are applied to two test cases, (1) a subsonic nozzle (M_∞ = 0.85), and (2) a supersonic inlet (M_∞ = 2.0). Conventional numerical solutions are first obtained for flow …

Effect Of Passive Flow-Control Devices On The Drug Of A Tractor-Trailer Model, Jagjit K. Ahuja

Mechanical & Aerospace Engineering Theses & Dissertations

The aerodynamic drag of tractor trailers is responsible for approximately half of the fuel consumption at highway speeds (55m.p.h.). Thus, it is important that vehicle drag be reduced in order to reduce operating costs and to conserve fuel. The purpose of the subject research conducted in the Old Dominion University Low-Speed Wind Tunnel was to determine the effect of various add-on flow-control devices, such as a cab-mounted flow deflector and gap seals between the tractor and the trailer. In addition, the effect of trailer rear-edge shaping has been studied. This was accomplished by contouring the trailer's rear end. It has …

Navier-Stokes Analysis Of Cold Gas Scramjet Nozzle-Afterbody Flowfields, Walter C. Engelund

Mechanical & Aerospace Engineering Theses & Dissertations

The recent renewal of interest in hypersonic aerodynamics, brought about largely in part due to the development of the National Aerospace Plane (NASP), is resulting in an increased reliance on computational fluid dynamics for flowfield data in this flight regime. The design of the nozzle-afterbody section for a hypersonic transport such as the NASP is currently underway, and is being conducted using both computational fluid dynamics and cold, non-reacting, simulant gas experimental models. In this study, a computational analysis is conducted for the flow through a scramjet nozzle-afterbody test section.

Computations have been performed for a cold gas simulation of …

Domain Decomposition For Multigrid, Finite Volume Flow Solvers, Victor Robert Lessard

Mechanical & Aerospace Engineering Theses & Dissertations

Computing the flow fields about three-dimensional complex configurations accurately becomes a difficult task, if it is attempted to generate a single, body fitted grid with proper clustering. The domain decomposition methods, which divide the computational domain into less complex subdomains, are extensively used to decrease the grid generation workload. A domain decomposition technique also allows the use of different solution methods for different subdomains. The objective of this work is to develop a domain decomposition method via overlapping/embedding the component grids, which is to be used by upwind, multigrid, finite volume solution algorithms. A computer code, given the name MaGGiE, …

Evaluation Of Equilibrium Turbulence For A Hypersonic Boundary Layer At Nonadiabatic Wall Conditions, Cindy W. Albertson

Mechanical & Aerospace Engineering Theses & Dissertations

This paper presents an experimental study to characterize the compressible turbulent boundary layer produced along a flat plate in the NASA Langley 8-Foot High Temperature Tunnel and determine the test conditions necessary to achieve equilibrium turbulence. In addition, the present study extends the data base for equilibrium compressible turbulent boundary layers over quasi-isothermal walls which are far from the adiabatic wall temperature. The measurements consist of pilot pressure, static pressure, and total temperature distributions in the boundary layer. A flat plate measuring 9.7 feet long and 4.3, feet wide was used for the study to provide a naturally turbulent boundary …

Calculations Of Three-Dimensional Transonic Flows Using The Implicit Formulation Of The Isenthalpic Euler Equations With Flux Vector Splitting, Frank E. Cannizzaro

Mechanical & Aerospace Engineering Theses & Dissertations

A numerical method for solving three-dimensional transonic flows using the isenthalpic formulation of the Euler equations is developed. The method uses van Leer's flux vector splitting to solve the implicit formulation of the governing equations, which are applied to a cell centered finite-volume scheme. A three factor spatial approximate factorization is implemented in solving the implicit part of the governing equations. Time marching to a steady state solution requires short computational times due to the relative efficiency of the basic method. Computational times are further reduced by the implementation of the multigrid acceleration technique, which provided converged solutions in approximately …

An Evaluation Of A Taylor-Galerkin Algorithm For High Speed Inviscid Flows Using Quadrilateral And Triangular Elements, Kim S. Bey

Mechanical & Aerospace Engineering Theses & Dissertations

The Taylor-Galerkin finite element algorithm is used to obtain solutions to the two-dimensional compressible Euler equations. The mathematical formulation of the algorithm is presented for a typical scalar equation. The derivation results in element equations which are assembled over the entire solution domain to obtain the system of equations that are solved explicitly. The algorithm has the unique feature that the finite element matrices can be evaluated in closed form, avoiding expensive numerical integration. Aspects of vector programming strategies and mesh generation important to an effective analysis procedure are also described. Solutions to supersonic flow problems with exact solutions are …

Implementation Of Uniform Perturbation Method For Potential Flow Past Axisymmetric And Two-Dimensional Bodies, Tin Chee Wong

Mechanical & Aerospace Engineering Theses & Dissertations

The aerodynamic characteristics of potential flow past an axisymmetric slender body and a thin airfoil are calculated by using a uniform perturbation analysis method. The method is based on the superposition of potentials of point singularities distributed inside the body. The strength distribution satisfies a linear integral equation by enforcing the flow tangency condition on the surface of the body. The complete uniform asymptotic expansion of its solution is obtained with respect to the slenderness ratio by modifying and adapting an existing technique. Results calculated by the perturbation analysis method are compared with the existing surface-singularity-panel method and some available …