The investigation of the vortical flow around the F117A Stealth Fighter is presented in
order to demonstrate the capability to resolve leading edge vortices with an adaptive
finite element solver for the Euler equations. The major goal is to capture vortex
breakdown at high angles of attack. This work presents the five main steps involved
in a typical study of the flow characteristics of a complete aircraft : the definition of
the model geometry, the realization of a suitable grid around the discretized model,
the implementation of a flow solver, the subsequent analysis of the flow field and the
comparison to experimental data sets. The computational data...
A solution method for the three-dimensional Euler equations is formulated and implemented.
The solver uses an unstructured mesh of tetrahedral cells and performs
adaptive refinement by mesh-point embedding to increase mesh resolution in regions
of interesting flow features. The fourth-difference artificial dissipation is increased to
a higher order of accuracy using the method of Holmes and Connell. A new method
of temporal integration is developed to accelerate the explicit computation of unsteady
flows. The solver is applied to the solution of the flow around a sharp edged delta wing,
with emphasis on the behavior of the leading edge vortex above the leeside of the wing at
An experimental investigation is made into the active control of the near-wall region of a turbulent boundary layer using a linear control scheme. System identification in the boundary layer provides optimal transfer functions that predict the downstream of characteristics of the streamwise velocity and wall pressure fluctuation using an array of upstream flush-mounted sensors that are sensitive to spanwise shear. Enhanced direction techniques isolated the large scale turbulent motion and improved the downstream correlations resulting in greater controllability. The techniques were based on the conditioned spectral analysis between adjacent sensors to extract the most correlated flow structures that span the...
Lindquist, Dana Rae
Lee, Kuok Ming
Euler and Navier-Stokes results are presented for a blunt delta wing at Mach
7.15 and 300 angle of attack. The viscous calculations were done at a Reynolds
number based on chord of 5.85 x 106 with freestream and wall temperatures set to
74K and 288K respectively.
The inviscid simulations were carried out using a finite volume, central difference
code written by Roberts  and Goodsell . The Navier-Stokes results were
obtained on the semi-implicit extension of the inviscid code, developed by Loyd
The inviscid results showed a strong shock on the windward side of the wing
at a stand-off angle of about -5' from the body. As the...
A novel semi-implicit scheme for the Navier-Stokes equations is presented and evaluated.
The semi-implicit scheme combines an implicit temporal integration in the bodynormal
directions with explicit temporal integrations in the streamwise and cross stream
directions. Thus, advantages of both explicit and implicit schemes are retained in the
semi-implicit scheme. Numerical stiffness due to disparate physical scales in the normal
direction is eliminated, since stability of the algorithm depends only on relatively coarse
streamwise and cross stream grid spacing, not on the typically fine normal spacing. Approximate
factorization is unnecessary and only one matrix inversion per multi-stage
time step is required. Computations show that while a explicit scheme employing...
We have developed an interactive graphics system for the display of three dimensional
CFD solutions on unstructured hexahedral grids. This system is implemented
on a high-performance graphics supercomputer. Visualization methods employed are
shaded color surface plots, integration of particle trajectories, interpolation of volumetric
data onto a plane, interpolation of planar data onto a line segment, and extraction
of numerical quantities from a plane. We have used this graphics system to examine the
inviscid flow about the NTF delta wing, as solved by Becker, and found that it allows us
to locate flow features quickly. We were unable to find a satisfactory method to visualize
the three dimensional mesh...
Yano, Masayuki; Darmofal, David L.
This report analyzes the behavior of three variants of the dual-weighted residual (DWR) error estimates applied to the p-dependent discretization that results from the BR2 discretization of a second-order PDE. Three error estimates are assessed using two metrics: local effectivities and global effectivity. A priori error analysis is carried out to study the convergence behavior of the local and global effectivities of the three estimates. Numerical results verify the a priori error analysis.
Willcox, Karen Elizabeth
Aeroelasticity is a critical consideration in the design of gas turbine engines, both for stability and forced response. Current aeroelastic models cannot provide high-fidelity aerodynamics in a form suitable for design or control applications. In this thesis low-order, high-fidelity aerodynamic models are developed using systematic model order reduction from computational fluid dynamic (CFD) methods. Reduction techniques are presented which use the proper orthogonal decomposition, and also a new approach for turbomachinery which is based on computing Arnoldi vectors. This method matches the input-output characteristic of the CFD model and includes the proper orthogonal decomposition as a special case. Here, reduction...
Willcox, Karen; Peraire, Jaime; White, Jacob
A linear reduced-order aerodynamic model is developed for aeroelastic analysis of turbo-machines. The basis vectors are constructed using a block Arnoldi method. Although the model is cast in the time domain in state-space form, the spatial periodicity of the problem is exploited in the frequency domain to obtain these vectors efficiently. The frequency domain proper orthogonal decomposition is identified as a special case of the Arnoldi method. The aerodynamic model is coupled with a simple structural model that has two degrees of freedom for each blade. The technique is applicable to viscous and three-dimensional problems as well as multi-stage problems...
Mughal, Bilal Hafeez
Several distinct issues important in integral approximations of the three-dimensional boundary-layer equations are addressed. One of these is the requirement, justified on the basis of the nature of the full differential equations, for hyperbolicity of integral equation systems. It is generally not feasible to analytically determine the mathematical character of these systems, except in very simple cases, because of the empiricism necessary for closure. Furthermore, the use of general systems is inhibited because there is no guarantee that they are hyperbolic. A novel method accommodating the role of both equations and closure, so that systems are always hyperbolic with physically-consistent...
An experimental investigation is made into the active control of the near-wall region of a turbulent boundary layer using a linear control scheme. System identification in the boundary layer provides optimal transfer functions that predict the downstream characteristics of the streamwise velocity and wall pressure fluctuation using an array of upstream flush-mounted sensors that are sensitive to spanwise shear. Enhanced detection techniques isolated the large scale turbulent motion and improved the downstream correlations resulting in greater controllability. The techniques were based on the conditioned spectral analysis between adjacent sensors to extract the most correlated flow structures that span the distance...
In this thesis we report on a new micromachined floating-element shear-stress sensor for turbulent boundary layer research. Applications in low shear-stress environments such as turbulent boundary layers require extremely high sensitivity to detect the small forces (O(nN)) and correspondingly small displacements (O(A)) of the floating-element. In addition, unsteady measurements in turbulent flows require sensors with high operating bandwidth (~20 kHz). These requirements render most of the existing shear-stress measurement techniques inadequate for this application. In response to the limitations of the existing devices, we have developed a sensor based on a new transduction scheme (optical position sensing by integrated photodiodes)....
Vailong, Hubert J. B.
One of the major difficulties faced in the numerical resolution of the equations of physics is to decide on the right balance between computational cost and solutions accuracy, and to determine how solutions errors affect some given “outputs of interest.” This thesis presents a technique to generate upper and lower bounds for outputs of hyperbolic partial differential equations. The outputs of interest considered are linear functionals of the solutions of the equations. The method is based on the construction of an “augmented” Lagrangian, which includes a formulation of the output as a quadratic form to be minimized and the equilibrium...
The primary goal of this thesis is the application of the proven stream-surface based Newton method to analysis/design of an axisymmetric nacelle with the actuator disk modeling of a fan. And to further utilize the benefits of the Newton method, full attention is given to the linearized prediction of three-dimensional flow from a base axisymmetric solution, with an aim at replacing costly three-dimensional flow computations during initial nacelle design stages. The resulting code is to be called AMIS (Axisymmetric Multiple-passage Interacting Stream_surface Euler solver) to denote the lineage of Newton solver family pioneered by Drela and Giles, although AMIS has...
In order to understand the effect of small scale forcing on turbulent flows and its implications on control, an experimental investigation is made into the forcing of the inertial scales in the wall region of a turbulent boundary layer. A wall-mounted resonant actuator is used to produce a local vortical structure in the streamwise direction which is convected downstream by the boundary layer flow. The frequency associated with this structure is governed by the resonant frequency of the device and falls in the range of the inertial scales at the Reynolds number of the experiment (Re[theta] [is approximately equal to]...
Israeli, Emily Renee
Natural flappers, such as birds and bats, effectively maneuver in transitional, low Reynolds number flow, outperforming any current small engineered flapping vehicle. Thus, engineers are inspired to investigate the flapping dynamics present in nature to further understand the non-tradional flow aerodynamics in which they operate. Undeniably the success of biological flapping flight is the exploitation of fluid structure interaction response i.e. wing mechanics, deformation, and morphing. Even though all these features are encountered in nature, it is important to note that natural flappers have not just adapted to optimize their aerodynamic behavior, they also have evolved due to biological constraints....
Stirling, Leia Abigail
Past spaceflight missions have shown that astronauts adapt their motor-control strategies to the microgravity environment. Even though astronauts undergo hundreds of training hours, the strategies for locomotion and orientation are not specifically prescribed. The majority of an astronaut’s motion-control strategies are developed underwater. While underwater training can be beneficial in certain aspects, such as learning which orientations an astronaut will encounter and becoming familiar with task timelines, it is not effective for self-learned motor-control strategies. Further, the development of unfamiliar tasks, such as reorienting without external forces, will most likely not occur naturally. Self-rotations—human-body rotations without external torques—are not only...
The present work aims to address the problem of fluid-structure interaction using a discontinuous Galerkin approach. Starting from the Navier-Stokes equations on a fixed domain, an arbitrary Lagrangian Eulerian (ALE) approach is used to derive the equations for the deforming domain. A geometric conservation law (GCL) is then introduced, which guarantees freestream preservation of the numerical scheme. The space discretization is performed using a discontinuous Galerkin method and time integration is performed using either an explicit four stage Runge-Kutta scheme or an implicit BDF2 scheme. The mapping parameters for the ALE formulation are then obtained using algorithms based on radial...
In many settings, distributed sensors provide dynamic measurements over a specified time horizon that can be used to reconstruct information such as parameters, states or initial conditions. This estimation task can be posed formally as an inverse problem: given a model and a set of measurements, estimate the parameters of interest. We consider the specific problem of computing in real-time the prediction of a contamination event, based on measurements obtained by mobile sensors. The spread of the contamination is modeled by the convection diffusion equation. A Bayesian approach to the inverse problem yields an estimate of the probability density function...