Recursos de colección

DSpace at MIT (104.280 recursos)

This site is a university repository providing access to the publication output of the institution. Registered users can set up email alerts to notify them of newly added relevant content. A certain level of encryption and security is embedded in the site which may cause some users accessibility problems.

Aerospace Computational Design Laboratory: Technical Reports

Mostrando recursos 1 - 20 de 33

  1. Investigation of the F117A Vortical Flow Characteristics Preliminary Results

    Vermeersch, Sabine
    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...

  2. Adaptive Mesh Euler Equation Computations of Vortex Breakdown in Delta Wing Flow

    Modiano, David
    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 high angle...

  3. System Identification and Active Control of a Turbulent Boundary Layer

    Rathnasingham, Ruben
    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...

  4. A Comparison of Numerical Schemes on Triangular and Quadrilateral Models

    Lindquist, Dana Rae

  5. Numerical Simulation of Hypersonic Flow Over a Blunt Leading Edge Delta Wing

    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 [21] and Goodsell [7]. The Navier-Stokes results were obtained on the semi-implicit extension of the inviscid code, developed by Loyd [17]. 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...

  6. A Semi-Implicit Navier-Stokes Solver and Its Application to a Study of Separated Flow about Blunt Delta Wings

    Loyd, Bernard
    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...

  7. Visualization of Three Dimensional CFD Results


    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...

  8. On Dual-Weighted Residual Error Estimates for p-Dependent Discretizations

    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.

  9. Reduced-order aerodynamic models for aeroelastic control of turbomachines

    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...

  10. An Arnoldi Approach for Generation of Reduced Order Models for Turbomachinery

    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...

  11. Integral methods for three-dimensional boundary layers

    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...

  12. System Identification and Active Control of a Turbulent Boundary Layer

    Rathnasingham, Ruben
    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...

  13. Silicon micromachined sensors and sensor arrays for shear-stress measurements in aerodynamic flows

    Padmanabhan, Aravind
    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)....

  14. A Posteriori Bounds for Linear Functional Outputs of Hyperbolic Partial Differential Equations

    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...

  15. Analysis and design of axisymmetric transonic flow with linearized three-dimensional flow prediction

    Ahn, Jon
    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...

  16. Small-Scale Forcing of a Turbulent Boundary Layer

    Lorkowski, Thomas
    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]...

  17. Simulations of a passively actuated oscillating airfoil using a Discontinuous Galerkin method

    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....

  18. Development of Astronaut Reorientation Methods: A Computational and Experimental Study

    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...

  19. Solution of Fluid-Structure Interaction Problems using a Discontinuous Galerkin Technique

    Mohnot, Anshul
    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...

  20. Model Reduction for Dynamic Sensor Steering: A Bayesian Approach to Inverse Problems

    Wogrin, Sonja
    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...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.