Multidimensional Compressible Framework for Modeling Biglobal Stability in Rocket Motors

Rocket motor stability analysis has historically been focused on two fundamental theories: the acoustic and the hydrodynamic. While the acoustic part examines the system at resonant states, the hydrodynamic component focuses on the fluid-wall interactions and the vortex shedding mechanisms which are responsible for exciting the system. Traditionally, the two concepts are studied independently and their results are then superposed for a more complete solution. In this study, we analyze the problem from a hydrodynamic standpoint and extend it to include compressibility. This is realized by reducing the linearized Navier-Stokes and energy equations to their biglobal form assuming a two-dimensional waveform with a sinusoidal temporal dependence. The suggested approach is found to be comprehensive, capturing both hydrodynamic and acoustic fields simultaneously. Doing so unifies the two phenomena commonly associated with combustion instability while accounting for interactions between resonant and non-resonant eigenmodes. In this work, results are compared and validated using analytical solutions of the vortico-acoustic waves, which incorporate a viscous correction at the wall. Regarding the hydrodynamic component, comparisons to numerical results verify the captured modes. Combined, they present an improved agreement with experimental data for the cold air injection setup. By retaining the influence of the mean flow on the unsteady motion, the technique straightforwardly displays a slight frequency shift from the Helmholtz type acoustic modes, thus confirming the behavior observed in numerous experiments. Moreover, the modal analysis extends over both the longitudinal and transverse modes, thus providing the full spectrum of the system modes related to both acoustics and hydrodynamics. In short, the present work provides physical insight into hydrodynamic-acoustic interactions leading to vortex synchronization and frequency shifting that may be associated with the amplified frequencies captured in live rocket firings. The framework presented here may be viewed as a substantial advancement in the field of biglobal stability, namely, in its ability to capture the full effects of compressibility and shearing simultaneously

High-order methods for computational fluid dynamics

2010/2011In the past two decades, the growing interest in the study of fluid flows involving discontinuities, such as shocks or high gradients, where a quadratic-convergent method may not provide a satisfactory solution, gave a notable impulse to the employment of high-order techniques. The present dissertation comprises the analysis and numerical testing of two high-order methods. The first one, belonging to the discontinuous finite-element class, is the discontinuous control-volume/finite-element method (DCVFEM) for the advection/ diffusion equation. The second method refers to the high-order finite-difference class, and is the mixed weighted non-oscillatory scheme (MWCS) for the solution of the compressible Euler equations. The methods are described from a formal point of view, a Fourier analysis is used to assess the dispersion and dissipation errors, and numerical simulations are conducted to confirm the theoretical results.XXIV Ciclo198

Annual research briefs, 1989

This report contains the 1989 annual progress reports of the Research Fellows of the Center for Turbulence Research. It is intended as a year end report to NASA, Ames Research Center which supports this group through core funding and by making available physical and intellectual resources. The Center for Turbulence Research is devoted to the fundamental study of turbulent flows; its objectives are to simulate advances in the physical understanding of turbulence, in turbulence modeling and simulation, and in turbulence control. The reports appearing in the following pages are grouped in the general areas of modeling, experimental research, theory, simulation and numerical methods, and compressible and reacting flows

The NASTRAN demonstration program manual (level 16.0)

The types of problems that can be solved with NASTRAN are presented. The nature of the problem, the underlying theory, the specific geometric and physical input quanties, and the comparison of theoretical and NASTRAN results are discussed. At least one problem for each of the rigid formats and nearly all of the elements or provided. The features of NASTRAN demonstrated by specific problems are described. The results obtained are valid

On finite element modelling of surface tension phenomena.

The objective of this work is to develop a computational framework for modelling the motion of liquid phase between moving particles associated with the processing of complex multiphase materials. The liquid phase may be present at various levels of saturation and necessarily includes numerous and irregular free surfaces. In this kind of situation the surface tension is dominant and governs the interparticle motion that plays a fundamental role during material processing. This work focuses on surface tension modelling using the finite element method. Two issues related to the modelling of surface tension are addressed in this thesis, the first one is the development of a finite element procedure capable of modelling accurately the motion of the free surface boundaries between the gas and liquid phases. The second issue is finite element modelling of surface tension at such boundaries. The finite element formulation is based on the use of the incremental flow formulation of the Lagrangian form of the initial boundary value problem governing the free surface flow. The incompressibility constraint associated with the Newtonian fluid employed in this work is imposed using the penalty method. With regard to the surface tension model, the constitutive model commonly known as the Laplace-Young equation is employed. In the Lagrangian framework the surface tension formulation emerges naturally through the weak form of the Laplace-Young equation and the use of the surface divergence theorem reduces the continuity requirement across the element boundary from to C[1] to C[0]. The performance of the finite element model of surface tension is validated by means of numerical examples for both equilibrium and dynamic cases. The finite element results are compared against both analytical solutions and experimental results

Notes on the 1966 Summer Study Program in Geophysical Fluid Dynamics at the Woods Hole Oceanographic Institution

Originally issued as Reference No. 66-46, series later renamed WHOI-.The lecturers, Drs. Howard, Stern and Veronis, have introduced the participants to several aspects of geophysical fluid dynamics at the frontiers of current research. Their choice of topic and its development was to serve, on one hand, a pedagogic function and, on the other, to suggest a variety of allied unsolved problems.National Science Foundatio

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

Advances in Modelling and Prediction on the Impact of Human Activities and Extreme Events on Environments

YesThis book is an edition of the Special Issue Advances in Modelling and Prediction on the Impact of Human Activities and Extreme Events on Environments that was published in Water journal