Numerical analysis of transient combustion response to acoustic oscillations in axisymmetric rocket motors

A numerical analysis of unsteady motions in solid rocket motors with a nozzle has been conducted. The formulation treats the complete conservation equations for the gas phase and the one-dimensional equations in the radial direction for the condensed phase. A fully coupled implicit scheme based on a dual time-stepping integration algorithm has been adopted to solve the governing equations and associated boundary conditions. After obtaining a steady state solution, periodic pressure oscillations are imposed at the head end to simulate acoustic oscillations of a traveling-wave motion in the combustion chamber. The amplitude of the pressure oscillation is 1.0 % of the mean pressure and the frequency is 1790 Hz, corresponding to the twice of the fundamental frequency of the chamber. Magnitude and phase of pressure and axial velocity fluctuations are influenced by the upstream reflecting wave from the nozzle wall. Axial velocity near surface region oscillates in phase advance manner with reference to the acoustic pressure. Large vorticity fluctuations are observed in near surface region. The mass-flow-rate at the nozzle exit periodically oscillates with a time delay compared to the imposed pressure oscillations at the head end

Applications of Various Methods of Analysis to Combustion Instabilities in Solid Propellant Rockets

Instabilities of motions in a combustion chamber are consequences of the coupled dynamics of combustion processes and of the flow in the chamber. The extreme complexities of the problem always require approximations of various sorts to make progress in understanding the mechanisms and behavior of combustion instabilities. This paper covers recent progress in the subject, mainly summarizing efforts in two areas: approximate analysis based on a form of Galerkin's method, particularly useful for understanding the global linear and nonlinear dynamics of combustion instabilities and numerical simulations intended to accommodate as fully as possible fundamental chemical processes in both the condensed and gaseous phases. One purpose of current work is to bring closer together these approaches to produce more comprehensive and detailed realistic results applicable to the interpretation of observations and for design of new rockets for both space and military applications. Particularly important are the goals of determining the connections between chemical composition and instabilities; and the influences of geometry on nonlinear behavior

Transient combustion responses of homogeneous propellants to acoustic oscillations in axisymmetric rocket motors

A numerical analysis of unsteady motions in solid rocket motors has been conducted. The formulation considers a 2-D axisymmetric combustion chamber and a choke nozzle, and treats the complete conservation equations accounting for turbulence closure and finiterate chemical kinetics in the gas phase and subsurface reactions. A fully coupled implicit scheme based on a dual time-stepping integration algorithm has been adopted to solve the governing equations and associated boundary conditions. Results of the steady-state calculations indicate that the distributions of pressure in the motor and Mach number in the nozzle are one-dimensional along the axial direction. Vorticity contours show similar pattern to those of Mach number in the combustion chamber. The nozzle has an influence on the flow and temperature fields in the combustion chamber. A narrow pressure pulse is imposed at the head end to simulate unsteady acoustic oscillations in the combustion chamber. When the front of the pulse reaches near the nozzle throat, pressure near the nozzle throat increases and blocks the hot gas flow from passing through the nozzle throat. Self-generated oscillations have similar frequencies to those of standing waves of the combustion chamber. Large vorticity fluctuations are observed in near surface region. The luminous flame zone responds to low-frequency pressure wave rather than highfrequency one. Temperature fluctuations in the primary flame zone of the head end oscillates independently of the imposed pressure oscillations while temperature fluctuations in downstream region show pressure-dependent oscillations

Numerical study of acoustic oscillations and combustion instabilities in solid propellant rocket

A numerical analysis of unsteady motions in solid rocket motors has been conducted. A fully coupled implicit scheme based on a dual time-stepping integration algorithm has been adopted to solve the governing equations and associated boundary conditions. A narrow pressure pulse is imposed at the head end to simulate unsteady acoustic oscillations in the combustion chamber. Pressure increases when the front of the pulse reaches near the nozzle area. Self-generated oscillations with frequency of standing wave propagates upstream in the combustion chamber. Investigation of transient response of gas-phase dynamics to traveling pressure wave and its effects on propellant combustion reveals several aspects: Combustion responses have a strong relationship with vorticity fluctuations in case of high turbulent intensity on the propellant surface. Temperature fluctuations of the propellant surface in the head end region seem to be very unstable and independent of the pressure wave. Surface temperature without turbulence effect looks more sensitive to temperature fluctuations in the primary flame zone. Stability of surface temperature is strongly related to turbulent intensity on the propellant surface

Failure of classical elasticity in auxetic foams

A recent derivation [P.H. Mott and C.M. Roland, Phys. Rev. B 80, 132104 (2009).] of the bounds on Poisson's ratio, v, for linearly elastic materials showed that the conventional lower limit, -1, is wrong, and that v cannot be less than 0.2 for classical elasticity to be valid. This is a significant result, since it is precisely for materials having small values of v that direct measurements are not feasible, so that v must be calculated from other elastic constants. Herein we measure directly Poisson's ratio for four materials, two for which the more restrictive bounds on v apply, and two having values below this limit of 0.2. We find that while the measured v for the former are equivalent to values calculated from the shear and tensile moduli, for two auxetic materials (v < 0), the equations of classical elasticity give inaccurate values of v. This is experimental corroboration that the correct lower limit on Poisson's ratio is 0.2 in order for classical elasticity to apply.Comment: 9 pages, 2 figure

Origin of the Immirzi Parameter

Using quadratic spinor techniques we demonstrate that the Immirzi parameter can be expressed as ratio between scalar and pseudo-scalar contributions in the theory and can be interpreted as a measure of how Einstein gravity differs from a generally constructed covariant theory for gravity. This interpretation is independent of how gravity is quantized. One of the important advantage of deriving the Immirzi parameter using the quadratic spinor techniques is to allow the introduction of renormalization scale associated with the Immirzi parameter through the expectation value of the spinor field upon quantization

Numerical Analysis of Solid Rocket Motor Instabilities With AP Composite Propellants

A non-steady model for the combustion of ammonium perchlorate composite propellants has been developed in order to be incorporated into a comprehensive gasdynamics model of solid rocket motor flow fields. The model including the heterogeneous combustion and turbulence mechanisms is applied to nonlinear combustion instability analyses. This paper describes the essential mechanisms and features of the model and discusses the methodology of non-steady calculations of the combustion instabilities of solid rocket motors

A Proposal for a Multi-Drive Heterogeneous Modular Pipe- Inspection Micro-Robot

This paper presents the architecture used to develop a micro-robot for narrow pipes inspection. Both the electromechanical design and the control scheme will be described. In pipe environments it is very useful to have a method to retrieve information of the state of the inside part of the pipes in order to detect damages, breaks and holes. Due to the di_erent types of pipes that exists, a modular approach with di_erent types of modules has been chosen in order to be able to adapt to the shape of the pipe and to chose the most appropriate gait. The micro-robot has been designed for narrow pipes, a _eld in which there are not many prototypes. The robot incorporates a camera module for visual inspection and several drive modules for locomotion and turn (helicoidal, inchworm, two degrees of freedom rotation). The control scheme is based on semi-distributed behavior control and is also described. A simulation environment is also presented for prototypes testing

Intercomparison of cloud properties in DYAMOND simulations over the Atlantic Ocean

We intercompared the cloud properties of the DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains (DYAMOND) simulation output over the Atlantic Ocean. The domain averaged outgoing longwave radiation (OLR) is relatively similar across the models, but the net shortwave radiation at the top of the atmosphere (NSR) shows large differences among the models. The models capture the triple modes of cloud systems corresponding to shallow, congestus, and high clouds, although their partition in these three categories is strongly model dependent. The simulated height of the shallow and congestus peaks is more robust than the peak of high clouds, whereas cloud water content exhibits larger intermodel differences than does cloud ice content. Furthermore, we investigated the resolution dependency of the vertical profiles of clouds for NICAM (Nonhydrostatic ICosahedral Atmospheric Model), ICON (Icosahedral Nonhydrostatic), and IFS (Integrated Forecasting System). We found that the averaged mixing ratio of ice clouds consistently increased with finer grid spacing. Such a consistent signal is not apparent for the mixing ratio of liquid clouds for shallow and congestus clouds. The impact of the grid spacing on OLR is smaller than on NSR and also much smaller than the intermodel differences