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Propulsion and Combustion
^ Analysis of Mean Flow and Turbulence Effects on Acoustic Response Threshold in Solid Propellant Rockets
R. A. Beddini,* Y. Lee
California Institute of Technology, CIT subcontract from ONR

Nonlinear combustion stability theories require and depend strongly on what is traditionally termed a velocity response function. Through computational solutions of a turbulence and combustion model, prior work has shown that a significant source of response to solid rocket aeroacoustics can result from the interaction between acoustically induced turbulence and combustion processes. This research effort undertakes an approximate analysis of the effects of mean and oscillatory flow on the velocity response threshold condition using linear, hydrodynamic stability theory. Recent results include the prediction of the threshold condition and the discovery of a new, parametrically excited vortex instability mode.

^ Stability of Flows through Porous Media at Large Reynolds Number
R. A. Beddini,* C. Low
University of Illinois

Porous walls are often used for the surfaces of rocket chambers and their experimental simulators. It has been experimentally observed that as the Reynolds number of the flow based on pore size becomes of the order 10 or more, the flow becomes unstable, with large magnitude nonuniformities. These disturbances are observed to be nearly random spatially, but temporally steady. This is a "pseudo-turbulence" phenomenon that has not been addressed analytically in the literature. The mechanism is related to the nonlinear drag terms in the equations of motion. Linear instability techniques are being employed to analyze the flow.

^ Flows in Star-Grained Propellants
J. Buckmaster*
U.S. Air Force Office of Scientific Research, F49620-96-1-0031, ASSERT F49620-97-0464; DOE Center for the Simulation of Advanced Rockets

The flow in a solid propellant rocket chamber is essentially inviscid, albeit rotational. In this study, researchers are concerned with the flow in the arms of star-grained propellants. Results are also applicable to the flow in propellant cracks, an important issue in accident scenarios.

^ Homogenization Issues in Modeling Heterogeneous Propellants
J. Buckmaster*
Center for Simulation of Advanced Rockets; Air Force Office of Scientific Research

In modeling the combustion of heterogeneous propellants, strategies are needed to account for oxidizer particles that are too small to resolve numerically. These particles are homogenized with the fuel binder, to form a mixture in which the larger resolvable particles are imbedded. The properties of the mixture (that is, heat conduction coefficient) have to be determined from the properties of the individual components and the characteristics of the small particles, which is the goal of this project.

^ Ignition Models for Solid Propellant Rocket Motors
J. Buckmaster;* P. Alavilli, T. L. Jackson (CSAR); M. Short (Theoret. & Appl. Mech.)
U.S. Air Force Office of Scientific Research, F49620-96-1-0031; DOE Center for the Simulation of Advanced Rockets

Solid propellant rocket motors are ignited by a flux of hot gases from an igniter at the head of the chamber. Modeling of the subsequent transients is an important issue, for if they are too violent the integrity of the motor can be compromised. Researchers are developing ignition models for inclusion in the large numerical code being developed within the Center for the Simulation of Advanced Rockets for the complete simulation of the rocket.

^ Toward a Numerical Simulation of the Combustion Layer in a Solid-Propellant Rocket Motor
J. Buckmaster;* T. L. Jackson, J. Hoeflinger (CSAR)
U.S. Air Force Office of Scientific Research, F49620-96-1-0031; DOE Center for the Simulation of Advanced Rockets

The Center for the Simulation of Advanced Rockets is concerned with the simulation of an entire solid propellant rocket system, the combustion, the gas flow and acoustics, the structure, and the material behavior. Different groups in various departments of the college are responsible for different ingredients in this study. This research team is concerned with the combustion processes that occur near the surface of the solid propellant and their detailed numerical simulation.

^ Multipass Herriot Cell for Density Diagnostics in Pulsed Thrusters
R. L. Burton,* E. Antonsen
U.S. Air Force Research Laboratory, F04700-98-W-1204
rburton@uiuc.edu

The low neutral density in the exhaust of a pulsed plasma thruster (PPT) can be measured if the optical path length is sufficiently long. This measurement, requiring at least 12 passes of a laser beam through the exhaust plume of the PPT, can be achieved with a Herriot cell coupled to an interferometer. This research effort has designed and fabricated a Herriot cell for PPT density measurements and is performing the measurements under typical PPT operating conditions. The resulting measurements will be used to validate gasdynamic models of PPT operation

^ Performance of Coaxial Teflon Pulsed Plasma Thrusters
R. L. Burton,* F. Rysanek, S. Jaeger
CU Aerospace, L.L.D., F49620-99-C-0065
rburton@uiuc.edu

Pulsed plasma thrusters (PPTs) with TeflonTM propellant can operate at low power and high specific impulse for such satellite propulsion objectives as attitude control, formation flying, and orbital transfer. The coaxial TeflonTM PPT has demonstrated much higher thrust impulse than other geometries, and the goal of this research is to increase the specific impulse of this device to the 1,000-second level, while reducing thermal and two-phase flow losses.


Summary of Engineering Research