N101-040 TITLE: Acoustic Stability Prediction In Solid Rocket Motors

TECHNOLOGY AREAS: Air Platform, Battlespace, Weapons

ACQUISITION PROGRAM: PMA-259, Air-to-Air Missile Systems

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OBJECTIVE: Develop a ballistic model coupled to a three-dimensional acoustic mode solver that improves solid rocket performance prediction ballistic and acoustic stability calculations.

DESCRIPTION: The Navy, Air Force, Army, and to some extent NASA, currently depend upon Air Force funded Solid propellant rocket motor Performance computer Program (SPP) to evaluate the acoustic stability of solid rocket motors. Recently, numerous development rocket motors have experienced stability concerns that are outside the predictive capability of the current stability codes. These include rate-mechanical relationships on stability and flow around stress relief slots that are found on nearly all tactical motors. It is proposed to increase the stability predictive capability of our current models to include these recently observed phenomena. The rate-mechanical anomalous behavior is believed to result in changes in local burning rate brought on by grain geometry stress and strain that result from motor pressurization, grain deformation, and uneven loads on the motor solid propellant grain. Vortical flow improvements will allow more accurate ballistic predictions resulting in better acoustical flow interactions around and from slots and fins in the motor grain. These interactions are believed to have caused or contributed to several recent motor problems. The current codes relay on outdated matrix solvers to predict the acoustic coupling with the ballistic fluid dynamics. Newer methods are available to improve both the accuracy and improved resolution of the internal fluid dynamics. Finally, with minor changes to the current ballistics code, prediction of the level of thrust oscillation for a given pressure oscillation would be a helpful feature to add to the current code. This feature would be useful to system engineers wanting to know at what level oscillatory combustion would affect the seeker and control sections.

PHASE I: Determine the feasibility of developing a ballistic model that couples to a three-dimensional acoustic mode solver. The models must be adaptable to the existing framework of current stability prediction models.

PHASE II: Develop and demonstrate prototype physical models and implement into the framework of an existing three-dimensional grain design and ballistics code. This will include stress and strain mechanical property models, vortical flow models, and improved numerical solvers.

PHASE III: Refine the code including operational manuals, test cases, and graphical interfaces and provide a variety of versions for transition into relevant computer platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Improved methods for evaluating the acoustic stability of solid rocket motors will be directly applicable to organizations providing commercial launch services to the satellite industry. Launch vehicles that are considered rely on solid rocket motors as a means of propulsion. Technology developed under this SBIR effort would provide improvements in the accuracy to predict solid rocket stability, yielding cost reductions in solid rocket motor development.

REFERENCES:
1. "Nonlinear Combustion Instabilities and Stochastic Sources" V.S. Burnley, Ph�D Thesis, California Institute of Technology, Pasadena, CA, 1996.

2. "Some Influences Of Nonlinear Energy Transfer Between The Mean Flow And Fluctuations," F.E.C. Culick, G.C. Isella, California Institute of Technology, Proceedings of the JANNAF Combustion Meeting, CPIA-PUB-662-Vol-II, Oct 97.

3. "Nonlinear Unsteady Combustion Of A Solid Propellant." G.A. Flandro, University of Tennessee, Proceedings of the JANNAF Combustion Meeting, CPIA-PUB-662-Vol-II, Oct 97.

4. "Two-Phase Turbulent Flow Interactions In A Simulated Rocket Motor With Acoustic Waves. W. Cai and V. Yang, Pennsylvania State University, Proceedings of the JANNAF Combustion Meeting, CPIA-PUB-662-Vol-II, Oct 97.

5. "Some Influences of Noise on Combustion Instabilities and Combustor Dynamics", F.E.C. Culick and C. Seywert, 36th JANNAF Combustion Meeting, Cocoa Beach, Florida, Oct 99.

6. "Stability Testing of Full Scale Tactical Motors," F.S. Blomshield, J.E. Crump, H.B. Mathes, R.A. Stalnaker and M.W. Beckstead, NAWCWD, China Lake, AIAA Journal of Propulsion and Power, Nol. 13. No. 3, pp. 349-355, May-June 1997.

7. "Nonlinear Stability Testing of Full-Scale Tactical Motors," F.S. Blomshield, J.E. Crump, H.B. Mathes, C.A. Beiter and M.W. Beckstead, NAWCWD, China Lake, AIAA Journal of Propulsion and Power, Nol. 13. No. 3, pp. 356-366, May-June 1997.

8. "Pulsed Motor Firings," F.S. Blomshield, NAWCWD, China Lake, NAWCWD TP 8444, March 2000.

KEYWORDS: Combustion; Solid Rockets; Stability; Grain Design; Ballistics; Performance Prediction

** TOPIC AUTHOR (TPOC) **

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