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CCS Seminar
Friday - November 19, 2010
12:00 noon
Physics Research Building - Room 595
3 Cummington Street

Professor Sheryl Grace - Mechanical Engineering -
Boston University

CFD Simulation of an Acoustic Igniter

The acoustic igniter is being considered as an ignition source to initiate combustion for space propulsion. The acoustic igniter relies on the interaction between a supersonic jet flow issuing from a nozzle and a resonance tube placed closely downstream to produce a dramatic increase in temperature in the resonance tube. The acoustic igniter systems have been shown to have two main operating modes that are dependent upon the jet’s first shock cell length and the position of the resonator. If the first shock cell is interrupted in the stable portion of the shock cell then the regurgitant mode is achieved. In this mode, temperature oscillations in the resonance tube occur on a time scale related to the axial extent of the tube. If the first shock cell is interrupted in its unstable region, the screech mode occurs. In this mode, intense heating at the end of the resonance tube is achieved and the oscillations in the tube are at very high frequency corresponding to the shock oscillation.

Most research related to acoustic igniters has been experimental. The current research strives to obtain a reliable computational method for analyzing the igniter. The simulations are performed using Overflow 2.1, a 3-D unsteady, compressible, finite-difference CFD code developed by NASA. A method for predicting the location of the Mach disc and shock cell length in a free-jet using Overflow has been demonstrated. Some trends that have been seen experimentally for the igniter have also been reproduced computationally. For instance a conical resonator shape leads to increased heating and a stepped resonator shape produces even more heating. However, because the switch between regurgitant and screech modes requires such perfect simulation of the shock, further research is needed in order to obtain accurate results for all igniter configurations and nozzle pressure ratios.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Page last updated on November 9, 2010. Please send comments to Cheryl Endicott

 

 


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