Instabilities acoustical

Acoustic instabilities involve the interactions of acoustic waves with the combustion processes. These instabilities are of high frequency and can be significant in certain situations but can successfully be avoided by suitable design (11,24). 

A discussion with 10 refs of combustion instability in solid-proplnt rocket engines. Two different types of instability are considered acoustic and non-acoustic instability... 

B6. Beckstead, M., Non-acoustic Instability of Solid Propellants, Ph.D. Thesis, Univ. of Utah, Salt Lake City, Utah, 1965. 

This chapter considers the first group of instabilities and introduces the analysis of processes implying an interaction with external flow-field perturbahons. This is exemplified by investigations of coupling between pressure waves and plane flames and also between an external acceleration field and flame fronts. The coupling between flow perturbations and flames giving rise to heat release unsteadiness and coupling with acoushc modes is considered in Chapter 5.2, which deals with the relationship between perturbed flame dynamics and radiated acoustic field, a fundamental process of thermo-acoustic instabilities. 

G. Searby and D. Rochwerger. A parametric acoustic instability in premixed flames. Journal of Fluid Mechanics, 231 529-543,1991. 

P. Clavin and J. Sun. Theory of acoustic instabilities of planar flames propagating in sprays or particle-laden gases. Combustion Science and Technology, 78 265-288, 1991. 

J.D. Buckmaster and P. Clavin. An acoustic instability theory for particle-cloud flames. Proceedings of the Combustion Institute, 24 29-36,1992. 

C. Clanet, G. Searby, and P. Clavin. Primary acoustic instability of flames propagating in tubes Cases of spray and premixed gas combustion. Journal of Fluid Mechanics, 385 157-197,1999. 

G. Searby. Acoustic instability in premixed flames. Combustion Science and Technology, 81 221-231, 1992. 

Perturbed Flame Dynamics and Thermo-Acoustic Instabilities... 

Block diagram of processes involved in thermo-acoustic instabilities. 

The fundamentals of combustion instability are presented by G. Searby in Chapter 5.1 and phenomena examined by him fall into two categories instability of flame fronts and thermo-acoustic instabilities. Each category can be subdivided further, and these are discussed. 

The physical properties are independent of pressure. (This assumption is valid only for density wave instability at high pressures it is not valid for acoustic instability.)... 

Kubota, N., Yano, Y, and Kuwahara, T, Particulate Damping of Acoustic Instability in RDX/AP Composite Propellant Combustion, AlAA-82-1223, AlAA, New York (1982). 

D.W. Rice, CombstnFlame 8(1), 21-8 (1964) CA 60, 14325 (1964) (Effect of compositional variables upon oscillatory combustion of solid rocket propellants) N ) R.W. Hart F.T. McClure, "Theory of Acoustic Instability in Solid Propellant Rocket Combustion , lOthSympCombstn (1965), pp 1047-65 N2) E.W. Price, "Experimental Solid Rocket Combustion Instability , Ibid, pp 1067-82 Qi) R.S. Levine, "Experimental Status of High Frequency Liquid Rocket Combustion Instability , Ibid, pp 1083-99 O2) L. Crocco,... 

L. Benoit and F. Nicoud. Numerical assessment of thermo-acoustic instabilities in gas turbines. Int. J. Numer. Meth. Fluids, 47(8-9) 849-855, 2005. 

Instabilities arise in combustion processes in many different ways a thorough classification is difficult to present because so many different phenomena may be involved. In one approach [1], a classification is based on the components of a system (such as a motor or an industrial boiler) that participate in the instability in an essential fashion. Three major categories are identified intrinsic instabilities, which may develop irrespective of whether the combustion occurs within a combustion chamber, chamber instabilities, which are specifically associated with the occurrence of combustion within a chamber, and system instabilities, which involve an interaction of processes occurring within a combustion chamber with processes operative in at least one other part of the system. Within each of the three major categories are several subcategories selected according to the nature of the physical processes that participate in the instability. Thus intrinsic instabilities may involve chemical-kinetic instabilities, diffusive-thermal instabilities, or hydrodynamic instabilities, for example. Chamber instabilities may be caused by acoustic instabilities, shock instabilities, or fiuid-dynamic instabilities within chambers, and system instabilities may be associated with feed-system interactions or exhaust-system interactions, for example, and have been assigned different specific names in different contexts. 

Acoustic Instabilities in Solid-Propellant Rocket Motors... 

Among the areas not covered here is that of intrinsic instabilities associated with chemical-kinetic mechanisms, as exhibited in cool-flame phenomena, for example these subjects are touched briefly in Section B.2.5.3. Intrinsic instabilities of detonations were considered in Section 6.3.1 and will not be revisited. Certain aspects of intrinsic instabilities of diffusion flames were mentioned briefly in Section 3.4.4 diffusion flames appear to exhibit fewer intrinsic instabilities than premixed flames, although under appropriate experimental conditions their effects can be observed, as indicated at the end of Section 9.5.2. Certain chamber instabilities that are not related to acoustic instabilities (such as Coanda effects—oscillatory attachment of flows to different walls) will not be discussed here, but reviews are available [1]. 

ACOUSTIC INSTABILITIES IN SOLID-PROPELLANT ROCKET MOTORS... 

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