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Entropy-involved energy measure study of intrinsic thermoacoustic oscillations.
- Source :
-
Applied Energy . Sep2016, Vol. 177, p570-578. 9p. - Publication Year :
- 2016
-
Abstract
- It is conventionally believed that there are no self-sustained thermoacoustic oscillations in the absence of acoustic modes in combustors. However, such oscillations (also known as intrinsic thermoacoustic instability) are recently found to occur in a premixed combustor with a mean flow present but no acoustic eigenmodes involved. Practical combustors are associated with entropy waves, pressure jump and mean flow, which are ignored in previous studies without justification. In this work, an entropy-involved energy measure is defined and used to study the stability behaviors of intrinsic thermoacoustic modes. The concepts and methods are exemplified with the classical time-delay n – τ unsteady heat release model. The intrinsic thermoacoustic eigenmodes are found to be related to not only a flame transfer/describing function but also the acoustic impedance at the flame, which is boundary-dependent. It is shown that the predicted frequency ω f r of the intrinsic modes and the critical gain n c depend on the ratio T ¯ 2 / T ¯ 1 between the after- and before-combustion temperatures and the inlet mean flow Mach number M ¯ 1 . Comparison is then made between the present results and those available in literature. Good agreement is obtained for ω f r . Furthermore, the predicted stability of intrinsic modes based on calculated n c is found to agree well with direct numerical simulations (DNS). It is also interesting to show that as T ¯ 2 / T ¯ 1 → 1 , the critical gain as predicted from the previous models is n c → + ∞ , which means that all intrinsic eigenmodes are stable. However, the present works shows that n c → 1.0 . Further illustration is then performed by conducting case studies of measured flame transfer and describing functions in premixed combustors. The present work opens up an alternative but more applicable way to study intrinsic thermoacoustic oscillations via the entropy-involved energy measure. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 03062619
- Volume :
- 177
- Database :
- Academic Search Index
- Journal :
- Applied Energy
- Publication Type :
- Academic Journal
- Accession number :
- 116630384
- Full Text :
- https://doi.org/10.1016/j.apenergy.2016.05.142