Thermo-acoustic behaviour of multiple flame burner decks: Transfer Function (de)composition

Abstract

The thermo-acoustic behaviour of multiple premixed laminar flames is analysed. The idea is used to (de)compose the flame Transfer Function (TF) of composite multiple flame configurations to/from the TF of constituent sub-systems of the flame. The TF superposition approach is based on the additive nature of the flame heat release rate. It is shown that the cumulative (total) flame TF can be represented as a weighted sum of elemental TF’s of the flame sub-systems where the weighting factors are related to the thermal power of the particular flames. On the basis of this approach, the thermo-acoustic TF’s of the burner decks with regular round hole perforation are experimentally studied. It is found that, the perforation hole diameter and the perforation pattern porosity are the governing parameters of the constituent TF’s. For burner decks with square patterns of unisize round holes the TF was studied as a function of the hole diameter, inter-hole spacing and mean flow rate. The TF composed via the superposition of TF’s measured for unisize perforations gives a good indication of the TF of the composite (multi-size) pattern if the elemental (unisize) TF’s are measured for the burner deck with the same porosity as the composite one. Possible simplifications and extensions of the proposed TF (de)composition principle are discussed. The practical perspective of this research is to offer an opportunity for the design of burner deck patterns with desirable acoustic characteristics.