항공용 가스터빈 연소기에서의 혼합기 노즐 형상의 단순화가 음향장 해석 결과에 미치는 영향

Effects of a Simplified Mixture Nozzle Geometry on the Acoustic Field in an Aero Gas Turbine Combustor

Abstract

A 3D FEM (Finite Element Method) based Helmholtz solver has been commonly used to characterize fundamental acoustic behavior and investigate dynamic instability features in many combustion systems. In this approach, a geometrical simplification of the target system has been generally made in order to reduce computational time and cost because a real combustor and fuel nozzle have a very complicated flow passage. The feasibility of these simplifications is quantitatively investigated in a small aero gas turbine nozzle in term of acoustic characteristics. It is found that the simplification in a nozzle geometry during the 3D FEM analysis process has no great influence on the acoustic modeling results, while the calculation complexity can be improved for a similar modeling accuracy.

Fig. 2 Simplification steps of the target fuel-air mixture nozzle for 3D acoustic modeling; (a) Case 1, (b) Case 2, (c) Case 3, (d) Case 4, (e) Case 5.

Fig. 3 Schematics of computational mesh: (a) Case 1, (b) Case 4, (c) Case 5

Fig. 4 Schematics of lab-scale gas turbine combustor for the experiments⁽¹⁴⁾ (top) and the numerical simulation (bottom).

Fig. 5 Calculation results of 1^st longitudinal and 1^st circumferential modal shape for (a) Case 1 and (b) Case 5

Fig. 6 Calculation result of 1^st longitudinal modal shape at combustor length of 1.9 m.

Fig. 1. (a) Sectional view and (b) nozzle schematics of the aero gas turbine combustor under development.

Table 1 Summary of geometrical changes for each case

Table 2 Operating conditions and gas properties

Table 3 Simplification effects of nozzle geometry on the predicted resonance frequency and required calculation time

Table 4 Frequency prediction results in a lab-scale combustor rig