Challenges in Gas Turbine Combustor Design for Combustion Dynamics
Gas Turbine combustors are prone to combustion dynamics. The coupling of the unsteady heat release in the flame with the natural acoustic resonance modes of the combustor duct causes the phenomena of combustion dynamics. The heat release and the pressure fluctuations are also affected by each other forming a feedback loop. The high magnitude pressure oscillations degrade the operation of the combustor or even lead to failure. Moreover, the difficulty in predicting and fixing combustion dynamics problems can lead to additional costs and delays in turbine development.
Fig. 1 Combustion instability loop
Engineering Solution
Numerous approaches are available to control combustion dynamics such as:
1. Passive control approaches: effective in limited frequency range (e.g. acoustic dampers)
2. Active control open-loop approaches: (e.g. modulating fuel/air mixture)
3. Active control closed-loop approaches: most adaptive (e.g. sensor/controller/dynamics actuator systems)
Computational Fluid Dynamics (CFD) methods are the most common physics based approaches to model the highly complex, reacting turbulent flow field present in Combustors. Manufacturers routinely use such simulations to predict combustion and pressure. The detailed flow and thermal information in turn is used to improve component design and/or include control mechanisms to reduce combustion instabilities and acoustics.
Ansys Solution Benefits
Several different physics contribute to combustor dynamics such as vaporization, convection, vortex dynamics, mixing dynamics, flame kinematics, chemical kinetics and acoustics. Ansys Fluent offers industry validated and accurate models to capture all of these physics. Better understanding of combustion dynamics utilizing Ansys helps avoiding noise and vibration issues.
Fig. 2 Unsteady pressure comparison for Purdue LDI combustor
Fig. 3 Frequency comparison for Purdue LDI combustor
Ozen Engineering Expertise
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