Object of Research
Core Noise in Aero-Engines
The competence team "Core Noise" explores the noise generating and noise transmission mechanisms in the core engine of aero-engines. The main focus lies on the combustor-turbine interaction targeting in detail the different combustion noise components.
The objective is to evaluate and reduce these different combustion noise generating mechanisms. This is necessary in order to extend the operational range of combustion chambers for modern, low pollutant aero-engines while still ensuring a stable and low noise combustion process.
Noise Generation in Combustion Systems
A combustion system like in aero-engines emits direct noise related to the unsteady combustion process itself and indirect combustion noise. The latter is generated by accelerated entropy and vorticity fluctuations in the outlet nozzle of the combustion chamber and in the subsequent turbine stages. The nozzle guide vanes (NGV) of the first turbine stage are choked under almost every relevant operating condition of aero-engines.
Model Gas Turbine Combustor (KBK) in Berlin for combustion noise research
The entropy noise phenomenon has been already simulated numerically, e.g. by the CFD/CAA team of the Hermann-Föttinger-Institut at the Technischen Universität Berlin and by the CERFACS team in Toulouse. The experimental evidence of the existence of entropy noise was provided at DLR Berlin in a generic test rig (EWG). Meanwhile similar investigations have been conducted concerning the experimental prove of the existence of vortex noise caused by accelerated vorticity fluctuations (VWG).
With the means of a model gas turbine combustor, driven with methane, the noise phenomenon of indirect combustion noise especially with respect to its contribution to the total combustion noise can be investigated and evaluated. This model combustor, terminated with a choked nozzle, can operated with self-excited combustion instabilities but also with controlled modulation of the fuel gas for synthetically generated entropy waves. The unsteady pressure field within the combustor and the exhaust duct is detected with hot gas microphone probes and the temperature fluctuations are resolved by fast double-wire thermocouple probes. The test rig allows a broad variation of thermal power, equivalence ratio, combustor length, contraction ratio of combustor outlet nozzle and the frequency and amplitude of the external excitation.
Model Gas Turbine Combustor (KBK)
Entropy Wave Generator (EWG) / Vorticity Wave Generator (VWG)