Assessment of synthetic entropy waves for indirect combustion noise experiments in gas turbines

Results indicate that, by assigning an optimal feeding pressure to the generation device, circular-shaped spots of hot air characterized by a sinusoidal temperature fluctuation and very weak pressure oscillations are injected into the main stream, properly simulating the entropy waves expected in the core of aero-engines. The amplitude of the temperature oscillation reduces during the stream-wise propagation of the wave and increasing the wave frequency. However, by adopting a proper insulation technology and assigning a sufficiently high thermal power to the generation device, temperature perturbations of the order of 30 K (i.e., 10% of the mean temperature level) at 90 Hz are achieved. These values match the target of entropy noise studies in the turbine test rig.