11th European Conference on Turbomachinery Fluid dynamics & Thermodynamics
The reduction of core-noise represents a crucial objective for the deployment of low noise propulsion systems. In this context the European Project RECORD - REsearch on COre noise ReDuction - aims at quantifying the impact of the turbine on direct and indirect combustion noise by means of a set of dedicated experiments carried out on an engine representative high pressure turbine, installed in the high-speed test rig of Politecnico di Milano (Italy). The aeroacoustic interaction of pressure, vorticity, and entropy waves with the turbine will be studied. This paper presents a novel Entropy Wave Generator (EWG) to simulate the entropy perturbations originated by gas turbine burners. The device, designed and manufactured by SMCPFA (Romania), is based on the alternated injection of hot/cold air upstream of the turbine, by using a two-way rotary valve. The entropy waves generated by the EWG were experimentally characterized in a dedicated test section at Politecnico di Milano. Tests were performed using different insulation systems, and investigating the propagation of entropy waves in both free-jet and immersed-jet configurations. Tests were performed by means of a fast thermocouple (frequency response ~300 Hz) and a pneumatic total pressure probe (frequency response ~400 Hz), specifically developed for the project. Results indicate that for an optimal feeding pressure the EWG generates circular-shaped spots of hot air characterized by a sinusoidal temperature fluctuation and weak pressure oscillations; the amplitude of the temperature oscillation reduces as the frequency increases, however resulting higher than 10 K at the engine-representative frequency of 100 Hz. This value matches the technical requirements of the EWG, making it suitable for entropy noise studies in the turbine test rig.