A new facility for hot stream acoustic liner testing

Aerospace industry is showing a growing interest to apply acoustic treatment in the exhaust ducts of turbofan engines to attenuate combustion and turbine noise. The design, optimisation and testing of hot stream liners require improved theoretical models and facilities to validate and evaluate the acoustic performances of these liners under realistic engine operating conditions. To extend the capabilities for liner testing, NLR has modified an existing burner rig. Main objective was to build a facility for hot stream liner testing up to a flow Mach number of 0.4 and a maximum temperature of 500 oC, which has been met. Both insertion loss and in-situ acoustic impedance measurements can be performed at maximum sound pressure levels of about 145 dB. In this paper, an overview will be given of the design and commissioning of the new facility, the instrumentation and the measurement techniques. Furthermore a selection of results will be presented on measured insertion losses and acoustic impedances.