Fan test rig for detailed investigation of noise generation mechanisms due to inflow disturbances

Kurzfassung

The need for the development of quieter fans for various future applications requires a detailed understanding of the aeroacoustic source mechanisms of fan noise in particular for complex installation arrangements. In order to conduct thorough experimental analyses, DLR developed and recently set in operation the new fan test rig CRAFT (Counter Rotating Acoustic Fan Test Rig) in Berlin. CRAFT is equipped with an Inflow Control Device to ensure a homogeneous base inflow. On the one hand, the fan stage features all relevant subsonic noise sources of large-scale aero engines. On the other, it is representative for urban/regional aircraft engines. Extensive measurement capabilities for stationary and instationary flow parameters are available by means of total pressure rakes and multi-hole probes resp. hot-wire anemometry. The acoustic field is captured with microphone arrays, either using regularly positioned or optimized, sparse arrays with substantially reduced sensor count for the application of advanced mode analysis techniques. The investigation of the impact of disturbed inflow being representative e.g. for the integration of the engine close to or even partly embedded into the fuselage, is made possible by an Inflow Distortion Device. A first series of experiments provides evidence of the complex relationships between the aerodynamic operation of the fan and the generated fan noise mechanisms. By this, the advanced measurement abilities and excellent boundary conditions of the new fan test rig CRAFT are demonstrated in detail.