A new major large-scale fan rig test facility, UFFA (Universal Fan Facility for Acoustic), has been designed with the objective to allow test bed changes for engine representative OGVs and bypass duct annulus and liners, for reduced build times, and higher fidelity investigation of aft fan noise technologies. An important enhancement consisted in the implementation of three Radial Mode Detection (RMD) devices in the bypass duct and further downstream in the nozzle equivalent plane. High effort was spend on the realisation of a wall-flush mounted sensor array, which has the advantage not to disturb the flow and the acoustic field. However, the separation of different radial mode contributions is realised only implicitly by the analysis of the axial wave number spectrum, which is particularly challenging if sensors are installed only at the outer duct wall. More robust from the numerical point of view is the established technique to directly measure the radial structure of the sound field with sensor rakes. It is one of the main objectives of this paper to verify whether both techniques deliver the same experimental results also at the high targeted frequencies up to kR=75. As the examination of recently obtained data revealed, the sensor rake measurements were influenced by aerodynamic perturbations originating from the fan rotor wakes. The radial mode analysis could be significantly improved by incorporation of appropriate aerodynamic eigenfunctions. Further investigated was the sensitivity of mode detection with sensor rakes against manufacturing and installation tolerances.

Modeling and understanding the vortex breakdown is a key issue of modern Lean Premixed Combustors. The main difficulty of the problem is the unsteady behavior of this type of flow: Large structures resulting from vortex breakdown and the swirling shear-layers, affect directly the flame stabilization leading to heat-release fluctuations and combustion instabilities. Consequently, one needs to capture and understand turbulent coherent structures dynamics for designing efficient burners. This task is particularly challenging since it deals with capturing coherent motions within a chaotic system and should be done using state-of-the art numerical and experimental techniques. The present work focuses on the experimental and numerical study of iso-thermal vortex breakdown in a conical swirler. Experimental investigations were performed with 2D Laser Doppler Velocimetry (LDV) and Hotwire Anemometry at the outlet of the combustor model. Averaged velocity fields and RMS values are showing a strong central recirculation zone. In addition, characteristic frequencies of the flow have been exhibited showing the strong influence of large scale turbulent fluctuation on the flow pattern. These measurements showed also the impact of different outlet geometries on the strength and position of the coherent structures of the flow. Further, Large Eddy Simulation (LES) has been used to obtain a 4D description of the flow. Comparison with LDV profiles showed a good agreement, indicating that the LES tool captures accurately the flow. The LES results were then processed for capturing and identifying the coherent structures. Firstly, characteristic frequencies were analyzed. Here also a good agreement with the experimental data was achieved. Secondly the cores of the vortices were visualized providing a good insight into the unsteady flow pattern. Finally, Proper Orthogonal Decomposition (POD) was applied to the 4D field in order to identify the contribution of different large scale fluctuation modes. The presence of the Precessing Vortex Core (PVC) corresponding to a pair of helical structures was captured.

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