A New Modular Fan Rig Noise Test and Radial Mode Detection Capability

Abstract

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.

Towards a Holistic Prediction of Fan Stage Tone Noise Mechanisms

“…Sound pressure is extracted from the acoustic simulation by use of a wavesplit technique as outlined in Moinier and Giles (2005). Further details on the acoustic measurement campaign and processing methods for noise can be found in Tapken et al (2011). Note that in that paper, data is obtained from radial mode detection (RMD) rings, whereas for this work only data from circumferential mode detection (CMD) rings were available.…”

“…Note that all azimuthal mode orders for these tones are below 50, the limit by which the computation mesh was designed. For a more involved analysis of the acoustic data collected during the measurement campaign, the reader may refer to Tapken et al (2011) which presents a larger set of noise results in a more pragmatic format. In essence, the results presented here in Figure 8 correspond Figures 27 and 28 of Tapken et al (2011).…”

“…For a more involved analysis of the acoustic data collected during the measurement campaign, the reader may refer to Tapken et al (2011) which presents a larger set of noise results in a more pragmatic format. In essence, the results presented here in Figure 8 correspond Figures 27 and 28 of Tapken et al (2011). The purpose here is simply a validation and instead focus is turned to the mechanisms of tone noise.…”

New modular fan rig for advanced aeroacoustic tests - Acoustic characterization of the facility

“…All of them use a Turbulence Control Screen (TCS), which is also referred to as Inlet Control Device (ICD), to reduce the inflow distortion at the fan intake and reproduce realistic in-flight conditions [18,23]. Furthermore, fan rigs usually support in-duct microphone arrays for unsteady wall-pressure measurements and modal decomposition [11,21]. Additionally, wind tunnel facilities with large test sections have also been used for aeroengine noise tests, which might be useful to assess fan noise from wind-cross, and angle-of-attack configurations, and innovative aeroengine architectures, such as Counter-Rotating Open Rotors (CROR) [4,14,20].…”

Deconvolution of Azimuthal Mode Detection Measurements

“…Such arrays don't provide information about radial modes. These can be measured by means of radial rakes instrumented with pressure transducers [7][8][9][10] or by means of a rotating axial transducer array mounted flush in the duct wall 8 . The most natural array for mode detection is a ring of equally spaced transducers.…”