Session: 40-04 Fan & Compressor Inflow Distortion Effects

Paper Number: 124839

124839 - Unsteady Flow, Turbulence and Acoustic Measurements on the Counter-Rotating DLR Turbo Fan Stage CRISPmulti, With and Without Inlet Distortions 

Future aircraft concepts will feature more and more a partial embedding of the engine in the fuselage. On the one hand, increasing the engine diameter generally reduces the specific fuel consumption. On the other hand, the contribution of the drag of the engine nacelle to the total drag of an aircraft also increases with the size.  Boundary layer ingestion (BLI) can have certain undesirable side effects in addition to the benefits mentioned above. Non-uniform distributions of velocity, flow turbulence and total pressure in the inflow of the engine intake are the results. The interaction of these flow distortion with the rotating engine blades leads to a change in aerodynamic performance characteristics, blade vibrations and the excitation of additional noise sources.

The German Aerospace Center (DLR) has carried out extensive aerodynamic, acoustic and vibration measurements on a representative counter-rotating turbo fan (CRISPmulti) stage under the influence of inlet disturbances. The measurements were carried out together with several DLR departments on the DLR Institute of Propulsion Technology's multistage two-shaft axial compressor test facility (M2VP) in Cologne, Germany.

The synthetic generation of a BLI-representative inhomogeneous inlet flow on a conventional fan test rig posed a particular challenge, as otherwise the inlet flow section is designed to ensure a low level of disturbances. In order to achieve a variable design on the distribution of the flow velocity or the total pressure of the inlet disturbance, an inlet distortion device was inserted radially into the inlet flow approximately 2.2 fan diameters upstream of the rotor 1 inlet. A subsequent flow straightener (honeycomb) ensures that no additional cross-flow components can arise in the radial and tangential directions.

In the presentation and in the paper, the effects of inlet disturbances on the turbulence parameters of the inlet flow are discussed in detail. In addition, the influence on the performance of the rotor stage and on the acoustic excitation of the fan will be discussed.

The unsteady flow field (turbulence intensity, spectral distribution, turbulent kinetic energy (TKE), turbulent length scale) was measured and analyzed using hot-wire anemometry in the inflow upstream of the rotors with and without inlet disturbances. Additional measurements between the two rotors and downstream of the second rotor were performed to obtain the average velocities as well as the fluctuating components of the velocity in the wake of each rotor blade.

After a resampling and phase locked averaging of the data, the local turbulence distributions at different radial positions were calculated.

Additional fan noise sources are excited by the inlet disturbances. These are analyzed in comparison to the undisturbed fan configuration for the same operating points. For this purpose, measurements were carried out with microphone arrays of microphones installed flush with the wall in the inflow duct, as well as a microphone array in the settling chamber upstream of the measurement section.

Due to the counter-rotating rotors, a complete radial mode analysis of the rotor-rotor interaction tones can be carried out with a fixed line array in the undisturbed case. In the disturbed inflow case, the disturbance fence is rotated in circumferential direction to scan the sound field step by step. The inhomogeneous distribution of the mean flow velocity interacts with each rotor to produce an additional tonal sound excitation at the associated harmonics of the blade passing frequencies and affects the rotor-rotor interaction tones. With the inflow distortion present, the interaction of the mean flow profile with rotor 1 becomes the level determining noise source.

The interaction with the spatially increased turbulence intensities leads to an increase in the broadband sound components. Future correlations of the aerodynamics and acoustics measurements should identify the relevant dependencies of the sound sources on the disturbance characteristics and provide indications for the development of efficient noise reduction measures.

Presenting Author: Robert Meyer German Aerospace Center (DLR)

Presenting Author Biography: Full name: Robert K. J. Meyer
- Title: Dr.-Ing.
- Education:
2000 Dr.-Ing. (Ph.D.) in Fluid Mechanics, Technical University of Berlin
1994 Dipl.-Ing. in Aerospace Engineering, Technical University of Berlin
-Profession:
Since 1999 Research scientist at DLR

- Actual position:
Acting Head of Engine Acoustics Department

German Aerospace Centre (DLR)
Institute of Propulsion Technology,
Dep. of Engine Acoustics

Authors:

Robert Meyer German Aerospace Center (DLR)
Ulf Tapken German Aerospace Center (DLR)
Lukas Klähn German Aerospace Center (DLR)
Maximilian Behn German Aerospace Center (DLR)
Timea Lengyel-Kampmannl German Aerospace Center (DLR)