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Steger M.,TU Berlin | Steger M.,Institute of Fluid Mechanics and Engineering Acoustics | Michel U.,German Aerospace Center | Michel U.,TU Berlin | And 4 more authors.
16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference) | Year: 2010

It is shown in a numerical study that the rotor-stator interaction tones radiated by an ultra-high-bypass ratio turbofan in upstream direction can be modified substantially by disturbing the flow near the trailing edge of the rotor blades with the aid of jets emanating from nozzles in the fan casing. The interaction between rotor blades and jets causes an additional sound field. The number of nozzles is identical to the number of vanes in the stator in order to generate the same azimuthal modes as those referred to rotor-stator interactions. By varying the azimuthal location of the nozzles the phase relationship between the primary sound field of rotor-stator and the secondary field of rotor-jet interaction is changed. The optimum position found here yields to a sound power reduction of up to 6dB for a single radial mode. However, other radial modes are increased. Up to the second harmonic of the blade passing frequency, a reasonable over-all sound power reduction of 2dB is achieved. This result is expected to improve after axial location, diameter, injection angles and massflow rate of the jets are included in a furthermore optimization process. The turbomachinery flow solver TRACE has been enhanced to cope with the extreme requirements of the unsteady flow field near the fan tips caused by the rotor-jet interaction. The accuracy of the numerical results is compared with experimental data from the baseline case with no flow control and shows excellent agreement. © 2010 by Mathias Steger, Ulf Michel, Graham Ashcroft, Frank Thiele.

Holewa A.,German Aerospace Center | Holewa A.,Institute of Propulsion Technology | Weckmuller C.,German Aerospace Center | Weckmuller C.,Institute of Propulsion Technology | And 2 more authors.
Journal of Propulsion and Power | Year: 2014

The present work is concerned with the impact of bifurcations, i.e., extensions of the pylon inside the bypass duct, on fan tonal noise radiated by civil turbofan engines. The investigation is carried out on a typical configuration composed of a rotor-stator stage, a row of struts, and one upper and one lower bifurcation. It relies on steady and unsteady Reynolds-averaged Navier-Stokes calculations for a thin streamtube at 60% rotor span. The comparison to the isolated fan stage is used to evidence the impact of the bifurcations and the struts. The strongly nonuniform mean flowfield created by the bifurcations downstream of the fan represents the main acoustic risk. As a first effect, tonal noise is generated by the rotor due to load fluctuations on the blades during the rotation. As a second effect, the rotor wakes impinging on two adjacent stator vanes feature different shapes according to the position of the vane relative to the bifurcations; as a consequence, different pressure fields are radiated by all the vanes. Instead of the discrete azimuthal mode spectrum typical of an isolated rotor-stator stage, as predicted by Tyler and Sofrin ("Axial Flow Compressor Noise Studies," SAE Transactions, Vol. 70, 1962, pp. 309-332), a broad mode spectrum is obtained for the acoustic field with bifurcations. Clearly, cutoff design is jeopardized, with, as a consequence, a significant increase of the sound power level by 2-3 dB at the blade passing frequency (1xBPF) and its harmonics. In the inlet, the shocks formed on the blades do not propagate as the corresponding pressure patterns are cut off. However, one can observe that their position along the chord moves back and forth during one revolution, which is expected to influence the generation of multiple tones, should it occur. © 2012 AIAA.

Busse S.,TU Berlin | Richter C.,TU Berlin | Richter C.,CFDCAA Group | Nitsch S.,TU Berlin | And 9 more authors.
16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference) | Year: 2010

This work examines the influences of cell interaction on the acoustic damping performance of a recently developed liner structure (similar to Helmholtz resonators). Due to the patented production process slots remain in the cell walls and thereby the liner is non-locally reacting. For comparison another test object almost without slots is analyzed likewise. The related acoustic properties in terms of energy dissipation calculated from microphone measurements are discussed. Improvements in measurement accuracy and data acquisition lead to very precise results for this study. The focus is then put on experiments to further understand the effects of inter-cellular communication. Besides, a numerical approach is utilized to educe the model parameters of a time domain impedance model. It is shown that the techniques developed for locally reacting liners provide important information to characterize this special type of liner. Moreover, the definition of the Level of Cell Interaction (LOCI) and Effective Communication Range (ECR) is introduced to quantify effects due to cell communication of non-locally reacting liners. © 2010 by S. Busse, C. Richter, S. Nitsch, F. Bake, L. Enghardt, F. Thiele, C. Kueckens and U. Mueller.

Wiederhold O.,TU Berlin | Wiederhold O.,Institute of Plant Technology | King R.,TU Berlin | King R.,Institute of Plant Technology | And 9 more authors.
AIAA Journal | Year: 2011

An adaptive control strategy is implemented in a single-input/single-output experiment to improve the aerodynamic performance of an axial turbofan. Pulsed blowing into the blade tip region is used to prevent flow separation. Aslope-seeking control approach is shown to be able to extend the operating region of the engine without an explicit process model. By this, flow separation can be mitigated for smaller flow coefficients. The proposed closed-loop control strategy is capable of both driving the system back to stable operating conditions automatically and stabilizing operation in the presence of large-amplitude disturbances. Moreover, it is possible to accelerate the closed-loop control performance by one order of magnitude, compared with classical extremum-seeking control. By this, an extended Kalman filter is applied that enables a rapid determination of gradients of the corresponding characteristic diagram. Copyright © 2011 by Olaf Wiederhold. Published by the American Institute of Aeronautics and Astronautics, Inc.

Imiela M.,German Aerospace Center | Imiela M.,Institute of Aerodynamics and Flow Technology | Wienke F.,German Aerospace Center | Wienke F.,Institute of Aeroelasticity | And 8 more authors.
33rd Wind Energy Symposium | Year: 2015

Reliable predictions for wind turbines become more and more difficult with the increase in overall size and weight. On the one hand external factors such as the influence of wind shear become more important for bigger turbines, internal factors such as structural layout and challenges in the manufacturing process need to be addressed on the other hand. Accurate aerodynamic simulations are an essential requirement for further analyses of aeroelastic stability and aeroacoustic footprint. While the calculations in all of these individual disciplines are challenging the combined simulation of all these disciplines, namely the multidisciplinary simulation is a tough but gainful undertaking. This task is being addressed in the DLR project MERWind which will be presented here. The focus of the paper lays on the aerodynamic and aeroelastic simulation of the NREL 5MW wind turbine using high-fidelity methods. © 2015, American Institute of Aeronautics and Astronautics Inc. All rights reserved.

Ashcroft G.,German Aerospace Center | Ashcroft G.,Institute of Propulsion Technology | Hixon R.,University of Toledo
16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference) | Year: 2010

A strategy for the derivation of non-dissipative prefactored compact schemes of high-order accuracy and very low dispersion error is developed and applied to derive spectral-like schemes for the evaluation of the first- and second-derivatives. The new approach enables compact difference stencils of arbitrary width, and therefore accuracy, to be reduced to systems of bi-diagonal matrices which can be solved independently. The derived schemes are analyzed in detail and applied to linear and nonlinear benchmark problems. The possibility of employing the derived prefactored compact schemes in a predictor-corrector fashion is investigated and shown to provide a practical way of reducing the operation count per stage. © 2010 by the authors.

Buske C.,German Aerospace Center | Buske C.,Institute of Propulsion Technology | Richter C.,TU Berlin | Richter C.,Institute of Fluid Mechanics and Engineering Acoustics | And 5 more authors.
AIAA Journal | Year: 2010

A zonal approach for the prediction of the far-field radiation from flows in lined ducts is investigated. The approach combines a high-order computational aeroacoustics scheme with the recently developed acoustic intensity-based method for the calculation of far-field radiations. The advantage over the application of an acoustic analogy is the usage of an open control surface for the acoustic input. The capability of the current hybrid approach was validated on the basis of two benchmark cases. One considers the sound radiation from a two-dimensional semi-infinite duct in which a small fraction of the walls close to outlet nozzle is lined. The second problem concerns the sound radiation from a bypass enginelike annular duct with lined and hardwalled configurations of the infinite centerbody and sheared flow conditions. A broadband time-domain impedance boundary condition based on the extended Helmholtz resonator model and the Ingard-Myers boundary condition is implemented in the computational aeroacoustic code to model the acoustic linings. Although mesh refinement may improve the solutions, the good agreements of analytical solutions and numerical results, in particular for the radiation characteristics, verify this approach as an accurate and efficient prediction tool. Copyright © 2010 by C. Buske, C. Richter, F. Thiele, C Yu, and M Zhuang Published by the American Institute of Aeronautics and Astronautics, Inc.

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