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16 results on '"Letzgus, Johannes"'

3. Assessment of Delayed Detached-Eddy Simulation of Dynamic Stall on a Rotor

Author

Letzgus, Johannes, Weihing, Pascal, Keßler, Manuel, Krämer, Ewald, Hirschel, Ernst Heinrich, Founding Editor, Schröder, Wolfgang, Series Editor, Boersma, Bendiks Jan, Series Editor, Fujii, Kozo, Series Editor, Haase, Werner, Series Editor, Leschziner, Michael A., Series Editor, Periaux, Jacques, Series Editor, Pirozzoli, Sergio, Series Editor, Rizzi, Arthur, Series Editor, Roux, Bernard, Series Editor, Shokin, Yurii I., Series Editor, Hoarau, Yannick, editor, Peng, Shia-Hui, editor, Schwamborn, Dieter, editor, Revell, Alistair, editor, and Mockett, Charles, editor

Published
2020
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4. Development of Alternative Shielding Functions for Detached-Eddy Simulations

Author

Weihing, Pascal, Letzgus, Johannes, Lutz, Thorsten, Krämer, Ewald, Hirschel, Ernst Heinrich, Founding Editor, Schröder, Wolfgang, Series Editor, Boersma, Bendiks Jan, Series Editor, Fujii, Kozo, Series Editor, Haase, Werner, Series Editor, Leschziner, Michael A., Series Editor, Periaux, Jacques, Series Editor, Pirozzoli, Sergio, Series Editor, Rizzi, Arthur, Series Editor, Roux, Bernard, Series Editor, Shokin, Yurii I., Series Editor, Hoarau, Yannick, editor, Peng, Shia-Hui, editor, Schwamborn, Dieter, editor, Revell, Alistair, editor, and Mockett, Charles, editor

Published
2020
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7. Hybrid RANS/LES Capabilities of the Flow Solver FLOWer—Application to Flow Around Wind Turbines

Author

Weihing, Pascal, Letzgus, Johannes, Bangga, Galih, Lutz, Thorsten, Krämer, Ewald, Schröder, Wolfgang, General editor, Boersma, Bendiks Jan, Series Editor, Fujii, Kozo, Series Editor, Haase, Werner, Series Editor, Hirschel, Ernst Heinrich, Founded by, Leschziner, Michael A., Series Editor, Periaux, Jacques, Series Editor, Pirozzoli, Sergio, Series Editor, Rizzi, Arthur, Series Editor, Roux, Bernard, Series Editor, Shokin, Yurii I., Series Editor, Hoarau, Yannick, editor, Peng, Shia-Hui, editor, Schwamborn, Dieter, editor, and Revell, Alistair, editor

Published
2018
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12. High-fidelity simulation of dynamic stall on helicopter rotors

Author

Letzgus, Johannes and Krämer, Ewald (Prof. Dr.-Ing.)

Abstract

High-fidelity CFD simulations of helicopter rotors are carried out to investigate the dynamic stall flow phenomenon. The simulations are based on two experimental test cases, namely a model rotor with high cyclic pitch control operated at DLR Göttingen, and a highly-loaded, high-speed turn flight of the Bluecopter demonstrator. URANS and DDES simulations are carried out using the flow solver FLOWer coupled with CAMRAD II. A validation of the numerical methods is conducted based on the experimental model-rotor case, which shows that the onset of dynamic stall and the associated load overshoots agree well in overall. An unprecedented comparison of instantaneous PIV and CFD results reveals that after stall onset, only the DDES captures the chaotic nature of separated flow and exhibits small-scale vortical structures that correlate nicely with the measurement. However, the DDES suffers from the numerical artifact of modeled-stress depletion leading to grid-induced separation. Therefore, several improvements to the so-called boundary-layer shielding are investigated for both dynamic stall cases and found to eliminate the issue. Also, a shear-layer-adaptive filter width is successfully applied to the LES mode of the DDES that promotes a more realistic development of flow instabilities in separated shear layers. Concerning the turn flight simulation of the Bluecopter, the computed main rotor control angles agree very well with the flight-test measurements. A comparison of the pitch-link loads shows a good correlation regarding the overall trends and a significant improvement over a lower-order analysis. However, the pitch-link-load amplitudes are still underpredicted. Furthermore, the flow field is found to be highly unsteady and complex throughout a large portion of the azimuth, exhibiting strong separation and multiple dynamic stall events that are partly triggered by blade-vortex interaction.

Published
2021
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