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51. Influence of free-stream turbulence on the boundary layer stability of a wind turbine airfoil and near wake

Author

Coelho Leite Fava, Thales, Lobo, B A, Nogueira, P A S, Schaffarczyk, A P, Breuer, M, Henningson, Dan S., Hanifi, Ardeshir, Coelho Leite Fava, Thales, Lobo, B A, Nogueira, P A S, Schaffarczyk, A P, Breuer, M, Henningson, Dan S., and Hanifi, Ardeshir

Abstract

Free-stream turbulence (FST) alters the boundary layer of wind turbine blades, changing the hydrodynamic stability and near wake. Large-eddy simulations (LES) of a blade section with a laminar separation bubble for several turbulence intensities (TI) and a Reynolds number of 100,000 are performed. The effects of boundary-layer streaks generated by FST on Tollmien-Schlichting (TS) and Kelvin-Helmholtz (KH) instabilities are analyzed with a model based on the parabolized stability equations (PSE). Two competing effects on flow stability are identified. The spanwise-averaged mean-flow distortion stabilizes primary TS/KH modes for increasing TI. However, this contribution seems dominant only for TI ≥ 8.6%. For lower TI, the spanwise-oscillating distortion caused by streaks destabilizes the flow, and the growth rates of secondary modal instabilities increase with the streak amplitude. The destabilization occurs mainly at spanwise locations with negative streaks since the inflection point shifts away from the wall, enhancing inviscid instabilities. Inflection points in the spanwise direction formed by the streaks also contribute to the destabilization. The modal structures from PSE and LES agree. Finally, the trailing-edge near-wake coherent structures are more energetic for TI ≥ 8.6% due to the partial stabilization of modal instabilities, delaying the turbulent breakdown., QC 20231030

Published
2023
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52. Numerical study of the hydrodynamic stability of a wind-turbine airfoil with a laminar separation bubble under free-stream turbulence

Author

Coelho Leite Fava, Thales, Lobo, B. A., Nogueira, P. A. S., Schaffarczyk, A. P., Breuer, M., Henningson, Dan S., Hanifi, Ardeshir, Coelho Leite Fava, Thales, Lobo, B. A., Nogueira, P. A. S., Schaffarczyk, A. P., Breuer, M., Henningson, Dan S., and Hanifi, Ardeshir

Abstract

The interaction of several instabilities and the influence of free-stream turbulence on laminar-turbulent transition on a 20% thick wind-turbine blade section with a laminar separation bubble (LSB) are investigated with wall-resolved large-eddy simulations (LES). Turbulence intensities (TI) of 0%, 2.2%, 4.5%, 8.6%, and 15.6% at chord Reynolds number 100,000 are considered. Linear receptivity occurs for the most energetic disturbances; high-frequency perturbations are excited via non-linear mechanisms for TI≥8.6%⁠. Unstable Tollmien–Schlichting (TS) waves appear in the inflectional flow region for TI≤4.5%⁠, shifting to inviscid Kelvin–Helmholtz (KH) modes upon separation and forming spanwise rolls. Sub-harmonic secondary instability occurs for TI=0%⁠, with rolls intertwining before transition. Streaks spanwise modulate the rolls and increase their growth rates with TI for TI≤4.5%⁠, reducing separation and shifting transition upstream. The TI=4.5% case presents the highest perturbations, leading to the smallest LSB and most upstream transition. Earlier inception of TS/KH modes occurs on low-speed streaks, inducing premature transition. However, for TI=8.6%⁠, the effect of the streaks is to stabilize the attached mean flow and front part of the LSB. This occurs due to the near-wall momentum deficit alleviation, leading to the transition delay and larger LSB than TI=4.5%⁠. This also suppresses separation and completely stabilizes TS/KH modes for TI=15.6%⁠. Linear stability theory predicts well the modal evolution for TI≤8.6%⁠. Optimal perturbation analysis accurately computes the streak development upstream of the inflectional flow region but indicates higher amplification than LES downstream due to the capture of low-frequency, oblique modal instabilities from the LSB. Only low-amplitude [ O(1%)] streaks displayed exponential growth in the LES since non-linearity precludes the appearance of these modes., QC 20230926

Published
2023
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56. Quantification of glacier kinematics by the use of Sentinel-1 data – a spatio-temporal analysis of GLOF-related glacier surface velocity parameters

Author

Chowdhury, A., Motagh, M., Schöne, T., and Breuer, M.

Abstract

As glaciers react to rising temperatures, the risk of glacial lake outburst floods (GLOFs) endangers downstream lives and infrastructures. To assess how C-band synthetic aperture radar data can be used to determine the timeframe of interest (TOI: includes a GLOF event), an intra-annual time-series analysis based on Sentinel-1 (S1) data was conducted covering six-month seasons (April – September) from 2017 – 2022 at the debris-covered Inylchek Glacier/Lake Merzbacher, Kyrgyzstan.In total, 90 Level-1 Ground Range Detected (High-Resolution, Dual-Pol) scenes were processed, and amplitude offset-tracking was executed. This way, 102 velocity maps (temporal baseline: 24 and 12 days) were generated. The spatio-temporal time-series analysis was performed in Geographic Information Systems with the maximum horizontal surface velocity (MSV) as the critical parameter.It is found that S1 data is suitable for detecting and quantifying horizontal glacier surface movement. The statistical analysis indicates that the MSV increased at the Inylchek Glacier during the observation period, e.g., median per season: Δmax. = 0.278 md-1. For all seasons, TOIs were calculated. Optical imagery captured by an in-situ meteorological station was used for verification, indicating that 66.7 % of the TOIs are accurate. The GLOFsat Lake Merzbacher documented in this study continue the inter-annual trend of occurring earlier during ablation seasons.The MSV shows high potential to serve as a parameter for isolating GLOFs. Further studies on the glacier dynamics are recommended by using complementing parameters and multi-source remote sensing data to enhance precision and accuracy. Remote sensing techniques pose great potential for monitoring and assessing GLOF risk., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023
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64. Flow–Induced Oscillation of a Flat Plate – A Fluid–Structure–Interaction Study Using Experiment and LES

Author

Gomes, J., Münsch, M., Breuer, M., Lienhart, H., Hirschel, Ernst Heinrich, editor, Schröder, Wolfgang, editor, Fujii, Kozo, editor, Haase, Werner, editor, van Leer, Bram, editor, Leschziner, Michael A., editor, Pandolfi, Maurizio, editor, Periaux, Jacques, editor, Rizzi, Arthur, editor, Roux, Bernard, editor, Shokin, Yurii I., editor, Dillmann, Andreas, editor, Heller, Gerd, editor, Klaas, Michael, editor, Kreplin, Hans-Peter, editor, and Nitsche, Wolfgang, editor

Published
2010
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65. Detached-Eddy Simulation of Supersonic Separated Flows

Author

Togiti, V., Breuer, M., Longo, J., Hirschel, Ernst Heinrich, editor, Schröder, Wolfgang, editor, Fujii, Kozo, editor, Haase, Werner, editor, van Leer, Bram, editor, Leschziner, Michael A., editor, Pandolfi, Maurizio, editor, Periaux, Jacques, editor, Rizzi, Arthur, editor, Roux, Bernard, editor, Shokin, Yurii I., editor, Peng, Shia-Hui, editor, and Doerffer, Piotr, editor

Published
2010
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66. The Ross operation: two decades of clinical experience

Author

on behalf of the German-Dutch Ross Registry, Bechtel, J. F. Matthias, Sievers, Hans-H., Hanke, T., Stierle, U., Bogers, A. J. J. J. C., Hemmer, W., Böhm, J. O., Rein, J. G., Botha, C. A., Lange, R., Hörer, J., Moritz, A., Wahlers, T., Franke, U. F. W., Breuer, M., Ferrari-Kühne, K., Hetzer, Roland, Hübler, M., Ziemer, G., Gorski, A. W., Takkenberg, J. J. M., Misfeld, M., Yankah, Charles A., editor, Weng, Yuguo, editor, and Hetzer, Roland, editor

Published
2010
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78. Numerical Computation of 3—D Turbulent Flow Around High—Speed Trains Under Side Wind Conditions

Author

Khier, W., Breuer, M., Durst, F., Hirschel, Ernst Heinrich, editor, Fujii, Kozo, editor, Haase, Werner, editor, van Leer, Bram, editor, Leschziner, Michael A., editor, Pandolfi, Maurizio, editor, Periaux, Jaques, editor, Rizzi, Arthur, editor, Roux, Bernard, editor, Schulte-Werning, Burkhard, editor, Grégoire, Rémi, editor, Malfatti, Antonio, editor, and Matschke, Gerd, editor

Published
2002
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80. Beam Polarisation Asymmetries in Meson Photoproduction at Graal

Author

Ajaka, J., Bellini, V., Bocquet, J. P., Breuer, M., Capogni, M., Castoldi, M., Ciciani, L., D’Angelo, A., Didelez, J. P., Di Salvo, R., Duval, M. A., Gaulard, C., Ghio, F., Girolami, B., Guidal, M., Hourany, E., Lapik, A., Kilvington, I., Kouznetsov, V., Sandri, P. Levi, Lleres, A., Moricciani, D., Nedorezov, V., Nicoletti, L., Perrin, C., Rebreyend, D., Renard, F., Rudnev, N. V., Schaerf, C., Turinge, A., Zucchiatti, A., Plessas, W., editor, Simula, Silvano, editor, Saghai, Bijan, editor, Mukhopadhyay, Nimai C., editor, and Burkert, Volker D., editor

Published
1999
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81. Beam Asymmetry Σ in Meson Photoproduction at GRAAL

Author

Renard, F., Ajaka, J., Bellini, V., Bocquet, J. P., Breuer, M., Capogni, M., Castoldi, M., Ciciani, L., D’Angelo, A., Didelez, J.-P., Di Salvo, R., Duval, M. A., Gaulard, C., Ghio, F., Girolami, B., Guidai, M., Hourany, E., Kilvington, I., Kouznetsov, V., Lapik, A., Sandri, P. Levi, Lleres, A., Moricciani, D., Nedorezov, V., Nicoletti, L., Perrin, C., Rebreyend, D., Rudnev, N. V., Schaerf, C., Turinge, A., Zucchiatti, A., Plessas, W., editor, Desplanques, Bertrand, editor, Protasov, Konstantin, editor, Silvestre-Brac, Bernard, editor, and Carbonell, Jaume, editor

Published
1999
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92. Photoproduction of Eta Mesons on Deuterium from Threshold to 1.2 GeV

Author

Hoffmann-Rothe, P., Hourany, E., Breuer, M., Didelez, J.-P., Rigney, M., Ajaka, J., Anton, G., Arends, J., Berrier-Ronsin, G., Beulertz, W., Blanpied, G., Bock, A., v. Edel, G., Frascaria, R., Helbing, K., Hey, J., Krebeck, M., Maass, R., Nöldeke, G., Preedom, B., Ritchie, B., Rosier, L., Saghai, B., Schumacher, M., Smend, F., Whisnant, S., Zucht, B., Mitter, H., editor, Plessas, W., editor, Adam, J., editor, Dobeš, J., editor, Mach, R., editor, Sotona, M., editor, and Dolejší, J., editor

Published
1996
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