Experimental data describing laminar separation bubbles developing under strong adverse pressure gradients, typical of Ultra-High-Lift turbine blades, have been analyzed to define empirical correlations able to predict the main features of the separated flow transition. Tests have been performed for three different Reynolds numbers and three different free-stream turbulence intensity levels. For each condition, around 4000 Particle Image Velocimetry (PIV) snapshots have been acquired. A wavelet based intermittency detection technique, able to identify the large scale vortices shed as a consequence of the separation, has been applied to the large amount of data to efficiently compute the intermittency function for the different conditions. The transition onset and end positions, as well as the turbulent spot production rate are evaluated. Thanks to the recent advancements in the understanding on the role played by Reynolds number and free-stream turbulence intensity on the dynamics leading to transition in separated flows, guest functions are proposed in the paper to fit the data. The proposed functions are able to mimic the effects of Reynolds number and free-stream turbulence intensity level on the receptivity process of the boundary layer in the attached part, on the disturbance exponential growth rate observed in the linear stability region of the separated shear layer, as well as on the nonlinear later stage of completing transition. Once identified the structure of the correlation functions, a fitting process with own and literature data allowed us to calibrate the unknown constants. Results reported in the paper show the ability of the proposed correlations to adequately predict the transition process in the case of separated flows. The correlation for the spot production rate here proposed extends the correlations proposed in liter-ature for attached (by-pass like) transition process, and could be used in γ–Reϑ codes, where the spot production rate appears as a source term in the intermittency function transport equation.
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ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition
June 11–15, 2018
Oslo, Norway
Conference Sponsors:
- International Gas Turbine Institute
ISBN:
978-0-7918-5101-2
PROCEEDINGS PAPER
Correlations for the Prediction of Intermittency and Turbulent Spot Production Rate in Separated Flows
M. Dellacasagrande,
M. Dellacasagrande
Universitá di Genova, Genova, Italy
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D. Lengani,
D. Lengani
Universitá di Genova, Genova, Italy
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P. Zunino
P. Zunino
Universitá di Genova, Genova, Italy
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M. Dellacasagrande
Universitá di Genova, Genova, Italy
R. Guida
Universitá di Genova, Genova, Italy
D. Lengani
Universitá di Genova, Genova, Italy
D. Simoni
Universitá di Genova, Genova, Italy
M. Ubaldi
Universitá di Genova, Genova, Italy
P. Zunino
Universitá di Genova, Genova, Italy
Paper No:
GT2018-75624, V02CT42A015; 10 pages
Published Online:
August 30, 2018
Citation
Dellacasagrande, M, Guida, R, Lengani, D, Simoni, D, Ubaldi, M, & Zunino, P. "Correlations for the Prediction of Intermittency and Turbulent Spot Production Rate in Separated Flows." Proceedings of the ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. Volume 2C: Turbomachinery. Oslo, Norway. June 11–15, 2018. V02CT42A015. ASME. https://doi.org/10.1115/GT2018-75624
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