Abstract
Flow past a NACA 65 blade cascade at Reynolds number 138, 500 is studied through weighted transient growth and Direct Numerical Simulations (DNS). The mechanism of bypass transition on the pressure side around the leading edge observed in a previous work [1] is examined. The weighted optimal initial perturbations have spanwise wavenumber 40π and are amplified via the Orr mechanism. At higher spanwise wavenumber, e.g. 120π, a free-stream optimal initial perturbation, upstream of the leading edge in the form of streamwise vortices, is obtained. In nonlinear evolution, this high-wavenumber optimal perturbation tilts the mean shear and generates spanwise periodic high and low-speed streaks. Then through a nonlinear lift-up mechanism, the low-speed streaks are lifted above the high-speed ones and generate a mean shear with inflectional points. This layout of streaks activates secondary instabilities and both inner and outer instabilities addressed in literature are observed.
Original language | English |
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Publication status | Published - 2019 |
Externally published | Yes |
Event | 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016 - Honolulu, United States Duration: 10 Apr 2016 → 15 Apr 2016 |
Conference
Conference | 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016 |
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Country/Territory | United States |
City | Honolulu |
Period | 10/04/16 → 15/04/16 |
Keywords
- Bypass transition
- Free-stream perturbations
- Nonlinear streaks