Bypass transition induced by free-stream noise in flow past a blade cascade

Xuerui Mao, Tamer Zaki, Spencer Sherwin, Hugh Blackburn

Research output: Contribution to conferencePaper


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 languageEnglish
Publication statusPublished - 1 Jan 2019
EventInternational Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2016 - Honolulu, United States of America
Duration: 10 Apr 201615 Apr 2016
Conference number: 16th


ConferenceInternational Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2016
Abbreviated titleISROMAC 2016
CountryUnited States of America


  • Bypass transition
  • Free-stream perturbations
  • Nonlinear streaks

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