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

Xuerui Mao*, Tamer Zaki, Spencer Sherwin, Hugh Blackburn

*Corresponding author for this work

Research output: Contribution to conferencePaperpeer-review

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 languageEnglish
Publication statusPublished - 2019
Externally publishedYes
Event16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016 - Honolulu, United States
Duration: 10 Apr 201615 Apr 2016

Conference

Conference16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016
Country/TerritoryUnited States
CityHonolulu
Period10/04/1615/04/16

Keywords

  • Bypass transition
  • Free-stream perturbations
  • Nonlinear streaks

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Mao, X., Zaki, T., Sherwin, S., & Blackburn, H. (2019). Bypass transition induced by free-stream noise in flow past a blade cascade. Paper presented at 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016, Honolulu, United States.