TY - CONF
T1 - Bypass transition induced by free-stream noise in flow past a blade cascade
AU - Mao, Xuerui
AU - Zaki, Tamer
AU - Sherwin, Spencer
AU - Blackburn, Hugh
N1 - Publisher Copyright:
© Open Archives of the 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016. All rights reserved.
PY - 2019
Y1 - 2019
N2 - 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.
AB - 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.
KW - Bypass transition
KW - Free-stream perturbations
KW - Nonlinear streaks
UR - http://www.scopus.com/inward/record.url?scp=85083946889&partnerID=8YFLogxK
M3 - Paper
AN - SCOPUS:85083946889
T2 - 16th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, ISROMAC 2016
Y2 - 10 April 2016 through 15 April 2016
ER -