Effects of 1 Hz imposed bulk flow unsteadiness on laminar/turbulent transition in a straight channel
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Authors
Coumes, Thomas M.
Subjects
Imposed bulk flow unsteadiness
Laminar/turbulent transition
Tollmien-Schlichting waves
Vortex and turbulent spots
Laminar/turbulent transition
Tollmien-Schlichting waves
Vortex and turbulent spots
Advisors
Ligrani, Phillip M.
Subramanian, Chelakara S.
Date of Issue
1989-12
Date
December 1989
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
Laminar/turbulent transition is studied in a straight channel with 1 Hz imposed bulk flow unsteadiness for Reynolds numbers of 1103 to 2715 and Strouhal numbers of 0.06045 to 0.02455. Channel aspect ratio is 40 to 1 with 12.7 cm height, 50.8 cm width and 4.27 cm in length. Observations, videos and photographs of smoke patterns show different subcritical transition events including Tollmien-Schlicting waves, vortex-array type motion evidenced by smoke swirls and ribbon like patterns, turbulent spots and fully turbulent flow. Fluctuating intensity magnitudes relative to velocities from imposed unsteadiness are determined form phase-averaged velocity traces. Of particular interest, is whether the imposed unsteadiness advances or delays transition events. With the conditions that were investigated, transition events begin to occur at lower Reynolds numbers and extend over a wider range of Reynolds numbers compared to flows with no imposed unsteadiness.
Type
Thesis
Description
Series/Report No
Department
Mechanical Engineering
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
Funder
Format
194 p.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.