Helical modes in boundary layer transition

Date
2016-11-01
Authors
Bose, Rikhi
Durbin, Paul
Durbin, Paul
Major Professor
Advisor
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Authors
Research Projects
Organizational Units
Aerospace Engineering
Organizational Unit
Journal Issue
Series
Department
Aerospace Engineering
Abstract

Observations are presented to show that in an adverse pressure gradient boundary layer, beneath free-stream turbulence, the interaction between Klebanoff streaks and naturally arising instability waves leads to helical disturbances which break down to form turbulent spots. This occurs under low to moderate levels, 1%–2%, of free-stream turbulence. At high levels of free-stream turbulence, conventional bypass mechanisms are seen. The helical structures are clearly identifiable in visualizations of isosurfaces of streamwise perturbation velocity. A direct numerical simulation also was performed in zero pressure gradient, with a time-periodic Tollmien-Schlichting wave eigenfunction at the inlet. Again, under a moderate level of free-stream turbulence, helices were observed, and found to trigger transition. Their wave speed is on the order of 12U∞, so helical breakdown can be viewed as a type of inner mode, secondary instability.

Comments

This article is published as Bose, Rikhi, and Paul A. Durbin. "Helical modes in boundary layer transition." Physical Review Fluids 1, no. 7 (2016): 073602. 10.1103/PhysRevFluids.1.073602. Posted with permission.

Description
Keywords
Citation
DOI
Collections