Turbulent Spot Observations within a Hypervelocity Boundary Layer on a 5-degree Half-Angle Cone
Laminar to turbulent transition is a critically important process in hypersonic vehicle design. Higher thermal loads, by half an order of magnitude or more, result from the increased heat transfer due to turbulent flow. Drag, skin friction, and other flow properties are also significantly impacted. Transition to turbulence in initially laminar boundary layers can occur along many paths. In low-speed flow under ideal conditions (quiet freestream, nominally smooth surfaces with favorable or zero pressure gradient and minimal crossflow) transition occurs over a finite distance and is associated with the creation and growth of propagating patches of turbulent flow, known as turbulent spots. Spots may be due to the breakdown of linear instabilities or induced by "bypass mechanisms" associated with nonideal effects in the flow or model. H.W. Emmons (1951) was the first to propose that laminar boundary layers break down through the convergence of spots, after observations of a water-table analogy to air flow. Spot formation has been studied extensively in subsonic flows, a recent review of past and current work on spots in incompressible flows is given by Strand and Goldstein (2011).
© 2012 American Institute of Aeronautics and Astronautics. The authors thank Mr. Bahram Valiferdowsi for his work with design, fabrication, and maintenance, and Prof. Hans Hornung for his advice and support. This project was sponsored by the Air Force Office of Scientific Research under award number FA9550-10-1-0491 and the NASA/AFOSR National Center for Hypersonic Research. The views expressed herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of AFOSR or the U.S. Government.
Accepted Version - jjewell_Turbulent_Spot_Propagation.pdf