Development of Instrumentation for Boundary Layer Transition Detection
Abstract
A steady state heat transfer technique is developed and evaluated for detecting boundary layer transition on a flat plate in incompressible flow. The method involves adhering encapsulated temperature sensitive liquid crystals to a constant heat flux surface. A heater composed of unidirectional carbon fibres is developed and tested with the aim of in-flight boundary layer transition detection on a natural laminar flow nacelle. The individual and combined influences of surface heating and favourable pressure gradient on boundary layer transition are considered. Heating is found to be a destabilising influence on the boundary layer while a favourable pressure gradient is a stabilising influence. A Stanton number correlates the movement of transition with heating for zero pressure gradient flat plate boundary layers. No similar correlation is found when a favourable pressure gradient accompanies the heating. Heating is more destabilising in a favourable pressure gradient than in zero pressure gradient. Shear sensitive liquid crystal is used to detect transition and to obtain, for the first time, quantitative measurements of surface shear stress in a transitional boundary layer. This involves calibrating the time required for the liquid crystal film to experience a texture change when subjected to a shearing force. Using this technique, shear sensitive liquid crystal shows promise for full coverage measurement of surface shear stress in low speed flows.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1991
- Accession Number
- ADA249982
Entities
People
- Steven B. Harrison
Organizations
- Air Force Institute of Technology