Abstract of
VISUALISATION OF TRANSITION ON AN AXISYMMETRIC BODY
USING SHEAR SENSITIVE LIQUID CRYSTALS
Savory E1, Sykes D M2 and Toy N1
1 Fluid Mechanics Research Group, Dept of Civil Eng, Univ of Surrey,
Guildford GU2 5XH, UK 2 Centre for 2 Aeronautics, Dept of Mech Eng
and Aero, City University, London EC1V OHB, UK
The present work is concerned with the development and application
of techniques for quantitative calibration and use of liquid crystals for measuring
surface skin friction under laminar, transitional and turbulent flow conditions.
The scope of the research has been two-fold. Firstly, laboratory calibrations
of different liquid crystal mixtures have been undertaken at Surrey University
using a mechanical rotational shear rig in conjunction with both a spectrophotometer
(for point measurement and assessment of the full spectrum of both the incident
and reflected light) and a 3-CCD video camera with a digital image processing
system (for full-field determination of the reflected colours in terms of HSI
co-ordinates). Secondly, aerodynamic tests, under subsonic and transonic conditions,
have been carried out using an axisymmetric body with an ogive nose in the slotted
wall transonic wind tunnel at City University.
The laboratory calibrations have indicated the manner in which the observed reflected
light from the crystal layer varies with the location and angle to the surface
of both the incident illumination and the receiving optics. The wind tunnel tests
showed that the crystal type BCN/165 (a mixture of cholesteric and chiral-nematic
crystals) gave the best overall performance in terms of both colour play and durability.
In addition, the experiments demonstrated the feasibility of the present approach
for the quantitative assessment of skin friction in laminar and turbulent flows,
coupled with the detection of the transition region.
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