High-speed flow visualisation using shear-sensitive liquid crystals

Madhavan, KT and Mukund, R (2009) High-speed flow visualisation using shear-sensitive liquid crystals. In: National Conference on Wind Tunnel Testing 2009-CP12, 12-14 Mar 2009, IISc., Bangalore.

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Detection of flow features like boundary layer separation, laminar-turbulent transition. shocks and vortices is of considerable importance in many applications in aerospace research and design. This has high relevance in the context of national aerospace programmes. Among many techniques available for detection of boundary layer transition and separation, Shear-Sensitive Liquid Crystals (SSLC) is one of the most inexpensive, safe and easy-to-use tool for visualizing flow features particularly at high speeds. The technique exploits the property of the cholesteric liquid crystals to the change wavelength of light reflected when the surface shear stress pattern changes. A thin coating of SSLC is applied on the surface under study (airfoil, wing or aircraft models), illuminated by a halogen flash lamp. When the surface shear stress over the model surface changes due to the flow, color of the liquid crystal changes from the basic red or maroon to organge, yellow, green, blue, in the order of increasing shear stress. Information on the flow features is extracted by analyzing the colour changes of images, preferably after image enhancement by filtering and edge detection and determination of Hue-Saturation-Visibility from RGB images. The technique was demonstrated at NAL by carrying out SSLC flow visualization at speeds ranging from Mach 0.8 to 2.5 on three different models, viz., a flat plate, a delta wing and a wing-body model; oil flow visualization was also done for comparison. Analysis of the visualization pictures revealed many features of the flow, including boundary layer separation/transition on the flat plate/wing body model and primary and secondary vortex patterns formed on the delta wing, thus successfully demonstrating the unique capabilities of the technique.

Item Type: Conference or Workshop Item (Paper)
Uncontrolled Keywords: Sensitive liquid crystals;Oil flow visualization;Airfoil;Aircraft models
Subjects: AERONAUTICS > Aerodynamics
Depositing User: Ms. Alphones Mary
Date Deposited: 28 Aug 2009
Last Modified: 24 May 2010 04:26
URI: http://nal-ir.nal.res.in/id/eprint/5174

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