Detection of separation in S-duct diffusers using shear sensitive liquid crystals

Abstract

In the present experimental investigation, shear sensitive liquid crystals have been successfully used to study the flow characteristics and detect separation in two-dimensional Sduct diffusers of different curvatures. Tapered-fin vortex generators in two different orientations were used to control flow separation that was observed on one of the curved walls of the diffuser. The results were verified by conventional oil flow visualization technique and excellent agreement was observed. In addition to visualization, detailed measurements that included wall static pressure, skin friction, diffuser exit total pressure and velocity distributions were taken in a uniform inlet flow with Reynolds number of 3.49 x 10 5 . These results are presented here in terms of skin friction distribution, distortion and total pressure loss coefficients. The extent of the separation zone (in terms of intensity of red distribution) in the diffuser with and without vortex generators (in both configurations) compared well with the Preston tube measurements. The present study demonstrates that shear sensitive liquid crystals can be efficiently used to study the flow physics in complex internal flows. In addition, the results also indicate that shear sensitive liquid crystals can be effectively used not only as flow visualization tool but also to gain quantitative information about the flow field in internal flows.

Measurements of wall-shear-stress distribution on an NACA0018 airfoil by liquid-crystal coating and near-wall particle image velocimetry (PIV)

“…This temperature range is lower than the clearing point, 48 • C, of the liquid crystal, below which the liquid crystal behaves as a shear-stress sensor. Therefore, the present liquid crystal is considered insensitive to temperature ranging from 0 • C to 48 • C. It should be mentioned that the surface-flow visualization by liquid-crystal coating has been successfully applied to the observation of separation and reattachment characteristics by Zhong (2002), Pradeep and Sullerey (2004) and Nakano et al (2007).…”