Leading Edge Film Cooling: Flow Visualization Using Thermochromic Liquid Crystals

摘要

An experimental technique based on wide-band liquid crystal thermography and transient one-dimensional heat conduction was used in a film cooling application. The technique combines a real-time true colour imaging system, for accurate colour rendition, with the use of a custom manufactured wide-band thermochromic liquid crystal and multiple event sampling for more accurate representation of the heat transfer characteristics. The colour change properties of the wide-band thermochromic liquid crystal were employed to determine the temperature of the surface of interest. The Hue component from the RGB (Red, Green, Blue) to HSL (Hue, Saturation, Lightness) colour space transformation was used in the colour calibration of the thermochromic liquid crystal and to determine the temperature history of the surface of interest. Flow visualizations from the real-time colour change of the thermochromic liquid crystal during the transient tests are presented in this study for two of the cases investigated. The film cooling layout features four rows of cooling holes placed at specified angles about the geometrical semi-cylindrical leading edge. The holes in each row are staggered with respect to the holes in the adjacent rows of cooling holes. The holes in each row have a compound-angle orientation. For the experiments presented here, the jets were heated to a temperature above the mainstream temperature. The transient tests provide an immediate and useful assessment of the jet coverage of the region downstream of injection. The relative contribution of the rows of cooling holes to the overall coverage can be examined this way.