Application of Temperature-Sensitive Paint in Water at DLR

Abstract

One Method to perform surface flow visualizations in water tunnel facilities is the temperature-sensitive paint (TSP) method, which is a thermographic method. In water facilities it is very beneficial to use the TSP method, because water is light-transmissive for the used wavelengths, the heat capacity of water is large and flow speeds and the propagation speeds are low. At low flow speeds thermographic methods are only capable of visualizing flow structures if a heat flux between model surface and fluid is generated. Therefore, only flow structures with a varying heat transfer coefficient can be detected. The heat flux can be generated, for example, with an electrical model heating. At DLR the possibility to use carbon fiber reinforced plastic as a resistive heater was adapted for the usage in water-facility models. First tests with a flat plate model were performed in the laminar water channel of the Institute of Aerodynamics and Gas Dynamics (University of Stuttgart). Exemplarily some results of a Blasius boundary-layer flow disturbed by a two dimensional surface excrescence, i.e. a forward-backward facing step configuration, the junction flow around a cylinder-shaped roughness element and measurements of the laminar to turbulent transition of a Blasius boundary layer are presented. The resistive heating with carbon fiber reinforced plastic proved to fulfill all requirements for the application of TSP in water facilities: lt is a robust and homogeneous heating. The aspects to implement the heating in more complex models are also described.