Thermally Sprayed Coating-Based Heating Systems for Boundary Layer Transition Detection — An Experimental Approach

Abstract

Boundary layers on surfaces will change from laminar to turbulent flow after a critical length. Due to the differing heat transfer coefficients of laminar and turbulent flow, the point of transition can be detected by heating the surface and measuring surface temperature by thermographic imaging. Locating the transition point is crucial for the aerodynamic optimization of components. In this study, fiber reinforced polymer composites (FRPCs) were chosen as the test substrate. Experiments were conducted using the flame spray process and NiCrAlY coatings. Multilayered coatings consisting of an aluminum bond coat, a layer of alumina as electrical insulation, and a heating layer of titania were fabricated by atmospheric plasma spraying. Free-flight tests were conducted with a functionalized winglet in order to assess the ability of thermally-sprayed heating elements to detect the location of transition of the flow regime. The results showed that the thermally-sprayed elements heat surfaces uniformly, with sufficient radiation losses for thermographic imaging. It was also shown that the change in temperature at the point of transition was readily observable using thermography.

Prediction of the Quality of Thermally Sprayed Copper Coatings on Laser-Structured CFRP Surfaces Using Hyperspectral Imaging

“…On the other hand, challenges must be overcome for the large-scale replacement of metal components with FRP components, including typical metal properties on the surfaces, such as those which enable wear and temperature resistance, electrical conductivity, or thermal isolation [2][3][4]. Therefore, to improve certain properties, a metallic coating can be applied to the FRP surface, for example, by thermal spraying [5][6][7][8][9][10][11][12]. In particular, for the case of carbon fiber-reinforced plastics (CFRP), different surface pre-treatment methods have been already investigated, such as sanding, pre-heating, etching, and even the application of additional layers.…”

“…In particular, for the case of carbon fiber-reinforced plastics (CFRP), different surface pre-treatment methods have been already investigated, such as sanding, pre-heating, etching, and even the application of additional layers. The most established surface pre-treatment method for cleaning and roughening the substrate surface is mechanical blasting [6,9,11,13,14]. Unfortunately, the highly accelerated and sharp-edged blasting particles (e.g., corundum) can damage the fibers near the surface [6].…”