Visualization of laminar–turbulent transition on rotating turbine blades

The detection of laminar–turbulent transition in aerodynamics is very important, however, it can be extremely challenging, especially for unsteady flows or moving surfaces. To understand and control transition effects and associated friction losses on aerodynamic components, optical methods have been developed as they potentially do not disturb transition processes. Temperature Decline Thermography (TDT) was recently introduced to visualize boundary layer phenomena on surfaces exposed to flow. The technique is based on transient infrared thermography with active heating, offering high spatial resolution and precise transition detection in stationary systems. However, to improve the efficiency of modern aircraft engines, transition detection on rotating blades is of particular importance. In this study, TDT was enhanced and qualified for use on rotating blades in gas turbines. For the first time, a proof of concept is provided for flow visualization on stationary vanes and rotating blades under realistic flow conditions. Despite the limited optical access in a turbine rig, it was possible to visualize the near-wall traces of boundary layer transitions, separation and vortex systems with high spatial resolution and low measurement uncertainty. The application of TDT in turbomachinery allows for a deeper understanding of flow phenomena and enables validation and support of numerical models for the development of highly efficient gas turbines.