Visualization and analysis of boundary layer transitions using infrared thermography

The United States Army Aviation and Missile Research, Development and Engineering Center (AMRDEC) has utilized Infrared (IR) cameras to analyze boundary layer transition on additively-manufactured and aluminum wings in half-scale wind tunnel testing. The primary goal of the testing was to collect transition data for validation of Computational Fluid Dynamic (CFD) models with traditional oil flow visualization methods. A secondary goal was to collect transition data using IR thermographic imagery. Using non-contact IR cameras allow for more measurements to be collected in a given time. This work focuses on the IR cameras, the testing (setup, results, and lessons learned), and post analysis of the data. Brief descriptions of the test assets and the cameras are given, followed by a description and discussion of strengths and weaknesses of different methods used to accentuate the thermal signature of the transitions. Lining the wing with a selfadhesive liner can increase the contrast of the transition signature passively, but active heating with a central heating element was shown not to be as effective. General lessons learned for test setup, camera selection, and techniques to increase thermal transition signature are provided within each section. By examining several runs, general observations about the airflow transitions are made. Image processing techniques were utilized to analyze the transition. These techniques and resulting toolsets for data analysis are described. Some of the initial results were analyzed to make some comparisons between the traditional oil flow visualization methods and the thermal imaging methods. The report shows that the oil does not affect the repeatability of the thermal signature, but that the transitions determined by the oil flow analysis and the thermal image do differ slightly. Also, the oil flow is able to visualize a region known as the laminar boundary layer separation, whereas, at this time, this phenomenon is still not apparent in the thermal imagery. Further analysis is ongoing to determine if that separation can actually be seen with this specific test configuration.