Transition Measurements on NLF(1)-0416 Airfoil Using Infrared Thermography

Accurate determination of transition location is of critical importance for a wide range of engineering applications from natural laminar-flow wing designs to wind turbine blade aerodynamics. There has been significant progress in transition prediction over the years but the efforts to advance the prediction capability are still on-going. One of the test cases used in a recent transition prediction workshop (The 1st AIAA CFD Transition Modeling and Prediction Workshop 2021) is the flow over NLF(1)-0416 airfoil, which is a 16% thick natural laminar-flow airfoil designed in early 1980s and tested at NASA Langley Low Turbulence Pressure Tunnel (LTPT) in a Reynolds number range of 1E6 to 9E6 and for a Mach number range from 0.1 to 0.4. In that study, transition measurements were conducted using oil flow visualization and by connecting a microphone to orifices on the model. In this presentation we will show the results of recent transition measurements on the same airfoil using infrared thermography. The measurements are performed in the new large-scale wind tunnel of the Center for Wind Energy Research (RÜZGEM) at the Middle East Technical University (METU) in Ankara, Turkey. The tests are performed in the 2.5 m x 2.5 m cross-section test section of the wind tunnel using a 0.9 m chord and 2.5 m span model for various Reynolds numbers from 1E6 to 4E6. Current transition measurement results will be compared to the previously obtained data from the NASA Langley LTPT.