Temperature-Sensitive Paint Visualization of the Transitional Separation Bubble over Wings at Reynolds Numbers of Several Ten Thousand

Abstract

Flow fields characterized by chord-based Reynolds numbers of several ten thousand over wings of conventional cross sections are analyzed below. Utilizing temperature-sensitive paint visualization and constant-temperature anemometry the results depict a laminar-to-turbulent transition process that develops over the wings. The visualizations were utilized in order to obtain the proper length scales which characterized the transition process and to allow effective use of the constant-temperature anemometry. Not only did the constant-temperature anemometry yielded a quantitative velocity measurement in the volume over the wings, it also complemented the low spectral resolution which characterized the visualization technique. Both experimental techniques depicted the evolution of stationary cellular flow structures over the wings along the transition process. These cellular flow structures were reported in recent publications and are associated with closed separation bubbles which are subjected to flow disturbances of finite amplitude. The volumetric time-accurate velocity measurements showed that the number of cellular flow structures was function of the wing aspect ratio; moreover, it allowed proper interpretation of the temperature-sensitive paint visualizations in regions of high velocity standard deviation.