NEUTRALLY BUOYANT BUBBLES USED AS FLOW TRACERS IN AIR

Research has been performed to determine the accuracy of neutrally buo yant and near-neutrally-buoyant bubbles used as flow tracers in an inc ompressible potential flowfield. Experimental and computational result s are presented to evaluate the quantitative accuracy of neutrally buo yant bubbles using a commercially available helium bubble generation s ystem. A two-dimensional experiment was conducted to determine actual bubble trajectories in the stagnation region of a NACA 0012 airfoil at 0-degrees angle of attack. A computational scheme evaluating the equa tion of motion for a single bubble was also used to determine the fact ors which affect a bubble's trajectory. The theoretical and computatio nal analysis have shown that neutrally buoyant bubbles will trace comp lex flow patterns faithfully in the flowfield of interest. Experimenta l analysis revealed that the use of bubbles generated by the commercia lly available system to trace flow patterns should be limited to quali tative measurements unless care is taken to ensure neutral buoyancy.