Vorticity field measurements using laser induced photochemical anemometry (LIPA)

Abstract

Non-intrusive long lifetime photochromic and/or photoluminescent chemicals can be used in liquid, solid or gaseous form to measure the kinematics of a flow over a region of space. A grid of laser lines passed through a fluid will impress a color change or cause long-time fluorescence of the fluid along the lines. As the fluid continues to move, it remains marked, thus distorting the grid. Only two successive pictures are needed to calculate the distortion of the marked fluid. Calibration requires only a clock and a ruler. The technique, called Laser Induced Photochemical Anemometry (LIPA), enables quantitative measurements of the instantaneous velocity, vorticity, strain rate, and Reynolds stress over an area in turbulent flows. It can be used for very slow flows up through hypersonic speeds. It can also be extended so as to make three-dimensional measurements of all kinematic quantities over an area. An error analysis of the technique shows its potential accuracy is high. Applications of LIP A in supersonic jets and in the wake of impulsively-started airfoils are discussed.Non-intrusive long lifetime photochromic and/or photoluminescent chemicals can be used in liquid, solid or gaseous form to measure the kinematics of a flow over a region of space. A grid of laser lines passed through a fluid will impress a color change or cause long-time fluorescence of the fluid along the lines. As the fluid continues to move, it remains marked, thus distorting the grid. Only two successive pictures are needed to calculate the distortion of the marked fluid. Calibration requires only a clock and a ruler. The technique, called Laser Induced Photochemical Anemometry (LIPA), enables quantitative measurements of the instantaneous velocity, vorticity, strain rate, and Reynolds stress over an area in turbulent flows. It can be used for very slow flows up through hypersonic speeds. It can also be extended so as to make three-dimensional measurements of all kinematic quantities over an area. An error analysis of the technique shows its potential accuracy is high. Applications of LIP A in superso...