A Preliminary Study for Quantitative Measurements of Density Fields by a Focusing Schlieren Method

A method for measuring a density field around an airfoil in a transonic flow by using a focusing schlieren technique is proposed. The focusing schlieren images are analysed to get the light intensity distribution through a Gaussian filter to remove the optical noise. Then a density field is calculated. In the present study, the density ratio in a transonic flow over a NACA0012 airfoil was calculated at y/c=0.236 above the airfoil. The step function scaling factor, β of 0, 0.01, 0.05 and 0.1, and the number of discrete steps used to model spread function, N of 3, 5 and 7 are tried to get density distribution. As β became large, density ratio became low. Similarly, as N became large, density ratio became low. This result indicates some feasibility of quantitative measurement with the focusing schlieren technique. However, a farther study should be performed to validate the present result.