Flow visualization using the Shadowgraphy techniqueShadowgraphy is one of the optical techniques for observing a flow in a transparent medium. The basic device consists of a light source and a recording plane onto which the shadow of the variable density field is projected. The technique is based on the variation of the refractive index of the transparent medium caused by the variation of density in the flow field. The experiment is carried out in the laboratory and the density gradient is created by generation of temperature gradient or any other means (fragrance diffusion). However, shading is not a suitable method for the quantitative measurement of fluid density, but is a convenient method for obtaining a rapid study of a flow in which the density changes in the manner described. The relative changes in light intensity in the observation plane, i.e. the shades of gray in the shadowgraph, are related to the refractive index field which can be correlated to the required density field. This experiment aims to understand the basic principles of shadowgraphy and perform simple data processing to gain insight into the shadowgraphy technique. Keywords: Shadowgraphy, MATLAB, Data Analysis, Cameras, Interferometry, Lenses, Schlieren, CausticsPACS: 42.35. ±p, 52.35.Tc, 42.15.Gy, 42.65. ± k, 42.30.VaIntroductionShadowgraphy - an optical measurement technique is a field measurement method (image formation method) based on the variation of the refractive index in the flow field. The density of a fluid varies with temperature, salinity and pressure. And the refractive index changes with the density of the fluid. If a screen is placed in front of the light source, these effects create shadows on the screen creating an image called a Shadowgraph. The image ca...... middle of paper ......mage to obtain the intensity fieldI6= rgb2gray(I4);l= 0.3; % distance between source and screenD= 0.1; % width of test sectionI7 = I6-I5;I8= I7./I5;I9 = I8/(l*D);% right side of the Poisson equationfigure,imshow(I5),figure,imshow(I6) ;figure, imshow(I7),figure,imshow(I9);gd= [3;4;0;400;400;0;0;0;800;800]; % generate a geometry description matrix by giving the coordinates of the vertices of the test volume dl= decsg(gd); % generating geometric decomposition matrix[pet]= initmesh(dl); % generating the initial PDE triangular mesh = poisolv(0,p,e,t,I9); % using poislv to solve the Poisson equation and giving the boundary conditions, the matrix [pet] and I9 as input n= exp(u); %obtaining refractive index fieldK= 0.23; % constant for air (in cm^3/gm)rho = (n-ones(size(n)))/K; % obtained density field using the Gladstone-Dale equation