Flow Visualization Using Shading Technique Shading is one of the optical techniques for observing flow in a transparent medium. The basic apparatus 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 change in the refractive index of the transparent medium caused by the change in density in the flow field. The experiment is carried out in the laboratory and the density gradient is created by generating a temperature gradient or any other means (scent diffusion). However, shading is not a suitable method for quantitative measurement of fluid density, but it is a convenient method for obtaining rapid detection 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 range which can be related to the required density range. This experiment aims to understand the basic principles of shadowgraphy and perform simple data processing to gain an overview of the shadow technique. Keywords: Shadowgraphy, MATLAB, Data Analysis, Cameras, Interferometry, Lenses, Schlieren, CausticPACS: 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 change in the refractive index in the flow field. The density of a fluid varies with temperature, salinity and pressure. Furthermore, 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 is located...... in the center of the sheet...... imagine obtaining the intensity field I6= rgb2gray(I4);l= 0.3; % distance of the source from the screenD= 0.1; % width of the test sectionI7 = I6-I5;I8= I7./I5;I9 = I8/(l*D);% right side of the Poisson equationfigure,show(I5),figure,show(I6);figure , imshow(I7),figure,imshow(I9);gd= [3;4;0;400;400;0;0;0;800;800]; % generation of the geometry description matrix providing the coordinates of the test vertices volumedl= decsg(gd); % generation of geometry decomposition matrix[pet]= initmesh(dl); % that generates the initial PDE triangular mesh = poisolv(0,p,e,t,I9); % using poisolv to solve the Poisson equation and providing boundary conditions, matrix [pet] and I9 as inputn= exp(u); %obtaining refractive index fieldK= 0.23; % constant for air (in cm^3/gm)rho = (n-ones(size(n)))/K; % obtaining the density field using the Gladstone-Dale equation