# An Animated Visualization Method for Large-Scale Unstructured Unsteady Flow
## 1 Introduction  
CFD (computational fluid dynamics) is a numerical simulation technique used to study fluid motion, heat transmission, and other phenomena by approximating complex flow field problems with a finite number of discrete points [1]. Numerous scientific phenomena are time-dependent, such as the development of thunderstorms, the combustion of substances, and the movement of ocean currents. The distribution of flow field characteristics corresponding to these conditions is related to both spatial and temporal variations. CFD simulations of time-dependent phenomena will produce a series of time-continuous flow field data, also known as unsteady flow field data. Typically, geometry modeling, mesh generation, and numerical solution are required to obtain simulated data for the flow field problem during the CFD simulation process. Finally, scientific visualization techniques are used to graphically represent the flow field characteristics encoded within the simulated data. Flow field data can be categorized as structured mesh, unstructured mesh, or hybrid mesh data based on the various mesh generation methodologies. Unstructured meshes do not have mathematically logical connections between their internal nodes. They have high generalizability, strong adaptability to regions with intricate flow fields, and flexible mesh generation. Using mesh adaptive refinement, they can increase the computational accuracy of specific regions and have been increasingly used to solve increasingly complex engineering problems. Unsteady flow field data basedon unstructured meshes is now a crucial and common type of flow field data for the investigation of complex time-varying phenomena. The data scale grows massively over time, which impedes the visualization and analysis of the unsteady flow field data. Data I/O delay, slow rendering, and inefficient interaction response are some of the main difficulties. Therefore, effective visualization techniques are needed to analyze such flow field data. Animation visualization is a general-purpose technique for displaying time series data and an essential technique for displaying unsteady flow fields. It imports and draws the flow field data of each time step in chronological order, forming an unsteady animation [2], and then displays the spatiotemporal characteristics of the unsteady flow field in animation form in a more comprehensive manner [3]. Unlike traditional animation, animation visualization does more than play pictures composed of pixels one after the other. Fundamental computer graphic elements like triangles form the base for animation visualization. The flow field mesh is rendered for display via graphic elements in flow field visualization. This rendering method can make use of computer graphic techniques like transformation matrices, which let the user manipulate the flow field image by panning, zooming, reflecting, and so on. Furthermore, the distribution of the flow field's physical quantities is represented by the values of the variables dispersed across the mesh. It allows the user to color the flow field mesh according to the scalar values of the variables and can also calculate to generate other graphs, such as isosurfaces. Users can interact in real time at any point during the animation visualization with the support of visualization techniques and flow field data. The rendering pipeline creates new images in real time based on the interaction parameters whenever the user interacts, for example, by rotating, panning, or changing the coloring variables. As a result, the animation visualization can offer a comprehensive study of the unsteady flow field. However, the application of animation visualization to unstructured unsteady flow fields still faces the following issues: (1) Each frame of the animation must acquire the flow field topology and variable information corresponding to the time step. Reading and constructing the unstructured mesh from the data file is a lengthy process due to the complexity and diversity of the unstructured mesh's topological elements.