Author: caesarwiratama

Another meshing technique to simplify the simulation is using Overset Mesh, which is cell-to-cell mappings between multiple disconnected mesh regions. This allows complex mesh geometry and motion without deforming the mesh discussed in the previous chapter; deforming mesh is often very prone to mesh quality problems, which leads to divergence. Figure 3.16. Overset Mesh Both… Read more

In some specific cases, we might not be able to use a constant-sized mesh model. For instance, when simulating air inside an inflated balloon, the outer mesh size, namely the balloon’s diameter, will increase due to fluid pressure. In more technical cases, such as the up-and-down movement of a piston in a cylinder or the… Read more

The meshing process cannot be entirely calculated analytically, such as mesh size, y+ size, mesh type, and so on. This occurs due to the nature of the geometry and physical phenomena itself, which is generally complex. For instance, it’s impractical to compute each component for the ‘perfect’ mesh in simulating a race car with specific… Read more

The quality of the mesh is crucial to ensure simulation results align with expectations, ensuring good visualization, and in certain conditions, a low-quality mesh can cause simulations to diverge or even error in the first iteration. Visually, we can assess the mesh quality based on its proportionality. However, this assessment is limited to the ability… Read more

The y+ calculation concept Is very useful for determining the minimum inflation layer thickness around the wall to accommodate the boundary layer. Mathematically, y+ defined as: (3.1) Where u,tau is the friction velocity around the wall, y is the closest distance to the wall, and  is the shear stress. The mathematical form above is not an equation but… Read more

In fluid mechanics theory, we recognize the presence of fluid flow conditions that tend to adhere to solid walls, also known as the no-slip condition. This condition causes the velocity gradient around the surface to have specific patterns determining several parameters like shear stress, convection coefficients, and others, forming a layer with a specific thickness… Read more

The shape of the control volume depends on the solver’s capabilities; structured-grid codes utilize quadrilaterals in 2D flow and hexahedrons in 3D flow. Meanwhile, unstructured grids use triangles in 2D flow and tetrahedrons in 3D flow Figure 3.2. Type of mesh In general, meshes composed of hexahedra offer advantages in terms of efficiency in the… Read more

Meshing or discretization is the process of dividing the continuous fluid domain into a discrete computational domain, allowing the generally nonlinear partial differential equations of fluid mechanics to be numerically solved (further details will be discussed in the solver theory chapter). Generally, smaller mesh sizes will yield more detailed and accurate computational results but will… Read more

Generally (simplified), the steps involved in the CFD process are summarized in the flowchart below: Figure 1.11. General (simplified) CFD workflow In common modern CFD packages, the geometry can be easily imported from Computer-Aided Design (CAD) software, such as Solidworks, Autodesk Inventor/Fusion 360, Catia, or an open-source modeler such as Blender with various extensions depending… Read more

Generally, the fundamental problem of CFD is solving the Navier-Stokes equations. Historically, the first method developed was 2D flow around an airfoil using conformal transformation, which was developed in the 1930s. Lewis Fry Richardson used the idea of calculating using finite differences. In 1922, he divided the physical space into cells in the book Weather… Read more