"Small white CFD Tour" 20 Building of computing area

What is a computed domain
How the calculation domain is created
Common modeling Software
the special place for calculating domain geometry
a specific method for extracting computational domain
Small White Summary

Since the last time I listened to a calf in the cafeteria. On the calculation of the grid, the small white decided to take a good tuition during the winter vacation about the division of the computational grid. In the previous small white also contacted some CFD software, such as FLUENT,CFX, in the process of doing the case with the city is someone else has provided a good computing grid, strictly speaking, the small white has not yet built a computational grid. This really talk about to create a mesh, small white is really ignorant, do not know where to start. Xiao Bai found the Huang.

"Sister-in-duty, we have finished the test, what is the task assigned to me to do?" "Small white in QQ asked."
"After the test, then you can seriously learn the content of fluid simulation, now the project is very short of hands." "Master Huang replied.
"Well, there are some questions to ask for leave." I practiced a lot of fluid calculation cases over the past six months, but there are still a lot of problems with real engineering problems. The basic question, such as the creation of a fluid computing area, is how? "Little White asked."

"You're talking about the construction of the computational domain, oh, there are some problems for the novice to pay attention to." ”

What is a computed domain

"First of all, you have to understand that the computational domain is the area to be considered for fluid calculation, which contains the time domain and the spatial domain ." The space domain is a long-width, high-dimensional geometry of the area we tell the computer to compute, and the time domain refers to the time range we tell the solver to consider. For example, to consider the characteristics of fluid flow inside a pipe, the spatial domain refers to the range of space that the fluid within the pipeline can reach, and the time domain depends on the time period we want to consider, whether it is 1 seconds or 1 hours, depending on ourselves. ”

"The fluid computing domain refers to the areas where the fluid can be reached , but we know that the CFD solver we are currently using can solve the thermal problem in addition to solving the flow problem." So although fluids cannot flow in solids, heat can, and temperatures can be distributed in solids. Therefore, in addition to the fluid domain in the fluid computing domain, there may also be solid areas. ”

"In addition to the fluid domain and the solid domain, in the fluid calculation process, some special models may also contain some special areas, they are some of the simplified form of fluid domain." For example, the porous region simulating multi-pore structure, simulating the source area of heating, and so on, these are also fluid domains, but simplifying the geometrical model only. ”

"All in all, the computational domain is the computing area we're going to tell the computer."

How the calculation domain is created

"Understand that the computational domain is the geometric model to be presented to the solver, so you understand?" "Little White asked."
"So to speak. "Huang answer."
"How are these geometries to be obtained?" "Little white continues to ask."

"There are many ways to create geometric models, and in most cases we use professional CAD software to generate computational models, especially for complex geometric models." Of course, some simple geometric models can also be created using CAE pre-processing software. "Huang said so.

Common modeling Software

"What are the more commonly used software?" "Little white continues to ask."
"Commonly used software such as mechanical CAD software, such as UG NX, pro/e, Catia, SolidWorks, etc., the medical field also has the use of CT imaging to generate geometry, and can even use some laser scanning methods to generate geometry. All in all, whichever method is used, the ultimate goal is to obtain a digital model. "Huang said.

Common Mechanical CAD software:

• Solidworks: It's easy to get started, the learning cycle is very short, usually one afternoon to be able to operate independently, the software was acquired by Dassault in the early years.
• Catia: Very powerful 3D modeling software, currently the core product of Dassault Systèmes.
• UG NX: Siemens ' 3D modeling software is powerful and comprehensive.
• Solidedge: The same belongs to Siemens, the direct competitor SolidWorks, the modeling method is simple, the software to the computer performance requirements are very high, low-profile computer may be a bit of a lag.
• PRO/E:PTC Company's 3D modeling software, the most modest.
  In addition, there are some non-mainstream software, such as inventor, rhino and so on. In fact, there are a lot of CAE pre-processing software, but also have more powerful geometric modeling functions, such as DM,SCDM in Ansys Workbench module, STAR ccm+ geometry creation module, etc., these pre-processing modules can also be used to create computational domain geometry.

the special place for calculating domain geometry

"Fluid computational domain geometry is no different from the geometric model in general sense, the only difference is that you are in and, the fluid computing field is characterized by the fluid flow through the region, so there are some differences with the solid geometry. or a pipe. For example, we say that the geometry of a pipe consists of characteristic parameters including the inner diameter of the pipe, the outer diameter, and the length of the pipe, which is a solid model, however, if you want to calculate the computational domain model created by the flow of fluid inside the pipe, you may only need the pipe bore and length parameters, Therefore, the pipe OD This parameter is not required. ”

"Therefore, in creating a fluid computational domain geometry, it is often necessary to use a special method to extract the computed area geometry from the solid geometry. While some of the external flow field of the entity geometry is considered, it is necessary to establish an external fluid computing domain. Regardless of whether the internal or external computing domain is considered, the method of geometric establishment can be implemented by Boolean operation . ”

a specific method for extracting computational domain

"Boolean operations are a common method of extracting fluid computational domains, although some CFD pre-processing software also provides some quick-to-create functions, but the principle is to use Boolean operations." More commonly used in the creation of computational domain, can take advantage of ansys DM in the fill and enclosure functions, but also can take advantage of the SCDM in the Ansys extract volume function, in fact, there are many software with these functions. ”

Small White Summary

• The calculated domain is the area considered by the fluid calculation, the computed field contains the time and space domains, and the area beyond the calculated domain is not considered by the solver.
• The fluid calculation domain may contain solid areas.
• Professional CAD software is often used to create computational domain geometries, sometimes using CAE pre-processing software.
• Boolean operations make it easy to create fluid domain geometries.

"Small white CFD Tour" 20 Building of computing area