Introduction to Computational Fluid Dynamics Simulation Tool - ANSYS CFX

Intended Learning Outcomes:

  1. Explain the components of a CFD code and the activities that are carried out in each module

  2. Explain the structure of ANSYS CFX, and its capabilities

  3. Model and Mesh a simple pipe geometry using ANSYS DesignModeler and Mesher

  4. Carry out a simulation simple internal fluid flow using ANSYS CFX using Workbench

Introduction

“Computational Fluid Dynamics (CFD) is the technique of replacing the Partial Differential Equations (PDE’S) governing the fluid flow by a set of algebraic equations and solving them using the digital computer”

The transport equations that govern the fluid motion or flow are,

    1. Continuity Equation

    2. Momentum Equation

    3. Energy Equation

Computational Fluid Dynamics (CFD) is the science of calculation of fluid flow and related variables using a computer. Usually the fluid body is divided into cells or elements forming a grid. Then the equations for unknown variables are solved for each grid. This requires good amount of computing resources. The availability of affordable high performance computing hardware and the introduction of user friendly interfaces have led to a tremendous increase of CFD usage into the industrial community. The Following are the Application areas of CFD.

  • Aerodynamics of aircraft and vehicles

  • Hydrodynamics of ships

  • Power plants

  • Turbo machinery

  • Electrical and electronics engineering

  • Chemical process engineering

  • External and internal environment of building

  • Marine engineering

  • Environmental engineering

  • Hydrology and oceanography

  • Meteorology

  • Biomedical engineering

Major advantages of CFD over the Experimental Fluid Dynamics

  1. Less time in design and development is significantly reduced

  2. CFD can simulate flow conditions which are not possible in experimental model tests

  3. CFD can provide a more detailed and comprehensive information

  4. CFD is more cost effective that the experimental setup

  5. CFD utilizes low energy

Procedure

Launching and Geometry

Step 1: Launch the ANSYS Workbench and Create a New Project/Open an Existing Project Step 2: Double Click on Geometry in the Component Systems, Geometry appears on the Project SchematicStep 3: Right Click on Geometry and Click on New DesignModeler GeometryStep 4: Click on the Units drop down Menu and select the appropriate unit system according to the modelStep 5: Go to Tree Outline View Select the appropriate plane for making the sketch and right clicking on the Plane and Select Look at. Step 6: Select the Sketching Tab in the Tree Outline View to enter the sketching modeStep 7: Select the Circle Command in the Draw Tab and make a circle of an arbitrary radius by selecting the origin as the center. Step 8: Click on the Dimensions tab and select the Diameter Tool, Click in the circumference of the arbitrary circle and Enter the desired diameter of the circle in the Details ViewStep 9: Click on the Extrude Tool from menu bar, then select the sketch to extrude and click on Apply in the Details View, Enter the depth of Extrusion and Click on Generate in the menu bar

Meshing

Step 10: Before proceeding the save the project in the workbench and Double Click on Mesh from the component systems and Link the Geometry and Mesh by Dragging a Link from Geometry to Mesh. Step 11: In the Outline Tree View, Click on Mesh and In the details view change the Physics Preference to CFD, Solver Preference to CFX, Element Size 10 mm, and Finally click on Generate in the Menu Bar.

Pre-Processing

Step 12: Save the project in the workbench, Double Click on the CFX in the Component System, Link the Mesh with Setup as we did for Meshing, and Right Click on Mesh and Update the Mesh. Finally Double Click on Setup to Launch CFX-Pre.Step 13: In the Outline Tree View, Expand the SYS-1.cmdb and Rename the Principal 3D Region as Pipe and Principal 2D Regions as Inlet, Outlet and Boundary with respect to the geometry. Step 14: In the Outline Tree View, Double Click on the Default Domain, Under the Basic Setting Tab Select the Materials as Water, and Under the Fluid Models Tab, Turbulence Option to be None(Laminar)Step 15: Select Insert from the Drop Down Menu Bar, Click on Boundary, Name the boundary as Inlet, under basic setting tab keep boundary type as inlet and set location as Inlet, under the Boundary Details Tab Enter the Normal Speed as 0.1 m/s and Click on Apply and Then Ok. Step 16: Similarly Set the Boundary Conditions for Outlet and Boundary Step 17: In the Outline Tree View, Double Click on Solver Control, Change the Maximum Iterations to 250, and Residual Target to 0.000001, Finally Apply and Click OK. Step 18: Finally Click on the Execution Control, and Click OK, This will write a CFX Command Language for the CFX-Solver.

Solving

Step 19: Save the Project and Double Click on Solution, to Launch CFX-Solver and Click on Start Run to Execute the Solver, and You will Find the Solver Window Opening and the Iterations starting, This operation will take time depending on your system specifications, mesh, physics and solver settings. Step 20: After the Iterations End, Close the Solver and save the Project

Post-Processing

Step 21: Double Click on the Results to Launch CFX-Post.Step 22: Select Insert from the Drop Down Menu, and Select Streamline and Click OK. In the Details view, Change Start From as Inlet, # of Points as 50 and Then Apply.