2D Channel Flow Simulation using CONVERGE CFD
Aim:
The main objective of this project was to setup a steady state fluid flow simulation in order to simulate and study the velocity, pressure, mass flow rate, and total cell count for all 3 base mesh sizes of the Rectangular Channel using CONVERGE Studio and analyse the mesh independent test by observing the difference between the contours and line plots generated by running the 3 case study.
Introduction
The report contains a detailed description of the simulation of 2d Channel flow using converge CFD software, solving it using CYGWIN and post-processing the result using ParaView. Various steps are discussed in this report while making a case set up for each case study. The report contains a detailed description of 3 case study with different grid sizing, line plots, and contours.
1.Geometry Creation
First of all, the box geometry was setup using converge CFD software.
Dx Dy Dz
CENTER 0.05 0.00 0.00
SIZE 0.1 0.01 0.01
*all dimension are in metre.
Each face of the box was split into triangles.
Image 1: Box geometry creation using Converge CFD along with Dimensions.
To create the box geometry, the create box option was used geometry panel on the left-hand side of the converge studio. All the normal vector were pointing out for this geometry, so we wanted it to point inside and normal to each surface. Normals point the direction of the fluid region generally. The command "Transform" was used to make the normal inside pointing the direction of the fluid region.
2.Boundary Creation
After creating the box Geometry, The Boundry tag was created along with different boundary id and coloring. A total of 5 different boundaries tag was created for 6 different faces of the box with each face split into two triangles. To create the boundaries naming, the "Boundary" command in the "Geometry" dock was used, and then the faces were appointed to appropriate tags along with id.
Image 2: Boundary creation representing the different id and color.
The five different boundaries were Inlet, Outlet, Top-Bottom-Walls, Front2d, and Back2d.
3.Case-Study Setup
The various parameter was considered while setup this case study. The case study setup dock was used to set up the problem which appears on the right-hand side of the converge studio.
Image 3: Case Setup Dock.
3.1 Application Type:
In order to run a steady-state simulation, firstly, under the Application type in the setup tree, a "Time-based" simulation must be selected.
3.2 Materials:
Under the material tab "Gas simulation" was selected and "Air" as a predefined mixture.
Gas: Air
Global Transport Parameters: Fixed value
by default, the following value is considered.
Prandtl Number : 0.9
Schmidt Number : 0.78
Species: Oxygen-O2 & Nitrogen-N2
3.3 Simulation Parameters
The Steady-state solver was selected for running this case study along with a "Pressure based" solver.
STEADY STATE SIMULATION:
These are the simulation we run if are just interested in the end result and not in how those results are getting formed with time. The time is in CYCLES for STEADY STATE SIMULATION.
The Following Simulation parameters were selected for running each simulation.
3.4: Boundary Conditions
In this tab, The volumetric region and physics for each boundary were defined.
| Boundary_Name | Boundary_Type | Paramter_Defined | Boundary ID |
| 1.Inlet | Inflow Pressure Inlet | 100001 Pa | 1 |
| 2.Outlet | OutFlow Pressure Outlet | 100000 Pa | 2 |
| 3.Top-Bottom-walls | Wall |
Specified Value(300k) No-Slip Condition |
3 |
| 4.Front2d | Two_D | 4 | |
| 5.Back2d | Two_D | 5 |
3.5: Initial Conditions and Events
Volumetric Region was created in order to assign this to all the boundary tag.
Species:- O2 (0.77) & N2 (0.23)
Pressure :100001Pa
Temperature:300K
3.6: Grid Control
The case study was run using 4 different mesh grid size. So different case study was set up in order to study the effect of value when the mesh is more refined.
3 different base mesh sizes are,
dx = 2.0e-4m, dy = 2.0e-4m, dz = 2.0e-4m
dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m
dx = 1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m
3.7 Output/Post-Processing
Post-Variable Selection- Existing value
Output Files- Time interval for writing 3D output files-100.0
The time interval for writing restart files -100.0
The case study was solved using CYGWIN and the post-processing was done in ParaView.
For post converting we used the following command
Case Study 1:
Mesh Genration: Base mesh Size
dx = 2e-4m, dy = 2e-4m, dz = 2e-4m
Fully Developed Velocity Flow Profile
Pressure Contour
Velocity Distribution
Velocity Animation
Pressure Animation
Mass Flow Rate- Area Weighted Average Report
Pressure- Area Weighted Average Report
Velocity- Area Weighted Average Report
Cells
Case Study 2:
Mesh Genration: Base mesh Size
dx = 1.5e-4m, dy = 1.5e-4m, dz = 1.5e-4m
Fully Developed Velocity Flow Profile
Pressure Contour
Velocity Distribution
Velocity Animation
Pressure Animation
Mass Flow Rate- Area Weighted Average Report
Pressure- Area Weighted Average Report
Velocity- Area Weighted Average Report
Cells
Case Study 3:
Mesh Genration: Base mesh Size
1.0e-4m, dy = 1.0e-4m, dz = 1.0e-4m
Fully Developed Velocity Flow Profile
Pressure Contour
Velocity Distribution
Velocity Animation
Pressure Animation
Mass Flow Rate- Area Weighted Average Report
Pressure- Area Weighted Average Report
Velocity- Area Weighted Average Report
Cells
Conclusion
The bound_id_1 and bound_id_2 represent the Inlet and outlet respectively for this geometry. It can be stated that as the overall cell count increases, the base mesh grid size reduces, resulting in more accurate findings but also increasing the computing time required to answer a case study. In comparison to the initial case study, the refined case study took longer to compute.
The mass flow rate plot shows us that the inlet mass flow rate will be negative and the outlet flow rate is positive and hence the mass flow rate is conserved overall. It negative at outlet becuase the fluid is leaving the CV.
Velocity plot shows us that inlet velocity is negative and the outlet is positive. The axial Velcoity increases with some factor at the outlet.
The pressure plot shows that total pressure at outlet increases because air along with velocity goes to the outlet and static pressure increases at inlet due to initial condition. At inlet BC 100001Pa where as at outlet the pressure of 100000 was choosen which is responsible for air motion along positive x-axis.
In the end, it can be concluded that this study is to study the result for mesh indepednt test. In which after certain number of cells the results remain unchanged as can be seen from above plots. The mesh quality with the medium mesh can be used to perform further simulation.