Week 3: Flow over a backward facing step
l. INTRODUCTION
The Backward-facing step is a standard geometry used for visualizing the recirculation flow and validating turbulence models. BFS flow is one representative model for separation flows, which is widely used in aerodynamic flows, condensers, vehicles, etc.
In this project, Converge studio was used to establish a working idea of airflow simulation through a backward-facing step under certain parameters, which will be established systematically in this project.
ll. OBJECTIVE
- Setup backward-facing step flow simulation.
- Run simulation for 3 different mesh sizes.
- PLot Velocity and pressure contours for all 3 mesh sizes.
- Show plots for velocity, pressure, mass flow rate, and total cell count for all 3 mesh sizes.
lll. PROCEDURE
GEOMETRY:
- Importing the downloaded geometry.
- Running diagnosis to check if there are any open edges or faces.
- Checking the orientation of Normals, the normals should be such that their orientation is pointing towards the fluid flow.
BOUNDARY FLAGGING:
The boundaries are flagged. The converge studio basically uses triangular blocks to create geometry. So by selecting the triangles boundaries are Flagged.
- Inlet
- Outlet
- Top and Bottom Wall
- Front 2D
- Back 2D
CASE SETUP:
- Application Type = Time-based
- Material = Air
- Gas simulation is checked. The species are O2 and N2.
- Simulation Parameter -
In Run Parameters- two main things to be considered
(a). Selected the following solver setting.
- Steady-State Monitor:
- Simulation Parameters:
- Solver Parameters[Steady-State]
- Boundary Conditions:
- Region and Initialization:
- Physical Models: Uncheck Turbulence Modeling in this Case.
- Grid Control:
- Post Variable Selection:
- Output Files:
- Once the case setup is complete all the input files are exported to a specific folder.
- Then Cygwin is used to solve the inputs and once the simulation is complete converge converts the data into a format that can be read by pareview.
- Post-processing is done in Paraview.
lV. RESULTS
1. Grid Size = 2e-3 m
- Mesh
- Mass Flow Rate Plots
- Velocity Plots
- Pressure Plots
- Total Cell Count plots
- Flow Separation
Velocity Contours
https://drive.google.com/file/d/1Stq7s5OtfRpz7Tm_Fk6x7-1UeHPZsXiy/view?usp=sharing
Pressure Contours
https://drive.google.com/file/d/1_2XEbo2LRoD1DqbOEJdM3QLby4bNWqk5/view?usp=sharing
2. Grid Size = 1.5e-3 m
- Mesh
- Mass Flow Rate
- Velocity Plots
- Pressure Plots
- Total Cell Count
- Flow Separation
Velocity Contour
https://drive.google.com/file/d/1u0l6fYi5RUoLf3wazS3xVOgKUTXPNW-c/view?usp=sharing
Pressure Contour
https://drive.google.com/file/d/1atSPdVHL-kp7JZtNyJ6R1drTL3w5h172/view?usp=sharing
3. Grid Size =1.0e-3 m
- Mesh
- Mass Flow Rate Plots
- Velocity Plot
- Pressure Plot
- Total Cell Count
- Flow Separation
Velocity Contour
https://drive.google.com/file/d/1IOTIbg-TbqlH202G6ZzVqrF5kEyQ59fJ/view?usp=sharing
Pressure Contour
https://drive.google.com/file/d/12OYRTpJHWsXG8f6owf8Qb3ULL_O1kKYt/view?usp=sharing
Observation:
- From pressure contours, it is clear that pressure is constant at the outlet boundary but decreases in the inlet boundary.
- Pressure reduces at the inlet, due to excessive momentum loss near the step wall, The flow separation resulting in a zone with a pressure gradient is called the recirculation zone.
- Near the step in geometry, we can see the separation of the flow. This is due to the effect of boundary layer separation. Due to this, there is a disturbance in pressure and velocity.
- When both inlets and outlets are compared we can observe a positive flow and a negative flow.