The present problem simulates the separation of fluid flow passing through a step and the effect of suction and blower control jets on controlling the separation of fluid using ANSYS Fluent software. This simulation is based on the information of a reference article “A force reduced-order approach for optimal control of turbulent flow over backward-facing step using POD analysis and perturbation method“, and its results are compared and validated with the results in the article.
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The present problem simulates the separation of fluid flow passing through a step and the effect of suction and blower control jets on controlling the separation of fluid using ANSYS Fluent software. This simulation is based on the information of a reference article “A force reduced-order approach for optimal control of turbulent flow over backward-facing step using POD analysis and perturbation method“, and its results are compared and validated with the results in the article. In this simulation, the fluid flow enters the channel horizontally at a speed equivalent to 1 ms-1 and then passes through a step to a height of 1 m within 30 m inside the channel, leading to separation.
Suction and blow control jets are used at the upper and lower edges of the stairs to control fluid separation. So that the fluid flow is blown into the channel from the bottom of the stairs and is sucked out from the top edge of the stairs. Therefore, the input speed equal to +1 m.s-1 has been used for the special blowing limit, and the input speed equal to -1 m.s-1 has been used for the suction limit.
Geometry & Mesh
The present model is designed in two dimensions using Design Modeler software. This model belongs to a part of a canal that has a step 1 m high. At the top edge of the stairs, the border is defined as a 0.1 m long sucker and at the bottom edge of the stairs, the boundary is defined as a 0.1 m long blower. We carry out the model’s meshing using ANSYS Meshing software. The mesh type is structured. The element number is 15000. The following figure shows the Mesh.
Fluid Separation CFD Simulation
We consider several assumptions to simulate the present model:
We perform a pressure-based solver.
The simulation is steady.
The gravity effect on the fluid is ignored.
The following table represents a summary of the defining steps of the problem and its solution:
Models (Fluid Separation)
Viscous
k-epsilon
k-epsilon model
RNG
near wall treatment
standard wall function
Boundary conditions (Fluid Separation)
Input
Velocity Inlet
velocity magnitude
1 m.s-1
Output
Outflow
flow rate weighting
1
Blow
Velocity Inlet
velocity magnitude
0.1 m.s-1
Suction
Velocity Inlet
velocity magnitude
-0.1 m.s-1
wall motion
stationary wall
Methods (Fluid Separation)
Pressure-Velocity Coupling
SIMPLE
pressure
standard
momentum
quick
turbulent kinetic energy
quick
turbulent dissipation rate
quick
Initialization (Fluid Separation)
Initialization methods
Hybrid
Paper Validation
The present simulation’s validation is based on the diagram in Figure 5 of the mentioned article. This diagram relates to changes in the value of horizontal velocity in terms of location in the horizontal direction. The study location is at the height of 0.04 m from the canal floor and in the area after the stairs and at a distance of 20 m after the stairs.
Results & Discussion
At the end of the solution process, two-dimensional contours related to turbulence, velocity, pressure, and kinetic energy are obtained.
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