Transient simulation of flow over a throttle body

Objectives:

• To import a 3D Geometry of elbow into CONVERGE studio.
• To add boundaries and setup the case in CONVERGE and run the elbow flow simulation using Cygwin.
• To post Process the results using Paraview

Importing the Geometry:

• Open the CONVERGE studio, drop the elbow.stl into the converge studio to import.

Remove the thickness:

• Click on the Boundary -> Find/clean -> Find.
• The Boundary fences for all the open edges and surfaces are highlighted.

• Click on Repair ->Delete-> select the Outer surface -> Apply.
• Similarly, Click on Repair ->Delete-> select the smaller surfaces at the ends of the elbow -> Apply.

Enclosing the inner Pipe

• Click on Repair -> Patch -> select the first open edge -> Apply.
• Click on Repair -> Patch -> select the second open edge -> Apply.

• Click on Normal Toggle, Perpendiculars to the triangular faces are pointing interior, but the throttle surface normals are pointing out.

Diagnosis:

• After importing the Geometry, to check the errors for 3D Geometry, click on Diagnosis, check for Intersections, open edges, Nonmanifold edges, Normal Orientation, check that all normals are pointing interior, Isolated triangles

• Click on Find for identifying the errors, find out the errors and remove the errors. In this case there are no errors.

Assigning the Boundaries

• From Geometry, select

Boundary -> Flag -> 'Click on +' for adding the required boundaries

• Select the 'Cursor pick' and 'triangle' for selecting the faces.
• Select the boundary, select the faces and click on Apply
• Right click on the Boundary for assigning the name for the selection.

Setting up the Case:

• Click on Case Setup -> Being Case Setup -> tick General flow -> Done

• Click on Materials, set the Predefined mixtures as Air, tick the boxes of Gas simulation and Reaction mechanism then click on Apply -> Yes(to overwrite gas.dat, mech.dat and therm dat) -> Done.

• Click on Global transport parameters -> Ok
• Click on Simulation Parameters -> Done

• From Simulation Parameters, click on Run parameters, set the solver to Transient then click on OK -> Yes(to load default tolerance/relaxation/PISO -> Yes(load the default of Non-Engine application.

• From Simulation Parameters,Click on Simulation time Parameters, assign the Start time, End time, Initial time-step, Minimum time-step, Maximum time-step and Maximum convection CFL limit

• Click on OK.
• From Simulation Parameters, Click on Solver parameters -> Ok.

• From Initial conditions & Events, click on  Regions and initialization, click on Add.
• From species, click on +Air

• Double click on Region Name, change the name to Volumetric_region
• Click on Ok.
• From Boundary conditions, Click on Boundary then
• Click on Elbow wall for assigning the boundary conditions
• select the Boundary Type as WALL

• Double click on Region name for Elbow wall, change the region name to volumetric_region.
• From Boundary conditions, Click on Boundary then
• Click on Throttle for assigning the boundary conditions
• select the Boundary Type as Wall
• From Velocity Boundary Condition select

- Wall motion type : Rotating

- Surface movement : MOVING

- specify Rotate center and Rotate about

- Tick use file

- then add second and Angle, for throttle movement, then mention a file name and                 click on accept

• Double click on Region name for Throttle, change the region name to volumetric_region.
• From Boundary conditions, Click on Boundary then
• Click on Inlet for assigning the boundary conditions
• select the Boundary Type as INFLOW
• From Pressure Boundary Conditions, change the total pressure to 1.5e5 Pa.
• From Species Boundary Condition, 'Click on +Air' to add species

• Double click on Region name for inlet, change the region name to volumetric_region.
• From Boundary conditions, Click on Boundary then
• Click on Outlet for assigning the boundary conditions
• select the Boundary Type as OUTFLOW
• From Pressure Boundary Conditions, change the total pressure to 1e5 Pa.
• From Species Boundary Condition, 'Click on +Air' to add species

• Double click on Region name for outlet, change the region name to volumetric_region.
• Click on Turbulence Modeling , then click Ok. To set the Default RNG k - epsilon model.

• From Grid Control, Click on  Base grid, change the Base grid size dx, dy, dz to 2e-3m then Click on Ok.

• Click on Grid control -> tick the fixed embedding ->Done.

• From Grid Control, Click on Fixed embedding -> 'Entity type - Boundary' -> 'Boundary ID - Top & Bottom Walls' -> 'Mode - PERMANENT' -> 'Scale - 3'_> 'Embed Layers -2' -> Ok.

• From Output/ Post Processing, Click on Post Variable selection -> Ok.

• From Output/ Post Processing, Click on Output files -> Ok.

Simulation Results:

The Elbow wall with throttle in transparent mode.

Mesh (dx = 2e-3;  dy = 2e-3;   dz = 2e-3):

Velocity Contour:

Velocity Contour with Glyph:

Pressure Contour:

Pressure Contour with Glyph:

Velocity Animation:

Velocity with Glyph Animation:

Pressure Animation:

Plotting Results:

Average Velocity:

Static Pressure:

Total Pressure:

Mass Flow Rate:

Total Cells:

Conclusion:

• Simulation time for transient is more as compared with Steady state solver.
• The velocity decreases, when the fluid is in impact with the throttle and it drastically increases to maximum when the fluid flows through the gap(i.e in between elbow wall and throttle) because of sudden change in the geometry, similarly there is lot more changes in fluid characterisitics over the throttle body with its movement.
• The pressure is very high when the fluid impacts the throttle and reduces within the gap because of sudden change in the geometry and the recirculation takes near the throttle and the flow becomes steady .
• The mass flow rate at inlet is equal to the mass flow rate at outlet, convergence is attained after some cycles then steady state is attained.
• The static pressure at inlet goes on decreasing and becomes stable, but the total pressure at outlet increases continously and becomes stable after steady state is attained.

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