Transient simulation of flow over a throttle body
Aim:
To Setup and run transient state simulation for flow over a throttle body.
Objective:
1.To calculate an end time for simulation.
2.To create an animation in which the throttle movement should be visible.Throttle movement should be as follow:
i.From 0 to 2 ms the valve should rotate by 25 degrees.
ii.From 2 to 4ms it should stay at 25 degrees.
iii.After which by 8ms the valve should get back to its original position.
Geometry:
Geometry of elbow pipe with throttle valve fitted inside is created in solidworks and then it is imported as .STL file in CONVERGE studio.
Fig: elbow is made transparent to view Throttle body.
Case Setup:
Material: Air
Initial Condition:
Preasure : 101325 Pa
Temperature : 300 k
Boundary Condition:
1.Inlet
Type: INFLOW
pressure: 1.5e5 Pa (Total Preassure)
2.Outlet
Type: OUTFLOW
pressure: 1e5 Pa (Static Preassure)
3. Elbow Wall
Type : Wall
4.Throttle Body
Type :wall
Motion :Rotating
Here to get the center of cylinder, go to Geomtry > Measure > Direction > arc normal and pick any three points lying on circumference of circle and copy it.
Simillarly.to get the axis of cylinder, go to Geomtry > Measure > Direction > triangle normal and copy the co-ordinates.
Now,the rotation of throttle plate should be as follow:
i.From 0 to 2 ms the valve should rotate by 25 degrees.
ii.From 2 to 4ms it should stay at 25 degrees.
iii.After which by 8ms the valve should get back to its original position.
Go to Rotate Rate and click on Use file and setup the above mentioned condition.
Run Parameters:
Solver: Transient
Simulation Time Parameters:
Start Time:0 S
End Time = Characteristic length/Velocity
= 0.2/191
= 0.00104 S
End Time = 0.00104*10 = 0.01 S (Approx)
Turbulence Modeling:
Turbulence Model: RNG k-ϵ
Mesh Size:
Mesh size is 2e-3 in X,Y & Z direction
Fixed Embedding:
This feature helps to refine grain size in particular area.
Boundary ID: Throttle Body
scale: 3
Embed layer : 2
Output Files:
Time interval for writting Text Files = 1e-6
Time interval for writting 3D Output file :
for 10 files,
Time interval for writting 3D Output file = end time/ 10
= 0.01/10
= 0.001 S
Result:
Mesh:
Fig:Grain refinement near Throttle body after fixed embedding
Mass Flow rate:
Average Velocity:
Total Preassure:
Static Preassure:
Total Cell Count:
Preassure Contour:
Velocity Contour:
Conclusion:
1. CONVERGE use Adaptive Mesh Refinement(AMR) technique to produce mesh hence,it is found drastic increase in total cell count when Throttle body moves from 0 to 2ms and the cell remains constant from 2 to 4 ms as Throttle body remains constant and again cell count decreases as Throttle body comes to original possition.
2.As Throttle body rotates there is an obstriction in flow of fluid and hence its velocity and hence kinetic energy of fluid is converted into preassure energy therefor Total Preassure increases.
3.Due to the rotation of throttle plate,wake region is formed on plate causing decceleration of flow leads to separation of flow hence decrease in static preassure at outlet.
4.Rotation of Throttle plate causing obstruction to the fluid flow increases the preassure gradient(preassure force in the direction of flow) forced fluid hence velocity of fluid flow increase therefore Mass flow rate increases at the outlet.