Transient simulation of flow over throttle body

Transient simulation of flow over throttle body

Introduction:

Throttle valves are mainly used to control the amount of air flow and hence fuel flow and mainly finds application in carburetted fuel systems like in Gasoline engines and various piping systems.

objective:

• To perform steady state simulation of flow in an elbow joint containing throttle valve.
• To post-process the results in Paraview software and analyse velocity and pressure contours.

Outline of project flow:

• Geometry set up
• Boundary Flagging
• Case set-up
  • boundary conditions
  • case set-up
  • simulation time parameters
  • defining turbulence model
• Running of simulation ]
• Postprocessing and analysis of results.

Geometry Set-up:

• Premodelled geometry is imported into the converge software
• Diagnosis is run to check if there are any errors.

Figure: Geometry of teh throttle valve

Figure: Geometry of the elbow with throttle valve

Setting up throttle motion:

• Since this is a transient analysis, we have to give motion to the throttle valve. We have to define an axis about which the throttle should rotate.
• using arc centre measurement, the Co-ordinates of the axis of the throttle is measured.
• These co-ordinates are pasted in the boundary condition of the throttle.

Case set-up:

1. It is a general flow case.
2. Oxygen (O2) and Nitrogen (N2) are the two main species.
3. Predefined mixture is air
4. Solver: Transient solver and simulation mode: Full hydrodynamic.
5. Simulation time parameters:
   • Start time: 0
   • End time: 0.01
   • Initial and minimum time step: 1e-9
   • Maximum time step: 1
6. Boundary Conditions:
   • Inlet: It is inflow boundary with pressure of 150000 pa.
   • Outlet: It is outflow boundary type with pressure of 100000 pa.
   • Wall: Elbow and throttle rotating for transient simulation.
   • For throttle:
     • wall motion type: Rotating
     • surface movement: moving.
     • Create a file to define the throttle motion (shown below)

The motion of the throttle is defined as follows:

Time (ms)	Angle (deg)
0	0
2	25
4	25
8	0

The coordinates for the rotate centre and rotate about are entered.

7. Regions and Initializations: region 0 is the volumetric flow region.

8. Turbulence model: RNG k-ɛ.

9. Grid size is 2mm along x, y, z directions.

10. Fixed embedding is used around the throttle with a scale size of 3mm and also the number of embed layers are also 3.

Meshing:

Figure: meshing around the throttle with fixed embedding of 3mm around the throttle and number of embed layers of 3.

Boundary Flagging:

Running of Simulation:

• The simulation was run and the summary is as shown in the figure below.

Results:

Total cells:

• The total number of cells is varying thoughout the cycle.
• The number of cells are constant between 2 to 4 ms and 8 to 10ms. This is the time period when the throttle motion is stationary.
• In converge, the number of cells vary when the geometry is in motion.

Mesh changes can be visualised in the following video.

Pressure contours:

• Below animation and figure shows the pressure contours over throttle body when the valve is in motion.
• The valve experiences a maximum pressure of 1.3 bar due to obstruction of the flow which is due to the conversion of Kinetic energy into pressure energy.

Figure: pressure contours over throttle valve

Figure: Pressure at the inlet of the elbow.

Figure: Pressure at the outlet of elbow

• High pressure variations during throtte valve movement is oberved (i.e is between 0 to 2 ms and 4 to 8 ms).

Mass flow rate:

Figure: Mass flow rate at the inlet and outlet.

Velocity:

Figure: Velocity variation

• From the mass flow rate and velocity graphs. we can observe that the variation is high during initial valve motion (between 0 to 2 ms) and it increases during second valve motion (between 4 to 8ms)
• When the valve is stationary, the velocity and mass flow rates are almost constant.
• Also, maximum flow velocity of 300 m/s was oberved.

Conclusion:

• From the above analysis, we can observe how the valve motion affects the pressure, velocity contours and mass flow rates.