Transient simulation of flow over a throttle body using Converge
INTRODUCTION :
All of the Spark ignited engines used throttle valve to maintain the air flow ratio close to stoichiometric ratio for efficient function of catalytic converter. In this project we will see how flow behaves over this throttle valve as the valve moves along its center shaft.
GEOMETRY:
The following figure was used to analyse the behaviour of flow over the throttle valve.
Green region indicates the inlet and the blue region indicates the outlet
The computational mesh of base grid size 2mm is generated over entire structure. To accurately simulate the flow over the throttle the mesh is refined around the throttle valve with permanent embedding of two layers and scale of 3 around this region.
The following figure shows close up image of mesh embedding around the throttle valve
Since we have to to simulate the transient behaviour of throttle valve it was given a rotation of 20 deg after 2 ms, 40 deg after 4 ms and 60 deg after 6 ms into the simulation time. The movement of throttle can be visuliased in video below
SIMULATION SETUP :
After flagging the appropriate boundaries and selecting the the material the simulation parameters are chosen. Transient solver is selected for simulating this flow.
Inlet:
Boundary type : Inflow
Specified total pressure : 1.1 x 10^5 Pa = 1.1 bar
Material: Air
Temperature: 300 k
Outlet
Boundary type : Outflow
Specified pressure : 1.0 x 10^5 Pa = 1 bar
Material: Air
Temperature: 300 k
Elbow
Boundary type : Wall
Wall Motion : Stationary
Velocity boundary condition: Law of wall
Temperature boundary condition: Law of wall
Throttle
Boundary type : Wall
Wall Motion : Rotating (Along the axis of centre of shaft of throttle valve)
Time (s) Angle
0.000 0
0.002 20
0.004 40
0.006 60
Velocity boundary condition: Law of wall
Temperature boundary condition: Law of wall
A volumetric region is generated to simulate the fluid flow and is initialized to the pressure of 101325 Pa and temperature of 300 K. RNG model is used to model the turbulence in the flow. simulation is run in parallel for around 0.1s with initial time step of 1x10^-9s and maximum time step of 1s to ensure convergence
PLOTS:
Velocity plots across Inlet and Outlet
Total and static pressure plot across Inlet
The total pressure is conserved in inlet as mentioned in boundary condition. The dynamic pressure increases with increase in velocity which is compensated by decrease in static pressure to conserve the total pressure.
Total and static pressure plot across Outlet
From the above graph we can see that after the throttle has closed 60deg mass flow has reduced and so has velocity which is why dynamic pressure has reduced and static pressure has increased
Total massflow across Inlet and Outlet
The inlet and outlet mass flow is equal in magnitude i.e 0.03 kg/s which shows the mass was conserved during the entire simulation
Total cell count per processor
The total cell count was close to 51000 at the beginning and the went on increasing as throttle moved. As the throttle stopped moving cell count stabilized. Total cells were divided in four processors each having roughly 15000 cells
Velocity contour across the elbow
Velocity profile as the throttle moves can be seen in this video
Pressure contour across elbow
Pressure profile as the throttle moves can be seen in this video
As we can see from this pressure contour diagram the pressure at the inlet is 1.1 bar as specified. We can see a high pressure area at the region where the flow first hits the throttle valve and region of low pressure area at the end of the throttle valve where the flow separates
Streamline across elbow
This streamline diagram helps us to to visualise the flow pattern around the throttle
Conclusion:
Transient simulation was performed on an elbow having a throttle valve and important parameters were calculated and plotted to analyse the the behaviour of flow around throttle valve