Transient simulation of flow over a throttle body
Aim: To setup case for transient state simulation for flow over throttle body in converge and to observe the fluid flow during the throttle valve rotation and discuss the results obtained.
Introduction:
The throttle valves are the devices that control the fluid flow by obstruction or constriction. The throttle valve is mainly used to monitor the fuel or air supply into the IC engine. Thus with the help of throttle valve the speed of the vehicle is controlled. In this project, the behaviour of the fluid when it is made to flow over the rotating throttle valve is studied. The transient state simlation for flow over throttle body is done with the help of converge cfd software. The case setup and results for the simulation is discussed below.
Geometry of the throttle body:
Boundary conditions
Inlet:
Boundary type = inlfow
Total pressure = 150 k pa
Temperature = 300k
Species = air
Outlet:
Boundary type = outflow
Static pressure = 100 k pa
Temperature = 300k
Species = air
Elbow wall:
Boundary type = wall
Wall motion type = stationary
Surface movement = fixed
throttle valve wall:
Boundary type = wall
Wall motion type = rotating
Surface movement = moving
Throttle valve shaft details for throttle wall rotation
Arc center : -7.6153092066133E-02 3.9077710839205E-02 2.0173289684608E-02
Arc diameter: 2.0013289141275E-03
Arc normal: -7.9436619318597E-01 -6.0743907321024E-01 -3.5136976904633E-04
Profile configuration of throttle valve at different time
Assigning volumetric fluid region to all the boundaries
Resion name = voumetric fluid used defined
Species = air
Pressure = 101325 pa
Temperature = 300k
Calculation of time for simulation:
The fluid velocity obtained from the steady state simulation is used to calculate the end time for the transient simulation.
Velocity of fluid (from steady state simulation) = 150 m/s
characteristic length of the throttle body = 0.1 m
time taken to complete the flow = 0.1/150 s = 0.0006 s
Hence the end time for the simulation is assumed to be 6 milliseconds (ie; 0.006 s)
Simulation parameters:
The given throttle body model is imported into the converge CFD software. The boundary conditions are flagged to all the respective regions and the air is added as the fluid medium into the volumetric region. The total pressure at inlet 150 k pascals and static pressure at outlet is 100 k pascals, due to this pressure difference the fluid steam flows from the inlet to the outlet.The PISO solver scheme (pressure implicit with splitting of operator) is prefered as this scheme gives accurate results and good wall treatment is done and gives stable solution. Transient state solver is used to observe the fluid stream behaviour as the throttle valve rotates with respect to time.
Mesh generated
Mesh details:
The above figure shows the mesh generated for the base grid size of 0.002 m and 3 embedding layers are added to refine the mesh near the walls of the throttle valve. The animation of mesh generation for throttle is shown below.
Mesh generation for throttle valve rotation
Results:
Velocity contour
Velocity vector plot
Velocity streamline animation
Velocity animation
Density contour
Pressure contour
Velocity plot
Mass flow rate plot
Total pressure plot
Static pressure plot
Total cell count
Conclusion:
- In the velocity contour, it can be seen that the high and low fluid velocity distribution takes place near the throttle valve. The high and low velocity distribution across the throttle valve is observed due to the rotation of the throttle valve.
- In the velocity streamline animation video, the change of fluid velocity near the throttle valve as it rotates with respect to time is observed clearly.
- When the throttle valve rotates, the flow area changes. The velocity of fluid is high when there is increase in flow area and velocity of fluid is low when there is decrease in flow area.
- In the pressure contour the same phenomenon is observed. The pressure ditribution changes as the flow area is changed.
- Due to change in pressure, the density of the fluid changes across the throttle valve. This can be observed in the density contour, the density of the fluid changes from 0.88 kg/m3 to 1.7 kg/m3.
- In the mass flow rate plot, the same flow rate values is observed through inlet and outlet. Thus, it can be said that flow is continuous. And the plot shows both positive and negative flow rate values which implies that mass is conserved.
- In the total pressure plot, the total pressure at outlet increases due to increase in the dynamic pressure which imparts motion to the fluid stream and the total pressure plot remains constant at inlet due to boundary condition.
- In the static pressure plot, the static pressure decreases at inlet as motion is imparted to the fluid which leads to increase in dynamic pressure and the static pressure remains constant at outlet due to boundary condition.
- In the total cell count plot it can be observed that the cell generation varies with respect to time, this is due to rotation of the throttle valve with respect to time. The cells are generated continuously as the throttle valve rotates or moves, hence the cell count variation is observed in the plot