Transient flow simulation over a throttle body
Abstract
A transient based simulation was performed over an elbow geometry with a throttle body. The pre-processing was performed with CONVERGE Studio software and the solver equations processing was run with Cygwin software. The pressure, velocity and temperature plots were analysed with CONVERGE line plotting module. The variable contours were analysed with Post-processing software, ParaView.
Geometry
The elbow geometry was imported into CONVERGE Studio. The elbow section is shown in Fig.1. The throttle surface is shown in Fig.2.
Figure 1 Elbow geometry
Figure 2 Throttle body
Fig.3 shows the boundaries and types assigned to the geometry.
Figure 3 Assigned boundaries
At the inlet boundary, a pressure of 1.5 bar was set whereas at the outflow, a pressure of 1 bar was assigned.
A pre-defined mixture as air with Nitrogen and Oxygen concentrations as 0.77 and 0.23 were set respectively.
A transient based steady state solver was used to solve the flow equations over a time-based scale.
Figure 4 Simulation time parameters
As shown in Fig.4, a start time of 0 and end time of 0.01 seconds was chosen for the simulation. Thus, the simulation was carried out for 10 milliseconds. An initial time step and minimum time step of 1e-9 seconds was inputted. Maximum time step of 1 second was chosen for the case.
As the throttle moves with an angle throughout the whole simulation, the throttle position configuration was done with specified angles on each time (second) step which is shown in Figure 5.
Figure 5 Throttle position configuration
RANS based RNG k-ε turbulence model was used for this case.
A base grid of 2e-3 metres was set up: dx= 2e-3 metres, dy= 2e-3 metres, dz= 2e-3 metres.
Fixed embedding was made use of with an embedding scale of 3 and 2 embed layers.
Embedding was specifically done on the throttle body to observe velocity and pressure contours onto the throttle inside the elbow body.
Post processing results
With the ParaView software, the throttle within the elbow geometry can be seen within in the middle as shown in Fig. 6.
Figure 6 Transparent elbow geometry
Figure 7 Surface with edges mesh elbow geometry
Figure 8 Level 3 Embedding level near throttle body
Figure 9 Velocity change with Throttle movement
At 0 second time, throttle position is at 0° angle. At 2 milliseconds, throttle rotates at 25° angle and remains at this position till 4 milliseconds. At 8 milliseconds, throttle body again retains its original position, that is, 0° angle.
Fig. 9 shows the velocity contour of the throttle body as it moves through an angle of 25° angle.
Figure 10 Pressure contour in elbow during throttle movement
Figure 11 Velocity contour in elbow during throttle movement
Figure 12 Pressure contour of sliced elbow body
Figure 13 Velocity contour of sliced elbow body
Figure 14 Mass flow rate plot at inflow and outflow
Conclusions
Simulation time is more in the transient case than the one with steady state solver. Refinement of mesh with smaller grid size (2e-3 metres) and fixed embedding made the case setup more complex with greater computational time to solve the problem, The pressure and velocity changes greatly over the throttle body as the throttle moves a certain angle causing a lot of fluctuations over the region.