Steady And Transient Flow Over a Throttle Body
Simulation of Flow Over a Throttle Body
Objective: To carry out a steady-state and transient (moving throttle body) simulation of the flow over a throttle body. To profile the pressure and velocity characteristics of the flow over the throttle body as the throttle rotates through the pipe.
Figure 1: Streamline Characteristics of the Flow-Velocity over the Throttle.
Meshing:
Figure 2: Meshing for Steady-State simulation
Figure 3: Meshing for Transient simulation of the Throttle body.
Data and Analysis:
Determining Time Step:
Average Flow Velocity = 190 m/s
Flow length = 0.2 m
Time for one flow cycle = `0.2/190 = 0.001 s`
End time step = time for 10 flow cycles = `10*0.001 = 0.01 s = 10 ms`
- Mass Flow Rate Profile
The mass flow rate profile showcases a passable symmetry that indicates the preservation of mass continuity. The mass flow rate into the system manifests as the magnitude of mass flow rate out of the system.
Figure 4: Mass Flow Rate for Steady-State
Figure 5: Mass Flow Rate for Transient (rotating Throttle)
- Pressure Profile
Total Pressure Plots:
The total pressure at the inlet remains at a steady 1.5 Bars. As flow assimilates a steady state, as cycles of flow circulate through the pipe the total pressure at the outlet converges to a steady value about 1.35 Bars. Thus, flow is established from region of higher pressure and naturally steadies out towards the region of lower pressure.
Figure 6: Total Pressure for Steady-State Analysis
Figure 7: Total Pressure for dynamic Throttle
Pressure Contours:
Towards the flow-ward side, where the flow first encounters the throttle we observe manifestation of stagnation points or high-pressure regions. This high-pressure region occurs because the fluid is blocked off by incidence with the bluff body, consequently boasting higher static pressure due to higher potential energy and a zeroing kinetic energy as the flow is isentropically zeroed. At backward side of the throttle, we witness regions of low static pressure as the flow is blocked off by the throttle. These low-pressure zones are what drive the re-circulations regions immediately after the flow separation and consequently the wake is established through the under-side of the throttle.
Figure 8: Pressure Contour for Steady-State Analysis
Upon the throttle itself, we observe typical flow profile over a cylinder hump. There are regions of higher pressures on either side of the humps with lowest pressures developing normal to the hump. The static pressure appears to drop as we climb to the trailing edge of the throttle as can be expected from a reducing volume of fluid above it. Static pressure is lowest at the trailing edge as this is the highest point and furthermore, boundary layer separation is initiated.
Figure 9: Transient Pressure Contour on the Mesh
Figure 10: Transient Pressure Contour with Throttle.
- Velocity Profile
Velocity Contours:
As the fluid loses kinetic energy at the stagnation points at the leading edge of the throttle, the fluid velocity is zeroed. As the throttle angles up to block more of the flow, more of the fluid is normal to the bluff body and thereafter more adverse regions of stagnation points develop with a zeroing fluid velocity. Over the hump, there are regions of higher pressures on either side of the hump which correspond to regions of lower velocity. On the other hand, region of lower pressure developing on the top of the hump coupled with preservation of volumetric flow manifests as regions of higher fluid velocity. This can be seen in the velocity contour of the throttle. As the pressure reduces towards the trailing edge of the throttle, the fluid velocity is naturally increased by nature of the pressure gradient. Towards the shielded end of the throttle, we observe the re-circulation zone. The presence of the lower pressure region causes flow to re-circulate in this region and we observe a zone of reduced velocity.
Figure 11: Velocity Contour for Steady-Throttle
Figure 12: Velocity Contour, Transient Throttle
Velocity Plots:
In the velocity plots for the cross-section just past the throttle, we observe velocity peaks towards the pipe sides as the fluid leaks from sides through regions of reduced cross-section. In the middle we observe velocity drops that indicate zones of flow re-circulation immediately manifested in the wake past the throttle.
Figure 13: Velocity Plot for Steady Throttle
Figure 14: Velocity Plot for Moving Throttle
- Cell Count
The figures below convey information pertaining the calls allotted to the processing cores during while computing the simulations for the steady and transient analysis.
Figure 15: Cell Count for Steady-State Simulation
Figure 16: Cell Count for Transient Simulation
Animation for Rotation of Throttle:
The animation depicts the development of more adverse wakes and re-circulation zones as the throttle blocks more of the flow.
Conclusion: The results of the simulation re-affirm three findings. Firstly, Bernoulli’s principle, regions of high velocity manifest at region of low pressure as flow manifests due to pressure gradient. Secondly, the Venturi effect can be observed such that region of constricted flows depict lower pressures. Finally, the energy continuity is conserved.