Week 4: Project - Steady state simulation of flow over a throttle body

Aim: To perform steady-state simulations over the throttle plate to comprehend the pressure and velocity distribution through the implementation of mesh generation strategy.

Introduction: When it comes designing the spark-ignition engine, amount of air and fuel entry into the system is very important.To regulate the power output there has to equipment which helps in achieving it .i.e throttle valve. The throttle is a device used in the internal combustion engines to control the fuel or air mass flow into the cylinder. It is located close to the intake manifold.

Geometry:

figure 1 - Throttle body diagram

2.Case Setup:

2.1 Mesh

Mesh size plays a vital role in producing accuracy and computational efficiency. Smaller mesh size results in better accuracy in simulated processes and it also increases computational time due to the fact that more number of the equation must be solved. Converge provides a wonderful feature called fixed embedding mesh which means only interested flow area could be refined and the rest of the domain is kept at base mesh size. For each fixed embedding, an embedding scale has to be provided and it must be a positive integer. The formula for computing the embedded scale grid size is:

`dxembed=(dxbase)/2^(embed-scale)`

Where dxbase=base grid size in x,y and z-direction

	Base Mesh	Fine Mesh
Base Grid Size, mm	3	2
Min Grid Size, mm	0.33 (Refinement Scale 3)	0.25 (Refinement Scale 3)
Max number of Cells	16888	35518

figure 2- a) Base Mesh 3mm figure b) Base Mesh 2mm

In the above figures, throttle embedding is shown , representing the area with the difference the cell size highlights the embedding used for the throttle plate.

3.Boundary Conditions

	Type	Fluid	Pressure and Temperature
Inlet	Inflow	Air(O2-0.23 and N2-0.77) by mass	1.5 bar
Outlet	Outflow	Air (O2-0.23 and N2-0.77) by mass	1 Bar
Throttle	Wall-Fixed	-	-
Elbow	Wall-Fixed	-	-

The flow is analysed using RNG K-epsilon model turbulence model.

3.Results:

3.1 Plots: Avg Mass flow rates

Avg Velocity:

Pressure plot for Mesh 3mm:

Pressure plot for Mesh 2mm:

Cell Counts:

3.2: Contours

Pressure Mesh 3 mm:

figure 3- a) Base Mesh 3mm figure b) Base Mesh 2mm

Velocity Mesh 3 mm:

figure 4- a) Base Mesh 3mm figure b) Base Mesh 2mm

In the above velocity contour, it is clearly visible that the velocity increases as the flow hits the throttle plate, velocity is higher at the upstream than downstream due to the pressure drop.

Throttle Mesh 3mm :

figure 5- a) Base Mesh 3mm figure b) Base Mesh 2mm

Conclusions: To summarise, after running the simulations it can be said that flow over throttle leads to an increase in the velocity as the flow hits the throttle plate and reduction in the local pressure in the domain due to flow being choked/obstructed. The quantities analysed in this simulation attain steady state which could be seen in the plots shown in the results section.