Modelling and simulation of flow through a flowbench

A 3D model of a flow bench is created and a baseline flow analysis is run. A plot of lift vs mass flow rate is obtained, also the pressure drop in the system. Flow bench is a device used to design the intake port. Usually, in the flowbench, we take the port which is required to be tested. Here in this project, we are simulating the intake port.

Cylinder dimensions

• Bore diameter is 50mm.
• Length of cylinder 100mm.
• Intake manifold diameter is 25mm.

Boundary conditions

• Inlet total pressure 172369[Pa] at temperature 293.2[K].
• Outlet static pressure 101325[Pa] at temperature 293.2[K].Wall type is taken as the real wall.

GRID DEPENDENCY TEST

Grid dependence test is also called as mesh dependence test, in the which the model is subjected to successive smaller cell sizes for calculations, that is the model is divided into a smaller number of parts called elements and calculations are made. As the element size decreases the error towards the results reduces. Now for the above 3D model, we run the simulation with 3 refining values. or a particular valve lift of 4mm.

For refining cells 2

For refining cells 3

For refining cells 4

From the above results, it can be seen that for the same inlet pressure, outlet pressure, wall conditions and the value lift of 4mm the velocity variations in the cut plots are different. Thus we can say that the results greatly depend on the level of refining the fluid cells. In the above problem, we see that the refining value of cells with 4 number has got a greater accuracy.

The table shows the level of refining, valve lift, mass flow rate, the pressure at inlet-outlet and the pressure drop in the system. The parametric study is conducted at three design points 1, 2 and 3 which is the level of refinement 2, 3 and 4 respectively. The grid dependency test is made for the same valve lift of 4mm.

Pressure drop with respect to the Design points

For the same lift value as the refining of cells increases the pressure drop value increases.

Total Pressure at the outlet with respect to the Design points

As the refining of cells increases the pressure at the outlet decreases to a larger value.

Mass Flow rate at the outlet with respect to the Design points

As the refining of cells increases the mass flow rate at the outlet increases for design point 2 and increases for design point 3, hence there is fluctuation in the results for the values of refining of the cells. Thus it is difficult to assume the best refining cell value in this case.

Considering the above three graphs the first two graphs tends to converge to a better solution as the refining of cells increases. Thus we choose the highest value of refining as 4 for the next parametric study to show the effect of valve lift on the mass flow rate.

EFFECT OF VALVE LIFT ON THE MASS FLOW RATE

We have decided the best refining value as 4, now parametric sweep to show the effect of valve lift on mass flow rate is run and the cut plots of the velocity variations are shown in the figures below.

For valve lift between 1mm and 8mm with each lift of 1mm, the cut plots are shown.

• We know that the pressure in the inlet manifold is more than the static pressure at the outlet [that is inlet manifold pressure 172369[Pa] is more than static pressure 101325[Pa] ].
• Initially when the valve is closed pressure in the cylinder will be same as the static pressure at the outlet.
• Gradually when there is a lift in the valve position by 1mm the pressure starts developing in the cylinder.
• When the valve lift position increases the pressure drop value reduces.
• Now since the pressure drop values decrease for the increase in valve lift between the inlet and the outlet, velocity of the gases flowing across the valve decreases which can be seen from the above cut-plots.

• The above table shows the valve lift, mass flow rate, pressure at inlet-outlet and the pressure drop in the system
• The parametric study is conducted at three design points 1, 2, 3, 4, 5, 6, 7 and 8 which is the valve lift 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, and 8mm respectively.
• The grid dependency test is made for the same refining value of 4. Graphs for pressure drop, mass flow rate and total pressure at the outlet with respect to the design points are made as follows.

Pressure drop with respect to the design points

• When the lift of the valve is small, pressure developing in the cylinder is at the lower rate.
• When the lift is large, pressure developing in the cylinder is at a higher rate.
• When there is a lift in the valve position the pressure developing in the cylinder is faster. Now the increases in pressure in the cylinder can also be stated as the decrease in the pressure drop.

Pressure drop=(inlet pressure - outlet pressure)

Inlet pressure remains the same and outlet pressure increases (can be seen in the below graph). Thus pressure drop has to reduce this can be seen in the above graph.

Total Pressure at the outlet with respect to the Design points increases as discussed above

Mass Flow rate with respect to the Design points

• When the lift of the valve is small, pressure developing in the cylinder is at the lower rate.
• And pressure developing is high when the lift is larger.
• Initially, the pressure drop is high hence the tendency of the gases to flow from the region of higher pressure to the lower pressure region is high.
• Hence we can say that the mass flow rate is more for a small lift in the valve position. And gradually decreases for higher values of the valve lift. This can be clearly seen in the above graph.