Modelling and flow simulation of a flowbench.

AIM: Obtain a lift vs mass flow rate plot for a flowbench by performing a flow simulation in solidworks.

OBJECTIVES:

• Design a flowbench
• Perform a flow simulation
• Perform a grid dependency test
• Obtain flow vs mass flow rate plot
• Derive a conclusion on observations

THEORY:

An air flow bench is a device used for testing the internal aerodynamic qualities of an engine component and is related to the more familiar wind tunnel.

It is used primarily for testing the intake and exhaust ports of cylinder heads of internal combustion engines. It is also used to test the flow capabilities of any component such as air filters, carburettors, manifolds or any other part that is required to flow gas. A flow bench is one of the primary tools of high-performance engine builders, and porting cylinder heads would be strictly hit or miss without it.

A flow bench consists of an air pump of some sort, a metering element, pressure and temperature measuring instruments such as manometers, and various controls. The test piece is attached in series with the pump and measuring element and air is pumped through the whole system. Therefore, all the air passing through the metering element also passes through the test piece. Because the volume flow rate through the metering element is known and the flow through the test piece is the same, it is also known. The mass flow rate can be calculated using the known pressure and temperature data to calculate air densities, and multiplying by the volume flow rate.

Fig: Flow-bench Schematic

PROCEDURE:

Designing a flowbench

Select Flow Simulation

Provide lids on inlet opening and base of the flowbench model.

Click on New Wizard and select following options –

Analysis type – Internal

Fluid type – Gas -> Air

Wall thermal condition – Adiabatic wall

Roughness – 0 micrometre

Pressure – 101325 Pa

Temperature - 293.2 K

Finish.

Insert boundaries, define inlet opening as total pressure and base of model as static pressure.

Insert global goal mass flow rate. Also insert surface goal mass flow rate selecting base lid of the model.

Insert Cut Plots in Front Plane for pressure and velocity.

Insert Flow trajectory for pressure and velocity, selecting inlet as opening.

Adjust mesh settings from global mesh settings and also enable advance channel refinement.

Create new parametric study-

Select dimension of the valve as input as variation of 5 with values ranging from 0.0005m to 0.001m.

Select both cut plots and flow trajectory as output parameters. Also Select surface goal as output parameter.

Finally click on run.

RESULTS:

Different velocity contour for different mesh setting (From 3 to 7)

We obtain accurate values as the mesh settings goes on increasing but it also consumes more computer resources and time to give the results. According to my system configuration mesh setting 4 gives optimal results.

Case 1: Valve lift = 0.1mm

Pressure Contour

Velocity Contour

Pressure trajectory

Velocity trajectory

Case 2: Valve lift = 0.7mm

Pressure Contour

Velocity Contour

Pressure trajectory

Velocity trajectory

Case 3: Valve lift = 1.3mm

Pressure Contour

Velocity Contour

Pressure trajectory

Velocity trajectory

Case 4: Valve lift = 1.9mm

Pressure Contour

Velocity Contour

Pressure trajectory

Velocity trajectory

Case 5: Valve lift = 2.5mm

Pressure Contour

Velocity Contour

Pressure trajectory

Velocity trajectory

Goal plot summary

Mass flow rate plot

CONCLUSION:

Grid Dependency Test:
The grid dependency test is taken to select and perform the optimum level of mesh for the mass flow rate in the profile geometry of the flow bench:

1. Initially, the grid dependency test is taken for level 3, level 4, level 5, level 6 & level7. On seeing the results of grid dependency, the value for level 7 shows an accurate and smoother value.
2. According to my system configuration, Optimum level for performing the simulation was observed at level 4. Thus, the level 4 is chosen for performing the flow simulation in flow bench geometry.

Mass Flow rate vs Valve lift:
Generally, Mass flow rate is the mass of a substance that passes per unit of time. From the graph, it is clear that as the value of valve lift increases, the mass flow rate increases this is due to the gap between the circular sweep profile and cylinder:

1. Initially, the valve lift is at 0.0001mm which shows that the gap is little that results in the high velocity at the valve lift point, and the pressure is heavy inside the circular profile. Hence the mass flow rate is low at this point.
2. As the valve lift value is increased from 0.0001mm to 0.0025mm, the gap is increased that results in an increase in mass flow rate.
3. As the valve lift is increases the mass flow rate is increases correspondingly.
4. At certain valve lift, the mass flow rate seems to be a constant valve. This is due to the gap between them provides enough space for the flow from a circular profile to the cylinder.