Modelling and simulation of flow through a flowbench

AIM:

Create a 3D model of a flow bench and run flow analysis

OBJECTIVES:

• Obtain a plot of lift vs mass flow rate
• Grid dependence test
  • For three grids run simulation at a particular valve lift
• Effect of valve lift on mass flow rate
  • From the best grid, run a parametric sweep to show the effect of valve lift on mass flow rate

INTRODUCTION:

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.

LIMITATIONS:

Flow bench test pressure are typically conducted at 10 to 28 inches of water (2.5 to 7 kPa) while a real engine may see 190 inches of water (47 kPa) pressure difference.

The flow bench tests using only air while a real engine usually uses air mixed with fuel droplets and fuel vapor, which is significantly different. Evaporating fuel passing through the port-runner has the effect of adding gas to and lowering the temperature of the air stream along the runner and giving the outlet flow rate slightly higher than the flow rate entering the port-runner. A port which flows dry air well might cause fuel droplets to fall out of suspension causing a loss of power not indicated by flow figures alone.

The proximity, shape and movement of the piston as well as the movement of the valve itself significantly alters the flow conditions in a real engine that do not exist in flow bench tests.

BODY OF THE CONTENT:

• 1^st Creating the geometry of the flow bench as shown below. (Adding transparency for better view)

• Now steps to be followed to perform flow simulation.
• Adding lids at the opening and the exit.
• Then creating a new wizard with internal flow, and taking air as fluid and as it is going to be a steady state flow there is no time dependency, everything else remains the same.
• Now for the boundary conditions at inlet taking the total pressure to be 1 atm and as over the introduction it is seen that the pressure difference is in range 2.5k to 7k pa so taking the static pressure at outlet to be 3.5k pa.
• In results adding cut plots and flow trajectory.
• Performing the grid dependency test.
• For grid level of 3 results obtained: -

• For grid level of 4 results obtained: -

• For grid level of 5 results obtained: -

As from the above results it can be seen that the number of iterations required to complete the simulation is more in case of level 5 as well as while running the simulation the number of fluid particles generated inside the mesh is much more in case of level 5.

Therefore, for the parametric study taking the grid level of 5 and performing the study, the given fig shown below illustrate how vale lift can be added in parametric study.

Giving the range to the valve lift and number of valve lift required and adding the results as mass flow rate, cut plot and flow trajectory.

RESULTS:

For 1^st valve lift:

For 2^nd valve lift:

For 3^rd valve lift:

For 4^th valve lift:

For 5^th valve lift:

For 6^th valve lift:

For 7^th valve lift:

CONCLUSION:

The graph of mass flow rate at different valve lift is shown below.

-ve sign indicates the mass is flowing out of the system therefore, from the above graph as well as from the results obtained it can be seen that the mass flow rate increases with the increase in valve lift.

As it was a made-up geometry the results were not that much accurate also it justifies the limitations of flow bench test.

from the design point 4 upto the 7 mass flow rate almost remains constant as the valve was almost completely open in all of those cases.