Modelling and simulation of flow through a flowbench

1. INTRODUCTION

An airflow bench is a device used for testing the internal aerodynamic qualities of an engine component and structure.

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 like air filters, carburetors, manifolds, or the other part that's required to flow gas. A flow bench is one among the tools of high-performance engine builders, and porting cylinder heads would be strictly hit or miss without it.

A flow bench consists of a vacuum pump of some sort, a metering element, pressure and temperature measuring instruments like manometers, and various controls. The test piece is attached to the pump and measuring element and air is pumped through the entire 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.

The airflow bench can give a wealth of data about the characteristics of a cylinder head or whatever part is tested. The result of the main interest is bulk flow. It is the volume of air that flows through the port in a given time. Expressed in cubic feet per minute or cubic meters per second/minute.

2. AIM

To create a 3D model of a flow bench, run flow analysis, and obtain a plot of lift vs. mass flow rate. Grid dependence test for three grids is taken at a particular valve lift and a parametric study is made to show the effect of valve lift on mass flow rate.

3. 3D MODEL & PROCEDURE

• Initially, the 3d model is created with 0.08m diameter for base cylinder and 0.02m diameter for the sweep. It is converted into a shell of 0.002m thickness.

• Once the model is created the valve is modeled inside the shell with the following value.

• Once everything is done the model is ready for flow simulation and the lid is added to the open ends.

• In the flow simulation wizard, the preliminary conditions are given and under the boundary conditions a static pressure equal to atmospheric pressure is given to the base and a total pressure of 4 times the atmospheric pressure is given to the lid in the swept model.
• Under goals, the mass flow rate is selected for surface goals.
• First, the grid dependency test was performed to find the accurate grid hence it was performed for the global mesh of sizes 4, 5 &7.
• Under this 5 is selected as it was accurate than 4 and consumes lesser time to calculate than grid 7.
• Then a parametric study is set for different valve points with a grid size of 5 and the simulation is performed.

4. RESULTS

a) Grid Dependency Test

VELOCITY CUT PLOT

GIRD SIZE 4

GIRD SIZE 5

GIRD SIZE 7

As said earlier the grid size of 5 is acceptable for this project and was optimal for my system configuration hence I have proceeded with this grid size for the parametric study.

b) EFFECT OF VALVE LIFT ON MASS FLOW RATE

In this study, a parametric study is created for a valve lift from 0.001m to 0.008 with 7 values in between the given points. The velocity and pressure plots are created after running the simulation.

• For valve lift 0.001m

At this point the pressure at the sweep region is high and velocity is low.

• For valve lift 0.0022m

As the valve moves down the velocity starts to increase and pressure starts to drop at certain regions.

• For valve lift 0.0033m

Pressure starts to drop in many regions.

• For valve lift 0.0045m

velocity starts to change in the lower body.

• For valve lift 0.0056m

Velocity starts changing throughout the lower body.

• For valve lift 0.0068m

The pressure difference is huge in this case when compared to the initial valve lift.

• For valve lift 0.008m

Form the above pressure and velocity plots it is evident that there is a drastic change in the velocity and pressure as the valve position varies.

• FLOW TRAJECTORY

This study shows the mass flow, through the given volume of space at different valve positions.

Valve Lift (m)	0.001	0.002	0.003	0.004	0.005	0.006	0.007
SG Mass Flow Rate 1 [kg/s]	0.043417197	0.094471415	0.131197813	0.152614878	0.159692472	0.160518949	0.160576601

The values in the table are plotted as a graph

5. CONCLUSION

It is evident from the simulation plots that the mass flow rate increases with an increase in valve lift. Initially, the valve is in such a position that it blocks the mass flow from the sweep to the lower boss base. As we change the valve position slightly the block is cleared. Moving the valve further, facilitates the movement of the air or other fluid to enter into the chamber below with minimal restrictions. At the final position or at 0.008m the pressure at the top is greatly reduced and the velocity increase in many regions showing the stable flow of the working fluid or gas. In order to get the results accurately grid dependency test is taken for automatic mesh 4,5 & 7. From the grid dependency test, we were able to find that size 5 has more accurate results than size 4 and produces faster results than size 7.