Modelling and simulation of flow through a flowbench

FLOW SIMULATION ANALYSIS THROUGH FLOW BENCH

AIM – Run flow simulation analysis of flow bench and obtain plot of lift vs. mass flow rate

OBJECTIVES-

1. Create 3D model of flow bench.
2. Run grid dependency test for three values of automatic initial mesh and choose the best value to run further study.
3. Run a parametric study for different values of valve lift. Obtain outlet mass flow rate and force on valve head.
4. Obtain plot of lift vs. 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.

Pressure is the continuous physical force exerted on or against an object by something (a fluid such as air) in contact with it. Static pressure is the pressure you have if the fluid isn't moving or if you are moving with the fluid. Air would press against you equally in all directions. It decreases with an increase in speed because of conservation law.

Total (or ram) pressure is the pressure a fluid exerts as it is brought to a stop. Total pressure is what acts on you as you face into the wind and the air collides with your body. Dynamic pressure is the pressure of a fluid that results from its motion. It is the difference between the total pressure and static pressure. Pilots rely on instruments that measure dynamic pressure to determine their airspeed.

PROCEDURE-

1. Click on New > Part. Sketch a circle of diameter 0.05 m in Front plane. Exit Sketch.
2. Clink on Extrude Boss/Base and put length 0.1m. Now create guide curve of two lines perpendicular. Give a fillet at corner of 0.03m.
3. Create a Reference plane perpendicular to end of guide curve. Make a circle of diameter 0.025m. Click on Sweep Boss/base.
4. Now click on Shell. Select end faces of inlet pipe and cylinder put thickness 0.002m.
5. Create valve cut section and make a revolved boss/base to get valve. Initially set valve lift value to 0.001m.
6. As computational internal fluid simulation is possible only water tight geometry i.e. in enclosed pipe, we need to click on lids in Flow simulation. Select cross sectional area on both ends to apply lids. Now save the part.
7. Click on Wizard in Flow Simulation. Use SI units. Select flow type internal. Select air as working fluid as water.
8. Now Right Click on Boundary conditions > Insert boundary conditions. Select inlet face and put total pressure p=1013250 Pa
9. Insert one more boundary condition. Put static pressure = 101325 Pa at outlet face of cylinder.
10. Click on Local initial mesh and select surface area of head of valve. Set level of mesh to 5.
11. In Results select Cut plot. Drag it parallel to front plane to desired location.
12. Select Surface goal plot and select mass flow rate for outlet. Again select surface goal to calculate force on valve head.
13. Click on Run. Wait for all iterations to finish.
14. Now start a New Parametric study. In input parameter select level of initial mesh (automatic mesh).
15. Add three design points with level of initial mesh (automatic mesh) as 3, 4 and 5 respectively.
16. Now start a New Parametric study. In input parameter select dimension parameter as valve lift design.
17. For values add range from 0.001m to 0.008 m. Set number of values to 7. Select output parameters as Cut plot and both goal plots.
18. Click on Run. Wait for all iterations to finish.
19. Click on Export button to draw a plot in Excel.

RESULTS:

Grid dependency test:

Design point 1:- Level of initial mesh = 3

Design point 2:- Level of initial mesh = 4

Design point 3:- Level of initial mesh = 5

We can clearly see that we get more uniform and accurate results in Design point 3. So, we use level of initial automatic mesh as 5 for valve lift analysis.

Valve lift analysis:

Design point 1:- Valve lift = 0.001m

Design point 2:- Valve lift = 0.00216666666666667 m

Design point 3:- Valve lift = 0.00333333333333333m

Design point 4:- Valve lift = 0.0045m

Design point 5:- Valve lift = 0.00566666666666667m

Design point 6:- Valve lift = 0.00683333333333333m

Design point 7:- Valve lift = 0.008m

Plot of lift vs. mass flow rate-

EXPLANATIONS AND CONCLUSIONS-

1. From plot we can easily see that mass flow rate increases with increase in valve lift.
2. Pressure drop becomes higher from inlet phase to valve head as valve lift increases.
3. Also, due to high pressure drop the flow velocity increases which will also reduces our pumping cost.
4. Mesh refinement helps to get more accurate result.
5. With flow trajectory we can easily see swirl inside in the cylinder.