Modelling and simulation of flow through a flowbench

AIM: To obtain a plot of lift vs mass flow rate of flow through a flow bench.

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, carburetors, 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.

THEORY: An engine makes power by moving air and fuel into and out of it. The more of both it can move, and the faster it can do it, the more power the engine makes. In theory, it’s pretty simple but in reality, it’s more complicated. There are thousands of factors that affect not only how much air, but also the quality of that air, that gets into an engine. The most restrictive, and therefore the most critical factors, are the cylinder head intake and exhaust ports. That’s why so much thought and design must go into a cylinder head for each application. New cylinder heads rated by several measurements but one of the most important to consider is cubic feet per minute (CFM) of air that can flow in both the intake and exhaust ports. The CFM rating should be tailored to the engine’s desired flow rate and power level, which could fill yet another book. A flow bench is a tool that lets you check what that flow is.

Airflow conditions must be measured at two locations, across the test piece, and across the metering element. The pressure difference across the test piece allows the standardization of tests from one to another. The pressure across the metering element allows calculation of the actual flow through the whole system. The pressure across the test piece is typically measured with a U tube manometer while, for increased sensitivity and accuracy, the pressure difference across the metering element is measured with an inclined manometer. One end of each manometer is connected to its respective plenum chamber while the other is open to the atmosphere.

SIMULATION SETUP: 
A basic flow bench model is created with dimensions shown below:

The valve height from the above picture is 0.002m.
Under the Solidworks add-in's tab, the Flow simulation feature is activated.

PRE-PROCESSING
Using the wizard tool flow type and fluid type are selected
1) Flow type: Internal flow
2) Fluid: Air
After selecting the above settings through the wizard tool, the following setup is done before solving:
Mesh grid size: level 3.
Local mesh-size at the valve: refined to level 4.
Boundary conditions:
1) Total Pressure at intake = 101325 Pa
2) Static pressure at exit = 51325 Pa
Goals: 
1) The global goal for calculating mass flow rate.
2) The surface goal for calculating mass flow rate at the exit.

SOLVING
With the above settings, this basic simulation is run to check whether the flow is flowing from intake to exit according to the pressure differences provided.

POST-PROCESSING
After running the basic simulation cut plot of velocity, flow trajectory plot, goal plot are inserted to observe the results of the above simulation. 
A new parametric study is started to perform a grid dependency test so as to select an appropriate mesh size to perform the study for calculating lift vs mass flow rate plot.

For the grid dependency test, global mesh size is selected as an input parameter, and values 3, 4, 5, 6, 7 are given as input for global mesh size so as to perform study for these 5 values. Surface goal plot, cut plot of velocity are given as output parameters for the study. The study is run and values are exported to excel file.

After performing the grid dependency test, the appropriate mesh size is selected from the results. A new parametric study is performed with input parameters as the selected mesh size(selected as value 6, explained in RESULTS) and valve lift dimension. 0m, 0.002m 0.004m, 0.006m, 0.008m, 0.01m are values for the input valve lift parameter so as to perform the study for each of these values. The cut plots of velocity and pressure, flow trajectory plot, surface goal plot are selected as output parameters. The study is run and values are exported to excel file, images of the output parameters calculated are also exported.

RESULT AND INFERENCES:

Results of the grid dependency test:

Mesh size = 3
Velocity plot:

Pressure plot:

Flow trajectory plot:

Mesh size = 4
Velocity plot:

Pressure plot:

Flow trajectory plot:

Mesh size = 5
Velocity plot:

Pressure plot:

Flow trajectory plot:

Mesh size = 6
Velocity plot:

Pressure plot:

Flow trajectory plot:

Mesh size = 7
Velocity plot:

Pressure plot:

Flow trajectory plot:


MESH SIZE VS MASS FLOW RATE:

From the above table, the mass flow rate for mesh size 6 and 7 are almost the same. So, for calculating valve lift vs mass flow rate the mesh size of 6 is selected to reduce the computational time for the study. 

Results of the flow at different valve lifts:

Velocity plot:
Valve lift = 0m


Valve lift = 0.002m


Valve lift = 0.004m


Valve lift = 0.006m


Valve lift = 0.008m


Valve lift = 0.01m

From the above plots, it can be observed that there is an increase in velocity near intake as the valve lift is increased.

Pressure plot:
Valve lift = 0m


Valve lift = 0.002m


Valve lift = 0.004m


Valve lift = 0.006m


Valve lift = 0.008m


Valve lift = 0.01m

From the above plots, it can be observed that there is a decrease in pressure near the valve as the valve lift is increased.

Flow trajectory plot:
Valve lift = 0m



Valve lift = 0.002m



Valve lift = 0.004m



Valve lift = 0.006m



Valve lift = 0.008m



Valve lift = 0.01m



Goal plot:

From the above plots, it can be observed that there is an increase in mass flow rate as the valve lift is increased.

CONCLUSION:
From the above study, it can be concluded that parameters such as pressure, velocity, mass flow rate, are important to understand while designing the flow bench. As the higher velocity rate improves the combustion of the fuel and can produce high power. This simulation helps to understand what happens in the suction stroke of an engine.