Modelling and simulation of flow through a flowbench
AIM -
Modelling and simulation of flow over a flowbench using Solidwork.
OBJECTIVE -
Obtaining a plot of lift vs mass flow rate.
Grid dependence test
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, 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, 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.
Typical Flow Bench schematic
DESIGN SETUP -
Above 3D model is of flowbench with the lift . This model is basically made through using sketch tool, Extrude tool , Circular sweep , Revolve. on the right side figure we see the cut section of flowbench and how the lift is constructed. The step end of lift is 8mm from the cylinder surface and this will help us to look the flow at different lift movement.
The dimension for cylinder is 50mm and it is extruded to 100mm length. A profile is created above the cylinder for inlet and at last the lift is constructed through the revolve command.
SIMULATION SETUP -
Analysis flow type - Internal
Type of flow - Air (Gases)
Boundary condition - velocity and total pressure
Goals - Surface mass flow rate
Meshing - Basic Mesh with 3 level mesh refinement.
Above figure shows the basic mesh .
After the mesh generation we build the new parametric study to learn the movement of lift and through this lift we actually see the flow of velocity in the cylinder. So, now we have seven different lift cases i.e., 1mm, 2mm, 3mm, 4mm, 5mm, 6mm and 7mm.
CASE 1 - Lift at 1mm
Velocity when lift is at 1mm
CASE 2 - Lift at 2mm
Velocity when lift is at 2mm
CASE 3 - Lift at 3mm
Velocity when lift is at 3mm
Here we see the lift at 3mm position moves inward and flow starts to spread.
CASE 4 - Lift at 4mm
Velocity when lift is at 4mm
As we saw in above case the flow was little but at 4mm inward the flow starts to spread violently.
CASE 5 - Lift at 5mm
Velocity when lift is at 5mm
As the lift moves inward the flow goes on increasing.
CASE 6 - Lift at 6mm
Velocity when lift is at 6mm
As the lift moves inward the flow goes on increasing.
CASE 7 - Lift at 7mm
Velocity when lift is at 7mm
So, finally when the lift opens totally we see the maximum amount of flow in the cylinder.
Effect of valve lift on mass flow rate -
import math
import matplotlib.pyplot as plt
# Plotting the plot for mass flow rate and lift
Lift = ([0.001],[0.002166667],[0.003333333],[0.0045],[0.005666667],[0.006833333],[0.008])
Mass_flow_rate = ([1.22921E-09],[9.40177E-10],[3.81588E-05],[0.000211809],[0.000249161],[0.000302733],[0.000302624])
plt.plot(Lift,Mass_flow_rate)
plt.xlabel('Lift')
plt.ylabel('Mass_flow_rate')
plt.show()
Above is the python programme to show the plot of effect of valve lift on mass flow rate.
Here we can see that as as the movement of lift goes on increasing the mass flow rate also increases gradually.
Grid Dependence Test - Grid convergence is the term used to describe the improvement of results by using successively smaller cell sizes for the calculations. A calculation should approach the correct answer as the mesh becomes finer, hence the term grid convergence.
So, we have to test the grid dependence and for that we had kept the valve lift at end position . Basically the mesh level of refinement for this test is kept at 2 , 3 , 4 . Here we will look at three grid cases along with velocity plot , pressure plot and flow trajectory.
Grid Dependence at 2 -
Velocity plot -
The velocity plot shows us the level of refinement at section near the lift as we see the mesh element are smaller then other section mesh element .
Pressure plot -
Grid Dependence at 3 -
Velocity plot -
Above velocity plot shows us the more finer mesh than the velocity plot at grid 2. We can the mesh element size smaller. this small mesh element helps the flow to move smoothly and we get better convergence results.
Pressure plot -
Flow trajectory -
Grid Dependence at 4 -
Velocity plot -
This is the best refinement of mesh and we can get more perfect results.
Pressure plot -
Flow trajectory -
CONCLUSION -
As more the valve lift the more is the flow inside cylinder.
The mass flow rate increase with the increase in lift movement and at last lift it get neutral(constant).
Higher the mesh refinement gets the best results for simulation and for this reason the level of refinement was selected as 4 .