Modelling and simulation of flow through a flowbench
AIM:
To model a flow bench valve, carry out grid dependence test and then, perform parametric study with the variation of the valve lift and check its impact on the mass flow rate at the outlet.
INTRODUCTION:
In this simulation, we will first model the setup with a valve in such a way that, we can change the valve lift by changing a single dimention. With this, we run a baseline simulation to have a look at the results. Then, we run grid dependence test on the entire simulation by changing the refinement of the grid for each case and then, chose the level of mesh refinement that best suits our case, and which gives the best results.
After the grid dependence test, we have selected the grid refinement for our simulation. Now, we run a parametric study for the simulation by changing the valve lift with that level of mesh refinement. While performing the parametric study, we add surface goals as the mass flow rate through the outlet to compare the dependence of the mass flow rate with the valve lift.
THEORY:
Grid dependence test and mesh refinement test are synonyms. They are a mean to find the appropriate mest quality for our simulation, where the same simulation is run with increasing mesh refinement till a point where the results dont change much even after increasing the refinement. The qualifty of mesh refinement greatly affects the end results of our simulation so, its very important to choose the right level of refinement for our simulation. Higher the level of mesh refinement, more accurate are the results but with extremely high refinement, the simulation time significantly increases. Hence, similar rersults can be obtained even with a slightly lowe level of refinement. So, choosing the appropriate level is important as it can help us to achieve more accurate results and also redue the simulation calculation time.
Flow through flowbench simulates the flow across a valve system and it helps us to visualize the flow and then change the parameters of the valve according to our needs and model the valve system for our requirements.
MODELLING AND SIMULATION:
The entire setup was modelled with the of simple extrusion, revolve boss and sweep boss and then, revolve boss was used on a front plane sketch to create the valve. And finally, the shell feature was used to make the setup hollow.
The valve lift can always be changed by simply changing the dimentions of the base sketch.
After modelling the setup, the baseline simulation was carried out with the help of a new flow wizard with water as flowing element, units as SI, and flow type as internal. Then, boundary conditions we added with inlet total pressure as 200000 pa and outlet static pressure as 101325 pa. And finally , with these parameters, the baseline simulation was run and the following results were obtained:
pressure cut plot:
velocity cut plot:
flow trajectory:
mass flow rate:
Now, the same simulation was carried out with different levels of cell refinements and the following results were obtained:
for mesh level-3:
velocity:
pressure:
for mesh level-4:
velocity:
pressure:
for mesh level-5:
velocity:
pressure:
flow rate variation:
By conducting the above grid test, we observe that by increasing the level of mesh, the results obtained significantly vary. With increase in the refinement, the mass flow rate keeps converging at a more accurate value. But with increase in the cell refinement, the calculation time also greatly increases since there are more cells to work on. So, we chose the refinement level as 5 for the rest of our study as it seems to produce more accurate results.
RESULTS:
case-1(valve lift=0.001m):
velocity cutplot:
pressure cutplot:
flow trajectory:
case-2(valve lift=0.00275m):
velocity cutplot:
pressure cutplot:
flow trajectory:
case-3(valve lift=0.0045m):
velocity cutplot:
pressure cutplot:
flow trajectory:
case-4(valve lift=0.00625m):
velocity cutplot:
pressure cutplot:
flow trajectory:
case-5(valve lift=0.008m):
velocity cutplot:
pressure cutplot:
flow trajectory:
OBSERVATIONS AND CONCLUSION:
mass flow rate variation:
From this plot, we get the relation between the valve lift and the mass flow rate. The mass flow rate drastically increases with the increase in the valve lift which is natural, as the opening increases with the increase of the valve lift and we can control the vale lift to get the desired mass flow rate at the outlet.
The grid dependence test can be very useful to save us from getting errored results, as it helps us to define the right mesh for our simulation as well as saves us a lot of time by defining the correct mesh level by not using the highest mesh level possible.