Simulating 2D Channel Flow using Converge CFD with different mesh sizes

Objective

Setting up 2D channel flow using converge CFD. Here we are using different mesh sizes to observe the variations of different attributes such as mass flow rate,Pressure,velocity and total cells generated .here we are using mesh sizes of

dx=dy=dz=2e-4

dx=dy=dz=1.5e-4

dx=dy=dz=1.0e-4

Steps involved in running Channel flow simulation

1)Geomentry Creation

2)Boundary flagging

3)Diagnosing the geomentry

4)Case Setup

5)Solve

5)Post processing the results

Geomentry

Here a rectangular geomentry with 0.1m x 0.01m x 0.01m is created to perform a analysis and then boundary flagging and Diagnosing the geomenty to check any intersections or any anomoly related to geomentry check is done then lastly checkinh the nornals directions whether inward or outward as the flow taking place inside the domains normals need to point inside.then case setup begins.

Case Setup

=>In case setup we select General flow and then we leave the input parameters under material are kept default the only thing we choose air as our fluid.

=>Going to simulation parameter we are going to choose steady state(Pressure-Based) and hydrosimulation(The main difference between Hydro and non-hydro is that no navier stokes equtions are solved in non-hydro it is only used to check our mesh changes while running simulation).then rest of then are set to default. Under Simulation time parameter cycles to run the simulation is set to 15000 with Initial and minimum time step of 1e-9 and maximum time step to 1 and rest are set to defaults

=>Coming to boundary there are 5 boundaries are flagged with different Boundary ID, thhey are

Inlet:Set to inflow Here are we are specifying pressure of 100001

Outlet:Set to outflow Specifying Pressure as 100000

Front wall and Back wall: Set to 2D because here we are running 2D simulation

top & bottom wall:Set to walls

All the boundaries are set to region0 with air at 100000 pa and 300K

=>Region 0 is created at initial condition and events.Here were are not performing turbulance simulation so we can turn off turbulance we are only concentrating on Laminar flow.

=>Mesh is created with base grid .Then postprossesing output files are set to defaults because the data which we are looking is already in default selections

Then we need to export the input files to a folder to start running a simulation.then by using CYgwin we are directing to the input file and simulation is stared by using an executable file and simulation is runned by using a single processor. After successfully running the simuylation we can post process the reults and look for the attributes variation with the mesh

Case I=>2e-4

Mesh

The mesh is generated with base mesh of 2e-4 along x,y and z axis with fixed embedding of scale 1 to layers 2

Velocity Contour

As we used fixed emmbedding at the top and bottom walls we can see the changes at walls more accurately at the walls the velocity is 0.067m/sec ~0 we can say nearly zero because of boundary effects or simply by newtons laws of viscosity we can interpret and at the center the velocity is high 1.3m/sec because there are no boundary effects

Pressure Contour

This contour helps us to understand the pressure expansion inside the fluid domain

Velocity Plot

If a simulation is ran for channel flow by the velocity plot we can eaily say whether the solution is right or wrong because this is the correct velocity profile for a channel floe if we plot along dy vs velocity we can see a parabolic curve and velocity at starting and ending points of dy will be almost 0

Pressure Plot

Mass flow rate at Inlet and outlet Plot

By looking at this plot we can come to a conclusion that solution has converged around 8000 cycles. so we can stop at 8000

Case II=>1.5e-4

Mesh

The mesh is generated with base mesh of 1.5e-4 along x,y and z axis with fixed embedding of scale 1 to layers 2

Velocity Contour

As we used fixed emmbedding at the top and bottom walls we can see the changes at walls more accurately at the walls the velocity is 0.0076m/sec ~0 we can say nearly zero because of boundary effects or simply by newtons laws of viscosity we can interpret and at the center the velocity is high 0.6 m/sec because there are no boundary effects.Here the solution didnt stabilize due to that we need to run simulation for extra cycles untill simulation reaches stable

Pressure Plot

This contour helps us to understand the pressure expansion inside the fluid domain

Velocity Plot

If a simulation is ran for channel flow by the velocity plot we can eaily say whether the solution is right or wrong because this is the correct velocity profile for a channel floe if we plot along dy vs velocity we can see a parabolic curve and velocity at starting and ending points of dy will be almost 0

Pressure Plot

Mass flow rate at Inlet and outlet Plot

By looking at this plot we can come to a conclusion that solution has converged around 8000 cycles. so we can stop at 8000

Totol Cells plot

Case III=>1e-4

Mesh

The mesh is generated with base mesh of 2e-4 along x,y and z axis with fixed embedding of scale 1 to layers 2

Velocity Contour

As we used fixed emmbedding at the top and bottom walls we can see the changes at walls more accurately at the walls the velocity is 0.027m/sec ~0 we can say nearly zero because of boundary effects or simply by newtons laws of viscosity we can interpret and at the center the velocity is high 1 m/sec because there are no boundary effects

Pressure Contour

This contour helps us to understand the pressure expansion inside the fluid domain

Velocity Plot

If a simulation is ran for channel flow by the velocity plot we can eaily say whether the solution is right or wrong because this is the correct velocity profile for a channel floe if we plot along dy vs velocity we can see a parabolic curve and velocity at starting and ending points of dy will be almost 0

Pressure Plot

Mass flow rate at Inlet and outlet Plot

By looking at this plot we can come to a conclusion that solution has converged around 8000 cycles. so we can stop at 8000

Conclusion:

Meshing is very important step while setting up any case if mesh is not fine or any problem relate to mesh divergence occurs and solution will blow up. So from this simulation we can find that contours are getting soother with respect to mesh sizes and plots are getting smoother too.The time taken for the siulation also increases tremendously if the mesh is soo fine because fine mesh produces more cells.More cells means more time is required to calculate the extra cells.