Week 3: Flow over a backward facing step

 PROCEDURE:

CREATING GEOMETRY:

* go into the create > vertex create the points as per the dimension neede and after that go into the traingles connect them using the options from vertex onces the 2d is drawn copy it or ofset it in z-direction.

check the normals and run the diagonis and make sure everything is clear and green tickmark.

Click on being case set up select application type time based.

selection of material:

check on gas simulation species , uncheck reaction simulation

solving parameters:

select steady state solver , full hydronomic and compressible flow.

in misc uncheck used share memory and check monitor steady state

in simulation time parameter privides balues.

select scheme pisco solver.

assignaning the boundary condition:

inflow boundary:

outflow boundary:

 top and bottom:

boundary type:WALL

wall motion: Stationary no slip.

front and back:

Boundary type :2D

Meshing generation:

• dx = dy = dz =2e-3m
• dx = dy = dz =1.5e-3m
• dx = dy = dz =1.2e-3m

RESULT:

Mesh size: 2e-3

velocity contour:

pressure contour:

vector plot:

avgerage velocity:

mass flow rate:

total pressure:

total cell count:

MESH SIZE: 1.5e-3m

velocity:

pressure contour:

vector plot:

total cell count:

mass flow rate:

total pressure:

average velocity:

MESH SIZE: 1.2e-3m

velocity contour:

pressure contour:

vector plot:

total cell:

total pressure:

mass flow rate:

avg velocity:

animation link:

https://youtu.be/csw3LsfRnWY

* Why flow sepration occur:

When fluid passes through body because of higher momentum in starting its find favourable pressure which causes fluid to flow in upstream but while flowing its countinues lossing its momentum transfer due to viscosity of fluid and induced shear stress when momentum transfer is not capable to overcome friction force due to shear stress at that point velocity and presssure gradient can be seen as zero point at which flow septares and as flow further move in upward direction because of positive pressure gradient due to that adverse pressure difference fluid start back and produces vortex.

CONCLUSION:

*Flow through backward face successfully simulated for coarse and fine mesh as above shown in fig

*as the grid size decreases cell count is increases and hence result become more accurate which can be shown from vector plot.

*while simulation to avoid fluctuation max.c.f.l convection limit choose as 10 (as per simulation)

*flow sepration is phenomena because of adverse pressure gradient at point as mentioned above.