Project : Transient simulation of flow over a throttle body

2D – Steady state simulation through an elbow which has a variable throttle plate using converge cfd

AIM:- the aim is to focus on simulating a elbow body having rotating throttle plate at the mid of the elbow, and analysing the pressure and velocity variation at various sections using Paraview, here the body is first modelled in solidworks , then exported in converge studio in stl file format, then setting up the case setup, running the simulation in Cygwin, and finally post processing it.

Geometry preparation and boundary condition:-

the geometry is initially modelled in solidworks and then exported in converge studio in the form of an stl file format, here we first change the scale of the geometry from millimeter to metre by scalling it with a factor of 0.001, then we check for any errors in the geometry , using the diagnosis to check for the below mentioned errors

Then we setup the boundary condition

here we set the boundaries for according to the various faces of the geometry

Then we look for the direction of the normals , they should be in the direction of the flow,before this we see that the geometry has a thickness , we first delete the thickness , delete the top surface of the body , after this we repair the open edges, then cover the inlet and outlet edges of the geometry.

The final image of the geometry after all the above steps looks like

Governing equation:-

The solution for CFD simulation is obtained by solving the Navier-Stokes (NS) equations. The equations comprise of 5 equations, namely the continuity, momentum (3 equations), and energy equations. The continuity and momentum equations are solved for all flow problems with the energy equation are optional and can be used only when heat transfer is taking place to save computation time.

Here we assume that there is no heat transfer and that the temperature is constant, leaving us with 4 equations now, the continuity, and 3 momentum equations, one for each axis direction

Case setup:-

• We first go in the application type and select the time based general flow application
• Then in the material we select air as our running material, and seletc on gas simulation due to air being the running fluid.
• In the global transport parameters the values of prandtl and schmidt numbers are kept default.
• Then in the simulation parameter, we go the run parameter , select transient state , full hydrodynamic simulation, and uncheck for the steady state monitor, and uncheck the shared memory box
• Then we go to the boundary conditions and provide inlet, outlet boundary condition, and wall boundary to the elbow wall and throttle plate,now we choose a normal to give the throttle a rotation about an axis, and choose a file in the throttle boundary and rotate it at 25 deg for the first 0.002 sec now to define the regions in the boundary go to the regions and initializations and set up a region 0, with air as a species., and then provide the region to all the boundaries.
• In the grid control we select the base grid as 0.002, and avail an option of fixed embeding to the throttle, this will make the mesh size along the throttle smaller than the mesh size in all the geometry, so that we get atleast 1 square mesh at the throttle boundary , which will help us to analyse the results in the later stage in a better way.
• Then we go to post processing and output files , and input the values according to the time interval for righting the 3D output and and restarting the output files.
• Now all the files are exported to the folder and the simulation is ran using Cygwin.

In the above pic the rotation centre and rotation about is selected

Post processing using paraview:-

Now here we open the file in paraview

Mesh

Here we can see how the mesh are formed near the throttle boundary, so as to have a smooth simulation.

Enlarged image of mesh near the throttle

Velocity contour at different sections

1. at the input of the elbow

At the start the velocity increase is smooth but at the mid range according to the color scale of the velocity magnitude

ii. at the section near the throttle

Here as we see the velocity is too fluctuating due to the curved shape of the body and rotation of the body and the obstruction of the throttle plate

iii.just below the throttle plate

iii. at the end of the elbow

Herealso the variation is sudden rise and down fall

Pressure variation at different sections

1. at the start of the elbow

Here at the start the pressure increase is maximum

1. pressure variation before the throttle

here just before the throttle we can see that the pressure increase above the throttle

iii. pressure variation at the end of the elbow

Here the pressure first increases and then decreases

Mass flow rate v/s cycles

Here we can see that the mass flow rate is flucatuating for the start of 0.002 seconds for which we have provided the rotation to the throttle

Total cell count

Here we can see that the total cell count is about 40,000 cells in total , due to the fixed embeding region created across the throttle

Velocity variation animation

velocity variation at the throttle plate

velocity variation for the elbow with rotating throttle

conclusion

here we can conclude that in the elbow body the cell count reaaches to 40000 due to fixed embeding at the throttle plate, so finer the mesh the better the results can be analysed. the velocity gradually increases in the elbow section of the body, at the throttle plate as the flow strickes the plate the pressure decreases and so the velocity reduces drastically and also at the portion above the throttle plate as the area is very small the velocity increases so we see the red color according to the color regime, for the pressure it increases at the start of the elbow and keeps on decreasing as the flow advances and reaches a low pressure at the throttle plate.since the throttle rotated for the first 25degs it closes the opening slightly which result the flow stop suddenly due to ehich the velocity increases.