Week 4.1: Project - Steady state simulation of flow over a throttle body

AIM:

Steady state simulation of flow over a throttle body.

OBJECTIVE:

• To set up and run the steady state simulation for flow over the throttle body.
• To plot pressure contour and velocity contour.
• To show the mesh, plots for pressure, velocity, mass flow rate and total cell count.
• To create an animation in which throttle movement should be visible.

THEORY:

The throttle valve is used in ic engines, is a circular disc placed near to the intake manifold which controls the mass flow rate of air fuel mixture entering the combustion chamber. Depending on the vacuum inside the intake manifold and throttle position, the flow rate keeps changing. When the valve is open, the air fuel mixture is sucked into the cylinder.

GEOMETRY SETUP:

• IMPORT GEOMETRY:

Geometry is imported to the workspace from the stl file given.

• SCALING THE GEOMETRY:

Converge uses dimensions in meters the scale is too large. So, need to scale down.

The geometry is scaled down by going to transform > scale and apply a scaling factor.

• DELETING THICKNESS:

As the flow is simulated inside the elbow so the thickness is not needed.

So, the outer layer of elbow is deleted by selecting the cursor pick option by angle and press D.

• CLOSING OPEN EDGE:

By going to patch under repair section and the open edges are selected and click apply. The open edges will be patched.

• CREATING BOUNDARIES:

The boundary are created for the geometry under boundary flag tab.

The boundaries are assigned to the faces and the name of the boundaries are edited and click apply.

• NORMAL ORIENTATION:

The orientation of normal are checked and its changed such that the normal points inwards by going to transform > normal

• DIAGNOSIS:

The diagnosis is runed and checked for problems for the geometry.

BEGIN CASE SETUP:

• APPLICATION TYPE:

On the right panel go to the case setup tab, select begin case setup.

Select the application type as time-based and select apply and done.

• MATERIALS:

Select materials and select the checkbox reaction mechanism then select the predefined mixture as air then click apply and done.

• GAS SIMULATION:

The default values are selected and press ok.

• GLOBAL TRANSPORT PROPERTIES:

Select global transport properties, keep the default values and press ok.

• RUN PARAMETERS:

Under solver tab select solver as steady-state solver

Under misc. tab enable steady-state monitor and disable the used shared memory.

• MISC TAB:

Under misc tab checking the steady-state monitor option and disabling use shared memory option and click ok.

• SIMULATION TIME PARAMETERS:

Set the start time, end time, initial, minimum and maximum time steps as shown above.

• SOLVER PARAMETERS:

Select the Navier-stokes solver type as pressure based and click ok.

• REGIONS AND INITIALIZATIONS:

The regions are created and air is added as species and mass fractions are changed to O2 as 0.23 and N2 as 0.77.

• BOUNDARY CONDITIONS:
• INLET:

For inlet, set the pressure boundary condition as specified value of 1.5e5 pa and select air for species boundary conditions.

OUTLET:

Set the outlet pressure boundary conditions as specified value of 100000 pa and for species backflow select air.

ELBOW WALL:

Select the elbow wall boundary as wall type with law of wall boundary conditions. And the temperature as law of wall of 300k.

THROTTLE:

The boundary type is wall and the boundary conditions are set to law of wall.

• STEADY STATE MONITOR:

The monitor variables are added and the minimum number of cycles, monitor start delay and sample sizes are defined.

• PHYSICAL MODEL:

The default values are selected and click ok.

• BASE GRID:

The base grid size of 0.02 m is defined and press ok.

• FIXED EMBEDDING:

As we need finer mesh near the throttle it can be achieved by using fixed embedding. The scale parameters determine the final size of element as dx/s^n and layers determine the number of layers of fine mesh along the boundary.

• POST VARIABLE SELECTION:

Keep the default values in typical variables tab.

• OUTPUT FILES:

The interval for writing 3d output data files and restarting outputs are defined.

• Exporting the input files to a folder
• Then the executable is pasted inside the folder
• The simulation is run in Cygwin.
• The postconvert executable is pasted in the output folder.
• The post conversion is done on Cygwin and converted into the type that paraview reads.
• The results are then post processed using paraview.

RESULTS:

MESH:

The fixed embedding creates finer mesh near the throttle.

VELOCITY CONTOUR:

From the above plot we can say that velocity is high near the gap between the throttle and the elbow wall due to reduced flow area at this section. The maximum velocity is 340m/s.

PRESSURE CONTOUR:

From the above plot, the side of the valve which faces the flow experiences high pressure and the less pressure is between throttle and elbow wall.

GLYPH:

This plot shows the velocity vector and the direction of flow.

STREAMLINE (VELOCITY):

This plot shows the streamline flow of velocity.

VELOCITY PROFILE:

INLET:

The velocity varies continuosly and achieves steady state after some number of cycles.

OUTLET:

From this plot, the velocity increases and then reaches steady state after some number of cycles..

PRESSURE PROFILE:

INLET:

The pressure at inlet is constant throughout the end of simulation.

OUTLET:

From this plot, we infer that pressure increases and then reaches the steady state.

CELL COUNT:

Number of cell count is 11019.

MASS FLOW RATE:

AT INLET:

AT OUTLET:

Mass flow rate at inlet and outlet are equal and the value is 0.0657kg/s. The mass flow rate reaches the steady state after some cycles.

ANIMATION OF CONTOUR PLOTS:

https://drive.google.com/file/d/15eqd4v7R7204PM-yDgS8fQIqh8khsNb2/view?usp=sharing

https://drive.google.com/file/d/1h1mgW_XcGQ_KqkSzs4bYjDk7nr3oBqIu/view?usp=sharing

https://drive.google.com/file/d/1lOsLiAjJlh6hX7D2_S9tL_eKlFjDKGQr/view?usp=sharing

The animation shows how the velocity changes with respect to time.

CONCLUSION:

The steady state simulation of throttle is performed and the results are obtained by using converge CFD.