Week 4.2: Project - Transient simulation of flow over a throttle body

AIM:

To run the simulation for a Transient state case of flow over a throttle body.

OBJECTIVE:

The main objective is to post process the results and show pressure and velocity conours.

To show the Mesh with surface with edges

Show the plots for pressure, velocity mass flow rate and total cell count.

Create an animation such that the throttle movement should be visible.

DESCRIPTION:

A throttle body is essentially a large air valve that sits between the intake manifold and the air intake pipe. An engine has one throttle body, which bolts to the intake manifold's plenum (the large air cavity in the center). A throttle body controls air flow into the engine, which crucial factor is for controlling the engine's air/fuel ratio. Throttle bodies comes in several shapes, sizes and configurations and can perform several tasks outside of their normal air-metering duties.

Throttle bodies usually use 'butterfly valves'. These valves consist of a casing with a large hole in the center, which is filled with a steel plate called as butterfly or throttle plate. The throttle shaft is a rod that passes through the housing and is connected to the throttle cable on the outside and the throttle plate on the inside. When the throttle shaft turns, it rotates the throttle plate, allowing air to go around it and into the engine.

STEPS FOR RUNNING THE SIMULATION:

Opening the .stl model of elbow in the Converge studio as follows

First checking up the diagonosis we see no errors

Creating boundary fence using Boundary>Find/clean as follows

As the geometry has some thickness to it, and we are not interested in heat transfer so we will delete the thickness of the elbow using Traingles by angle selection as follows

Now after deletion

Now if we run the diagnosis we get the open edges error as there are in with yellow edge colour

Using Repair>Patch with open edge selection we select and fill the openings

Assigning the boundaries using flagging

For outlet

Now hiding the part using Traingle any box selection to see the throttle

By using surface pick for throttle

Now looking for normals we see they are pointing inwards which is correct as fuild flow is inside

Now checking the diagnosis we see no errors

Now setting up the Case

As we are doing the Non-reacting simulation we are not concerned with the IC engines so we select the time based

Simulating only for the gas flow so we select materials as Air

Now for run parameters as here valve is moving in transient case

No hydro dynamic because for each and every time step it creates a mesh

As to complete one flow in elbow its taking 0.2/80 = 0.0025 sec so for 4 flows it takes 0.01sec

And solver parameters- pressure based

Now for boundaries

Throttle as its moving we hide the triangles using angle selection and find center of rotation

So by using Measure>Direction>arc normal we take any three vertex and apply we get the result as follows

Arc center : -7.6153236548646E-02 3.9077515348148E-02 2.0174228237257E-02

Arc diameter: 1.9999182604589E-03

Arc normal: 7.9437526563656E-01 6.0742730975362E-01 -2.6651931999326E-05

Using Use file option we give the rotation degrees

For elbow wall

For inlet with inflow with 1.5bar pressure and with Air flow

For outlet, outflow with static pressure 1bar

Now assigning the region

Turbulence model we go with RNG k-epsilon

And we use 2mm base grid

Fixed embedding

Output files

Then running the case set-up after exporting the input files to the folder using Cygwin.

By using the application mpiexec.exe & converge.exe by command line 'mpiexec.exe -n 2 converge.exe restricted' we run the simulation till results are converged.

Then using converge and paraview post processing results are observed and studied.

RESULTS:

The Mesh looks as follows with grid embedding

The Mass flow rate plots are

The velocity contours are

At 1milli second

At 2milli second

At 5milli second

At 8 milli second

At 10 milli second

The Velocity streamline is

At 1 ms

At 2 ms

At 5 ms

At 8 ms

At 10ms

The Velocity plots are

The Pressure contours are

At 1milli second

At 2 milli second

At 5 milli second

At 8 milli second

At 10 milli second

The pressure plots are

The static pressure plots are

Total cell count plot is

Animation for velocity is

Animation for pressure is

CONCLUSION:

As the throttle rotates there is an obstruction in the flow of fluid and hence its velocity and hence kinetic energy of the fluid is converted into pressure energy therefore total pressure increases.

Due to rotation of the throttle plate, the wake region is formed on the plate causing decceleration of flow which leads to separation of flow hence a decrease in static pressure at the outlet is seen.

Rotation of throttle plate is causing obstruction to the fluid flow which increases the pressure gradient (pressure force in the direction of the flow) forced fluid hence the velocity of fluid flow increases and therefore the mass flow rate at the outlet increases.

From the contour plots of velocity and pressure it is observed that the movement of the throttle impacts the velocity and pressure in the region near the throttle valve.Also, the movement of the throttle has an impact on the cell count untill 2ms.