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

1. Title – Transient state simulation of flow over a throttle body.

2. Objective –

• To create the model of a throttle body in converge Software.
• To set up the case with proper grid size, material and boundary conditions.
• To solve the case using Cygwin terminal and convert the result for Paraview software.
• To import output files in Paraview and generate required contours and plots.

3. Introduction –

Generally, throttle body is tube containing pivoting valve, which is used to regulate the fluid flow in the body. It is mostly used in engines to regulate flow of air mostly, Some, systems use a throttle body with two smaller throats and butterflies instead of one large one. in older carbureted engines, the throttle body is built into the carburetor and via mechanical means and engine vacuum, more fuel is delivered as the valve opens.

Throttle body, itself is associated with many issues like temperature rise, wear and tear etc. so simulation of throttle in throttle body is becomes important, we can find temperature of throttle, mass flow rate with respect to throttle opening, fluid velocity and pressure. In this simulation we are going to simulate flow over throttle body and will generate pressure and velocity contour, which will better insights about throttle functioning.

4. Procedure –

We performed 2D Transient state simulation for flow over throttle body, for that following procedure was followed -

1. Starting with application type, which is time based, since it is not related to IC engine applications.

Case setup - application type -

2. Air chosen as fluid material and reaction mechanism was enabled.

Material -

3. In run parameters Transient state chosen as solver type, because we wanted to capture dynamic behaviour of throttle, simulation mode was chosen as full hydrodynamic because we want to simulate with effects of fluid also.

Run parameter -

4. In simulation time parameter start time 0s, end time 0.01s, initial time step - 1e-09s, minimum time step – 1e-09s, maximum time step 1s was chosen. End time was decided by flow through time, for that we used following formula-

flow through time = Characteristic length of pipe/ average inlet velocity

flow through time = 2(m)/80(m/s) = 0.025s

flow through time is the time pipe bears flow of fluid one time. so we took 0.01s, it would capture complete flow four time.

Simualtion time parameter -

5. In boundary conditions Elbow wall, inlet, outlet and throttled was defined. Inlet was set with pressure value of 1.5e+05, similarly outlet was set with 1e+05. Elbow wall was fixed with law of wall. Air was fluid so it was also selected in inflow and outflow.

Boundary conditions -

Inlet -

Outlet -

Elbow wall -

6. We wanted to rotate throttle so, in boundary conditions of throttle, wall motion type was – rotating selected with surface movement moving. To rotate throttle, one will require rotating centre and rotating reference point. So, to calculate this, triangle normal was calculated of triangle which is on the top of pin. Measure>direction>triangle normal. For rotating rate file was chosen, which contain rotating conditions, like throttle is at 0degree at beginning and it should get 25degree rotation at 2ms and it will be maintained till and after it, it gets original position.

Throttle -

Rotating rate file -

7. We went with default turbulence model which was Reynolds Averaged Navier Stokes k-epsilon model.

Turbulence model -

8. In grid control fixed embedding was enabled to get finer mesh near defined area. Grid size was set to 0.002m.

Grid size -

9. We wanted finer mesh around throttle, in fixed embedding boundary selected as throttle with mode permanent. Scale was selected as 2 means we got 0.001m mesh near throttle. Embedded layer was set at 2, which added 2 layers to the boundary.

Fixed embedding -

10. Post variable selection allows us to select variables which we want to analyse in post processor. Converge has some variables as defaults, so went unchanged.

11. In output files time interval for writing 3D output files was kept 0.001s, because we wanted 10 output files. Time interval for writing text output was kept 1e-06s, time interval for writing restarting output was kept 0.01s, one should not worry about this parameter because it is useful only when simulation crashes, since our simulation is simple so we took value 0.01s.

Output files -

12. Input files exported in a folder and these solved using Cygwin terminal.

13. Files were converted into converge 3D postprocessing option and postprocessed in Paraview.

5. Results –

Mesh -

Velocity contour –

Pressure contour –

Velocity plot –

Pressure plot-

Mass flow rate –

Cell count –

Animation -

https://drive.google.com/file/d/1UcyWUawocB9EomihLpYeHvCxtp6dd-u-/view?usp=sharing

https://drive.google.com/file/d/13nJ31fJ8wLkQ9LY5DBadfm6Kbr7S7Slp/view?usp=sharing

5. Results –

Pressure and velocity contour has created to visualize high pressure and maximum velocity areas, the contour is also help us to see area around, means how throttle is affecting fluid flow. Besides them, velocity, pressure, mass flow rate and cell count plot also created. Values of these parameters are fluctuating at beginning of simulation but after some cycles these are getting steady values. Fluctuation is due to throttle rotation, at the end values are getting steady, because throttle got initial position. Pressure difference is the only cause of fluid flow here, we got values at outlet(maximum) – velocity -225.3m/s, pressure – 136839pa, mass flow rate -0.066kg/s.

6. Conclusion –

The Transient state simulation of flow over throttle body has performed and this time throttle was rotating. Results are validating theory, like we see velocity contour we can find the effect of throttle body, it is working as an obstacle and in narrower region velocity is maximum and fluid layers adjacent to throttle possess zero velocity, because here fluid particle is colliding with throttle and losing momentum. Fluid slow is decreases after 2ms because throttle rotates and got new position at 25degree and after 8ms throttle was fully opened. Similarly, pressure is low where velocity is high. We can conclude that throttle design, area around throttle affects the results most.