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

Aim: - To run a steady state simulation for flow over throttle body.

Objective: -

1. To setup a case for steady state simulation for flow over throttle body model in Converge CFD.
2. To post process the result and plot velocity and pressure contours along with mass flow rate variations.

Introduction: -

Throttle – It is mechanism by which fluid flow is managed by constriction or obstruction. informally, it refers to any mechanism by which the power or speed of an engine is regulated, by increased or decreased by the restriction of inlet gases. The method of restriction is usually butterfly valve for internal combustion engines.

Throttle Body – It is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main.

Throttle Body

Model Geometry:

The model outer layer triangles are deleted which resembles thickness as no CHT (Conjugate Heat transfer) analysis is done and only fluid volume is used.

The steady state simulation is done when the valve is fully opened positions as maximum mass-flow-rate is concern for max energy input.

Case Setup: -

1. Time Based application type.
2. Gas simulation with Air as predefined mixture

3. Pressure Based Steady State Solver is used with Compressible Gas Flow solver and PISO Navier-Stokes’s solver scheme.
4. The solution run for 15000 cycles with minimum time step of 1e-9 s and maximum up to 1 sec.

5. Boundary Condition:
   1. Inlet - Type = Inflow, Pressure = 1.5e5 Pa, Species = O2:0.23, N2: 0.77
   2. Outlet - Type = outflow, Pressure = 1e5 Pa, Species = O2:0.23, N2: 0.77
   3. Elbow – Type = wall, No slip Condition
   4. Throttle - Type = wall, No slip Condition

6. Volumetric Region are initialized with mass fraction of O2: 0.23 and N2: 0.77. The boundaries are assigned their region type.

7. An Average Velocity and Mass-flow-rate monitor is set to monitor velocity and mass flow rate during simulation.

8. RNG K-epsilon is used for turbulence modelling with recommended values.

9. Base grids of 2e-3 m are generated for all axis. Fixed embedding is also added to top and Bottom wall to get better results.

10. 3D output data is written after every 50 cycles.

11. The input files are exported to a folder to further solving.

Solving using Cygwin:

An executable “mpiexec.exe” is placed with the exported folder. The Cygwin directory is navigated to the above saved folder and following code is entered to solve the problem.

"mpiexec.exe -n 2 "C:\Program Files\Convergent_Science\CONVERGE\3.0.16\bin\intelmpi\converge.exe" restricted </dev/null> logfile &"

where address in quotes gives the path of folder containing input file exported earlier.

Post-Processing:

Post-Processing is done with the help of Converge CFD post processing tab –

with these the output 3D data is converted in ‘.vtm’ file and contours and animations are prepared though ParaView.

Results: -

Mesh -

Average Veocity - Average Density -

Mass-flow-rate

Velocity Contour - Pressure Contour -

Velocity profile at mid plane slice -

Velocity and Pressure Distribution across Butterfly

Conclusion: -

• The steady state simulation is done for flow over throttle body with 0.5 atm pressure difference across the model.
• The velocity at inlet is 16.14 m/sec as pressure is higher while velocity at outlet is around 199.12 m/s as pressure decreases at outlet.