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

Aim:

Set up and run the steady state simulation for flow over throttle body.

Post process the results and show pressure and velocity contours.

Show the mesh (i.e surface with edges)

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

Introduction:

The throttle body is an important part of the air intake system that controls the air flowing into the engine. It’s located between air intake and engine manifold where fresh air is pulled into the engine for the combustion process. The amount of air allowed into the engine during this process controlled by the butterfly valve. The butterfly valve is a pivoting flat valve controlled by the gas pedal via cable or wire if controlled electronically. When pressing the peddle, the throttle body opens to allow more air flow into the manifold. The computer inside the vehicle works with sensors to ensure that the engine receives the perfect balance of fuel and air.

Filth, carbon, and dirt can build up in the housing creating problems with air flow. Known as coking, the normally smooth service for air to travel becomes full of gunk and creates an imbalance. This interrupts that perfect mixture of air and fuel which can cause the butterfly valve to get stuck. A stuck valve can cause surging or even stalling. This is why it’s important to have a good air filter for the vehicle. A fresh filter helps prevent dirt buildup on the surface of the butterfly valve. Poor idling or stalling when coming to a stop is another sign that may have an issue with the throttle body.

Modelling the problem in Converge Software

The 3D model is imported in the software.

Each of the face is given a boundary name and allotted an ID.

The throttle is placed inside the elbow body

After this normal orientation is checked and then changed to the normal pointing inward to the body.

Since this is a steady state problem,the procedure to setup it is shown in the steps below.

In the materials tab "Air" is selected and species tab is checked.

In the gas simulation tab,default setting are set

In the global transport parameters,defaults are kept to be same.

Oxygen and Nitrogen species are added in the species tab.

In the Run parameters tab,steady state solver is selected along with simulation mode to be in full hydrodynamic and solver used to be compressible.

Also in the misc tab,steady state monitor is tuned on for the convergence of results and shared memory tab is made off.

Average velocity monitor variables is selected.

The minimum number of cycles to be executed for steady state solver are set at 10000.

monitor start delay and sample size are set at 200 and 1000 respectively,as shown below.

In the time parameters tab,end time is set to be at 15000 cycles and initial ,minimum time steps to be 1e-09 and maximum time step is set at 1s.

PISO scheme is selected for solving the navier strokes equation and other values are set to be at the default.

In these parameters,pressure term's precondition is set to be none

For the turbulence modelling RNGk-ε">RNGk−εdZ/dt=F(Z,t,a)model is chosen with default values.

For initialization,a zone of different gases with unity summation of mass fraction and arbitary values is set.

Further the type of boundary and zone is set to all .Throttle is kept to be a non moving fixed wall.While the inlet and outlet pressure are kept at 150000pa and 100000pa respectively.

Grid sizing:

3 different size of grid are selected which are.

Mesh no. dx dy dz

1. 0.01 0.01 0.01

2. 0.006 0.006 0.006

3. 0.003 0.003 0.003

Along with this grid size ,fixed enbracing is set at the Throttle wall with the scale factor of 3 and ebedded layers to be 2, to make the mesh more finer in the area.

Mesh 1-

Mesh 2-

Mesh 3-

For getting the output values the required entities are selected.

Number of cycles for 3d output data is set to be 100 cycles.

Finally the data files are exported which are solved by using the solver.

The input files are solved by using the cygwin.

Output:

Mesh 1

Mass flow Rate plot at inlet and outlet.

Average velocity plot at inet and outlet.

Total pressure plot at inlet and outlet-

Total number of cells plot-

Streamlines-

Velocity variation-

Pressure variation-

Mesh 2

Mass flow Rate plot at inlet and outlet-

Average velocity plot at inlet and outlet-

Total pressure plot at inlet and outlet-

Total number of cells plot-

Streamlines-

Velocity Variation-

Pressure variation-

Mesh 3

Mesh flow Rate plot at inlet and outlet-

Average velocity plot at inlet and outlet-

Total pressure plot at inlet and outlet=

Total Number of cells plot-

Streamlines-

Velocity Variation-

Pressure variation-

Conclusions:

1. As the mesh size is reduced the variation in the velocity is captured very accurately near the throttle body.
2. The used turbulence model is accurate in predicting this problem.
3. Due to the introduction of fixed embedding, flow behaviour is accurately achieved near the boundary.
4. Stagnation point point is created in the localised area.