Project : Transient simulation of flow over a throttle body

AIM:

To simulate and study flow around the throttle valve in an elbow rotating with certain configuration.

OBJECTIVE:

1)To setup case for transient flow over throttle body.

2)To simulate the flow and post process in paraview.

INTRODUCTION:

Throttle is a flow control mechanism used for various applications related to flow.Such as IC engine applications HVAC application.The working of throttle is simply by reducing or increasing the flow area to either reduce or increase the amount of flow in relation to pressure.One example of throttle valve is Butterfly valve.

The flow we are simulating in this case is simple construction of following throttle body.

GEOMETRY:

The geometry dimensions are as follows

Lx=0.106314 m

Ly=0.119998 m

Lz=0.0171742

Case Setup:

Boundary Flagging:

Application Type:

Selecting Time Based Simulation With air as predefined mixture.

1)Gas Simulation:Keeping default values

2)Global Transport Properties:Keeping default values

3)Run parameters:

Using Transient pressure based solver

4)Steady state monitor

Turning off steady state monitor.

5)Simulation Time Parameter:

The end time is kept at 0.01 sec by calculating approximate time of flow air takes to reach outlet and then taking sufficient time for valve movement.The main characteristic dimensions of elbow is around 0.1 m so we can approximate the length of pipe may be around 0.2 m.From the plots for velocity of steady state simulation, we can see average velocity from inlet is around 200 m/s.So time to pass air from pipe once it require is 0.001 sec.So taking total time as 10 time of this i.e 0.01 sec.

The minimum time step is kept at 1e-9 sec and maximum at 1 sec

6)Solver parameters:Pressure Based solver

Boundary Conditions:

1)Inlet :

Inflow boundary condition with 150000 Pa of pressure at 300 k with air as intake.

2)Outlet:

Outflow Boundary condition with atm pressure of 100000 Pa if any backflow is there it is of air.

3) Wall:

Stationary Wall.

For turbulent flow LAW OF WALL is to be applied.

4)Throttle

Rotating wall boundary is chosen by taking arc normal as rotation vector and arc centre as rotation for movement of throttle.

New file Throttle_position is used for specifying time vs angle parameter of throttle.

Throttle_position:

Throttle Position Graph with time:

Region and Initialization:

Initial condition :

Create a region inside the geometry consisting air at atm conditions.

Turbulence Modeling:

Keeping it as RNG k-ε model.

Base Grid:

0.002 m for dx dy dz

Fixed Embedding

Boundary Embedding of Permanent Type For Throttle with 2 layer and scaling factor 3.

Output files:

Writing Output files for every 0.001 sec so that we can have 10 post files.

Results:

1.Velocity Contours:

Over Throttle:

2.Pressure Contours:

Over Throttle:

3)Mesh:

4)Stremlines:

5)Mass flow rate

6)Average velocity plot

7)total pressure plot:

8)total cell count:

Conclusions:

1)Total cell count increases as throttle rotates and then reduces as throttle goes back to its original postion.

2)Pressure at outlet of pipe builds up as air flow throgh elbow.

3)The veolcities are higher around throttle.

4)mass flow rate can be controlled according to throttle position.