SIMULATION OF TRANSIENT FLOW THROUGH A BUTTERFLY THROTTLE VALVE THROUGH 25 DEGREE ROTATION

OBJECTIVE

To simulate flow through throttle body through 25 degree rotation of the throttle plate w.r.t. time.

TIME STEP CALCULATION

Bounding box is activated.

l_x = 0.106; l_y = 0.119.

Characteristic length of the elbow = l = 0.2 m.

Average inlet velocity from the steady state = V = 190 m/s/

t = l/V = 0.2/190 = 1.05e-3 s.

For 10 cycles of fluid flow, the simulation time would be 0.01 s.

SIMULATION GEOMETRY

Same geometry is used as the steady state simulation.

SIMULA/TION SETUP

• Inlet, Outlet and Elbow_Wall and Throttle are assigned.
• Fluid for the current simulation is air.
• Inlet Conditions:

1. 1. Pressure: 1.5 bar
   2. Temperature: 300K
   3. Velocity: zero Gradient

• Outlet Conditions:

1. 1. Pressure: 1 bar
   2. Velocity: zero Gradient
   3. Temperature: 300 K

• Elbow_wall

1. 1. Wall Boundary Condition.
   2. Temperature: 300 K
   3. Law of wall function is selected as turbulence model is utilized in the current study

• Throttle_wall

1. 1. Wall Boundary Condition.
   2. Temperature: 300 K
   3. Law of wall function is selected as turbulence model is utilized in the current study.
   4. Throttle is rotated about its central axis and the fluid flow is analyzed. The rotation scheme can be seen in the graph below:

1. 1. 0 to 2 ms : rotates from 0 to 25 degrees.
   2. 2 to 4 ms : stationary at 25 degrees.
   3. 4 to 8 ms : rotates back from 25 to 0 degrees
   4. 8 to 10 ms : stationary at 0 degrees.

• Turbulence Model: RNG k-epsilon
• Initial Conditions:

1. 1. Pressure: 101325 Pa
   2. Velocity: 0
   3. Temperature: 300 K
   4. Air is used as species with 0.23 O2 and 0.77 N2.

• Meshing and Cell Count Plot Against time

1. 1. Base Mesh: 0.002 m.
   2. Embedding: 3 layers, fixed scale of 2.

• • 0 to 2 ms : Platerotates from 0 to 25 degrees. Cell count continuously keeps on changing.
  • 2 to 4 ms : Plate stationary at 25 degrees. Cell count remains constant.
  • 4 to 8 ms : rotates back from 25 to 0 degrees. Cell count changes continuously.
  • 8 to 10 ms : stationary at 0 degrees. Cell count remains constant.

RESULTS

1. ANIMATION COMPILATION

The results have been compiled in a single 1 minute video. The video contains the following in sequence:

1. Rotation of the throttle plate
2. Mesh embeddment of the throttle plate while rotation
3. Velocity Contours
4. Pressure Contours
5. Velocity Vectors
6. Streamlines

2. VELOCITY VECTORS AND PRESSURE CONTOURS AT 25 DEGREE

3. MASS FLOW RATE

OBSERVATIONS AND INFERENCES

1. Velocity is almost uniform initially and decreases below the throttle plate as the plate closes up. It becomes further uniform as the throttle plate opens up again.
2. Streamlines are random below the throttle plate. As the flow moves farther from the plate, vectors start to alogn in the direction normal to the pipe again.
3. At 25 degrees (pressure contour above) a pressure buildup can be observed above the plate. Pressure below the throttle plate decreases as the plate closes and released again as it open up again.
4. The mirror image (almost) of the inlet and outlet flow rates indicated consistensy with the conservation of mass. The error margin is 6.7e-5 Kg/s imbalance in the mass of inlet and outlet which is a good degree of conservation of mass.
5. Seperation and recirculation of the flow due to rotation of the throttle valve is clearly captured by the streamlines.
6. Inlet Pressure is higher than that of the outlet as the flow occurs from high to low pressure region.