Transient simulation of flow over a throttle body

Transient simulation of flow over a throttle body

I. Overview

In the current project, a transient simulation of flow over a throttle valve, placed in a pipe-elbow, is performed using CONVERGE CFD.

II. Geometry

The geometry used for performing simulation is attached below.

III. Material

Air (Predefined mixture) is used as the working fluid for performing gas simulation. Accordingy, the following global properties are utilized:

Turbulent Prandtl number: 0.9

Turbulent Schmidt number: 0.78

IV. Solver

The three dimensional Navier Stokes equations are solved using CONVERGE solver with the following settings:

i. Solver: Transient, Pressure-based

ii. Navier-Stokes solver scheme: PISO

iii. Simulation mode: Full hydrodynamic

iv. Gas flow solver: Compressible

v. Initial time-step: 1e-9s

vi. Minimum time-step: 1e-9s

vii. Maximum time-step: 1s

V. Initial conditions

The following settings are applied as the initial conditions:

Velocity: X-component: 0; Y-component: 0; Z-component: 0

Temperature: 300K

Pressure: 101325Pa

Species: Mass fractions: Oxygen: 0.23; Nitrogen: 0.77

VI. Boundary conditions

The following boundary conditions are applied:

1. Inlet: INFLOW type boundary condition is applied with the following settings:

Total pressure: 151987.5Pa

Velocity: Zero normal gradient

Temperature: 300K

Species: Mass fractions: Oxygen: 0.23; Nitrogen: 0.77

Turbulent kinetic energy (tke): Intensity=0.02 (fraction)

Turbulent dissipation (eps): Length scale=0.003m

2. Outlet: OUTFLOW type bundary condition is applied with the following settings:

Pressure: 101325Pa

Velocity: Zero normal gradient

Temperature backflow: 300K

Species backflow: Mass fractions: Oxygen:0.23; Nitrogen: 0.77

Turbulent kinetic energy (tke) backflow: Intensity=0.02 (fraction)

Turbulent dissipation (eps) backflow: Length scale=0.003m

3. Elbow_wall: WALL type boundary condition is applied with the following settings:

Wall motion type: Stationary

Surface movement: FIXED

Velocity: Law of wall

Temperature: Law of wall; 300K

Turbulent kinetic energy (tke): Zero normal gradient

Turbulent dissipation (eps): Wall model

4. Throttle: WALL type boundary condition is applied with the following settings:

Wall motion type: Rotating

Surface movement: MOVING

Velocity: Law of wall

Temperature: Law of wall; 300K

Turbulent kinetic energy (tke): Zero normal gradient

Turbulent dissipation (eps): Wall model

Throttle movement profile:

i. 0 to 2ms - The valve rotates by 25 degrees.

ii. 2 to 4ms - The valve remains at 25 degrees.

iii. 4 to 8ms - The valve returns to its original position

VII. Grid

Computational grid with the following features is used for performing simulation:

i. Base grid size: dx=dy=dz=0.002m.

ii. Fixed embedding: Enabled; Entity type: Boundary; Boundary ID: Throttle; Mode: PERMANENT, Scale: 3, Embed layers: 2

The figure attached below shows the computational grid

VIII. Results

1. Mass flow rate

Mass flow rate at inlet and outlet is plotted over time.

2. Average velocity

Average velocity at inlet and outlet is plotted over time.

3. Static pressure

Static pressure at inlet and outlet is plotted over time.

4. Cell count ranks

Cell count ranks are plotted over time. Since the mesh keeps changing with time, due to throttle movement, the cell count is also not constant.

5. Pressure contours

Pressure contours are plotted over a cut-plane at t=10ms.

6. Velocity contours

Velocity contours are plotted over a cut-plane at t=10ms.

7. Velocity vectors

Velocity vectors are plotted over a cut-plane at t=10ms.

IX. Animations

1. Streamlines

The animation attached below shows the evolution of streamlines on a cut-plane with time.

2. Velocity contours

The animation attached below shows the evolutionof velocity contours on a cut-plane with time.

X. Discussions

1. The plot for mass flow rate indicates a good mass balance between inlet and outlet.

2. The plot for average velocity shows that the average velocity at the outlet (at t=10ms) is 226.286m/s.

3. Pressure contours show maximum and minimum pressure values near the upstream and downstream locations of the throttle valve respectively.

4. Velocity contours show that a maximum velocity of 330m/s is achieved in the passage between throttle valve and pipe.

5. The animations show the influence of throttle movement on the nearby velocity field and streamlines.