Steady state simulation of flow over a throttle body

Steady state simulation of flow over a throttle body

I. Overview

In the current project, steady-state 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: Steady-state solver, 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

For performing steady-state simulation, the steady-state monitor is set up using average velocity at the outlet.

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 ofwall; 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: 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

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 are plotted over simulation cycles.

2. Average velocity

Average velocity at inlet and outlet are plotted over simulation cycles.

3. Static pressure

Static pressure at inlet and outlet are plotted over simulation cycles.

4. Cell count ranks

Cell count ranks are plotted over simulation cycles. According to the grid specifications 35518 computational cells are generated.

5. Pressure contours

Steady-state pressure contours are plotted over a cut-plane.

6. Velocity contours

Steady-state velocity contours are plotted over a cut-plane.

7. Velocity vectors

Steady-state velocity vectors are plotted over a cut-plane.

IX. Animations

1. Streamlines

The animation attached below displays the evolution of streamlines on a cut-plane over the simulation cycles.

2. Velocity contours

The animation attached below displays the evolution of velocity vectors on a cut-plane over the simulation cycles.

X. Discussions

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

2. The plot for average velocity indicates that the average velocity at the outlet is 224.082m/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 310m/s is achieved in the passage between throttle valve and pipe.