Week 4: Project - Steady state simulation of flow over a throttle body

Objective: The aim of this project is to study the Steady-state analysis of Flow over the Throttle body and examine the parameters like velocity, pressure, and mass flow rate at both inlet and outlet by using the Converge Studio software.

Introduction: Throttling Valve

Throttling valves are a type of valve that can be used to start, stop, and regulate the flow of fluid through a pump. Throttling valves are used to regulate the flow, temperature, or pressure of the service. These valves can move to any position within the stroke of the valve and hold that position, including the full-open and full-closed positions. Therefore they can act as on-off valves also.

Throttling valves are equipped with actuators or actuation systems, which provide greater thrust and positioning capability, as well as automatic control. Few throttle valve designs are also provided with a hand-operated manual handwheel but accuracy is a concern there.

• Some of the applications are :

In an internal combustion engine, the throttle is a means of controlling an engine's power by regulating the amount of fuel or air entering the engine. In a motor vehicle, the control used by the driver to regulate power is sometimes called the throttle, accelerator, or gas pedal.

Steam locomotives normally have the throttle or regulator in a characteristic steam dome at the top of the boiler (although not all boilers feature these). The additional height afforded by the dome helps to avoid any liquid (e.g. from bubbles on the surface of the boiler water) being drawn into the throttle valve, which could damage it, or lead to priming.

Geometry:

• The geometry we have imported is an elbow pipe geometry, placing the throttle valve a the bend of the pipe.
• The throttle valve inside the elbow pipe is fixed to the walls of the elbow, and the rotation movement of the throttle valve has maintained by a pin that is attached to it. 

• We can see the throttle valve which is inside the elbow by hiding a quarter part of the elbow by choosing a perfect axis.
• The throttle valve looks like:

• We can see the cylinder in the above figure, it is the pin that attaches with the throttle body and maintains the movement of the valve.

Case Setup:

Application Type - Time-Based

Materials - Air (Mixture of O2 & N2)

Simulation Parameters:

• Simulation time parameters: Number of cycles - 15000

                                                   Initial time step - 1e-9

                                                   Minimum time step - 1e-9

                                                   Maximum time step - 1

Boundary Conditions:

1) Inlet:

• Boundary type: INFLOW
• Pressure: 150000 Pa
• Fluid: Air (O2 - 23%, N2 - 77%)

2) Outlet:

• Boundary type: OUTFLOW
• Pressure: 100000 Pa

 3) Throttle Wall:

• Boundary type: WALL
• Wall motion type: Stationary
• Surface movement type: Fixed

 4) Elbow Wall:

• Boundary type: WALL
• Surface movement: Fixed

Physical Model:

• Turbulence Model: RNG K-Epsilon

Grid Control:

• Base grid: 0.002 (dx,dy,dz)

Fixed Embedding:

• Entity type: Boundary
• Scale:3
• Layers: 2

Output/Post-processing

• Output files: 

1. Time Interval for writing 3D files: 1000 cycles
2. Max. Number of restart files saved: 3

Meshing:

CONVERGE automatically generates an optimized Cartesian mesh at runtime and dynamically refines the mesh throughout the simulation using AMR. All of this remains the same in CONVERGE 3.0, and you can still use meshes exactly as they were in all previous versions of CONVERGE.

• The Base grid is given as 0.002 in all the dx, dy, dz directions.

• The fixed embedding method has been used to refine the mesh at the throttle area because the flow gets resisted in that environment only.
• We can observe in the above figure, the throttle area has been given more number of elements because of the embedding method.

Velocity:

• In the contour, we observe the max. velocity was obtained at the outlet, but before that the max. velocity obtained at the narrow passage between the elbow wall and the throttle valve.
• It happens because the cross-section area gets reduced at that place.
• The max. velocity recorded inside the elbow is 195.984 m/s.
• The least velocity recorded in the elbow is at two places: one is on the throttle valve, and the other region is behind the throttle valve as it separates the flow. Due to flow separation, the wake or negative pressure zones were created.
• The min. velocity recorded is 2.6 m/s.

• The sudden shock visible in the above graph is because at that place the flow hits the throttle valve ad gets separated hence lost its velocity.
• The outlet velocity is more than the inlet velocity. This is the phenomenon we have to study and analyze in these kinds of simulations.

Velocity Animation: https://youtu.be/5e_HWpf3FRs

Pressure:

• The above figure represents the pressure contour. The max. pressure was obtained at the left side of the throttle valve because flow hits there and reversed while passing through that region. We call it as the flow gets staggered.
• The lower pressure was obtained at the outlet of the elbow and also at the narrow passage between the elbow wall and throttle valve.

• Here in the above plot, we can see that the pressure is decreasing from the starting of the simulation. But at a point, the pressure gets a sudden drop and rise. This is where the flow hits the throttle and staggered.
• The max. pressure is 1.5 bar, and Min. pressure recorded is 100008Pa.

Pressure Animation: https://youtu.be/6cILswWm0MM

Mass Flow Rate:

• Here from the graph, we can see that the results reached the steady-state after 4000 cycles.
• The mass flow rate data is monitored by a monitor point in the case setup called Steady-state monitor.
• The Max. flow rate is recorded as 0.05 Kg/s. The Mass flow rate is gradually increasing because the pressure is gradually decreasing.

Total Cell-Count:

• To speed up the simulation we have included the 4 processors into the simulation instead of running on 1 processor.
• Here as we used the base grid of 0.002 meters and the fixed embedding method, the total cells have been reached nearly 36000.
• While running the simulation, the four processors have divided the total number of cells almost equally.

Conclusion:

• The flow over a throttle body simulation has been performed and analyzed in the steady-state conditions.
• Applied the Fixed Embedding method to refine the mesh at the surrounding region of the location of the throttle valve by making the Throttle valve as Boundary condition.
• Here we can conclude that usage of the throttle valve in the elbow or any pipe increases the velocity and reduces the pressure built inside.
• We can observe from the graphs that pressure is decreasing and at the same time, the velocity gets increased, which is an analyzed point.