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

Aim: 

• To perform the Steady State Simulation over the throttle body in Converge studio and observe the plots of pressure, Velocity, Mass flow rate and the total Count cells.
• Post Process the result using Para view and shows the Pressure and Velocity Contours and made a animations for the flow with a different angles to demonstrate the flow over the throttle body in both scenarios.

Introduction:

A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.

An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term throttle has come to refer, informally, to any mechanism by which the power or speed of an engine is regulated, such as a car's accelerator pedal. What is often termed a throttle (in an aviation context) is also called a thrust lever, particularly for jet engine powered aircraft. For a steam locomotive, the valve which controls the steam is known as the regulator.

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.

For a gasoline engine, the throttle most commonly regulates the amount of air and fuel allowed to enter the engine. Recently, for a GDI engine, the throttle regulates the amount of air allowed to enter the engine. The throttle of a diesel, when present, regulates the air flow into the engine.

In fuel injected engines, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main.

Importing Geometry and Assign the boundary:

Import the geometry into the Converge studio and clean up the geometry by using some tools which are available in the converge.

Geometry with Thickness:

Delete the thickness part of the throttle body which is not necessary for us. After completed this process then we have free edges by using the patch command we can close the free edges.

Geometry without Thickness and Closed the free edges:

Enable the vectors on the geometry make sure that all the normal should be facing inside the fluid domain The below figure shows the vectors outside the domain convert them into inside where the fluid is going.

Now check for the errors in the geometry by opening the diagnosis dock and then find if no errors are there means we can proceed to the case setup.

Now Assign the boundaries name to the geometry

Case setup for Simulation:

• Application Type – Time Based
• The flow is general flow which contains the air as a Material.
• Air contains a Species mixture of O2 and N2 which will flow through the required geometry.
• Global Transport Parameters the Prandtl number is 0.9 and the Schmidt number is 0.78.

Simulation Parameters:

• In the Run Parameter: Solver we used is Steady state and the simulation mode = Full hydrodynamic in the mic state we enable the Solver Momentum, Solve Species.
• In Simulation time Parameters we set the values for start time as 0 cycles and end time 15000 cycles and the initial and Minimum time setup for 1e-9 and remaining values are put to default.
• In the Solver Parameters, the Navier stock equation should be Pressure based solver and remaining should be default.
• The number of cycles for the 2e-3 mesh is 15000 in order to converge the solution.

Initialization and Boundary Conditions:

• In the initialization region change the name of the Region as a volumetric region and the values assigned for the temperature and pressure is 300k and 101325.0 Pascal and add the species O2 and N2 with the mole fraction of 0.23 and 0.77.
• The pressure at the inlet is 150000 Pascal and the temperature should be 300 k and the boundary type is INFLOW
• The pressure at the outlet is 100000 Pascal and the temperature should be 300 k and the boundary type is OUTFLOW.
• For the Elbow wall boundary should be the wall type with a Law of wall boundary condition and temperature should be 300k.
• For the throttle the boundary type is WALL type with the Law of wall as a boundary condition and temperature should be 300k.

Physical Models:

• In the physical models enable the Turbulence Modelling and the solver should be selected as RNG K-e and put the remaining values as a default.

Grid Control:

• In the Grid control enable the Fixed Embedding and Base grid
• Enter the base grid values and then go to the fixed Embedding add the
• Entity type=Boundary
• Boundary ID=Throttle
• Mode =Permanent
• Scale=2
• Embedded layers=3

After entered all the values click on apply.

Output and Post Processing:

• Post variable Selection and Output files are the default values.
• In the output files we have given time interval to write the 3D output data=150 cycles, thus the outputs of the simulation files be stored after 150 cycles.

Post-Processing:

I have done the post processing of the results for all three cases using the converge studio and paraview. Post processing is actually used in order to get the desired Output by running the simulation

Results:

Mesh Profile:

As we can observe that the mesh around the throttle is due to the use of embedded layer.

Velocity Contour:

Velocity Contour with Vectors and Streamlines:

      

Velocity Contours on the faces of the Throttle:

  

• The velocity is high at the junction (indicates red colour) is due to the amount of air particles passing through them is less and also the area is less so the velocity is increases and the other side the pressure is more so that the velocity is less.By observing the vectors image the vectors at the where the velocity is high at that point the vectors are passing through it whereas on the other side the vectors are diverging and going out of the surface so that the velocity is less. 
• The pressure energy is converted into the kinetic energy so that the velocity is significantly start increasing after passing through the throttle body because the throttle value is not completely sealed with the walls.so that the velocity obtained at the outlet is 250-280 m/sec.

Velocity Animation:

Pressure Contour:

Pressure Contour on Throttle body:

  

• The pressure is high at the one side and the other side the pressure is minimum.
• As the pressure is high at the throttle body where the fluid first interacts with the throttle body indicates with Red colour when the pressure is directly hits the body and the lower pressure is at the places where the surface of the wall and the throttle body interacts.
• As the pressure is high because of direct attack of fluid particles on the throttle and the pressure is low at the walls because the amount of air is flowing through this very low which causes the low pressure.
• The pressure gradient is formed after the attack of air particles on the throttle body so that the pressure is reduced and moves toward the outlet.This is main reason to drive the fluid in the system.

Pressure Animation:

Mass flow rate plot for the Steady state of Throttle Body:

• There is a Fluctuations in the flow till some cycles after the solution is converged and the mass flow rate looks like stable.
• The mass flow rate is same at both inlet and outlet. Hence the law of conservation of mass is achieved.

Velocity plot for the Steady state of Throttle Body:

• A negative velocity is achieved at inlet due to the backward moment of  velocity in the domain that is occurred due to the pressure difference.The inlet velocity is 190m/sec and the outlet velocity is 220 m/sec. There is fluctuations in both velocities at the time of starting after that in converges after a few cycles. At outlet the velocity is increased due to pressure gradient and when the flow is full developed the velocity becomes neutral.

Total Pressure plot for the Steady state of Throttle Body:

• Total pressure in the domain before its enter at the inlet is 150000 Pascal kept constant and the outlet pressure given is 100000 Pascal as the simulation starts running the outlet pressure starts changing its nature and fluctuations for up to 8000 cycles this is because of the movement of the particles on the throttle valve and after passing the valve it achieves the convergence so from that step the static pressure is constant.

Static Pressure plot for the Steady state of Throttle Body:

• Static pressure is the pressure of the fluid at rest i.e when the fluid is not entered into the domain at the inlet is 150000 Pascal and once the air is allowed into the domain as the simulation starts the inlet static pressure starts changing its nature and fluctuations for up to 6000 cycles and achieve the convergence after that as the pressure is flowing from the high pressure region to low pressure region and the outlet static pressure is 100000 Pascal because at the outlet no fluid moment is there.

Total Number of Cells Count for the Steady state of Throttle Body:

• The total number of cells are approximately 16000 cells with a mesh size of 2e-3 and with embedded layer of 3 with scale 2.

Conclusions:

• Steady state simulation of throttle body in converge studio and generated the contour and plots successfully.
• The flow is not restricted in the system because the throttle is fully open.