Turbo Charger Simulation Project

Turbo Charger Simulation Project using Converge Cfd

Aim: The aim of the project is to simulate a turbo charger body for different pressure case and compare the speed of those cases

What is a turbo Charger

A turbocharger is a device fitted to a vehicle’s engine that is designed to improve the overall efficiency and increase performance. This is the reason why many auto manufacturers are choosing to turbocharge their vehicles. A turbo is made up of two halves joined together by a shaft. On one side, hot exhaust gasses spin the turbine that is connected to another turbine which sucks air in and compresses it into the engine. This compression is what gives the engine the extra power and efficiency because as more air can go in the combustion chamber, more fuel can be added for more power. In addition to the extra power, turbochargers are sometimes referred to as devices that offer “free power” because unlike a supercharger, it does not require the engine’s power to drive it. The hot and expanding gasses coming out of the engine are what power a turbocharger so there is no drain of the engine’s net power. Turbocharged engines are also not affected in the same way as naturally aspirated engines are when they go at higher altitudes. The higher in altitude a naturally aspirated engine climbs, the harder it becomes for it to get oxygen due to the thinning atmosphere. A turbocharger gets around this problem because it forces the oxygen into the engine’s combustion chamber, sometimes at 2 times the pressure of the atmosphere.

Geometry cleanup and boundary setup:

• The geometry is first modelled in a 3D CAD software, then imported into the Converge studio in the form of an .stl file.
• The places where the boundary has a thickness is deleted as we are intrested in simulating the faces in contact with the working fluid.
• The Geometry is being scaled down according to the Converge standard units.
• Then thye boundaries are assigned.

• The Turbo Charger is then diagonised for any errors, if it is error free then we move on to case setup.

Case Setup:

• Time based application is selected for the above simulation.
• Air is used as the simulating material.
• Redlich-Kwong is used as gas simulation equation, while keeping the other parameters same.
• Global Transport parameters are kept untouched.
• For run parameter in the simulation parameters Transient solver is used with simulation mode as full hydrodynamic, and gas flow solver as compressible. The steady state monitor and used shared memory aree unchecked.
• For simulation time parameter start time is selected as 0.0 sec and end time as 0.006 sec, initial and minimum time step as 1e-9 sec and max time step as 1 sec.

The max time is calculated as taking the RPM as 100000 so accordingly in RPS it is 1666.67 , time for 1 rotation is 0.0006 and time for 10 rotation is 0.006 which is used for simulating the above geometry.

• For solver parameter pressure based solver is used and other parameters unchanged.
• Before selecting the boundary parameters , regions and initialisations is selected as region 0 with temperature as 500K.
• Now in boundary for inlet inflow boundary is selected taking pressure as 2.5 Pa for 1^st case and 3Pa for 2^ndfor outlet outfolw boundary is selected with a pressure of 1 Pa to maintain a ratio of 2.5 and 3.0 in the respective cases. Casing is selected as fixed stationary boundary, for turbine wheel wall type boundary is selected keeping the wall motion as FSI (Fluid Structure Interface) because the wheel is rotating while being in contact with the fluid.
• For turbulance model RNG k-ε is used .
• For FSI rigid FSI object is used with turbine wheel as a boundary

• A base grid of 2mm was used .
• In the output file the time interval for writing 3D output is selected as 6e-5 so as to get 100 post output files, time interval for writing text output is 1e-9, and maximum number of restart files saved is 3.
• After the case setup the calculation part is being carried out in CYGWIN.

It took approximatedly 6 hours to simulate for the 1^st case

And 6 hours to simulate the 2^nd case for 3Pa.

Governing equation

The solution for CFD simulation is obtained by solving the Navier-Stokes (NS) equations. The equations comprise of 5 equations, namely the continuity, momentum (3 equations), and energy equations. The continuity and momentum equations are solved for all flow problems with the energy equation are optional and can be used only when heat transfer is taking place to save computation time.

The results are then finally analysed in paraview.

• Before this the post out files are converted to .vtk binary files, which is the readable format for paraview.

Case 1: comparision of fsi angle

For the above grapg we can see that for 3 Pa case the angle goes on increasing on a negative side.

Case 2: Comparision of pressure

As we see that the pressure for 3Pa is higher than that of at 2.5Pa, which was the condition we made the simulation for.

Case 3 : Comparision of mass flow rate

Pressure at 2.5Pa

Pressure at 3Pa

Velocity at 2.5Pa case

Velocity at 3Pa Case

Anmimation of Turbine wheel at 2.5Pa

Anmimation of Turbine wheel at 3Pa