STAR-CD at Fiat Powertrain Technologies Angelo Rosetti, Fiat Powertrain Technologies
STAR-CD is used to support the engine design process of Fiat Powertrain Technologies (FPT) in Arese. Advanced CFD calculations are usually performed, such as 1D-3D coupled analyses, cylinder head and block water jacket, manifold analyses and intake runner cold flow. Some spray-injection and combustion simulations have been performed with the latest multi-hole injector configurations. Here 1D- 3D coupled and water cooling jacket analyses will be described.
1D-3D Coupled analyses are used to design manifolds. The one dimensional code GT-Power v6.1 and STAR-CD are used on Linux RH Enterprise3 machines.
Simulations are usually performed in full load condition, for the maximum power rpm and sometimes for the maximum torque rpm determination. Seven engine cycles are run, six of them to reach convergence and the last one to write results. A 0.5 degree crankangle- step is usually set, to get the best compromise between analysis speed and accuracy.
In order to provide faster results to the design engineer,
a particular cluster has recently been built, made of only one Linux machine
“n” number of WM-Vare Linux virtual machines mounted on Windows technical workstations. Each of these technical workstations have 2 processors; when you want to run a simulation with the cluster you simply have to “turn on” the virtual machine from Windows and you
get a Linux machine. Then you have only to decide how many processors you want to add to the mini-cluster (only one or both of them). In that way you can work on a machine and use it with one processor with Windows and use the other processor for the Linux cluster: so you can decide how many machines to use among those available on your office! A Linux cluster has been preferred because of es-ice and ICE calculations can be run.
The results obtained are analysed and discussed together with the designer. Velocity field, pressure, temperature, pressure waves, Mach number, flow separation and mass flow rate balance between cylinders are the quantities usually observed. A complete analysis for one manifold solution (meshing process, running, post process and report building) takes about 4 to 5 working days, depending on the mesh complexity. Figure 1 shows the mesh of a six cylinder engine intake manifold, the mesh contains about 400K cells, with one extrusion layer of about 1mm. The Standard K-ε turbulence model has been used. Figure 2 shows an instantaneous velocity field of some runner sections; Figure 3 shows the mach number of only one runner section.
Water Cooling Jacket Analysis
The water jacket analyses performed at FPT are usually part of the complete thermo-structural analysis of the whole cylinder head and block. From the CFD code the wall heat transfer coefficients are passed to the FEM code in order to make the thermo-structural calculation. STAR-CD is then used to control all the water flow distribution inside the head and the block; furthermore the gasket hole position and dimension are optimized in order to keep the metal temperature regulated for all parts of the engine.
The standard calculation is usually represented by a steady run in maximum power condition. The mass flow is the inlet condition and the exact coolant properties are specified.
Both isothermal and non isothermal analyses can be performed and thanks to the flexibility of STAR-CD, boiling effect are taken into account, using an appropriate user subroutine. The Rohsenow nucleate boiling model has been used to correct the one-phase wall heat flux in case of critical wall temperature values.
Figure 4 shows a complete mesh of the water cooling jacket of the cylinder block and head for a four cylinder engine. The mesh consists of about 800K cells. The coolant enters from the block and goes out of two outlets: one going to the radiator and the other to the interior compartment. The position of the gasket holes, that connect the cyl. block and head, are very important for the whole thermal balance of the engine: the role of the calculation is to best fit their position.
As known, the exhaust valve bridge in the cylinder head is the critical point for monitoring for the thermal behaviour of the engine and an organized coolant motion without stagnation on the exhaust side is the starting point for water cooling jacket design. Cylinder head pressure, wall heat transfer coefficients and temperature can be observed respectively in Figure 5, 6 and 7.
STAR-CD is the CFD simulation software used in the engine design and analysis department of FPT, Arese Site. The article is an overview of how coupled 1D-3D and water cooling jacket CFD analyses are typically performed and clearly shows the fundamental role of the simulations in the design process of modern automotive engines.
01: Intake manifold of a six cylinder engine
02: Velocity field – Runner section
03: Mach number – Runner section
04: Water cooling jacket mesh of a 4 cylinder engine
05: Pressure filed- Water cooling jacket of a four cylinder engine
06: Wall heat transfer coefficients – Water jacket four clinder engine
07: Temperature field – Water jacket of a four cylinder engine