Fluid properties are used to determine the initial values of the state variables and to initialize other terms in the governing equations. The fluid therefore must be initialized for any transient simulation. Determination of initial fluid properties requires:
Initial temperature for each computational region.
Initial species composition for each computational region, in terms of mole or mass fractions. For in-cylinder regions, this may be the composition of pure air (for example, 79% nitrogen, 21% oxygen), a mixture of exhaust gas (for exhaust-gas recirculation) and air, or a pre-mixed charge of pre-vaporized fuel, air, and/or exhaust gas.
Initial turbulence kinetic-energy density for each computational region. In an internal combustion engine, the initial turbulence kinetic-energy density (TKEI) is specified as a fraction of the total kinetic energy that is turbulent kinetic energy, where the total kinetic energy is determined based on the mean piston speed. In non-engine applications TKEI is the actual turbulent kinetic energy with a value typically about 10% of the mean flow kinetic energy 0.5* u 2.
Initial turbulence length scale (TLS) for each computation region. If TLS > 0.0, its value is used to determine an initial (uniform) value of ε , which will be proportional to the TLS value. If TLS = 0.0, the initial ε value will instead be proportional to the distance from the cell center to the nearest solid wall.