+47 67 57 21 00
Combustion modeling in ANSYS CFD
Modeling of combustion requires special attention. The coupling between turbulence and chemical reaction and the highly non-linear relation between the temperature and the reaction rate prohibit the use of “standard” CFD models for this type of flows. This is particularly true for highly exothermal processes, like combustion, where a large amount of heat is released during the reaction. Several fluid properties change with temperature, which can make the simulation numerically tricky.
Combustion has been an area of focus since the early days of CFD. ANSYS CFD (ANSYS FLUENT and ANSYS CFX) contains advanced models for simulating many different kinds of reactive flows. Validations have proven the models to be highly accurate. For combustion purposes, the models are based on the level of “premixedness” of fuel and oxidizer:
Premixed combustion models. These models are appropriate in situations where the fuel and oxidizer are completely mixed into one common stream before entering the domain. Examples of systems that can be modeled using the premixed models are lean-premixed gas turbine combustors, aspirated internal combustion engines, and gas-leak explosions.
Non premixed combustion models. In many situations, the fuel and oxidizer are introduced in the domain via two distinct streams. Such situations include pulverized coal furnaces, diesel internal-combustion engines, and pool fires.
Partly premixed combustion models. These models are somewhere in between the two previous ones. They can be used in situations where the premixed stream enters a quiescent atmosphere, simulating lean premixed combustors with diffusion pilot flames, and imperfectly premixed inlets.
In the following example, a pure methane stream is introduced in a channel of flowing air. Near the outlet (top) of the domain there is a horizontal pipe that is being heated by the flame. The inlet temperature of the methane and air is 300 K. To simulate the combustion, one of the non premixed models is used. In movie1, the temperature is shown on a 2D intersection. Movie2 shows the temperature distribution on the pipe surface. The results obtained can be used in a subsequent FEM analysis to estimate the structural impact of the fire on the pipe.
Movie1:
Movie 2: