Modelling Exhaust Systems Using One-Dimensional Methods 2002-01-0005
The benefits of computer simulation of complex internal and external flow problems are well understood. Three-dimensional computational fluid dynamic (CFD) models are commonly being used to model exhaust systems to ensure that design back-pressures, levels are not exceeded, whilst meeting noise and vibration, weight and volume constraints so as to optimise the overall design. CFD models for such systems are usually large (typically hundreds of thousands of cells) and take considerable time to construct, validate and analyse. In general it is impractical to represent a complete system in a single CFD model.
One-dimensional models of internal flow in piping systems provide significant advantages over three-dimensional CFD by both reducing model complexity and the computational time required to perform a simulation in some applications. Use of such models permit networks consisting of many components to be modelled in their entirety.
By incorporating the effects of the complex branched and looped flow passages in the mufflers in a one dimensional form combined with the thermodynamics along the system as well as the pressure losses in Catalysts and Diesel Particulate Filters, high simulation accuracy levels have been obtained when one dimensional computational results have been compared to rig tests. This paper describes the modelling techniques used in the FLOWMASTER computer program to achieve such accurate solutions to the design of complete exhaust systems.