CFD simulation and emissions prediction from a helicopter engine

The increasing attention on air pollution phenomena such as the direct emission of pollutants and greenhouse gases have led the political authorities to standardize air traffic emissions. The emissions from a gas turbine engine are like those coming from an internal combustion engine. Much attention is paid to the reduction of nitrogen oxides, in line with the ambitious global targets. To achieve this objective, detailed studies of the conditions which favor the reduction of pollutants are required. The experimental tests are expensive and therefore they are often accompanied by predictive models such as Computational Fluid Dynamics (CFD) codes. This thesis work has as primary aim to conduct the fluid dynamics simulation of a combustor used in aviation in order to predict flows, temperature fields and emissions. This activity has been carried out using Fluent and a Kinetic Post-Processor (KPP). The analyzed combustor is the RR-Allison 250 C20R model, mounted on many helicopters and small aircrafts. An experimental campaign, done using the helicopter PZL SW-4, allowed to acquire a large set of data that was used in this work to create reliable boundary conditions and to validate the CFD results. A 3D combustor model was created and the flow field solved adopting a RANS approach. Special attention was dedicated to the modeling of the spray, the turbulence-chemistry interactions and the fuel properties. A very difficult challenge was to predict the emissions of CO and unburned hydrocarbons. To pursue this goal, we used a specific Kinetic Post-Processor developed at the Politecnico of Milan. The comparison with measured emissions and temperature data have shown that the model is able to correctly characterize the combustor exit temperature and emissions as a function of engine power.