Session: 01-05 Engine Performance and Cycle Design III

Paper Number: 152085

Assessing the Impact of Turbofan Engine Design on Aircraft Contrail Properties 

The effective radiative forcing due to contrails is estimated to be at least of equal magnitude to CO₂ emissions. For the aviation sector to achieve its net-zero emission goal by 2050, the effect of contrail and contrail cirrus on the environment must be properly understood and their adverse effects mitigated. Previously, the effect of aircraft design, particularly the interaction between the exhaust jet and wingtip vortex, was shown to significantly impact the resulting contrail development during the jet and vortex regime. To better assess the environmental impact of the current and future aircraft fleet, a detailed turbofan engine cycle model with particle emission prediction has been developed and incorporated into in-house CFD code HYDRA to increase the fidelity of contrail simulations.

A detailed thermodynamic model, based upon and validated against modern turbofan data, was developed to build a family of engines with varying architecture. Each generic engine was modelled around a single design point of 70,000lbf nominal thrust at sea level static (SLS) conditions. An energy balance between the internal core and bypass flow was ensured whilst varying engine design parameters such as bypass ratio (BPR) and overall pressure ratio (OPR). Each engine provides a viable powerplant for the NASA Common Research Model (CRM) aircraft, which is representative of a modern, medium haul, twin-aisle airliner where the SLS thrust class is appropriate. Engine BPR was swept from 2 to 15 to represent the older (BPR<5) and modern (5<BPR<10) engines which power the current and near-future aircraft fleet. Ultra-high BPR engines (BPR>10) were also modelled to represent the future progression in turbofan technologies. As such, the trend of thermodynamic efficiency improvements in the core was also captured.

The engine model was expanded upon to predict the non-volatile particulate matter emissions, with such particles being the dominant condensation nuclei for ice crystal formation in hydrocarbon-burning aircraft. The emissions prediction was attained via a machine learning model trained on the ICAO Emissions Databank based on inputs from the developed thermodynamic cycles. The model was separated to account for Rich-Quench-Lean and lean-burn combustion technology. These details are not typically captured within standard thermodynamic models and formed an additional design parameter within the study. The resulting engine family model provided the physical behaviour for a realistic representation of operational performance for the CRM at steady state cruise (M0.85, FL390).

The outputs of the engine model were further linked to a parametric CRM model allowing for nacelle sizing requirements to be met. This sizing accounts for the reduction in specific thrust produced by higher bypass ratio engines and consequently allows for the drag increase due to greater surface area to be captured. Power-on, full aircraft, RANS CFD simulations were conducted within HYDRA using its contrail microphysics, with cruise conditions being achieved by throttling each engine, altering the fuel burn and particulate emissions. Qualitative verification versus contrail flight test campaigns involving differing engines was conducted to validate the methodology. The studied design parameters dictated an engine’s sizing, fuel consumption, exhaust conditions and emissions, all of which were found to significantly influence the resulting contrail formation and its evolution behind the aircraft. These impact the contrail’s optical properties and hence the adverse effect on the environment. The assessment allows contrail properties to also be considered in future choices on engine design alongside those relating to the fuel burn and hence CO₂ emissions.

Presenting Author: Joseph Ramsay Rolls-Royce plc.

Presenting Author Biography: Final year PhD student at the University of Sheffield, working within the Fluid Mechanics team at Rolls-Royce in Derby, UK. I have a strong interest in aerodynamics and CFD which was formed whilst attaining a Master's degree from the University of Sheffield, and I am now researching the pathways to net-zero aviation with respect to aircraft contrails as part of the EU research project NEXTAIR.

Authors:

Joseph Ramsay Rolls-Royce plc.
Indi Tristanto Rolls-Royce plc.
Shahrokh Shahpar Rolls-Royce plc.
Alistair John University of Sheffield