Multidisciplinary Assessment of the Control of the Propellers of a Pusher Geared Open Rotor—Part II: Impact on Fuel Consumption, Engine Weight, Certification Noise, and NOx Emissions

Abstract

Due to their high propulsive efficiency, counter-rotating open rotors (CRORs) have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. However, this novel engine architecture presents many design and operational challenges both at engine and aircraft level. The assessment of the impact of the main low-pressure preliminary design and control parameters of CRORs on mission fuel burn, certification noise, and emissions is necessary at preliminary design stages in order to identify optimum design regions. These assessments may also aid the development process when compromises need to be performed as a consequence of design, operational, or regulatory constraints. Part I of this two-part publication presents a novel 0D performance model for counter-rotating propellers (CRPs) allowing an independent definition of the design and operation of each of the propellers. In Part II, the novel CRP model is used to create an engine performance model of a geared open rotor (GOR). This engine model is integrated in a multidisciplinary simulation platform which was used to assess the impact of the control of the propellers, on specific fuel consumption (SFC), engine weight, certification noise, and NOx emission, for a GOR with a 10% clipped rear propeller designed for a 160 PAX and 5700 NM aircraft. The main conclusions of the study are: (1) Minimum SFC control schedules were identified for climb, cruise, and descent (high-rotational speeds for high thrust and low-rotational speeds for low thrust), (2) SFC reductions up to 2% in cruise and 23% in descent can be achieved by using the minimum SFC control. However, the relatively high SFC reductions in descent SFC result in ∼3.5% fuel saving for a 500 NM and ∼0.7% fuel saving for a full range mission, (3) at least 2–3 dB noise reductions for both sideline and flyover can be achieved by reducing the rotational speeds of the propellers at a cost of ∼6% increase of landing and takeoff cycle (LTO) NOx and 10 K increase in turbine entry temperature, (4) approach noise can be reduced by at least 2 dB by reducing CRP rotational speeds with an associated reduction of ∼0.6% in LTO NOx, and (5) the control of the CRP at takeoff has a large impact on differential planetary gearbox (DPGB) weight, but it is almost identical in magnitude and opposite to the change in low-pressure turbine (LPT) and CRP weight. Consequently, the control of the CRP at takeoff has a negligible impact in overall engine weight.