Off-design performance analysis of hybridised aircraft gas turbine

Abstract

An advanced geared turbofan with year 2035 technology level assumptions was established and used for the hybridisation study in this paper. By boosting the low-speed shaft of the turbofan with electrical power through the accessory gearbox, a parallel hybrid concept was set up. Focusing on the off-design performance of the hybridised gas turbine, electrical power input to the shaft, defined as positive hybridisation in this context, generally moves the compressor operation towards surge. On the other hand, the negative hybridisation, which is to reverse the power flow direction can improve the part-load operations of the turbofan and minimise the use of compressor handling bleeds. For the pre-defined mission given in the paper, negative hybridisation of descent, approach and landing, and taxi operations with 580 kW, 240 kW and 650 kW, respectively was found sufficient to keep a minimum compressor surge margin requirement without handling bleed.Looking at the hybridisation of key operating points, boosting the cruise operation of the baseline geared turbofan is, however, detrimental to the engine efficiency as it is pushing the cruise operation further away from the energy optimal design point. Without major modifications to the engine design, the benefit of the hybridisation appears primarily at the thermomechanical design point, the hot-day take-off. With the constraint of the turbine blade metal temperature in mind, a 500kW positive hybridisation at hot-day take-off gave cruise specific fuel consumption (SFC) reduction up to 0.5%, mainly because of reduced cooling flow requirement. Through the introduction of typical electrical power system performance characteristics and engine performance exchange rates, a first principles assessment is illustrated. By applying the strategies discussed in the paper, a 3% reduction in block fuel burn can be expected, if a higher power density electrical power system can be achieved.

Assessment of a Turbo-Electric Aircraft Configuration with Aft-Propulsion Using Boundary Layer Ingestion

“…The thrust requirements of the main mission points are summarized in the following Table 1: Table 1. Major aircraft mission and performance parameters, as well as thrust requirements (per engine) for the mission points considered [6]. Since the concept clearly aims at fuel burn benefits at Cruise conditions, only the main mission points for the aerodynamic and thermal design of the gas turbine, as well as cruise were included in the sensitivity analysis.…”

“…The thrust requirements of the main mission points are summarized in the following Table 1: Table 1. Major aircraft mission and performance parameters, as well as thrust requirements (per engine) for the mission points considered [6].…”

“…Those exchange rates translated the change in cruise SFC, weight and drag into a respective change in mission fuel burn; all necessary details regarding this conversion are provided in Section 4.3.3. More information on the mission characteristics and resulting engine performance of the baseline engine Aerospace 2019, 6,134 5 of 42 at all ratings can be found in Reference [6] and Table A1 in the Appendix A. Regarding the aircraft geometry, the Central Reference Aircraft Data System (CeRAS) model in Common Parametric Aircraft Configuration Schema (CPACS) format was available [16] representing a validated and re-engineered version of an A320.…”

“…Entry into service (EIS) 2035 component polytropic efficiency levels and maximal metal temperatures were being introduced into the performance model. The values for the engine specific thrust (SFN), gas generator overall pressure ratio (OPR), jet velocity ratio VcoldQhot and pressure ratio split exponent (PRn) at Cruise conditions emerged from a performance optimization of this particular engine as described in greater detail in Reference [6]. Those values or respective limitations were fixed in the present study by applying a multi-point cycle synthesis for different and relevant mission points (for the BLI cases the main engine's fan inlet mass flow w 2 was fixed rather than SFN (see Section 4)); here mainly the aerodynamic design point hot-day Top of Climb (TOC) and hot-day Take-Off (TO).…”

“…The first two points have been addressed in several studies, and their potential benefits were quantified, e.g., in References [3][4][5][6]. The third point entails a large variety of possible configurations and arrangements, of which one was selected and is subject to the present study: The chosen configuration comprises a conventional tube-and-wing aircraft with two main under-wing engines producing the major portion of the required thrust.…”