Methodology to assess the performance of an aircraft concept with distributed propulsion and boundary layer ingestion using a parametric approach

Abstract

The performance benefits of boundary layer ingestion in aircraft with distributed propulsion have been extensively studied in the past. These studies have indicated that propulsion system integration issues such as distortion and intake pressure losses could mitigate the expected benefits. This paper introduces and develops a methodology that enables the assessment of different propulsion system designs, which are optimized to be less sensitive to the effects of the aforementioned issues. The study models the propulsor array and main engine performance at design point using a parametric approach, and further at component level, the study focuses on identifying optimum propulsor configurations, in terms of propulsor pressure ratio and BL capture sheet height. At a system level, the study assesses the effects of splitting the thrust between the propulsor array and main engines. The figure of merit used in the optimization is the TSFC. The suitability of the concepts is further assessed using performance predictions for HTS electrical motors. For the purpose of this study, the NASA N3-X aircraft concept is selected as baseline configuration, where the different propulsion designs are tested. As the study focuses on performance assessment of the propulsion system, sizing implication issues and aircraft performance installations effects have not been included in the analysis. The results from the parametric analysis corroborated previous studies regarding the high sensitivity of the propulsion system performance to intake losses and BL inlet conditions. As the study found low-power consumption configurations at these operating conditions, this may be considered as a major issue. The system analysis from the study indicated that splitting the thrust between propulsors and main engines results in improved system efficiency with beneficial effects in fuel savings. When a 2% increase in intake pressure losses and a similar reduction in fan efficiency were assumed due to boundary layer ingestion, the study found an optimum configuration with 65% of thrust delivered by the propulsor array. To summarize, the present work built on past research further contributes to the field through the inclusion of the thrust split as a key variable in the propulsion system design. The thrust split, when introduced, enabled reduction of the detrimental effects of intake losses on the overall system performance. Additionally, as it reduces the power required for the propulsor array, it is expected to reduce the operating power of HTS and cooling systems and therefore improve the effectiveness of the concept.

Design Point Analysis of an Hybrid Fuel Cell Gas Turbine Cycle for Advanced Distributed Propulsion Systems

“…3,8 However, these benefits can be achieved only with small levels of distortion, as increased inlet flow distortion dramatically reduces fan efficiency and mitigates the benefits as observed in chapter. 28 This issue is also aggravated by the associated intake pressure losses and electric equipment efficiencies.…”

Innovative Propulsion Systems and CFD Simulation for Fixed Wings UAVs

“…The concept of thrust split has been well explored in many different manned aerial concepts, such as the N3-X [1,6] and Cranfield [3,16,17]. This technology, for manned concepts, which presents distributed propulsion, was observed as a way of enhancing propulsive efficiency and fuel consumption, while reducing the high transmission losses (electrical transmission systems) and integration aerodynamic effects between propulsion and airframe [10].…”

“…The latter variable enables to calculate the fan diameter through mass conservation and the fan power based on the isentropic thermodynamic relations for incompressible flow. This process is further explained in [3] In Figure 3(a), the total power remains the same, as it is assumed that the aircraft drag remains constant (this assumption, however, will depend on the distributed propulsion array); furthermore, for the calculation of the propulsor power, it is assumed that the flow entering the distributed propulsors presents the same velocity for all the propulsors. In Figure 3(a),i ti s observed how the power required per fan reduces as more fans are implemented in the distributed arrangement and additionally shows the benefit of working with low fan pressure ratios.…”

“…Recently, the growing environmental awareness has again motivated initiatives for the search of more efficient propulsion systems. Numerous renowned institutions [1][2][3] have taken the leap to study concepts with distributed propulsion and observed an achievable 8% benefit in terms of thrust specific fuel consumption (TSFC) compared with today's aircraft [2]. However, for civil aviation, the implementation of this technology is still a challenge, due to mechanical design constraints and safety issues.…”

“…where F DP is the thrust delivered by the propulsor array and F N is the net intrinsic net thrust [3].…”