# A Power Based Analysis for a Transonic Transport Aircraft Configuration through 3D RANS Simulations
## 1 Introduction  
Boundary layer ingestion (BLI) has been studied as a promising technology that utilizes favorable airframe propulsion integration to reduce aircraft fuel consumption. BLI has been adopted by novel aircraft concepts, such as Boeing blended wing body aircraft [1], silent aircraft [2], MIT D8 aircraft [3, 4], the \"propulsive fuselage\" concept [5], H2020 CENTERLINE aircraft [6], and NASA STARC-ABL aircraft [7, 8]. The benefits due to BLI range from 3% to 10% for these aircraft concepts. The flow mechanisms of power saving due to BLI were recognized and explained by [PERSON] [9] in the early days. The flow mechanisms of BLI have become clear since the introduction of power-based methods, which enabled the quantitative study of the actual power consumptions of aircraft using BLI. [PERSON] [10] introduced a power balance method to evaluate mechanical power in the flow field, showing that the power consumption associated with the aircraft wake and jet is eliminated by BLI, as shown in Figure 1. [PERSON] et al. [11, 12] established an exergy-based method to include thermal power in the study of BLI. [PERSON] et al. [13, 14] utilized a mechanical power analysis to show that a BLI propulsor utilizes the power of the ingested boundary layer flow as input power and reduces the wasted power in the downstream flow. These power-based methods are different from a traditional method that breaks down the aerodynamic force imposed on aircraft surfaces [15]. Power-based methods evaluate the power in the flow field around the aircraft so that the actual power consumption of the aircraft is calculated without ambiguity [16]. Recent efforts were made to inspect the potential benefits of BLI in detailed aircraft design. Computational fluid dynamics (CFD) simulation has been widely used as a tool to design aircraft shapes. Power-based methods are adopted to access the power terms in the flow field in the postprocessing of simulations. [PERSON] et al. [17] performed ananalysis of axisymmetric fuselage-propulsor configurations to evaluate the power savings due to BLI. [PERSON] and [PERSON] [18] employed Reynolds-averaged Navier-Stokes (RANS) simulations to study the potential benefit of BLI with a 2D axisymmetric fuselage geometry. [PERSON] et al. [19] performed 2D CFD simulations to optimize the shape of an axisymmetric fuselage using BLI in transonic flight conditions. Besides the aforementioned studies using 2D simulations, 3D flow simulations are employed in the study of BLI. [PERSON] et al. [20] presented a study to optimize fuselage geometry based on a common 3D research model to evaluate the benefit of BLI. [PERSON] and [PERSON] [21] addressed the flow distortion issue of BLI by optimizing fuselage geometry through 3D RANS simulation. [PERSON] et al. [22] employed 3D RANS analysis to perform the optimization of a coupled aeropropulsive aircraft model with BLI. Previous works using power-based methods combined with CFD simulations were based on a well-defined control volume so that the power terms of the entire flow field could be evaluated [17; 18; 19; 20]. Nevertheless, the simplicity of control volume was not capable of studying the detailed process of power conversion in these previous works. This limitation prevents the investigation of how aircraft components influence the power conversion process. This incapability suggests further development of power-based analysis. To deal with this issue, this study introduces a segregated 3D computational domain aiming to trace the changing process of power terms in the flow field over a typical transonic transport aircraft. With this improved power-based analysis, to the knowledge of the authors, this is the first time that the detailed process of power conversion in a 3D simulated flow field over an aircraft has been examined and visualized.