00260 AN AUTOMATED APPROACH FOR THE AERODYNAMIC DESIGN OF CLOSE- COUPLED PROPULSION/AIRFRAME CONFIGURATIONS Jesús Matesanz-García (1), Robert Christie (2), Fernando Tejero(3), David MacManus(4), and Alexander Heidebrecht (5) (1)Cranfield University Propulsion Engineering Centre, Cranfield, Bedfordshire, UK. Email: Jesus.Matesanz- [email protected], (2)(3)(4)(5) Cranfield University Propulsion Engineering Centre, Cranfield, Bedfordshire, UK. KEYWORDS: Novel aircraft configurations, propulsive efficiency, the application of boundary layer ingestion, propulsive fuselage, aerodynamic improvements to reduce the overall aerodynamic performance, Class Shape aircraft drag, or the reduction of the total weight of Transformations, CFD, Design Space Exploration, the system. Within this context, different novel multi-objective optimizations, genetic algorithm aircraft propulsion configurations have been proposed [2 4]. A common feature of many of these ABSTRACT: – novel configurations is the closer integration of the Reducing aircraft emissions is a key element in propulsive system with the aircraft airframe. Hence, mitigating the environmental impact of aviation. an increase of the aerodynamic coupling is Within this context, different novel aircraft expected for these novel configurations. To assess propulsion configurations have been proposed. A the viability of these novel integrated propulsive common feature of many of these novel systems it is vital to evaluate the effect of the configurations is the closer integration of the propulsion-airframe interactions on the propulsive system and the aircraft airframe with an aerodynamic performance of the installation. expected increase of the aerodynamic coupling. Traditionally, the different elements of the Therefore, is necessary to assess the performance aerodynamic installation of the propulsive system of the aerodynamic installation of the propulsive (intake, nacelle and exhaust) have been analysed system of these configurations with a systematic and designed separately [5 7]. However, the closer approach. – coupling between the airframe and the propulsive A systematic and automated methodology for the system of the novel configurations requires the design and performance evaluation of embedded analysis of the installation as whole. Thus, it is propulsion systems is defined. This methodology is necessary to evaluate the effect of the interaction of demonstrated with a Boundary Layer Ingestion the different elements of the installation and with the propulsive fuselage concept. This approach covers airframe for each of the novel configurations. To the geometry design of the selected configuration, develop the highly integrated concepts it is essential an automatic aerodynamic numerical computation to study the requirements of the future installation and a novel performance evaluation for the design. architectures. Intake, nacelle and exhaust A Design Space Exploration was performed to characteristics must be studied to determine the characterize the relative importance of the individual impact on the aerodynamic performance of the parameters of the geometry and their correlation novel aircraft configurations. with the key performance metrics. Finally, a multi- As a consequence of the closer integration of the objective optimization was carried to demonstrate propulsion system, an increased level of intake the capabilities of this approach. distortion is expected. Accordingly, previous 1. INTRODUCTION research on installation aerodynamics has mainly focused on intake design. Optimization of the intake 1.1. Background has been investigated for highly integrated intakes Reducing aircraft emissions is seen as a key for Blended Wing Body configurations by Rodríguez element in mitigating the environmental impact of [8] and Kim et al. [9]. Similarly, Kenway et al. [10] aviation. National governments and international optimized a STARC-ABL BLI propulsor intake for agencies have committed to reduce the net aviation minimum distortion. Some numerical studies have CO2 emissions by 50% for the year 2050, based on been carried out for the full installation of different 2005 levels [1]. This reduction of the emissions can configurations such as the STARC-ABL [11]. be partially achieved by the increase of the Nevertheless, there is a lack of work on the effect of 1 the nacelle and exhaust design, and the interaction methodology is required that can assess the intake, of the whole installation. A direct effect of the strong nacelle and exhaust aerodynamics for these new coupling between the airframe and the propulsion close coupled configurations. This is the main aim system is that the conventional performance of the current work. analysis methodologies could no longer be The potential benefits of BLI configurations have applying. Consequently, it is necessary to revise the been addressed by Smith [19], Felder et al. [12], methodologies for the requirements of the novel Hall et al. [17], Blumenthal et al. [20], and Uranga et systems. This challenge requires the application of al. [18]. Most of the work focused on the potential a novel systematic approach for the design and performance and power saving benefit of the BLI analysis of the configurations for different flight configurations. However, besides the intake conditions. This includes aspects such as the performance analysis, the importance of the design of an integrated intake, cowl and exhaust aerodynamic installation of the full propulsive system. It is essential to develop a methodology to system has been neglected. Nacelle and exhaust evaluate the effect of the aerodynamic installation design can have a fundamental effect on the overall on the performance of the propulsive system of system aerodynamic performance. Additionally, the these new configurations. highly embedded configurations need to minimize 1.2. Aircraft configuration the intake distortion without penalising the aerodynamic performance of the propulsor. Thus, a The growing number of novel aircraft concepts with multi objective approach is required for the study of different characteristics complicates the the aerodynamic installation performance. development of a common approach. Therefore, it is necessary to bound the configurations into groups As a case study for the installation aerodynamic with similar characteristics and target each of them design, a fuselage based BLI system similar to with a consistent methodology. The main relevant previous studies [11,14,15]. This concept is based novel technologies proposed to date can be broadly on an annular propulsor positioned on the fuselage divided into two groups. The first group comprises aft section. For the study, a 2D axisymmetric model disruptive aircraft layout systems. In this group are of the BLI propulsor is implemented on a medium- airframe concepts such as the Blended Wing Body sized single-aisle aircraft. [8,12]. The second group comprises concepts that 1.3. Scope of this work keep the conventional tube and wing configuration [10,11,13–15]. The second group is of particular The aim of this work is to demonstrate a interest, because some of the novel characteristics methodology for the design of the propulsion proposed could be applied to existing aircraft system installation and airframe integration for designs without a redesign of the full airframe. close-coupled configurations. Therefore, a Therefore, it is of interest to provide an assessment systematic automated approach has been of the performance of this group of configurations developed for the geometry generation, CFD and to investigate the potential benefits and modelling and aerodynamic performance limitations. evaluation. This methodology is designed to provide an appropriate environment to perform Design Within both groups, a common concept is the Space Explorations (DSE) and optimizations. The Boundary Layer Ingestion (BLI) [11,13,16]. The development of this approach was based on the main idea behind these configurations is the following stages: improvement of the aerodynamic performance of the aircraft by ingesting a fraction of the airframe 1. Revision of the aerodynamic performance boundary layer with a propulsion system and filling evaluation method for the novel concepts with the jet the momentum deficit of the wake of the 2. Development of a geometry design aircraft [17–19]. methodology for the aerodynamic installation of a BLI propulsive fuselage The main challenge on the design of these new configuration. The methodology will be configurations is the change of the conventional based on the use of Class Shape location of the propulsion system in favour of a Transformations (CST) [5,21 23] closer integration with the airframe. Highly – 3. Generation of an automated CFD integrated positions closer to the fuselage are methodology for the axisymmetric designs preferred to reduce its drag contribution. However, 4. Design Space Exploration (DSE) for a the installation design must reduce the penalties particular propulsor installation location from the embedded system such as the additional 5. Optimization methodology development drag generation or the increase in distortion levels applying a genetic algorithm at the fan face. Consequently, a new design 2 2. Thrust-drag bookkeeping and performance (1) evaluation 휙 푝푟푒 = −퐹 퐺0 + 퐹 퐹,퐹 + 휃퐼푛푡푎푘푒 + 휃푓푢푠 (2) 2.1. Thrust and drag bookkeeping ∗ 퐷 = 휙푝푟푒 + 휙푛푎푐 (3) Drela [24] proposed the Power Balance Method ∗ which has been used to evaluate the performance 퐺푃 퐹 = 퐹 푂퐺푉 − 휃 푛표푧푧푙푒,푢푝 − 휃푛표푧푧푙푒,푑표푤푛