An aerodynamic shape optimisation capability based on a discrete adjoint solver for Navier- Stokes flows is developed and applied to a Blended Wing-Body future transport aircraft. The optimisation is gradient-based and employs either directly a Sequential Quadratic Programming optimiser or a variable-fidelity optimisation method that combines low- and high-fidelity models. The shape deformations are parameterised using a B´ezier-Bernstein formulation and the structured grid is automatically deformed to represent the design changes. The flow solver at the heart of this optimisation chain is a Reynolds averaged Navier- Stokes code for multiblock structured grids. It uses Osher’s approximate Riemann solver for accurate shock and boundary layer capturing, an implicit temporal discretisation and the algebraic turbulence model of Baldwin-Lomax. The discrete Navier-Stokes adjoint solver based on this CFD code shares the same implicit formulation but has to calculate accurately the flow Jacobian. This implies a linearisation of the Baldwin-Lomax model. The accuracy of the resulting adjoint solver is verified through comparison with finitedifference. The aerodynamic shape optimisation chain is applied to an aerofoil drag minimisation problem. This serves as a test case to try and reduce computing time by simplifying the fidelity of the model. The simplifications investigated include changing the convergence level of the adjoint solver, reducing the grid size and modifying the physical model of the adjoint solver independently or in the entire optimisation process. A feasible optimiser and the use of a penalty function are also tested. The variable-fidelity method proves to be the most ef- ficient formulation so it is employed for the three-dimensional optimisations in addition to parallelisation of the flow and adjoint solvers with OpenMP. A three-dimensional Navier- Stokes optimisation of the ONERA M6 wing is presented. After describing the concept of Blended Wing-Body and the studies carried out on this aircraft, several aerodynamic optimisations are performed on this geometry with the capability developed in this thesis.

An aerodynamic shape optimisation capability based on a discrete adjoint solver for Navier-Stokes flows is developed and applied to a Blended Wing-Body future transport aircraft. The optimisation is gradient-based and employs either directly a Sequential Quadratic Programming optimiser or a variable-fidelity optimisation method that combines low- and high-fidelity models. The shape deformations are parameterised using a B´ezier-Bernstein formulation and the structured grid is automatically deformed to represent the design changes. The flow solver at the heart of this optimisation chain is a Reynolds averaged Navier- Stokes code for multiblock structured grids. It uses Osher’s approximate Riemann solver for accurate shock and boundary layer capturing, an implicit temporal discretisation and the algebraic turbulence model of Baldwin-Lomax. The discrete Navier-Stokes adjoint solver based on this CFD code shares the same implicit formulation but has to calculate accurately the flow Jacobian. This implies a linearisation of the Baldwin-Lomax model. The accuracy of the resulting adjoint solver is verified through comparison with finitedifference. The aerodynamic shape optimisation chain is applied to an aerofoil drag minimisation problem. This serves as a test case to try and reduce computing time by simplifying the fidelity of the model. The simplifications investigated include changing the convergence level of the adjoint solver, reducing the grid size and modifying the physical model of the adjoint solver independently or in the entire optimisation process. A feasible optimiser and the use of a penalty function are also tested. The variable-fidelity method proves to be the most efficient formulation so it is employed for the three-dimensional optimisations in addition to parallelisation of the flow and adjoint solvers with OpenMP. A three-dimensional Navier-Stokes optimisation of the ONERA M6 wing is presented. After describing the concept of Blended Wing-Body and the studies carried out on this aircraft, several aerodynamic optimisations are performed on this geometry with the capability developed in this thesis.

In recent years unconventional aircraft configurations, such as Blended-Wing-Body (BWB) aircraft, are being investigated and researched with the aim to develop more efficient aircraft configurations, in particular for very large transport aircraft that are more efficient and environmentally-friendly. The BWB configuration designates an alternative aircraft configuration where the wing and fuselage are integrated which results essentially in a hybrid flying wing shape. The first example of a BWB design was researched at the Loughead Company in the United States of America in 1917. The Junkers G. 38, the largest land plane in the world at the time, was produced in 1929 for Luft Hansa (present day; Lufthansa). Since 1939 Northrop Aircraft Inc. (USA), currently Northrop Grumman Corporation and the Horten brothers (Germany) investigated and developed BWB aircraft for military purposes. At present, the major aircraft industries and several universities has been researching the BWB concept aircraft for civil and military activities, although the BWB design concept has not been adapted for civil transport yet. The B-2 Spirit, (produced by the Northrop Corporation) has been used in military service since the late 1980s. The BWB design seems to show greater potential for very large passenger transport aircraft. A NASA BWB research team found an 800 passenger BWB concept consumed 27 percent less fuel per passenger per flight operation than an equivalent conventional configuration (Leiebeck 2005). The purpose of this research is to assess the aerodynamic efficiency of a BWB aircraft with respect to a conventional configuration, and to identify design issues that determine the effectiveness of BWB performance as a function of aircraft payload capacity. The approach was undertaken to develop a new conceptual design of a BWB aircraft using Computational Aided Design (CAD) tools and Computational Fluid Dynamics (CFD) software. An existing high-capacity aircraft, the Airbus A380 Contents RMIT University, Australia was modelled, and its aerodynamic characteristics assessed using CFD to enable comparison with the BWB design. The BWB design had to be compatible with airports that took conventional aircraft, meaning a wingspan of not more than 80 meters for what the International Civil Aviation Organisation (ICAO) regulation calls class 7 airports (Amano 2001). From the literature review, five contentions were addressed; i. Is a BWB aircraft design more aerodynamically efficient than a conventional aircraft configuration? ii. How does the BWB compare overall with a conventional design configuration? iii. What is the trade-off between conventional designs and a BWB arrangement? iv. What mission requirements, such as payload and endurance, will a BWB design concept become attractive for? v. What are the practical issues associated with the BWB design that need to be addressed? In an aircraft multidisciplinary design environment, there are two major branches of engineering science; CFD analysis and structural analysis; which is required to commence producing an aircraft. In this research, conceptual BWB designs and CFD simulations were iterated to evaluate the aerodynamic performance of an optimal BWB design, and a theoretical calculation of structural analysis was done based on the CFD results. The following hypothesis was prompted; A BWB configuration has superior in flight performance due to a higher Lift-to-Drag (L/D) ratio, and could improve upon existing conventional aircraft, in the areas of noise emission, fuel consumption and Direct Operation Cost (DOC) on service. However, a BWB configuration needs to employ a new structural system for passenger safety procedures, such as passenger ingress/egress. The research confirmed that the BWB configuration achieves higher aerodynamic performance with an achievement of the current airport compatibility issue. The beneficial results of the BWB design were that the parasite drag was decreased and the spanwise body as a whole can generate lift. In a BWB design environment, several advanced computational techniques were required to compute a CFD simulation with the CAD model using pre-processing and CFD software.

The focus of this thesis is to analyse the flight characteristics of the blended wingbody (BWB) unmanned aerial vehicle (UAV) Green Raven currently being developed by students at the Royal Institute of Technology (KTH) in Stockholm,Sweden. The purpose of evaluating a BWB aircraft is due to its potential increasein fuel efficiency and payload compared to conventional aircrafts which would enable more sustainable flights. The analysis is conducted in ANSYS Fluent 2020R2 where the goals are to extrapolate lift, drag and pitching moment coefficients,aerodynamic efficiency and evaluate stall patterns. The analysis is conducted with free stream velocities from 5 m/s to 40 m/s with5 m/s increments at angles of attack from −4◦ to stall plus 4◦. The result of thisthesis is that an analysis have not been able to be conducted due to a lack ofcomputational power. Thusly, the conclusion to this thesis is that to be able toperform a complete analysis of the Green Raven, a more powerful computer needsto be used.

The student inclusive Green Raven project of the KTH-Aero faculty requireda small blended wing model of their new flying wing design. The small scalemodel will be used for various flight tests. The goal of this specific project was tocreate an internal structure for the small scale model, including an outer shell.Two-dimensional drawings were created and tested in a simulation software.The model was then drawn in cad. Lastly the wing was strength tested inAnsys mechanical. The beams in the structure are made of Scots pine due toits accessibility and good strength to weight ratio. The outer shell is made outof fiberglass. A quick connection between the wing and the main body wasimplemented for easy transportation. All final testing indicate that the finaldesign had sufficient strength regarding the initial load requirements.

The work summarized in this report aims to investigate how a drone airplane design can be optimized to create a safer and more efficient sea rescue by providing staff with an early picture, performing search missions and aiding communication through visual contact. A flying wing is in theory one of the most efficient designs for a fixed wing aircraft, at the same time as it also offers high structural efficiency for its given size. In this report, an overview of aerodynamics, stability and flying quality for a flying wing is discussed and analysed. XFLR5 was used for this project, and a comparison between the analytical results and wind tunnel test data for a prototype was conducted. A strong correlation was found between the theoretical analyses and the wind tunnel data. A simple control solution using only one set of elevons has been proposed and simulated, resulting in Level 1 dynamic stability for all modes except Dutch-roll (where the drone’s damping is 𝜁𝑑𝑟=0.07 and the requirement for Level 1 is 𝜁𝑑𝑟=0.08). For the range of angle of attack used, the autopilot system will have to trim the drone in flight to achieve stability. As the drone only has one set of control surfaces there will be a loss of efficiency in this scenario, meaning that 𝐶𝐿/𝐶𝐷 = 15.7 for loiter speed of 15 𝑚/𝑠 and 7.9 for full speed at 35 𝑚/𝑠. In regular flight, with a total mass <1 𝑘𝑔, the drone is able to fly at full speed for 214 𝑘𝑚 or loiter for 6.3 ℎ with a battery package of 130 𝑊ℎ. As such, the objective of this project was achieved, and the proposed design met the given requirements. / betet som sammanfattas i denna rapport syftar till att undersöka huruvida ett drönar-flygplan bäst kan utformas för att skapa en säkrare och effektivare sjöräddning genom att ge räddningspersonalen en tidig överblick, utföra sökuppdrag och bistå till kommunikation genom visuell kontakt. En flygande vinge är i teorin en av de mest effektiva konstruktionerna för ett flygplan, likaså erbjuder den en hög strukturell effektivitet för en given storlek. I denna rapport diskuteras och genomförs en översikt över aerodynamik, stabilitet och flygkvalitet hos en flygande vinge. XFLR5 användes för detta projekt, och en jämförelse mellan analysresultaten och ett vindtunneltest med en prototyp genomfördes. I allmänhet är överenskommelsen mellan de teoretiska analyserna och vindtunneldatan god. En enkel lösning som enbart består av en uppsättning kontrollytor har föreslagits och simulerats, vilket resulterar i en Nivå 1 dynamisk stabilitet för alla lägen utom Dutch-roll, där drönarens dämpning är 𝜁𝑑𝑟 = 0.07 och kravet för Nivå 1 är 𝜁𝑑𝑟 = 0.08. Autopilotsystemet behöver trimma drönaren under flygning för att uppnå nödvändig stabilitet för det spann av attackvinklar som används, med endast en uppsättning kontrollytor, vilket minskar effektiviteten för BWB-drönaren till 𝐶𝐿/𝐶𝐷=15.7 för cirkuleringshastigheten på 15 𝑚/𝑠 och 7.9 för full hastighet vid 35 𝑚/𝑠. Drönaren kan flyga i full hastighet i 214 𝑘𝑚 eller cirkulera runt olycksplatsen under 6.3 timmar med ett batteripaket på 130 𝑊ℎ, med en vikt som är lägre än 1 𝑘𝑔. Målen med detta projekt uppnåddes och drönaren utformades enligt kraven.