An aerothermodynamic performance analysis is conducted for a supersonic transport propulsion system, evaluating the feasibility of a single-stage and a two-stage fan configuration. The propulsion system is modeled using a parametric approach, incorporating variations in fan pressure ratio, bypass ratio, and high-pressure turbine inlet temperature to assess their impact on cruise and off-design performance. A two-shock external compression intake is assumed. The analysis is performed for a cruise speed of Mach 1.7 at an altitude of 60,000 feet, similar to the cruise conditions proposed for the Boom aircraft. The results demonstrate that the two-stage fan configuration offers superior performance, achieving an 8.5% increase in specific range compared to the single-stage fan while maintaining a reduced fan diameter and lower overall engine mass. The off-design analysis reveals a significant performance penalty associated with the long-proposed idea of boom-less, overland supersonic cruise. A 22% reduction in specific range is predicted when shifting from a Mach 0.95 to Mach 1.2 over land cruise. The off-design analysis further highlights the efficiency advantages of the two-stage fan, with a 3.5% reduction in specific fuel consumption at lower Mach numbers and a broader operational envelope.

Concentrated vortex flows contribute to the aerodynamic performance of aircraft at elevated load conditions. For military interests, the vortex flows are exploited at maneuver conditions of combat aircraft and missiles. For transport interests, the vortex flows are exploited at takeoff and landing conditions as well as at select transonic conditions. Aircraft applications of these vortex flows are reviewed with a historical perspective followed by a discussion of the underlying physics of a concentrated vortex flow. A hierarchy of computational fluid dynamics simulation technology is then presented followed by findings from a capability survey for predicting concentrated vortex flows with computational fluid dynamics. Results are focused on military and civil fixed-wing aircraft; only limited results are included for missiles, and rotary-wing applications are not assessed. Opportunities for predictive capability advancement are then reported with comments related to digital transformation interests. A hierarchical approach that merges a physics-based perspective of the concentrated vortex flows with a systems engineering viewpoint of the air vehicle is also used to frame much of the discussion.

In the early era of aviation, Frederick Lanchester was both an inventor and a theoretician driven by the need for a theory of flight that would reduce the guesswork in designing new aircraft. His book Aerodynamics in 1907 laid down the early foundations of such a theory. The theory with contributions from others, notably Ludwig Prandtl, was refined to become the basis for the sleek designs of WWII aircraft brought about with little guesswork. New technology changed aircraft design radically with the increased speed of jet propulsion reaching into the transonic range with nonlinear aerodynamics. In the late 1940s and early 1950s substantial guesswork returned to aircraft design. The legacy of Lanchester et al., however, lived on with the development of computational fluid dynamics (CFD) that could guide designers through nonlinear transonic effects. This article presents a historical sketch of how CFD developed, illustrated with examples explaining some of the difficulties overcome in the design of the first-generation swept-wing transonic fighters. The historical study is forensic CFD in search for the likely explanation of the designer's choice for the wing shape that went into production a long time ago. The capability of current CFD applied to the aerodynamics of aircraft with slender wings is surveyed. The cases discussed involve flow patterns with coherent vortices over hybrid wings and wings of moderate sweep. Vortex-flow aerodynamics pertains to understanding the interaction of concentrated vortices with aircraft components. Modern Reynolds-Averaged Navier-Stokes (RANS) technology is useful to predict attached flow. But vortex interaction with other vortices and breakdown lead to unsteady, largely separated flow which has been found out of scope for RANS. Direct simulation of the Navier-Stokes equations is out of computational reach in the foreseeable future, and the need for better physical modeling is evident. Both cruise performance and stalling characteristics are influenced by strong interactions. Two important aspects of wing-flow physics are discussed: separation from a smooth surface that creates a vortex, and vortex bursting, the abrupt breakdown of a vortex with a subsequent loss of lift. Vortex aerodynamics of not-so-slender wings encounter particularly challenging problems, and it is shown how the design of early-generation operational aircraft surmounted these difficulties. Through use of forensic CFD, the article concludes with two case studies of aerodynamic design: how the Saab J29A wing maintains control authority near stall, and how the Saab J32 mitigates pitch-up instability at high incidence.

Separated flows often set aerodynamic limits for an aircraft flight envelope, and many of these flows remain difficult to predict with Computational Fluid Dynamics (CFD). This paper reviews and explores how CFD simulations have been used for predicting separated flows, and the associated aerodynamic performance, throughout the flight envelope, giving special focus to military aircraft. The review entails: a summary of the physics of flow separation that is especially difficult to model accurately; an historical sketch of seven decades of CFD developments to meet many of the challenges of separated flow predictions; three case studies for an assessment of the current CFD capabilities; and future prospects for further improvements in the CFD simulations using direct numerical simulations (DNS). DNS can be utilized as a virtual wind tunnel to understand complex separated flow and the results used in modelling improvements for RANS and LES CFD methods. Several examples of the capabilities of DNS methods to predict separated aeronautical flows are given. However, significant advances are still needed for separated flow simulations to become practical with reliability comparable to those of attached flow simulations. A possible path forward for future work to achieve this goal is included.

Recent Unmanned Combat Air Vehicle (UCAV) configurations have not-so-slender wings with moderate leading-edge sweepangles of 45◦ to 60◦. Planforms vary from pure delta to diamond and even lambda more or less blended wing bodies with a relatively small thickness ratio at the inner wing/fuselage region. The performance and low-observable signature considerations require a compromise between a small radar cross-section and lifting surface shapes for long range and sufficient agility. The airflow is governed largely by the progression of vortices shed from the wing leading edge which interact and produce non-linear aerodynamics. Like early swept wing fighters like the Saab 32 the UCAV may exhibit undesirable flying characteristics over part of the envelope with tip stall and pitch-up. Such problems were mitigated by vortex control "devices" like leading edge fences and notches which violate the low observable requirement. The AVT-181 SACCON is a well studied case. We attempt to improve its stalling characteristics by mimicking the leading edge fence action by a configuration of very small vortex generators and study their effect by CFD.

Separated flows often set aerodynamic limits for an aircraft flight envelope, and many of these flows remain difficult to predict with Computational Fluid Dynamics. This paper reviews and explores how CFD simulations have been used for predicting separated flows, and the associated aerodynamic performance, throughout the flight envelope, giving special focus to NATO aircraft. The review entails: a summary of the physics of flow separation that is especially difficult to model numerically; an historical sketch of seven decades of CFD developments to meet many of the challenges of separated flow predictions; six case studies for an assessment of the current CFD capabilities; and future prospects for further improvements in the CFD simulations. Significant advances are still needed for separated flow simulations to become practical with reliabilities comparable to attached flow simulations. Some recommendations for future work are included.

Fluid mechanical aspects of separated and vortical flow in aircraft wing aerodynamics are treated. The focus is on two wing classes: (1) large aspect-ratio wings and (2) small aspect-ratio delta-type wings. Aerodynamic design issues in general are not dealt with. Discrete numerical simulation methods play a progressively larger role in aircraft design and development. Accordingly, in the introduction to the book the different mathematical models are considered, which underlie the aerodynamic computation methods (panel methods, RANS and scale-resolving methods). Special methods are the Euler methods, which as rather inexpensive methods embrace compressibility effects and also permit to describe lifting-wing flow. The concept of the kinematically active and inactive vorticity content of shear layers gives insight into many flow phenomena, but also, with the second break of symmetry---the first one is due to the Kutta condition---an explanation of lifting-wing flow fields. The prerequisite is an extended definition of separation: “flow-off separation” at sharp trailing edges of class (1) wings and at sharp leading edges of class (2) wings. The vorticity-content concept, with a compatibility condition for flow-off separation at sharp edges, permits to understand the properties of the evolving trailing vortex layer and the resulting pair of trailing vortices of class (1) wings. The concept also shows that Euler methods at sharp delta or strake leading edges of class (2) wings can give reliable results. Three main topics are treated: 1) Basic Principles are considered first: Boundary-layer flow, vortex theory, the vorticity content of shear layers, Euler solutions for lifting wings, the Kutta condition in reality and the topology of skin-friction and velocity fields. 2) Unit Problems treat isolated flow phenomena of the two wing classes. Capabilities of panel and Euler methods are investigated. One Unit Problem is the flow past the wing of the NASA Common Research Model. Other Unit Problems concern the lee-side vortex system appearing at the Vortex-Flow Experiment 1 and 2 sharp- and blunt-edged delta configurations, at a delta wing with partly round leading edges, and also at the Blunt Delta Wing at hypersonic speed. 3) Selected Flow Problems of the two wing classes. In short sections practical design problems are discussed. The treatment of flow past fuselages, although desirable, was not possible in the frame of this book.

Purpose The purpose of this paper is to present the status of the on-going development of the new computerized environment for aircraft synthesis and integrated optimization methods (CEASIOM) and to compare results of different aerodynamic tools. The concurrent design of aircraft is an extremely interdisciplinary activity incorporating simultaneous consideration of complex, tightly coupled systems, functions and requirements. The design task is to achieve an optimal integration of all components into an efficient, robust and reliable aircraft with high performance that can be manufactured with low technical and financial risks, and has an affordable life-cycle cost. Design/methodology/approach CEASIOM (www.ceasiom.com) is a framework that integrates discipline-specific tools like computer-aided design, mesh generation, computational fluid dynamics (CFD), stability and control analysis and structural analysis, all for the purpose of aircraft conceptual design. Findings A new CEASIOM version is under development within EU Project AGILE (www.agile-project.eu), by adopting the CPACS XML data-format for representation of all design data pertaining to the aircraft under development. Research limitations/implications Results obtained from different methods have been compared and analyzed. Some differences have been observed; however, they are mainly due to the different physical modelizations that are used by each of these methods. Originality/value This paper summarizes the current status of the development of the new CEASIOM software, in particular for the following modules: CPACS file visualizer and editor CPACSupdater (Matlab) Automatic unstructured (Euler) & hybrid (RANS) mesh generation by sumo Multi-fidelity CFD solvers: Digital Datcom (Empirical), Tornado (VLM), Edge-Euler & SU2-Euler, Edge-RANS & SU2-RANS Data fusion tool: aerodynamic coefficients fusion from variable fidelity CFD tools above to compile complete aero-table for flight analysis and simulation.

Purpose - A collaborative design environment is needed for multidisciplinary design optimization (MDO) process, based on all the modules those for different design/analysis disciplines, and a systematic coupling should be made to carry out aerodynamic shape optimization (ASO), which is an important part of MDO. Design/methodology/approach - Computerized environment for aircraft synthesis and integrated optimization methods (CEASIOM)-ASO is developed based on loosely coupling all the existing modules of CEASIOM by MATLAB scripts. The optimization problem is broken down into small sub-problems, which is called "sequential design approach", allowing the engineer in the loop. Findings - CEASIOM-ASO shows excellent design abilities on the test case of designing a blended wing body flying in transonic speed, with around 45 per cent drag reduction and all the constraints fulfilled. Practical implications - Authors built a complete and systematic technique for aerodynamic wing shape optimization based on the existing computational design framework CEASIOM, from geometry parametrization, meshing to optimization. Originality/value - CEASIOM-ASO provides an optimization technique with loosely coupled modules in CEASIOM design framework, allowing engineer in the loop to follow the "sequential approach" of the design, which is less "myopic" than sticking to gradient-based optimization for the whole process. Meanwhile, it is easily to be parallelized.

This article presents an aeroelastic study of CAWAPI F-16XL aircraft. The structural model of this aircraft is not publicly available and is therefore replaced by a structural model estimate that is constructed based on data available in public literature. The aeroelastic solution is done using solution for two flight conditions-FC70 and FC25. The primary task is to assess the importance of the aeroelastic effects on the FC70 solution and to assess whether large discrepancies are observed at flight condition FC70 between the computational and experimental data.