Aircraft Aerodynamic Design Research Articles

Dissipation and time step scaling strategies for low and high Mach number flows

Aircraft aerodynamic design often involves evaluating flow conditions that span low subsonic to transonic or even supersonic Mach numbers. Compressible flow solvers are a natural choice for such design problems, but these solvers suffer from reduced accuracy and efficiency at low Mach numbers. In addition, simulations with supersonic conditions can be challenging to converge because of large gradients in the flow field. This paper presents three contributions to address these issues in the context of an approximate Newton–Krylov solver for the Reynolds-averaged Navier–Stokes equations. First, we propose a method for scaling the artificial dissipation terms in the Jameson–Schmidt–Turkel scheme to improve its accuracy at low Mach numbers while retaining the simplicity of the original scalar dissipation formulation. Second, we show that characteristic time-stepping combined with an approximate Newton method can accelerate convergence for low Mach number flows by reducing the stiffness in the linear system for each Newton iteration. Third, we introduce a dissipation-based continuation method for flows with shocks that improves robustness and accelerates convergence without sacrificing accuracy. These methods can make compressible flow solvers more accurate and efficient across low and high Mach number regimes.

Wall-Modeled Large-Eddy Simulation with Second-Order-Accurate Upwind Scheme

In aircraft aerodynamic design, it is essential for certification by analysis to estimate aircraft aerodynamic characteristics with high fidelity across the full flight envelope using computational fluid dynamics. Improving accuracy of the simulation of unsteady flows such as transonic buffet is one of the problems. Wall-modeled large-eddy simulation (WMLES) is expected to improve the accuracy. In this study, three quantitative requirements for the matching points, where LES feeds the wall model with flow variables, are proposed to ensure the accuracy of the WMLES with a second-order-accurate upwind scheme that is often used for engineering codes. These requirements are related to 1) matching point height, 2) the number of cells below the matching point, and 3) grid resolution at the matching point. The proposed requirements are assessed on a flat-plate turbulent boundary layer and a shock/turbulent boundary-layer interaction flow. As a result, it is clarified that all of the requirements are necessary to ensure the accuracy in terms of mean velocity, Reynolds stresses, and skin friction.

2D Numerical Study on the Flow Mechanisms of Boundary Layer Ingestion through Power-Based Analysis

This paper aims to establish an approach of power bookkeeping in a numerical study. To study the process of power conversion coursed in the flow field, the methodology employs a power-based analysis to quantify power terms. This approach is examined in a simulation of jet flow and then applied to the cases of an isolated actuator disc and an isolated flat plate. Eventually, a numerical simulation is carried out for the boundary layer ingestion (BLI) case that integrates the flat plate and a wake-filling actuator disc. This study quantitatively discusses the mechanisms of BLI under the conditions of laminar and turbulent flow. The proposed power-based analysis might offer insights for the aircraft aerodynamic design using favorable airframe propulsion integration.

Design and Research on the Hinged Cover of the Fuselage of Civil Aircraft

Due to the complexity of aircraft interior system, some systems need to design components installed in the fuselage, which will open in the fuselage on the formation, at the same time as the aircraft aerodynamic design requirements, the system must be in the form of the opening cover is closed, so in the design of the fuselage flap design system is particularly important. This paper mainly introduces a hinged cover in common design points and design points of cap shape.

A Blended Continuation Method for Solving Steady Inviscid Flow

Steady flow field solving is wieldly used in aircraft aerodynamic design, efficiency of steady flow field solving has great influnence on efficiency of aircraft aerodynamic design. A continuation method that blended Laplacian operator and pseudo time marching method for solving steady inviscid flow problem is proposed. In steady flow problem, the field is usually initialized as an uniform field before starting iteration. This resulted in the fact that the initial residual in only nonzero on wall boundary. Based on this feature, Laplacian operator is introduced to accelarate convergence at the starting stage of nonlinear solving. At the ending stage of nonlinear solving, the blended continuation term is biased to pseduo time marching method to avoid over dissipation graduately. To establish a complete continuation method, the starting, evolution and termination method are also described. At last, the proposed continuation method is implemented in a finite element solver, and tested aginst GAMM channel and NACA0012 foil subsonic and transonic cases. Numerical test results confirmed that the blended continuation method could get an efficency improvement about 1/3 to 1/4 comparing with stand alone Laplacian continuation and much more better than pure pseudo time marching method.

Analytic determination of tandem-scheme aircraft aerodynamic characteristics

In present article analytic method of downwash after wing, lift coefficient and pitching moment coefficient determination for tandem-scheme aircraft was upgraded. Mathematical model is based on Bio-Savart formula and avoid approximate calculus of indefinite integrals in contrast to classical theory. Instead of it new approach consists on numerical computing of definite integrals with high accuracy (error less than 10­-5 was achieved). Method is appropriate for low Mach number and for any Reynolds number. Theoretical results calculated according to proposed method were compared with wind tunnel experiment data and showed good agreement.Developed mathematical model allows optimization of tandem-scheme aircraft aerodynamic design with different objective function. In the next works method will be expanded on the lateral aerodynamic characteristics.

Aerodynamic analysis of a light aircraft at different design stages

During the evolution of an airplane aerodynamic design, proper calculation methods and software tools should be utilized, which correspond to the airplane category and project development level. In case of light aircraft, the general trend is the application of analytical and semiempirical methods at the initial stages, combined with simplified - inviscid CFD computational models, and fairly complex viscous CFD analyses at higher design levels. At the present stage of light aviation development, it is assumed that the contemporary design tools for each of those steps should be appropriate enough, so that they actually verify and additionally fine-tune each other's results. This paper describes the calculation tools and methods applied during the aerodynamic analyses of a new light aircraft at different development stages, and compares the results obtained by them, with the aim to verify and support the above statement, considering light aircraft aerodynamic design.

An industrial view on numerical simulation for aircraft aerodynamic design

In Airbus view, one major objective for the aircraft industry is the reduction of aircraft development lead-time and the provision of robust solutions with highly improved quality. In that context it is important to exploit all opportunities provided by enhanced or new classes of numerical simulation tools, e.g. high fidelity multi-disciplinary Computational Fluid Dynamics (CFD) and powerful High Performance Computing (HPC) capabilities.To help meet the challenge of superior product development it will finally be essential to numerically ‘flight-test’ a virtual aircraft with all its multi-disciplinary interactions in a computer environment and to compile all of the data required for the development and certification with guaranteed accuracy in a reduced time frame. Numerical simulation is foreseen to provide a tremendous increase in aircraft design efficiency and quality over the next decades. This concept is considered by Airbus as one of the long term main objectives for aircraft development.Progress in HPC will essentially contribute to achieve this goal. Considerable changes of aircraft design processes and way of working will lead to significant reduction of development times while including more and more disciplines in the early phases of design activities in order to find an overall optimum aircraft design.Aerodynamic Design deals with the development of outer shapes of an aircraft, optimizing for its performance, handling qualities and loads. A major ingredient to the design process is the numerical simulation of the external airflow. The capabilities to predict the flow not only near the design point but also under other challenging conditions in a given flight envelope is a prerequisite for optimization towards market requirements.Since it began about 50 years ago, CFD has made important progress in terms of accuracy of the physical models, robustness and efficiency of the nonlinear solution algorithms and reliability of the overall prediction approach. This trend will continue over the next decades. In our view, along with the increasing capability to model and compute all major multi-disciplinary aspects of an aircraft, in the long term it will become possible to ‘fly’ and investigate the complete aircraft in the computer.Currently numerical simulation provides good means to analyse the flow around the aircraft in detail, although the regime of flow separation onset up to maximum lift conditions is still not modelled accurately enough, nonlinearities and turbulence modelling for separated flows are still a major concern.It was not only the increase in HPC power that made more sophisticated Navier-Stokes solving enter the daily industrial design process. Better understanding and mathematical analysis of the system of Navier-Stokes equations led to more powerful algorithms, to more capable software and more comprehensive analysis of aircraft flows.However, a lot work remains to be done. Next decade’s goal will be to better exploit more accurate and efficient numerical formulations, advanced turbulence models and to achieve a fully flexible and automatic CFD capability that works in a fully adaptive manner, providing the best quality solution at minimum cost and time. This will lead to a complete change in the way future aircraft will be designed.

Aerodynamics of heat exchangers for high-altitude aircraft

Reduction of convective beat transfer with altitude dictates unusually large beat exchangers for piston- engined high-altitude aircraft The relatively large aircraft drag fraction associated with cooling at high altitudes makes the efficient design of the entire heat exchanger installation an essential part of the aircraft's aerodynamic design. The parameters that directly influence cooling drag are developed in the context of high-altitude flight Candidate wing airfoils that incorporate heat exchangers are examined. Such integrated wing-airfoil/heat-exchanger installations appear to be attractive alternatives to isolated heat.exchanger installations. Examples are drawn from integrated installations on existing or planned high-altitude aircraft.