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Abstract
Following a brief introduction of the development history of the supersonic commercial transport (SCT), the characteristics of several developing supersonic business jets are given. The conceptual design research of the small supersonic commercial transport being served during the period 2020-2035 and their possible configurations and features are described, too. Due to sonic boom reduction being one of the main tasks for developing SCT, some optimal design methods for reducing sonic boom are discussed in detail in the present paper, which are the design method based on linearized theory, sonic boom mitigation method using inverse design of coupling Euler solver (Cart3D) and adjoint method, the approach of advanced sonic boom prediction using augmented Burgers equation, the formulation that boom propagation and CFD are formally coupled for the purpose of obtaining gradients of a ground-based objective with respect to the aircraft shape design variables, as well as the optimization and adjoint-based CFD for the conceptual design of low sonic boom aircraft. ©, 2015, AAAS Press of Chinese Society of Aeronautics and Astronautics. All right reserved.
... 音爆是由飞行器在超声速飞行时产生的激波和膨胀波 系在大气中演化, 传播到地面引起的巨大爆炸声, 是超声 速飞行中特有的一种气动声学现象 [1,2] . 图 1 为音爆产生、 传播和"N"型波形成示意图 [3] . ...
... ONIC boom, which is associated with the propagation and evolution of shock and expansion waves generated by a cruising supersonic aircraft, may weaken the hearing ability of human beings, disturb normal life of creatures, and even damage some buildings. It is one of the core issues that prohibit a civil transport from flying at a supersonic speed over land [1]. For the next-generation environmentally-compatible supersonic transport, the loudness of sonic boom has to be reduced to an acceptable level. ...
An adjoint-based methodology for design optimization of unsteady turbulent flows on dynamic unstructured grids is described. The implementation relies on an existing unsteady three-dimensional unstructured grid solver capable of dynamic mesh simulations and discrete adjoint capabilities previously developed for steady flows. The discrete equations for the primal and adjoint systems are presented for the backward-difference family of time-integration schemes on both static and dynamic grids. The consistency of sensitivity derivatives is established via comparisons with complex-variable computations. The current work is believed to be the first verified implementation of an adjoint-based optimization methodology for the true time-dependent formulation of the Navier-Stokes equations in a practical computational code. Large-scale shape optimizations are demonstrated for turbulent flows over a tiltrotor geometry and a simulated aeroelastic motion of a fighter jet.
A fast frequency domain method for predicting sonic boom propagation was proposed based on classical Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation. Furthermore, the sonic boom properties along the normal direction to the shock front were obtained by augmenting the Mach angle into the equation. To demonstrate the feasibility of the method, the results were compared with the experimental data of the model C presented in NASA TD N-161. The flow field of the supersonic moving vehicle was first calculated by a computational fluid dynamics (CFD) method with different grids. Then, the sonic boom propagation was computed based on the proposed KZK model with the input of the Fourier analysis results from CFD. The prediction results are in good agreement with NASA experimental data. It is also shown that the sonic boom decays rapidly in the near field due to the nonlinearity effects. In the far field, the sonic boom becomes axisymmetric gradually due to the effect of sound diffraction. After long distance propagation, the sound energy is concentrated on low frequency component.
Now one of the most important factors of a successful civil aircraft design is applying computational fluid dynamic (CFD) numerical methods and software, especially the design tools, to the design. In the present paper, historic development and application of the inverse design concept and numerical optimization methods based on low and high fidelity models are described briefly. The International Aerodynamic Optimization Design Computation Workshop, which will be held soon, is introduced. Optimization methods of design based on the Navier-Stokes solver are discussed in detail, including the requirements to them and their construction issues. Numerical examples of OPTIMAS applying to a wing-body fairing shape design and a blended wing body (BWB) shape design have shown the efficiency of OPTIMAS for use as a daily design tool for civil transport design.
High fidelity sonic boom prediction and low sonic boom design methods are key technologies of next generation supersonic aircraft. By coupling a modified SGD (Seebass-George-Darden) method, a high fidelity sonic boom prediction method and a Pareto genetic algorithm, a hybrid optimizing approach is developed. The parameters of the SGD method are optimized and an equivalent area distribution with a lower sonic boom overpressure and large available volume can be obtained. By using the optimized equivalent area distribution, a low boom layout can be designed. A low sonic boom configuration mixed optimizing environment is developed, which integrates sonic boom analysis, perceived loudness analysis, available volume calculation and equivalent area distribution generation. The low sonic boom configuration mixed optimizing environment can be used in the conceptual design phase. The optimized layout is a joint wing configuration with a blunt nose. The sonic boom overpressure decreases by 14.51% and the available volume increases nearly 15.08%. Due to the different strengths of the after shock wave, the relationship between the PLdB and roll angle is complex. The after shock of the sonic boom should be optimized in future work for mitigating PLdB.
High fidelity sonic boom prediction and low sonic boom design method is one of the key technologies of next generation environment-friendly supersonic aircraft which has a direct bearing on the feasibility of commercial operation and operation economics. This paper developes a high fidelity sonic boom prediction method based on computational fluid dynamic (CFD), the wave form parameter method and the MARK-VII method. The design of a quiet spike is studied by using the high fidelity sonic boom prediction method. It is found that the critical length of the quiet spike is important. If the length of a quiet spike is shorter than its critical length, the shock wave of the spike will coalesce with the nose shock, which can lead to invalidation of the quiet spike. On the other hand, if the length of the spike is longer than the critical length, the sonic boom will increase too. The critical length of a quiet spike varies with the flight altitude and flight Mach number; therefore the length of a quiet spike changes with flight condition. Multi-order quiet spikes can produce multi-weak shocks to replace the strong nose shock, which can suppress the sonic boom level more effectively. At the same time, the length of each order of spike should be equal to the critical length. Different nose shapes of a quiet spike can produce different detached shocks and shock detachment distances, which can lead to different drag coefficients and temperatures. But the influence of nose shape on far field sonic boom is not obvious. The sonic boom of the quiet spike layout is lower than the original layout, but the drag coefficient is slightly increased.
High fidelity sonic boom prediction method is developed based on near field CFD method and far field waveform parameter method. The structured/unstructured hybrid grid is set up to use both advantages for more accurate and efficient sonic boom prediction. And then the optimization method is constructed by coupling high fidelity sonic boom prediction method, response surface model and Pareto genetic algorithm. It can be found that nacelle has significant influence in sonic boom level and aerodynamic performance. The location of nacelle is optimized by using the sonic boom and aerodynamic optimization method. The design results indicate that response surface model can satisfy the requirement of precision. Three optimized layouts are chosen by different preferences in Pareto front. Through optimization, the sonic boom level and aerodynamic performance are improved.
Sonic boom has become the most critical technology limiting civil aircraft's supersonic flight over land. To realize sonic boom reduction for supersonic aircraft, thus making supersonic flight over land available, will bring a huge potential market. Based on the SGD (Seebass-George-Darden) method, a procedure involving inverse design has been set up, which allows for complete analysis of lower sonic boom and aerodynamic performance. A "shuttle" configuration is developed for the first time. The results reveal that the proposed "shuttle" configuration achieves a better balance between the design demands of lower sonic boom and aerodynamic performance. Both balanced deployment of lifting surface along the longitudinal direction of the fuselage and double S-shaped design of the front body can contribute to the sonic boom reduction, providing a useful reference for designing next-generation high-speed civil transport with low sonic boom.
There have been many attempts to reduce or eliminate the sonic boom. Such attempts fall into two categories: (1) aerodynamic minimization and (2) exotic configurations. In the first category changes in the entropy and the Bernoulli constant are neglected and equivalent body shapes required to minimize the overpressure, the shock pressure rise and the impulse are deduced. These results include the beneficial effects of atmospheric stratification. In the second category, the effective length of the aircraft is increased or its base area decreased by modifying the Bernoulli constant a significant fraction of the flow past the aircraft. A figure of merit is introduced which makes it possible to judge the effectiveness of the latter schemes.
This paper introduces a tool for boom optimization using smoothest shape modifications. This, tool allows interactive inverse design optimization to develop a fuselage shape that yields a low-boom aircraft configuration. A fundamental reason for developing this boom optimization tool is the need to generate feasible low-boom conceptual designs that are appropriate for further refinement using computational-fluid-dynamics-based preliminary design methods. The boom optimization tool was not developed to provide a numerical solution to the inverse design problem. Instead, it was intended to help designers find the right configuration among an infinite number of possible configurations that are equally good using any numerical figure of merit. This boom optimization tool uses the smoothest shape modification strategy for modifying the fuselage radius distribution at 100 or more longitudinal locations to find a smooth fuselage shape, which reduces the discrepancies between the design and target equivalent area distributions over any specified range of effective distance. For any given supersonic concept (with wing, fuselage, nacelles, tails, and/or canards), a designer can examine the differences between the design and target equivalent areas, decide which part of the design equivalent area curve needs to be modified, choose a desirable rate for the reduction of the discrepancies over the specified range, and select a parameter for smoothness control of the fuselage shape. The boom optimization tool will then generate a fuselage shape based on the designer's inputs in a matter of seconds'. Using this tool, within a few hours, a designer can either generate a realistic fuselage shape that yields a supersonic configuration with a low-boom ground signature or quickly eliminate any configuration that cannot achieve low-boom characteristics with fuselage shaping alone. A conceptual design case study is documented to demonstrate how this boom optimization tool can be used to develop a low-boom supersonic concept from a low-drag supersonic concept. The paper also contains a study on how perturbations in the equivalent area distribution affect the ground signature shape and how new target area distributions for low-boom signatures can be constructed using superposition of equivalent area distributions derived from the Seebass-George-Darden theory.
The development of a new sonic boom prediction methodology is discussed. By solving Burgers' equation, the new method is able to predict accurately the thickness of the shock waves in a boom signal, resulting in a smoothly varying, continuous signal. The resultant signal allows for spectral analysis and the calculation of sonic boom noise metrics. The effects of aircraft maneuvers and accelerations, as well as signal propagation through a real, stratified, windy atmosphere are taken into account through a ray tracing approach. The new method is efficient and accurate, making it a useful tool in the development of supersonic cruise aircraft.
An improved approach for conceptual supersonic aircraft design is developed and presented. The proposed approach consists of two basic elements: 1) geometry parameterization and discretization, and 2) improved linearized analyses. The geometry generation and discretization scheme creates arbitrarily refined, unstructured geometries quickly and efficiently. Improved linearized tools allow geometric effects to be better captured than existing linearized analysis. The geometry generation and improved linear analyses are coupled to a shape optimization procedure to obtain the geometric shape parameters that simultaneously optimize sonic boom intensity on the ground and lift to drag ratio. Results of this preliminary optimization are presented and discussed.
Civil aviation progress in the last 40 years has included a significant expansion of the small civil aircraft market involving regional jets, business jets, and the emerging personal jets. A significant factor in the growth of the small civil aircraft market is the value of time. Recognition of the ever-increasing value of time has lead to increased interest in the feasibility of a small supersonic civil aircraft. The step to supersonic speeds offers the potential of a dramatic decrease in travel time. Feasibility studies of a small quiet supersonic jet (QSJ) have been conducted. Market research, environmental concerns, program and design requirements, and vehicle characteristics are summarized. Areas for concentrated future supersonic aeronautics research and development efforts are highlighted.
A cut-cell approach to computational fluid dynamics that uses the median dual of a tetrahedral background grid is described. The discrete adjoint is also calculated for an adaptive method to control error in a specified Output. The adaptive method is applied to sonic boom prediction by specifying an integral of offbody pressure signature as the output. These predicted signatures are compared to wind-tunnel measurements to validate the method for sonic boom prediction. Accurate midfield sonic boom pressure signatures are calculated with the Euler equations without the use of hybrid grid or signature propagation methods. Highly refined, shock-aligned anisotropic grids are produced by this method from coarse isotropic grids created without prior knowledge of shock locations. A heuristic reconstruction limiter provides stable flow and adjoint solution schemes while producing similar signatures to Barth-Jespersen and Venkatakrishnan limiters. The use of cut cells with an output-based adaptive scheme automates the volume grid generation task after a triangular mesh is generated for the cut surface.
An exploratory study is performed to investigate the use of a time-dependent discrete
adjoint methodology for design optimization of a high-lift wing configuration augmented
with an active flow control system. The location and blowing parameters associated with a
series of jet actuation orifices are used as design variables. In addition, a geometric
parameterization scheme is developed to provide a compact set of design variables
describing the wing shape. The scaling of the implementation is studied using several
thousand processors and it is found that asynchronous file operations can greatly improve
the overall performance of the approach in such massively parallel environments. Three
design examples are presented which seek to maximize the mean value of the lift
coefficient for the coupled system, and results demonstrate improvements as high as 27%
relative to the lift obtained with non-optimized actuation. This lift gain is more than
three times the incremental lift provided by the non-optimized actuation.
We present a new approach for the computation of shape sensitivities using the discrete adjoint and flow-sensitivity methods on Cartesian meshes with general polyhedral cells (cut-cells) at the wall boundaries. By directly linearizing geometric constructors of the cut-cells, an efficient and robust computation of shape sensitivities is achieved for problems governed by the Euler equations. The accuracy of the linearization is verified by the use of a model problem with an exact solution. Verification studies show that the convergence rate of gradients is second-order for design variables that do not alter the boundary shape, and is reduced to first-order for shape design problems. The approach is applied to several three-dimensional problems, including inverse design and shape optimization of a re-entry capsule in hypersonic flow. The results show that reliable approximations of the gradient are obtained in all cases. The approach is well-suited for geometry control via computer-aided design, and is especially effective for conceptual design studies with complex geometry where fast turn-around time is required.
The NASA Tetrahedral Unstructured Software System (TetrUSS) was developed during the 1990's to provide a rapid aerodynamic analysis and design capability to applied aerodynamicists. The system is comprised of loosely integrated, user-friendly software that enables the application of advanced Euler and Navier-Stokes tetrahedral finite volume technology to complex aerodynamic problems. TetrUSS has matured well because of the generous feedback from many willing users representing a broad cross-section of background and skill levels. This paper presents an overview of the current capabilities of the TetrUSS system along with some representative results from selected applications.
This paper presents new lower bounds for sonic booms based on minimizing either the overpressure or the shock strength of the positive part of the boom wave. The results are not restricted to the limit of large distance from the aircraft. They reduce to the Jones lower bound infinitely far from the aircraft in a uniform atmosphere but they give reductions from the Jones lower bound of the order of 50% for planned supersonic transport conditions. This is because the asymptotic results of Jones are approached very slowly (as r^-1/4) in a uniform atmosphere and are never reached in the real atmosphere. The direct application of these results depends upon additionally keeping the tail shock intensity less than or equal to that of the front shock. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.
Sonic boom minimization including front and rear shocks, exemplified by SST aircraft
Simple method for determining sonic boom waveshapes and amplitudes in a still stratified atmosphere is presented. The effects of acoustic impedance, ray tube area, and nonlinear wave steepening and shock formation are each treated separately. By restricting consideration to the waves directly below an aircraft in steady flight, it is possible to present all the information needed to calculate wave shapes and amplitudes without use of a computer. The results for the U S Standard Atmosphere are presented and compared to those calculated for various model atmospheres and to the results of various approximations.
Sonic boom theory for steady flight in atmosphere without winds, discussing sonic boom reduction by aerodynamic means