Aerodynamic Constraints Research Articles

Flatness-based path planning for fixed-wing UAVs in tight formation under synergistic aerodynamic constraints

Flatness-based path planning for fixed-wing UAVs in tight formation under synergistic aerodynamic constraints

Longitudinal dynamic envelope solution and transition path optimization based on reachability analysis for fixed-wing VTOL UAVs

Flight velocity and tilt angle are commonly employed to define the safe region for fixed-wing vertical take-off and landing (FW-VTOL) UAVs as they undergo tilting, referred to as the transition corridor. Nevertheless, the transition corridor only considers the aircraft's limitations in a quasi-stationary condition and ignores the additional constraints introduced by the aircraft's kinematic behavior. To obtain a more accurate safe state space, the concept of the dynamic envelope was proposed by previous researchers. The dynamic envelope of UAV represents the safe state space taking into account aerodynamic constraints and kinematic constraints. Solving the dynamic envelope has consistently remained a focal point of research in the field. This study introduces an innovative approach that employs reachability analysis to solve the dynamic envelope of the FW-VTOL UAV during the transition stage. Building upon this, it proposes a safety index for the transition path, optimized to determine the safest transition path. Subsequently, specific case studies verified the effectiveness of the solution process and optimization method. The designed optimal path enhances safety by 9.71% compared to the basic path, signifying its practical significance in mitigating risk during the transition stage of FW-VTOL UAVs. Furthermore, the attributes of the transition path are analyzed based on two aspects: (A) a comparison between the optimal transition path and the two-dimensional transition path with a constant angle of attack; (B) an examination of how key UAV design parameters influence the transition path's safety. Overall, the methodology and general rules proposed in this study provide a theoretical basis and technical support for improving the security of FW-VTOL UAVs in the transition stage.

Real-time optimization control of variable rotor speed based on Helicopter/ turboshaft engine on-board composite system

In order to adequately leverage the advantages of coaxial compound helicopters (CCH) to enhance overall performance and efficiency through variable rotor speed, and to improve the fuel economy of the composite propulsion system, a real-time optimization control method of variable rotor speed based on helicopter/turboshaft engine on-board composite system is proposed. Firstly, a steady-state model of the CCH required power and an on-board inverse model of the turboshaft engine based on an improved deep neural network propulsion system model (AdamDNN-PSM) are established. On this basis, an on-board adaptive model based on adaptive square root Kalman filter (ASRUKF) estimator is employed to correct the precision of the on-board inverse model and to track the real engine state. Finally, by adopting the feasible sequence quadratic programming (FSQP) method, an optimal speed rotor (OSR) is obtained through real-time optimization control, which reduces fuel consumption during cruising while considering both the geometric and aerodynamic constraints of the rotor. The simulation results demonstrate that the accuracy and real-time performance of the on-board inverse model have been significantly improved. The real-time optimization control method for OSR effectively reduces fuel consumption during cruising and enhances the CCH performance of the entire flight envelope.

A composite planning method considering avoidance of multiple no-fly zones

Aiming at the problem that multiple no-fly zones need to be avoided in the reentry process of aircraft, a composite programming method combining conjugate gradient and dynamic programming is proposed. The method divides the reentry flight trajectory into two parts: the longitudinal plane and the transverse plane. The longitudinal plane uses the conjugate gradient method to guide the aircraft to meet the minimum mass of the thermal protection system during the whole flight. The horizontal plane mainly uses the dynamic programming method to obtain a reasonable obstacle avoidance route and inversely calculates the change law of the heading angle. The simulation results show that the three-dimensional reentry trajectory can reasonably solve the problem of avoiding multiple no-fly zones and meeting the aerodynamic constraints of the flight process.

Theoretical morphospace analysis of neuropteran wings reveals little evidence of optimization for flight performance

Abstract The wing is the key evolutionary innovation of pterygote insects and wing morphology is commonly envisaged as finely attuned to functional performance. Here, we use a theoretical morphospace approach to analyse the evolution of disparity and functional optimality in neuropteran wings, thus, investigating how wings are adapted for flight and how varied factors constrain wing shape. Analysing 738 neuropteran wings from the Permian to the present, we construct a theoretical morphospace with 1092 hypothetical shapes. These theoretical wings were subjected to functional analysis, creating performance landscapes for aerodynamic traits. We used a Pareto ranking scheme to create an optimality landscape for the trade-off between functional traits, which identifies wings with a convex leading edge as optimal. After projecting neuropteran wings onto this optimal landscape, we find that neuropterans do not occupy this optimal region. Aerodynamic constraint is evident solely in increasing aspect ratio, increasing the lift-to-drag ratio and therefore flight efficiency. Phylomorphospaces reveal a large overlap between different neuropteran clades, reflecting convergence on these same functionally sub-optimal wing shapes. Forewings and hindwings are subject to different evolutionary constraints with forewings more aerodynamically related and hindwings more phylogenetically related. The theoretical morphology approach facilitates morphological analyses without prior assumptions of adaptive optimality.

Direct Method of Aerodynamic Shape Optimization For Supersonic Aircraft Design

The efficient direct optimization method for Supersonic Aircraft Design is presented. Aerodynamic drag and sonic boom signature parameters are used as the objective functions minimized under geometric and aerodynamic constraints. The method combines Newton based algorithm with Euler space-marching solver. The efficiency of the method is demonstrated on examples of two- and three-dimensional aerodynamic design. Nose shapes that ensure minimum wave drag for specified constraints on the overall size are defined. It is shown that the near-optimal axisymmetric noses have a flat forward face. The median surface of a complex plane form wing with minimal drag due to lift is constructed. The simplest shape deformation of the wing providing the main part of aerodynamic drag diminishing is established. To profile the aircraft wing and fuselage providing optimal sonic boom parameters approaches of theory for sonic boom propagation are included in the method. The initial shock intensity as the primary value of the pressure signature is minimized. The results obtained within the framework of the Eulers equations and simplified flow models are compared.

Turbine Endwall Contouring Through Advanced Optimization Techniques

AbstractNon-axisymmetric endwall profiling offers features to simultaneously mitigate aerodynamic losses and hot gas ingestion in axial turbines. This paper presents an optimization methodology to generate a contoured surface integrated with real geometrical effects such as blade fillets and a rim seal channel with the aim of achieving higher efficiencies while reducing hot gas ingestion. The contoured rotor platform is constructed using a B-spline surface clamped in the axial direction. In the azimuthal direction, the surface is unclamped to allow geometrical continuity across the periodic boundaries. The endwall parameterization is used to optimize a rotor hub platform of a high-pressure turbine stage. A differential evolution optimizer is used to rank individuals in terms of efficiency. The single-objective optimization is set to maximize the aerodynamic efficiency and it is defined such that it accounts for the flow non-uniformity through a mixed-out averaging procedure. Engine representative conditions typical of a two-stage high-pressure turbine are used as boundary conditions. Geometrical and aerodynamic constraints are set to guarantee a fair comparison among individuals and to meet engine requirements. Two surface parameterizations, which use a different number of design variables but share the same construction strategy, are presented to show the trade-off between the number of degrees-of-freedom and the aerodynamic improvement. Different purge flow conditions are considered to assess the robustness of the optimization results at off-design conditions for relevant geometries. The aim of this paper is to show the advanced shape flexibility of the implemented parameterization for contoured platforms featuring technological effects such as blade fillet and rim seal channel. The work provides design guidelines to setup engine-realistic constraints for endwall contour optimization of turbine stages.

Efficient Data-Driven Off-Design Constraint Modeling for Practical Aerodynamic Shape Optimization

Off-design constraints are essential in practical aerodynamic shape optimization. Physics-based data-driven modeling has shown to be a feasible way to formulate generalizable off-design constraints. However, two issues hinder the adoption of this approach: inadequate physical mechanism studies and the requirement of massive training data. To address these issues, we propose a feature-oriented data-driven model to learn fundamental physical mechanisms from high-dimensional data. This is achieved by finding low-dimensional latent space relevant to the investigated off-design performance. Then, we customize the constraint model based on the learned physical mechanisms, improving generalizability without relying on prior knowledge. We also propose a Bayesian-optimization-based sampling method to adjust the training data distribution, prioritizing samples with good aerodynamic performance. This uneven sampling strategy improves data efficiency by ensuring accuracy when approaching optimal aerodynamic shapes. The effectiveness of the proposed methods is shown in a low-Reynolds-number airfoil design optimization case and a transonic airfoil design optimization case. We obtain generalizable data-driven off-design aerodynamic models with no prior physical studies, and we reduce the training data volume by 95% compared with a conventional data-driven approach. This work lays the technical foundation for sample-efficient and generalizable data-driven modeling of off-design aerodynamic constraints.

Drag Reduction Design of Transonic Airfoil Based on Particle Swarm Optimization Algorithm

The particle swarm optimization algorithm was introduced and the six-hump camelback function problem was verified and tested. The flow field of the RAE2822 airfoil was simulated by the Navier-Stokes equation and compared with the experiment very well. Based on the aerodynamic optimization case of an airfoil, an optimization design and drag reduction design with a lift coefficient fixed were developed. In this problem, geometric constraints and aerodynamic constraints are both involved. A population of 30 individuals was generated. The CST airfoil parameterized method was used to generate the new airfoil, and the dynamic mesh technique was used to update the new mesh. The aerodynamic characteristics of each airfoil was simulated by Navier-Stokes equation and obtain the individual fitness value. A total of 20 iterations of the design were carried out. There was a strong shock wave and a large shock drag in the baseline airfoil transonic flow. The shock strength is obviously weakened after optimization. The pressure drag is obviously reduced, and the lift-drag ratio is increased by 75%.

Place typology and evolution of implosives in Indo-Aryan languages

Abstract It is widely known that implosives are prevalent in African languages. While Sindhi is considered a textbook example of implosives in Indo-Aryan, the exact distribution of implosives, their development, and place typology are still poorly understood. The present study investigates the typology and evolution of implosives in Indo-Aryan languages and shows that the relationship between implosion and place of articulation in these languages is different from what is seen in global studies. We argue that the relatively high frequency of retroflex implosives in Indo-Aryan languages is due to the high frequency of retroflexes in those languages in general. The findings also indicate that South Asia is another hotspot where languages possess typologically-overloaded inventories of implosives at bilabial, dental-alveolar, retroflex, palatal, and/or velar places of articulation. The aerodynamic constraints and articulatory similarities between implosives and voiced geminates indicate a plausible sound change which led to the evolution of implosives in Indo-Aryan languages.

Motion Planning of Unmanned Aerial Vehicle Based on Rapid-exploration Random Tree Algorithm

In the study of route planning problems in complex environments, in order to reduce the flight cost of unmanned aerial vehicles (UAVs), it is necessary to achieve a better balance between planning time and path quality. This paper utilizes the Rapid-exploration Random Tree (RRT) algorithm for motion planning of a fixed-wing UAV and a multi-rotor UAV (i.e., a quad-rotor UAV), and gives the origin and destination locations on a 3-D map. By following aerodynamic constraints such as maximum roll angle, flight path angle, and airspeed, a collision-free and flight-friendly path is found through simulation. In addition, this paper employs a path smoothing algorithm to simplify the 3-D Dubins path and generates the shortest trajectory. The simulation results show that the RRT and the optimization method have faster convergence speed and shorter search time, reduce redundant planning points, shorten the planning track, and improve the track planning efficiency.

The nonexistence of the plain bilabial trill phoneme

Phonetic studies of bilabial trills in phonemic systems show that they are preceded immediately by an oral stop closure, e.g., /mbʙ, bʙ, pʙ̥/. A plain bilabial trill without a preceding oral stop closure /ʙ/ is not known to occur as an individual phoneme in any language. On the contrary, plain apical /r/ and uvular /ʀ/ trill phonemes that lack a preceding oral stop closure occur in many languages. The nonexistence of /ʙ/ is likely due to the fact that it does not meet the specific aerodynamic conditions necessary for its production (Maddieson 1989). In this paper, I examine a crosslinguistic sample of consonant inventories containing both bilabial and apical trills. I find that these inventories show an implicational tendency: For each phoneme containing a bilabial trill, there is usually a corresponding phoneme containing an apical trill that shares the same values for voicing and prenasalization. These phonemes always include an oral stop closure preceding the trill, and they pattern as obstruents. In addition, these consonant inventories usually include a plain apical trill phoneme (which patterns as a sonorant), but lack a plain bilabial trill phoneme. The most common such inventory (e.g., found extensively in Austronesian) includes three trills /mbʙ, ndr, r/, while larger inventories are found in the Democratic Republic of the Congo and South Sudan, e.g., Mangbetu /pʙ̥, bʙ, mbʙ, tr̥, dr, ndr, r/. While a plain bilabial trill does not emerge due to aerodynamic constraints, resulting in a gap in the system, symmetry appears to favor the emergence of bilabial stop-trill phonemes in languages that have corresponding apical stop-trill phonemes.

Flight Trajectories Optimization of Fixed-Wing UAV by Bank-Turn Mechanism

This paper addresses an optimization of Unmanned Aerial Vehicle (UAV) flight trajectories by bank-turn mechanism for a fixed-wing UAV at a constant altitude. The flight trajectories should be optimal and stay in the UAV flight operational area. The maneuver planning is conducted in two steps, which are UAV path planning and UAV flight trajectory planning. For the first step, the Bezier curve is employed as a maneuvering path. The path planning optimization objective is to minimize the path length while satisfying maximum curvature and collision avoidance constraints. The flight trajectories optimization objective is to minimize maneuvering time and load factor considering, minimum/maximum speed, minimum/maximum acceleration, maximum roll angle, maximum turn rate, and aerodynamics constraints. The variable speed trajectory generation is developed within allowable speed zone considering these UAV flight constraints by employing meta-heuristic optimizations. Results show that the PSO have outperformed the GA and the GWO for both steps of path planning and trajectory planning. The variable speed has succeeded in reducing the load factor during the bank-turn mechanism using the Bezier curve. The variable speed is recommended to be conducted when the result of the maneuvering path involve the lower turning radius. A simultaneous on arrival target mission has also succeeded to be conducted using the combination of the variable speed and constant speed strategies.

Body and wing size, but not wing shape, vary along a large-scale latitudinal gradient in a damselfly

Large-scale latitudinal studies that include both north and south edge populations and address sex differences are needed to understand how selection has shaped trait variation. We quantified the variation of flight-related morphological traits (body size, wing size, ratio between wing size and body size, and wing shape) along the whole latitudinal distribution of the damselfly Lestes sponsa, spanning over 2700 km. We tested predictions of geographic variation in the flight-related traits as a signature of: (1) stronger natural selection to improve dispersal in males and females at edge populations; (2) stronger sexual selection to improve reproduction (fecundity in females and sexual behaviors in males) at edge populations. We found that body size and wing size showed a U-shaped latitudinal pattern, while wing ratio showed the inverse shape. However, wing shape varied very little along the latitudinal gradient. We also detected sex-differences in the latitudinal patterns of variation. We discuss how latitudinal differences in natural and sexual selection regimes can lead to the observed quadratic patterns of variation in body and wing morphology via direct or indirect selection. We also discuss the lack of latitudinal variation in wing shape, possibly due to aerodynamic constraints.

Multi-objective aerodynamic optimization of flying-wing configuration based on adjoint method

In order to solve the multi-objective multi-constraint design in aerodynamic design of flying wing, the aerodynamic optimization design based on the adjoint method is studied. In terms of the principle of the adjoint equation, the boundary conditions and the gradient equations are derived. The Navier-Stokes equations and adjoint aerodynamic optimization design method are adopted, the optimization design of the transonic drag reduction for the two different aspect ratio of the flying wing configurations is carried out. The results of the optimization design are as follows: Under the condition of satisfying the aerodynamic and geometric constraints, the transonic shock resistance of the flying wing is weakened to a great extent, which proves that the developed method has high optimization efficiency and good optimization effect in the multi-objective multi-constraint aerodynamic design of the flying wing.

Design of Thrust-Optimized Scramjet Nozzle and Its Concise Estimation Method

This Paper is a computational investigation of a scramjet nozzle design based on maximum thrust theory and its feasibility analysis. A new design method for a two-dimensional complete thrust-optimized single expansion ramp nozzle under aerodynamic constraints by applying the method of characteristics is proposed. The carefully chosen verification and validation benchmarks confirm the accuracy, effectiveness, and superiority of the current method. Results indicate that the introduced design method has comprehensive advantages over the traditional approach under design/off-design conditions. Specifically, the maximum increase in axial thrust reaches 6.38%, and the maximum increase in lift exceeds 180%. Necessary conditions of the thrust-optimized nozzle design are deduced combining Prandtl–Meyer relation and corner conditions, which provides a direct judgment criterion for the rationality of initial design conditions, and leads to a concise dimension estimation method. Relative errors of no more than 5% demonstrate the credibility of this approach through a comparison with the theoretical solutions. The refined structure topology of the thrust-optimized single expansion ramp nozzle further reveals the equivalent relations between the aerodynamic and geometric design conditions based on the estimation results.

Moth wings are acoustic metamaterials

Intense predation pressure from echolocating bats has led to the evolution of a host of anti-bat defences in nocturnal moths. The wings of moths are covered in scales that exhibit intricate shapes and sculpted nano structures. Here, we reveal that this scale layer forms a metamaterial ultrasound absorber that is 111 times thinner than the longest absorbed wavelength. Both experimental and numerical analyses of individual scale vibrodynamics reveal that the first three resonances of moth scales lie within the typical echolocation frequency range of bats, whilst scale shape diversity on the wing results in a broad resonance distribution. Individual scales form the resonant unit-cells on the wing and collectively they generate hard to attain broadband deep-subwavelength absorption. Numerical modelling confirms that the acoustic properties of moth wings originate from the interaction of differently tuned single scale resonators, creating emergent acoustic performance beyond that of its elements, confirming broadband metamaterial absorber functionality. This sound absorber provides moth wings with acoustic camouflage against echolocating bats, it combines broadband absorption of all frequencies used by bats with light and ultrathin structures that meet aerodynamic constraints on wing weight and thickness.

Aerodynamic optimization of the last stage turbine blade for an industrial gas turbine

A multi-objective, aerodynamic optimization of the last stage turbine blade of an 100Hz industrial gas turbine is presented. We aim at maximizing the stage’s efficiency, while at the same time meeting mechanical integrity. The optimization procedure was build, during the optimization process the mass flow rate and stage meridian were kept constant to obtain the required stage loading without changing the operating point. The optimized geometry are chosen taking into account aerodynamic constraints as well as mechanical constrains, such as centrifugal stress and bending stress. The SST turbulence model was used to calculate the flow field of the original and optimized stage, respectively. The geometry of the original and optimized blade was compared. The stage efficiency of the design point and under different operate conditions were compared. Stage and blade efficiency along span was analyzed in details. The blade loading at root mid top span of the original and optimized blade were discussed. Detailed flow field analysis shows that, after optimization, the peak Mach number of the root span profile was decreased from 1.22 to 1.09, which improves the flow field. Profile loss and end wall loss were also reduced. After optimization, maximum centrifugal stress and the maximum air bending stress were decreased which leads to improved blade life and safety. The number of blades and b/h were suggested for the last stage blade.

Bayesian optimisation for low-noise aerofoil design with aerodynamic constraints

This paper presents an optimisation approach for designing low-noise Outlet Guide Vanes (OGVs) for fan broadband noise generated due to the interaction of turbulence and a cascade of 2-dimensional aerofoils. The paper demonstrates the usage of Bayesian optimisation with constraints to reduce the computation cost of optimisation. The prediction is based on Fourier synthesis of the impinging turbulence and the aerofoil response is predicted for each vortical modal component. A linearised unsteady Navier-Stokes solver is used to predict the aerofoil response due to an incoming harmonic vortical gust. This paper shows that to achieve noise reductions of 0.5 dB the penalty on the aerodynamic performance of 33% is observed compared to baseline aerofoil. Hence, the geometry changes such as thickness and nose radius can’t reduce broadband noise without effecting aerodynamic performance.

Moth wings are acoustic metamaterials

Metamaterials assemble multiple subwavelength elements to create structures with extraordinary physical properties (1-4). Optical metamaterials are rare in nature and no natural acoustic metamaterials are known. Here, we reveal that the intricate scale layer on moth wings forms a metamaterial ultrasound absorber (peak absorption = 72% of sound intensity at 78 kHz) that is 111 times thinner than the longest absorbed wavelength. Individual scales act as resonant (5) unit cells that are linked via a shared wing membrane to form this metamaterial, and collectively they generate hard-to-attain broadband deep-subwavelength absorption. Their collective absorption exceeds the sum of their individual contributions. This sound absorber provides moth wings with acoustic camouflage (6) against echolocating bats. It combines broadband absorption of all frequencies used by bats with light and ultrathin structures that meet aerodynamic constraints on wing weight and thickness. The morphological implementation seen in this evolved acoustic metamaterial reveals enticing ways to design high-performance noise mitigation devices.