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Purpose This study aims to use computational fluid dynamics (CFD) to understand and quantify the overall blockage within a transonic axial flow compressor (AFC), and to develop an efficient collaborative design optimization method for compressor aerodynamic performance and stability in conjunction with a surrogate-assisted optimization technique. Design/methodology/approach A quantification method for the overall blockage is developed to integrate the effect of regional blockages on compressor aerodynamic stability and performance. A well-defined overall blockage factor combined with efficiency drives the optimizer to seek the optimum blade designs with both high efficiency and wide-range stability. An adaptive Kriging-based optimization technique is adopted to efficiently search for Pareto front solutions. Steady and unsteady numerical simulations are used for the performance and flow field analysis of the datum and optimum designs. Findings The proposed method not only remarkably improves the compressor efficiency but also significantly enhances the compressor operating stability with fewer CFD calls. These achievements are mainly attributed to the improvement of specific flow behaviors oriented by the objectives, including the attenuation of the shock and weakening of the tip leakage flow/shock interaction intensity. Originality/value CFD-based design optimization of AFC is inherently time-consuming, which becomes even trickier when optimizing aerodynamic stability since the stall margin relies on a complete simulation of the performance curve. The proposed method could be a good solution to the collaborative design optimization of aerodynamic performance and stability for transonic AFC.

The stability and galloping characteristics of iced quad bundle conductor are studied in this paper. Firstly, the aerodynamic coefficients of iced quad bundle conductor and single conductor under four different working conditions are obtained by wind tunnel test. Secondly, the equivalent aerodynamic coefficients at the central axis of the quad bundle conductor are obtained, and the equivalent aerodynamic coefficients are compared with the aerodynamic coefficients of each sub-conductor of the quad bundle conductor. Then, based on the Den Hartog instability mechanism and Nigol instability mechanism, the stable and unstable range of the equivalent coefficients of the quad bundle conductor are analyzed. Finally, the galloping characteristics of the quad bundle conductor are studied by combining with the equivalent aerodynamic coefficients at the central axis of quad bundle conductor. The results of the wind tunnel test show that the aerodynamic coefficients increase with the decreasing of the wind speed. The stability analyses show that the higher the wind speed is, the smaller the Den Hartog coefficient is the easier the Den Hartog’ galloping would occur. Furthermore, the higher the wind speed is, the smaller the Nigol coefficient is, the easier the Nigol’ galloping would occur. The analysis of galloping characteristics shows that when the conductor is located at stable state, the displacement in the y-axis direction would be much greater than the displacement in the z-axis direction.

Interceptors operate at wide range of operating conditions in terms of Mach number, altitude and angle of attack. The aerodynamic design caters for such wide operating envelope by appropriate sizing of lifting and control surfaces for meeting the normal acceleration capability requirements. The wide range of operating conditions leads to an inevitable spread in center of pressure location and hence spread in static stability. The performance of control design is a strong function of the aerodynamic static stability. The total operating envelope can be bifurcated into statically stable and unstable zones and the aerodynamic lifting surface location can be used as a control parameter to identify the neutral stability point. During the homing phase lesser static stability is desirable for good speed of response, hence the lifting surface location needs to be chosen based on the capability of control to handle instability. This paper analyses the limitations of autopilot design for the control of an unstable interceptor and brings out a method to identify the optimum aerodynamic lifting surface location for efficiently managing static margin while satisfying the control limitations and homing phase performance. This provides an input on the most appropriate lifting surface location to the aerodynamic designer during the initial CFD based aerodynamic characterisation stage itself, before commencing the rigorous wind tunnel based characterisation.

In the age of globalization, commercial aviation plays a central role in maintaining our international connectivity by providing fast air transport services for passengers and freight. However, the upper limit of the aircraft flight envelope, i.e., its operational limit in the high-speed (transonic) regime, is usually fixed by the occurrence of transonic aeroelastic effects. These harmful structural vibrations are associated with an aerodynamic instability called transonic buffet. It refers to shock wave oscillations occurring on the aircraft wings, which induce unsteady aerodynamic loads acting on the wing structure. Since the structural response can cause severe structural damage endangering flight safety, the aviation industry is highly interested in suppressing transonic buffet to extend the flight envelope to higher aircraft speeds. In this contribution, we demonstrate experimentally that the application of porous trailing edges substantially attenuates the buffet phenomenon. Since porous trailing edges have the additional benefit of reducing acoustic aircraft emissions, they could prospectively provide faster air transport with reduced noise emissions. Transonic buffet is a ubiquitous challenge in commercial aviation since it can result in catastrophic structural failure of the aircraft wings. Here, authors experimentally show that this critical aerodynamic phenomenon can be mitigated using a carefully designed porous trailing edge on the wing.

Instability evolution in a transitional hypersonic boundary layer and its effects on aerodynamic heating are investigated over a 260 mm long flared cone. Experiments are conducted in a Mach 6 wind tunnel using Rayleigh-scattering flow visualization, fast-response pressure sensors, fluorescent temperature-sensitive paint (TSP) and particle image velocimetry (PIV). Calculations are also performed based on both the parabolized stability equations (PSE) and direct numerical simulations (DNS). Four unit Reynolds numbers are studied, 5.4, 7.6, 9.7 and $11.7\\times 10^{6}~\\text{m}^{-1}$ . It is found that there exist two peaks of surface-temperature rise along the streamwise direction of the model. The first one (denoted as HS) is at the region where the second-mode instability reaches its maximum value. The second one (denoted as HT) is at the region where the transition is completed. Increasing the unit Reynolds number promotes the second-mode dissipation but increases the strength of local aerodynamic heating at HS. Furthermore, the heat generation rates induced by the dilatation and shear processes (respectively denoted as $w_{\\unicode[STIX]{x1D703}}$ and $w_{\\unicode[STIX]{x1D714}}$ ) were investigated. The former item includes both the pressure work $w_{\\unicode[STIX]{x1D703}1}$ and dilatational viscous dissipation $w_{\\unicode[STIX]{x1D703}2}$ . The aerodynamic heating in HS mainly arose from the high-frequency compression and expansion of fluid accompanying the second mode. The dilatation heating, especially $w_{\\unicode[STIX]{x1D703}1}$ , was more than five times its shear counterpart. In a limited region, the underestimated $w_{\\unicode[STIX]{x1D703}2}$ was also larger than $w_{\\unicode[STIX]{x1D714}}$ . As the second-mode waves decay downstream, the low-frequency waves continue to grow, with the consequent shear-induced heating increasing. The latter brings about a second, weaker growth of surface-temperature HT. A theoretical analysis is provided to interpret the temperature distribution resulting from the aerodynamic heating.

Pressure measurements for rigid models fail to take aeroelastic effects into account, as well as forced vibration tests only consider the effect of an oscillating model on wind flow and cannot include the feedback from wind flow to the oscillating model. To investigate the characteristics of unsteady aerodynamic forces and predict the aeroelastic response of a tapered prism during VIV–galloping, hybrid aeroelastic-pressure balance (HAPB) wind tunnel tests at different reduced wind velocities were carried out. Unsteady pressures and tip responses of a tapered test model were synchronously observed. Both the aerodynamic and aeroelastic characteristics of the tapered prism during VIV–galloping instability were discussed in terms of aeroelastic response, force spectrum, coherence coefficient and pressure distribution. Subsequently, the VIV–galloping response was predicted by unsteady aerodynamic forces and compared to quasi-static calculations and experimental results. It was found that large-amplitude periodic vibrations took place at approximately twice the onset wind speed of VIV, which was recognized as VIV–galloping. Moreover, structural oscillation would have a significant effect on aerodynamic characteristics in the crosswind direction. In addition, the HAPB test was efficacious in measuring unsteady aerodynamic forces on the test model, which were effective to predict VIV–galloping instability of bluff bodies.

The Blended Wing Body (BWB) aircraft is a non-conventional aerodynamic configuration that merges the fuselage and wings into a seamless structure, offering significant advantages in fuel efficiency, payload capacity, and aerodynamic efficiency. However, the absence of conventional tail units introduces aerodynamic and stability challenges that require careful design optimization. This study investigates the aerodynamic and static stability characteristics of a baseline BWB design from the European Distributed Multi-Disciplinary Design and Optimization (EU MOB) project. The analysis is performed using a mid-fidelity numerical tool based on the vortex lattice method, incorporating geometric and mass properties from previous studies. Aerodynamic curves and static stability derivatives are evaluated across a specific flight regime and compared with existing literature verifying the suitability of the used tool for preliminary aerodynamic and stability assessments. Subsequently, a parametric study is conducted to assess the effects of varying winglet design parameters, including height, sweep, cant, and toe angles, on aerodynamic efficiency and static stability characteristics. The results demonstrate that optimized winglet configurations can enhance lift-to-drag ratio and improve static stability characteristics without significantly increasing drag. These findings provide valuable insights into the role of winglets in improving BWB aircraft performance and contribute to the optimization of next-generation aerodynamic designs.

Plants cover a large fraction of the Earth’s land mass despite most species having limited to no mobility. To transport their propagules, many plants have evolved mechanisms to disperse their seeds using the wind 1 – 4 . A dandelion seed, for example, has a bristly filament structure that decreases its terminal velocity and helps orient the seed as it wafts to the ground 5 . Inspired by this, we demonstrate wind dispersal of battery-free wireless sensing devices. Our millimetre-scale devices weigh 30 milligrams and are designed on a flexible substrate using programmable, off-the-shelf parts to enable scalability and flexibility for various sensing and computing applications. The system is powered using lightweight solar cells and an energy harvesting circuit that is robust to low and variable light conditions, and has a backscatter communication link that enables data transmission. To achieve the wide-area dispersal and upright landing that is necessary for solar power harvesting, we developed dandelion-inspired, thin-film porous structures that achieve a terminal velocity of 0.87 ± 0.02 metres per second and aerodynamic stability with a probability of upright landing of over 95%. Our results in outdoor environments demonstrate that these devices can travel 50–100 metres in gentle to moderate breeze. Finally, in natural systems, variance in individual seed morphology causes some seeds to fall closer and others to travel farther. We adopt a similar approach and show how we can modulate the porosity and diameter of the structures to achieve dispersal variation across devices. A dandelion-inspired wireless solar-powered sensing device weighing 30 milligrams that transmits data through radio backscatter achieves dispersal over a wide area by travelling on the breeze, and successfully lands upright.

The influence of environmental steady aerodynamic loads on the both carbody hunting motion and bogie hunting motion stability of high-speed trains (HSTs) is presented in this paper. A lateral HST dynamics model with 17 degrees of freedom (DOFs) is established to reflect the dynamic characteristics of carbody hunting and bogie hunting motions. The nonlinear creep force saturation and variable friction coefficient nonlinear characteristics are considered in the model. Then the continuous modal tracking method and numerical simulation method are used to evaluate the hunting stability and acquire the bifurcation diagram, respectively. The linear hunting stability and bifurcation behavior, subject to different wheel/rail match equivalent conicity and friction coefficient conditions, are investigated in detail for both the carbody and bogie hunting motions. The results show that crosswind aerodynamic loads will change the normal wheel/rail force and quasi-static contact position. Additionally, the creep coefficient and creep force saturation modified coefficient, which are closely related to hunting stability, will also be affected. The crosswind aerodynamic loads can significantly impact the hunting stability and bifurcation characteristics, especially under condition of small friction coefficient. The double grazing phenomenon with occurrence of carbody hunting motion will change to single grazing phenomenon when the crosswind aerodynamics loads are large enough.

Inspired by the wave-rider idea and momentum principle, the vehicle with inverted dihedral and momentum lift augmentation is a new aerodynamic configuration of high-speed gliding vehicle in the near-space, which has achieved a high lift-to-drag ratio and long-distance sliding. Numerical simulation of aerodynamic characteristics and stability of the aircraft are carried out in this paper. The lift-to-drag characteristics, longitudinal-directional stability and lateral-directional stability are evaluated based on the National Numerical Wind tunnel’s high-speed simulation software, named NNW-HyFLOW. An unstructured/hybrid grid is used in the calculation at the typical ballistic points of altitude of 10-75km and Mach number of 3-25. The results shows that the lift-to-drag ratio reaches a peak value of 4.11 at the altitude of 30km and attack angle of 8°. This value is decreased when the altitude raises. The usable lift-to-drag ratio is over 3 in the glide phase range from 30 to 50 kilometres. This vehicle shows better longitudinal-directional stability at large angles of attack than at small in the reentry phase and glide phase, which can be optimized by adjusting the center of mass or pitching rudder. It has a weak instability in the lateral direction at small angle of attack in the glide phase. Therefore, it is suggested to avoid to work at the high altitude with a small angle of attack. Or, the lateral-directional stability can be strengthened at this altitude by improving the V-tail.