Abstracts:In this review, the research progress of bio-inspired polarized skylight navigation is evaluated from the perspectives of theoretical basis, information detection, sensor design, and navigation realization. First, the theory for characterizing the polarization mode of the skylight was introduced. Second, using sunlight, moonlight, and ocean as backgrounds, the measurement results of skylight polarization distribution under different weather conditions are described to compare the variation patterns. Third, the development history and research outcomes of bionic polarization navigation sensor for polarized skylight detection and navigation information calculation are categorized into two types, namely non-imaging and imaging types. In precision measurement, the non-imaging type is higher than the imaging type, and the accuracy that it can reach is ± 0.1° of navigation accuracy without drift error. Fourth, two polarized skylight orientation algorithms, E-vector-based method and Solar Meridian-Anti Solar Meridian (SM-ASM)-based method are summarized. Fifth, this review details the combined application of polarized skylight navigation sensors and Inertial Navigation System (INS), Global Navigation Satellite System (GNSS), Vision, Simultaneous Localization and Mapping (SLAM), and other navigation systems. The yaw and trajectory accuracy can be increased by about 40% compared to classical navigation system in complex outdoor environments. Finally, the future development trends of polarization navigation are presented.

Abstracts:The spontaneous growth and evolution mechanism of metal whiskers have long been scientific problems. With the development of the integration of electronic and electrical productions, short circuits and system failures are raised by metal whiskers continuously. In the meantime, the related theories and mechanisms of whiskering problem are still vague, leading to a deficiency in the studies of environmental factors influencing the whisker phenomenon. Besides, the extreme environments such as aerospace, have been proven the accelerators to the formation of metal whiskers, resulting in a severe threaten to equipment and devices working in such environments including satellite and military equipment. To establish a comprehensive understanding to the whiskering process associated with their applicable control strategies, this study analyzes the growth phenomenon, influencing factors, formation process and evolution mechanism of metal whiskers in extreme service environments, puts forward the corresponding controlling strategies, offers a reference for the establishment of Chinese extreme aerospace strategic environment, and improves the reliability of aerospace systems.

Abstracts:As the pivotal test equipment of aero-engines design, finalization, improvement, modification, etc., the Altitude Ground Test Facilities (AGTF) plays an important role in the research and development of the aero-engines. With the rapid development of advanced high-performance aero-engine, the increasing demand of high-altitude simulation test is driving AGTF to improve its test ability and level of automation and intelligence. The modeling method, simulation tool, and control technology are the key factors to support the improvement of the AGTF control system. The main purpose of this paper is to provide an overview of modeling methods, simulation tools, and control technologies in AGTF control system for future research. First, it reviews the evolution of AGTF in the world, from the early formative stage to integration stage. Then, the mathematical modeling method of AGTF for control application is overviewed. Furthermore, the simulation tools used in the AGTF control system are overviewed from numerical simulation to hardware-in-loop simulation and further to semi-physical simulation. Meanwhile, the control technologies used in the AGTF control system are summarized from single-variable control to multivariable integrated control, and from classical control theory to modern control theory. Finally, recommendations for future research are outlined. Therefore, this review article provides extensive literature information for the modeling, simulation, and control design of AGTF for control application.

Abstracts:In this paper, a model is established with application of the spectral-wave guide method, which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations. Based on this calculation model, some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out, and some physical mechanisms can be discovered. The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing; and mirror-symmetric structure liner will converge the energy of opposite modes. Relying on this mechanism, the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations. In particular, the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise. The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source. Furthermore, the effects of non-uniform flow are considered in the model, then distinction of noise attenuation and scattered modes energy in different flows is shown. A possible mechanism is proposed that refraction effects in complex flows lead to the distinction. These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.

Abstracts:Ducted fans are widely used in various applications of Unmanned Aerial Vehicles (UAVs) due to the high efficiency, low noise and high safety. The unsteady characteristics of ducted fans flying near the ground are significant, which may bring stability problems. In this paper, the sliding mesh technology is applied and the Unsteady Reynolds Averaged Navier-Stokes (URANS) method is adopted to evaluate the influence of ground on the aerodynamic performance of ducted fans. The time-averaged results show that the ground leads to the decrease of duct thrust, the increase of rotor thrust and the decrease of total thrust. The transient results show that there exist small-scale stall cells with circumferential movements in ground effect. The stall cells start to appear at the blade root when the height is 0.8 rotor radius distance, and arise at both the blade root and tip when the height drops to 0.2. It is found that the unsteady cells rotate between blade passages with an approximate relative speed of 30%-80% of the fan speed, and lead to thrust fluctuations up to 37% of the total thrust. The results are essential to the flight control design of the ducted fan flying vehicle, to ensure its stability in ground effect.

Abstracts:Machine learning has been widely utilized in flow field modeling and aerodynamic optimization. However, most applications are limited to two-dimensional problems. The dimensionality and the cost per simulation of three-dimensional problems are so high that it is often too expensive to prepare sufficient samples. Therefore, transfer learning has become a promising approach to reuse well-trained two-dimensional models and greatly reduce the need for samples for three-dimensional problems. This paper proposes to reuse the baseline models trained on supercritical airfoils to predict finite-span swept supercritical wings, where the simple swept theory is embedded to improve the prediction accuracy. Two baseline models are investigated: one is commonly referred to as the forward problem of predicting the pressure coefficient distribution based on the geometry, and the other is the inverse problem that predicts the geometry based on the pressure coefficient distribution. Two transfer learning strategies are compared for both baseline models. The transferred models are then tested on complete wings. The results show that transfer learning requires only approximately 500 wing samples to achieve good prediction accuracy on different wing planforms and different free stream conditions. Compared to the two baseline models, the transferred models reduce the prediction error by 60% and 80%, respectively.

Abstracts:The variable cycle engine is distinguished by its highly adjustable compression system, whose aerodynamic characteristic is extremely complex. To explore the regulation range of a double bypass engine compression system, a multi-dimensional analysis method is developed, through which the coupling mechanism between the compressor component and the bypass is examined. The operation zones of the compressor components and the bypass system are proposed, and the operation range of the compression system is obtained by calculating the overlapping part of the operation zones. The results show that in the double bypass mode, there exists a minimum mode selector valve area and a minimum core driven fan stage stall margin that ensures a feasible bypass flow, the two parameters correspond to each other. Under the given fan and core driven fan stage conditions, the maximum value of the inner bypass ratio is restricted by the upper limit of the forward variable area bypass injector and the maximum Mach number in the total bypass, while the minimum value of the inner bypass ratio depends on the lower limit of the forward variable area bypass injector geometry and the system recirculation margin. The single bypass mode is a unique condition of the double bypass mode, as the operation zone of the compressor component degenerates from a two-dimensional surface to a straight line. There are multiple bypass states available in the single bypass mode, while the regulation range of the bypass ratio is jointly restricted by the operation range of the high pressure compressor and the aerodynamic boundary of the forward variable area bypass injector.

Abstracts:A 2% scale, cruising version of a 450-seat class Blended-Wing-Body (BWB) transport was tested in the China Aerodynamic Research and Development Center’s FL-26 2.4-by-2.4-meter subsonic wind tunnel. The focus of the wind tunnel test was to investigate the aerodynamic performance of the latest BWB transport design, which would also aid in choosing a final engine arrangement in the three most potential engine integration layouts. The wind tunnel model can be tested with and without the nacelle and has three sets of different nacelle/tail integration positions. Computational Fluid Dynamics (CFD) simulations were performed in engine-aircraft integration design to find appropriate nacelle installing parameters of each layout. The comparison of CFD with experimental results shows good agreement. Wind tunnel measurements indicate that the tail-mounted engine layout produces the minimum drag penalty, while the fuselage-mounted engine layout increases drag the most. Experimental pressure measurement illustrates the effect of nacelle integration on the wing-body surface pressure distribution. This experimental and numerical research provides a reference for future BWB Propulsion-Airframe Integration (PAI) design.

Abstracts:An efficient Advancing Layer Method (ALM) is presented to create semi-structured prisms on viscous walls, in which a procedure that checks possible front intersections is essential to its efficiency. This paper develops various novel schemes to improve the algorithm’s efficiency precisely while not sacrificing its robustness and the resulting mesh quality. First, it employs a set of new techniques, and data structures are developed to improve the efficiency of the front-check procedure. Then, within each octant, a new filter is developed to reduce the intersection computations in the searching process. In addition, data structures are well designed to store the contiguously accessed data in each computing-intensive loop in a contiguous space for a potentially better cache hit ratio. We built a geometry model library formed by examples of industrial complexity to demonstrate the practicability of the algorithm. All the efforts mentioned above enable us to reduce the percentage of computing time taken by intersection check to an acceptable level (approximately 26%), which make it no longer be the most time-consuming part.

Abstracts:Aerodynamic noise of High-Lift Devices (HLDs) is one of the main sources of airframe noise, and has immediate impacts on the airworthiness certification, environmental protection and security of commercial aircraft. In this study, a novel hybrid method is proposed for the aerodynamic noise prediction of HLD. A negative Spalart-Allmaras (S-A) turbulence model based Improved Delayed Detached Eddy Simulation (IDDES) method coupling with AFT-2017b transition model is developed, in order to elaborately simulate the complex flow field around the HLD and thus obtain the information of acoustic sources. A Farassat-Kirchhoff hybrid method is developed to filter the spurious noise sources caused by the vortex motions in solving the Ffowcs Williams-Hawkings (FW-H) equation with permeable integral surfaces, and accurately predict the far-field noise radiation of the HLD. The results of the 30P30N HLD indicate that, the computational Sound Pressure Levels (SPLs) obtained by the Farassat-Kirchhoff hybrid method conform well with the experimental ones in the spectrum for the given observation point, and are more accurate than those obtained by the Farassat 1A method. Based on the hybrid method, the acoustic directivity of the HLD of a commercial aircraft is obtained, and the variation of the SPLs in the spectrum with the deflection angle of the slat is analyzed.