Aerodynamic Method Research Articles

Advances in aerodynamic, structural design and test technology of variable geometry turbines

The variable geometry turbine is one of the technical means to effectively improve the part-load performance, part-load condition stability and manoeuvrability of gas turbines, aeroengines or even turbochargers. However, the design of the variable geometry turbine is very difficult, and the decrease in efficiency offsets some of the engine cycle benefits caused by turbine variable geometry. Therefore, it is very necessary to carry out research on variable geometry turbine technology so that the technology can be successfully applied to various types of gas turbine engines as soon as possible. This paper summarizes and analyzes the recent advances in the field of aerodynamic, structural design and test of variable geometry turbines. This review covers the following topics that are important for variable geometry turbine designs: (1) flow mechanisms and aerodynamic characteristics, (2) wide-condition aerodynamic design method for turbine blades, (3) variable vane turning design method, (4) structural design technology of variable vane system and (5) aerodynamic characteristics and reliability test technology for variable geometry turbines. The emphasis is placed on the variable vane turning design method. We also present our own insights regarding the current research trends and the prospects for future developments.

Optimal design of aeroacoustic airfoils with owl-inspired trailing-edge serrations

The trailing-edge serration that imitates the silent owl wing is used as a flow control method to suppress the aerodynamic noise generated from the rotating wind turbine blade. Recent studies have found that the addition of serrations could degrade the overall aerodynamic performance of the airfoil. To this end, an optimal design method for airfoils with the trailing-edge serration is developed. Combined with the modeling methods of aerodynamics for serrations, the fundamental parameters of serrations are integrated into the optimal design of wind turbine airfoils. Specifically, based on the existing multidisciplinary optimization method for airfoils, the aerodynamic prediction and evaluation module for the serrated airfoil was introduced to develop an aerodynamic–structural optimal design platform. In this way, a novel serrated airfoil equipped with high aerodynamic performance can be designed. Compared with the reference airfoil, the maximum lift-to-drag ratio and lift coefficient of the optimal serrated airfoil at the design point have been increased by 1.9% and 32.5%, while the aerodynamic noise could also be reduced. Finally, experiments were conducted in an anechoic chamber to verify the noise-reduction level of the optimal serrated airfoil, which sufficiently demonstrate the capability to improve the comprehensive performance of the airfoil using such a developed optimal scheme.

A novel approach to calculating induced drag from computational fluid dynamics

Early aerodynamic mathematical methods rely on potential flow concepts that formally isolate aerodynamic drag into a profile and an induced drag component. The more recent evolution of Navier–Stokes-based Computational Fluid Dynamics (CFD) methods typically directly computes aerodynamic forces. It does so using surface integration of pressure and viscous forces, which does not readily enable conventional separation of profile and induced drag. Isolating induced drag from aerodynamic drag is not well developed using CFD, leading to the present effort that derives a mathematical framework to extract induced drag from CFD model results. The present approach builds on mass, momentum, and energy equation control volume analysis performed within the CFD results. We find that the energy equation provides the necessary means for the closure of quantifying induced drag within the context of minor assumptions. In addition, the results indicate an interesting character in the development of energy losses in the context of induced drag associated with flow reorganization into a tip vortex. The results from the approach indicate accuracy in the method as displayed with good correlation to predictions from analytical and potential flow methods for a variety of wing planforms. Results indicate a novel and efficient method to extract induced drag from CFD models.

Data-driven modeling for unsteady aerodynamics and aeroelasticity

Aerodynamic modeling plays an important role in multiphysics and design problems, in addition to experiment and numerical simulation, due to its low-dimensional representation of unsteady aerodynamics. However, in the traditional study of aerodynamics, developing aerodynamic and flow models relies on classical theoretical (potential flow) and empirical investigation, which limits the accuracy and extensibility. Recently, with significant progress in high-fidelity computational fluid dynamic simulation and advanced experimental techniques, very large and diverse fluid data becomes available. This rapid growth of data leads to the development of data-driven aerodynamic and flow modeling. Through advanced mathematical methods from control theory, data science and machine learning, a lot of data-driven aerodynamic models have been proposed. These models are not only more accurate than theoretical models, but also require very low computational cost compared with numerical simulation. At the same time, they help to gain physical insights on flow mechanism, and have shown great potential in engineering applications like flow control, aeroelasticity and optimization. In this review paper, we introduce three typical data-driven methods, including system identification, feature extraction and data fusion. In particular, main approaches to improve the performance of data-driven models in accuracy, stability and generalization capability are reported. The efficacy of data-driven methods in modeling unsteady aerodynamics is described by several benchmark cases in fluid mechanics and aeroelasticity. Finally, future development and potential applications in related areas are concluded.

A New Aerodynamic Optimization Method with the Consideration of Dynamic Stability

Dynamic stability is significantly important for flying quality evaluation and control system design of the advanced aircraft, and it should be considered in the initial aerodynamic design process. However, most of the conventional aerodynamic optimizations only focus on static performances and the dynamic motion has never been included. In this study, a new optimization method considering both dynamic stability and general lift-to-drag ratio performance has been developed. First, the longitudinal combined dynamic derivative based on the small amplitude oscillation method is calculated. Then, combined with the PSO (particle swarm optimization) algorithm, a dynamic stability derivative that must not be decreased is added to the constraints of optimization and the lift-drag ratio is chosen as the optimization objective. Finally, a new aerodynamic optimization method can be built. We take NACA0012 as an example to validate this method. The results show that the dynamic derivative calculation method is effective and conventional optimization design can significantly improve the lift-drag ratio. However, the dynamic stability is enormously changed at the same time. By contrast, the new optimization method can improve the lift-drag performance while maintaining the dynamic stability.

Validation of Low Fidelity Propeller-Wing Modeling Method at Low Reynolds Number

An introduction of slipstream effects induced by the distributed propeller at low Reynolds number will lead to notable reductions in aerodynamics efficiency with significance changes of the free-stream properties of the wing. To address the issues, a set of reasonable aerodynamic design method for multiple propeller-wing integration is necessary to capture the wing aerodynamics performances behaviour at low Reynolds number. In that respect, the flow condition of a rectangular wing with NACA0012 airfoil section under the influence of the propeller slipstream was simulated and validated using low-order fidelity solver. A validation of the methods chosen found to be assuring in comparison with experimental data. The effects of various parameters were taken into account like the angle of attack, the rotational speed, the thrust and the power required. The aerodynamic aspect of the propeller-wing integration for a number of actuator disks propeller modelled distributed along the span of the wing of the aircraft is measured. The results show the role of propeller diameter and the numbers installed along the wingspan lead to a significance increase on lift performance and lift to drag ratio.

A Phased Aerodynamic Optimization Method for Compressors Based on Multi-Degrees-of-Freedom Surface Parameterization

A Phased Aerodynamic Optimization Method for Compressors Based on Multi-Degrees-of-Freedom Surface Parameterization

ON AIR FLOW STRUCTURE IN STATION VENTILATION CONNECTIONS OF SUBWAYS

One of the important microclimatic criteria for the comfort and safety of passenger transportation in subways is dust concentration in passenger and staff area. It is known that fine dust concentration in subways is significantly exceeded relative to the permissible regulatory level. To reduce the dust concentration to the maximum allowable level, it is necessary to filter the tunnel air not only for the systems of local ventilation of staff rooms, but also for tunnel ventilation and general ventilation of passenger rooms at the stations. It is better to install filters in station ventilation connections, since significant circulating air flows pass through them. To determine the type and parameters of filters, it is required to know the magnitude and direction of an airflow rate, i.e. the structure of its velocity field. Due to the complex topology and presence of separation zones, the airflow structure, gradient of air velocities in the cross-section of ventilation connections and, accordingly, justification of filter installation locations in a ventilation connection requires a separate study. The paper substantiates a decomposition approach to mathematical modeling of aerodynamic processes by transition from a linear open-loop model of the subway line to a closed circular one; geometric parameters of the adopted design model; mathematical statement of the problem. Computational aerodynamics methods allowed determining the minimum, average and maximum projections of air velocity on the normal to the cross section of a ventilation connection and air flows through this cross section. This makes it possible to justify the requirements for the placement and operating parameters of the filtration equipment.

An improved aerodynamic performance optimization method of 3-D low Reynolds number rotor blade

Abstract In this paper, an improved aerodynamic performance optimization method for 3-D low Reynolds number (Re) rotor blade is proposed. A conventional optimization procedure of blade is usually divided into three parts, such as the parameterization method, the fitness value evaluation and the optimization algorithm. This work is mainly focused on the first two parts. The parametrization method, Camber-FFD, is presented based on the camber parametrization method and the free-form deformation algorithm (FFD). The shape of 3-D blade is parameterized by the incidence angles and the coordinates of the maximum camber points. The fitness value evaluation has been realized with the help of an adaptive topological back propagation multi-layer forward artificial neural network (BP-MLFANN). During the training of BP-MLFANN, the hybrid particle swarm optimization method combined with the modified very fast simulate annealing algorithm (HPSO-MVFSA) is adopted to determine the neural network topology adaptively. To verify the effectiveness of this aerodynamic optimization method, the aerodynamic performance of a 3-D low-Re blade, such as Blade D900, is optimized, and the results are compared and analyzed based on the experiments and simulations. It is proved that this aerodynamic optimization method is feasible.

An improved aerodynamic performance optimization method of 3-D low Reynolds number rotor blade

Abstract In this paper, an improved aerodynamic performance optimization method for 3-D low Reynolds number (Re) rotor blade is proposed. A conventional optimization procedure of blade is usually divided into three parts, such as the parameterization method, the fitness value evaluation and the optimization algorithm. This work is mainly focused on the first two parts. The parametrization method, Camber-FFD, is presented based on the camber parametrization method and the free-form deformation algorithm (FFD). The shape of 3-D blade is parameterized by the incidence angles and the coordinates of the maximum camber points. The fitness value evaluation has been realized with the help of an adaptive topological back propagation multi-layer forward artificial neural network (BP-MLFANN). During the training of BP-MLFANN, the hybrid particle swarm optimization method combined with the modified very fast simulate annealing algorithm (HPSO-MVFSA) is adopted to determine the neural network topology adaptively. To verify the effectiveness of this aerodynamic optimization method, the aerodynamic performance of a 3-D low-Re blade, such as Blade D900, is optimized, and the results are compared and analyzed based on the experiments and simulations. It is proved that this aerodynamic optimization method is feasible.

Development of the mathematical model for the tilt-rotor aircraft

In this paper, main challenges of the urban air mobility concept are discussed and comparison of the different aircraft types, capable of performing vertical take-off and landing for compliance to the urban aerial mobility concept is provided. The mathematical model for the tilt-rotor aircraft is derived by the Newton-Euler method. This model takes into account all the forces and moments applied to the aircraft. Aerodynamic characteristics for the developed aircraft were obtained using virtual aerodynamic blowing method. Simulation results of the tilt-rotor aircraft motion on the various flight stages, including vertical take-off and landing, horizontal flight and transition stages are presented.

Aerodynamic and flight dynamic iterative simulation method of a joined wing aircraft

Aerodynamic and flight dynamic iterative simulation method of a joined wing aircraft

Multi-objective aerodynamic optimization of high-speed train heads based on the PDE parametric modeling

With the increasing running speed, the aerodynamic issues of high-speed trains are being raised and impact the running stability and energy efficiency. The optimization design of the head shape is significantly important in improving the aerodynamic performance of high-speed trains. Existing aerodynamic optimization methods are limited by the parametric modeling methods of train heads which are unable to accurately and completely parameterize both global shapes and local details. Due to this reason, they cannot optimize both global and local shapes of train heads. In order to tackle this problem, we propose a novel multi-objective aerodynamic optimization method of high-speed train heads based on the partial differential equation (PDE) parametric modeling. With this method, the half of a train head is parameterized with 17 PDE surface patches which describe global shapes and local details and keep the surface smooth. We take the aerodynamic drag and lift as optimization objectives; divide the optimization design process into two stages: global optimization and local optimization; and develop global and local optimization methods, respectively. In the first stage, the non-dominated sorting genetic algorithm (NSGA-II) is adopted to obtain the framework of the train head with an optimized global shape. In the second stage, Latin hypercube sampling (LHS) is applied in the local shape optimization of the PDE surface patches determined by the optimized framework to improve local details. The effectiveness of our proposed method is demonstrated by better aerodynamic performance achieved from the optimization solutions in global and local optimization stages in comparison with the original high-speed train head.

Research on Aerodynamic Optimization Method of Multistage Axial Compressor under Multiple Working Conditions Based on Phased Parameterization Strategy

Multistage axial compressor is the key component of aeroengine and gas turbine to realize energy conversion. In order to avoid the “curse of dimensionality” problem in the global optimization process of AL-31F four-stage low-pressure compressor under multiple working conditions, an optimization method based on phased parameterization strategy is proposed. The method uses the idea of “exploration before exploitation” for reference and divides the optimization process into two phases. In the first phase, the traditional parametric modification method based on stacking line is adopted; in the second phase, the full-blade surface parametric modification method with significant low-dimensional characteristics is adopted. Based on the improved artificial bee colony algorithm, a multitask concurrent optimization system is built on the supercomputing platform, and the engineering optimization solution is obtained within 91 hours. The optimization results are as follows: under the condition of meeting the constraints, the adiabatic efficiency is increased by 0.3% and the surge margin is 4.0% at the design speed; the adiabatic efficiency is increased by 0.8% and the surge margin is 2.3% at the off-design speed. These results verify the usefulness and reliability of the optimization method in the field of aerodynamic optimization of a multistage axial flow compressor.

Comparative analysis of sorption-active fillers and methods of their introduction into a polymer matrix in the process of spinning fibrous composite materials by a solution aerodynamic method

A comparative analysis of the efficiency of the most common types of adsorbents of various natures in a test environment with high humidity for obtaining filled fibrous sorption-active materials by the method of solution aerodynamic spinning is carried out. The influence of the spinning methods, the composition and structure of the obtained sorption-active filled fibrous materials, the nature of the polymer matrix, and the type of organic test substances on the protective properties of materials has been studied.

Aerodynamic design optimization of a hypersonic rocket sled deflector using the free-form deformation technique

An aerodynamic design optimization of a hypersonic rocket sled deflector is presented using the free-form deformation (FFD) technique. The objective is to optimize the aerodynamic shape of the hypersonic rocket sled deflector to increase its negative lift and enhance the motion stability of the rocket sled. The FFD technique is selected as the aerodynamic shape parameterization method, and the continuous adjoint method based on the gradient method is used to search the optimization in the geometric shape parameter space; the computational fluid dynamics method for a hypersonic rocket sled is employed. An automatic design optimization method for the deflector is carried out based on the aerodynamic requirements of the rocket sled. The optimization results show that the optimized deflector meets the design requirement of increasing the negative lift under the constraint of drag. By improving the pressure distribution on the surface of the deflector, the negative lift is increased by 7.39%, which confirms the effectiveness of the proposed method.

An object-oriented method for fully coupled analysis of floating offshore wind turbines through mapping of aerodynamic coefficients

This work presents a novel object-oriented approach to model the fully-coupled dynamic response of floating offshore wind turbines (FOWTs). The key features offered by the method are the following: 1) its structure naturally allows for easy implementation of arbitrary platform geometries and platform/rotor configurations, 2) the analysis time is significantly faster than that of standard codes and results are accurate in situations where rotor dynamic contribution is negligible, and 3) an extremely flexible modeling environment is offered by the object-oriented nature of Modelica. Moreover, the current modeling facility used for the code development is open source and is naturally suitable for code sharing. In the present method, the aerodynamic model computes the aerodynamic loads through the mapping of steady-state aerodynamic coefficients. This modeling approach can be placed at the intersection between simplified aerodynamic methods, such as TDHMill, and full beam element/momentum-based aerodynamic methods. Aerodynamic loads obtained from the coefficients mapping are composed of a concentrated thrust and a concentrated torque. The thrust acts at the hub, while the torque is applied at the rotor low-speed shaft of a simplified rigid rotor equation of motion (EoM) used to emulate the rotor response. The aerodynamic coefficients are computed in FAST for a baseline 5 MW wind turbine. A standard rotor-collective blade-pitch control model is implemented. The system is assumed to be rigid. Linear hydrodynamics is employed to compute hydrodynamic loads. The industry-standard numerical-panel code Sesam-Wadam (DNV-GL) is used to preprocess the frequency-domain hydrodynamic problem. Validation of the code considers a standard spar-buoy platform, based on the Offshore Code Comparison Collaboration (OC3-Hywind). The dynamic response is tested in terms of free-decay response, Response Amplitude Operator (RAO), and the time histories and power spectral densities (PSDs) of several load cases including irregular waves and turbulent wind. The resulting model is benchmarked against well-known code-to-code comparisons and a good agreement is obtained.

A detailed energy budget analysis of river supercooling and the importance of accurately quantifying net radiation to predict ice formation

AbstractRiver supercooling and ice formation is a regular occurrence throughout the winter in northern countries. The resulting frazil ice production can obstruct the flow through intakes along the river, causing major problems for hydropower and water treatment facilities, among others. Therefore, river ice modellers attempt to calculate the river energy budget and predict when supercooling will occur in order to anticipate and mitigate the effects of potential intake blockages. Despite this, very few energy budget studies have taken place during freeze‐up, and none have specifically analysed individual supercooling events. To improve our understanding of the freeze‐up energy budget detailed measurements of air temperature, relative humidity, barometric pressure, wind speed and direction, short‐ and longwave radiation, and water temperature were made on the Dauphin River in Manitoba. During the river freeze‐up period of late October to early November 2019, a total of six supercooling events were recorded. Analysis of the energy budget throughout the supercooling period revealed that the most significant heat source was net shortwave radiation, reaching up to 298 W/m2, while the most significant heat loss was net longwave radiation, accounting for losses of up to 135 W/m2. Longwave radiation was also the most significant heat flux overall during the individual supercooling events, accounting for up to 84% of the total heat flux irrespective of flux direction, highlighting the importance of properly quantifying this flux during energy budget calculations. Five different sensible (Qh) and latent (Qe) heat flux calculations were also compared, using the bulk aerodynamic method as the baseline. It was found that the Priestley and Taylor method most‐closely matched the bulk aerodynamic method on a daily timescale with an average offset of 8.5 W/m2 for Qh and 10.1 W/m2 for Qe, while a Dalton‐type equation provided by Webb and Zhang was the most similar on a sub‐daily timescale with average offsets of 20.0 and 14.7 W/m2 for Qh and Qe, respectively.

프로펠러 효과를 반영 가능한 패널 기반 신속 공력 해석 기법 개발

전기동력 분산추진 비행체는 다수의 프로펠러로 인하여 복잡한 프로펠러 후류 유동 및 기체와의 상호간섭이 발생한다. 이에 따라 초기설계 단계에서는 다양한 형상과 비행 조건에 대하여 프로펠러 구동 효과를 반영한 신속 공력 및 하중 해석이 요구된다. 본 연구에서는 프로펠러 효과를 고려할 수 있는 패널 기반의 효율적인 공력해석 기법을 개발, 검증하였다. Actuator Disk Theory(ADT)에 기반하여 프로펠러 후류 영역의 유도 속도장을 계산하고, 이를 3차원 정상 용출-중첩 패널기법의 비행체 표면 경계조건에 반영하였다. 한국항공우주연구원의 Quad Tilt Propeller(QTP) 비행체 단독 프로펠러와 선행 실험 연구의 프로펠러-날개 형상을 벤치마크 문제로 선정하여 해석을 수행하였다. Actuator 기법 기반의 전산유체역학(CFD) 결과와의 비교를 통해 프로펠러의 후류 속도장과 프로펠러 구동에 따른 날개의 공력하중 분포 변화를 검증하였다. 자율비행 개인용 항공기(Optional Piloted PAV, OPPAV)와 QTP 공력해석에 기법을 적용하고, CFD와의 해석 소요 시간 및 결과 비교, 분석을 통해 기법의 실용성과 타당성을 확인하였다.

Luminescent properties of doped amorphous and polycrystalline Y3Al5O12‐Al2O3

AbstractTransparent polycrystalline ceramics (TPCs) are crystalline materials with single‐crystal‐like transparency, which, however, have to rely on fabrication processes with a relatively high cost. Here, we produced lab‐scale TPCs based on the typical refractory Y2O3‐Al2O3 system, through full congruent crystallization of the parent glass prepared by aerodynamic levitation melting method. Doping of the glass and TPCs by rare‐earth (RE) ions (Ce3+, Tb3+, Nd3+, and Yb3+) and transition‐metal (TM) ions (Cr3+) results in strong visible and near‐infrared (NIR) photoluminescence with high quantum yield. The dominance of Stark splitting of the emission band for RE and TM ions in the TPCs as compared with that of the glass confirms crystallization of the parent glasses.