Aerodynamic System Research Articles

Exploring the potential benefits of using metasurface for galloping energy harvesting

Inspired by the successful applications of metasurfaces in many other fields, this paper aims to explore the potential application of metasurfaces in designing aerodynamic systems. Bluff bodies are proposed to be wrapped in metasurfaces for improving galloping energy harvesting. Three different metasurfaces with convex cylinder, tri-prim, and wedge ornaments are designed. A general aeroelastic model for a galloping energy harvester is developed. The aerodynamic force is represented by a polynomial function with its coefficients being determined from three-dimensional CFD simulations. Subsequently, physical prototypes of the proposed galloping piezoelectric energy harvesters are fabricated, and experimental tests are conducted. The theoretical model is validated by the experimental results. The analytical method and three-dimensional CFD simulation are combined to predict the dynamic responses of the metasurface-wrapped GPEHs. Besides, the results show that the metasurface can significantly change the aerodynamic characteristics of the bluff body, and it is learned that a bluff body wrapped in convex cylinder metasurface could bring benefits for promoting galloping energy harvesting performance. Further experimental studies are conducted to reveal the effects of convex ornament parameters on the galloping energy harvesting performance. It is found that using the metasurface distributed with convex cylinder ornaments of diameter 6 mm and height 9 mm leads to the largest vibration displacement and largest voltage output. Compared to the typical GPEH, the maximum vibration displacement and maximum output voltage of the proposed galloping piezoelectric energy harvester can be increased by 26.81% and 26.14%, respectively. The vortex shedding processes around the wind flow fields near the bluff bodies wrapped in metasurfaces are simulated. The underlying aerodynamic mechanism of the influence of the metasurfaces is unveiled. Finally, based on the validated theoretical model, a parametric study is carried out to investigate the effects of the load resistance and electromechanical coupling strength on the galloping energy harvesting performance. It is concluded that increasing the coupling strength to a certain level and tuning the load resistance to the optimal value could further improve the power output. However, when the electromechanical coupling strength increases to a certain extent, the power output will reach the saturation state, and the coupling strength is extremely large. Therefore, a piezoelectric element with a moderate coupling coefficient is recommended for practical applications from the perspective of economic benefit.

Data-driven prediction of unsteady pressure distributions based on deep learning

In the present work, an efficient Reduced-Order Model is developed for the prediction of motion-induced unsteady pressure distributions. The model is trained on the basis of synthetic data generated by full-order Computational Fluid Dynamics (CFD) simulations. The nonlinear identification task is to predict a snapshot representing the pressure distribution for the current time step based on respective snapshots of previous time steps and applied excitation. Once a Reduced-Order Model is conditioned on training data, it can predict sequences of the pressure distribution in a recurrent manner based on the excitation signal. Hence, it is able to capture the motion-induced nonlinear unsteady aerodynamics for a given configuration at fixed free-stream conditions. In this way, computationally extensive CFD simulations can be substituted by the application of the more efficient Reduced-Order Model. The nonlinear behavior of the aerodynamic system is captured based on a deep convolutional neural network. The performance of the Reduced-Order Model is demonstrated based on the LANN (Lockheed-Georgia, Air Force Flight Dynamics Laboratory, NASA-Langley and NLR) wing performing high-amplitude pitching motion in transonic flow. The unsteady aerodynamics of the considered test case is dominated by nonlinear effects due to complex moving shock structures both on the upper and lower surface of the wing. The Reduced-Order Model yields a superior prediction accuracy at a speed-up of more than three orders of magnitude compared to the employed CFD method.

In situ synchrotron XRD measurements during solidification of a melt in the CaO–SiO2 system using an aerodynamic levitation system

Phase formation and evolution was investigated in the CaO–SiO2 system in the range of 70–80 mol% CaO. The samples were container-less processed in an aerodynamic levitation system and crystallization was followed in situ by synchrotron x-ray diffraction at the beamline P21.1 at the German electron synchrotron (DESY). Modification changes of di- and tricalcium silicate were observed and occurred at lower temperatures than under equilibrium conditions. Despite deep sample undercooling, no metastable phase formation was observed within the measurement timescale of 1 s. For the given cooling rates ranging from 300 K s−1 to about 1 K s−1, no decomposition of tricalcium silicate was observed. No differences in phase evolution were observed between reducing and oxidizing conditions imposed by the levitation gas (Ar and Ar + O2). We demonstrate that this setup has great potential to follow crystallization in refractory oxide liquids in situ. For sub-second primary phase formation faster detection and for polymorph detection adjustments in resolution have to be implemented.

Hybrid Laminar Flow Control on A320 Fin: Retrofit Design and Sample Results

A flight test with a simplified hybrid laminar flow control (HLFC) system on the vertical tail plane (VTP) of an A320 aircraft was performed in April/May 2018. This HLFC system was a prototype for a simplified system that might be attractive for drag reduction of commercial long-range aircraft. The paper presents the design principles of a simplified HLFC system, including passive suction, and shows their application to aerodynamic and suction system design for the retrofit of an A320 VTP. Furthermore, sample flight test results will be presented and discussed.

Model Predictive Control of Nonlinear MIMO Systems Based on Adaptive Orthogonal Polynomial Networks

This paper considers a new design of model predictive control based on specific models in the form of adaptive orthogonal polynomial networks, built around a specially tailored basis of generalized orthogonal functions. Polynomial model has a single layer structure and a smaller number of model parameters than classical neural networks, usually used for model predictive control design, leading to lower complexity and shorter calculation time. Desired property of adaptability of the model is achieved by using additional variable factors inside the orthogonal basis. The designed controller was applied in control of twin-rotor aero-dynamic system as a representative of nonlinear multiple input-multiple output systems and compared to the other state-of-the-art control algorithms.

Theories and Applications of CFD–DEM Coupling Approach for Granular Flow: A Review

Bio-particulate matter includes grains, cereal crops, and biomass that are considered discrete materials with irregular size and shape. Although the flow of these particles can behave like a continuum fluid at times, their discontinuous behavior cannot be simulated with traditional continuum-based modeling. The Discrete Element Method (DEM), coupled with Computational Fluid Dynamics (CFD), is considered a promising numerical method that can model discrete particles by tracking the motion of each particle in fluid flow. DEM has been extensively used in the field of engineering, where its application is starting to achieve the popularity in agricultural processing. While CFD has been able to simulate the complex fluid flows with a quantitative and qualitative description of the temporal and spatial change of the flow field. This paper reviews the recent strategies and the existing applications of the CFD–DEM coupling approach in aerodynamic systems of bio-particles. It mainly represents four principal aspects: the definition of aerodynamic systems with its principals, modeling of particle motion including interaction forces of particle–particle and particle–fluid in the system, CFD–DEM coupling methodologies, and drag correlation models with theoretical developments, and the applications of aerodynamic systems related to the agricultural field. The existing published literature indicates that CFD–DEM is a promising approach to study the bio-particulate matter behavior immersed in fluid flow, and it could be benefiting from developing and optimizing the device's geometry and the operations. The main findings are discussed and summarized as a part of the review, where future developments and challenges are highlighted.

Research on the Stability of an Air-to-Air Missile Compound Control System with a Pulse Modulator

Based on pulse modulator, a method of lateral force and aerodynamic compound control system design in air-to-air missile and the stability is studied. First, the lateral force is assumed to be continuous and blended with aerodynamic fins accordding to a certain proportion, and the compound control is designed based on three-loop control method. Then the switch order of direct force device is obtained based on the pulse modulator. At last, the stability of control system is analysed based on describing function method, and then the parameter of pulse modulator is properly chosen. Simulation results show the validity of the proposed design.

Sliding Mode Control for the Regulation Problem of an Aerodynamic Angular System: Experimental Platform and Validation

Based on a previous theoretical work, this paper focuses on the experimental validation of a sliding mode control (SMC) technique applied to an aerodynamic angular system (AAS). To do so, an aerodynamic experimental platform is presented together with its electronic interface and its closed-loop behavior generated by the aforementioned SMC strategy. The control performance is widely reviewed under different regulation tasks and gain variations. Experimental results prove that the control strategy guarantees a stable behavior. Moreover, the robustness of the control strategy is proved when the system is subject to the influence of external disturbances.

Control of vortex shedding around a circular cylinder using bubble tabs in the laminar flow regime

Vortex induced vibration (VIV) is the major cause of several catastrophic disasters due to fatigue failures induced by drag and lift forces in aerodynamic systems. This study investigates the control of VIV phenomenon through passive bubble tab(s) having a small diameter (d) relative to the main circular cylinder (D) in a two-dimensional (2-D) flow domain. Using ANSYS Fluent computational software, flow analysis was conducted at a Reynolds number (Re) of 80 for various bubble tab configurations at different spacing ratios (x/D) and diameter ratios (d/D). The drag coefficient, the velocity and pressure contours, along with the flow streamlines in eachcase were studied. The results indicated the optimized tab(s) positions for different spacing ratios, diameter ratios, and configurations. The study effectively established that passive bubble tabs can potentially control VIV associated with flows around a circular cylinder.
 Keywords: Vortex Shedding; Drag Coefficient; Circular Cylinder; Bubble Tab(S); Spacing Ratio; Diameter Ratio.

Correction to: Innovative aerodynamic grain separation system for plant harvesting in sloped areas: problems, research and optimization of parameters

This article presents the main problems associated with cereal harvesting in sloping areas. The presented innovative aerodynamic system supporting the separating unit of combine harvester can be one of the ways to counteract the negative effects of harvesting machines work on slopes. The Monte Carlo numerical method, presented in this article, was applied in the optimization of an aerodynamic sieve separation process on an inclined terrain. The given variables are the transverse slope of separator α (of the sieve), longitudinal slope β and the output of the main and side fans. The Monte Carlo method makes it possible to determine an optimized set of parameters (α = 10°, β = 2.8°, δ = 9°), the output of the main fan (0.67 m3 s−1) and the output of the side fan (1.86 m3 s−1), allowing to obtain the best indicator values of 2.1% grain loss and 97.5% grain purity.

On the use of metasurface for Vortex-Induced vibration suppression or energy harvesting

This paper explores the use of metasurface in designing an aerodynamic system for potential vortex-induced vibration (VIV) suppression or energy harvesting. Four kinds of metasurface patterns are designed to decorate an ordinary cylinder bluff body for modifying its aerodynamic characteristics. A theoretical model is developed for the VIV system by describing the wake as a van der Pol oscillator. The aerodynamic parameters, i.e., the lift and drag coefficients, used in the theoretical model, are determined from three-dimensional CFD simulations. A wind tunnel experiment is conducted to validate the theoretical model and investigate the aerodynamic behaviors of the VIV systems with different bluff bodies. It is found that the metasurface pattern has a significant influence on the aerodynamic characteristics of the bluff body. Using different metasurface patterns to decorate the bluff body, the vortex-induced vibration of the system could be either enhanced or suppressed, compared with the baseline reference using an ordinary bluff body with a smooth surface. Furthermore, the vortex shedding processes are simulated to give further insights into the wake oscillating motions. The roles of the metasurface in suppressing or enhancing the vortex-induced vibration are reasonably explained: the existence of metasurfaces could alter the flow field around the bluff bodies and consequently the aerodynamic force. In addition, based on the validated theoretical model, it is learned from a parametric study that the power output reaches saturation when the electromechanical coupling strength is increased to a certain level. Therefore, piezoelectric transducers with moderate coupling coefficients are recommended for practical applications from the cost-effective perspective.

Numerical investigation on supersaturation phenomenon of humid air in the humidification process

In order to improve the safety and stability of pneumatic equipment, in this paper, the supersaturation phenomenon of humid air and its formation, evolution mechanism during the humidification process, are revealed and evaluated in detail with the defined evaluation criterion. In term of the finite difference method, the integrated mathematical models for humidification process are established, considering the unsaturated, saturated and supersaturated state of humid air. The influence laws of the specified critical parameters on the supersaturation characteristics of humid air are obtained at off-design conditions. The simulation results first reveal that the effects of specific surface area of porous media on the supersaturation phenomenon is affinitive with the liquid-gas ratio. It is found that a lower value both of inlet water temperature and inlet relative humidity will slightly weaken the entrainment ratio, while the inlet air temperature has a significant reaction to it, with a minimum value of 1.5 × 10−3 kgkg−1 at the conditions of Twi = 70°C, φi = 0.5 and Tai = 30°C. It is also obtained that raising the inlet wet-bulb temperature is effective to reduce the entrainment ratio. Furthermore, in the process of the development of supersaturation phenomenon, the entrainment ratio increases rapidly at the humid air outlet for all the cases, which are of great value for humidity control in aerodynamic systems.

A review on thin film fast response heat transfer gauges

In this paper, an effort has been made to compile various research investigations done so far on fast response gauges for the short duration measurement in the transient state. The review paper is not only about summarization of all-important research work; rather, a detailed review on the development of the fast response gauges, its application, and various methods of heat estimation from the measured transient temperature history is also presented. Before discussing the development of fast response gauges, various heat flux measurement techniques and newer trends in heat transfer gauges are presented. The focus of this Review is mainly on the thin-film gauge, a robust fast response temperature detector best suited for the short duration measurement. The literature on the application of thin-film gauges for various engineering systems such as turbomachinery and aerodynamic heating systems is broadly categorized as single-layered and multi-layered gauges. The applications for the internal combustion engine and low heat flux measurement are also discussed later. The summary tables with studies arranged in chronological order are also provided. Finally, the estimation of the heat transfer rate from the measured transient temperature data is presented.

Real-Time Performance Analysis of PIDD2 Controller for Nonlinear Twin Rotor TITO Aerodynamical System

Twin-rotor two-input two-output (TITO) aerodynamical system (TRAS) is a highly non-linear system with a cross-coupling effect. The objective of the controller design in TRAS is to track the trajectory of azimuth and pitch angles, reach the desired azimuth and pitch angle positions, and stabilize TRAS in the presence of significant cross-coupling. The coupling effect between the main rotor and tail rotor is a severe issue for the controller design. So, this paper proposes a proportional integral derivative double derivative (PIDD2) controller design for TRAS, first time. Further, the tuning of PIDD2 controller is carried out via a modified grey wolf optimizer (MGWO). Besides, the real-time hardware-in-loop (HIL) implementation of the PIDD2 controller with the TRAS laboratory prototype setup is carried out, first-time. Moreover, It is tested under external disturbances for robustness and effectiveness analyses. In addition, this paper performs both simulations as well as hardware results analyses. These analyses reveal that the experimental results are found to match closely with simulation results. Finally, the efficacy of the proposed control design approach is presented by comparing it with the recently published controldesign schemes.

Heat transfer with interface effects in high-enthalpy and high-speed flow: Modelling review and recent progress

Aerodynamics, aerothermodynamics and thermal protection system response in high-enthalpy and high-speed flow is heat transfer with interface effects in nature. Modelling and simulation of these phenomena are of vital significance to ensure high-speed flight thermal safety. The heat transfer phenomena related with gas-surface interaction, interface heterogeneous reactions and microstructure morphology in high-enthalpy and high-speed flow were summarized. The modelling of interface effects and the corresponding coupling algorithms for computational fluid dynamics (CFD) and related approaches were reviewed. Recent research activities for interface problems in high-enthalpy and high-speed flow at China Aerodynamics Research and Development Center were discussed. They mainly focus on practical solutions of computational fluid dynamics with viscous wall boundary conditions, multi-zone coupling for fluid-thermal interaction and cross-scale algorithms of CFD coupled with smaller scale theoretical approaches. Finally, further perspectives about heat transfer with interface effects were proposed, including mesoscale experimental verification, interface cross-scale modelling and accuracy/uncertainty of coupling algorithms.

Innovative aerodynamic grain separation system for plant harvesting in sloped areas: problems, research and optimization of parameters

This article presents the main problems associated with cereal harvesting in sloping areas. The presented innovative aerodynamic system supporting the separating unit of combine harvester can be one of the ways to counteract the negative effects of harvesting machines work on slopes. The Monte Carlo numerical method, presented in this article, was applied in the optimization of an aerodynamic sieve separation process on an inclined terrain. The given variables are the transverse slope of separator α (of the sieve), longitudinal slope β and the output of the main and side fans. The Monte Carlo method makes it possible to determine an optimized set of parameters (α = 10°, β = 2.8°, δ = 9°), the output of the main fan (0.67 m3 s−1) and the output of the side fan (1.86 m3 s−1), allowing to obtain the best indicator values of 2.1% grain loss and 97.5% grain purity.

Influence of the PVD process conditions on the incorporation of TiN nanoparticles into magnetron sputtered CrN thin films

CrTiN thin films are known to form a solid solution independent from the Ti content. Using a novel spatially separated synthesis approach, consisting of magnetron sputtering and atmospheric-pressure arc evaporation, artificial CrTiN nanocomposites were deposited. For the nanocomposite formation, TiN nanoparticles were synthesized using a transferred arc reactor and directly injected into growing CrN thin films using an aerodynamic lens system. The CrN and CrTiN thin films were deposited using various deposition conditions, such as heating power, substrate rotation velocity, nanoparticle injection distance, and cathode setup. The deposited thin films were analyzed regarding their physical structure, microstructure and mechanical properties. Based on the investigations, between 0.02 and 0.11 at.-% of TiN nanoparticles are embedded in the CrN matrix dependent on the deposition parameters. 2D GI-XRD experiments using synchrotron radiation confirm the nanocomposite structure for the two thin films with the highest TiN nanoparticle content. The crystallite size of the CrN thin film decreases from 9.4 ± 2.3 nm to 5.3 ± 1.2 nm due to the embedding of the nanoparticles. Concerning the physical structure, the nanoparticle injection leads to a change of the texture, as shown by the Debbye-Scherrer rings. Based on TEM-investigations, TiN nanoparticle agglomerates lead to a coarser microstructure of the CrN matrix. The hardness of the thin films is not significantly affected by the nanoparticle embedment. The nanoparticle injection distance and cathode setup reveal the highest impact on the film properties.

Review of Adaptive Shock Control Systems

Drag reduction plays a major role in future aircraft design in order to lower emissions in aviation. In transonic flight, the transonic shock induces wave drag and thus increases the overall aircraft drag and hence emissions. In the past decades, shock control has been investigated intensively from an aerodynamic point of view and has proven its efficacy in terms of reducing wave drag. Furthermore, a number of concepts for shock control bumps (SCBs) that can adapt their position and height have been introduced. The implementation of adaptive SCBs requires a trade-off between aerodynamic benefits, system complexity and overall robustness. The challenge is to find a system with low complexity which still generates sufficient aerodynamic improvement to attain an overall system benefit. The objectives of this paper are to summarize adaptive concepts for shock control, and to evaluate and compare them in terms of their advantages and challenges of their system integrity so as to offer a basis for robust comparisons. The investigated concepts include different actuation systems as conventional spoiler actuators, shape memory alloys (SMAs) or pressurized elements. Near-term applications are seen for spoiler actuator concepts while highest controllability is identified for concepts several with smaller actuators such as SMAs.

Design of an Adaptive Linear Quadratic Regulator for a Twin Rotor Aerodynamic System

This paper deals with a twin rotor aerodynamic system (TRAS), which is a multi-input multi-output (MIMO) system with high crosscoupling between its two channels. It proposes an adaptive linear quadratic regulator (ALQR) to stabilize this system. The justification for using an adaptation technique is that the conventional LQR—designed by linearizing the TRAS about a certain equilibrium point—can no longer achieve the design specifications when the system operating point deviates significantly from the equilibrium point. To introduce an adaptation mechanism in the system, formulas for determining the operating points of the TRAS in terms of the reference inputs are deduced, and the linearized TRAS model is parameterized in terms of the reference inputs so that when the reference inputs change, a new LQR is designed with respect to these new reference inputs, resulting in an ALQR. To demonstrate the superiority of the ALQR over the LQR, transient response specifications (rise time, settling time, and percentage overshoot) as well as integral square error (ISE), integral absolute error (IAE), integral time squared error (ITSE), and integral time absolute error (ITAE) are calculated for both systems. The main contribution of this paper is that it identifies the operating range by its width and its position with respect to the equilibrium point (width, position), and it investigates the effect of these two attributes on the performance of the closed-loop system by considering five cases with different width and position. Simulation results (carried out by MATLAB) show that the ALQR outperforms the LQR and the PID controller in all cases, and its superiority becomes more significant for cases that are characterized by a large deviation from the equilibrium point.

Designing optimal models of nonlinear MIMO systems based on orthogonal polynomial neural networks

ABSTRACT This paper presents a new method for modelling of dynamic systems by using specially designed orthogonal polynomial neural networks. These networks utilize the feature that the basis made of orthogonal functions can be used for approximation of arbitrary function, while their property of orthogonality enables optimal performances in the sense of both convergence time and approximation error. In this regard, generalized quasi-orthogonal polynomials, specifically tailored for the application in the modelling of complex dynamic systems with time-varying behaviour, are considered. Adaptivity of the designed model is achieved by using variable factors inside the orthogonal basis. The designed orthogonal neural network is applied in modelling of laboratory twin-rotor aero-dynamic system as a representative of nonlinear multiple input-multiple output systems. Detailed comparative analysis is performed for a different number of polynomials in expansion with the purpose of finding the optimal model in the sense of trade-off between model accuracy and complexity.