Aerodynamic Part Research Articles

Measurement of the low-wavenumber component within a turbulent wall pressure by an inverse problem of vibration.

An experimental validation is implemented for the measurement of a weak acoustic component within a turbulent wall pressure by an inverse problem of vibration. The turbulent flow is generated by a forward-facing step in a wind tunnel. In addition to the flow, an acoustic source with a low level excites the plate and plays the role of an additional acoustic component to be identified. The inverse methods called the force analysis technique and the corrected force analysis technique are used to compute the wall pressure fluctuations from the measurement of the plate vibration using an array of 13 accelerometers. The results show that contrary to the conventional techniques using pressure sensors, the inverse methods have a very good signal-to-noise ratio at the low wavenumbers. Indeed, the plate vibration is much more sensitive to the acoustic component than to the aerodynamic part. Moreover, this study shows that both methods can be used to isolate the weak acoustic part and identify its frequency spectrum.

The modeling and numerical simulations of wind turbine generation system with free vortex method and simulink

This paper mainly focuses on the modeling and simulation of the doubly fed induction generator (DFIG) based wind turbine generation system. In this paper, a new method which combines the mechanical part and electrical part is presented to model the wind turbine generation system. The turbine rotor blade is modeled by the lifting line model and the aerodynamic forces are solved by the improved free vortex wakes method with the supplementary of two dimensional aerodynamic data (three dimensional corrected). The control system of pitching and generator with voltage oriented control (VOC) are established in Matlab/Simulink. The drive train is also modeled with two mass model. In order to realize the coupling computation of the wind turbine model, a data link is built to transfer the parameters between aerodynamic part and electrical part. In this way, the interaction between turbine rotor and generator could be predicted. The validations are firstly made to ensure the reliability of the model. Then the performance of a 1.5MW wind turbine is investigated with this integrated model under different wind and symmetrical grid voltage dip condition.

Aerodynamic instability performance of twin box girders for long-span bridges

Twin box girders are a popular choice among long-span bridge engineers, and the aerodynamic performance of such a system is critical to the stability of a bridge under wind excitation. Two groups of twin-box girders with six representative slot width ratios varying from 0% to 100% were utilised to investigate the influence of different wind fairing shapes on aerodynamic instability performance for both torsional divergence and flutter of the girders. The girders with two wind fairing shapes for various slot ratios were investigated by wind tunnel tests and theoretical analyses. Based on the experimental results of static wind loads and critical flutter wind velocities, the symmetry of wind fairing only showed an influence on the development pattern of drag force coefficients and the flutter performance was only significantly affected when the slot width ratio was over 40%. It is also shown that the effect of structural stiffness variation caused by the change of slot width ratio cannot be neglected in stationary torsional divergence analysis. The flutter performance of twin box girders with asymmetric wind fairing is sensitive to slot width ratio due to the existence of optimal slot width, which is opposite to the case with symmetric wind fairing, especially when this ratio is over 40%. Different aerodynamic damping parts contributing to the torsional aerodynamic damping and the participation level of each degree of freedom (DOF) were analysed through a two-dimensional three degree of freedom (2D-3DOF) method, and the results indicate that the improvement in flutter performance can be mainly attributed to the decrease in aerodynamic negative damping Part F (caused by the couple effect of the torsional and vertical motion) and the increase of participation level in heaving motion at the flutter onset. Particle Image Velocimetry (PIV) techniques were further employed to reveal that the change in central slot width ratio and the symmetry of wind fairing have a great influence on the vortices’ characteristics, especially in the central slot region when the slot ratio is over 40%. This was determined by observing the flow structures around the deck sections in terms of wind velocity field and vortex characteristics.

Simulation of DFIG wind turbines for transient studies: An alternative approach based on symbolic–numeric computations

This paper describes an alternative approach based on symbolic and numeric computations to simulate wind turbines equipped with doubly fed induction generator (DFIG). The actuator disk theory is used to represent the aerodynamic part, and the one-mass model simulates the mechanical part. The 5th-order induction generator is selected to model the electric machine, being this approach suitable to estimate the DFIG performance under transient conditions. The corresponding non-linear integro-differential equation system has been reduced to a linear state-space system by using an ad hoc local linearization. This novel symbolic–numeric computation (SNC) method has been implemented by using two different software-packages, with the purpose of solving simultaneously a remarkable number of individual wind turbine models submitted to different wind speed profiles and/or grid voltage waveforms.The obtained results are compared with traditional finite difference discretization (FDD) methods, widely proposed for this type of studies. The results offer a remarkable agreement between the proposed SNC method and the FDD solutions, considering variations of both wind speed profiles and electrical transient events. In this way, real voltage dips collected in Spanish wind farms are used as input voltage waveforms to evaluate the suitability of the proposed solution under transient disturbances when a large amount of individual wind turbines are simultaneously simulated. In this way, a comparison of computational time costs considering different number of wind turbines and integration time-steps is also included in the paper. From this comparison, the proposed SNC method presents clear advantages in terms of computational time cost requirements under both steady-state and transient studies.

Study of Ditching Characteristics of Transport Aircraft by Global Moving Mesh Method

This paper numerically investigates the ditching characteristics of the NACA TN 2929 model. In the simulation method, the Reynolds-averaged Navier–Stokes equation and realizable turbulence model are solved by the finite volume method; the volume-of-fluid method is used to capture the water–air interface; the six-degree-of-freedom model and the global-moving-mesh method are used to deal with the relative motion between the water and the object. Global moving mesh is a new dynamic-mesh method, which is proposed to simulate water-entry problems. In global moving mesh, the whole computational domain and boundaries move together with the object to avoid the high computational expense and low-quality mesh in the traditional mesh-deformation method. This numerical method is applied to simulate the water impact of a two-dimensional cylinder in free fall, and the results show a good agreement with the experimental data. The effect of each aerodynamic part of the NACA TN 2929 model on the ditching behavior is studied in detail, and the results show that aerodynamic loads cannot be ignored when analyzing the ditching motion of the aircraft.

A genetic algorithm for a self-learning parameterization of an aerodynamic part feeding system for high-speed assembly

The aerodynamic feeding technology developed at the IFA allows feeding rates up to 800 parts per minute while maintaining high reliability and variant flexibility. The machine's setup procedure requires the adaptation of only four machine parameters. Currently, optimal parameter configurations need to be identified manually. This task is greatly time-consuming and requires a high level of expertise.Prospectively, the machine should utilize an algorithm that autonomously identifies optimal parameter configurations for new workpieces to realize fast setup procedures. This paper presents a genetic algorithm for a self-learning feeding system that has been validated in comprehensive simulation studies.

Continuous and Discrete Adjoint Approach Based on Lattice Boltzmann Method in Aerodynamic Optimization Part I: Mathematical Derivation of Adjoint Lattice Boltzmann Equations

AbstractThe significance of flow optimization utilizing the lattice Boltzmann (LB) method becomes obvious regarding its advantages as a novel flow field solution method compared to the other conventional computational fluid dynamics techniques. These unique characteristics of the LB method form the main idea of its application to optimization problems. In this research, for the first time, both continuous and discrete adjoint equations were extracted based on the LB method using a general procedure with low implementation cost. The proposed approach could be performed similarly for any optimization problem with the corresponding cost function and design variables vector. Moreover, this approach was not limited to flow fields and could be employed for steady as well as unsteady flows. Initially, the continuous and discrete adjoint LB equations and the cost function gradient vector were derived mathematically in detail using the continuous and discrete LB equations in space and time, respectively. Meanwhile, new adjoint concepts in lattice space were introduced. Finally, the analytical evaluation of the adjoint distribution functions and the cost function gradients was carried out.

Development of Silicon Nitride‐Based Ceramic Radomes — A Review

Radome is an aerodynamic structural part attached to the fore‐end of a missile. It transmits electromagnetic signals with minimum attenuation and also protects radar communication system, and thus, the radomes are made of ceramics as they have desirable properties required by the radomes. The flexural strength, dielectric constant, and loss tangent values of various ceramic materials used in the development of radomes are important in the selection of radome materials. Different nose cone shapes of missile radomes are also important. Ceramic materials show variational properties with sintering time, temperature, and other additives. The existing different near‐net shape fabrication techniques for manufacturing of ceramic radomes are discussed and compared. Gelcasting is one of the manufacturing techniques to produce radomes with homogeneous and high green strength. Gelcast parts of silicon nitride ceramics are hard, tough, brittle, and wear‐resistant and are difficult to machine using conventional methods of machining. Therefore, laser‐assisted machining is used for fine finish of ceramic radomes with excellent surface integrity and productivity. This paper deals with a review of development of ceramic radomes, manufacturing methods for variety of applications.

Laminar-turbulent transition prediction module for LOGOS package

The present work is devoted to a description and substantiation of an original module for computing the location of laminar-turbulent transition in subsonic boundary layer flows, which is based on the eN-method and enables more accurate computations of the flow around bodies in the presence of the so-called natural transition to turbulence in the boundary layer. A combined work of the module and the RANS solver from the aerodynamic part of the LOGOS package is demonstrated by the example of the flow past a flat plate. The obtained computed locations of the beginning and the end of the laminar-turbulent transition coincide with known reference values.

PMSG Wind Energy Conversion System: Modeling and Control

In this paper, a model of a variable speed wind turbine using a permanent magnet synchronous generator (PMSG) is presented and the control schemes are proposed. The model presents the aerodynamic part of the wind turbine, the mechanic and the electric parts. Simulations have been conducted with Matlab/Simulink to validate the model and the proposed control schemes.

Design and Experimental Results of a Quad-Rotor Control System

Multi-rotor is one of the emerging Unmanned Aerial Vehicle platforms. This paper covers the design, fabrication, modeling and testing of a quad-rotor control system. To take into account the salient nonlinearities, a model with six degrees of freedom nonlinear dynamics and some linear approximation of the aerodynamic part are used when extracting a linear model and designing a attitude controller. We obtained a linear model from experimental data using system identification method and developed attitude control algorithm. The control algorithm was realized using an on a board microprocessor and verified through experiment in real environment.

Wind Turbine Control Strategy Enabling Mechanical Stress Reduction Based on Dynamic Model Including Blade Oscillation Effects

The paper presents a coupled electrical aerodynamic model for a three blade wind-turbine dynamic analysis. The model is based on a blade element representation of the aerodynamic load part combined with an aeroelastic beam element for the dynamic analysis of a real rotor blade, including top tower acceleration. The model involves reduced computation time enabling to be applied in control system hardware. Such an analysis is very promising for obtaining controllers involving compromises among contradictory targets such as energy capture maximization and mechanical stresses reduction in the aerodynamic part.

Dynamic modeling of the airship with Matlab using geometrical aerodynamic parameters

Airships provide an attractive solution to many challenges in the aviation industry. The buoyancy force offered by the airship enables to be used for long endurance aero applications. Key objective is to operate the vehicle with a sufficient level of autonomy under extreme range of atmospheric and wind conditions. In order to achieve these goals, a guidance and control system is needed which controls the airship in air at the specified height. The accurate control system first requires an accurate model of the airship dynamics. Based on six degrees of freedom, an airship dynamic model is presented in this paper. The aerodynamic part of the model is taken from the geometrical configuration of the vehicle instead of expensive wind tunnel test setup. The computer simulation algorithm is then derived and the easily available Matlab environment is used to simulate it and its initial validation for YEZ-2A airship is demonstrated.

Theoretical and experimental investigations of the dynamics of cantilevered flexible plates subjected to axial flow

In this paper, the dynamics of cantilevered flexible plates subjected to axial flow is investigated theoretically and experimentally. A nonlinear equation of motion of the plate based on the inextensibility assumption, coupled with an unsteady lumped vortex model for the aerodynamic part is used to analyze the instability and post-critical dynamical behaviour of this fluid–structure system theoretically. Experiments have been conducted in a 3 ft×2 ft (914 mm×610 mm) cross-section wind tunnel, using polypropylene carbonate (PPC) films, thin brass plates, polyethylene terephthalate (PET) sheets, and type 304 stainless steel sheets, with maximum dimensions 224 mm×168 mm. In the experiments, time traces, power spectral densities (PSDs), phase-plane plots, Poincaré maps, probability density functions (PDFs) and autocorrelations are used to characterize the motions of the system. Periodic and chaotic oscillations have been observed in the experiments. It has also been observed that flutter arises via a subcritical bifurcation involving hysteresis for large aspect ratio plates; this hysteresis does not occur for low aspect ratio plates. The hysteresis phenomenon is considered to be due to spanwise deformation of the plates. The effect of aspect ratio on critical flow velocity is investigated. The experimental critical flow velocities for flutter onset are in good agreement with the theoretically predicted values.

Fluid/structure interaction in numerical aeroelastic simulation

This paper describes a fluid/structure interaction method for application in aeroelastic analyses of aircraft in transonic flow. The method is based on an improved time integration scheme of a linear structural model being loosely coupled to non-linear Euler/Reynolds-averaged Navier–Stokes equations for the aerodynamic part. Two- and three-dimensional test cases are presented which demonstrate the adequate accuracy and good efficiency for use in aircraft design practice.

Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient.

Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(-)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously used for calculating the gliding performance of a peregrine. The accuracy with which drag coefficients measured on wingless bird bodies in a wind tunnel represent the C(D,par) of a living bird is unknown. Another method for determining C(D,par) selects values that improve the fit between speeds predicted by mathematical models and those observed in living birds. This method yields lower values for C(D,par) (0.05-0.07) than wind tunnel measurements, and the present study suggests a value of 0.1 for raptors as a compromise.

Aerodynamic Part Feeding: Development of Aerodynamic Orienting Devices

Because of the pressure for continuous rationalisation, companies, especially in industrialised countries, have to reduce their unit costs. A common way to fulfil this demand is to reduce labour costs by using fully automatic assembly systems. The assembly process itself has been optimised using many disciplines. Assembly has become more flexible and faster. This rapid improvement, however, cannot be observed in the area of part-feeding systems. In spite of the fact that part feeding is a key technology for high efficiency in fully automated assembly systems, the devices which provide the assembly processes with small parts have not generally improved in the last decades. Hence, innovative feeding technologies based on aerodynamic effects are being developed at the Institute of Production Systems. In this paper we focus on the orientation function of the feeding process.

On the Coupling of Aerodynamic and Structural Design

The symbol of the Hessian for a static aeroelastic optimization model problem is analyzed for the optimization of a plate's shape and rigidity distribution with respect to a given cost function. The flow is modeled by the small-disturbance full-potential equation and the structure is modeled by an isotropic (von Kármán) plate equation. The cost function consists of both aerodynamic and structural terms. In the new analysis the symbol of the cost function Hessian near the minimum is approximated for the nonsmooth error components in the shape and rigidity. The result indicates that the system can be decoupled to two single discipline subminimization problems which will effectively converge to the multidisciplinary optimal solution. The result also indicates that the structure part in the Hessian is well conditioned while the aerodynamic part is ill conditioned. Applications of the result to optimization strategies are discussed and demonstrated numerically.

Evidence of high deposition of ultrafine particles at Mauna Loa Observatory

Few measurements exist for the dry deposition of ultrafine particles (diameters less than about 10 nm) under realistic field conditions. Recently refined screen-diffusion techniques have sufficient sensitivity to measure radon ( 222Rn) progeny under low-level outdoor conditions. Vertical gradients of ultrafine radon progeny at Mauna Loa Observatory were measured for a range of atmospheric conditions. Gradients were generally stronger, for example, than previously reported for the reactive vapor HNO 3 under comparable meteorological conditions. Gradient analysis indicated a mean deposition velocity for unstable conditions and moderate winds of 5.2 ± 0.9 cm s −1 at a reference height of 18 m. Estimated deposition velocities for lower reference heights were higher for many daytime conditions. These results are higher than suggested by some models and references, and indicate that the aerodynamic part of deposition might be greater than sometimes assumed. At Mauna Loa Observatory, dry deposition could be more important than previously thought for reduction of the concentration of certain reactive trace gases and ultrafine particles sampled near ground.

Evaporation of crude oil at sea

A simple model for describing the simultaneous evaporation and spreading of oil spills at sea has been developed and tested. A previously reported theory was used for calculating the aerodynamic part of the evaporation process. Here, the thermodynamic part, i.e. the oil characterization and the weathering processes, is described in detail. By comparison with the results of laboratory evaporation experiments and sea trials the model is shown to work quite adequately. Also, the influence of the mixing of oil into the water column, e.g. due to wave action, is shown to be small enough to be neglected. The spreading model was purposely kept as simple as possible, in view of the uncertain influences of wave action and emulsion formation. The velocity of the edge of the oil slick is prescribed and a critical thickness beyond which the slick stops spreading is introduced. The latter turns out to have a significant influence on the rate of evaporation. Examples of crude evaporation are given and the influence of temperature and wind velocity is investigated.