Aerodynamic Tools Research Articles

Comparison of Blade Element Method and CFD Simulations of a 10 MW Wind Turbine

The present studies deliver the computational investigations of a 10 MW turbine with a diameter of 205.8 m developed within the framework of the AVATAR (Advanced Aerodynamic Tools for Large Rotors) project. The simulations were carried out using two methods with different fidelity levels, namely the computational fluid dynamics (CFD) and blade element and momentum (BEM) approaches. For this purpose, a new BEM code namely B-GO was developed employing several correction terms and three different polar and spatial interpolation options. Several flow conditions were considered in the simulations, ranging from the design condition to the off-design condition where massive flow separation takes place, challenging the validity of the BEM approach. An excellent agreement is obtained between the BEM computations and the 3D CFD results for all blade regions, even when massive flow separation occurs on the blade inboard area. The results demonstrate that the selection of the polar data can influence the accuracy of the BEM results significantly, where the 3D polar datasets extracted from the CFD simulations are considered the best. The BEM prediction depends on the interpolation order and the blade segment discretization.

Optimization of Variable-Camber Continuous Trailing-Edge Flap Configuration for Drag Reduction

The variable-camber continuous trailing-edge flap is a novel control surface technology designed to serve as an aeroelastic wing shaping control device. Capable of minimizing drag throughout an aircraft flight envelope, use of the variable-camber continuous trailing-edge flap technology is examined on a flexible-wing transport aircraft configuration known as the NASA generic transport model. Drag reduction studies at various flight conditions are conducted in order to examine the performance of different flap configurations with selected camber deflection profiles. Rapid optimization of the design space is achieved by using aerodynamic–structural modeling based on a vortex lattice method coupled with transonic small disturbance and integral boundary-layer solutions. The begin cruise optimization results show that a parabolic flap deflection profile configuration with three-cambered-segments achieves the largest drag reduction of 8.4% as compared to a clean wing configuration. The configuration is used to run additional optimizations measuring performance benefits at different flight conditions including 20% fuel end cruise, a design lift coefficient, and a Mach overspeed condition. The optimization framework and initial results produce insights that can be used to refine the optimization of variable-camber continuous trailing-edge flap configurations with higher-fidelity aerodynamic tools.

High-resolution simulation for rotorcraft aerodynamics in hovering and vertical descending flight using a hybrid method

A high-resolution simulation tool for rotorcraft aerodynamics is developed by coupling CFD with a Vorticity Transport Model (VTM). An Eulerian-based CFD module is used to model the blade near body flowfield, and a Lagrangian-based VTM module is employed for vortex tracking in the far wake. The coupling procedure is implemented by transmitting vortex sources to the VTM module and feeding boundary conditions back to the CFD module. The presented CFD/VTM hybrid solver is firstly validated by hover cases of three different rotor configurations. Simulation results, including the blade surface pressure distribution, rotor downwash, and hover figure of merit, exhibit favorable correlations with available experimental data. Then, a rotor operated in vertical descending flight with a fixed collective pitch is investigated. It is shown that the CFD/VTM coupling method is suitable for rotor wake simulation. Wake instabilities (far wake breakdown in hover and toroidal wake pattern in the vortex ring state) are successfully demonstrated with a moderate computational cost.

Computational Modelling of Rectangular Sub-Boundary Layer Vortex Generators

Vortex generators (VGs) are increasingly used in the wind turbine manufacture industry as flow control devices to improve rotor blade aerodynamic performance. Nevertheless, VGs may produce excess residual drag in some applications. The so-called sub-boundary layer VGs can provide an effective flow-separation control with lower drag than the conventional VGs. The main objective of this study is to investigate how well the simulations can reproduce the physics of the flow of the primary vortex generated by rectangular sub-boundary layer VGs mounted on a flat plate with a negligible pressure gradient with an angle of attack of the vane to the oncoming flow of β = 18°. Three devices with aspect ratio values of 2, 2.5 and 3 are qualitatively and quantitatively compared. To that end, computational simulations have been carried out using the RANS (Reynolds averaged Navier–Stokes) method and at Reynolds number Re = 2600 based on the boundary layer momentum thickness θ at the VG position. The computational results show good agreement with the experimental data provided by the Advanced Aerodynamic Tools of Large Rotors (AVATAR) European project for the development and validation of aerodynamic models. Finally, the results indicate that the highest VG seems to be more suitable for separation control applications.

Benchmarking New CEASIOM with CPACS adoption for aerodynamic analysis and flight simulation

PurposeThe purpose of this paper is to present the status of the on-going development of the new computerized environment for aircraft synthesis and integrated optimization methods (CEASIOM) and to compare results of different aerodynamic tools. The concurrent design of aircraft is an extremely interdisciplinary activity incorporating simultaneous consideration of complex, tightly coupled systems, functions and requirements. The design task is to achieve an optimal integration of all components into an efficient, robust and reliable aircraft with high performance that can be manufactured with low technical and financial risks, and has an affordable life-cycle cost.Design/methodology/approachCEASIOM (www.ceasiom.com) is a framework that integrates discipline-specific tools like computer-aided design, mesh generation, computational fluid dynamics (CFD), stability and control analysis and structural analysis, all for the purpose of aircraft conceptual design.FindingsA new CEASIOM version is under development within EU Project AGILE (www.agile-project.eu), by adopting the CPACS XML data-format for representation of all design data pertaining to the aircraft under development.Research limitations/implicationsResults obtained from different methods have been compared and analyzed. Some differences have been observed; however, they are mainly due to the different physical modelizations that are used by each of these methods.Originality/valueThis paper summarizes the current status of the development of the new CEASIOM software, in particular for the following modules: CPACS file visualizer and editor CPACSupdater (Matlab) Automatic unstructured (Euler) & hybrid (RANS) mesh generation by sumo Multi-fidelity CFD solvers: Digital Datcom (Empirical), Tornado (VLM), Edge-Euler & SU2-Euler, Edge-RANS & SU2-RANS Data fusion tool: aerodynamic coefficients fusion from variable fidelity CFD tools above to compile complete aero-table for flight analysis and simulation.

The nonaxismmetric endwall aerodynamic optimization design for a large turbine cascade with a midgap

The nonaxisymmetric endwall has been verified to be an effective method in reducing the endwall secondary flow loss. Some assembly features, such as the midgap in the hub of real aircraft engines, may have an influence on the endwall secondary flow. In the present work, a nonaxisymmetric endwall with midgap structure is designed for a large linear turbine cascade. A nonaxisymmetric endwall optimization design procedure is developed to minimize the total pressure loss coefficient at the passage exit. The profile of the endwall is designed using automatic numerical optimization with the Kriging surrogate method. The numerical simulation based on a transition shear stress transport model is used as the aerodynamic evaluation tool for the optimization system. When the midgap is considered in the design, mixing loss between midgap flows and main flow is significantly reduced. However, the loss relative to the passage vortex is increased to some extent.

The Aerodynamic Analysis of a Rotating Wind Turbine by Viscous-Coupled 3D Panel Method

In addition to the many typical failure mechanisms that afflict wind turbines, units in Taiwan are also susceptible to catastrophic failure from typhoon-induced extreme loads. A key component of the strategy to prevent such failures is a fast, accurate aerodynamic analysis tool through which a fuller understanding of aerodynamic loads acting on the units may be derived. To this end, a viscous-coupled 3D panel method is herewith proposed, which introduces a novel approach to simulating the severe flow separation so prevalent around wind turbine rotors. The validity of the current method’s results was assessed by code-to-code comparison with RANS data for a commercial 2 MW wind turbine rotor. Along the outboard and inboard regions of the rotor, pressure distributions predicted by the current method showed excellent agreement with the RANS data, while pressure data along the midspan region were slightly more conservative. The power curve predicted by the current method was also more conservative than that predicted by the RANS solver, but correlated very well with that provided by the turbine manufacturer. Taking into account the high degree of comparability with the more sophisticated RANS solver, the excellent agreement with the official data, and the considerably reduced computational expense, the author believes the proposed method could be a powerful standalone tool for the design and analysis of wind turbine blades, or could be applied to the emerging field of wind farm layout design by providing accurate body force input to actuator line rotors within full Navier-Stokes models of multi-unit wind farms.

CFD studies on rotational augmentation at the inboard sections of a 10 MW wind turbine rotor

In the analysis of the aerodynamic performance of wind turbines, the need to account for the effects of rotation is important as engineering models often failed to predict these phenomena. Investigations are carried out by employing an unsteady computational fluid dynamics (CFD) approach on a generic 10 MW AVATAR (Advanced Aerodynamic Tools for Large Rotors) blade. The focus of the studies is the evaluation of the 3D effect characteristics on thick airfoils in the root area. For preliminary studies, 2D simulations of the airfoils constructing the blade and 3D simulations of the turbine near the rated conditions are carried out. The 2D simulations are in good agreement with available measurements within the linear lift region, but the accuracy deteriorates in the post stall region. For the 3D wind turbine rotor results, the prediction is consistent with other CFD computations obtained from the literature. Further calculations of the rotor are conducted at 5 different wind speeds ranging from below to above the rated conditions, which correspond to 5 different angles of attack. The CFD simulations demonstrate that the lift coefficient increases in the blade root region compared to the 2D conditions caused by the centrifugal pumping and Coriolis force via the reduction of the boundary layer thickness and separation delay. The Coriolis force effect decreases with the increasing wind speed and radial position. In addition, the aerodynamic behaviour of the blade inboard region is influenced by the shedding direction of the trailing vortices. The occurrence of downwash is observed causing a local increase in the drag coefficient.

An innovative route from wind tunnel experiments to flight dynamics analysis for a highly swept flying wing

A flying wing configuration with highly swept leading edges and low aspect ratio such as the generic UCAV configuration DLR-F19 is very attractive for military applications due to its very favorable stealth capabilities. As the assurance of good flying qualities, however, is a critical aspect for such a configuration, it should be considered early in the design process. This paper presents an innovative way to derive a flight dynamics model from wind tunnel experiments by applying a system identification approach, normally employed for flight test. This allows the modelling of nonlinear aerodynamic effects and provides a model which can be directly integrated into flight dynamics simulations. New wind tunnel maneuvers are applied which significantly reduce the time of the wind tunnel experiments and improve the quality of the aerodynamic dataset generation. The aerodynamic model is then integrated into a 6-DoF simulation environment in order to perform a flight dynamics analysis of the UCAV configuration. The purpose of this analysis is to compare the flying qualities as derived from wind tunnel data with the results determined on the basis of data from VSAERO, a low-fidelity aerodynamic tool used in preliminary aircraft design.

Results of the AVATAR project for the validation of 2D aerodynamic models with experimental data of the DU95W180 airfoil with unsteady flap

The FP7 AdVanced Aerodynamic Tools for lArge Rotors - Avatar project aims to develop and validate advanced aerodynamic models, to be used in integral design codes for the next generation of large scale wind turbines (10-20MW). One of the approaches towards reaching rotors for 10-20MW size is the application of flow control devices, such as flaps. In Task 3.2: Development of aerodynamic codes for modelling of flow devices on aerofoils and, rotors of the Avatar project, aerodynamic codes are benchmarked and validated against the experimental data of a DU95W180 airfoil in steady and unsteady flow, for different angle of attack and flap settings, including unsteady oscillatory trailing-edge-flap motion, carried out within the framework of WP3: Models for Flow Devices and Flow Control, Task 3.1: CFD and Experimental Database. The aerodynamics codes are: AdaptFoil2D, Foil2W, FLOWer, MaPFlow, OpenFOAM, Q3UIC, ATEFlap. The codes include unsteady Eulerian CFD simulations with grid deformation, panel models and indicial engineering models. The validation cases correspond to 18 steady flow cases, and 42 unsteady flow cases, for varying angle of attack, flap deflection and reduced frequency, with free and forced transition. The validation of the models show varying degrees of agreement, varying between models and flow cases.

Aerodynamic Damping on a Semisubmersible Floating Foundation for Wind Turbines

The objective of this work is to study the effect of the rotor thrust on the motions of a semisubmersible floating foundation for Horizontal Axis Wind Turbines (HAWT). The main targets are the drift motions and the additional damping caused by the operating rotor, so-called aerodynamic damping. The semisubmersible used in the Offshore Code Comparison Collaboration Continuation (OC4) project, which operated under International Energy Agency (IEA) Wind Task 30, is chosen for this study. Two numerical models are built in aNyPHATAS, a coupled hydrodynamic and aerodynamic tool for simulations of floating wind turbines. The numerical model of the original design of the semisubmersible (OC4), and a numerical model calibrated against model tests (OC5) are compared with measurements. For practical reasons, the physical model at the scale of the basin needs to be adjusted. One key modification is done on the rotor of the wind turbine so that its performance remains equivalent while Froude scaling is applied. This comparison is done for two load cases: operational waves only, operational waves and steady wind simultaneously with a turbine operating at fixed rotation speed (without control). It serves to check the extent to which a design concept and a physical model built at small scale match.

Analysis of the high Reynolds number 2D tests on a wind turbine airfoil performed at two different wind tunnels

2D wind tunnel tests at high Reynolds numbers have been done within the EU FP7 AVATAR project (Advanced Aerodynamic Tools of lArge Rotors) on the DU00-W-212 airfoil and at two different test facilities: the DNW High Pressure Wind Tunnel in Gottingen (HDG) and the LM Wind Power in-house wind tunnel. Two conditions of Reynolds numbers have been performed in both tests: 3 and 6 million. The Mach number and turbulence intensity values are similar in both wind tunnels at the 3 million Reynolds number test, while they are significantly different at 6 million Reynolds number. The paper presents a comparison of the data obtained from the two wind tunnels, showing good repeatability at 3 million Reynolds number and differences at 6 million Reynolds number that are consistent with the different Mach number and turbulence intensity values.

Morphing wing optimization for steady level flight

This paper presents the basic results of the morphing wing planform optimization of an experimental unmanned air vehicle for minimum drag at steady level flight. The aerodynamic design tool that consists of the three-dimensional panel method, two-dimensional boundary layer solution and generalized reduced gradient method-based optimization is appropriate for fixed wing and morphing wing conceptual and preliminary design. The morphing concept is implemented into the solution with the geometric constraints of the wing planform and the airfoil shape design variables. The drag that is created by other components of the aircraft is calculated according to empirical formulas. Wing drag and aircraft drag comparisons between baseline wing (BASE), optimum fixed wing and morphing wing are discussed with the obtained planform and airfoil shapes.

Efficient Analysis of HALE Aircraft Structure for Static Aeroelastic Behavior

AbstractIn this work, the static aeroelastic behavior of flexible aircraft with a high aspect ratio wing undergoing large static deformations has been investigated analytically and numerically. Toward this end, a nonlinear structural model based on a simple one-dimensional nonlinear beam theory is used. An efficient evaluation of static deformation of the entire high-altitude long-endurance (HALE) airplane is developed by adopting the single beam model to the wing, the fuselage, the vertical fin, and the tail, and merging all the substructures together. This model can deal with arbitrarily large displacements and rotations of the whole airplane by use of Euler angles and can account for various structural couplings. Static results due to simple external loads are shown for demonstration. Then, the paper discusses coupling the beam model with several aerodynamic models to investigate the static aeroelastic performance of the high aspect ratio wing. Comparisons of the aerodynamic tools are made in terms of ...

A Hypersonic Aircraft Optimization Tool with Strong Aerothermoelastic Coupling

The design and optimization of hypersonic aircraft is severely impacted by the high temperatures encountered during flight as they can lead to high thermal stresses and a significant reduction in material strength and stiffness. This reduction in rigidity of the structure requires innovative structural concepts and a stronger focus on aerothermoelastic deformations in the early design and optimization phase of the design cycle. This imposes the need for a closer coupling of the aerodynamic, thermal and structural design tools than is currently in practice. The paper presents a multi-disciplinary, closely coupled optimization suite that is suitable for preliminary design in the hypersonic regime. The time varying temperature distribution is applied through an equilibrium analysis, and is coupled to the aerodynamics through the Tranair® solver. An analysis of the effect that the aerothermodynamic coupling has on the sizing of the aircraft is given, along with the effect of skin buckling. It is shown that the coupling of the aerothermodynamics drives the sizing of the structure and therefore must be considered for hypersonic applications.

The Impact of Low-Speed Fan Design on Noise: An Exploratory Study

The steady evolution since the 1950s toward higher bypass ratio engines has enhanced the acoustic role of the fan compared to the jet. This paper addresses the following question: Does a further decrease in fan pressure ratio (FPR) and rotor tip speed provide a significant reduction of fan broadband and tonal noise? The paper presents two conceptual parametric studies conducted with a fast analytical aerodynamic and acoustic prediction tool. The tool includes an aerodynamic fan design model which provides the quantities necessary to assess the tradeoff between efficiency and noise at given thrust conditions. The fan acoustic model has a theoretical formulation for broadband and tonal noise sources which is not based on empirical correlations; it is applied on conventional and contrarotating fan concepts. The first study proposes a variation of the design FPR and evaluates for each concept its impact on noise at three acoustic off-design points. The results obtained, which are in line with a past NASA study, indicate that the optimum pressure ratio in terms of fan noise is well below the fuel-burn optimum. Significant noise reductions of the broadband and tonal interaction components can be achieved with fans operating in a fully subsonic domain. Alternatively, designing at higher speed and pressure ratio near the fuel-burn optimum may invite to consider the contrarotating fan as a candidate: it performs very well in terms of buzz-saw and broadband noise compared to the conventional fan. The second study addresses the variation of design rotor tip speed at constant FPR. Although reduced tip speed may suppress buzz-saw noise, the increased loading related to it implies large blade solidities and wakes which causes a significant increase in broadband noise. Thus, there is an optimum loading that will depend on the severity of fan inflow distortion and on the onset of buzz-saw noise. Here again these conclusions confirm some experimental work performed by NASA on two different fans, and by Rolls-Royce on a third one.

Aerodynamic wind-turbine rotor design using surrogate modeling and three-dimensional viscous–inviscid interaction technique

In this paper a surrogate optimization methodology using a three-dimensional viscous-inviscid interaction code for the aerodynamic design of wind-turbine rotors is presented. The framework presents a unique approach because it does not require the commonly-used blade element momentum (BEM) method. The three-dimensional viscous-inviscid interaction code used here is the accurate and fast MIRAS code developed at the Technical University of Denmark. In comparison with BEM, MIRAS is a higher-fidelity aerodynamic tool and thus more computationally expensive as well. Designing a rotor using MIRAS instead of an inexpensive BEM code represents a challenge, which is resolved by using the proposed surrogate-based approach. As a verification case, the methodology is applied to design a model wind-turbine rotor and is compared in detail with the one designed with BEM. Results demonstrate that nearly identical aerodynamic performance can be achieved using the new design method and that the methodology is effective for the aerodynamic design of wind-turbine rotors.

Aerodynamic Design of Separate-Jet Exhausts for Future Civil Aero-engines—Part I: Parametric Geometry Definition and Computational Fluid Dynamics Approach

This paper presents the development of an integrated approach which targets the aerodynamic design of separate-jet exhaust systems for future gas-turbine aero-engines. The proposed framework comprises a series of fundamental modeling theories which are applicable to engine performance simulation, parametric geometry definition, viscous/compressible flow solution, and design space exploration (DSE). A mathematical method has been developed based on class-shape transformation (CST) functions for the geometric design of axisymmetric engines with separate-jet exhausts. Design is carried out based on a set of standard nozzle design parameters along with the flow capacities established from zero-dimensional (0D) cycle analysis. The developed approach has been coupled with an automatic mesh generation and a Reynolds averaged Navier–Stokes (RANS) flow-field solution method, thus forming a complete aerodynamic design tool for separate-jet exhaust systems. The employed aerodynamic method has initially been validated against experimental measurements conducted on a small-scale turbine powered simulator (TPS) nacelle. The developed tool has been subsequently coupled with a comprehensive DSE method based on Latin-hypercube sampling. The overall framework has been deployed to investigate the design space of two civil aero-engines with separate-jet exhausts, representative of current and future architectures, respectively. The inter-relationship between the exhaust systems' thrust and discharge coefficients has been thoroughly quantified. The dominant design variables that affect the aerodynamic performance of both investigated exhaust systems have been determined. A comparative evaluation has been carried out between the optimum exhaust design subdomains established for each engine. The proposed method enables the aerodynamic design of separate-jet exhaust systems for a designated engine cycle, using only a limited set of intuitive design variables. Furthermore, it enables the quantification and correlation of the aerodynamic behavior of separate-jet exhaust systems for designated civil aero-engine architectures. Therefore, it constitutes an enabling technology toward the identification of the fundamental aerodynamic mechanisms that govern the exhaust system performance for a user-specified engine cycle.

A CFD-informed quasi-steady model of flapping wing aerodynamics.

Aerodynamic performance and agility during flapping flight are determined by the combination of wing shape and kinematics. The degree of morphological and kinematic optimisation is unknown and depends upon a large parameter space. Aimed at providing an accurate and computationally inexpensive modelling tool for flapping-wing aerodynamics, we propose a novel CFD (computational fluid dynamics)-informed quasi-steady model (CIQSM), which assumes that the aerodynamic forces on a flapping wing can be decomposed into the quasi-steady forces and parameterised based on CFD results. Using least-squares fitting, we determine a set of proportional coefficients for the quasi-steady model relating wing kinematics to instantaneous aerodynamic force and torque; we calculate power with the product of quasi-steady torques and angular velocity. With the quasi-steady model fully and independently parameterised on the basis of high-fidelity CFD modelling, it is capable of predicting flapping-wing aerodynamic forces and power more accurately than the conventional blade element model (BEM) does. The improvement can be attributed to, for instance, taking into account the effects of the induced downwash and the wing tip vortex on the force generation and power consumption. Our model is validated by comparing the aerodynamics of a CFD model and the present quasi-steady model using the example case of a hovering hawkmoth. It demonstrates that the CIQSM outperforms the conventional BEM while remaining computationally cheap, and hence can be an effective tool for revealing the mechanisms of optimization and control of kinematics and morphology in flapping-wing flight for both bio-flyers and unmanned air systems.

Semi-analytical static aeroelastic analysis and response of flexible subsonic wings

A semi-analytical model for the combined static aeroelastic analysis and response of flexible subsonic wings is presented. Based on a general variational formulation, the proposed aeroelastic models allow any arbitrary distribution of the flexible wing’s physical properties and provide with a continuous solution of the wing’s displacement along the span, as suitable for parametric optimisation studies within preliminary wing design. Numerical results which provide sound insights on the behaviour of a flexible wing in subsonic flow are obtained and critically discussed for all aeroelastic models, with respect to the most relevant aerodynamic and structural parameters as well as the computational efficiency. Different degrees of fidelity are considered for the aerodynamic modelling and the formulated modified strip theory is shown to be an excellent compromise between the lower complexity of standard strip theory and the higher accuracy of lifting line theory. The modified strip theory is hence suggested as a general and effective steady aerodynamic tool for the multidisciplinary design and optimisation of flexible wings in the subsonic regime.