Imperial College London

Rafael Palacios

Faculty of EngineeringDepartment of Aeronautics

Professor in Computational Aeroelasticity



+44 (0)20 7594 5075r.palacios CV




338City and Guilds BuildingSouth Kensington Campus





Publication Type

170 results found

Muñoz-Simón A, Wynn A, Palacios R, 2021, Some modelling improvements for prediction of wind turbine rotor loads in turbulent wind, Wind Energy, ISSN: 1095-4244

This paper investigates the accuracy of three aerodynamic models to compute loads on wind turbine rotors under turbulent inflow: Blade Element Momentum (BEM); Unsteady Vortex LatticeMethod (UVLM) and Large Eddy Simulation with Actuator Line (LES-AL). Turbulent inflow conditions are numerically generated with a new approach that combines control of turbulence andrealistic velocity spectrum by using Mann boxes and LES simulations, respectively. Several deficiencies of the tested models are found and overcome through proposed improvements. First,the BEM assumption of independent radial sections does not hold in turbulent cases with longblades. Thus, a spatial filter to account for the interaction of radial sections in BEM is designedthrough the analysis of these interactions with UVLM. Second, the absence of viscous drag inUVLM is observed to lead to a very high rotor power coefficient, and it is shown that this canbe mitigated by including drag in UVLM with a BEM-like-approach through look-up tables. Third,the free wake model in UVLM, required to accurately capture rotor thrust, significantly increasescomputational cost. For this reason, a new wake discretisation scheme for the wake convectionequation in UVLM is proposed, in which a coarse discretisation is employed far from the solidsurfaces, which significantly reduces the computational time. Finally, these improvements andthe performance of the three fidelities are analysed in a reference 10 MW wind turbine rotordemonstrating, in general, good agreement.

Journal article

Artola M, Goizueta N, Wynn A, Palacios Ret al., 2021, Aeroelastic control and estimation with a minimal nonlinear modal description, AIAA Journal: devoted to aerospace research and development, Vol: 59, Pages: 2697-2713, ISSN: 0001-1452

Modal-based, nonlinear Moving Horizon Estimation (MHE) and Model Predictive Control(MPC) strategies for very flexible aeroelastic systems are presented. They are underpinned by an aeroelastic model built from a 1D intrinsic (based on strains and velocities) description of geometrically-nonlinear beams and an unsteady Vortex Lattice aerodynamic model. Construction of a nonlinear, modal-based, reduced order model of the aeroelastic system, employing a state-space realisation of the linearised aerodynamics around an arbitrary reference point, allows us to capture the main nonlinear geometrical couplings at a very low computational cost. Embedding this model in both MHE and MPC strategies, which solve the system continuous-time adjoints efficiently to compute sensitivities, lays the foundations for real-time estimation and control of highly flexible aeroelastic systems. Finally, the performance and versatility of the framework operating in the nonlinear regime is demonstrated on two very flexible wing models, with notably different dynamics, and on two different control setups: a gust-load alleviation problem on a very high aspect ratio wing with slower dynamics, which involves substantial deflections; and flutter suppression on a flexible wing with significantly faster dynamics, where an unconventional nonlinear stabilisation mechanism is unveiled.

Journal article

Artola M, Wynn A, Palacios R, 2021, Modal-based model predictive control of multibody very flexible structures, 21st IFAC World Congress on Automatic Control - Meeting Societal Challenges, Publisher: Elsevier, Pages: 7472-7478, ISSN: 2405-8963

A model predictive control strategy for flexible multibody structures undergoing large deformations is presented. The dynamics of such structures are highly nonlinear, with local effects introduced by the joint constraints and distributed effects arising from the structure’s increased flexibility, from which arbitrary large deflections and rotations can be expected. A modal-based nonlinear reduced order model of an intrinsic description (based on velocities and strains) of geometrically-exact beams is used to underpin the internal model. This low-order model, constructed using the linearised eigenfunctions of the constrained structures, is a set of nonlinear ordinary differential equations in time (i.e. no algebraic equations are present) thus facilitating analysis and demonstrating successful control. Numerical examples are presented based on a very flexible hinged two-link manipulator.

Conference paper

Artola M, Wynn A, Palacios R, 2021, Modal-based nonlinear model predictive control for 3D very flexible structures, IEEE Transactions on Automatic Control, ISSN: 0018-9286

In this paper a novel NMPC scheme is derived, which is tailored to the underlying structure of the intrinsic description of geometrically exact nonlinear beams (in which velocities and strains are primary variables). This is an important class of PDE models whose behaviour is fundamental to the performance of flexible structural systems (e.g., wind turbines, High-Altitude Long-Endurance aircraft). Furthermore, this class contains the much-studied Euler-Bernoulli and Timoshenko beam models, but has significant additional complexity (to capture 3D effects and arbitrarily large displacements) and requires explicit computation of rotations in the PDE dynamics to account for orientation-dependent forces such as gravity. A challenge presented by this formulation is that uncontrollable modes necessarily appear in any finite dimensional approximation to the PDE dynamics. We show, however, that an NMPC scheme can be constructed in which the error introduced by the uncontrollable modes can be explicitly controlled. Furthermore, in challenging numerical examples exhibiting considerable deformation and nonlinear effects, it is demonstrated that the asymptotic error can be made insignificant (from a practical perspective) usingour NMPC scheme and excellent performance is obtained evenwhen applied to a highly resolved numerical simulation of thePDEs. We also present a generalisation of Kelvin-Voigt dampingto the intrinsic description of geometrically-exact beams. Finally,special emphasis is placed on constructing a framework suitablefor real-time NMPC control, where the particular structure ofthe underlying PDEs is exploited to obtain both efficient finite-dimensional models and numerical schemes.

Journal article

Cea A, Palacios R, 2021, A non-intrusive geometrically nonlinear augmentation to generic linear aeroelastic models, Journal of Fluids and Structures, Vol: 101, ISSN: 0889-9746

A new approach to build geometrically-nonlinear dynamic aeroelastic models is proposed that only uses information typically available in linear aeroelastic analyses, namely a generic (linear) finite-element model and frequency-domain aerodynamic influence coefficient matrices (AICs). Good computational efficiency is achieved through a two-step process: Firstly, a geometric reduction of the structure is carried out through static or dynamic condensation on nodes along the main load paths of the vehicle. Secondly, manipulation of the resulting linear normal modes (LNMs), the condensed stiffness and mass matrices, and the nodal coordinates provides the modal coefficients of the intrinsic beam equations along these load paths. This preserves the LNMs of the original problem and augments them with the geometrically nonlinear terms of beam theory. The structural description is in material coordinates and modal AICs are thus naturally included as follower forces. Numerical examples include cantilever wings built using detailed models, for which effects such as nonlinear aeroelastic equilibrium, nonlinear dynamics and structural-driven limit-cycle oscillations are shown. Results demonstrate the ability of the methodology to seamlessly and efficiently incorporate critical nonlinear effects to (linear) arbitrarily large aeroelastic models of high aspect ratio wings.

Journal article

Goizueta N, Wynn A, Palacios R, 2021, Parametric Krylov-based order reduction of aircraft aeroelastic models, AIAA Scitech 2021 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-25

We present an interpolation-based scheme to obtain in real-time linearised aeroelastic models of very flexible aircraft at any flight condition within the flight envelope. First, in an offline phase, a library of reduced-order linear aeroelastic models is computed by finding the nonlinear equilibrium (trimmed aircraft) using a nonlinear, geometrically-exact beam formulation coupled with an Unsteady Vortex Lattice Method. Subsequent linearisation is achieved analytically and followed by reduction using Krylov subspace methods. The interpolation is performed directly on the reduced-order system matrices, which are projected onto a congruent coordinate system for compatibility. Any interpolation scheme of choice can be used, and the size of the models permits real-time computation.

Conference paper

Artola M, Goizueta N, Wynn A, Palacios Ret al., 2021, Proof of concept for a hardware-in-the-loop nonlinear control framework for very flexible aircraft, AIAA Scitech 2021 Forum, Publisher:, Pages: 1-26

Nonlinear Moving Horizon Estimation (MHE) and Model Predictive Control (MPC) strategies for very flexible aircraft are presented. They are underpinned by a nonlinear reduced-order model built upon the structure’s natural modes of vibration. This internal model aims for a minimal realisation of the aircraft which retains sufficient information to enable efficient real-time estimation and control. It is based on a modal intrinsic description of geometrically-nonlinear beams and a linearised unsteady vortex lattice aerodynamic model. Numerical evidence has shown that models of this form are able to capture the main nonlinear geometrical couplings at a very low computational cost. This opens the door to MHE and MPC strategies, which are naturally more computationally demanding than other linear conventional strategies, but are more versatile and able to provide control in the usually neglected nonlinear regime. The proposed control framework is tested on models built in an in-house open-source nonlinear aeroelasticity simulation and analysis package, to emulate the controller performance on a realistic plant model. Very satisfactory results are obtained in a flutter suppression problem involving a very flexible clamped wing, where the nonlinearity of the problem is leveraged by the internal model to achieve stabilisation, and a payload drop control of a very flexible HALE aircraft.

Conference paper

Goizueta N, Wynn A, Palacios R, Drachinsky A, Raveh DEet al., 2021, Flutter prediction for a very flexible wing wind tunnel test, AIAA Scitech 2021 Forum, Pages: 1-17

Two different nonlinear aeroelastic tool sets, SHARPy and the Modal Rotation Method (MRM), have been employed to predict and design a wind tunnel flutter test campaign of a very flexible wing, the Pazy Wing, as part of the 3rd Aeroelastic Prediction Workshop. The first method, SHARPy, uses geometrically exact beams coupled with an Unsteady Vortex Lattice, which is linearised about a deformed configuration, reduced by means of Krylov subspaces and analysed to compute the stability boundaries of the wing. The MRM is based on structural modal data, from either beam models or finite element models, coupled with a doublet-lattice aerodynamic model from ZAERO of the straight wing configuration. The excellent agreement between numerical and experimental data for structural-only and static aeroelastic analyses paves the way for predicting the stability boundaries of the Pre-Pazy wing with sufficient confidence for the safe design of a flutter wind tunnel test campaign.

Conference paper

Wang Y, Zhao X, Palacios R, Otsuka Ket al., 2021, Unsteady aeroelasticity of slender wings with leading-edge separation, Pages: 1-23

We present a medium-fidelity aeroelastic framework for computing intermittently separating 3D flows around slender aero-structures with a significantly reduced computational cost than CFD-based method. In which, we propose a modified 3D vortex panel method with leading-edge separation controlled by the leading-edge suction parameter theory, and demonstrate its incorporation in a coupled aeroelastic solver for the dynamic response of these systems. Numerical verifications and simulations are presented on both attached and separated aeroelastic test cases, demonstrating the capability of the proposed method.

Conference paper

Gomes P, Economon TD, Palacios R, 2021, Sustainable high-performance optimizations in su2, Pages: 1-18

Over a period of approximately 18 months, we have achieved an average 4-fold performance increase of the open source multiphysics suite SU2 through implementation optimizations (e.g. vectorization), and for some problems an additional 10-fold improvement via algorithmic changes. We have implemented a hybrid parallelization strategy (MPI + OpenMP) that improves the scalability of the code and allows key algorithms (such as multigrid) to maintain their effectiveness at small number of nodes per core. Our work has maintained the generality and versatility of the code by not relying on optimizations specific to given compilers, architectures, or physics. Furthermore, we maintain, or lower, the level of C++ knowledge needed for new developers. In this paper we document the implementation and algorithmic changes, give an overview of the details that allow implementing the hybrid parallel and vectorization frameworks in a way that hides the low-level complexity from high-level algorithm development. We demonstrate the improvements on benchmark problems known to the aeronautics community, and derive best practice guidelines to use the new capabilities.

Conference paper

Cea A, Palacios R, 2021, A non-intrusive nonlinear aeroelastic extension of loads packages with application to a long range transport aircraft configuration, Pages: 1-23

A new method for constructing geometrically-nonlinear aeroelastic systems from standard linear models is applied to an industry-level aircraft configuration. The new approach seamlessly integrates with current aeroelastic load packages performing linear analysis based on generic finite-element models (FEMs) and aerodynamic influence coefficient matrices (AICs). We generalize the methodology to incorporate control inputs, find the trimmed aircraft state, or generate gusts disturbances, which can be employed separately or combined to obtain a simplified flight dynamics model for load analysis. An initial study of the aeroelastic response of a long range aircraft is presented. Linear and nonlinear results are introduced in static and dynamic computations of manoeuvres, trim, and gust disturbances. These are compared to commercial software calculations, showing the need for geometrically nonlinear analysis in the production environment of airplanes with ultra high aspect ratio wings.

Conference paper

Lahooti M, Palacios R, Sherwin SJ, 2021, Thick strip method for efficient large-eddy simulations of flexible wings in stall, Pages: 1-20

An efficient computational method is presented based on the thick strip method for Large-Eddy simulation of flexible wings in stall. Fluid domain is break down into series of smaller 3k strips which one independently solved using implicit LES method. Force and moments are obtained from each strips and used to evolved the nonlinear dynamics of the structure. High deformation response of high-altitude long-endurance wing under several angle of attacks leading to the stall regions are presented to show the capability of proposed FSI method.

Conference paper

Artola M, Wynn A, Palacios R, 2021, Generalized Kelvin–Voigt damping models for geometrically nonlinear beams, AIAA Journal: devoted to aerospace research and development, Vol: 59, Pages: 356-365, ISSN: 0001-1452

Strain-rate-based damping is investigated in the strong form of the intrinsic equations of three-dimensional geometrically exact beams. Kelvin–Voigt damping, often limited in the literature to linear or two-dimensional beam models, is generalized to the three-dimensional case, including rigid-body motions. The result is an elegant infinite-dimensional description of geometrically exact beams that facilitates theoretical analysis and sets the baseline for any chosen numerical implementation. In particular, the dissipation rates and equilibrium points of the system are derived for the most general case and for one in which a first-order approximation of the resulting damping terms is taken. Finally, numerical examples are given that validate the resulting model against a nonlinear damped Euler–Bernoulli beam (where detail is given on how an equivalent description using our intrinsic formulation is obtained) and support the analytical results of energy decay rates and equilibrium solutions caused by damping. Throughout the paper, the relevance of damping higher-order terms, arising from the geometrically exact description, to the accurate prediction of its effect on the dynamics of highly flexible structures is highlighted.

Journal article

Otsuka K, Carre AD, Palacios R, 2021, Nonlinear static and dynamic analysis framework for very flexible multibody aircraft with propellers, Pages: 1-23

A nonlinear static and dynamic aeroelastic analysis framework for high aspect ratio wings with propellers is described. The aerodynamic effect of propellers is considered. The high computational cost required for modeling aerodynamic interaction between the wing and propeller wake is reduced by taking advantage of the relatively slow dynamics of the wing. Consequently, the propeller wake is modeled as a straight vortex cylinder that does not require a computationally expensive wake updating process. By leveraging the smallness of the propeller, we propose an averaged vortex cylinder method that calculates the induced velocities of the propeller vortex cylinder efficiently without suffering from a numerical singularity and loss of accuracy. The induced velocities are considered in the wing aerodynamic force calculation using an unsteady vortex lattice method. We also propose an efficient propeller cylinder coordinate generation method modeling the propeller-attached wing by absolute nodal coordinate formulation with a multibody dynamic theory. The developed framework is validated by comparison with other frameworks and formulations. A nonlinear static analysis on a representative high-aspect-ratio wing demonstrates that the propeller-induced axial velocity has a larger effect on the increase in deflection than the tangential velocity. The nonlinear dynamic results show that the propeller may decrease the deflection amplitude.

Conference paper

Muñoz-Simón A, Palacios R, Wynn A, 2020, Scripts illustrating some modelling improvements for prediction of wind turbine rotor loads in turbulent wind

This repository contains some files to complement the publication "Some modelling improvements for prediction of wind turbine rotor loads in turbulent wind".


Gomes P, Palacios R, 2020, Aerodynamic-driven topology optimization of compliant airfoils, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 62, Pages: 2117-2130, ISSN: 1615-147X

A strategy for density-based topology optimization of fluid-structure interaction problems is proposed that deals with some shortcomings associated to non stiffness-based design. The goal is to improve the passive aerodynamic shape adaptation of highly compliant airfoils at multiple operating points. A two-step solution process is proposed that decouples global aeroelastic performance goals from the search of a solid-void topology on the structure. In the first step, a reference fully coupled fluid-structure problem is solved without explicitly penalizing non-discreteness in the resulting topology. A regularization step is then performed that solves an inverse design problem, akin to those in compliant mechanism design, which produces a discrete-topology structure with the same response to the fluid loads. Simulations are carried out with the multi-physics suite SU2, which includes Reynolds-averaged Navier-Stokes modeling of the fluid and hyper-elastic material behavior of the geometrically nonlinear structure. Gradient-based optimization is used with the exterior penalty method and a large-scale quasi-Newton unconstrained optimizer. Coupled aerostructural sensitivities are obtained via an algorithmic differentiation based coupled discrete adjoint solver. Numerical examples on a compliant aerofoil with performance objectives at two Mach numbers are presented.

Journal article

Muñoz-Simón A, Palacios R, Wynn A, 2020, Benchmarking different fidelities in wind turbine aerodynamics under yaw, The Science of Making Torque from Wind (TORQUE 2020), Publisher: IOP Publishing, Pages: 1-11, ISSN: 1742-6588

This paper analyses the aerodynamics of wind turbines under yaw with different modelling fidelities (BEM, BEM with skewed wake model, UVLM and LES-AL). First of all, models are compared in a zero-yaw case to demonstrate their accuracy in prediction of out-of-plane loads and the discrepancy of UVLM in the in-plane loads due to the lack of viscous drag. Secondly, the yaw aerodynamics are described through the advancing/retreating and skewed wake effects, which are appropriately captured by UVLM and LES-AL and lead to an incorrect prediction of the location of maximum and minimum loading along a revolution by BEM. Further, when a skew-wake model is included in BEM, it predicts the correct locations but exhibits overly large loading variations. These predictions are consistent for all yaw angles studied (γ = 10° − 30°). All solvers predict similar decrease of root-bending moments, rotor power and thrust coefficients up to a yaw angle of 10°. However, at larger yaw angles, BEM overpredicts this decrease of coefficients with the yaw angle due to the unsuccessful performance of yaw corrections as opposed to UVLM that inherently accounts for three-dimensional effects. This study demonstrates the need to use computational models that can account for three-dimensional effects in the computation of aerodynamic loads for yaw angles above 10°.

Conference paper

Wang C, Muñóz-Simon A, Deskos G, Laizet S, Palacios R, Campagnolo F, Bottasso CLet al., 2020, Code-to-code-to-experiment validation of LES-ALM wind farm simulators, Journal of Physics: Conference Series, Vol: 1618, Pages: 1-8, ISSN: 1742-6588

The aim of this work is to present a detailed code-to-code comparison of two Large-Eddy Simulation (LES) solvers. Corresponding experimental measurements are used as a reference to validate the quality of the CFD simulations. The comparison highlights the effects of solver order on the solutions, and it tries to answer the question of whether a high order solver is necessary to capture the main characteristics of a wind farm. Both solvers were used on different grids to study their convergence behavior. While both solvers show a good match with experimental measurements, it appears that the low order solver is more accurate and substantially cheaper in terms of computational cost.

Journal article

Del Carre de la Portilla A, Palacios R, 2020, Simulation and optimization of takeoff maneuvers of very flexible aircraft, Journal of Aircraft: devoted to aeronautical science and technology, Vol: 57, Pages: 1097-1110, ISSN: 0021-8669

A generic framework for the simulation of transient dynamics in nonlinear aeroelasticity is presented that is suitable for flexible aircraft maneuver optimization. Aircraft are modeled using a flexible multibody dynamics approach built on geometrically nonlinear composite beam elements, and the unsteady aerodynamics on their lifting surfaces is modeled using vortex lattices with free or prescribed wakes. The open loop response to commanded inputs and external constraints is then fed into a Bayesian optimization framework, which adaptively samples the configuration space to identify optimal maneuvers. As a representative example, the proposed approach is demonstrated on a catapult-assisted takeoff. The specific modeling challenges associated to that problem are first discussed, including the effect of aircraft flexibility. An optimality measure based on ground clearance and wing root loads is then defined. It is finally shown that the link that ramp-length constraints introduce between acceleration, release speed, and wing root loads is the main driver in the optimal solution.

Journal article

Deskos G, del Carre A, Palacios R, 2020, Assessment of low-altitude atmospheric turbulence models for aircraft aeroelasticity, Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD

Working paper

Deskos G, Del Carre de la Portilla A, Palacios R, 2020, Assessment of low-altitude atmospheric turbulence models for aircraft aeroelasticity, Journal of Fluids and Structures, Vol: 95, Pages: 1-19, ISSN: 0889-9746

We investigate the dynamic aeroelastic response of large but slow aircraft in low-altitude atmospheric turbulence. To this end, three turbulence models of increasing fidelity, namely, the one-dimensional von Kármán model, the two-dimensional Kaimal model and full three-dimensional wind fields extracted from large-eddy simulations (LES) are used to simulate ambient turbulence near the ground. Load calculations and flight trajectory predictions are conducted for a representative high-aspect-ratio wing aircraft, using a fully coupled nonlinear flight dynamics/aeroelastic model, when it operates in background atmospheric turbulence generated by the aforementioned models. Comparison of load envelopes and spectral content, on vehicles of varying flexibility, shows strong dependency between the selected turbulence model and aircraft aeroelastic response (e.g. 58% difference in the predicted magnitude of the wing root bending moment between LES and von Kármán models). This is mainly due to the presence of large flow structures at low altitudes that have comparable dimensions to the vehicle, and which despite the relatively small wind speeds within the Earth boundary layer, result in overall high load events for slow-moving vehicles. Results show that one-dimensional models that do not capture those effects provide fairly non-conservative load estimates and are unsuitable for very flexible airframe design.

Journal article

Deskos G, Laizet S, Palacios R, 2020, WInc3D: a novel framework for turbulence-resolving simulations of wind farm wake interactions, Wind Energy, Vol: 23, Pages: 779-794, ISSN: 1095-4244

A fast and efficient turbulence‐resolving computational framework, dubbed as WInc3D (Wind Incompressible 3‐Dimensional solver), is presented and validated in this paper. WInc3D offers a unified, highly scalable, high‐fidelity framework for the study of the flow structures and turbulence of wind farm wakes and their impact on the individual turbines' power and loads. Its unique properties lie on the use of higher‐order numerical schemes with “spectral‐like” accuracy, a highly efficient parallelisation strategy which allows the code to scale up to O(104) computing processors and software compactness (use of only native solvers/models) with virtually no dependence to external libraries. The work presents an overview of the current modelling capabilities along with model validation. The presented applications demonstrate the ability of WInc3D to be used for testing farm‐level optimal control strategies using turbine wakes under yawed conditions. Examples are provided for two turbines operating in‐line as well as a small array of 16 turbines operating under “Greedy” and “Co‐operative” yaw angle settings. These large‐scale simulations were performed with up to 8192 computational cores for under 24 hours, for a computational domain discretised with O(109) mesh nodes.

Journal article

Del Carre de la Portilla A, Goizueta N, Muñoz-Simón A, Palacios Ret al., 2020, SHARPy: A dynamic aeroelastic simulation toolbox for very flexible aircraft and wind turbines

SHARPy v1.1.1 is the latest release, consolidating v1.1 with some minor bug fixes and features.Changelog 1.1.1 (2020-02-03)


Maraniello S, Palacios R, 2020, Parametric reduced-order modelling of the unsteady vortex-lattice method, AIAA Journal: devoted to aerospace research and development, Vol: 58, Pages: 2206-2220, ISSN: 0001-1452

A method for frequency-limited balancing of the unsteady vortex-lattice equations is introduced that results in compact models suitable for computational-intensive applicationsin load analysis, aeroelastic optimisation, and control synthesis. The balancing algorithmrelies on a frequency-domain solution of the vortex-lattice equations that effectively eliminates the cost associated to the wake states. It is obtained from a Z-transform of theunderlying discrete-time equations, and requires no additional geometrical or kinematicassumptions for the lifting surfaces. Parametric reduced-order modelling is demonstratedthrough interpolation over (a) projection matrices, (b) state-space realisations and (c)transfer functions, which trade accuracy, robustness and cost. Methods are finally exemplified in the dynamic stability of a T-tail configuration with varying incidence. Numericalstudies show that a very small number of balanced realisations is sufficient to accuratelycapture the unconventional aeroelastic response of this system, which includes in-planekinematics and steady loads, over a wide range of operation conditions.

Journal article

Muñoz-Simón A, Wynn A, Palacios R, 2020, Unsteady and three-dimensional aerodynamic effects on wind turbine rotor loads, AIAA Scitech 2020 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-22

The paper investigates the use of vortex methods in the computation of important flows for wind turbine aerodynamics. These flows are characterised by inflow velocity unsteadiness, spatial variations and non-zero spanwise component. First, computational vortex methods are shown to match analytical solutions on simple geometries. Second, these geometries will be studied to reveal the effects of these flows on airfoil aerodynamics: unsteady damping and load reduction when subjected to side slip or spanwise inflow velocity variations. Finally, vortex methods will be compared with traditional BEM methods in full wind turbine configurations under real operating inflows such as shear, yaw and turbulence which are characterised by unsteadiness and three-dimensional effects. Vortex methods allow quantifying the error of BEM methods for these conditions.

Conference paper

Artola M, Goizueta N, Wynn A, Palacios Ret al., 2020, Modal-based nonlinear estimation and control for highly flexible aeroelastic systems, AIAA Scitech 2020 Forum, Publisher: American Institute of Aeronautics and Astronautics, Pages: 1-23

Modal-based, nonlinear Moving Horizon Estimation (MHE) and Model Predictive Control (MPC) strategies for highly flexible aeroelastic systems are presented. The aeroelastic model is built from a 1D intrinsic (based on strains and velocities) description of geometrically-nonlinear beams and an unsteady Vortex Lattice aerodynamic model. Construction of a nonlinear modal-based reduced order model of the aeroelastic system, employing a state-space realisation of the linearised aerodynamics around an arbitrary equilibrium point, allows us to capture the main nonlinear geometrical couplings at a very low computational cost. Embedding this model in both MHE and MPC strategies, which solve the system's continuous-time adjoints efficiently to compute sensitivities, lays the foundations for real-time estimation and control of highly flexible aeroelastic systems.

Conference paper

Del Carre A, Deskos G, Palacios R, 2020, Realistic turbulence effects in low altitude dynamics of very flexible aircraft

The focus are the challenges associated with the low-altitude part of the mission of very flexible aircraft, namely the launching procedure and the atmospheric boundary layer response. First, the robustness of a catapult-assisted take off to changes in incoming flow velocity and sideslip angle is assessed. Results show how the sideslip angle affects the launch manoeuvre, defining a safe range and analysing how an increasing sideslip alters the structural dynamics and trajectory of the aircraft. Next, continuous turbulence response of the X-HALE, a multi-tail, span-loaded nonlinear aeroelasticity testbed is computed for a classic von kármán spectrum and a time-varying high-fidelity LES simulation of the atmospheric boundary layer. It is shown that the structural responses obtained with the two statistically equivalent flow fields (same mean velocity and turbulent intensity) differ by an order of magnitude, highlighting the importance of span-varying gust load analysis on very flexible aircraft.

Conference paper

Gomes P, Palacios R, 2020, Aerodynamic driven multidisciplinary topology optimization of compliant airfoils

We propose a strategy for density-based topology optimization of fluid structure interaction problems that deals with some short-comings associated with non stiffness-based design problems. The method is demonstrated on a problem where we seek to improve the passive load alleviation characteristics of a highly compliant airfoil at high speed while producing sufficient lift at a lower speed. The fluid structure interaction is simulated with the multi-physics suite SU2, which includes RANS modelling of the fluid and hyper-elastic material behaviour of the geometrically-nonlinear structure. Gradient-based optimization is used with the coupled aerostructural sensitivities being obtained via an algorithmic differentiation-based coupled discrete adjoint solver.

Conference paper

Burghardt O, Gauger NR, Gomes P, Palacios R, Kattmann T, Economon TDet al., 2020, Coupled discrete adjoints for multiphysics in su2, Pages: 1-12

Many optimization problems in fluid dynamics are naturally constituted in a larger multiphysics setting, the most prominent ones nowadays being fluid-structure interaction and conjugate heat transfer or combinations of them. In the context of partitioned solution approaches, and from a software perspective, this means that two or more solvers are coupled by exchanging data at common physical boundaries during the simulation. Optimization methods relying on discrete adjoint solutions have to consider such couplings in order to give accurate gradients. This article presents a methodology for how coupled multiphysics adjoints can be computed efficiently in a way that is also independent of the choice or configuration of the underlying physical problem. Based on an implementation in SU2 (an open-source multiphysics simulation and design software1 ) we demonstrate how the same algorithm can be applied for shape sensitivity analysis on a conjugate heat transfer as well as a fluid-structure interaction test case.

Conference paper

Venkatesan-Crome C, Palacios R, 2020, A discrete adjoint solver for time-domain fluid-structure interaction problems with large deformations

Progress in the development of computational methodology for time-accurate, non-linear, fluid-structure interaction problems including sensitivity determination using discrete adjoint analysis is presented. Three-field partitioned FSI solver structure, made up of the fluid, structural and mesh domain, is employed. For both the primal and discrete adjoint analysis, the individual domains are initially discussed ahead of the fully coupled FSI solver. Single domain results for structural and fluid problems are initially presented for an axially loaded bar and pitching NACA 0012 airfoil respectively. Dynamic coupled FSI problem proposed in this work is a flexible NACA 0012 airfoil under unsteady aerodynamic load resulting in shock induced vibrations.

Conference paper

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