74 results found
Wang T, Santer M, 2023, Rigid-foldable parabolic deployable reflector concept based on the origami flasher pattern, Journal of Spacecraft and Rockets, ISSN: 0022-4650
This paper presents a novel deployable reflector concept based on the origami flasher pattern. The proposed folding architecture achieves rigid foldability for flasher patterns applied to doubly curved surfaces, allowing parabolic reflectors to be divided into a number of rigid panels for efficient stowage. Such an architecture provides an intermediate solution between current rigid-surface and flexible-surface reflectors, offering both surface precision and stowage compactness. The proposed patterns have a positive-finite degree of mobility, and so reliable and deterministic deployment is realized through suitable actuation. A Bayesian optimization approach is used in conjunction with kinematics and collision models in order to find optimal stowage patterns that accommodate finite thickness panels and supporting structures. For the generated optimal patterns, panel split line geometries are designed analytically to eliminate gaps while avoiding collision at panel edges during folding.
Soltani Z, Santer M, 2022, Refined unified formulation for efficient folding and unfolding analyses of slender thin-walled structures, AIAA Journal: devoted to aerospace research and development, Vol: 60, ISSN: 0001-1452
We present a high-fidelity refined unified nonlinear finite element formulation for the efficient and robust analysis of slender thin-walled bodies during highly nonlinear deformation. Our formulation utilizes an independent discretization of the displacement field along the beam axis and over the cross section. By matching different refinements in different cross sections, it is able to apply higher-order beam theories in highly deformed regions, to capture complex buckling and postbuckling behavior, whilst retaining the computational efficiency offered by lower refinements elsewhere. The exemplar structure for this paper is the tape spring—a commonly proposed component of deployable structures with ability to combine self-deployment, via a release of stored strain energy, with locking into a relatively stiff geometric configuration with a curved cross section. To simulate localized folds due to a flattening of the cross section, the arc-length method with an automatic increment technique is employed.
Kunakorn-ong P, Soltani Z, Santer M, 2022, Optimal design of tube flexure cut-out geometries for deployment performance, Acta Astronautica, Vol: 197, Pages: 35-45, ISSN: 0094-5765
A design methodology is proposed for deployable tube flexures made of ultra-thin carbon fiber composite. The methodology is developed to achieve desired stowage and deployment performance in the absence of material failure. The cut-out shape in the tube flexure is determined by means of a Bayesian optimization technique. The objective function is defined based on both desired moment characteristics and Hashin failure criteria. Multiple cut-out parameterization schemes are presented. Bayesian optimization is shown to be effective and significant performance improvements are achieved thought use of spline-based optimization in comparison to more conventional forms. The efficiency of the approach is validated via experiment.
Gramola M, Bruce P, Santer M, 2022, Passive control of 3D adaptive shock control bumps using a sealed cavity, Journal of Fluids and Structures, Vol: 112, Pages: 1-19, ISSN: 0889-9746
This paper presents a Fluid-Structure-Interaction study of a novel passive adaptive shock control bump concept. A flexible plate, clamped on all sides and placed above a sealed cavity, was tested beneath a Mach 1.4 normal shock in the Imperial College London supersonic wind tunnel. The plate was actuated into the shape of a 3D shock control bump by passively controlling the cavity pressure through an array of breather holes. Preliminary experiments were performed with active control of cavity pressure (via a vacuum tank) at Mach 1.4 and 2 to illustrate the potential of this concept. Full-field surface measurement techniques, namely photogrammetry and pressure sensitive paint, were employed in addition to static pressure tappings and schlieren photography. Results confirmed that cavity pressure plays a key role in determining the aerostructural behaviour of the flexible plate. In addition, it was found that carefully placed breather holes allowed the plate to deform into a 3D shock control bump when a shock was on the flexible region and remain flat otherwise. This shows significant potential for improving the off-design behaviour of adaptive shock control bumps.
Soltani Z, Santer M, 2022, A high-fidelity refined unified nonlinear formulation for efficient folding and unfolding analyses of self-deployable slender thin-walled structures, AIAA Journal: devoted to aerospace research and development, ISSN: 0001-1452
We present a high-fidelity refined unified nonlinear finite element formulation for the efficient and robust analysis of slender thin-walled bodies during highly nonlinear deformation. Our formulation utilizes an independent discretization of the displacement field along the beam axis and over the cross section. By matching different refinements in different cross sections, it is able to apply higher order beam theories in highly deformed regions, to capture complex buckling and post-buckling behaviour, whilst retaining the computational efficiency offered by lower refinements elsewhere. The exemplar structure for this paper is the tape spring — a commonly-proposed component of deployable structures with ability to combine self-deployment, via a release of stored strain energy, with locking into a relatively stiff geometric configuration with a curved cross section. To simulate localized folds due to a flattening of the cross section, the arc-length method with an automatic increment technique is employed.
Thillaithevan D, Bruce P, Santer M, 2022, Robust multiscale optimization accounting for spatially-varying material uncertainties, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 65, Pages: 1-18, ISSN: 1615-147X
In this work we demonstrate a methodologyfor performing robust optimization using multivariableparameterized lattice microstructures. By introducingmaterial uncertainties at the microscale, we are able tosimulate the variations in geometry that occur duringthe manufacturing stage and design structures which aretolerant to variations in the microscale geometry. Weimpose both uniform and spatially-varying, non-uniformmaterial uncertainties to generate structures which, interms of standard deviation, are up to 77% more robustin the non-spatially uncertainty varying case, and 74%more robust in the spatially-varying case. We also explore the utility of imposing spatially-varying materialuncertainties compared to using homogeneous, uniformmaterial uncertainties, which are much less computationally expensive. It is found that when designs thathave been optimized assuming uniform uncertainties aresubject to spatially-varying uncertainties, their standarddeviations of compliance are similar to designs optimizedassuming spatially-varying uncertainties. However, theirmean compliances are far higher in comparison to designs generated by assuming spatially-varying materialuncertainties.
Nightingale M, Hewson R, Santer M, et al., 2022, Multiscale Optimization of Resonant Frequencies in a Payload Attach Fitting Using a Metamaterial Lattice Approach
In this work a method of tailoring the resonant frequencies of a Payload Attach Fitting (PAF) is presented. The work uses a multiscale, functionally-graded metamaterial optimization approach to predict and alter the structural and dynamic properties of the PAF tower. This allows for tailoring of the resonant frequencies of the PAF-payload system in order to avoid dangerous resonant modes. The metamaterial used is a 7 member, body-centered lattice structure with spatially-varying truss radii. An interior point algorithm is employed where the truss radii represent the design variables and the unit cell structural properties are homogenized for use in the macro scale optimization. The capabilities of the method to tailor resonant frequencies is demonstrated by maximizing the sum of the first 3 resonant frequencies of the tower. These frequencies are then compared with the resonant frequencies of the original tower with the same payload and boundary conditions. A mode shape tracking algorithm and corresponding constraint have also been implemented in the optimization. For the same mass, the multiscale approach is able to increase the first resonant frequency by 26.6 %. The sum of the first 3 resonant frequencies is also increased by 20.0 %. This ability to control resonant frequencies offers greater functionality and improved flexibility. Engineers are able to tailor structures for multiple launch environments whilst also reducing weight and costs of the PAF structures.
Murphy R, Hewson R, Santer M, 2021, In-loop additive manufacturing constraints for open-walled microstructures, Additive Manufacturing, Vol: 48, Pages: 1-17, ISSN: 2214-8604
The derivation and integration of novel in-loop additive manufacturing constraints for open-walled microstructures within a multiscale optimization framework is presented. Problematic fabrication features are discouraged in-loopthrough the application of an augmented projection filter and two relaxed binary integral constraints, which prohibit the formation of unsupported members,isolated assemblies of overhanging members and slender members during optimization. Through the application of these constraints, it is possible to deriveself-supporting, hierarchical structures with varying topology, suitable for fabrication through AM processes. Two classical compliance minimization problemsare solved using both the base framework with a prohibitive lower bound constraint applied on member radius to guarantee manufacturability and the baseframework with integrated in-loop AM constraints. In both cases, the presentwork leads to a significant increase in the mechanical performance.Keywords: Structural optimization, Multiscale methods, Design for additivemanufacturing, Length scale control, Overhang control
Imediegwu C, Murphy R, Hewson R, et al., 2021, Multiscale thermal and thermo-structural optimization of three-dimensional lattice structures, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 65, Pages: 1-21, ISSN: 1615-147X
This paper develops a robust framework forthe multiscale design of three-dimensional lattices with macroscopically tailored thermal and thermo-structural characteristics. A multiscale approach is implemented where the discrete evaluations of small-scale lattice unitcell characteristics are converted to response surfacemodels so that the properties exist as continuous functions of the lattice micro-parameters. The derived frame-work constitutes free material optimization in the space of manufacturable lattice micro-architecture. The optimization of individual lattice member dimensions is enabled by the adjoint method and the explicit expressions of the response surface material property sensitivities. The approach is demonstrated by solving thermaland thermo-structural optimization problems, significantly extending previous work which focused on linear structural response. The thermal optimization solu-tion shows a design with improved optimality compared to the SIMP methodology. The thermo-structural optimization solution demonstrates the method’s capability for attaining a prescribed displacement in response to temperature gradients.
Murphy R, Imediegwu C, Hewson R, et al., 2021, Multiscale structural optimisation with concurrent coupling between scales, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 63, Pages: 1721-1741, ISSN: 1615-147X
A robust three-dimensional multiscale structural optimization framework with concurrent coupling between scales is presented. Concurrent coupling ensures that only the microscale data required to evaluate the macroscale model during each iteration of optimization is collected and results in considerable computational savings. This represents the principal novelty of this framework and permits a previously intractable number of design variables to be used in the parametrization of the microscale geometry, which in turn enables accessibility to a greater range of extremal point properties during optimization. Additionally, the microscale data collected during optimization is stored in a re-usable database, further reducing the computational expense of optimization. Application of this methodology enables structures with precise functionally-graded mechanical properties over two-scales to be derived, which satisfy one or multiple functional objectives. Two classical compliance minimization problems are solved within this paper and benchmarked against a Solid Isotropic Material with Penalization (SIMP) based topology optimization. Only a small fraction of the microstructure database is required to derive the optimized multiscale solutions, which demonstrates a significant reduction in the computational expense of optimization in comparison to contemporary sequential frameworks. In addition, both cases demonstrate a significant reduction in the compliance functional in comparison to the equivalent SIMP based optimizations.
O'Driscoll D, Santer M, Bruce P, 2021, Design and dynamic analysis of rigid foldable aeroshells for atmospheric entry, Journal of Spacecraft and Rockets, Vol: 58, Pages: 741-753, ISSN: 0022-4650
A novel rigid deployable aeroshell architecture has been developed, where rigid panels with a thermal protectionsystem layer are connected between retractable ribs. Following origami principles, an optimal fold pattern is selectedand imposed on the panels to ensure efficient flat stowage during launch and repeatable deployment. The designprocess includes minimizing the number of folds to reduce stacking height and maximizing the angles between eachfold line to avoid an unfavorable aerothermodynamic response. The dynamic behavior of the optimal design isanalyzed with the aid of a dynamic multibody analysis model. Results from the dynamic model show that the processof deployment is highly sensitive to panel geometry (especially panel thickness and hinge design). Robust, repeatable,and controllable deployment is most readily achieved with a small (but nonzero) panel thickness and selection ofinterpanel hinges, which allow a degree of over-rotation, avoiding a premature hard stop, which would otherwiseprevent full deployment. Modeled results have been verified through experimental testing of a 0.4-m-diam scalemodel.
Nightingale M, Hewson R, Santer M, 2021, Multiscale optimisation of resonant frequencies for lattice-based additive manufactured structures, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 63, Pages: 1187-1201, ISSN: 1615-147X
This paper introduces a novel methodology for the optimisation of resonant frequencies in three-dimensional lattice structures. The method uses a multiscale approach in which the homogenised material properties of the lattice unit cell are defined by the spatially varying lattice parameters. Material properties derived from precomputed simulations of the small scale lattice are projected onto response surfaces, thereby describing the large-scale metamaterial properties as polynomial functions of the small-scale parameters. Resonant frequencies and mode shapes are obtained through the eigenvalue analysis of the large-scale finite element model which provides the basis for deriving the frequency sensitivities. Frequency tailoring is achieved by imposing constraints on the resonant frequency for a compliance minimisation optimisation. A sorting method based on the Modal Assurance Criterion allows for specific mode shapes to be optimised whilst simultaneously reducing the impact of localised modes on the optimisation. Three cases of frequency constraints are investigated and compared with an unconstrained optimisation to demonstrate the algorithms applicability. The results show that the optimisation is capable of handling strict frequency constraints and with the use of the modal tracking can even alter the original ordering of the resonant mode shapes. Frequency tailoring allows for improved functionality of compliance-minimised aerospace components by avoiding resonant frequencies and hence dynamic stresses.
O'Driscoll D, Bruce PJ, Santer MJ, 2021, Hypersonic foldable Aeroshell for THermal protection using ORigami (HATHOR): evaluation of deployable structural rigidity during descent, AIAA Scitech 2021 Forum, Publisher: American Institute of Aeronautics and Astronautics
Garland MGC, Santer M, Morrison JF, 2021, Control of Cellular Separation Using Adaptive Surface Structures, Notes on Numerical Fluid Mechanics and Multidisciplinary Design, Pages: 73-80
The three-dimensional separation that gives rise to the formation of stall cells is shown to consist primarily of two discrete frequencies. The higher is the well known vortex shedding mode. However, at frequencies roughly ten times lower, the whole cell oscillates. Both features are clearly evident in both modal decomposition of the velocity field and surface pressure spectra.
Soltani Z, Santer M, 2020, The determination and enhancement of compliant modes for high-amplitude actuation in lattices, International Journal of Solids and Structures, Vol: 206, Pages: 124-136, ISSN: 0020-7683
This paper details the nonlinear design of adaptive lattices by determination and enhancement of compliant modes and optimizing the designed structure for delivering high amplitude actuation. The particular focus is the kagome lattice geometry—a pattern with some unique and useful actuation properties. Developing a novel design tool, the stiffness matrix of the beam assembly is calculated using a developed second-order geometrically nonlinear beam finite element formulation allowing large rotations. Based on this formulation in conjunction with singular value decomposition of the stiffness matrix, the modal optimization technique reduces the continuous structure with many degrees of freedom to a small number of low energy modes, which form the basis of designing the adaptive structure. For delivering high-amplitude actuation, the designed structure needs to be re-optimized due to changes in the nonlinear stiffness matrix under large deformation. This is performed via Bayesian optimization and by removing some internal members of the lattice. The integrity and feasibility of the optimum design is guaranteed via defining some constraints on removed members.
Thillaithevan D, Bruce P, Santer M, 2020, Stress constrained optimization using graded lattice microstructures, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 63, Pages: 721-740, ISSN: 1615-147X
In this work we propose a novel method for predicting stress within a multiscale lattice optimization framework. On the microscale, a scalable stress is captured for each microstructure within a large, full factorial design of experiments. A multivariate polynomial response surface model is used to represent the microstructure material properties. Unlike the traditional solid isotropic material with a penalisation based stress approach of penalising stress values or using the homogenized stress, we propose the use of real microscale stress components with macroscale strains through linear superposition. To examine the accuracy of the multiscale stress method, full-scale finite element simulations with non-periodic boundary conditions were performed. Using a range of microstructure gradings, it was determined that 6 layers of microstructures were required to achieve periodicity within the full-scale model. The effectiveness of the multiscale stress model was then examined. Using various graded structures and two load cases, our methodology was shown to replicate the von Mises stress in the centre of the unit lattice cells to within 10\% in the majority of the test cases. Finally, three stress-constrained optimization problems were solved to demonstrate the effectiveness of the method. Two stress constrained weight minimization problems were demonstrated, alongside a stress constrained target deformation problem. In all cases, the optimizer was able to sufficiently reduce the objective while respecting the imposed stress constraint.
Gramola M, Bruce P, Santer M, 2020, Off-design performance of 2D adaptive shock control bumps, Journal of Fluids and Structures, Vol: 93, ISSN: 0889-9746
Adaptive shock control bumps can exploit the on-design drag-reducing potential of 2D bumps, while mitigating their off-design performance deterioration through geometric modifications. In this study, experiments and simulations have been employed to investigate the wave-drag reducing potential of (actuated and unconstrained) 2D adaptive shock control bumps over a wide range of shock positions. Experiments were carried out in the Imperial College supersonic wind tunnel, modelling the adaptive bump as a flexible surface placed beneath a Mach 1.4 shock wave. 2D RANS CFD simulations of the flow in a parallel channel with a solid bump complement experiments. Wave drag was demonstrated to be proportional to the ratio of inlet to exit stagnation pressure in a blow-down wind tunnel for a given shock position. The shock exhibits a hysteretic behaviour when travelling in the wind tunnel working section, governed by the wave drag reducing potential of the bump. The actuated adaptive bump tested reduces wave drag over a wider operational envelope than solid bumps as experiments revealed the presence of three preferred structural configurations, which lead to a significantly enlarged hysteresis region. Finally, tests on unconstrained bumps were shown to increase wave drag, both on- and off-design, due to the unfavourable bump shapes that result from (only) passive actuation, suggesting that some constraints are required to achieve desirable surface deformations.
O'Driscoll D, Bruce PJ, Santer MJ, 2020, Origami-based TPS Folding Concept for Deployable Mars Entry Vehicles, AIAA Scitech 2020 Forum, Publisher: American Institute of Aeronautics and Astronautics
Murphy R, Imediegwu C, Hewson R, et al., 2020, Multiscale concurrent multi-objective structural optimization of a goose neck hinge
A robust multiscale concurrent optimization framework, which enables the precise functional-grading of mechanical properties within structures over two-scales, is presented within this paper and applied to a practical aerospace application — the mass minimization of a Goose Neck Hinge. The novelty of this framework lies in the concurrent nature of the response surface which enables the efficient calculation of small-scale mechanical properties during large-scale optimization. The efficacy of this approach permits a large number of design variables to be used in the parameterization of the small-scale without incurring a significant computational expense. The mass minimization of the Goose Neck Hinge constitutes a multi-objective optimization problem, constrained by a single maximum displacement constraint. Optimization of the Goose Neck Hinge was undertaken using both the framework presented within this paper and a density based topology optimization, to understand the relative performance of the multiscale framework to an industry standard method for structural optimization. The optimized multiscale geometry was able to satisfy the maximum displacement constraint using 20% less material than the density based topology optimization. This indicates that this framework has the potential to deliver a new generation of optimized aerospace structures.
Garland MGC, Santer MS, Morrison JF, 2019, Control of cellular separation using adaptive surfaces, Journal of Fluids and Structures, Vol: 91, ISSN: 0889-9746
We report results from an experimental investigation of the three-dimensional separation produced by a high-lift aerofoil at moderate incidence, with constant section, where the separation is controlled by the implementation of an adaptive surface. Mean and time-resolved measurements are made using a NASA GA(W)-1 aerofoil with AR=6 at Re c =3.5×10 5 . Surface oil visualisation and stereo Particle Image Velocimetry (PIV) are used to explore the flow field. The mean topology of the flow identifies characteristic spanwise periodic behaviour, “stall cells” along the surface of the model. Analysis of the time-dependent surface pressure shows two distinct frequencies within the flow field. The higher frequency appears at a Strouhal number, St≈0.2, representative of vortex shedding, and the typical von Kármán vortex street. The lower frequency appears at St≈0.02, observed as a global fluctuation in stall-cell extent. This lower frequency is apparent in many separated flows, but in the present context, appears to have received only little attention. It correlates with widely observed low-frequency unsteadiness in the wing loading around stall. While this mode is analogous to that observed in other types of separation, here the streamwise extent of the separation varies because the flow is separating from a curved surface rather than from a sharp edge; the width of the separated region also varies. We show that fully-reversible point actuations of an actuated surface with auxetic structure, introduced immediately upstream of the saddle point at the leading edge of the stall cell, reduce the extent of the separated region.
Imediegwu C, Murphy R, Hewson R, et al., 2019, Multi-scale structural optimization towards three-dimensional printable structures, Structural and Multidisciplinary Optimization: computer-aided optimal design of stressed solids and multidisciplinary systems, Vol: 60, Pages: 513-525, ISSN: 1615-147X
This paper develops a robust framework for the multiscale design of three-dimensional lattices with macroscopically tailored structural characteristics. The work exploits the high process flexibility and precision of additive manufacturing to the physical realization of complex microstructure of metamaterials by developing and implementing a multiscale approach. Structures derived from such metamaterials exhibit properties which differ from that of the constituent base material. A periodic microscale model is developed whose geometric parameterization enables smoothly changing properties and for which the connectivity of neighboring microstructures in the large-scale domain is guaranteed by slowly changing large-scale descriptions of the lattice parameters. A lattice-based functional grading of material is derived using the finite element method with sensitivities derived by the adjoint method. The novelty of the work lies in the use of multiple geometry-based small-scale design parameters for optimization problems in three-dimensional real space. The approach is demonstrated by solving a classical compliance minimization problem. The results show improved optimality compared to commonly implemented structural optimization algorithms.
Peacocke L, Bruce P, Santer M, 2019, Coupled aerostructural modeling of deployable aerodecelerators for Mars entry, Journal of Spacecraft and Rockets, Vol: 56, Pages: 1221-1230, ISSN: 0022-4650
An analysis of deployable aerodecelerators has been performed using a developed six-degree-of-freedom entry trajectory simulator coupled with a structural model of the deployable structural members, or ribs, to investigate the effect of aerodecelerator flexibility on the trajectory and configuration design. The modified Newtonian method is used in the entry trajectory simulator, and the deployable ribs are modeled as Euler–Bernoulli beams. It is shown that, although flexibility is beneficial in reducing the mass and volume of the deployed ribs, an increase in peak heat flux will result. However, if mass savings from flexible ribs can be reallocated toward increasing the diameter of the entry vehicle, significant benefits can be gained.
Gramola M, Bruce PJK, Santer M, 2019, Experimental and numerical study of 2D adaptive shock control bumps, 3AF International Conference
Gramola M, Bruce PJ, Santer MJ, 2019, FSI study of 2D adaptive shock control bumps, AIAA Scitech 2019 Forum, Publisher: American Institute of Aeronautics and Astronautics
Murphy RD, Imediegwu C, Hewson R, et al., 2019, Multiscale concurrent optimization towards additively manufactured structures, AIAA Scitech 2019 Forum, Publisher: American Institute of Aeronautics and Astronautics
This work establishes a robust concurrent multiscale optimization framework which facilitates the precise functional-grading of mechanical properties within structures, over two scales.The novelty lies in the concurrent nature of the response surface which connects the small-scalegeometry to the large-scale domain. A concurrent implementation enables an efficient application of computational resources, such that a large number of design variables can be usedwithout a significant computational penalty. This framework also takes advantage of the process flexibility and precision of additive manufacturing techniques to ensure that all optimizedstructures are manufacturable and suitable for an aerospace based application. A complianceminimization case is compared against a standard topology optimization algorithm, resultingin superior functional values and demonstrates the efficacy of the presented approach. A further application of this framework is highlighted through a target deformation case, where acomplex deformation field is obtained through simple loading conditions. Results from both ofthe example problems indicate that this framework has potential within the field of adaptivestructures, to inspire a new generation of multifunctional designs.
Gramola M, Bruce PJK, Santer M, 2019, Photogrammetry for accurate model deformation measurement in a supersonic wind tunnel, Experiments in Fluids, Vol: 60, ISSN: 0723-4864
The interest in adaptive devices for high-speed applications leads to the need for an accurate and reliable technique to obtain model deformation measurements during experiments. Point-tracking photogrammetry has been applied to supersonic wind tunnel testing, using four Phantom high-speed cameras placed on either side of the working section, where coded targets were applied to the surface of interest. Calibration experiments on a solid plate beneath a =1.4 normal shock and a =2 oblique shock allowed the quantification of the sources of optical distortion, namely the wind tunnel glass windows and aerodynamic effects (the lower pressure in the working section and the interaction between shock waves and the boundary layer). A correction matrix was applied to account for the optical distortion due to the glass, and the root-mean-square error due to aerodynamic effects (<0.03 mm) is believed to be negligible for applications with significant displacements (of the order of 1 mm). The application of photogrammetry to a flexible shock control bump has shown that the bump shape can be detected accurately, while disclosing some complex 3D effects that could not have been revealed by spanwise-averaged techniques such as schlieren photography.
Gramola M, Bruce P, Santer M, 2018, Experimental FSI study of adaptive shock control bumps, Journal of Fluids and Structures, Vol: 81, Pages: 361-377, ISSN: 0889-9746
The shock stabilisation and wave drag reduction potential of a two-dimensional adaptive shock control bump has been studied in the Imperial College supersonic wind tunnel. The bump was modelled as a flexible aluminium alloy plate deformed through spanwise actuation, and several bump heights were tested beneath a Mach 1.4 transonic shock wave. Schlieren images and static pressure readings along the flexible plate allowed the study of the λλ-shock structure generated by the bifurcation of the normal shock for a range of shock positions. All bumps tested were found to increase shock stability, but wave drag reduction was only observed for shocks close to the leading edge of the flexible plate. Positive deformations of the flexible plate for downstream shocks are believed to reduce supersonic flow reacceleration, and hence the strength of the rear leg of the λλ-shock and wave drag, in comparison to a solid bump with the same shape. The position of the rear leg of the λλ-shock was found to exhibit a bistable behaviour, and this is hypothesised to be caused by a complex coupling of aerodynamic and structural instabilities.
Imediegwu C, Murphy R, Hewson RW, et al., 2018, Multiscale structural and thermal optimization towards 3D printable structures, The 9th International Conference on Computational Methods
Bird J, Santer M, Morrison J, 2018, Experimental control of turbulent boundary layers with in-plane travelling waves, Flow, Turbulence and Combustion, Vol: 100, Pages: 1015-1035, ISSN: 1386-6184
The experimental control of turbulent boundary layers using stream-wise travelling waves of spanwise wall velocity, produced using a novel activesurface, is outlined in this paper. The innovative surface comprises a pneu-matically actuated compliant structure based on the kagome lattice geometry,supporting a pre-tensioned membrane skin. Careful design of the structureenables waves of variable length and speed to be produced in the flat surfacein a robust and repeatable way, at frequencies and amplitudes known to havea favourable influence on the boundary layer. Two surfaces were developed,a preliminary module extending 152 mm in the streamwise direction, and alonger one with a fetch of 2.9 m so that the boundary layer can adjust to thenew surface condition imposed by the forcing. With a shorter, 1.5 m portionof the surface actuated, generating an upstream-travelling wave, a drag re-duction of 21.5% was recorded in the boundary layer withReτ= 1125. Atthe same flow conditions, a downstream-travelling produced a much smallerdrag reduction of 2.6%, agreeing with the observed trends in current simula-tions. The drag reduction was determined with constant temperature hot-wiremeasurements of the mean velocity gradient in the viscous sublayer, while si-multaneous laser Doppler vibrometer measurements of the surface recorded thewall motion. Despite the mechanics of the dynamic surface resulting in someout-of-plane motion (which is small in comparison to the in-plane streamwisemovement), the positive drag reduction results are encouraging for future in-vestigations at higher Reynolds numbers.
Jinks E, Bruce P, Santer M, 2018, Optimisation of adaptive shock control bumps with structural constraints, Aerospace Science and Technology, Vol: 77, Pages: 332-343, ISSN: 1270-9638
This paper presents the results from a study to design an optimal adaptiveshock control bump for a transonic aerofoil. An optimisation frameworkcomprising aerodynamic and structural computational tools has been used toassess the performance of candidate adaptive bump geometries based on a novelsurface-pressure-based performance metric. The geometry of the optimal resultantdesign is a unique feature of its adaptivity; being strongly inuencedby the (passive) aerodynamic pressure forces on the exible surface as well asthe (active) displacement constraints. This optimal geometry bifurcates theshock-wave and carefully manages the recovering post-shock ow to maximisepressure-smearing in the shock-region with only a small penalty in L=D for theaerofoil. Short adaptive bumps (with small imposed displacements) generallyperform better than taller ones, and maintain their performance advantage fora wide range of bump positions, suggesting good robustness to variations inshock position, which are an inevitable feature of a real-world ight application.Such devices may o er advantages over conventional ( xed geometry) shockcontrol bumps, where optimal performance is achieved with taller devices, atthe expense of poor robustness to variations in shock position.Keywords: Shock Control Bumps; Aeroelastic Optimisation
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