Publications
199 results found
Wang Y, Zhao X, Graham M, et al., 2022, Vortex force map for incompressible multi-body flows with application to wing-flap configurations, JOURNAL OF FLUID MECHANICS, Vol: 953, ISSN: 0022-1120
Milne IA, Kimmoun O, Graham JMR, et al., 2021, An experimental and numerical study of the resonant flow between a hull and a wall, JOURNAL OF FLUID MECHANICS, Vol: 930, ISSN: 0022-1120
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- Citations: 7
Zheng S, Bruce P, Cuvier C, et al., 2021, The non-equilibrium dissipation scaling in large Reynolds number turbulence generated by rectangular fractal grids, Physical Review Fluids, Vol: 6, ISSN: 2469-990X
In this paper, the turbulence fields generated by a group of modified fractal grids, referred to as the rectangular fractal grids (RFGs), are documented and discussed. The experiments were carried out using hot-wire anemometry in three facilities at Imperial College London and the Laboratory of Fluid Mechanics in Lille, France. Due to the large Reynolds number of the resulting turbulence, several data processing methods for turbulence properties are carefully evaluated. Two spectral models were adopted, respectively, to correct the large and small wave-number ranges of the measured spectrum. After the technical discussion, the measurement results are presented in terms of one-point statistics, length scales, homogeneity, isotropy, and dissipation. The main conclusions are twofold. First, the location of maximum turbulence intensity xpeak is shown to be independent of the inlet Reynolds number but dependent on the ratio between the lengths of the largest grid bars in the transverse and vertical directions. This is crucial to the production of prescribed features of turbulent flows in laboratory. Second, these RFG-generated turbulent flows are shown to be quasihomogeneous in the decay region for x/xpeak>1.5, but the isotropy is poorer than that of the previous studied fractal square grid-generated turbulence. In the beginning of the decay region, a decreasing pattern of the integral length scale Lu and Taylor microscale λ was observed, yet the ratio Lu/λ remained roughly constant along the centerline, so Cε∼Re−1λ, complying with the nonequilibrium scaling relation reported in previous studies for various turbulent flows.
Graham J, 2021, Aerodynamics of horizontal axis wind turbines, Wind Energy Handbook, Publisher: John Wiley & Sons, Pages: 39-149, ISBN: 9781119451099
These are complemented by new sections on blade add-ons and noise in the aerodynamics chapters, which now also include a description of the Leishman-Beddoes dynamic stall model and an extended introduction to Computational Fluid Dynamics ...
Graham J, 2021, Further aerodynamic topics for wind turbines, Wind Energy Handbook 3, Publisher: John Wiley and Sons Ltd, Pages: 153-225
Milne IA, Graham JMR, Coles DS, 2021, On the scaling of turbulence in a high Reynolds number tidal flow, JOURNAL OF FLUID MECHANICS, Vol: 915, ISSN: 0022-1120
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- Citations: 2
Sherwin S, Lahooti M, Bao Y, et al., 2021, The thick strip method for slender body fluid structure interaction
For slender body fluid structure interaction which arise in problems such as the vortex induced vibration of oil riser pipes[1], flexible wings [2] or parked wind turbine blades, there is a natural separation of spatial scales between the fluid and structural problem. Nevertheless the large scale dynamics of the structure can have a notable impact on the fluid flow, for example leading to large scale separation which then modify the fluid forces applied to the structure. To resolve the full scale fluid structure interaction problem at realistic flow conditions/Reynolds number is typically prohibitive even on the largest HPC systems currently available. A reasonable modelling approach to address these challenging problems is to leverage the scale separation between the fluid and structural problem and only model the fluid on a strip at a series of locations along the slender body. Earlier approaches to this type of modelling used potential flow, two-dimensional U-RANS or even empirical data, in "thin" strip approximations. However these approaches were unable to capture the near body anisotropic or transitional flow features which are often responsible for energising the slender body dynamics. In [1] we proposed a generalized "thick" strip method where we adopt a finite thickness strip, which is still thin compared to the slender body, within which we apply an under-resolved Direct Numerical Simulation uDNS or implicit Large Eddy Simulation iLES modelling to capture the anisotropic flow behaviour and if sufficiently resolved the transitional nature of the flow. Within each strip we apply a high fidelity spectral/hp element-Fourier approximation using the Nektar++ package [3]. In this presentation we will outline the development and application of the thick strip modelling method for vortex induced problem of riser pipes and wind turbine blades. We will also discuss the challenges of the high fidelity modelling using spectral/hp element approximati
Li J, Wang Y, Graham M, et al., 2021, Evaluating Unsteady Fluid Dynamic Forces in Viscous Flows from the Vorticity Field, AIAA JOURNAL, Vol: 59, Pages: 22-33, ISSN: 0001-1452
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- Citations: 3
Li J, Zhao X, Graham M, 2020, Vortex force maps for three-dimensional unsteady flows with application to a delta wing, JOURNAL OF FLUID MECHANICS, Vol: 900, ISSN: 0022-1120
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- Citations: 8
Li J, Wang Y, Graham M, et al., 2020, Vortex moment map for unsteady incompressible viscous flows, JOURNAL OF FLUID MECHANICS, Vol: 891, ISSN: 0022-1120
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- Citations: 7
Deskos G, Payne GS, Gaurier B, et al., 2020, On the spectral behaviour of the turbulence-driven power fluctuations of horizontal-axis turbines, Journal of Fluid Mechanics, Vol: 904, ISSN: 0022-1120
In this article we consider the spectral behaviour of turbulence-driven power fluctuations for a single horizontal-axis turbine. To this end, a small-scale instrumented axial-flow hydrokinetic turbine model is deployed in the long water flume situated in the laboratory facilities of IFREMER in Boulogne-sur-Mer, France, and synchronous measurements of the upstream velocity and the rotor are collected for different tip-speed ratios. The study confirms previous findings suggesting that the power spectra follow the velocity spectra behaviour in the large scales region and a steeper power law slope behaviour over the inertial frequency sub-range. However, we show that both the amplitude of the power spectra and low-pass filtering effect over the inertial sub-range also depend on the rotor aero/hydrodynamics (e.g.) and the approaching flow deceleration and not solely on the rotational effects. In addition, we present a novel semi-analytical model to predict the dominant blade-passing frequency harmonics in the high-frequency regime using the rotationally sampled spectra technique. For all calculations, the distortion of incoming turbulence is taken into account.
Graham JMR, 2020, Transverse forces on cylinders in random waves.
A quasi steady equation has been used with success to predict transverse forces on circular cylinders in sinusoidal oscillatory flow and waves. It has also been used previously to analyze the broadening of the spectrum of transverse force due to vortex shedding on bluff bodies in unidirectional turbulent flows. Considers the case of a circular cylinder in random oscillatory flows and unidirectional random waves. Time histories of transverse force and associated broadband spectra are computed using the same quasi steady equation and comparisons are made with measurements on a vertical cylinder in random waves using a JONSWOP spectrum for the incident waves.
Milne IA, Graham JMR, 2019, Turbulence velocity spectra and intensities in the inflow of a turbine rotor, JOURNAL OF FLUID MECHANICS, Vol: 870, ISSN: 0022-1120
Nguyen S, Corey M, Chan W, et al., 2019, Experimental determination of the aerodynamic coefficients of spinning bodies, The Aeronautical Journal, Vol: 123, Pages: 678-705, ISSN: 0001-9240
To accurately predict the probabilities of impact damage to aircraft from runway debris, it is important to understand and quantify the aerodynamic forces that contribute to runway debris lofting. These lift and drag forces were therefore measured in experiments with various bodies spun over a range of angular velocities and Reynolds numbers. For a smooth sphere, the Magnus effect was observed for ratios of spin speed to flow speed between 0.3 and 0.4, but a negative Magnus force was observed at high Reynolds numbers as a transitional boundary layer region was approached. Similar relationships between lift and spin rate were found for both cube- and cylinder-shaped test objects, particularly with a ratio of spin speed to flow speed above 0.3, which suggested comparable separation patterns between rapidly spinning cubes and cylinders. A tumbling smooth ellipsoid had aerodynamic characteristics similar to that of a smooth sphere at a high spin rate. Surface roughness in the form of attached sandpaper increased the average lift on the cylinder by 24%, and approximately doubled the lift acting on the ellipsoid in both rolling and tumbling configurations.
Bao Y, Zhu HB, Huan P, et al., 2019, Numerical prediction of vortex-induced vibration of flexible riser with thick strip method, Journal of Fluids and Structures, ISSN: 0889-9746
We present numerical prediction results of vortex-induced vibration (VIV) of a long flexible tensioned riser subject to uniform currents. The VIV model of long length-to-diameter ratio is considered and ‘thick’ strip technique based on high-order spectral/hp element method is employed for computational simulation. The model parameter of the riser for the simulation is chosen according to the dimensional counterparts used in the experimental tests in Lehn (2003). The numerical results are displayed in terms of motion responses, hydrodynamic forces and wake patterns as well and compared and discussed with the available data in the literature.
Milne IA, Tong F, Graham JMR, 2019, VORTEX SHEDDING AND ROLL DAMPING FOR HULLS WITH ROUNDED BILGES, 38th ASME International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2019), Publisher: AMER SOC MECHANICAL ENGINEERS, ISSN: 2153-4772
Zheng S, Bruce PJK, Graham JMR, et al., 2018, Weakly sheared turbulent flows generated by multiscale inhomogeneous grids, Journal of Fluid Mechanics, Vol: 848, Pages: 788-820, ISSN: 0022-1120
A group of three multiscale inhomogeneous grids have been tested to generate different types of turbulent shear flows with different mean shear rate and turbulence intensity profiles. Cross hot-wire measurements were taken in a wind tunnel with Reynolds number ReD of 6000–20 000, based on the width of the vertical bars of the grid and the incoming flow velocity. The effect of local drag coefficient CD on the mean velocity profile is discussed first, and then by modifying the vertical barsto obtain a uniform aspect ratio the mean velocity profile is shown to be predictable using the local blockage ratio profile. It is also shown that, at a streamwise location x = xm, the turbulence intensity profile along the vertical direction u0(y) scales with the wake interaction length x peak∗,n = 0.21g2n/(αCDwn) (α is a constant characterizing the incoming flow condition, and gn, wn are the gap and width of the vertical bars,respectively, at layer n) such that (u0/Un) 2β2 (CDwn/x peak ∗,n) −1 ∼ (xm/x peak ∗,n) b, where β is a constant determined by the free-stream turbulence level, Un is the local mean velocity and b is a dimensionless power law constant. A general framework of grid design method based on these scalings is proposed and discussed. From the evolutionof the shear stress coefficient ρ(x), integral length scale L(x) and the dissipation coefficient C (x), a simple turbulent kinetic energy model is proposed that describes the evolution of our grid generated turbulence field using one centreline measurement and one vertical profile of u 0(y) at the beginning of the evolution. The results calculated from our model agree well with our measurements in the streamwiseextent up to x/H ≈ 2.5, where H is the height of the grid, suggesting that it might be possible to design some shear flows with desired mean velocity and turbulence intensity profiles by designing the geometry of a passive grid.
Jamieson P, Graham JMR, Hart E, et al., 2018, Formulation of the General Momentum Equations, 7th Conference on Science of Making Torque from Wind (TORQUE), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Bao Y, Palacios R, Graham M, et al., 2018, A strip modelling of flow past a freely vibrating cable, ERCOFTAC Series, Vol: 24, Pages: 221-227, ISSN: 1382-4309
© 2018, Springer International Publishing AG. Vortex-induced vibration of long flexible structures with cylindrical cross-section are widely encountered in various engineering fields.
Milne IA, Graham JMR, 2018, VORTEX SHEDDING FROM HULLS IN CLOSE PROXIMITY WITH RELATIVE MOTION, 37th ASME International Conference on Ocean, Offshore and Arctic Engineering, Publisher: AMER SOC MECHANICAL ENGINEERS, ISSN: 2153-4772
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- Citations: 5
Gage SA, Graham JMR, 2017, Static split duct roof ventilators, BUILDING RESEARCH AND INFORMATION, Vol: 28, Pages: 234-244, ISSN: 0961-3218
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- Citations: 15
Bakis KN, Massaro M, Williams MS, et al., 2017, Passive Control of Bridge Wind-Induced Instabilities by Tuned Mass Dampers and Movable Flaps, JOURNAL OF ENGINEERING MECHANICS, Vol: 143, ISSN: 0733-9399
Rainbird J, Peiro J, Graham JM, 2017, Poststall Airfoil Performance and Vertical-Axis Wind Turbines, JOURNAL OF PROPULSION AND POWER, Vol: 33, Pages: 1053-1062, ISSN: 0748-4658
Graham JMR, 2017, Rapid distortion of turbulence into an open turbine rotor, Journal of Fluid Mechanics, Vol: 825, Pages: 764-794, ISSN: 0022-1120
Rapid distortion of turbulence (RDT) theory is applied to homogeneous, isotropic turbulence incident on a horizontal axis turbine rotor such as a wind turbine or tidal-stream turbine. The mean flow field of the rotor which distorts the turbulence is represented by the commonly used axisymmetric actuator disc model due to Betz and Joukowski. The fluctuating streamwise component of the turbulence distorted by this field is calculated at the actuator disc plane. Turbulence velocity intensities and spectra are evaluated for general ratios of turbulence integral length scale to the rotor diameter, including the small-scale limit for which the original homogeneous strain analysis of Batchelor and Proudman may be applied. The distortion of the mean velocity profile of an incident rotor wake which may be considered a zero frequency disturbance relevant to wind and tidal turbine operation in large arrays is also analysed by the same method, treating it as a deterministic disturbance in the incident flow.
González-Salcedo A, Aparicio-Sanchez M, Munduate X, et al., 2017, A computationally-efficient panel code for unsteady airfoil modelling including dynamic stall
A new approach based on inviscid panel methods has been developed for airfoils undergoing unsteady kinematics. The model is tailored to practical applications related to wind turbines, taking into account accuracy and computational cost considerations. It is able to represent rigid or deformable airfoils, attached and separated flow focusing also on unsteady cases including dynamic stall. An extensive validation has been carried out including steady and unsteady conditions, while simulations of airfoils with trailing edge flaps have also been performed.
González-Salcedo A, Aparicio-Sanchez M, Munduate X, et al., 2017, A computationally-efficient panel code for unsteady airfoil modelling including dynamic stall
© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. A new approach based on inviscid panel methods has been developed for airfoils undergoing unsteady kinematics. The model is tailored to practical applications related to wind turbines, taking into account accuracy and computational cost considerations. It is able to represent rigid or deformable airfoils, attached and separated flow focusing also on unsteady cases including dynamic stall. An extensive validation has been carried out including steady and unsteady conditions, while simulations of airfoils with trailing edge flaps have also been performed.
Graham JMR, 2017, Transverse forces on cylinders in random waves, International Conference on Flow Induced Vibrations, Publisher: BHRA
A quasi steady equation has been used with success to predict transverse forces on circular cylinders in sinusoidal oscillatory flow and waves. It has also been used previously to analyze the broadening of the spectrum of transverse force due to vortex shedding on bluff bodies in unidirectional turbulent flows. Considers the case of a circular cylinder in random oscillatory flows and unidirectional random waves. Time histories of transverse force and associated broadband spectra are computed using the same quasi steady equation and comparisons are made with measurements on a vertical cylinder in random waves using a JONSWOP spectrum for the incident waves.
Bakis KN, Massaro M, Williams MS, et al., 2017, Introducing the flap mass damper for controlling bridge aeroelastic instabilities
© 9th Asia Pacific Conference on Wind Engineering, APCWE 2017. All Rights Reserved. This study investigates the control of bridge deck flutter and torsional divergence instabilities, using a novel passive approach. The control system design study is based on a sectional flexible bridge model interacting with a constant velocity airstream. The control configuration incorporates the properties of movable flaps, seen as extensions of the bridge deck, and of a tuned mass damper (TMD). This combined mechanical system, referred to as the flap mass damper (FMD), combines favourable aerodynamic properties of the flaps with a driving force provided by the vibrating mass inside the hollow deck. A further advantage is that the deck’s motion is transmitted to the flaps passively without requiring complex external linkages. Special attention is given to ensuring that the control configuration attains optimum robustness properties and thus maximizes uncertainty tolerance.
Bakis KN, Massaro M, Williams MS, et al., 2017, Introducing the flap mass damper for controlling bridge aeroelastic instabilities
This study investigates the control of bridge deck flutter and torsional divergence instabilities, using a novel passive approach. The control system design study is based on a sectional flexible bridge model interacting with a constant velocity airstream. The control configuration incorporates the properties of movable flaps, seen as extensions of the bridge deck, and of a tuned mass damper (TMD). This combined mechanical system, referred to as the flap mass damper (FMD), combines favourable aerodynamic properties of the flaps with a driving force provided by the vibrating mass inside the hollow deck. A further advantage is that the deck’s motion is transmitted to the flaps passively without requiring complex external linkages. Special attention is given to ensuring that the control configuration attains optimum robustness properties and thus maximizes uncertainty tolerance.
Graham JMR, 2017, Application of discrete vortex methods to the computation of separated flows., NUMERICAL METHODS FOR FLUID DYNAMICS II, Pages: 273-302
Considers discrete vortex methods, in particular the modelling of separated low speed flows around two dimensional bodies. Discusses the representation of vortex sheets and considers impulsively started flow past a sharp edge (separating shear layer from a semi infinite wedge). Describes a concentrated point vortex representation. Multi vortex representation of the vortex sheet shed from an edge may be treated in several ways. Studies separation from a continuous surface, secondary separation, the cloud in cell method (and flow past a normal flat plate as a example), vortex decay and three dimensional effects. Outlines application to separated flows on aerofoils. (C.J.U.)
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