Free-stream turbulence effects on long-span bridge aerodynamics

The importance of vortex induced vibrations (VIV) in the design of bridge decks is becoming more apparent (Wu and Kareem, 2012). Generally, experimental literature presents a bridge deck situated in a smooth flow, though bridges are usually subjected to the inherent turbulence of atmospheric wind. According to the results of Matsumoto et al. (1993), the effects of turbulence on VIV are rather complicated, this is mainly due to an interaction between the vortices in the wake, and vortices induced by the structure motion. The impacts of turbulence on the motion-induced forces are uncertain due to a limited understanding of this issue. Wu and Kareem (2012) also present a conjecture, suggesting that turbulence can enhance or diminish the structural response, depending on whether the dominant vortices are generated from the motion of the structure, or vortex shedding in the wake. This numerical investigation aims to verify this hypothesis, while studying the effects of turbulence on the structural response, aerodynamic forces, correlations, and wake characteristics for a dynamic bridge deck. Some effects of freestream turbulence on a rectangular bridge deck undergoing VIV are presented. Heaving motion of the model under a smooth flow is presenting with a peak r.m.s. response y/D 3% in a close agreement with the equivalent wind tunnel experiment. Introducing turbulence into the flow reduces the peak rms response by 50%, which is in accordance with observations in the literature. This abstract also reports the effects of turbulence on the spanwise correlation of pressure on the bridge deck surfaces. Due to the dominance of the structural motion, the correlations for the dynamic cases at lock-in were markedly increased in comparison to the equivalent static case. The presence of turbulence has also shown to reduce the correlation across the span for both static and dynamic cases. It can therefore be deduced that turbulence reduces the strength of the leading edge (motion-induced) vortices of the structure, and accordingly its VIV response. Sensitivity studies of the effects of turbulence intensity and integral length scales were conducted. Effects of turbulence on the pitching motion were studied as well. Detailed results will be reported in the conference

Large-eddy simulation of dispersion: comparison between elevated source and ground level source

Large-eddy simulation (LES) is used to calculate the concentration fluctuations of passive plumes from an elevated source (ES) and a ground-level source (GLS) in a turbulent boundary layer over a rough wall. The mean concentration, relative fluctuations and spectra are found to be in good agreement with the wind-tunnel measurements for both ES and GLS. In particular, the calculated relative fluctuation level for GLS is quite satisfactory, suggesting that the LES is reliable and the calculated instantaneous data can be used for further post-processing. Animations are shown of the meandering of the plumes, which is one of the main features to the numerical simulations. Extreme value theory (EVT), in the form of the generalized Pareto distribution (GPD), is applied to model the upper tail of the probability density function of the concentration time series collected at many typical locations for GLS and ES from both LES and experiments. The relative maxima (defined as maximum concentration normalized by the local mean concentration) and return levels estimated from the numerical data are in good agreement with those from the experimental data. The relative maxima can be larger than 50. The success of the comparisons suggests that we can achieve significant insight into the physics of dispersion in turbulent flows by combining LES and EVT

Modelling the effect of freestream turbulence on dynamic stall of wind turbine blades

Large-eddy simulations of flow over a pitching airfoil are conducted to study the effect of freestream turbulence on the aerodynamic characteristics. A primary field of applications of this study is wind turbine aerodynamics. The wind turbines operate in yaw in large scale variations of wind direction due to very large turbulence eddies, and the blades operate in a periodically oscillating condition. The pitching frequency of the airfoil corresponds to a typical rotating frequency of modern large wind turbines. A divergence-free synthetic turbulence inflow is applied at the upstream region of the pitching airfoil to investigate the effect of small-scale freestream turbulence on dynamic stall. Phase-averaged lift, drag and moment of the pitching airfoil show good agreement with experimental data in the literature. Characteristic phenomena of dynamic stall, such as leading edge vortex motions, are analysed and quantified. The effect of the small-scale upstream turbulence is significant on the lift coefficient during the downstroke. The power spectral density of the streamwise velocity sampled from one point in the wake shows that the inertial sub-range tends to extend towards the pitching mode for the turbulent inflow, while there is a distinctive spectral gap for the laminar inflo

Research data for project DIPLOS (Dispersion of localised releases in a street network), Part3

Dataset Support for: Xie &amp; Fuka A note on spatial averaging and shear stresses within urban canopies Boundary-Layer Meteorology</span

Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids

The 3-dimensional incompressible Rayleigh-Taylor instability is numerically studied through the large-eddy-simulation (LES) approach based on the passive scalar transport model. Both the instantaneous velocity and the passive scalar fields excited by sinusoidal perturbation and random perturbation are simulated. A full treatment of the whole evolution process of the instability is addressed. To verify the reliability of the LES code, the averaged turbulent energy as well as the flux of passive scalar are calculated at both the resolved scale and the subgrid scale. Our results show good agreement with the experimental and other numerical work. The LES method has proved to be an effective approach to the Rayleigh-Taylor instability

Dataset for LES and RANS for turbulent flow over arrays of wall-mounted obstacles, Flow Turbulence and Combustion

Dataset supporting paper Xie, Z-T, Castro, IP (2006) LES and RANS for turbulent flow over arrays of wall-mounted obstacles, Flow Turbulence and Combustion, 76(3), 291-312, DOI: 10.1007/s10494-006-9018-6</span

Dataset of Thermal Stratification Effects on Turbulence and Dispersion in Internal and External Boundary Layers

The data supports the paper: Sessa V, Xie Z-T, Herring S. Thermal Stratification Effects on Turbulence and Dispersion in Internal and External Boundary Layers. Boundary-Layer Meteorology.</span

Data for Turbulence and dispersion below and above the interface of the internal and the external boundary layers

Data supporting the paper Sessa, V., Xie, Z-T., &amp; Herring, S. (2018). Turbulence and dispersion below and above the interface of the internal and the external boundary layers. Journal of Wind Engineering and Industrial Aerodynamics, 182, 189-201. DOI: 10.1016/j.jweia.2018.09.021</span

Dataset for Large-eddy simulation of flows over random urban-like obstacles, Boundary-Layer Meteorology

Dataset supporting the paper: Xie, ZT., Coceal, O. &amp; Castro, I.P. Boundary-Layer Meteorol (2008) 129: 1. https://doi.org/10.1007/s10546-008-9290-1 </span

Research data for project DIPLOS (Dispersion of localised releases in a street network), Part2

Dataset Support: Fuka, Xie, Castro, Hayden, Carpentierri &amp; Robins Scalar fluxes near a tall building in an aligned array of rectangular buildings Boundary-Layer Meteorology</span