Horia Hangan

Wind-driven rain studies. A C-FD-E approach

Abstract Wind-driven rain studies provide the main input to problems such as: precipitation protection, sealing and drainage accumulation. A computational fluid dynamics (CFD) methodology is developed and used to reproduce previously developed wind tunnel experiments on generic buildings. Wetting factors are calculated and compared for two geometries. The methodology is further applied to real cases. The cornice effect on the upper part of a low-rise building facade as well as the wetting and downwash on a sloped face of a high-rise building are investigated.

Wake Control Based on Spanwise Sinusoidal Perturbations

The effectiveness of a passive sinusoidal perturbation method, applied on the upstream faces of square cylinders at a wavelength that corresponds to the wavelength of the intermediate wake instability mode, is experimentally investigated. Hot-wire measurements are taken to examine the effect of three different sinusoidal perturbation amplitudes as compared to the straight cylinder case. Good agreement is found between high- and low-Reynolds-number results, suggesting that the main flow dynamics features, as well as the flow control method efficiency, are Reynolds independent. Two sets of measurements are taken: in the near and in the intermediate to far wake. The near-wake measurements show that the method is very effective in mitigating the von Karman vortices as previously found, whereas the intermediate to far wake measurements indicate that the wake decay is accelerated by the sinusoidal perturbations, therefore, being beneficial in the reduction of wake aeroelastic instabilities.

A wavelet pattern recognition technique for identifying flow structures in cylinder generated wakes

Abstract A pattern recognition technique, applied in wavelet space, with enhanced capabilities of identifying multiple flow templates based on scale is introduced and applied to the turbulent, intermediate wake region of a circular cylinder. The advantage of this enhanced pattern recognition technique is two-folded: (i) the wavelet templates can be easily identified based on the sharp definition of modulus maxima lines and (ii) the scale separation in wavelet space allows for the identification of multiple structures. This new technique is used to investigate the relationship between the primary (spanwise) and secondary (streamwise) wake structures. The analysis relates the interactions between these two flow structures to a local loss of periodicity in the Karman vortex street.

Buffeting for 2D and 3D sharp-edged bluff bodies

Abstract Aerodynamic buffeting is experimentally investigated for moderate Reynolds number, turbulent flows around two- and three-dimensional bluff bodies in tandem. Combining flow visualizations, surface pressure and velocity measurements, changes in aerodynamic loading and macroscale flow features are related. For large obstacle separations, it is found that when surface-mounted prisms are placed in thin boundary layers, loading and wake dynamics are similar to those found for cylinders suspended in free streams. However, important differences are identified for smaller gaps, which can be generally attributed to greater streamline curvature for three-dimensional configurations.

Pressure distribution, aerodynamic forces and dynamic response of box bridge sections

Static and dynamic wind tunnel tests were carried out in smooth flow on a section model of the Sunshine Skyway Bridge. Deck surface pressures, support forces, structural response, as well as wake flow velocities were measured in the tests. In this paper, a first step is made to investigate the characteristics of the aeroelastic behaviour of a bridge deck, by relating the mean and fluctuating aerodynamic forces, deck pressure distributions and dynamic response at different wind speeds, and by comparing their values with those measured on the stationary deck. Three different response regimes of forced motion, torsional vortex shedding lock-in and torsional flutter were observed, associated with different ranges of the oncoming wind speed. In the forced vibration regime the aerodynamic forces and the pressure distributions compare very well to those measured in the static tests, indicating a quasi-steady behaviour. In the lock-in and flutter regimes, however, these quantities take values quite different from those measured on the stationary model, showing the nature of the aeroelastic interaction.

Buffeting of two-dimensional bluff bodies

Abstract The paper presents the results of a detailed buffeting analysis for 2D, sharp-edged bluff bodies. The analysis relates to extensive wind tunnel pressure tests on various shaped models in tandem and staggered arrangements for smooth, large- and small-scale turbulent flows. Based on load coefficients, Strouhal number, flow visualisations and spectral analysis, a partition of the buffeting domain is proposed and the flow mechanics is investigated. A parametric load buffeting model is defined for square prisms in tandem arrangement. The model proves to be a useful tool for various geometries (relative body dimensions and spacing) in both smooth and large-scale turbulent flows.

Analytical Solutions for a Family of Gaussian Impinging Jets

Various types of impinging jet flows are analytically modeled using inviscidfree Gaussian jet solutions superimposed with experimentally fitted boundary layer models. Improved (more robust) and simplified solutions to existing models are defined. Velocity profiles, surface pressure distributions, and streamline plots are calculated for circular, plane, and annular impinging jets. The models show excellent agreement with existing experimental results in both laminar and turbulent conditions and for different Reynolds numbers.

Microscale Computational Fluid Dynamics Simulation for Wind Mapping Over Complex Topographic Terrains

Wind mapping is of utmost importance in various wind energy and wind engineering applications. The available wind atlases usually provide wind data with low spatial resolution relative to the wind turbine height and usually neglect the effect of topographic features with relatively large or sudden changes in elevation. Two benchmark cases are studied for computational fluid dynamics (CFD) model evaluation on smooth two-dimensional (2D) and three-dimensional (3D) hills. Thereafter, a procedure is introduced to build CFD model of a complex terrain with high terrain roughness heights (dense urban area with skyscrapers) starting from existing topography maps in order to properly extend the wind atlas data over complex terrains. CFD simulations are carried out on a 1:3000 scale model of complex topographic area using Reynolds averaged Navier–Stokes (RANS) equations along with shear stress transport (SST) k-ω turbulence model and the results are compared with the wind tunnel measurements on the same model. The study shows that CFD simulations can be successfully used in qualifying and quantifying the flow over complex topography consisting of a wide range of roughness heights, enabling to map the flow structure with very high spatial resolution.

Field data analysis and weather scenario of a downburst event in Livorno, Italy on 1 October 2012

AbstractThe Mediterranean is a “hot spot” for the genesis of different types of severe weather events, including potentially damaging wind phenomena like downbursts, whose occurrence and evolution in this geographical region have not been documented in the literature. This paper is part of an interdisciplinary collaboration between atmospheric scientists and wind engineers with the objective of conducting a comprehensive analysis of the field measurements and weather scenarios related to nonsynoptic wind systems in this area. The downburst that struck the Livorno coast of Italy at about 1310 local time 1 October 2012 is investigated as a relevant test case for such severe wind events. The wind velocity records detected by ultrasonic anemometers, part of a monitoring network created for the European “Wind and Ports” and “Wind, Ports and Sea” projects, are analyzed and decomposed in order to inspect the main statistical features of this transient event. The analysis of the meteorological precursors to this ...

Case study: Numerical simulations for comfort assessment and optimization of the ventilation design for complex atriums

Abstract HVAC efficiency studies are carried out for two large and complex (in terms of geometry and boundary conditions) atriums. In addition to the usual steady state velocity and temperature fields, an innovative transient solution for the mixture fraction of freshly supplied air into the domain is obtained. Correlations between flow patterns (local recirculations), temperature field and transient distribution of fresh air are inferred. The results of the simulations are used by the HVAC engineers to optimize the ventilation designs.