查看更多>>摘要：A ceiling fan is one of the cost-effective alternatives for poverty-ridden societies and tropical countries short on natural resources. However, due to the inherent working principle, a lot of losses occur during electrical to mechanical energy conversion. Apart from losses, other problems associated with conventional ceiling fans are buffeting airflow, internal heating, and dirt accumulation on fan blades. Recently, the idea of a bladeless ceiling fan has been patented which has the potential to resolve most of the issues associated with the conventional fans, however, no details have been shared regarding flow physics and their effectiveness in constrained spaces. In this study, an annular type bladeless ceiling fan is computationally analyzed in a standard empty room (4m x 4m x 4m) environment. Parametric analysis of different design features such as fan radius, height from the ceiling and floor, fan jet width, mass flow rate, and orientations was studied and their effect on the perceived comfort level in terms of velocity spread and average velocities were captured computationally. The results show that the fan height in the close vicinity of ceiling does not affect the flow field in the occupied zones, however, as the fan gets closer to the floor the velocity field in the occupied zone changes due to creation of a strong vortex at the center of floor. Thus, fan installation closer to the ceiling (less than 0.5m from the ceiling) is a preferred choice. With an increase in fan radius from 0.3m to 0.5m, an increment of 33% was observed in velocity spread thus increasing the zone of influence. A finer jet width under the same volume flow rate produces higher velocities across the room e.g. 2 mm jet produces 36% higher average velocities as compared to 4 mm jet, which effectively increases zone of influence. Effect of jet orientation was also studied and a 90 degrees (straight down) orientation produced better overall velocity spread in comparison with 110 degrees and 130 degrees orientation. In comparison with conventional fans, a minimum of 57% increment in velocity spread was recorded for all bladeless fan configurations under consideration in the present work. The flow physics of bladeless fan has prospects for further increment in the zone of influence by optimizing the geometric features in light of present work.
Buscariolo, Filipe F.Hoessler, JulienMoxey, DavidJassim, Ayad...
16页
查看更多>>摘要：Emerging commercial and academic tools are regularly being applied to the design of road and race cars, but there currently are no well-established benchmark cases to study the aerodynamics of race car wings in ground effect. In this paper we propose a new test case, with a relatively complex geometry, supported by the availability of CAD model and experimental results. We refer to the test case as the Imperial Front Wing, originally based on the front wing and endplate design of the McLaren 17D race car. A comparison of different resolutions of a high fidelity spectral/hp element simulation using under-resolved DNS/implicit LES approach with fourth and fifth polynomial order is presented. The results demonstrate good correlation to both the wall-bounded streaklines obtained by oil flow visualization and experimental PIV results, correctly predicting key characteristics of the time-averaged flow structures, namely intensity, contours and locations. This study highlights the resolution requirements in capturing salient flow features arising from this type of challenging geometry, providing an interesting test case for both traditional and emerging high-fidelity simulations.
查看更多>>摘要：Large deformation can occur in super-long span cable-stayed bridges at high wind speeds, resulting in the effective wind attack angle of the bridge deck exceeding the stall angle of attack. The unloading of wind loads due to the stall can lead to a change in the pattern and mechanism of wind-induced static instability, on which few studies have been conducted. Wind-induced static instability analyses are applied on a super-long-span cable-stayed bridge with a closed steel box deck. The instability pattern and mechanism after the effective wind attack angle exceeds the stall angle are investigated. The influence of initial attack angle and span length on the unloading is discussed. Results show that for positive attack angles when the negative aerodynamic stiffness approaches the structural stiffness, the bridge may not experience wind-induced static instability but can restabilize after a jump in the deformation. For negative attack angles, the structure can fail due to the fracture of cables, but the unloading may decrease the growth rate of cable stress and thus improve the critical wind speed. The unloading effect can remarkably increase the critical wind speed for larger attack angles, and the improvement effect increases with span length and the initial attack angle.
查看更多>>摘要：Many wind-induced collapse events of super-large cooling tower have been taken place in history. Existing norms are limited within local excessive strength or buckling failure of the tower body, but ignore the follow-up phenomena after the general continuous collapse caused by local damages. Hence, they are difficult to disclose the wind-induced collapse mechanism and failure mechanism of super-large cooling tower. A case study on the world highest (228 m) cooling tower under construction in Northwest China was carried out. Variations of multi-scale wall thickness and reinforcement ratio at different positions of the tower body were considered by the layered shell element modeling method. The wind loads on the cooling tower surface were acquired through a wind tunnel test of pressure measurement on the rigid body. Displacement and internal force responses of the tower body under typical wind speeds were analyzed by combining the incremental dynamic analysis (IDA), thus determining the critical wind speed. Three redistribution of internal forces mechanisms during collapse of tower body were extracted based on the stress variation indexes before and after the node failure. Moreover, the development paths of three collapse mechanisms among units with different thicknesses of the tower body were discussed. Finally, the wind-induced failure criteria of super-large cooling tower structure were proposed based on throat deformation of the tower body. Research results demonstrated that the layered shell element model could simulate the full process of collapse of super-large cooling tower effectively and a central damage area from the throat of windward side to the center of tower body was formed. Subsequently, a crack network was formed after diffusion of the damage area along the circumferential and meridian until the complete collapse. Three redistribution mechanisms of internal forces during the collapse of the super-large cooling tower were proposed, including the sliding surface mechanism, rotating hinge mechanism and slipping surface mechanism. The super-large cooling tower structure developed wind-induced failure and collapse when the deformation failure index is delta & GE; 1.5%. It is of great significance to the design and construction of super-large cooling towers.
查看更多>>摘要：A complete characterization of the atmospheric boundary-layer winds essentially involves speed, direction and duration. While extensive statistical analyses have been carried out to determine wind speed and directionality for appropriate wind design of buildings, there is a lack of similar research effort for wind duration. Although wind duration may have limited effects on linear, elastic structural response, it can present significant impor-tance in the consideration of nonlinear, inelastic response due to damage accumulation and cyclic deterioration of strength and stiffness. Recent advances of performance-based wind design methodology allow the controlled nonlinear, inelastic deformation of buildings under strong winds, and hence place a demand on statistical investigation of wind duration. In this study, the wind data used for probabilistic duration analysis result from a refined hurricane track model. Specifically, both environmental flow and Coriolis force (the beta effect) are integrated into the translation module for improved modeling of hurricane movement. Based on the numerically generated wind data, the wind duration measured with the over-threshold method (i.e., uniform duration) is obtained. Furthermore, a statistical analysis framework is developed to jointly consider wind duration, speed and direction. A case study is conducted to demonstrate the efficacy of the proposed statistical analysis framework for characterization and quantification of duration in wind climate consideration. Finally, structural wind perfor-mance of a simplified single-degree-of freedom system is examined to highlight the importance of incorporating duration consideration into the performance-based wind design.
Spence, Seymour M. J.McCormick, JasonIvanov, Valeriy Y.Abdelhady, Ahmed U....
11页
查看更多>>摘要：Hurricanes can have adverse effects on residential communities and pose a significant risk to their economic prosperity. The ingress of water into a building due to wind-driven rain (WDR) and inland flooding can cause significant damage leading to downtime or temporary loss of housing. Existing frameworks focus on estimating the amount of water ingress due to WDR and inland flooding separately. This paper provides a comprehensive framework that considers both WDR and inland flooding when estimating the amount of water ingress into residential buildings due to hurricane rainfall. The framework estimates the water ingress due to WDR by combining the WDR intensity with the perforated area of the building envelopes. The intensity of the WDR is quantified using an Eulerian Multi-phase Model. The buildings' envelope is considered susceptible to damage from the impact of windborne debris and excessive dynamic wind pressure. The framework to characterize and quantify inland flooding uses a coupled hydrologic-hydrodynamic model to estimate the inundation depth at each building. A case study consisting of a residential community in Houston, TX, which is subject to Hurricane Harvey illustrates the ability of the framework to capture the influence of WDR and inland flooding when quantifying water ingress.
查看更多>>摘要：The verification and validation (V & V) of multi-fidelity turbulence models is crucial for the efficient and reliable industrial application of computational fluid dynamics (CFD). This study aims to evaluate the performance of detached eddy simulation (DES) modeling approaches embedded with various unsteady Reynolds Averaged Navier-Stokes (URANS) models in simulating the turbulent flow fields over a steep-sloped hill. And the highfidelity numerical methodology based on the DES model was proposed and analyzed in the context of URANS modes, mesh resolution and sampling duration. In comparison with the experimental data, the shear stress transport (SST) k -w based DDES (Delayed Detached eddy simulation) turbulence model (DDES SST k-omega) could better predict the profiles of mean velocity and turbulence fluctuation, while the Spalart-Allmaras (S-A) based DES and DDES turbulence models show its stronger capability to reproduce the spectral characteristics. Additionally, in contrast to DES S-A and DDES S-A, a larger time-averaged separation bubble was predicted by DES SST k-omega and DDES SST k-omega. Moreover, the instantaneous flow patterns such as the formation and evolution of turbulent eddies in the hill wake could be reasonably reproduced by DES S-A and DDES S-A. Furthermore, the numerical results obtained from DES models were sensitive to URANS modes and vertical mesh resolution but trivially affected by the increase in sampling time after reaching the statistical convergence.
查看更多>>摘要：High-speed railway lines are widely distributed worldwide. The surrounding wind environment of such railway lines is complex, which significantly affects the safety of high-speed train operations. Using a combination of the computational fluid dynamics method of improved delayed detached eddy simulation and sliding grid technology, the effects of one-and two-side windbreak walls on the unsteady aerodynamic performance of a highspeed train running under a crosswind on a double-track railway line with an embankment and the flow-field characteristics around the train were systematically studied. The grid independence and numerical methods used in this study were verified. The results showed that when the windbreak wall was absent, the aerodynamic performance of the train running on the upstream railway line was the poorest, while the train running on the downstream railway line exhibited large aerodynamic fluctuations. The windbreak wall significantly reduced the aerodynamic force and its fluctuation; the one-and two-side windbreak walls had different effects on the unsteady aerodynamic performance of trains running on the upstream and downstream railway lines under a crosswind. The one-side windbreak wall could restrain the aerodynamic fluctuation of the train more and is thus preferred from the perspective of construction effort and cost.
查看更多>>摘要：For lightweight and lightly damped structures such as chimneys, solar towers, tall buildings and so forth, an increased crosswind response due to vortex shedding may trigger significant aero-elastic feedback between wind and structure, leading to undesired crosswind response. This study addressed estimation of the crosswind responses of tall and slender structures, where the aero-elastic effect is considered by generalized Van der Pol-type aerodynamic damping. Firstly, the nonlinear motion equation arising from nonlinear aerodynamic damping was solved by the equivalent nonlinear equation method and an analytical solution was obtained to estimate the crosswind response. Next, the accuracy of the present solution was verified by comparison with stochastic simulated results. Finally, the present analytical solution was applied to estimate the crosswind responses of square tall buildings and verified by experimental data. It was found that the present method can predict statistics of crosswind response efficiently and with satisfactory accuracy.
NSTL
Elsevier