• Wind and Structures
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• v.17 no.4
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• pp.379-397
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• 2013

Large Eddy Simulations (LES) were carried out to investigate the aerodynamic characteristics of a rectangular cylinder with side ratio B/D=5 at Reynolds number Re=22,000 (based on cylinder thickness). Particular attention was devoted to the effects of velocity shear in the oncoming flow. Time-averaged and unsteady flow patterns around the cylinder were studied to enhance understanding of the effects of velocity shear. The simulation results showed that the Strouhal number has no significant variation with oncoming velocity shear, while the peak fluctuation frequency of the drag coefficient becomes identical to that of the lift coefficient with increase in velocity shear. The intermittently-reattached flow that features the aerodynamics of the 5:1 rectangular cylinder in non-shear flow becomes more stably reattached on the high-velocity side, and more stably separated on the low-velocity side. Both the mean and fluctuating drag coefficients increase slightly with increase in velocity shear. The mean and fluctuating lift and moment coefficients increase almost linearly with velocity shear. Lift force acts from the high-velocity side to the low-velocity side, which is similar to that of a circular cylinder but opposite to that of a square cylinder under the same oncoming shear flow.

• Wind and Structures
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• v.17 no.5
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• pp.479-494
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• 2013

The vehicle-induced aerodynamic loads bring vibrations to some of the highway sound barriers, for they are designed in consideration of natural wind loads only. As references to the previous field experiment, the vehicle-induced aerodynamic loads is investigated by numerical and theoretical methodologies. The numerical results are compared to the experimental one and proved to be available. By analyzing the flow field achieved in the numerical simulation, the potential flow is proved to be the main source of both head and wake impact, so the theoretical model is also validated. The results from the two methodologies show that the shorter vehicle length would produce larger negative pressure peak as the head impact and wake impact overlapping with each other, and together with the fast speed, it would lead to a wake without vortex shedding, which makes the potential hypothesis more accurate. It also proves the expectation in vehicle-induced aerodynamic loads on Highway Sound Barriers Part1: Field Experiment, that max/min pressure is proportional to the square of vehicle speed and inverse square of separation distance.

• Wind and Structures
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• v.34 no.1
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• pp.101-113
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• 2022

We experimentally investigate the high-Reynolds flow around a rectangular cylinder of aspect ratio 5:1. This configuration is the object of the international BARC benchmark. Wind tunnel tests have been carried out for the flow at zero angle of attack and a Reynolds number, based on the crossflow cylinder length and on the freestream velocity, equal, to 40 000. Velocity measurements are obtained by using hot-wire anemometry along 50 different cross-flow traverses on the cylinder side and in the near wake. Differential pressure measurements are acquired on multiple streamwise sections of the model. The obtained measurements are in a good agreement with the state-of-the-art experiments. For the first time among the several contributions to the BARC benchmark, detailed flow measurements are acquired in the region near the cylinder side and in the near-wake flow. The edges and the thickness of the shear layers detaching from the upstream edges are derived from velocity measurements. Furthermore, we compute the flow frequencies characterizing the roll-up of the shear layers, the evolution of vortical structures near the cylinder side and the vortex shedding in the wake.

• Wind and Structures
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• v.35 no.3
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• pp.213-227
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• 2022

The design of a building is a complex process that encompasses different fields: one of the most relevant is nowadays the energetic one, which has led to the introduction of new typologies of building envelopes. Among them, the Permeable Double Skin Façades (PDSF) are capable to reduce the solar impact and so to improve the energetic performances of the building. However, the aerodynamic characterization of a building with a PDSF is still little investigated in the current literature. The present paper proposes an experimental study to highlight the modifications induced by the outer porous façade in the aerodynamics of a building. A dedicated wind tunnel study is conducted on a rigid model of a prismatic high-rise building, where different façade configurations are tested. Specifically, the single-layer façade is compared to two PDSFs, the former realized with perforated metal and the latter with expanded metal. Outcomes of the tests allow estimating the cladding loads for all the configurations, quantifying the shielding effects ascribable to the porous layers that are translated in a significant reduction of the design pressure that could be up to 50%. Moreover, the impact of the PDSFs on the vortex shedding is investigated, suggesting the capability of the façade to suppress the generation of synchronised vortices and so mitigate the structural response of the building.

• Journal of Energy Engineering
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• v.24 no.3
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• pp.109-114
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single circular cylinder was established from the present CFD study.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.419-428
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• 2020

The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v²-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v²-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v²-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.

• Journal of the Korean Institute of Gas
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• v.20 no.2
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• pp.23-29
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• 2016

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift and drag fluctuation over the fin tube was investigated. The derived nondimensional lift PSD was compared with the results of the previous experimental studies and the characteristics of lift and drag PSD over a single fin tube was established from the present CFD study.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.211-216
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift fluctuation over the fin tube was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single fin tube was established from the present CFD study.

• Journal of the Korean Institute of Gas
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• v.19 no.4
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• pp.35-40
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced a single circular cylinder and calculated with the unsteady laminar flow over the cylinder. The characteristics of vortex shedding and lift and drag fluctuation over the cylinder was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift and drag PSD over a single circular cylinder was established from the present CFD study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.5
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• pp.456-466
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• 2010

Typical combustion instability such as DC-Shift found in the hybrid rocket motor is characterized by non-linearity. DC-Shift can occur in two different realizations. One is so-called a positive shift of measured DC voltage where the pressure increase suddenly. The other is a negative shift where the pressure drops abruptly. In the present work, specifically the negative DC-Shift was investigated to analyze the effect of oxidizer flow condition and the resonance between fundamental frequency and other ones, such as Helmholtz frequency, and acoustic frequency. Results show a peak frequency of several hundreds HZ shifts as combustion proceeds. A negative DC-shift was found as the result of phase cancellation between two dominant frequency, combustion frequency and flow related frequency. Still is it required to study further to identify the change of dominance of frequency during the combustion.