Takashi Maruyama

Optimization of roughness parameters for staggered arrayed cubic blocks using experimental data

Abstract The roughness parameters introduced in a refined k −ϵ turbulence model were optimized for relevant application on staggered arrayed cubic blocks. The roughness parameters were adjusted so that the values of calculated surface drag agree with those of experimental data. Variations of roughness parameters for the roughness volume density and the angle of roughness elements relative to the wind were obtained. Simulated flows using the optimized roughness parameters showed good agreement with experimental data.

Large eddy simulation of the turbulent boundary layer behind roughness elements using an artificially generated inflow

Abstract A turbulent boundary layer at high Reynolds number generated by a rough surface was calculated by large eddy simulation (hereafter abbreviated as LES). The inflow wind fluctuations conditioned by the experimental data were generated artificially. The velocities at the inlet boundary were interpolated in Fourier space as stochastic processes in a conditional random field so as to realize the equivalent statistical quantities of experimental results. The calculated turbulent field just behind the roughness elements was compared with the experimental data and examined. The calculated result shows rather good agreement regarding the mean wind field and the turbulent energy spectra in the low frequency. Otherwise the energy of the high-frequency wind fluctuation decreased and the wind fluctuations were less correlated in the calculated results.

Surface and inlet boundary conditions for the simulation of turbulent boundary layer over complex rough surfaces

Abstract Simulation methods of numerical calculation of turbulent boundary layer over complex rough surfaces such as urban area are reviewed. Turbulent boundary flows over rough surfaces calculated by different methods are examined. Firstly, the treatment of roughness as a surface boundary condition and the modeling of roughness effect are discussed. Secondly, the generation methods of turbulent fields at the inflow boundary are presented and the effect of the inflow boundary condition is discussed.

Sensitivity of Tornado Dynamics to Soil Debris Loading

AbstractPast numerical simulation studies found that debris loading from sand-sized particles may substantially affect tornado dynamics, causing reductions in near-surface wind speeds up to 50%. To further examine debris loading effects, simulations are performed using a large-eddy simulation model with a two-way drag force coupling between air and sand. Simulations encompass a large range of surface debris fluxes that cause negligible to substantial impact on tornado dynamics for a high-swirl tornado vortex simulation.Simulations are considered for a specific case with a single vortex flow type (swirl ratio, intensity, and translation velocity) and a fixed set of debris and aerodynamic parameters. Thus, it is stressed that these findings apply to the specific flow and debris parameters herein and would likely vary for different flows or debris parameters. For this specific case, initial surface debris fluxes are varied over a factor of 16 384, and debris cloud mass varies by only 42% of this range becaus...

New evaluation technique for WTG design wind speed using a CFD-model-based unsteady flow simulation with wind direction changes

Because a significant portion of the topography in Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of wind turbine generators (WTG). We have developed a CFD model for unsteady flow called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, computational prediction of airflow over complex terrain). The RIAM-COMPACT CFD model is based on large eddy simulation (LES). The computational domain of RIAM-COMPACT can extend from several meters to several kilometers, and RIAM-COMPACT can predict airflow and gas diffusion over complex terrain with high accuracy. The present paper proposes a technique for evaluating the deployment location of a WTG. The proposed technique employs the RIAM-COMPACT CFD model and simulates a continuous wind direction change over 360 degrees.

Simultaneous wind measurements over two sites using Doppler sodars

Abstract In wind-resistant design of buildings and structures, it is very important to accurately assess the design wind speed at a particular site, considering the variation in wind speed with terrain roughness. In this study, the authors attempt to find a reasonable method for estimating design wind speed for a given terrain roughness, through simultaneous observations of atmospheric boundary layer wind speeds over two sites with different roughnesses using Doppler sodars. The mean wind speed profiles at the two sites during the same storms were compared to study the variation in mean wind speed as this is affected by inland terrain roughness.

A REVERSED-PHASE THIN-LAYER CHROMATOGRAPHY/SCANNING DENSITOMETRIC METHOD FOR THE ANALYSIS OF GARDENIA YELLOW IN FOOD USING CROCETIN AS AN INDICATOR

In the present study, a TLC method for the analysis of gardenia yellow in foods using crocetin as an indicator was developed. Gardenia yellow was extracted from food samples with methanol or hydrous methanol, and after the extract was evaporated, the residue was dissolved in water and the pH was adjusted to 11 or above with 1 mol/L NaOH. The resultant mixture was occasionally stirred, then allowed to stand in a water bath at 50°C for 30 minutes. Subsequently, the pH of the mixture was slightly acidified using hydrochloric acid. It was then purified through a C18 cartridge before being subjected to the TLC analysis. The TLC conditions were as follows: plate, RP-18F254S (Art. 15389, E. Merck); solvent system, acetonitrile-tetrahydrofuran-0.1 mol/L oxalic acid (7:8:7). The visible absorption spectrum of the color was measured using scanning densitometry without isolation of the color. In order to investigate the capability of the present method, 37 commercial foods were analyzed, and their chromatographic behaviors and spectra were observed. The separation and the spectra obtained were not affected by coexisting substances in the foods, and the spots always gave the same Rf values and spectra as the standard, along with good reproducibility. The present method is considered to be useful for the rapid analysis of gardenia yellow in foods.

Climate model-based probabilistic assessment of wind risk for residential buildings under projected future climate

The present paper investigates the impact of the global climate change on typhoon-induced wind risk for residential buildings in Japan. It is based on (1) the output from a climate model for an assumed climate change scenario, (2) probabilistic typhoon hazard modelling, (3) reliability-based fragility modelling and (4) failure cost modelling. The objective of the present paper is to demonstrate the availability and effectiveness of a general methodology for carrying out the impact assessment. It also aims at clarifying missing information required for a more precise and reliable impact assessment. Under the employed climate model, assumed climate scenario and vulnerability model and other assumptions made in the present paper, it is found that the typhoon-induced wind risks for residential buildings in Japan are not likely to change significantly in the future.

A WIND TUNNEL TEST ON THE BOUNDARY LAYER CHARACTERISTICS ABOVE AN URBAN AREA

Abstract In an effort to improve the understanding of wind flow in an urban environment, simulation experiments in the wind tunnel were carried out using a 1/250 scale urban model and staggered arrayed cubic blocks. The results show that the boundary layer can be divided into three regions in height. In the upper region i.e. the wake region, the mean wind velocity distributions deviate from the logarithmic law. In the middle region i.e. the log region, the logarithmic law can be applied. The velocity gradient in this region is smaller than that in the wake region. In the lower region i.e. the urban canopy, which is directly affected by the roughness elements, the mean wind profiles were considered theoretically. Finally some field and laboratory data were compared with the results.

Numerical simulation of boundary layer wind tunnel

Abstract The boundary layer wind tunnel was simulated numerically. The three-dimensional simulation method of turbulent boundary layer over rough surfaces using a refined κ-ϵ turbulence model was examined and its applicability is shown by comparing the numerical results with experimental data. Using the simulating method described here, wind characteristics over rough surfaces and effect of incident flow on the square cylinder were examined numerically. The good applicability of the simulation results indicate that these preliminary calculations could be a powerful tool in the design of actual wind tunnel tests.