The drag and lift forces acting on a rotating rigid sphere in a homogeneous linear shear flow are numerically studied by means of a three-dimensional numerical simulation. The effects of both the fluid shear and rotational speed of the sphere on the drag and lift forces are estimated for particle Reynolds numbers of 1 6 Re p 6 500.The results show that the drag forces both on a stationary sphere in a linear shear flow and on a rotating sphere in a uniform unsheared flow increase with increasing the fluid shear and rotational speed. The lift force on a stationary sphere in a linear shear flow acts from the low-fluid-velocity side to the high-fluid-velocity side for low particle Reynolds numbers of Re p < 60, whereas it acts from the high-velocity side to the low-velocity side for high particle Reynolds numbers of Re p > 60. The change of the direction of the lift force can be explained well by considering the contributions of pressure and viscous forces to the total lift in terms of flow separation. The predicted direction of the lift force for high particle Reynolds numbers is also examined through a visualization experiment of an iron particle falling in a linear shear flow of a glycerin solution. On the other hand, the lift force on a rotating sphere in a uniform unsheared flow acts in the same direction independent of particle Reynolds numbers. Approximate expressions for the drag and lift coefficients for a rotating sphere in a linear shear flow are proposed over the wide range of 1 6 Re p 6 500. † Present address:

Combustion measurements based on optical diagnostics techniques, which allow noninvasive measurements of velocity, density, temperature, pressure, and species concentration, have recently become of major interest as tools not only for clarifying the combustion mechanism but also for validating the computational results for the combustion fields. In this study, the combustion characteristics of a pulverized coal flame are investigated using advanced optical diagnostics. A laboratory-scale pulverized coal combustion burner is specially fabricated. Velocity and shape of nonspherical pulverized coal particles, light emissions from a local point, and temperature in the flame are measured by shadow Doppler particle analyzer (SDPA), a specially designed receiving optics (multicolor integrated receiving optics, MICRO), and a two-color radiation pyrometer, respectively. The simultaneous measurement of OH planar laser-induced fluorescence (OH-PLIF) and Mie scattering image of pulverized coal particles is performed to examine spatial relation of combustion reaction zone and pulverized coal particle. The results show that the sizeclassified diameter and velocity of the pulverized coal particles in the flame can be measured well by SDPA. The measurements of the OH chemiluminescence and CH band light emission from a local point in the flame using MICRO and the simultaneous measurement of the instantaneous OH-PLIF and Mie scattering image of pulverized coal are effective for evaluating the pulverized coal flames and investigating their detailed flame structure.

.[1] Momentum transfer across the wind-driven breaking air-water interface under strong wind conditions was experimentally investigated using a high-speed wind-wave tank together with field measurements at normal wind speeds. An eddy correlation method was utilized to measure roughness length and drag coefficient from wind velocity components measured by laser Doppler and phase Doppler anemometers. As a result, a new model for the roughness length and drag coefficient was proposed for predicting momentum transfer across the sea surface under both normal and strong wind conditions using the universal relationship between energy and significant frequency of wind waves normalized by the roughness length. The model shows that the roughness length and drag coefficient are uniquely determined at all wind speeds by energy and significant frequency of wind waves, and they can be given against U 10 only from the measurements of the wave parameters and one-point mean air velocity in the logarithmic law region. Citation: Takagaki, N., S. Komori, N. Suzuki, K. Iwano, T. Kuramoto, S. Shimada, R. Kurose, and K. Takahashi (2012), Strong correlation between the drag coefficient and the shape of the wind sea spectrum over a broad range of wind speeds, Geophys.

Two-dimensional direct numerical simulation is applied to spray flames stabilized in a laminar counterflow, and the detailed behavior is studied in terms of the droplet group combustion. The stretch ratio of the laminar counterflow is 40 l/s. n-decane (C10H22) is used as a liquid spray fuel, and a one-step global reaction is employed for the combustion reaction model. The results show that with increasing the issued liquid fuel mass fraction, two types of spray combustion appear in front of and inside the high gaseous temperature region, i.e., “premixed-like combustion” and “diffusion-like combustion,” respectively. A droplet group combustion behavior is observed in the diffusion-like combustion region. This diffusion-like combustion, however, disappears when the issued droplet size becomes small, because the droplets complete their evaporation before entering into the high gaseous temperature region. The droplet group combustion tends to reduce the gaseous temperature. This is caused mainly by the suppression of combustion reaction due to the lack of oxygen and partially by the energy exchange through the convective heat transfer between droplets and gaseous phase. The gaseous temperature reduction is promoted by the latent heat of vaporization of the droplets. The use of the parcel approach has a risk of causing a delay of combustion reaction, since the partial fuel vapor pressure increases at limited locations, which suppresses the global droplet evaporation rate.

A two-step global reaction scheme for the volatile matter of coal is proposed, and the unsteady coal particle and combustion behaviors in a turbulent pulverized coal jet flame are investigated by performing a direct numerical simulation (DNS) employing the proposed global reaction scheme. The two-step global reaction scheme is constructed to take into account the properties of the volatile matter such as transport coefficients, laminar flame speed and unburned gas temperature and to be applicable to various coal types, and it is validated by comparing the results with those obtained by the detailed reaction mechanism which includes 158 chemical species and 1804 reactions. The validity of the DNS is also assessed by comparing the results with those in the previous experiment (Hwang et al., Energy & Fuels, 2005), and the unsteady coal particle motions and combustion characteristics are examined in detail. The results show that the proposed two-step global reaction scheme for the volatile matter of coal can precisely predict the laminar flame speed and burned gas temperature for various coal types from bituminous to low-rank coals over wide ranges of conditions of equivalence ratios, pressures and unburned gas temperatures. In addition, it can correctly take into account the effects of dilutions by H 2 O and CO 2 which compromise the evaporated moisture from coal and products of char reaction. It is also verified that a lab-scale turbulent pulverized coal jet flame is well predicted by the DNS em

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