Effect Of Turbulent Kinetic Energy Research Articles

Simulation of Pulverized Coal Combustion Process Considering Turbulence-Radiation Interaction.

In this paper, the combustion process of a 350 MW opposite pulverized coal combustion boiler is studied using a combined field test and numerical simulation. Considering the turbulence-radiation interaction (TRI) effect caused by turbulent particle pulsation during the combustion process, the TRI model is modified by introducing optical factors. The interaction between the optical thickness and the radiation pulsation of pulverized coal particles during the combustion process is studied to learn the influences of turbulent particle combustion on radiative heat transfer. According to the analysis of the TRI influence on pulverized coal combustion, the temperature of the cross section decreases with TRI. Compared with the traditional radiation model calculation, the time-average temperature of the cross section is reduced by 49.85 K, and the deviation from the experimental data is reduced by 1.54%. It is proved that the temperature distribution in the furnace considering TRI is closer to reality. In the numerical simulation of the TRI sensitivity to the optical thickness of the particles, it is found that with TRI, the increase of optical thickness will strengthen the effect of turbulent kinetic energy in the combustion area. Due to the increase in particle density, the content of the main radiation medium produced by combustion, H2O and CO2, increases and the radiation effect in the furnace is enhanced. In the fire area with dense particles, the average temperature of the cross section increases by 28 K. Hence, the change in optical thickness causes the change of TRI parameters, and the TRI effect becomes more significant with the increase of particle load.

A simplified semi-empirical model for long-range low-frequency noise propagation in the turbulent atmosphere

We present a semi-empirical long-range low-frequency acoustic propagation model, which accounts for atmospheric turbulence. Ostashev and Wilson’s scattering model is combined with a ray-theory based refraction model to account for turbulent scattering and refraction via a turbulent absorption coefficient. The coefficient is ascertained via integration of scattered energy. The model is formulated, calibrated, and validated via corresponding experiments conducted within the National Science Foundation Boundary Layer Wind Tunnel. The predictions of the newly proposed ‘bridging model’ match the wind tunnel experimental data with an average error of 11.9%. Example predictions are shown to quantify the effect of turbulent kinetic energy and turbulent integral length scale on long-range infrasound propagation. To demonstrate the approach, we present predictions of the propagation of noise from a tornado and a nonlinear wave.

Numerical study on the pulsating energy evolution in the cavitating flow around a mini Cascade

Cavitation is arguably a highly turbulent phenomenon in the liquid flow system. The cavitating flow around a mini cascade was carried out to investigate the turbulent characteristics and pulsation mechanisms. The results demonstrate that cavitation can significantly affect the turbulence velocity fluctuation and turbulence anisotropy, and intensively alter the local turbulent energy. To better provide an understanding of fundamental mechanisms dictating time-averaged pulsating energy, the inhomogeneity of the local concentration of pulsating energy at the vapor–liquid interface and the turbulent vortex core involves different fundamental mechanisms are expounded thoroughly through the ability of the time-averaged turbulent kinetic energy and the time-averaged pulsating entropy. The pulsating energy of cavitating flow around the mini cascade is basically obtained from the time-averaged flow, while the surrounding dissipative mechanisms are driven by the diffusion and dissipation terms. Further, the new definition of viscous diffusion term is derived based on the resolved turbulent kinetic energy, which can also clearly delineate the diffusion effect of turbulent kinetic energy produced by the molecule viscosity. Finally, the turbulent kinetic energy and pulsating enstrophy transport mechanisms inside the shedding vortex are revealed as significant characteristics of the interaction between vortex dynamics and turbulence–cavitation.

AN EVALUATION OF SUSPENDED SEDIMENT CONCENTRATION MODELS UNDER BREAKING WAVES

Implementing the effects of turbulent kinetic energy (TKE) is essential in producing accurate suspended sediment concentration (SSC) models, especially under breaking wave conditions. SSC is commonly attributed to two different turbulent sources under breaking wave conditions: 1) bed-friction and 2) breaking-induced turbulent vortices. Numerous studies have endeavoured to quantify the effects of TKE and incorporate them into SSC models. To name a few: Mocke & Smith (1992, henceforth MS92), Shibayama & Rattanapitikon (1993, henceforth SR93), Jayaratne & Shibayama (2007, henceforth JS07), and Yoon et al. (2015, henceforth Y15). The present study evaluates these 4 existing SSC models and validates them against recently published datasets from the ‘CROSSTEX’ (Yoon & Cox, 2010), ‘SandT-Pro’ (Ribberink et al., 2014) and ‘SINBAD’ (vdZ et al. 2015) projects. Following critical evaluation, suggestions are made to enhance existing SSC models, and these findings are then incorporated into producing two new SSC models that indicate improved accuracy.

Effect of turbulent kinetic energy on dry powder inhaler performance

Dry powder inhalers (DPIs) have been extensively used for delivering medication to the lungs. Different designs of DPI devices affect the aerosolization processes of the drug particles. The processes cannot be easily visualized in experiments, thus computational fluid dynamics were used to investigate the turbulence kinetic energy and particle impaction. In this research, 3 size ranges of lactose carrier and the Cyclohaler® and Inhalator® devices were used as models for the computational simulations. The velocity vector, the turbulence kinetic energy (TKE) and particle trajectory were obtained. An aerosol dispersion experiment was performed using the Andersen Cascade Impactor. The TKE was directly related to the flow-rate. The TKE in the Cyclohaler® was lower than that in the Inhalator® due to its narrow geometry and this resulted in a high velocity air-flow. In the Cyclohaler® the probability of deagglomeration by impaction was high because of the cyclone-like design while the cross grid of the Inhalator® was an important factor for deagglomeration of the particles. The FPF varied from 7 to 30% and the FPF increased as the flow-rate increased. The MMAD was in the range of 4–6μm. The carrier size also affected the probability of deagglomeration at 60 and 90L/min, but not at 30L/min. In summary, maximizing the TKE and the particle impaction rate by adding a grid and providing a cyclone-like design was key factor to achieve a high deagglomeration of the particles.

The effect of turbulent kinetic energy on inferred ion temperature from neutron spectra

Measuring the width of the energy spectrum of fusion-produced neutrons from deuterium (DD) or deuterium-tritium (DT) plasmas is a commonly used method for determining the ion temperature in inertial confinement fusion (ICF) implosions. In a plasma with a Maxwellian distribution of ion energies, the spread in neutron energy arises from the thermal spread in the center-of-mass velocities of reacting pairs of ions. Fluid velocities in ICF are of a similar magnitude as the center-of-mass velocities and can lead to further broadening of the neutron spectrum, leading to erroneous inference of ion temperature. Motion of the reacting plasma will affect DD and DT neutrons differently, leading to disagreement between ion temperatures inferred from the two reactions. This effect may be a contributor to observations over the past decades of ion temperatures higher than expected from simulations, ion temperatures in disagreement with observed yields, and different temperatures measured in the same implosion from DD and DT neutrons. This difference in broadening of DD and DT neutrons also provides a measure of turbulent motion in a fusion plasma.

The importance of turbulent kinetic energy on transport of juvenile clams ( Mya arenaria)

Soft-shell clam, Mya arenaria, culture on the east coast of Canada is characterized by high loss following seeding. To evaluate the importance of passive transport due to currents, an experimental flume study was designed. The purpose was to measure the effects of hydrodynamic conditions, substrate, and clam size on dispersal in controlled laboratory condition and to interpret these results in relation to field measurements. Unidirectional currents with gradual increasing velocities (0 to 60 cm s − 1 ) were applied to three substrates (muddy sand, medium sand, and coarse sand) in which clams from one of three size classes (10, 15, and 20 mm) had burrowed. We also examined the resulting effects of turbulent kinetic energy on the erosion of medium-grain sand and clams from the three size classes. Turbulent energy was created with a homemade device acting on the unidirectional currents. Nearly 95% of buried clams (all substrates and size classes together) were unaffected by unidirectional currents of up to 60 cm s − 1 , but only 10% withstood turbulent kinetic energy of 10.1 J m − 3 , a level that is lower than that measured in the field during an autumnal storm. The transport of clams was found to be directly related to substrate erosion-levels.

Effect of turbulent kinetic energy on the spatial distribution of chlorophyll a in a small coastal lagoon

In order to observe the effect of turbulent kinetic energy (TKE) on the spatial distribution of chlorophyll a, four spatial variations were analysed (two during high and two during low tide) on 15 and 16 April, 1989 in Puerto Don Juan. Observations were made of buoy drifts and tidal height, and surface water samples were taken at 20 stations to determine chlorophyll a concentration in each variation. A pattern for ebb conditions is inferred, which shows a direct relationship between a smooth bottom slope and a high concentration of chlorophyll a. For flow conditions, the relationship is inverse. We suggest that the higher concentrations of chlorophyll a are due to a simple mechanical process of accumulation in areas with certain morphological characteristics that attenuate the TKE. That is, the speed of transport of the phytoplankton that enters the lagoon decreases on reaching areas of low TKE, causing stagnation of the particles. This long-term pattern produces high concentrations in the inner part of the lagoon, resulting in higher concentrations of chlorophyll a at the innermost stations. When the tide begins to ebb, these patches of high concentration are transported to the outer part of the lagoon.