High Turbulence Intensity Research Articles

Numerical Simulation of the Interaction between Phosphorus and Sediment Based on the Modified Langmuir Equation

Phosphorus is the primary factor that limits eutrophication of surface waters in aquatic environments. Sediment particles have a strong affinity to phosphorus due to the high specific surface areas and surface active sites. In this paper, a numerical model containing hydrodynamics, sediment, and phosphorus module based on improved Langmuir equation is established, where the processes of adsorption and desorption are considered. Through the statistical analysis of the physical experiment data, the fitting formulas of two important parameters in the Langmuir equation are obtained, which are the adsorption coefficient, ka, and the ratio k between the adsorption coefficient and the desorption coefficient. In order to simulate the experimental flume and get a constant and uniform water flow, a periodical numerical flume is built by adding a streamwise body force, Fx. The adsorbed phosphorus by sediment and the dissolved phosphorus in the water are separately added into the Advection Diffusion equation as a source term to simulate the interaction between them. The result of the numerical model turns out to be well matched with that of the physical experiment and can thus provide the basis for further analysis. With the application of the numerical model to some new and relative cases, the conclusion will be drawn through an afterwards analysis. The concentration of dissolved phosphorus proves to be unevenly distributed along the depth and the maximum value approximately appears in the 3/4 water depth because both the high velocity in the top layer and the high turbulence intensity in the bottom layer can promote sediment adsorption on phosphorus.

Comparison of Diesel Engine Efficiency and Combustion Characteristics Between Different Bore Engines

This study investigates the effects of engine bore size on diesel engine performance and combustion characteristics, including in-cylinder pressure, ignition delay, burn duration, and fuel conversion efficiency, using experiments between two diesel engines of different bore sizes. This study is part of a larger effort to discover how fuel property effects on combustion, engine efficiency, and emissions may change for differently sized engines. For this specific study, which is centered only on diagnosing the role of engine bore size on engine efficiency for a typical fuel, the engine and combustion characteristics are investigated at various injection timings between two differently sized engines. The two engines are nearly identical, except bore size, stroke length, and consequently displacement. Although most of this diagnosis is done with experimental results, a one-dimensional model is also used to calculate turbulence intensities with respect to geometric factors; these results help to explain observed differences in heat transfer characteristics of the two engines. The results are compared at the same brake mean effective pressure (BMEP) and show that engine bore size has a significant impact on the indicated efficiency. It is found that the larger bore engine has a higher indicated efficiency than the smaller displaced engine. Although the larger engine has higher turbulence intensities, longer burn durations, and higher exhaust temperature, the lower surface area to volume ratio and lower reaction temperature leads to lower heat losses to the cylinder walls. The difference in the heat loss to the cylinder walls between the two engines is found to increase with increasing engine load. In addition, due to the smaller volume-normalized friction loss, the larger sized engine also has higher mechanical efficiency. In the net, since the brake efficiency is a function of indicated efficiency and mechanical efficiency, the larger sized engine has higher brake efficiency with the difference in brake efficiency between the two engines increasing with increasing engine load. In the interest of efficiency, larger bore designs for a given displacement (i.e., shorter strokes or few number of cylinders) could be a means for future efficiency gains.

Direct numerical simulations of turbulent catalytic and gas-phase combustion of H2/air over Pt at practically-relevant Reynolds numbers

Three-dimensional direct numerical simulations of turbulent catalytic and gas-phase H2/air combustion at a fuel-lean equivalence ratio φ=0.18 were performed in platinum-coated planar channels at two industrially-relevant flow conditions (inlet friction Reynolds numbers Reτ= 182 and 385) using detailed hetero-/homogeneous chemical reaction mechanisms. The preferential diffusion of hydrogen and oxygen, which was responsible for creating significantly higher surface equivalence ratios φw compared to the bulk gas-phase φ, was appreciably suppressed by turbulence at Reτ= 385. The higher turbulence intensity at this Reτ resulted in larger near-wall hydrogen excess that in turn yielded shorter homogeneous ignition distances compared to the lower Reτ case. Gas-phase ignition proceeded from isolated ignition kernels that subsequently formed axially elongated flames confined close to the catalytic walls. The coupling of catalytic and gas-phase chemistry inhibited homogeneous ignition, since at the vicinity of the ignition kernels the OH, H and O radical fluxes to the underlying catalytic wall were net-adsorptive and furthermore hydrogen was depleted by the catalytic reactions. The flame topology included alternating vigorously-burning and extinguished elongated streamwise stripes at Reτ=182 or islands at Reτ=385. The extinguished gas-phase reaction zones at Reτ=385 were characterized by underlying intense catalytic reaction rates. The flame topology and spatiotemporal correlation of the isolated burning and extinguished gaseous zones indicated that significant surface temperature non-uniformities could be obtained in practical catalytic reactors.

Measurements of local droplet velocities in horizontal gas-liquid pipe flow with low liquid loading

New data on streamwise droplet velocity profiles for low liquid loading pipe flows are reported. The fluids used in the experiments are SF6 (gas-phase) and Exxsol D60 (oil-phase). Experiments are conducted in a 10 cm pipe diameter high-pressure (∼780 kPa, absolute) flow loop to reproduce gas-condensate field conditions. Instantaneous streamwise velocity data, obtained using the non-intrusive Laser Doppler Anemometry (LDA) technique, are used to calculate mean and root-mean-squared (RMS) local velocities. Asymmetric droplet velocity profiles with respect to the pipe center-line are observed especially for the stratified low atomization flow conditions. However, as the flow momentum increases, the droplet velocity profiles seem to become more symmetric. Also, these data suggest that, irrespective of the conditions studied, the single-phase gas flow characteristics are preserved closer to the top pipe wall. The data from the LDA imply that the bottom pipe half region is highly influenced by the gas-liquid interfacial characteristics. This results in high streamwise turbulence intensity in the region influenced by the interfacial waves (interfacial turbulence). An isokinetic sampling instrument is also used to measure the local instantaneous dynamic pressure. The dynamic pressure and the locally extracted liquid (droplets) volume rate under isokinetic conditions are used to calculate local fluid velocity. Excellent agreement has been obtained when comparing this calculated local velocity from the isokinetic instrument to the LDA data.

Numerical simulation of the impact of atmospheric turbulence on a wind turbine in complex terrain

In this study, which was part of the project AssiSt, numerical analyses of wind turbine power, loads and wake development in the extreme wind conditions found on a complex terrain site in northern Spain have been performed. The turbine is located near the edge of a characteristic cliff. Realistic atmospheric inflow conditions are prescribed by propagation of highly resolved meteorologic data of the LES code PALM in the aerodynamic solver FLOWer. The global features of the flow field in the complex terrain site were investigated showing significant inclination angles, high turbulence intensities and a characteristic mixing mechanism of high and low momentum velocity layers. Further, the wake development and its deflection and deformation was analyzed. Finally, the turbine’s load response was investigated, showing severe fatigue loading as consequence of the highly unsteady inflow conditions.

The turbulence scales of a wind turbine wake: A revisit of extended k-epsilon models

The turbulence time and length scales of a single wind turbine wake subjected to atmospheric turbulence are calculated from two large eddy simulations that differ in ambient turbulence intensity. The smallest turbulence length scale in the wake is about half the rotor radius and it increases for higher ambient turbulence levels. The large eddy simulations are compared with Reynolds-averaged Navier-Stokes simulations employing the standard and three extended k-ε models: the k-ε-fP model of van der Laan, the k-ε model of Shih and k-ε model of Durbin. It is shown that all three extended k-ε models can be written in a similar form. All Reynolds-averaged Navier-Stokes based turbulence models predict turbulence time scales that are comparable to the turbulence time scales of the large eddy simulations. The standard k-ε model underpredicts the velocity deficit because the turbulence length scale is overpredicted compared to the large eddy simulations. The performance of the k-ε model of Durbin shows to be very dependent on the ambient turbulence level and it is therefore less suited for wind turbine wake simulations. The k-ε model of Shih and the k-ε-fP model of van der Laan are recommended to be used for wind turbine wake simulations because their results are similar and compare well with results of large eddy simulations for both a low and high ambient turbulence intensity due to a limitation of the turbulence length scale in the near wake.

Analysis of the flame–wall interaction in premixed turbulent combustion

The present work focuses on the flame–wall interaction (FWI) based on direct numerical simulations (DNS) of a head-on premixed flame quenching configuration at the statistically stationary state. The effects of FWI on the turbulent flame temperature, wall heat flux, flame dynamics and flow structures were investigated. In turbulent head-on quenching, particularly for high turbulence intensity, the distorted flames generally consist of the head-on flame part and the entrained flame part. The flame properties are jointly influenced by turbulence, heat generation from chemical reactions and heat loss to the cold wall boundary. For the present FWI configuration, as the wall is approached, the ‘influence zone’ can be identified as the region within which the flame temperature, scalar gradient and flame dilatation start to decrease, whereas the wall heat flux tends to increase. As the distance to the wall drops below the flame-quenching distance, approximately where the wall heat flux reaches its maximum value, chemical reactions become negligibly weak inside the ‘quenching zone’. A simplified counter-flow model is also proposed. With the reasonably proposed relation between the flame speed and the flame temperature, the model solutions match well with the DNS results, both qualitatively and quantitatively. Moreover, near-wall statistics of some important flame properties, including the flame dilatation, reaction progress variable gradient, tangential strain rate and curvature were analysed in detail under different wall boundary conditions.

The influence of wind speed on airflow and fine particle transport within different building layouts of an industrial city

ABSTRACTIn atmospheric environment, the layout difference of urban buildings has a powerful influence on accelerating or inhibiting the dispersion of particle matters (PM). In industrial cities, buildings of variable heights can obstruct the diffusion of PM from industrial stacks. In this study, PM dispersed within building groups was simulated by Reynolds-averaged Navier-Stokes equations coupled Lagrangian approach. Four typical street building arrangements were used: (a) a low-rise building block with Height/base H/b = 1 (b = 20 m); (b) step-up building layout (H/b = 1, 2, 3, 4); (c) step-down building layout (H/b = 4, 3, 2, 1); (d) high-rise building block (H/b = 5). Profiles of stream functions and turbulence intensity were used to examine the effect of various building layouts on atmospheric airflow. Here, concepts of particle suspension fraction and concentration distribution were used to evaluate the effect of wind speed on fine particle transport. These parameters showed that step-up building layouts accelerated top airflow and diffused more particles into street canyons, likely having adverse effects on resident health. In renewal old industry areas, the step-down building arrangement which can hinder PM dispersion from high-level stacks should be constructed preferentially. High turbulent intensity results in formation of a strong vortex that hinders particles into the street canyons. It is found that an increase in wind speed enhanced particle transport and reduced local particle concentrations, however, it did not affect the relative location of high particle concentration zones, which are related to building height and layout.Implications: This study has demonstrated the height variation and layout of urban architecture affect the local concentration distribution of particulate matter (PM) in the atmosphere and for the first time that wind velocity has particular effects on PM transport in various building groups. The findings may have general implications in optimization the building layout based on particle transport characteristics during the renewal of industrial cities. For city planners, the results and conclusions are useful for improving the local air quality. The study method also can be used to calculate the explosion risk of industrial dust for people who live in industrial cities.

Generating atmospheric turbulence using passive grids in an expansion test section of a wind tunnel

Generating atmospheric turbulence in wind tunnels is an important issue in the study of wind turbine aerodynamics. A turbulent inlet is usually generated using passive grids. However, to obtain an atmospheric-like flow field relatively large length scales (L∼30 cm) and high turbulence intensities (I∼15%) need to be reproduced. In this work, the passive grid technique has been used in combination with a downstream expansion test section in order to investigate the generation of atmospheric like turbulence, with the possibility of varying both the turbulence intensity and the integral length scale of the flow field independently. Four passive grids with different mesh and bar sizes were used with four wind velocities and five downstream measurement positions. It was found that the flow field is isotropic and homogeneous for distances less than what is recommended in literature (x/M∼5). The effect of the expansion on the turbulence characteristics is also investigated in detail for the first time. The study confirms that by adding an expansion test section it is possible to increase both turbulence intensity and integral length scale downstream from the grid with limited impact on the overall flow quality in terms of anisotropy and energy spectra.

Study of the spray characteristics of a diesel surrogate for diesel engines under sub/supercritical states injected into atmospheric environment

The spray characteristics of hydrocarbon fuel under superheated and supercritical conditions are quite different from the traditional liquid fuel injection. In this study, the macroscopic liquid phase and vapor phase spray geometry of n-heptane was investigated by Backlit Shadowgraph and Schlieren method to investigate the differences of spray pattern under various operation conditions such as fuel temperature, injection pressure and nozzle diameter. Furthermore, both the overall and near-field spray structures were analyzed to reveal the internal mechanism. During the experiments, the ambient environment was kept constant at atmospheric condition (25 °C, 0.1 MPa), the injection pressure was varied from 3 MPa to 5 MPa, always higher than the fuel critical pressure, and the fuel temperature was changed from 25 °C to 300 °C, spanning from liquid to supercritical state. Four different spray regimes have been identified based on the fuel temperature and spray geometry: liquid regime, flash boiling regime, near-critical regime and supercritical regime. Injection paths were analyzed on the basis of thermodynamic principle. The results showed that the fuel temperature has a minor effect on the macroscopic liquid phase and vapor phase characteristics below saturated-vapor temperature of 98 °C at the liquid regime. As the temperature is increased to about 200 °C, which is in the flash boiling regime, the local spray spreading angle of both the liquid and vapor phases increases, the downstream liquid phase of spray disappears gradually and high-intensity turbulence appears in the vapor phase image. At the near-critical regime where the fuel temperature is from 200 °C to the critical point (267 °C), the local spray angle of vapor phase begins to decrease and only a small area of liquid phase at the nozzle exit can be seen, while both the shock and flash boiling are visible. When the fuel temperature goes beyond the critical point locating in supercritical regime, the fuel spray is similar to a gas jet. The steady shock structure called Mach disk was observed and the fuel temperature has little influence on the Mach disk position and diameter in the supercritical regime. However, the fuel pressure and nozzle diameter significantly affect the Mach disk position and diameter.

Morphospecies-dependent disaggregation of colonies of the cyanobacterium Microcystis under high turbulent mixing

Preventing formation of large colonies and reducing colony size of the cyanobacterium Microcystis may lead to reductions in bloom formation. Here we investigated the effects of artificial mixing on morphology and disaggregation dynamics of Microcystis colonies in vivo, using a stirring device and a laser particle analyzer. The turbulent dissipation rate (ε) was varied from 0.020 to 0.364 m2 s−3. We hypothesized that colonies of M. aeruginosa and M. ichthyoblabe would be more susceptible to disaggregation from turbulent mixing than colonies of M. wesenbergii. Our results showed that colony size of M. aeruginosa and M. ichthyoblabe decreased with increased turbulence intensity and duration of stirring for ε > 0.094 m2 s−3, while M. wesenbergii showed less obvious changes in colony size with mixing. Spherical M. wesenbergii colonies exposed to high turbulence intensities for 30 min gradually transitioned to colony morphologies similar to M. ichthyoblabe and M. aeruginosa-like colonies (irregular, elongated or lobed, with distinct holes). Our results suggest that turbulent mixing is an important factor driving morphological changes of Microcystis colonies, and artificial mixing may effectively reduce colony size of Microcystis, thereby preventing bloom formation.

Estimate the Performance of Catalytic Converter Using Turbulence Induce Devices

In this manuscript, the experimental setup was designed and fabricated for optimizing the parameters of a catalytic converter of INDICA V2 exhaust system. Three turbulence intensify devices, namely Swirl Venturi, Swirl Blades and Swirl Contour, were close-fitted before the catalytic converter. The heating element is embedded in its body and thermocouples are used for knowing the performance at various temperature. The experiments were carried out with and without devices also with and without heating of catalytic converter. The emission was characterized by various engine speed. The results showed that catalytic converter effectiveness and efficiency increases when close-fitted the devices before the catalytic converter with heating. Among these devices, Swirl Blades was more effective and it reduces the CO and HC emission by 33.86%, and by 30.56% respectively. Flow Simulation of these devices was carried out using finite volume method. The obtained simulation shows that transport coefficient of catalytic converter enhances using these devices because of high turbulence intensity at the inlet of the catalytic converter. This research concluded that the heating of the catalytic converter and using the Swirl Blades device before it reduces the air pollution significantly of diesel engine motor vehicle.

Lagrangian analysis of sweeping jets measured by time-resolved particle image velocimetry

The flow dynamics of a sweeping jet generated by a fluidic oscillator is experimentally investigated by time-resolved particle image velocimetry (TR-PIV). Lagrangian transformation is applied to the measured flow fields to better determine the characteristics of the jet flow outside the oscillator. Upon increasing the Reynolds number from Re = 2.5 × 103 to 11.7 × 103, which respectively corresponds to the occurrences of straight and deflected jet columns, the spreading angle of the external jet increases and reaches its saturation value. The overall performance of the flow fields is first examined in Eulerian space. At the higher Reynolds number, the momentum is more directed at the maximum deflected positions of the jet. A clear weak flow is then induced at the middle of the far field region from the jet nozzle. The induced jet column is also bent significantly into a curved shape. To examine the variations of the jet flows with different column shapes, Lagrangian transformation is applied to the measured flow fields by attaching a rotating reference frame on the jet column. It is found that the large bending angle of the jet column at the higher Reynolds number induces higher fluctuations and more uneven oscillation patterns in the jet flow. In the far field region at the higher Reynolds number, the time-averaged jet velocity decreases faster, with higher turbulence intensities than those at the lower Reynolds number. The phase-dependent jet flow fields confirm that the peak velocity and the jet width also have higher fluctuations at the higher Reynolds number. In addition, the jet bending angle in the far field region shows more uneven oscillation patterns compared with those in the near field region. These highly fluctuating and uneven flow behaviors contribute to the uneven distribution of the jet momentum at the higher Reynolds number in Eulerian space. Finally, different fluctuating behaviors of the jet flow due to the different jet shapes are also revealed by Lagrangian dynamic mode decomposition (DMD).

Rotor-Stator Mixers: From Batch to Continuous Mode of Operation—A Review

Although continuous production processes are often desired, many processing industries still work in batch mode due to technical limitations. Transitioning to continuous production requires an in-depth understanding of how each unit operation is affected by the shift. This contribution reviews the scientific understanding of similarities and differences between emulsification in turbulent rotor-stator mixers (also known as high-speed mixers) operated in batch and continuous mode. Rotor-stator mixers are found in many chemical processing industries, and are considered the standard tool for mixing and emulsification of high viscosity products. Since the same rotor-stator heads are often used in both modes of operation, it is sometimes assumed that transitioning from batch to continuous rotor-stator mixers is straight-forward. However, this is not always the case, as has been shown in comparative experimental studies. This review summarizes and critically compares the current understanding of differences between these two operating modes, focusing on shaft power draw, pumping power, efficiency in producing a narrow region of high intensity turbulence, and implications for product quality differences when transitioning from batch to continuous rotor-stator mixers.

Investigation of the fuel effects on burning velocity and flame structure of turbulent premixed flames based on leading points concept

ABSTRACTThe measurements on flame structure and burning velocities of C3H8/air, CH4/air and CO/H2/air turbulent premixed flames were conducted. Various experimental conditions for these mixtures were considered to understand the molecular and thermal diffusion process in turbulent flame, which was referred to the fuel effects. The fuel effects are interpreted as local burning velocity variation caused by molecular and thermal diffusivity with stretch effect. Leading points concept is a promising scaling approach to incorporate the fuel effects in turbulent flames recently. In this article, data across a variety of equivalence ratio and hydrogen fractions were obtained using Bunsen burner. Flame front was detected with OH-PLIF technique and turbulent burning velocity ST referred to leading edge was derived. A new leading points characteristic speed SL,LP was presented invoking both negative and positive Markstein number mixtures, revising the previous model in literature which is only suitable for negative Markstein number fuels. The turbulent burning velocity ST under relatively weak turbulence intensity in this study and data of high turbulence intensity, high pressure from literature were renormalized with SL,LP instead of SL,0 based on leading points concept, where SL,0 is the unstretched laminar flame speed. The results show that all the data sets were collapsed well which validated the significance of SL,LP in normalizing ST of different mixtures. An empirical formula for turbulent burning velocity correlation was obtained as . This formula is similar to that of Kobayashi; however, it shows superiority in incorporating the fuel effects.

Submerged turbulent twin jets interacting with a free surface and a solid wall

The mean flow properties and turbulence characteristics of submerged twin jets interacting with a free surface or a solid wall are investigated using particle image velocimetry. The experiments were performed with two parallel round nozzles of transverse separation ratio, G/d = 2, where d is the nozzle diameter, and jet exit Reynolds number, Re = 5000. The effects of offset ratio and boundary condition were investigated by positioning one of the jets closer to a free surface or a solid wall at offset heights of 1d, 2d and 4d, while the other jet is sufficiently far from the opposite boundary. The results indicate that the decay rate of the jet closer to the boundary decreased with offset ratio but was independent of boundary condition. The effects of the boundary condition on the mean velocities and Reynolds stresses were confined to the immediate vicinity of the boundary. In this region, the transverse turbulence intensity and Reynolds shear stress were reduced, but the reduction was more dramatic near the wall than the free surface. Unlike the solid wall, the relaxation of the no-slip condition at the free surface and the reduction in transverse turbulence intensity gave rise to high streamwise turbulence intensity at the free surface. As offset ratio decreased, the surface mean velocities and turbulence intensities beyond the attachment point increased considerably. Two-point auto-correlations of the velocity fluctuations demonstrated that the spatial coherence of the turbulence structures increases with increasing offset ratio and the extents of the transverse auto-correlation, Rvv are reduced in the far field near the solid wall compared to the free surface cases.

Raindrop fall velocities from an optical array probe and 2-D video disdrometer

Abstract. We report on fall speed measurements of raindrops in light-to-heavy rain events from two climatically different regimes (Greeley, Colorado, and Huntsville, Alabama) using the high-resolution (50 µm) Meteorological Particle Spectrometer (MPS) and a third-generation (170 µm resolution) 2-D video disdrometer (2DVD). To mitigate wind effects, especially for the small drops, both instruments were installed within a 2∕3-scale Double Fence Intercomparison Reference (DFIR) enclosure. Two cases involved light-to-moderate wind speeds/gusts while the third case was a tornadic supercell and several squall lines that passed over the site with high wind speeds/gusts. As a proxy for turbulent intensity, maximum wind speeds from 10 m height at the instrumented site recorded every 3 s were differenced with the 5 min average wind speeds and then squared. The fall speeds vs. size from 0.1 to 2 and >0.7 mm were derived from the MPS and the 2DVD, respectively. Consistency of fall speeds from the two instruments in the overlap region (0.7–2 mm) gave confidence in the data quality and processing methodologies. Our results indicate that under low turbulence, the mean fall speeds agree well with fits to the terminal velocity measured in the laboratory by Gunn and Kinzer from 100 µm up to precipitation sizes. The histograms of fall speeds for 0.5, 0.7, 1 and 1.5 mm sizes were examined in detail under the same conditions. The histogram shapes for the 1 and 1.5 mm sizes were symmetric and in good agreement between the two instruments with no evidence of skewness or of sub- or super-terminal fall speeds. The histograms of the smaller 0.5 and 0.7 mm drops from MPS, while generally symmetric, showed that occasional occurrences of sub- and super-terminal fall speeds could not be ruled out. In the supercell case, the very strong gusts and inferred high turbulence intensity caused a significant broadening of the fall speed distributions with negative skewness (for drops of 1.3, 2 and 3 mm). The mean fall speeds were also found to decrease nearly linearly with increasing turbulent intensity attaining values about 25–30 % less than the terminal velocity of Gunn–Kinzer, i.e., sub-terminal fall speeds.

Heat transfer simulation of unsteady swirling flow in a vortex tube

Effectiveness of not-adiabatic vortex tube application in the cooling systems of gas turbine blades depends on characteristics of swirling flows formed in the energy separation chamber. An analysis of the flow structure in the vortex tube channels has shown a presence of a complex three-dimensional spiral vortex, formed under relatively high turbulence intensity and vortex core precession. This indicates the presence of a significant unsteady flow in the energy separation chamber of the vortex tube that has a great influence on convective heat transfer of the swirling flow to the inner surface of tube. The paper contains the results of investigation of gas dynamics and heat transfer in the vortex tube taking into account the flow unsteadiness.

Mechanism of Film Cooling with One Inlet and Double Outlet Hole Injection at Various Turbulence Intensities

Abstract The trunk-branch hole was designed as a novel film cooling concept, which aims for improving film cooling performance by producing anti-vortex. The trunk-branch hole is easily manufactured in comparison with the expanded hole since it consists of two cylindrical holes. The effect of turbulence on the film cooling effectiveness with a trunk-branch hole injection was investigated at the blowing ratios of 0.5, 1.0, 1.5 and 2.0 by numerical simulation. The turbulence intensities from 0.4 % to 20 % were considered. The realizable k − ε $k - \varepsilon $ turbulence model and the enhanced wall function were used. The more effective anti-vortex occurs at the low blowing ratio of 0.5 %. The high turbulence intensity causes the effectiveness evenly distributed in the spanwise direction. The increase of turbulence intensity leads to a slight decrease of the spanwise averaged effectiveness at the low blowing ratio of 0.5, but a significant increase at the high blowing ratios of 1.5 and 2.0. The optimal blowing ratio of the averaged surface effectiveness is improved from 1.0 to 1.5 when the turbulence intensity increases from 0.4 % to 20 %.

Soot concentration and primary particle size in swirl-stabilized non-premixed turbulent flames of ethylene and air

Turbulent non-premixed swirl-stabilized flames were investigated experimentally in a gas turbine model combustor with optical access. Velocity and soot concentration fields were measured for three levels of air flow for a fixed flow rate of ethylene as the fuel. Stereoscopic particle image velocimetry was used to get the three-dimensional velocity field data within the combustor. The time-averaged soot volume fractions and primary soot particles sizes were obtained using the laser induced incandescence technique. These two measurements were conducted separately, but under the identical experimental flow conditions. The velocity measurements showed a region of high velocity flow, sandwiched between inner and outer recirculation zones. The boundaries of the recirculation zones in all three cases displayed very high turbulence intensities. Most of the soot was found to be within the inner recirculation zone, and the regions having maximum time-averaged soot concentrations grew radially outward with axial height. The soot concentrations showed a strong dependence on air flow rate; a small increase in air flow rate caused a significant reduction in soot concentrations. The primary soot particle diameters inferred from laser induced incandescence measurements covered the range from 30 to 50 nm.