Large Turbulent Eddies Research Articles

Water and solute exchange through flat streambeds induced by large turbulent eddies

Summary The mixing of stream water and subsurface water in the hyporheic zone is an important function of fluvial ecosystems. Among the factors that drive water exchange between a stream and its sediments, turbulence is the most ubiquitous as rivers are always in turbulent flow regime. However, there is still much uncertainty about the role of turbulent processes in hyporheic exchange, probably because of the complex nonlinearities that characterize the dynamics of turbulent velocity and pressure fluctuations. In this paper, we adopt a numerical modeling approach to investigate the relationship between turbulent pressure properties and the resulting features of surface–subsurface exchange. In particular, we discuss the importance of large coherent structures of turbulence in driving exchange at depths that are much larger than the penetration depth of small turbulent eddies. The results of the numerical simulations elucidate the response of turbulent hyporheic exchange to changes in stream depth.

On flow-fields in a high pressure homogenizer and its implication on drop fragmentation

The hydrodynamics of the High Pressure Homogenizer has been investigated in order to increase the understanding of the emulsification process. Fragmentation of drops in the homogenizer is generally assumed to be caused by cavitation and/or turbulence. Both processes are investigated experimentally in order to find its location in the HPH valve region. Cavitation was visualized by investigating light scattered in a HPH valve model with optical access. Detailed measurements of the one phase flow turbulence were obtained by Particle Image Velocimetry (PIV) on a carefully scaled model. The effects of dispersed phase flow volume fraction on the continuous phase turbulence was studied with refractive index matched PIV. The experiments show cavitation being focused in the first half of the gap whereas turbulence intensities are very low inside the gap. The turbulence is most effective in the outlet chamber downstream of the narrow gap. This is even more evident for the turbulent eddies of sizes comparable to the drops that are well known to be most efficient for the fragmentation. Increasing the disperse phase volume fraction does not alter the conclusion of highest turbulence downstream in the gap, however, it leads to an increase in energy of large turbulent eddies and a decrease in the energy of small sale eddies. This would imply a relative increase of the strength of the turbulent viscous mechanism compared to the turbulent inertial mechanism when increasing the volume fraction of dispersed phase. When comparing these findings on with visualizations of drop break-up; turbulence rather than cavitation seems to be the dominant mechanism of fragmentation in these geometries.

GRAVITATIONAL RADIATION FROM HYDRODYNAMIC TURBULENCE IN A DIFFERENTIALLY ROTATING NEUTRON STAR

(Abridged.) The mean-square current quadrupole moment associated with vorticity fluctuations in high-Reynolds-number turbulence in a differentially rotating neutron star is calculated analytically, as are the amplitude and decoherence time of the resulting, stochastic gravitational wave signal. The calculation resolves the subtle question of whether the signal is dominated by the smallest or largest turbulent eddies: for the Kolmogorov-like power spectrum observed in superfluid spherical Couette simulations, the wave strain is controlled by the largest eddies, and the decoherence time approximately equals the maximum eddy turnover time. For a neutron star with spin frequency $\nu_s$ and Rossby number $Ro$, at a distance $d$ from Earth, the root-mean-square wave strain reaches $h_{RMS} \approx 3\times 10^{-24} Ro^3 (\nu_s / 30 Hz)^3 (d/1 kpc)^{-1}$. A cross-correlation search can detect such a source in principle, because the signal decoheres over the time-scale $\tau_c \approx 10^{-3} Ro^{-1} (\nu_s / 30 Hz)^{-1} s$, which is adequately sampled by existing long-baseline interferometers. Hence hydrodynamic turbulence imposes a fundamental noise floor on gravitational wave observations of neutron stars, although its polluting effect may be muted by partial decoherence in the hectohertz band, where current continuous-wave searches are concentrated, for the highest frequency (and hence most powerful) sources.

Modelling algae transport in coastal areas with a shallow water equation model including wave effects

The transport of algae in the marine environment is becoming a major issue for integrated sustainable coastal management and can be nowadays investigated through numerical modelling. The Shallow Water Equations are a suitable tool for this purpose. In the framework of the present study, they are used to perform predictions of algae transport in the vicinity of a harbour, combined to a 3rd generation spectral wave model to take account of near-shore currents induced by wave breaking in the surf zone. The simulated paths of algae have been proved to be very sensitive to the effects of those wave-induced currents and exhibit a behaviour in acceptable agreement with on site observations. In particular, the effects of waves on currents is required to qualitatively predict the large recirculation pattern observed in the vicinity of one of the dykes of the harbour. This recirculation is suspected to be one of the major mechanisms of algae dynamics in this area of the coast. Stochastic (random-walk) diffusion was also tested to account for local dispersion of algae due to large turbulent eddies.

Flow simulation in industrial cyclone separator

The problem of ash settling on super-heater tube bank, due to improper velocity distribution, in the cyclone separator used at Circulating Fluidized Bed Combustion (CFBC) has been investigated by means of computational fluid dynamic techniques. With the help of Computational Aided Design (CAD) software packages, the geometries of recycling cyclone, has been constructed. With the suitable domain decomposition for the cyclone geometry, multi-block structured mesh has been generated and exported to commercial Computational Fluid Dynamic (CFD) solver – TASCflow. After assembling these grids in the flow solver, duplicate elements at mating surfaces are eliminated through generalized grid interfaces. Incompressible viscous flow for the specified flow conditions are simulated and numerical results are interpreted through contour plots and streak lines. The velocity distribution pattern obtained from the analysis exhibits strong flow recirculation with large turbulent eddies in the cyclone outlet. The analysis also observed high pressure drop across the cyclone separator. To improve the velocity distribution and to reduce the pressure drop, geometry has been modified with the deflector plates in the outlet duct and repeated the simulation. The results obtained for modified geometry are encouraging and shown the improved velocity distribution pattern in the outlet duct. The calculation of particle trajectories depends upon Stokes number, relative velocity of fluid/particles and concentration of particles. If the Stokes number, defined as the ratio of particle response time to system response time is less than one, particles motion is inline with the fluid motion. If the Stokes number is greater than one, particle motion deviates the fluid streams. Effects of these particle impacts are significant on component surface, especially, when they reacts/rebounds the wall surfaces.

Large‐Eddy Simulation of Maritime Deep Tropical Convection

This study represents an attempt to apply Large‐Eddy Simulation (LES) resolution to simulate deep tropical convection in near equilibrium for 24 hours over an area of about 205 × 205 km2, which is comparable to that of a typical horizontal grid cell in a global climate model. The simulation is driven by large‐scale thermodynamic tendencies derived from mean conditions during the GATE Phase III field experiment. The LES uses 2048 × 2048 × 256 grid points with horizontal grid spacing of 100 m and vertical grid spacing ranging from 50 m in the boundary layer to 100 m in the free troposphere. The simulation reaches a near equilibrium deep convection regime in 12 hours. The simulated vertical cloud distribution exhibits a tri‐modal vertical distribution of deep, middle and shallow clouds similar to that often observed in Tropics. A sensitivity experiment in which cold pools are suppressed by switching off the evaporation of precipitation results in much lower amounts of shallow and congestus clouds. Unlike the benchmark LES where the new deep clouds tend to appear along the edges of spreading cold pools, the deep clouds in the no‐cold‐pool experiment tend to reappear at the sites of the previous deep clouds and tend to be surrounded by extensive areas of sporadic shallow clouds. The vertical velocity statistics of updraft and downdraft cores below 6 km height are compared to aircraft observations made during GATE. The comparison shows generally good agreement, and strongly suggests that the LES simulation can be used as a benchmark to represent the dynamics of tropical deep convection on scales ranging from large turbulent eddies to mesoscale convective systems. The effect of horizontal grid resolution is examined by running the same case with progressively larger grid sizes of 200, 400, 800, and 1600 m. These runs show a reasonable agreement with the benchmark LES in statistics such as convective available potential energy, convective inhibition, cloud fraction, precipitation rates, and surface latent and sensible fluxes. All runs reveal a tri‐model cloud distribution in the vertical. However, there are differences in the updraft‐core cloud statistics, and convergence of statistical properties is found only between the LES benchmark and the run with 200 m grid size. The effect of vertical grid resolution is also investigated with another run that uses a typical cloud‐resolving model (CRM) horizontal grid size on the order of 1 km and only 64 vertical levels. A comparison to the run with 256 vertical levels shows different vertical cloud distributions. It is concluded that representation of the often observed tri‐modal vertical distribution of clouds requires a vertical grid spacing in the range of 50‐100 m in mid‐to‐low troposphere.

Subgrid Scale Modeling in Large-Eddy Simulation of Turbulent Combustion Using Premixed Flamelet Chemistry

Large-eddy simulation (LES) of turbulent combustion with premixed flamelets is investigated in this paper. The approach solves the filtered Navier-Stokes equations supplemented with two transport equations, one for the mixture fraction and another for a progress variable. The LES premixed flamelet approach is tested for two flows: a premixed preheated Bunsen flame and a partially premixed diffusion flame (Sandia Flame D). In the first case, we compare the LES with a direct numerical simulation (DNS). Four non-trivial models for the chemical source term are considered for the Bunsen flame: the standard presumed beta-pdf model, and three new propositions (simpler than the beta-pdf model): the filtered flamelet model, the shift-filter model and the shift-inversion model. A priori and a posteriori tests are performed for these subgrid reaction models. In the present preheated Bunsen flame, the filtered flamelet model gives the best results in a priori tests. The LES tests for the Bunsen flame are limited to a case in which the filter width is only slightly larger than the flame thickness. According to the a posteriori tests the three models (beta-pdf, filtered flamelet and shift-inversion) show more or less the same results as the trivial model, in which subgrid reaction effects are ignored, while the shift-filter model leads to worse results. Since LES needs to resolve the large turbulent eddies, the LES filter width is bounded by a maximum. For the present Bunsen flame this means that the filter width should be of the order of the flame thickness or smaller. In this regime, the effects of subgrid reaction and subgrid flame wrinkling turn out to be quite modest. The LES-results of the second case (Sandia Flame D) are compared to experimental data. Satisfactory agreement is obtained for the main species. Comparison is made between different eddy-viscosity models for the subgrid turbulence, and the Smagorinsky eddy-viscosity is found to give worse results than eddy-viscosities that are not dominated by the mean shear.

A Mean Flow Model for Polymer and Fiber Turbulent Drag Reduction

Abstract We present a one-parameter model that fits quantitatively the mean velocity profiles from experiments and numerical simulations of drag-reduced wall-bounded flows of dilute solutions of polymers and non-Brownian fibers in the low and modest drag reduction regime. The model is based on a viscous mechanism of drag reduction, in which either extended polymers or non-Brownian fibers increase the extensional viscosity of the fluid and thereby suppress both small and large turbulent eddies and reduce momentum transfer to the wall, resulting in drag reduction. Our model provides a rheological interpretation of the upward parallel shift S+ in the mean velocity profile upon addition of polymer, observed by Virk. We show that Virk’s correlations for the dependence on polymer molecular weight and concentration of the onset wall shear stress and slope increment on the Prandtl-Karman plot can be translated to two dimensionless numbers, namely an onset Weissenberg number and an asymptotic Trouton ratio of maximum extensional viscosity to zero-shear viscosity. We believe that our model, while simple, captures the essential features of drag reduction that are universal to flexible polymers and fibers, and, unlike the Virk phenomenology, can easily be extended to flows with inhomogeneous polymer or fiber concentration fields.

Phytoplankton blooms and fish recruitment rate: effects of spatial distribution

We consider the spatio-temporal dynamics of a spatially-structured generalization of the phytoplankton-zooplankton-fish larvae model system proposed earlier (Biktashev et al., 2003, J. Plankton Res. 5, 21–33; James et al., 2003, Ecol. Model. 160, 77–90). In contrast to Pitchford and Brindley (2001, Bull. Math. Biol. 63, 527–546), who were concerned with small scale patchiness (i.e., 1–10 m), on which the (stochastic) raptorial behaviour of individual larvae is important, we address here the much larger scale ‘patchy’ problems (i.e., 10–100 km), on which both larvae and plankton may be regarded as passive tracers of the fluid motion, dispersed and mixed by the turbulent diffusion processes. In particular, we study the dependence of the fish recruitment on carrying capacities of the plankton subsystem and on spatio-temporal evolution of that subsystem with respect to the larvae hatching site(s). It is shown that the main features found both in the nonstructured and age-structured spatially uniform models are observed in the spatially structured case, but that spatial effects can significantly modify the overall quantitative outcome. Spatial patterns in the metamorphosed fish distribution are a consequence of quasi-local interaction of larvae with plankton, in which the dispersion of larvae by large scale turbulent eddies plays little part due to the relatively short timescale of the larvae development. As a result, in a strong phyto/zooplankton subsystem, with fast reproduction rate and large carrying capacity of phytoplankton and high conversion ratio of zooplankton, recruitment success depends only on the localization and timing of the hatching with respect to the plankton patches. In a weak phyto/zooplankton system, with slow reproduction rate and small carrying capacity of phytoplankton and low conversion ratio of zooplankton, the larvae may significantly influence the evolution of the plankton patches, which may lead to nontrivial cooperative effects between different patches of larvae. However, in this case, recruitment is very low.

Turbulence and fossil turbulence in oceans and lakes

Turbulence is defined as an eddy-like state of fluid motion where the intertial-vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Energy cascades of irrotational flows from large scales to small are non-turbulent, even if they supply energy to turbulence. Turbulent flows are rotational and cascade from small scales to large, with feedback. Viscous forces limit the smallest turbulent eddy size to the Kolmogorov scale. In stratified fluids, buoyancy forces limit large vertical overturns to the Ozmidov scale and convert the largest turbulent eddies into a unique class of saturated, non-propagating, internal waves, termed fossil-vorticity-turbulence. These waves have the same energy but different properties and spectral forms than the original turbulence patch. The Gibson (1980, 1986) theory of fossil turbulence applies universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified fluid as its growth is constrained and fossilized by buoyancy forces. Quantitative hydrodynamic-phase-diagrams (HPDs) from the theory are used to classify microstructure patches according to their hydrodynamic states. When analyzed in HPD space, previously published oceanic datasets showed their dominant microstructure patches are fossilized at large scales in all layers. Laboratory and field measurements suggested phytoplankton species with different swimming abilities adjust their growth strategies by pattern recognition of turbulence-fossil-turbulence dissipation and persistence times that predict survival-relevant surface layer sea changes. New data collected near a Honolulu waste-water outfall showed the small-to-large evolution of oceanic turbulence microstructure from active to fossil states, and revealed the ability of fossil-density-tubulence patches to absorb, and vertically radiate, internal wave energy, information, and enhanced turbulent-mixing-rates toward the sea surface so that the submerged waste-field could be detected from a space satellite (Bondur and Filatov, 2003).

Large-eddy simulation of turbulent flow in a channel with rib roughness

Turbulent flow in a channel with transverse rib roughness on one wall is investigated by large-eddy simulation (LES). The spacing of the roughness elements is varied to reproduce the so-called d- and k-type roughness, and an intermediate roughness between the two. The time–mean and instantaneous flows are analyzed. The LES results agree with the rather limited laboratory observations in flows with rib roughness, and provide new insights into the effects of roughness on the mean flow as well as the turbulence structure. In d-type roughness, the outer flow almost rides over the roughness layer, in the mean, with the separation eddies confined to the gaps between the ribs. For intermediate roughness, between the d-type and k-type, the mean separation region is about the same size as the cavity between the ribs, but the outer flow is affected by large turbulent eddies emanating from the roughness layer. For k-type roughness, separation and reattachment occur between two adjoining ribs, much larger and more frequent eddies are thrown into the outer flow, resulting in strong interaction between the roughness layer and the outer flow. Time and space averaged velocity profiles show the well-known downward shift of the semi-logarithmic portion of the law of the wall. This result is quite surprising in view of the grossly varying spatial structure of the instantaneous flow.

On the Application of a Lagrangian Particle–Puff Model to Elevated Sources in Surface Layers with Neutral Stability

A Lagrangian particle‐puff model is presented for predicting the statistical properties of tracers dispersing from elevated sources into surface layers with neutral stability. The model is based upon F. A. Gifford’s meandering-plume concept and includes a Lagrangian stochastic model for treating plume meander caused by large turbulent eddies. Model predictions for mean concentrations, root-mean-square fluctuating concentrations, and intermittency factors are shown to be in fair agreement with experimental data for compact-area and line sources.

A first-order closure model for the wind flow within and above vegetation canopies

A first-order closure model that has the general utility for predicting the wind flow within and above vegetation canopies is presented. Parameterization schemes that took into account the influence of large turbulent eddies were developed for the Reynolds stress and the mixing length in the model. The results predicted by the model were compared with measured data for wind speeds within and above six types of vegetation canopy, including agricultural crops, deciduous and coniferous forests, and a rubber tree plantation during fully leafed, partially leafed and leafless periods. The predicted results agreed well with the measured data; the root-mean-square errors in the predicted wind speeds (non-dimensionalized by the friction velocity above the canopy) were about 0.2 or less for all of the canopies. The secondary wind maxima that occurred in the lower canopies were also correctly predicted. The influence of foliage density on the wind profiles within and above a vegetation canopy was successfully simulated by the model for a rubber tree plantation during fully leafed, partially leafed and leafless periods. The bulk momentum transfer coefficients ( C M) and the values of λ (which are defined by z 0= λ( h− d), where z 0 is the roughness and d is the zero-displacement height of the canopy) for the vegetation canopies were also studied, and the relationships C Mh=0.0618 exp(0.792 C F) and λ=0.209 exp(0.414 C F) were determined; here, C Mh is the bulk momentum transfer coefficient at the canopy top; C F= C d PAI z max/ h, where C d is the effective drag coefficient of the canopy, PAI is the plant area index and z max is the height at which the plant area density is maximum. The values of λ ranged from 0.22 to 0.32 for the canopies studied.

A generalisation of Prandtl's model for 3D open channel flows

The paper presents generalisation of the old Prandtl mixing-length hypothesis (MLH) for three-dimensional (3D) flows to provide engineers with a new tool to calculate the mean velocity distribution in turbulent open channel flows. These flows are usually not isotropic, i.e. turbulence may have different length scales in different directions. Hence, at every point of the flow a symmetrical second-order tensor with dimension of length should be given. The components of this tensor are specified based on the structure of the largest turbulent eddies. To demonstrate the usefulness of the proposed model, the Reynolds equations with the new turbulence model are solved and calculated streamwise velocity contours are compared with the measurement results. The importance of turbulent structure (sizes of the largest eddies and their growth rate) in forming the streamwise velocity contours is shown.

98/00557 Gas concentration profiles and NO x formation in circulating fluidized bed combustion

The problem of ash settling on super-heater tube bank, due to improper velocity distribution, in the cyclone separator used at Circulating Fluidized Bed Combustion (CFBC) has been investigated by means of computational fluid dynamic techniques. With the help of Computational Aided Design (CAD) software packages, the geometries of recycling cyclone, has been constructed. With the suitable domain decomposition for the cyclone geometry, multi-block structured mesh has been generated and exported to commercial Computational Fluid Dynamic (CFD) solver – TASCflow. After assembling these grids in the flow solver, duplicate elements at mating surfaces are eliminated through generalized grid interfaces. Incompressible viscous flow for the specified flow conditions are simulated and numerical results are interpreted through contour plots and streak lines. The velocity distribution pattern obtained from the analysis exhibits strong flow recirculation with large turbulent eddies in the cyclone outlet. The analysis also observed high pressure drop across the cyclone separator. To improve the velocity distribution and to reduce the pressure drop, geometry has been modified with the deflector plates in the outlet duct and repeated the simulation. The results obtained for modified geometry are encouraging and shown the improved velocity distribution pattern in the outlet duct. The calculation of particle trajectories depends upon Stokes number, relative velocity of fluid/particles and concentration of particles. If the Stokes number, defined as the ratio of particle response time to system response time is less than one, particles motion is inline with the fluid motion. If the Stokes number is greater than one, particle motion deviates the fluid streams. Effects of these particle impacts are significant on component surface, especially, when they reacts/rebounds the wall surfaces.

Turbulence effects on droplet growth and size distribution in clouds—A review

The paper is focused on inertia effects among drops moving within a turbulent cloud on size distribution evolution and formation of rain. Two related mechanisms are discussed: (1) the occurrence of inertia-induced relative velocities between drops falling within a turbulent flow, and (2) the tendency of inertial drops to concentrate within certain areas of turbulent flow with a corresponding concentration decrease elsewhere. It is shown that these turbulence-induced mechanisms lead to a broadening of the droplet spectrum during the early stages of cloud formation. Turbulence also decreases the minimum size of droplets are able to collide with the smaller ones. Thus, turbulence seems to bridge drop growth by condensation and coagulation.Due to the non-linear nature of the kinetic equation of coalescence, effects of positive fluctuations of drop concentration dominate and lead to a faster droplet spectrum broadening. Turbulence effects for ice particles, especially ice crystals and snowflakes, are expected to be much more pronounced than those demonstrated for water drops, because of a smaller terminal fall velocity of ice particles and a comparably large mass. Large turbulent eddies can concentrate ice crystals within certain areas, where ice crystals concentration will be substantially greater than mean ice crystal concentration. Thus, turbulence can contribute to the formation of high ice crystal concentration observed in mixed-phase clouds.The investigation of turbulence effects in clouds drop evolution is a field currently undergoing very rapid development. Some unsolved problems are discussed.

Direct Numerical Simulations of Wake Vortices in Intense Homogeneous Turbulence

Three-dimensional direct numerical simulations of a vortex pair placed in an homogeneous turbulent ® eld are presented. The phenomenon of interaction between the vortices and the turbulence is analyzed in detail from two simulations calculated on a 135 3 nodes mesh grid (one case with axial core velocity, the other without). The results show that the role of large and small turbulent eddies can be separated into two fairly independent mechanisms. The large structures are stretched by velocity gradients induced by the vortex pair. That leads to the formation of both tubes of vorticity spinning azimuthally around each vortex and associated axial velocity sheets. These structures cause a strong decrease of the maximal velocity and the curvature of the vortices. These deformations induced by the turbulence initiate an antisymmetric long-wave instability of the pair, which will probably lead to the collapse of the vortices. Concurrently, the small structures can enhance the diffusion of the vorticity out of the vortex core. From this analysis and scale considerations, the correct form for a model of decay of the vortices is derived. On the other hand, nine simulations on a 81 3 nodes mesh grid are used to determine the sensibility of the results to the random turbulent initial conditions.

Evolution of large eddies in compressible shear layers

The evolution of large turbulent eddies has been investigated in seven supersonic shear layers with average convective Mach numbers Mc¯ ranging from 0.22 to 0.86 and with large variation in density and velocity ratios. A two-laser, single-detector planar laser-induced fluorescence technique was used to visualize the flow and its evolution. Two-dimensional pattern matching yielded the convective velocity of the eddies. For Mc¯>0.3, fast and slow modes of eddy propagation were detected in supersonic–subsonic and supersonic–supersonic combinations, respectively. An empirical model for the convective velocity is proposed. Plan views reveal coexistence of two- and three-dimensional disturbances. Interaction among eddies appears significantly suppressed. The findings have direct impact on supersonic jet noise and are very relevant to supersonic combustion.

High Freestream Turbulence Effects on Turbulent Boundary Layers

High freestream turbulence levels significantly alter the characteristics of turbulent boundary layers. Numerous studies have been conducted with freestreams having turbulence levels of 7 percent or less, but studies using turbulence levels greater than 10 percent have been essentially limited to the effects on wall shear stress and heat transfer. This paper presents measurements of the boundary layer statistics for the interaction between a turbulent boundary layer and a freestream with turbulence levels ranging from 10 to 20 percent. The boundary layer statistics reported in this paper include mean and rms velocities, velocity correlation coefficients, length scales, and power spectra. Although the freestream turbulent eddies penetrate into the boundary layer at high freestream turbulence levels, as shown through spectra and length scale measurements, the mean velocity profile still exhibits a log-linear region. Direct measurements of total shear stress (turbulent shear stress and viscous shear stress) confirm the validity of the log-law at high freestream turbulence levels. Velocity defects in the outer region of the boundary layer were significantly decreased resulting in negative wake parameters. Fluctuating rms velocities were only affected when the freestream turbulence levels exceeded the levels of the boundary layer generated rms velocities. Length scales and power spectra measurements showed large scale turbulent eddies penetrate to within y+ = 15 of the wall.

Experimental methods in multiphase flows

The research in the field of multiphase flows has been advanced as a result of the availability of optical diagnostics that allow the simultaneous measurement of the particle size and velocity of the dispersed phase. This capability also allows the measurement of the continuous phase turbulence parameters in the presence of the dispersed phase. The phase Doppler method has been a key method in providing this information. As an extension of the well-known laser Doppler velocimeter (LDV), it represents a major step in allowing the LDV instrument to be applied to the experimentation in multiphase flows. The phase Doppler method is described and the measurement characteristics are discussed along with the limitations of the method. Strategies for addressing these limitations which include the problems with high number densities and particle deformations are also presented. Evaluations of the measurement capability provide a credible measure of the instrument performance. The phase Doppler method is limited to the measurement of spherical particles, droplets or bubbles. In order to address the measurement of non-spherical particles, a new method based on near-forward light scatter detection is presented. This method utilizes the light scattering intensity to establish the particle size. The ambiguity that occurs as a result of random trajectories through the Gaussian beam intensity distribution is resolved with a confocal beam optical configuration along with a solution of the light scattering equations to obtain the particle trajectory through the beams. Because of the contemporary interest in the imaging methods, a brief discussion on the methods including particle imaging velocimetry (PIV) is provided. Although this method has not been extended to simultaneous particle size and velocity measurement, efforts are being made to reach this goal. The work concludes with some representative examples of the measurements in two-phase turbulent flows that are now possible. These measurements have been used to verify the drag coefficient and evaluate the particle response in turbulent flows. The particle interaction with large scale turbulent eddies has also been studied and some examples of these data are provided.