Turbulent Droplet Research Articles

Droplet dynamics in homogeneous isotropic turbulence with the immersed boundary-lattice Boltzmann method.

We develop a numerical method for simulating the dynamics of a droplet immersed in a generic time-dependent velocity gradient field. This approach is grounded on the hybrid coupling between the lattice Boltzmann (LB) method, employed for the flow simulation, and the immersed boundary (IB) method, utilized to couple the droplet with the surrounding fluid. We show how to enrich the numerical scheme with a mesh regularization technique, allowing droplets to sustain large deformations. The resulting methodology is adapted to simulate the dynamics of droplets in homogeneous and isotropic turbulence, with the characteristic size of the droplet being smaller than the characteristic Kolmogorov scale of the outer turbulent flow. We report statistical results for droplet deformation and orientation collected from an ensemble of turbulent trajectories, as well as comparisons with theoretical models in the limit of small deformation.

On the breakup frequency of bubbles and droplets in turbulence: A compilation and evaluation of experimental data

The dispersed phase in liquid–liquid emulsions and air–liquid mixtures can often be fragmented into smaller sizes by the surrounding turbulent carrier phase. The critical parameter that controls this process is the breakup frequency, which is defined from the breakup kernel in the population balance equation. The breakup frequency controls how long it takes for the dispersed phase to reach the terminal size distribution for given turbulence. In this article, we try to summarize the key experimental results and compile the existing datasets under a consistent framework to find out what is the characteristic timescale of the problem and how to account for the inner density and viscosity of the dispersed phase. Furthermore, by pointing out the inconsistency of existing experimental data, the key important unsolved questions and related problems on the breakup frequency of bubbles and droplets are discussed.

Deformation and Breakup of Bubbles and Drops in Turbulence

Fragmentation of bubbles and droplets in turbulence produces a dispersed phase spanning a broad range of scales, encompassing everything from droplets in nanoemulsions to centimeter-sized bubbles entrained in breaking waves. Along with deformation, fragmentation plays a crucial role in enhancing interfacial area, with far-reaching implications across various industries, including food, pharmaceuticals, and ocean engineering. However, understanding and modeling these processes are challenging due to the complexity of anisotropic and inhomogeneous turbulence typically involved, the unknown residence time in regions with different turbulence intensities, and difficulties arising from the density and viscosity ratios. Despite these challenges, recent advances have provided new insights into the underlying physics of deformation and fragmentation in turbulence. This review summarizes existing works in various fields, highlighting key results and uncertainties, and examining the impact on turbulence modulation, drag reduction, and heat and mass transfer.

Effects of secondary breakup, collision dynamics, gravity and evaporation on droplet size distribution in a pressure-swirl JET A-1 spray

Size and velocity of droplets in pressure-swirl sprays vary with distance downstream the nozzle. This study aims to explain the phenomena contributing to size-resolved spatial variation of the drop size distribution for Jet A-1 spray from a small pressure swirl atomizer injected into quiescent ambient air at atmospheric conditions. The effects of secondary breakup, droplet collisions, gravity, drag-driven spray dispersion, and evaporation are evaluated. Phase Doppler anemometer (PDA) was used to resolve the velocity and size of the droplets in radial profiles at several axial distances (Z) from the nozzle exit at injection pressures between 0.5 and 1.5 MPa. The droplet motion and collision dynamics were qualitatively characterised by high-speed imaging. The analysis focused on areas along 1) the spray axis and 2) the liquid sheet direction. The first area covers small droplets with marginal evolution, while the mean drop size in the second area significantly increases downstream. The local drop size distribution and its axial evolution results from a combined effect of ballistic filtering (drifting of small droplets from periphery to spray centre and large droplets vice versa), centrifugal and turbulent droplet dispersion, and droplet collisions (increasing drop size with distance). The relative droplet-gas velocity was found at investigated Z positions too small for drag-driven secondary droplet breakup to occur. Evaporation of Jet A-1 sprayed at room temperature and pressure into still atmosphere reduces the drop size marginally. Trajectory of all drop sizes is insignificantly altered by gravity. The smallest droplets are strongly drag-driven to the spray axis, while large ones disperse centrifugally and have sufficient momentum to neglect the gravity. Combining results from imaging and laser diagnostics, various collision outcomes were identified, with a conclusion that these depend on the size and velocity of colliding droplets. Coalescing collisions dominate and strongly increase the mean drop size downstream the spray at off-axis positions while insignificantly contribute along the spray axis. The drop size span factor reduces with Z as separative collisions between large droplets and mixed-type collisions between small and large droplets narrow the drop size distribution. The above effects can be most easily amplified for drop size reduction via modification of physical properties of sprayed liquid by its heating.

Collision Statistics of Droplets in Turbulence Considering Lubrication Interactions, Mobility of Interfaces, and Non-continuum Molecular Effects

Collision statistics of same-size aerodynamically interacting droplets in homogeneous isotropic turbulence is examined via hybrid direct numerical simulations combined with Lagrangian particle tracking under a point-particle assumption and a one-way momentum coupling. The simulations are performed both in the absence and presence of gravity for various droplet Stokes numbers (0.1–2) over a wide range of liquid water contents (LWCs = 1–30 g/m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {g/m}^3$$\\end{document}). Also, the effects of using different representations of the lubrication forces, i.e. a continuum and a non-continuum one, have been investigated. The results have highlighted the importance of considering the aerodynamic interaction, especially in the presence of gravity for the systems that have high LWCs. Likewise, taking the lubrication force into account shows a notable change in statistics, but a non-continuum representation yields results that are close to the continuum one. In addition, the impact of modeling droplets as fluid drops instead of rigid particles has been examined. Obtaining quite close statistics under both cases demonstrates that a rigid particle assumption for water droplets in air is sufficiently accurate owing to the high water-to-air viscosity ratio. Moreover, the collision efficiency is shown to be in the range 60–100% in the absence of gravity, which approaches 100% as the LWC is enlarged. In the presence of gravity, however, the efficiency grows, with both the Stokes number and the LWC, to values as high as 300%. Finally, for settling droplet systems, the enhancement factor due to turbulence is quantified, exhibiting a growth with the LWC and a reduction with the Stokes number.

Settling behavior of polydisperse droplets in homogeneous isotropic turbulence

The settling behavior of polydisperse droplets in homogeneous and isotropic turbulence was measured by an ultra-high-resolution two-dimensional Particle Image Velocimetry. The aim of the present study is to provide new insight on the dependence of multi-scale particle settling behavior on characteristic parameters of two-phase turbulent flow via a sophisticate conditional analysis. The relative settling strength (defined as the ratio of mean droplet settling velocity to root mean square velocity of turbulence), whose effect on droplet settling behavior is of the primary interest, ranges as SvL=0.5–2.0. The turbulence Taylor Reynolds number is Reλ=200–300, and the droplet Stokes number is Stp=0.1–10. Voronoï analysis is performed to obtain the concentration field of discrete droplets from particle images. Particle structures including clusters or voids are detected, and the droplet settling velocities corresponding to various probing conditions, such as Stp, local particle concentration, and size of particle structures, were then analyzed. For the present configuration (droplet net sedimentation), there is a non-monotonic dependency of the settling velocity on local particle concentration. The negative correlation between them occurs in the moderate-concentration sub-regime and is insensitive to the variation of SvL, in which individual droplets interact with turbulent flow independently. It can be well explained by the commonly invoked preferential sweeping mechanisms. On the other hand, the dense-concentration regime, in which droplets prefer to accumulate into clusters, presents a positive correlation; namely, the conditional-averaged settling velocity decreases with the increase in local particle concentration. In this sub-regime, it is not the scale of single particles but the scale of particle clusters and the relative strength of turbulence (measured by SvL) that jointly determines the droplet settling behavior. Such a process, to our knowledge, is consistent with the so-called multi-scale preferential sweeping effect.

Intermittency and collisions of fast sedimenting droplets in turbulence

The formation of large drops via collisions of droplets in warm clouds constitutes a major unsolved problem in rain prediction studies. Often typical turbulent accelerations of parcels of air that generate collisions are much smaller than gravitational acceleration. We manage to provide a complete theory in the limit of small accelerations and confirm it by direct numerical simulations of the Navier-Stokes turbulence. However, the theory is limited to Reynolds numbers much smaller than those in clouds, where, as we show, huge Reynolds number can overturn many existing paradigms.

Efficient CFD modelling of bulk condensation, fog transport and re-evaporation for application to containment scale

Formation of fog due to bulk condensation during a Beyond Design Basis Accident (BDBA) in a water-cooled nuclear reactor is of high safety relevance with regard to the flammability of the containment atmosphere and its interaction with several other safety relevant phenomena such as aerosol transport. Bulk condensation of steam in the presence of non-condensable gases is modelled using ‘return to saturation in constant timescale’ method in single-phase system as mass sink. The fog droplets formed as a result of condensation is transported as passive scalar in an Eulerian frame by considering the effects of convection by the gas mixture, turbulent and Brownian diffusion and droplet drift due to gravitation, drag and inertial forces. The model formulation is based on the assumption that fog volume fraction is fairly low (<1%) so that droplet–droplet interactions and the effect of droplets on the gas flow are negligible. The present work considers only spherical fog droplets of fixed diameter and evolution of droplet by coalescence and breakup is neglected. The effect of different droplet sizes is investigated in the validation cases to understand its consequence on the results. It is also assumed that the fog droplets are always in thermal equilibrium with the surrounding gas mixture. The re-evaporation of the transported fog droplets in regions where gas temperature is higher than saturation temperature is also incorporated into the solver. The model was numerically implemented to the containmentFOAM CFD package based on OpenFOAM. The verification of the phase change(condensation & evaporation) model by simulating the mixing of a cold and hot air–steam–fog mixture gave good agreement with Mollier diagram theory in terms of both final mixture temperature and quantity of steam and fog. The droplets drift transport model was validated by aerosol flow through a bent pipe investigating the effect of droplet Stokes number on deposition efficiency. The performance of the bulk condensation model was further validated and assessed by including the interaction with other relevant containment phenomena (e.g., wall condensation, multispecies transport) on SETCOM experimental facility (Forschungszentrum Jülich, Germany) and a technical scale THAI experiment (Becker Technologies, Germany). The results indicated that the inclusion of bulk condensation model improved the predictive capabilities of containmentFOAM, i.e., the consistency of simulation and measurements for these experiments.

Experimental study of the spray characteristics of twin-fluid atomization: Focusing on the annular flow regime

The characteristics of twin-fluid atomization operating in the annular flow regime were studied experimentally under various gas-to-liquid ratios (GLRs) and injection pressures. The macroscopic morphology of the spray was obtained by shadowgraph, while the droplet size and velocity were measured using a phase-Doppler particle analyzer technique. It was found that the spray cone angle increases almost linearly with the GLR, and the axial distance required for droplet coalescence to outweigh the breakup decreases with increasing GLR. The Sauter mean diameter (SMD) first decreases and then increases along the axial direction due to the competition between turbulent breakup and droplet coalescence. The droplet size follows a lognormal distribution; the droplet velocity distribution is closer to a lognormal distribution under large GLRs, while it follows normal distribution with GLR = 3%. Regarding the radial distribution, low GLRs (3% and 5%) lead to a bimodal spatial velocity distribution, while for large GLRs, the droplet velocity decreases monotonically toward the far field. The spray tends to become more stable with increasing GLR and injection pressure Pinj, whereas the SMD increases with increasing Pinj. The underlying atomization mechanism in a twin-fluid injector in the annular flow state can be regarded as the disintegration of the initial liquid sheet by longitudinal Kelvin–Helmholtz instability followed by transverse Rayleigh–Taylor instability, which yields a direct proportionality of the droplet size to the initial liquid sheet thickness ΔL. Subsequently, for high Pinj, the gas core shrinks and ΔL increases, which results in an increased SMD but enhanced atomization efficiency ΔL/SMD.

Turbulent droplet breakage probability: Analysis of fitting parameters for two commonly used models

Droplet breakage in liquid–liquid systems is an important physical process in manufacturing operations throughout the chemical, food, and pharmaceutical industries. Although several mathematical models have been developed to describe droplet breakage in agitated liquid emulsions, the utility of these models is limited by the fact that they incorporate multiple fitting parameters that must be determined empirically for specified fluid pairs and flow conditions. In this work, analytical expressions that can be evaluated without need to perform droplet breakage experiments have been developed for parameters associated with droplet breakage probability in two commonly used breakage models. These expressions were derived by applying dimensional analysis and by using a hypothesis regarding breakage probability that is based upon competition between disruptive and restorative stresses on droplets. Data used for validation of the proposed equations for the breakage probability parameters were obtained from previously published reports of droplet breakage in heterogeneous flow devices, as well as from experiments performed in a von Kármán box designed to produce homogeneous turbulence. Comparison of the droplet breakage probability predictions using the derived expressions for the breakage parameters show generally good agreement with experimental data.

Spatial correlations and relative velocities of polydisperse droplets in homogeneous isotropic turbulence

We investigate the motions of polydisperse droplets in homogeneous and isotropic turbulence at Reynolds numbers Reλ=200–300. The emphasize is put on the parameter dependences of spatial velocity correlations (SVCs) and relative velocities (RVs) of droplets, which are relevant to particle transport and dispersion in turbulence and have been less studied in experiments. The Kolmogorov-scale Stokes number is Stp=10−1–101, and the settling parameter, i.e., the ratio of particle settling velocity to fluid velocity fluctuations, is SvL=0.5–2.0. Using high-resolution measurements, we can resolve the motions of turbulence and droplet over a wide range of scales (10−1η to 102η, η is Kolmogorov length). The parabolic behavior in droplet SVCs near the origin is observed, similar to turbulence. The droplet SVCs are smaller than turbulence for all scales and decrease with both Stp and SvL. At large scales, the droplet RVs, smaller than those of turbulence due to the inertial filtering effect, also decrease with Stp and SvL. At small scales, the path-history effect leads to larger droplet RVs than fluid RVs. Interestingly, we find RVs present a non-monotonic trend with Stp and reach a valley at Stp≈1.0. It may originate from particle clustering and preferential sweeping effects, which both prevail at Stp≈1.0. It is also found that droplet motions are less intermittent than turbulence. This is in contrast to the previous observations by simulations with the gravity effect being ignored. The intermittency of droplet RVs decreases with SvL due to the diminished droplet–turbulence interactions, and it presents opposite trends with Stp for small and large scales. Finally, the balance between the effects of path histories and turbulent structures makes the velocity statistics of droplets quasi-independent from the scale in the range of the dissipative scale (r≲5η).

Investigation of cloud droplets velocity extraction based on depth expansion and self-fusion of reconstructed hologram.

The velocity of cloud droplets has a significant effect on the investigation of the turbulence-cloud microphysics interaction mechanism. The paper proposes an in-line digital holographic interferometry (DHI) technique based on depth expansion and self-fusion algorithm to simultaneously extract particle velocity from eight holograms. In comparison to the two-frame exposure method, the extraction efficiency of velocity is raised by threefold, and the number of reference particles used for particle registration is increased to eight. The experimental results obtained in the cloud chamber show that the velocity of cloud droplets increases fourfold from the stabilization phase to the dissipation phase. The measurement deviations of two phases are 1.138 and 1.153 mm/s, respectively. Additionally, this method provides a rapid solution for three-dimensional particle velocimetry investigation of turbulent field stacking and cloud droplets collisions.

TU Delft COVID-app: A tool to democratize CFD simulations for SARS-CoV-2 infection risk analysis

This work describes a modelling approach to SARS-CoV-2 dispersion based on experiments. The main goal is the development of an application integrated in Ansys Fluent to enable computational fluid dynamics (CFD) users to set up, in a relatively short time, complex simulations of virion-laden droplet dispersion for calculating the probability of SARS-CoV-2 infection in real life scenarios. The software application, referred to as TU Delft COVID-app, includes the modelling of human expiratory activities, unsteady and turbulent convection, droplet evaporation and thermal coupling. Data describing human expiratory activities have been obtained from selected studies involving measurements of the expelled droplets and the air flow during coughing, sneezing and breathing. Particle Image Velocimetry (PIV) measurements of the transient air flow expelled by a person while reciting a speech have been conducted with and without a surgical mask. The instantaneous velocity fields from PIV are used to determine the velocity flow rates used in the numerical simulations, while the average velocity fields are used for validation. Furthermore, the effect of surgical masks and N95 respirators on particle filtration and the probability of SARS-CoV-2 infection from a dose-response model have also been implemented in the application. Finally, the work includes a case-study of SARS-CoV-2 infection risk analysis during a conversation across a dining/meeting table that demonstrates the capability of the newly developed application.

Scaling of Droplet Breakup in High-Pressure Homogenizer Orifices. Part II: Visualization of the Turbulent Droplet Breakup

Emulsion formation is of great interest in the chemical and food industry and droplet breakup is the key process. Droplet breakup in a quiet or laminar flow is well understood, however, actual in-dustrial processes are always in the turbulent flow regime, leading to more complex droplet breakup phenomena. Since high resolution optical measurements on microscopic scales are extremely dif-ficult to perform, many aspects of the turbulent droplet breakup are physically unclear. To over-come this problem, scaled experimental setups (with scaling factors of 5 and 50) are used in con-junction with an original scale setup for reference. In addition to the geometric scaling, other non-dimensional numbers such as the Reynolds number, the viscosity ratio and the density ratio were kept constant. The scaling allows observation of the phenomena on macroscopic scales, whereby the objective is to show that the scaling approach makes it possible to directly transfer the findings from the macro- to the micro-/original scale. In this paper, which follows Part I where the flow fields were compared and found to be similar, it is shown by breakup visualizations that the turbulent droplet breakup process is similar on all scales. This makes it possible to transfer the results of detailed parameter variations investigated on the macro scale to the micro scale. The evaluation and analysis of the results imply that the droplet breakup is triggered and strongly influenced by the intensity and scales of the turbulent flow motion.

Two-Phase Turbulence Statistics from High Fidelity Dispersed Droplet Flow Simulations in a Pressurized Water Reactor (PWR) Sub-Channel with Mixing Vanes

In the dispersed flow film boiling regime (DFFB), which exists under post-LOCA (loss-of-coolant accident) conditions in pressurized water reactors (PWRs), there is a complex interplay between droplet dynamics and turbulence in the surrounding steam. Experiments have accredited particular significance to droplet collision with the spacer-grids and mixing vane structures and their consequent positive feedback to the heat transfer recorded in the immediate downstream vicinity. Enabled by high-performance computing (HPC) systems and a massively parallel finite element-based flow solver—PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis)—this work presents high fidelity interface capturing, two-phase, adiabatic simulations in a PWR sub-channel with spacer grids and mixing vanes. Selected flow conditions for the simulations are informed by the experimental data found in the literature, including the steam Reynolds number and collision Weber number (Wec={40,80}), and are characteristic of the DFFB regime. Data were collected from the simulations at an unprecedented resolution, which provides detailed insights into the continuous phase turbulence statistics, highlighting the effects of the presence of droplets and the comparative effect of different Weber numbers on turbulence in the surrounding steam. Further, axial evolution of droplet dynamics was analyzed through cross-sectionally averaged quantities, including droplet volume, surface area and Sauter mean diameter (SMD). The downstream SMD values agree well with the existing empirical correlations for the selected range of Wec. The high-resolution data repository from the simulations herein is expected to be of significance to guide model development for system-level thermal hydraulic codes.

Turbulence, evaporation and combustion interactions in n-heptane droplets under high pressure conditions using DNS

The evaporation and combustion of n-heptane droplets under high pressure (20 atm) conditions were investigated using three-dimensional direct numerical simulations (DNS) in the present work. Two ambient temperatures were considered, i.e. 860 K and 1180 K. Low-temperature combustion, which is controlled by low-temperature chemical pathways, occurs in the 860 K cases while single-stage combustion occurs in the 1180 K cases. Droplet evaporation and combustion in isotropic turbulence were considered. The interactions of turbulence, evaporation and combustion in a cloud of droplets were explored. It was found that turbulence promotes the evaporation process. The temperature and mixture-fraction are negatively correlated after evaporation, which impacts the subsequent ignition process. For both low-temperature and single-stage combustion, ignition occurs in regions with low scalar dissipation rate. Low-temperature ignition first appears in lean mixtures while single-stage ignition in rich mixtures. Ignition kernels evolve into reaction fronts, which propagate towards thermally and compositionally stratified mixture and consume the remaining fuel. Spontaneous ignition front is dominant in low-temperature combustion while deflagrative front is playing an important role in single-stage combustion. The interactions of turbulence and the reaction front structures were examined. Cylindrical elements are the most probable shape of the reaction front for turbulent droplet combustion. The reaction front normal is misaligned with the vorticity vector for both low-temperature and single-stage combustion, indicating that the vortical structures preferentially locate along the tangential plane of the reaction front, which promotes the observed cylindrical reaction front structures in turbulent combustion of droplets.

Influence of atomizing core on droplet dynamic behavior and machining characteristics under synergistically enhanced twin-fluid spray

The droplet dynamic behavior of spraying during the manufacturing process affects tool life, cooling, and lubrication. A detailed understanding of droplet dynamic behavior is required to improve the surface quality while reducing the cutting fluid consumption. In this study, quantitative measurements for droplet diameter, number concentration, and axial velocity were carried out through a phase Doppler particle analyzer technique. The droplet characteristic spatial distributions of a standard twin-fluid nozzle (STN) and a novel twin-fluid nozzle (NTN) under different gas-to-liquid mass ratio (GLR) values were analyzed in detail. The results showed that the high-speed internal gas flow of an atomizing core has a significant effect on improving the synergistically enhanced atomization behavior, and more smaller droplets and an increased droplet momentum are easily obtained. Furthermore, a better spatial distribution of atomization characteristics can be achieved under a higher GLR of 4.3%. Furthermore, the effects of the novel atomizing core structural parameters on the droplet mean velocity spatial distribution, droplet turbulence, and root mean square velocity fluctuation were investigated. The results also showed that the improved NTN can effectively improve the spray atomization performance and droplet dynamic characteristics. In addition, comparative studies of the effect of the atomizing core structure on the machining performance were performed. Compared with the STN, the improved NTN achieves a significant reduction in cutting temperature, tool wear, and surface roughness of 17.25%, 33.96%, and 37.83%, respectively, owing to the better droplet dynamic characteristics and spatial distribution of spray atomization characteristics.

Investigation of the droplet-carrying characteristics of the gas flow in multiphase pump valves

In high gas-bearing conditions, the oil phase—in the form of droplets— often enters the reciprocating multiphase pump via the valves. Understanding the droplet-carrying characteristics of the gas flow is important for determining the transport capacity and stability of multiphase pump valves. In this paper, the turbulent gas flow and droplet movement behaviors in three typical valves of the reciprocating multiphase pumps were studied mainly by the theoretical analysis, the numerical simulation of computational fluid dynamics (CFD) and the verification test of particle image velocimetry (PIV). The steady and transient droplet trajectories, concentration distributions, and passing capacities were comprehensively studied with different valve openings, Reynolds numbers, and two-phase slip conditions. The results show that the ball valve performs steadily during the transport of the small to large droplets, while the cone valve and the disk valve perform well when transporting the small droplets with d≤250μm and the medium-sized droplets with 300μm≤d≤600μm under the initial conditions, respectively. Finally, the correlations of the volume mean diameter (dvm) of the droplets successfully passing through the cavities were proposed for the three valves. The results of this study are beneficial to help optimize and design new high-efficiency multiphase transport systems.

Evaporating droplets in shear turbulence

This paper investigates droplets that evaporate and cluster in shear turbulence with direct numerical simulations. The flows are statistically stationary and homogeneous, which reduces the physical complexity and simplifies the statistical analysis. The mass loadings are about 0.1, the Stokes numbers are about 1, and the Taylor-scale Reynolds numbers are about 60. The simulations show that the clusters are anisotropic and inclined toward the flow direction on large scales, but isotropic on small scales. When the mass loading increases, the clusters contain more droplets, but their size remains unchanged, and the droplets in clusters experience higher vapor mass fractions. When the Stokes number increases, the clusters contain fewer droplets and become larger, and the droplets in clusters experience lower vapor mass fractions. When the Reynolds number increases, the clusters contain more, smaller droplets and become smaller, and the inclination angles of the clusters change.

Experimental investigation of the evaporation of suspended mono-sized heptane droplets in turbulence intensities approaching unity

For decades, experimental investigations of turbulent droplet evaporation have generally followed one of two distinct paths: wind tunnel experiments, which generate significant mean flow but low turbulence intensity, and stirred chamber configurations, which yield the opposite characteristics. The present study bridges the gap between these two established techniques by modifying a fan-stirred spherical chamber to incorporate a controllable mean flow while retaining the attributes of highly-energetic homogeneous and isotropic turbulence. Heptane droplets with a fixed initial diameter, d0, of 500 ± 10 µm are suspended on the intersection of two microfibers and evaporated in pockets of high-intensity turbulence (27% < Tu < 103%) at small mean flow droplet Reynolds numbers, Red, of 10 and 50. A rigorous series of particle image velocimetry (PIV) tests mapped the homogeneous and isotropic turbulent flow regions for various combinations of fan speed, and a two-dimensional translating fiber support system allowed the precise spatial placement of the droplet for subsequent evaporation studies. PIV results indicate the generation of isotropic flow regions that satisfy 0.9 ≤ urms/vrms ≤ 1.1 with a minimum diameter of 20d0 at each test condition. The steady-state droplet evaporation rate, K, increases quasi-linearly with turbulence intensity at both Reynolds numbers, with steeper improvement associated with higher Red. A comparison with zero-mean flow data reveals that the mean velocity component remains a significant contributor to the droplet evaporation rate at both tested Reynolds numbers over the explored range of turbulence intensity. Subsequent analysis indicates that the mean flow attenuates the effect of turbulence. The findings are of fundamental and practical interest, as vaporization in high turbulence intensity is a plausible scenario for small droplets subject to a moderate slip velocity.