Serial crystallography requires large numbers of microcrystals and robust strategies to rapidly apply substrates to initiate reactions in time-resolved studies. Here, we report the use of droplet miniaturization for the controlled production of uniform crystals, providing an avenue for controlled substrate addition and synchronous reaction initiation. The approach was evaluated using two enzymatic systems, yielding 3 µm crystals of lysozyme and 2 µm crystals of Pdx1, an Arabidopsis enzyme involved in vitamin B6 biosynthesis. A seeding strategy was used to overcome the improbability of Pdx1 nucleation occurring with diminishing droplet volumes. Convection within droplets was exploited for rapid crystal mixing with ligands. Mixing times of <2 ms were achieved. Droplet microfluidics for crystal size engineering and rapid micromixing can be utilized to advance time-resolved serial crystallography.

Mean-flow measurements of turbulent boundary layers over porous walls (permeable and rough) with varying pore size (s), permeability (K) and thickness (h) are presented across a wide range of friction Reynolds numbers (Re-tau asymptotic to 2000-18 000) and permeability based Reynolds numbers (Re-K asymptotic to 1.5-60). The mean wall shear stress was determined using a floating element drag balance and the boundary layer profiles were acquired using hot-wire anemometry. Substrate permeability is shown to increase the magnitude of the mean velocity deficit. The use of a modified indicator function, assuming "universal " values for von Karman constant (K = 0.39) supports previous results where a strongly modified logarithmic region was observed. The indicator function was also used to estimate the zero-plane displacement (y(d)), the roughness function (delta U+), and equivalent sandgrain roughness (k(s)). At high Reynolds numbers, the roughness function data collapses on to the Nikuradse's fully rough asymptote. However, at low roughness Reynolds numbers (k(s)(+) < 100), we observe the flow to be transitionally rough, evolving with Nikuradse-type behavior. The equivalent sandgrain roughness k(s) for each substrate appears to include roughness and permeability contributions. These two contributions can be separated using data obtained from the same substrates with different thickness. This may allow us to model the porous wall as a combination of rough and permeable wall.

The future of single cell diversity screens involves ever-larger sample sizes, dictating the need for higher throughput methods with low analytical noise to accurately describe the nature of the cellular system. Current approaches are limited by the Poisson statistic, requiring dilute cell suspensions and associated losses in throughput. In this contribution, we apply Dean entrainment to both cell and bead inputs, defining different volume packets to effect efficient co-encapsulation. Volume ratio scaling was explored to identify optimal conditions. This enabled the co-encapsulation of single cells with reporter beads at rates of ∼1 million cells per hour, while increasing assay signal-to-noise with cell multiplet rates of ∼2.5% and capturing ∼70% of cells. The method, called Pirouette coupling, extends our capacity to investigate biological systems.

Abstract The motion of thin curved falling particles is ubiquitous in both nature and industry but is not yet widely examined. Here, we describe an experimental study on the dynamics of thin cylindrical shells resembling broken bottle fragments settling through quiescent fluid and homogeneous anisotropic turbulence. The particles have Archimedes numbers based on the mean descent velocity $0.75 \times 10^{4} \lesssim Ar \lesssim 2.75 \times 10^{4}$. Turbulence reaching a Reynolds number of $Re_\lambda \approx 100$ is generated in a water tank using random jet arrays mounted in a coplanar configuration. After the flow becomes statistically stationary, a particle is released and its three-dimensional motion is recorded using two orthogonally positioned high-speed cameras. We propose a simple pendulum model that accurately captures the velocity fluctuations of the particles in still fluid and find that differences in the falling style might be explained by a closer alignment between the particle's pitch angle and its velocity vector. By comparing the trajectories under background turbulence with the quiescent fluid cases, we measure a decrease in the mean descent velocity in turbulence for the conditions tested. We also study the secondary motion of the particles and identify descent events that are unique to turbulence such as ‘long gliding’ and ‘rapid rotation’ events. Lastly, we show an increase in the radial dispersion of the particles under background turbulence and correlate the time scale of descent events with the local settling velocity.

This paper describes an experimental investigation of the dynamics of freely falling thin circular disks settling through turbulence. The patterns of the three-dimensional disk motion are studied using an orthogonal arrangement of two high speed cameras. Turbulence is generated in a water tank using a random jet array facility where the jets are mounted in a co-planar configuration. The facility is run continuously until turbulence reaches a statistically stationary state, then, all water pumps are turned off simultaneously and a disk is released after a given waiting time. Contrary to spherical particles, finite-size inertial disks show an increase in the descent velocity for turbulence velocity fluctuations smaller than the particle descent velocity in quiescent flow. Thus, we observe a severe increase of the mean descent velocity of the disk with increasing magnitude of the turbulence velocity fluctuations (up to 20% of the velocity in quiescent flow for the disk with higher dimensionless inertia I*). We also observe descent events that do not exist for disks falling in still fluid; i.e. 'slow tumbling' events and 'levitating' events. Finally, we show that the dominant frequency of the particle oscillatory motion decreases for increasing descent velocity and that particles exhibit oscillatory frequencies that never exceed the dominant frequency in quiescent flow by more than 30 %.

We experimentally investigate the temporal decay of homogeneous anisotropic turbulence, monitoring the evolution of velocity fluctuations, dissipation and turbulent length scales over time. We employ an apparatus in which two facing random jet arrays of water pumps generate turbulence with negligible mean flow and shear over a volume that is much larger than the initial characteristic turbulent large scale of the flow. The Reynolds number based on the Taylor microscale for forced turbulence is $Re_{\unicode[STIX]{x1D706}}\approx 580$ and the axial-to-radial ratio of the root mean square velocity fluctuations is $1.22$ . Two velocity components are measured by particle image velocimetry at the symmetry plane of the water tank. Measurements are taken for both ‘stationary’ forced turbulence and natural decaying turbulence. For decaying turbulence, power-law fits to the decay of turbulent kinetic energy reveal two regions over time; in the near-field region ( $t/t_{L}<10$ , $t_{L}$ is the integral time scale of the forced turbulence) a decay exponent $m\approx -2.3$ is found whereas for the far-field region ( $t/t_{L}>10$ ) the value of the decay exponent was found to be affected by turbulence saturation. The near-field exhibits features of non-equilibrium turbulence with constant $L/\unicode[STIX]{x1D706}$ and varying $C_{\unicode[STIX]{x1D716}}$ (dissipation constant). We found a decay exponent $m\approx -1.4$ for the unsaturated regime and $m\approx -1.8$ for the saturated regime, in good agreement with previous numerical and experimental studies. We also observe a fast evolution towards isotropy at small scales, whereas anisotropy at large scales remains in the flow over more than $100t_{L}$ . Direct estimates of dissipation are obtained and the decay exponent agrees well with the prediction $m_{\unicode[STIX]{x1D716}}=m-1$ throughout the decay process.

This paper presents a study of the terminal fall velocity, drag coefficient and descent style of 'wavy-edge' flat particles. Being highly non-spherical and with a size of up to a few centimetres, these particles show strong self-induced motions that lead to various falling styles that result in distinct drag coefficients. This study is based on experimental measurements of the instantaneous 3D velocity and particle trajectory settling in water. A disk of D = 30 mm, t = 1.5 mm and rho = 1.38 g/cm(3) is manufactured as a reference particle. The disk was initially designed to lie within the Galileo number - dimensionless moment of inertia (G - I*) domain corresponding to the fluttering regime. A total of 35 other particles with the same frontal area and material properties were manufactured. These are manufactured to have different amplitudes (a) of the sinusoidal wave on the edge and number of cycles (N) around the entire perimeter. Thus, 5 sets of particles are manufactured with different relative wave amplitudes: i.e. a/D = 0.03. 0.05, 0.1, 0.15, 0.2. Each set consisting of 7 particles from N = 4 to N = 10. The isoperimetric quotient is used as a measure of the particle circularity and is also linked with different characteristic settling behaviors. Disks and other planar particles with small aiD ratio were found to descent preferably with 'Planar zigzag' behavior with events of high tilted angle. In contrast, particles with high aID ratio were found to follow a more uniform descent with low tilted angle to the vertical motion. The differences in projected frontal area were shown not to be sufficient to compensate the differences in descent velocity, leading to unequal drag coefficients. Therefore, we believe that the falling styles of these irregular particles go hand by hand with characteristic wake structures, as shown for disks with various dimensionless moment of inertia, that enhance the descent of particles with low circularity. (C) 2018 Elsevier Ltd. All rights reserved.

Despite the ubiquity of turbulent flows with non-spherical particles, it has been only relatively recently that experiments have been developed to measure the motion and orientation of individual particles in a turbulent environment. Early experimental work was focused on particle motion in complex cases relevant to specific applications; Bernstein and Shapiro [1] measured the orientation of glass fibre cylindrical particles suspended in a laminar and turbulent shear flow in a water tunnel and Noel and Sassen [2] among others focused on ice crystals in clouds. Fibre-like particles have been extensively investigated during the last decades due to their direct application to several industrial sectors such as the papermaking industry, as reviewed in Voth and Soldati [3]. However, most of the research done on these flows is focused on the orientation, preferential concentration and alignment of the fibres with the turbulent flow while these are suspended and not on the turbulence effect on the particle settling rate. Also, the severe differences in the dynamics of the fibres compared with the finite-size inertial disks investigated here represents a clear differentiator between these systems.

The aim of this chapter is to investigate experimentally the effect of the frontal geometry on the settling dynamics of planar particles in quiescent flow. The question “What if the disc has a wavy edge?” formulated in Moffat (J Fluid Mech 720:1–4, 2013) is extended here not only to sinusoidal edge particles but to sharp edge polygons and three studies are combined to tackle this question. First, particle tracking experiments of disk-like particles with the perimeter described by sinusoidal functions are performed. We differentiate trajectories according to the degree of out of plane motion and obtain a drag correlation function that depends on the particle geometry. Second, trajectories of N-sided polygons with the same material properties and frontal area but different number of sides are also investigated by particle tracking experiments and a simple pendulum model is found to represent accurately the descent motion of these particles once the mean descent velocity is known. Finally, we perform measurements of the instantaneous three-dimensional velocity field on the wake of several of these polygons. We observe severe differences in the shedding mechanisms and these are related to the descent style of the particles.

The wake characteristics of various thin particles with identical material properties but different frontal geometries (disks, hexagonal plates and square plates) are examined by means of three dimensional measurements of the instantaneous velocity field. The reference particle is a circular disk that lies within the Reynolds number—dimensionless moment of inertia domain ( $$Re-I^*$$ ) corresponding to the fluttering regime, as defined by Willmarth et al. (Phys Fluids 7:197–208, 1964). Hexagonal and square plates are manufactured to have the same frontal area and material properties of the reference particle. Three dimensional trajectories obtained from high-speed imaging show that disks preferably adopt a quasi-2D oscillatory descent; i.e. ‘planar zig-zag’, whereas particles with less circularity adopt three dimensional trajectories more frequently; i.e. ‘transitional’ and ‘spiral’ descent. The wake behind free-falling disks is found to be a succession of hairpin vortices shed off at every turning point linked by a pair of counter rotating vortices that grow downstream from the leading edge of the disk. In contrast, square plates describing ‘spiral’ descent show an almost time-independent wake morphology with large-scale vortex shedding around the entire perimeter of the particle. The large-scale wake structures of hexagonal plates resemble either the disks’ or the squares’ depending on the falling regime that they adopt. Finally, we compare the dimensionless vorticity distribution in the wake of the particles and found that this also depends on the falling style that the particle adopts during the descent.

This chapter presents an experimental facility designed to generate and control turbulence in a laboratory. This consists of a modified version of the random jet array (RJA) proposed in Bellani and Variano (Exp Fluids 55:1646–1666, 2013, [1]) that allows us to generate homogeneous and anisotropic turbulence. Moreover, this zero-mean flow facility can be used to investigate the temporal decay of turbulence without invoking Taylor’s hypothesis. Thus, the aim of this chapter is twofold: first present the facility designed and second investigate the evolution of anisotropic turbulence over time and evaluate the spatial confinement effect. Once these two questions are answered we will have the tools to examine how different turbulent flows modify the descent style of large inertial particles; and this, at the same time will give us some insight into the particle behaviour inside Aquavitrum’s tank. This chapter is structured as follows; in Sect. 3.1 we introduce zero-mean flow facilities used to generate turbulence and we detail experimental and numerical results on the decay of turbulence with and without confinement effects, in Sect. 3.2 we present the experimental setup and the measurement technique, Sects. 3.3 and 3.4 show the results for stationary and decay turbulence, respectively, and we conclude in Sect. 3.5.

The effect of particle edge geometry on the descent motion of freely falling planar particles is examined through experiments. Various planar particles, such as disk and polygons, with identical frontal areas (A(p)) and different number of edges (or perimeter) are used. All particles are designed such that their values of Galileo number (G) and dimensionless moment of inertia (I*) correspond to the previously identified fluttering regime of particle motion. Several modes of secondary motion are observed for the same particle and conditions, and these are not equally probable. This probability depends on the particle shape. Disks and heptagons were found to prefer a "planar zig-zag" behavior. These planarmotions are composed of gliding sweeps and turning sections. As the number of sides in the polygon decreases, i.e., for hexagons and pentagons, the trajectory transitions to a more three-dimensional form. These trajectories were found to be restricted to one plane per swing, but the subsequent swings are in other planes. Further decrease in number of sides to a square results in the trajectories having a severe out-of-plane motion. These subregimes of particle motion within the fluttering regime are consistent with those reported for disks in previous studies. Based on this information, a length scale that accounts for the frontal area of the particles and its edge geometry (i.e., perimeter) is proposed. This length scale represents an approach to determine an equivalent disk for planar particles such that the phase diagram in the Reynolds number (Re) and dimensionless moment of inertia (I*) domain can be used to characterize the motion of planar particles with different frontal geometries. However, further experiments covering other domains of the regime map are needed to verify its universality.

The free fall motion of a thin disk with small dimensionless moment of inertia was investigated experimentally and compared with the motion of a thin square plate. Both thin particles share the same frontal area but have a significant difference in the dimensionless moment of inertia, being I∗ ≈ 5 · 10−3 for the disk and I∗ ≈ 1.7 · 10−3 for the square plate. The disk trajectory is characterised by a quasi-2D oscillatory motion, while the square plate trajectory shows severe 3D motion. The wake characteristics of these particles is investigated by means of three-dimensional measurements of the instantaneous velocity field (V3V). The wake behind free falling disks is shown to be as a succession of hairpin vortices shed off at every turning point linked by means of a pair of counter rotating vortices that grow from the leading edge of the disk. Contrary, the wake behind square plates appears to be more uniform with no vortical structure shed off from the main turbulent wash.

This experimental investigation deals with the influence of free-stream turbulence (FST) produced by an active grid on the skin friction of a zero-pressure-gradient turbulent boundary layer. Wall shear stress is obtained by oil-film interferometry. In addition, hot-wire anemometry was performed to obtain wall-normal profiles of streamwise velocity. This enables the skin friction to be deduced from the mean profile. Both methods show remarkable agreement for every test case. Although skin friction is shown to increase with FST, the trend with Reynolds number is found to be similar to cases without FST. Furthermore, once the change in the friction velocity is accounted for, the self-similarity of the logarithmic region and below (i.e. law of the wall) appears to hold for all FST cases investigated.

Mixed municipal solid waste currently landfilled contains a high percentage of packaging glass, varying from 33% to 80% by weight according to several sample characterizations, due to the lack of high throughput separation technology. The hydrodynamic separator proposed is a closed-loop device developed to separate co-mingled waste into plastics, glass and other dense particles and organic sludge. The glass and other dense material stream is cleaned by the system, permitting efficient downstream optical sorting to take out metals and ceramics and, if required, glass sorted by colour. The plastics and the organic sludge are separate, processable waste streams. As the solid waste is introduced in the separator, the action of water jets located on the ramps of a fixed sinusoidal-shape bottom and the presence of hydrofoils at the upper part of the tank produce a flow pattern that lead plastics towards its collection point on the surface, while glass and ceramics are settled to the bottom of the tank and transported to the extraction point. Organics and other fine particles are obtained from lamellas, before reintroducing the clarified fluid into the flow loop. The sludge obtained from this process is suitable for feedstock to Anaerobic Digestion processes. In the present paper the equipment and the methodology is described and the physical principles of the separation process are explained. Results from a full scale trial designed to process 9.7 tonnes per hour at a municipal UK waste site operating in Nov 2015 – Feb 2016 are presented.

The use of a short-duration laser as a light source for Schlieren flow visualization is described. The coherent nature of this light source has been removed using the laser-induced fluorescence principle. The quality of the speckle-free pictures obtained competes with the one achieved using conventional illumination techniques. Flow features are frozen in space thanks to the short duration of the laser flashes. The applicability of the technique is demonstrated with the characterization of hypersonic conical boundary layers at Mach 11. Pairs of images have been obtained using successive laser flashes with a separation time down to 2 μs. Instantaneous convection velocities and spectral properties of the dominant boundary layer disturbances have been determined. These characteristics compare favorably with the values determined from synchronized time-resolved wall pressure measurements.