Controlled Flow Conditions Research Articles

Fluidic Interface for Surface-based DNA Origami Studies.

Traditionally, the use of DNA origami nanostructures (DONs) to study early cell signaling processes has been conducted using standard laboratory equipment with DONs typically utilized in solution. Surface-based technologies simplify the microscopic analysis of cells treated with DON agents by anchoring them to solid substrates, thus avoiding the complications of receptor-mediated endocytosis. A robust microfluidic platform for real-time monitoring and precise functionalization of surfaces with DONs was developed here. The combination of controlled flow conditions with an upright total internal reflection fluorescence microscope enabled the kinetic analysis of the immobilization of DONs on DNA-functionalized surfaces. The results revealed that DON morphology and binding tags influence the binding kinetics and that DON hybridization on surfaces is more effective in microfluidic devices with larger-than-standard dimensions, addressing the low diffusivity challenge of DONs. The platform enabled the decoration of DONs with protein-binding ligands and in situ investigation of ligand occupancy on DONs to produce high-quality bioactive surfaces. These surfaces were used to recruit and activate the epidermal growth factor receptor (EGFR) through clustering in the membranes of living cancer cells (MCF-7) using an antagonistic antibody (Panitumumab). The activation was quantified depending on the interligand distances of the EGFR-targeting antibody.

Numerical investigation of drag reduction effects on a track bicycle fork using wings with a wavy leading edge

AbstractReynolds‐averaged Navier–Stokes (RANS) and large‐eddy simulations (LES) of the flow around wings with a wavy leading edge (WLE) are conducted in order to assess the capabilities of a passive flow control strategy for drag reduction. The intended application is indoor track cycling with controlled flow conditions. A section of a single fork rod is investigated in order to make the numerical simulations feasible. The present study reveals that net drag reduction is possible by a nonsinusoidal modification of the leading edge of the wing. However, the drag reduction effect remains limited to a few percent. While RANS and LES yield the same drag coefficient for a reference case, RANS underestimates the drag reduction effect for a longer wing and the WLE cases, but exhibits otherwise a qualitatively similar trend as the LES. With the aid of RANS, an optimal geometry is obtained defined by the wavelength‐to‐chord length ratio of and the amplitude‐to‐chord length ratio of . Corresponding LES results give an indication of the origin of drag reduction by a hampered vortex shedding. The generation of smaller and more streamwise oriented vortical flow structures at the trailing edge and behind the WLE wing is correlated with significantly reduced lift fluctuations and drag reduction.

Anchor chains—A simple low‐cost device to assist passage of small‐bodied mass fish

AbstractAttention has been placed on a variety of barriers that hinder fish passage in modern times. The most prevalent fish barriers were culverts which have negatively impacted waterway connectivity and fish habitats. For small‐bodied mass fish, high barrel velocities and turbulence have reduced fish swimming performance because of their weak swimming capabilities. In the present study, physical testing was conducted under controlled flow conditions to assess the extent and magnitude of turbulence characteristics, secondary flow and low‐velocity zones in a 0.5‐m‐wide box culvert barrel. Two cases were investigated; a reference case consisting of a smooth rectangular channel and a low‐cost design solution to improve upstream fish migration consisting of a single galvanized anchor chain fitted within a smooth rectangular channel. The single anchor chain was positioned towards one corner of the channel to induce asymmetric flow, reducing overall energy losses and enhancing the existing low‐velocity zone in the adjacent channel corner. The anchor chain induced a strong turbulent flow motion away from the anchor chain, characterized by higher Reynolds stress and turbulent kinetic energy, along with a distinct channel flow asymmetry. Conversely, the low‐velocity zone, between the anchor chain and the bottom channel corner, was significantly expanded with reduced longitudinal mean velocities and turbulent scales. Whilst the anchor chain link contributed to some complex localized wake flow, the anchor chain also influenced the distributions of normal turbulent stresses (v'z2 – v'y2), which in turn influenced the location of secondary flow cells. This secondary flow redirected low momentum fluid into the low‐velocity zones, setting the conditions for the favorable upstream passage of small‐bodied mass fish species.

Unveiling nutrient flow-mediated stress in plant roots using an on-chip phytofluidic device.

The initial emergence of the primary root from a germinating seed is a pivotal phase that influences a plant's survival. Abiotic factors such as pH, nutrient availability, and soil composition significantly affect root morphology and architecture. Of particular interest is the impact of nutrient flow on thigmomorphogenesis, a response to mechanical stimulation in early root growth, which remains largely unexplored. This study explores the intricate factors influencing early root system development, with a focus on the cooperative correlation between nutrient uptake and its flow dynamics. Using a physiologically as well as ecologically relevant, portable, and cost-effective microfluidic system for the controlled fluid environments offering hydraulic conductivity comparable to that of the soil, this study analyzes the interplay between nutrient flow and root growth post-germination. Emphasizing the relationship between root growth and nitrogen uptake, the findings reveal that nutrient flow significantly influences early root morphology, leading to increased length and improved nutrient uptake, varying with the flow rate. The experimental findings are supported by mechanical and plant stress-related fluid flow-root interaction simulations and quantitative determination of nitrogen uptake using the total Kjeldahl nitrogen (TKN) method. The microfluidic approach offers novel insights into plant root dynamics under controlled flow conditions, filling a critical research gap. By providing a high-resolution platform, this study contributes to the understanding of how fluid-flow-assisted nutrient uptake and pressure affect root cell behavior, which, in turn, induces mechanical stress leading to thigmomorphogenesis. The findings hold implications for comprehending root responses to changing environmental conditions, paving the way for innovative agricultural and environmental management strategies.

Capturing physiological hemodynamic flow and mechanosensitive cell signaling in vessel-on-a-chip platforms.

Recent advances in organ chip (or, "organ-on-a-chip") technologies and microphysiological systems (MPS) have enabled in vitro investigation of endothelial cell function in biomimetic three-dimensional environments under controlled fluid flow conditions. Many current organ chip models include a vascular compartment; however, the design and implementation of these vessel-on-a-chip components varies, with consequently varied impact on their ability to capture and reproduce hemodynamic flow and associated mechanosensitive signaling that regulates key characteristics of healthy, intact vasculature. In this review, we introduce organ chip and vessel-on-a-chip technology in the context of existing in vitro and in vivo vascular models. We then briefly discuss the importance of mechanosensitive signaling for vascular development and function, with focus on the major mechanosensitive signaling pathways involved. Next, we summarize recent advances in MPS and organ chips with an integrated vascular component, with an emphasis on comparing both the biomimicry and adaptability of the diverse approaches used for supporting and integrating intravascular flow. We review current data showing how intravascular flow and fluid shear stress impacts vessel development and function in MPS platforms and relate this to existing work in cell culture and animal models. Lastly, we highlight new insights obtained from MPS and organ chip models of mechanosensitive signaling in endothelial cells, and how this contributes to a deeper understanding of vessel growth and function in vivo. We expect this review will be of broad interest to vascular biologists, physiologists, and cardiovascular physicians as an introduction to organ chip platforms that can serve as viable model systems for investigating mechanosensitive signaling and other aspects of vascular physiology.

Cell Patterning Technology on Polymethyl Methacrylate through Controlled Physicochemical and Biochemical Functionalization.

In recent years, innovative cell-based biosensing systems have been developed, showing impact in healthcare and life science research. Now, there is a need to design mass-production processes to enable their commercialization and reach society. However, current protocols for their fabrication employ materials that are not optimal for industrial production, and their preparation requires several chemical coating steps, resulting in cumbersome protocols. We have developed a simplified two-step method for generating controlled cell patterns on PMMA, a durable and transparent material frequently employed in the mass manufacturing of microfluidic devices. It involves air plasma and microcontact printing. This approach allows the formation of well-defined cell arrays on PMMA without the need for blocking agents to define the patterns. Patterns of various adherent cell types in dozens of individual cell cultures, allowing the regulation of cell-material and cell-cell interactions, were developed. These cell patterns were integrated into a microfluidic device, and their viability for more than 20 h under controlled flow conditions was demonstrated. This work demonstrated the potential to adapt polymeric cytophobic materials to simple fabrication protocols of cell-based microsystems, leveraging the possibilities for commercialization.

Impairment of platelet function in both mild and severe COVID-19 patients.

Abnormalities of platelet function were reported in patients with severe COVID-19 (severe-C), but few data are available in patients with mild COVID-19 (mild-C) and after COVID-19 recovery. The aim of this study was to investigate platelet parameters in mild-C patients (n = 51), with no evidence of pneumonia, and severe-C patients (n = 49), during the acute phase and after recovery, compared to 43 healthy controls. Both mild-C and severe-C patients displayed increased circulating activated platelets, low δ-granule content (ADP, serotonin), impaired platelet activation by collagen (light transmission aggregometry) and impaired platelet thrombus formation on collagen-coated surfaces under controlled flow conditions (300/s shear rate). The observed abnormalities were more marked in severe-C patients than in mild-C patients. Overall, 61% (30/49) of mild-C and 73% (33/45) of severe-C patients displayed at least one abnormal platelet parameter. In a subgroup of just 13 patients who showed no persisting signs/symptoms of COVID-19 and were re-evaluated at least 1 month after recovery, 11 of the 13 subjects exhibited normalization of platelet parameters. In conclusion, mild abnormalities of platelet parameters were present not only in severe-C but also, albeit to a lesser extent, in mild-C patients during the acute phase of COVID-19 and normalized in most tested patients after clinical recovery.

Role of inherent anisotropy in infiltration mechanism of suffusion with irregular granular skeletons

Suffusion, the process of particle migration and clogging within porous media, exerts a remarkable impact on various natural and engineered systems. Properties of the coarse-grained skeletons are crucial during suffusion, while the influence of the inherent anisotropy remains insufficiently explored. In this study, numerical model using the coupled computational fluid dynamics and the discrete element method (CFD-DEM) is performed to simulate the suffusion evolution of different fabric anisotropy configurations under controlled flow conditions. Granular skeletons are generated considering different initial rotational degrees of freedom (RDoFs) and orientations of irregular coarse particles, based on which the motion mechanism of migratory fines is investigated. The infiltration process is quantified by multi-scale parameters, including particle distribution, velocity evolution, visualization of pores and throats, force network, contact statistics and anisotropic characteristics. The results illustrate the non-negligible influence of inherent anisotropy on pore structure, consequently impacting the motion behavior of fine particles and the stress transmission within the granular skeletons. Such insights will contribute to advancing a fundamental understanding of suffusion, which enables the development of effective strategies for predicting and controlling in geotechnical and environmental engineering catastrophes.

A Newly Developed Inverted Rotating Disk Electrode (IRDE) Setup for the Investigation of Photoelectrochemical Reactions

A new setup for an inverted rotating disk electrode (IRDE) was developed for the investigation of photoassisted or photoelectrochemical processes involving mass transfer reactions, as in electrodeposition or etching processes. In this setup, rotation of the disk electrode is achieved by magnetic coupling between a driver magnet (i.e. a magnetic stirrer) and the follower magnet included in the sample holder. For photoelectrochemical experiments, the cell allows a homogeneous illumination and removal of gaseous reaction products, while still providing leak tightness. In this way, controlled flow conditions are provided with the possibility to simultaneously illuminate the sample surface from a distance as small as 20 mm. At the same time gases formed during the reaction can easily ascend through the electrolyte.The light source is placed on top of the cell and illumination is done through the electrolyte. A low liquid level (≥ 15 mm) allows a small distance between the sample and the light source and therefore a high light intensity on the sample surface. Illumination is done using a high-power LED. Due to the high power, thermal effects need to be taken into consideration and especially an effective cooling of the LED is essential.As a wide band gap semiconductor, silicon carbide (SiC) has gained large interest due to its high chemical and physical stability. Since photoassisted anodic etching of n-type 4H silicon carbide in potassium hydroxide solutions [1] requires both UV illumination and the removal of gaseous reaction products, this reaction is investigated in the newly developed IRDE setup. Possible applications for such a process are defect decoration [2], trench etching, and dicing.Photoassisted anodic etching of n-type SiC occurs in three steps: (1) hole generation in the material through illumination with light with an energy higher than the bandgap of the semiconductor (2) oxidation of silicon and carbon through the holes driven to the semiconductor-electrolyte interface by an external potential and (3) dissolution of the oxidation products in the electrolyte. In accordance with the three steps of the reaction, different processes can be limiting: For low light intensities (either through a large distance between the sample and the LED or through low driving currents through the LED) the number of photon-induced holes is limiting. At low electrolyte concentrations, the transport of hydroxyl ions and the dissolution of the oxidation products determine the etch rate. For high light intensities and high electrolyte concentrations, the external potential and thereby the oxidation reaction are limiting for the overall current flow. These different reaction regimes can be distinguished in cyclic voltammetry measurements in the newly developed IRDE cell.[1] D. H. van Dorp und J. J. Kelly, „Photoelectrochemistry of 4H–SiC in KOH solutions,“ Journal of Electroanalytical Chemistry, Bd. 599, Nr. 2, pp. 260-266, 2007.[2] J. L. Weyher, S. Lazar, J. Borysiuk und J. Pernot, „Defect-selective etching of SiC,“ physica status solidi, Bd. 202, Nr. 4, pp. 578-583, 2005. Figure 1

Cell Adhesion and Biofilm Formation Analysis.

Cell adhesion to surfaces and ulterior biofilm formation are critical processes in microbial development since living in biofilms is the preferred way of life within microorganisms. These processes are known to influence not only microorganisms development in the environment, but also their participation in biotechnological processes and have been the focus of intense research that as a matter of fact, was mainly directed to the bacterial domain. Archaea also adhere to surfaces and have been shown forming biofilms, but studies performed until present did not exploit the diversity of methods probed to be useful along bacterial biofilm research.An experimental setup is described here with the aim of stimulating archaeal biofilm research. It can be used for studying cell adhesion and biofilm formation under controlled flow conditions and allows performing in situ optical microscopy (phase contrast, fluorescence, or confocal) and/or spectroscopic techniques (UV-Vis, IR, or Raman) to determine structural and functional biofilm features and their evolution in time. Variants are described with specific aims as working in anaerobiosis and allow sampling of biological material along time.

Physical modelling of pipe culverts to assist upstream fish passage

AbstractRoad crossings and culverts may adversely impact the stream network connectivity and fish habitats of the catchment. Research into the passage of small‐body‐mass fish in pipe culverts has been relatively limited, compared to the literature for box culverts. For small‐bodied and juvenile fish species, the excessive barrel velocities are often a major hindrance, because of their weak swimming capabilities. In the present study, some physical testing of low‐velocity‐zones was undertaken in standard pipe culvert. The physical modelling was conducted under controlled flow conditions to test comparatively three designs, aiming to minimise the change in energy losses and to maximise low‐velocity zones and secondary circulation conducive to small‐body‐mass fish passage. In the whole pipe culvert experiment (Model 1), both baffle and longitudinal rail boundary treatments provided low‐velocity zones. The baffles however induced a strongly turbulent flow, associated with substantially larger energy dissipation than the reference smooth boundary pipe culvert. The longitudinal rail boundary treatment produced energy losses comparable to the smooth boundary reference configuration. Both boundary treatments were tested comparatively at near‐full‐scale (Model 2) to quantify the low‐velocity‐zone (LVZ) characteristics. The small longitudinal rail (0.06 m × 0.02 m), installed at 30° from the centreline, induced some flow asymmetry, as well as some low‐velocity‐zones on both sides of the rail. Some strong secondary motion was further observed as the combined effect of the flow asymmetry and singularities of the rail corners. The secondary motion structure was markedly different, and the distributions of the normal turbulent stresses (vz′2 − vy′2) showed key differences between the two boundary treatments, with the sharp corners of the rail contributing to the generation of secondary motion and in turn slow‐velocity regions facilitating the upstream passage of small‐body‐mass fish species and juveniles of larger fish.

Kinetics of platelet adhesion to a fibrinogen-coated surface in whole blood under flow conditions.

AimTo test a novel method of assessment of platelet adhesion to a fibrinogen‐coated surface in whole blood under flow conditions.MethodsWe developed a fluidic device that mimics blood flow in vessels. The method of detection of platelet adhesion is based on recording of a scattered laser light signal from a fibrinogen‐covered surface. Testing was performed in platelet‐rich plasma (PRP) and whole blood of healthy volunteers. Control measurements were performed, followed by tests with inhibition of platelet GPIIa/IIIb and GPIb receptors. Then, the same testing sequence was performed in whole blood of persons with autoimmune thrombocytopenia and type 3 von Willebrand disease.ResultsThe change in intensity of scattered light was 2.7 (2.4; 4.1) times higher in whole blood (0.2 ± 0.08V, n = 7) than in PRP (0.05 ± 0.02 V, n = 7), p < 0.01. The blocking of GP IIb/IIIa receptors decreased the intensity of scattered light to 8.5 (6.5;12)%; the blocking of GPIb receptors decreased it to 34 (23;58)%, p < 0.01. In the whole blood of a person with autoimmune thrombocytopenia, the inhibition of GPIb receptors decreased platelet adhesion, but no effect was observed in type 3 von Willebrand disease. Inhibition of platelet GPIIb/IIIa receptors alone or combined inhibition of GPIb and GPIIb/IIIa receptors resulted in almost total suppression of adhesion in both cases.ConclusionOur system effectively registers platelet adhesion to a fibrinogen‐coated surface under controlled‐flow conditions and may successfully be applied to the investigation of platelet adhesion kinetics.

Assessing the mobility of veterinary drugs with column experiments using different soils and under controlled flow conditions

Veterinary pharmaceuticals are pollutants that received much attention during the last 20 years. Macrocyclic lactones are a class of drugs globally used in animal and human health, as well as crops protection. Some of its members are key substances for global food security. In this research, the mobility of eprinomectin (EPM) in soil columns (25 cm soil height; 10 cm diameter) was assessed for the first time. Soil density in the columns was 1.1–1.2 g/cm3. Porosity was 0.54–0.60. Three different soil types were used (agricultural, pastoral, wetland). In the experiment, chloride was used as a non-reactive tracer to determine the hydrodynamic conditions in the columns. Therefore, water velocity (v) was 0.146–0.151 cm/h, dispersion coefficient (D) 0.011–0.017 cm2/h and dispersivity (D/v) was 0.072–0.121. Our results showed that the drug remained in the top layers of the columns, after applying an extreme irrigation scenario. The retardation factor for EPM was 43.4–54.5 while for chloride was 0.99–1. EPM fraction (% of applied mass) in 0–1 cm was 13.8–18.0% and in 1–5 cm was 53.3–73.0%. An amount 13–29% was irreversibly bound or degraded during this experiment. From a soil management perspective, the continuous application of EPM contaminated manure, could result in high concentrations in the top 10 cm of the soil profile. Soil column experiments, where hydrodynamic conditions are well defined, are useful for the environmental impact assessment of veterinary pharmaceuticals.

Sectional model of a prairie buffer strip in a laboratory flume for water quality research

AbstractVegetative buffers have shown promising results in reducing runoff volume, sediment, nutrients, and manure‐borne contaminants in runoff from agricultural fields. Although these vegetative buffer systems have been extensively tested in field and plot‐scale studies that utilize either natural or simulated rainfall, studies of such systems under highly controlled conditions in the laboratory have been limited. Here, we present the development of a new system for laboratory testing of a full‐scale, sectional, physical model of a new practice under the Continuous Conservation Reserve Program (CRP) Clean Lakes, Estuaries, and Rivers (CLEAR) Initiative, CP‐43 Prairie Strips. This work includes the extraction of prairie strip sections from the field and their integration into an existing laboratory flume facility with specific auxiliary features to facilitate overland flow experimentation. As a proof of concept run, a potassium chloride (KCl) tracer study was conducted to verify system functionality and inform future work. The tracer pulse was injected under saturated conditions and the response was monitored through surface water (upstream and downstream of the prairie strip model) and subsurface water (infiltrated) sampling with continuous flow rate monitoring at the sampling locations. The tracer test provided highly resolved breakthrough curves (BTCs) with 93.5% of the injected tracer mass recovered, and provided useful information on flow partitioning, velocities, and dispersion characteristics along the surface and through the subsurface profile of the model. This model prairie strip system is expected to be useful in optimizing the performance of prairie strips under highly controlled flow and contaminant source conditions.

Cover Image 2, Volume 4, Issue 1

Agrosystems, Geosciences & EnvironmentVolume 4, Issue 1 e20147 COVER IMAGEFree Access Cover Image 2, Volume 4, Issue 1 First published: 03 February 2021 https://doi.org/10.1002/agg2.20147AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract On the cover: Vegetative buffers have shown promising results in reducing runoff volume, sediment, nutrients, and manure borne contaminants in runoff from agricultural fields. Here, we present the development of a new system for laboratory testing of a full scale, sectional, physical model. This model prairie strip system is expected to be useful in optimizing the performance of prairie strips under highly controlled flow and contaminant source conditions. See Craig et al., “Sectional model of a prairie buffer strip in a laboratory flume for water quality research.” https://doi.org/10.1002/agg2.20133 Photo by Leigh Ann Long. Volume4, Issue12021e20147 RelatedInformation

Measurement of Flux at Sediment–Water Interface Using a Seepage Meter under Controlled Flow Conditions

The accuracy of groundwater flux measurement using a seepage meter was evaluated through a series of laboratory experiments under controlled flow conditions. Simulated groundwater influx and outflux rates were measured using a seepage meter, and the results were compared with the known water flux rates in our controlled tank flow system. Differences induced by the use of two different types of collection bag (Types 1 and 2) were also evaluated. The slopes of the trend lines between the controlled influx rate and influx as measured by the seepage meter were 0.6669 (for Type 1 bag) and 0.8563 (for Type 2 bag), suggesting that the groundwater influx rate as measured by the seepage meter may be less than the actual rate. This may be due to the resistance of the collection bags and head loss induced at the tubing orifice. With respect to outflux measurement, the slopes of the trend line were 1.3534 (for Type 1 bags) and 1.4748 (for Type 2 bags), suggesting that the outflux rate as measured by the seepage meter may be more than the actual rate. The size and wall thickness of the collection bag used affected the measured flux rates. This study suggests that, as long as errors can be identified, seepage meters can be a reliable means of studying groundwater–surface water interactions.

How full-height sidewall baffles affect box culvert capacity: balancing fish passage and discharge requirements

ABSTRACT Low-level river crossings and culverts deliver valuable transportation and hydraulic control services to the society, but have negative impacts in terms of upstream fish passage. Recently, full-height sidewall baffles have been imposed in north-eastern Australia to assist upstream passage of small-bodied fish in box culverts, although the impact on the culvert discharge capacity was ignored. Detailed physical modelling was conducted under controlled flow conditions in a near-full-scale culvert barrel channel, equipped with such full-height sidewall baffles. The results provide a quantitative assessment of the impact of full-height sidewall baffles on the discharge capacity of box culverts. Applications were developed for single- and multi-cell box culverts, and practical implications are discussed.

Flow-controlled fluoroscopic angiography for the assessment of vascular integrity in bioengineered kidneys.

Perfusion decellularization has been proposed as a promising method for generating nonimmunogenic organs from allogeneic or xenogeneic donors. Several imaging modalities have been used to assess vascular integrity in bioengineered organs with no consistency in the methodology used. Here, we studied the use of fluoroscopic angiography performed under controlled flow conditions for vascular integrity assessment in bioengineered kidneys. Porcine kidneys underwent ex vivo angiography before and after perfusion decellularization. Arterial and venous patencies were defined as visualization of contrast medium (CM) in distal capillaries and renal vein, respectively. Changes in vascular permeability were visualized and quantified. No differences in patency were detected in decellularized kidneys compared with native kidneys. However, focal parenchymal opacities and significant delay in CM clearance were detected in decellularized kidneys, indicating increased permeability. Biopsy-induced leakage was visualized in both groups, with digital subtraction angiography revealing minimal CM leakage earlier than nonsubtracted fluoroscopy. In summary, quantitative assessment of vascular permeability should be coupled with patency when studying the effect of perfusion decellularization on kidney vasculature. Flow-controlled angiography should be considered as the method of choice for vascular assessment in bioengineered kidneys. Adopting this methodology for organs premodified ex vivo under normothermic machine perfusion settings is also suggested.

Outdoor measurements of relationship between canopy flow and wall pressure distributions of a block within urban-like block array

Research on indoor ventilation is mainly conducted utilizing wind-tunnel experiments and computational fluid dynamics simulations under controlled flow conditions. However, with these techniques, the effects of the actual urban boundary-layer flow with variable wind directions and turbulence on the ventilation performance of a building surrounded by various buildings remain unresolved. Therefore, we conducted outdoor experiments at the Comprehensive Outdoor Scale Model experiment site to evaluate the mutual relationships between wall pressure of a building within a square array, in which cubical blocks are aligned in same spanwise position in a row, and atmospheric urban boundary-layer flow. The dataset consisting of the simultaneous measurements of the wall pressure acting on a target block and the air flow around it was analyzed statistically. The results demonstrate that the distributions of wind pressure coefficient significantly change with the approaching wind direction, while similar cavity flow patterns such as the downward flow at windward wall and the upward flow at leeward wall are observed regardless of the wind direction. Additionally, the pressure coefficient is more sensitive to the approaching wind direction at the side-edge than at the center of the block surface. Moreover, the temporal and spatial distributions of wall pressure are highly correlated with the fluctuating flow above the canopy rather than the turbulence generated within the canopy.

On turbulence and turbulent events in a breaking bore

A breaking bore is a highly unsteady turbulent motion that may affect both riverine and estuarine systems. Like many steady turbulent flows, the turbulent motion is dominated by intense coherent structure and turbulent event activities. A novel analysis of unsteady turbulent events is developed for transient breaking bores in which turbulent bursting events are defined in terms of the instantaneous relative turbulent flux. Using new physical data collected in a large facility under controlled flow conditions, the data analysis is applied to a breaking bore. The unsteady event data show some intense bursting during the flow deceleration associated with the bore passage. The results indicate that a turbulent event analysis may deliver valuable quantitative details into the turbulent bursts beneath bores, with applications relevant to turbulent mixing and sedimentary processes.