Low Turbulence Environment Research Articles

Large eddy simulation and linear stability analysis of active sway control for wind turbine array wake

The convective instability of wind turbine wakes allows specific upstream forcing to amplify downstream, leading to increased wake meandering and replenishment, thereby providing a theoretical basis for active wake control. In this study, the active sway control—a strategy previously proven to enhance wake recovery at the single wind turbine level—is analyzed at the turbine array level. The similarity and differences between individual turbine wakes and the wake array are analyzed using large eddy simulations and linear stability analysis, considering both uniform and turbulent inflow conditions. For cases with uniform inflow, large eddy simulations reveal significant meandering motion in the wake array induced by active sway control at a motion amplitude of 1% rotor diameter, consistent with previous studies of standalone wind turbine wakes. Nevertheless, the sensitive frequency for the wake array extends down to St = 0.125 below the limit of St > 0.2 for a single wake, and the optimal control frequency for the standalone turbine wake becomes suboptimal for the array. Linear stability analysis reveals the underlying mechanism of this frequency shift as changes in the shear-layer instability due to the overlap of upstream and downstream wakes and is capable to provide fast estimation of optimal control frequencies. When inflow turbulence intensity increases, the gain of active sway control is reduced, underscoring the importance of low-turbulence environment for successfully implementing the active sway control. The reduction in wake response is captured by the linear stability analysis if the base flow accounts for the faster wake expansion caused by inflow turbulence.

How accurate are ultrasonic anemometers, calibrated in a laminar wind tunnel, under turbulent conditions?

Two ultrasonic anemometers, namely the Gill HS-100 and the Anemoment TriSonica Mini, were placed in the VKI L-1A wind tunnel to assess their accuracy and precision. A comparison was made between these instruments and a Prandtl probe, using a range of wind speeds up to 20 m/s, eighteen azimuth angles (wind directions) at 20° intervals, five tilt angles ranging from -10 to 10°, and two levels of turbulence. As the normal level of turbulence in the wind tunnel, determined by hot wire anemometry, is less than 1%, a grid was installed to allow a second level of turbulence of 6.1% to be evaluated. The analysis shows that the Gill HS-100 accurately measures wind speed in low turbulence conditions in accordance with the manufacturer’s specifications. However, in a turbulent atmosphere, the measured wind speeds are not only overestimated by 2-8% compared to the Prandtl probe but also show a systematic shift compared to the low turbulence case. As expected from the manufacturer’s specifications, the TriSonica Mini is less accurate and precise than the HS-100. In a low-turbulence environment, it fails to meet the manufacturer’s specifications. In a more turbulent atmosphere, however, it matches and even outperforms the HS-100, making it suitable for real-world applications. However, it did show reduced accuracy at non-horizontal wind angles, requiring careful consideration for drone-based measurements. More complex calibrations involving multiple turbulence levels could be considered for both anemometers. However, the feasibility of this approach remains uncertain in light of the results obtained.

Alginate Beads as a Promising Tool for Successful Production of Viable and Pluripotent Human-Induced Pluripotent Stem Cells in a 3D Culture System.

Two-dimensional (2D)-based cell culture systems, limited by their inherent heterogeneity and scalability, are a bottleneck in the production of high-quality cells for downstream biomedical applications. Finding the optimal conditions for large-scale stem cell culture while maintaining good cellular status is challenging. The aim of this study was to assess the effects of three-dimensional (3D) culture on the viability, proliferation, self-renewal, and differentiation of human induced pluripotent stem cells (IPSCs). Various culture conditions were evaluated to determine the optimal conditions to maintain the viability and proliferation of human IPSCs in a 3D environment: static versus dynamic culture, type of adhesion protein added to alginate (Matrigel™ versus gelatin), and the addition of Y-27632t on long-term 3D culture. The proliferation ability of the cells was evaluated via the MTS proliferation assay; the expression levels of the pluripotency markers Nanog and Oct3/4, PAX6 as an ectoderm marker, and laminin-5 and fibronectin as markers of extracellular matrix synthesis were assessed; and HIF1α and HIF2α levels were measured using quantitative reverse transcription polymerase chain reaction. Using a high-aspect-ratio vessel bioreactor with a gentle, low-sheer, and low-turbulence environment with sufficient oxygenation and effective mass transfer of nutrients and waste, we verified its ability to promote cell proliferation and self-renewal. The findings showed that human IPSCs have the ability to maintain pluripotency in a feeder-free system and by inhibiting ROCK signaling and using hypoxia to improve single-cell viability in 3D culture. Furthermore, these cells demonstrated increased self-renewal and proliferation when inoculated as single cells in 3D alginate beads by adding RI during the culture period. Dynamic 3D culture is desirable for the large-scale expansion of undifferentiated human IPSCs.

Performance of the porous disk wind turbine model at a high Reynolds number: Solidity distribution and length scales effects

A new design methodology for porous disk wind turbine modeling is proposed, where a disk is matched to a horizontal axis wind turbine (HAWT) on (i) thrust coefficient, (ii) radial solidity distribution, and (iii) length scale criteria. Three disk designs are tested, allowing for isolation of the effects of each criterion, with performance evaluated through experimental wake comparisons with a model HAWT at a diameter-based Reynolds number of 4 × 106 and free-stream turbulence intensity of 1.2%. Wake velocity measurements reveal excellent agreement on mean profiles in the near wake (as early as 112 diameters downstream) when the rotor’s radial solidity distribution is incorporated into the disk design. Higher order velocity statistics can also be matched farther downstream (312 diameters). To match the higher order moments, the disk must generate near wake turbulence of similar characteristics to the rotor, since this turbulence dominates the development of the wake in a high Reynolds number, low free-stream turbulence environment. This is achieved by the third design criterion, where physical features that match the rotor length scales are incorporated. Thus, including all three criteria in a single porous disk yields a model that performs well at field-relevant Reynolds numbers, is not performance dependent on the free-stream turbulence intensity, and does not require iterative tuning.

Size selectivity of a novel non-mesh codend (the Modular Harvesting System) in a New Zealand deepwater fishery

The Modular Harvesting System (MHS) is an inflatable membrane-like fabric tube with escapement holes that replaces the mesh codend of a trawl, and is designed to reduce damage to catch by providing fish a low-flow, low-turbulence environment that allows them to maintain swimming control and avoid compaction during trawling and haulback. The MHS gear is now used within New Zealand’s most valuable finfish fishery, deepwater hoki/blue grenadier (Merlucciidae, Macruronus novaezelandiae). This work presents the novel research used to estimate the size selectivity of the MHS gear, and to compare this to the selectivity of the conventional mesh trawl. Management objectives required estimates of the absolute size-selectivity of both the MHS and conventional gears, and also an estimate of their relative selectivity. An innovative statistical power analysis was developed to specify the required number of twin-trawl tows and number of fish to measure to ensure the desired statistical power to detect a meaningful difference between conventional and MHS gears. A novel twin-trawl experiment was employed whereby the conventional and MHS gears were each paired with a nonselective control, and then the conventional and MHS trawls were paired. All catch data were simultaneously analyzed in a hybrid selectivity model. The MHS and conventional gears had similar estimated size-selectivity curves, and they were not significantly different.

Automatic Transition Prediction in a Navier–Stokes Solver Using Linear Stability Theory

A structured Reynolds-averaged Navier–Stokes solver is directly coupled to a linear stability theory (LST) solver to include the effect of laminar–turbulent transition in the flow simulations. The flowfield variables of the flow solver are used to both find streamlines along which transition can be predicted and to provide the LST code with the required boundary-layer profiles. Instabilities included in the analysis are of the Tollmien–Schlichting and crossflow nature relevant to high-Reynolds-number flows in low turbulence environments. The coupling is fully automated and can therefore be used efficiently in the analysis and design of geometries with external flows. The Technical University of Braunschweig’s sickle wing with spanwise-varying crossflow and the natural laminar flow version of the Common Research Model are simulated under various conditions. Applications to these relevant three-dimensional test cases showcase the capability of the method to model the real flow physics. Advantages and challenges of the approach with regard to future design endeavors are discussed.

A low‐cost underwater particle tracking velocimetry system for measuring in situ particle flux and sedimentation rate in low‐turbulence environments

AbstractWe describe a low‐cost three‐dimensional underwater particle tracking velocimetry system to directly measure particle settling rate and flux in low‐turbulence aquatic environments. The system consists of two waterproof cameras that acquire stereoscopic videos of sinking particles at 48 frames s−1 over a tunable sampling volume of about 45 × 25 × 24 cm. A dedicated software package has been developed to allow evaluation of particle velocities, concentration and flux, but also of morphometric parameters such as particle area, sinking angle, shape irregularity, and density. Our method offers several advantages over traditional approaches, like sediment trap or expensive in situ camera systems: (1) it does not require beforehand particle collection and handling; (2) it is not subjected to sediment trap biases from turbulence, horizontal advection, or presence of swimmers, that may alter particulate load and flux; (3) the camera system enables faster data processing and flux computation at higher spatial resolution; (4) apart from the particle settling rates, the particle size distribution, and morphology is determined. We tested the camera system in Lake Stechlin (Germany) in low turbulence and mean flow, and analyzed the morphological properties and settling rates of particles to determine their sinking behavior. The particle flux assessed from conventional sediment trap measurements agreed well with that determined by our system. By this, the low‐cost approach demonstrated its reliability in low turbulence environments and a strong potential to provide new insights into particulate carbon transport in aquatic systems. Extension of the method to more turbulent and advective conditions is also discussed.

Investigating the influence of performance measurement on learning, entrepreneurial orientation and performance in turbulent markets

PurposeThis study aims to examine how comprehensive performance measurement systems (CPMS) influence entrepreneurial orientation, market-focussed learning (MFL) and employees’ perceptions of firm performance within a service-provision context. It also considers the moderating effect of low and high levels of perceived market-turbulence (low-turbulence environments [LMT] vs highly turbulent environments [HMT]) on the relationships between these concepts.Design/methodology/approachPLS-SEM was used to test the hypothesised relationships using survey responses from 198 employees of a leading multi-branch travel agency in Iran.FindingsThe findings demonstrate that CPMS positively influence MFL and, in doing so, have a positive effect on perceptions of firm performance. However, the findings also suggest that CPMS negatively influence entrepreneurial orientation, and therefore can also negatively influence perceptions of firm performance. Further, the relationships between CPMS, entrepreneurial orientation, MFL and firm performance are stronger for HMT when compared to LMT for all relationships.Practical implicationsIndustry managers should adapt their CPMS to include measures specific to intra-organisational entrepreneurship and innovation and should pursue greater understanding of changing customer preferences.Originality/valueThis study highlights the importance of MFL as a means of avoiding the negative impact of underdeveloped market research on performance in the turbulent Iranian context. Contrary to previous literature, it provides an example of how CPMS can negatively influence entrepreneurial orientation in such environments.

Marketing capability, technical capability or degree of product innovation: what really matters in leveraging the sales of technology-based start-ups

The objective of this study was to analyse the influence of incubator marketing support on the product performance of incubated NTBFs. The study's theoretical contribution sheds new light on NPD in incubated NTBFs by analysing the effect of an important type of incubator support on NPD: incubator marketing support. A total of 512 target NTBFs were identified and 250 participated in the survey. We found that incubator marketing support positively influences marketing capability. Marketing capability is a key factor for promoting sales growth in both low and high turbulence environments, although the effect is more pronounced in low turbulence environments.

Performance of 120 Gbps single channel coherent DP-16-QAM in terrestrial FSO link under different weather conditions

The performance of a 120 Gbps single-carrier coherent transceiver system is evaluated in a terrestrial Free Space Optical Link (FSOL) under the haze, rain, and fog weather conditions. In-phase and Quadrature (IQ) based Dual Polarization 16 Quadrature Amplitude Modulation (DP-16-QAM) is implemented in OptiSystem v.13 simulation platform with homodyne detection and Digital Signal Processing (DSP) at the receiver. The IQ based optical modulator and the DSP unit can be fabricated in the form of Integrated Circuits (ICs) help to keep the system cost low. The system performance is evaluated in terms of Optical Signal to Noise Ratio (OSNR) requirements at an acceptable Bit Error Rate (BER ≤ 2 × 10−3, i.e., below the FEC limit) under low turbulence environment. Simulation results show that the system maintains good OSNR performance under severe weather conditions. This transceiver system shall be useful in short-reach, low-cost, high-capacity, robust communication link with dynamic environmental conditions.

Cambios estacionales en conjuntos de dinoflagelados epifíticos cerca de la costa norte de la Península de Yucatán, Golfo de México

Se estudió a los dinoflagelados epífitos en 250 muestras de 10 sitios en Chelem (una laguna rodeada parcialmente por manglar) y Dzilam de Bravo (una localidad costera expuesta), en la costa norte de la Península de Yucatán, obtenidas durante cinco exploraciones en 2008-2009. Se midió la temperatura, salinidad, turbidez, pH, oxígeno disuelto, nitratos, nitritos, fosfatos, silicatos, urea, clorofila-a extraída de la columna de agua, precipitación, así como velocidad y dirección del viento. El sistema de la laguna de Chelem reveló menor variabilidad de las características físico-químicas comparado con la localidad expuesta de Dzilam de Bravo. Los dinoflagelados se encontraron asociados con todos los macrófitos hospederos incluyendo cuatro especies de pastos marinos y 33 de macroalgas representantes de 24 géneros. Un total de 20 taxa de dinoflagelados correspondientes a 12 géneros se obtuvieron de estos sustratos. El género Prorocentrum incluyó la mayor cantidad de especies. La variación en la abundancia promedio de dinoflagelados epifíticos en ambas localidades osciló entre ~200 y 3500 células g-1 de peso húmedo de sustrato. La abundancia de células en los sitios, en contraste, varió entre ~100 y >25 000 células g-1. Esta variación es típica de la distribución en parches de estas especies en el tiempo y el espacio. En general, Prorocentrum rhathymum (máximo 2.41x104 células g-1) fue la especie más abundante en las muestras. Otras especies abundantes fueron Bysmatrum caponii (máximo 1.19x104 células g-1) y Amphidinium cf. carterae (máximo 3.69x103 células g-1). La abundancia máxima deGambierdiscus spp. se presentó en mayo y noviembre (9.90x103 células g-1) en Chelem cuando la temperatura varió de 24.5 a 30.2 °C. Los datos obtenidos muestran que el mayor potencial para el flujo de ciguatoxinas a través de la red trófica puede encontrarse en ambientes protegidos de turbulencia baja, donde la salinidad es alta, los nutrientes abundantes y la temperatura de agua entre 24 y 31 oC.

Validation of OpenFoam for heavy gas dispersion applications

In the present paper heavy gas dispersion calculations were performed with OpenFoam. For a wind tunnel test case, numerical data was validated with experiments. For a full scale numerical experiment, a code to code comparison was performed with numerical results obtained from Fluent. The validation was performed in a gravity driven environment (slope), where the heavy gas induced the turbulence. For the code to code comparison, a hypothetical heavy gas release into a strongly turbulent atmospheric boundary layer including terrain effects was selected. The investigations were performed for SF6 and CO2 as heavy gases applying the standard k–ɛ turbulence model. A strong interaction of the heavy gas with the turbulence is present which results in a strong damping of the turbulence and therefore reduced heavy gas mixing. Especially this interaction, based on the buoyancy effects, was studied in order to ensure that the turbulence-buoyancy coupling is the main driver for the reduced mixing and not the global behaviour of the turbulence modelling.For both test cases, comparisons were performed between OpenFoam and Fluent solutions which were mainly in good agreement with each other. Beside steady state solutions, the time accuracy was investigated. In the low turbulence environment (wind tunnel test) which for both codes (laminar solutions) was in good agreement, also with the experimental data. The turbulent solutions of OpenFoam were in much better agreement with the experimental results than the Fluent solutions. Within the strong turbulence environment, both codes showed an excellent comparability.

Rotating Cell Culture Systems for Human Cell Culture: Human Trophoblast Cells as a Model

The field of human trophoblast research aids in understanding the complex environment established during placentation. Due to the nature of these studies, human in vivo experimentation is impossible. A combination of primary cultures, explant cultures and trophoblast cell lines support our understanding of invasion of the uterine wall and remodeling of uterine spiral arteries by extravillous trophoblast cells (EVTs), which is required for successful establishment of pregnancy. Despite the wealth of knowledge gleaned from such models, it is accepted that in vitro cell culture models using EVT-like cell lines display altered cellular properties when compared to their in vivo counterparts. Cells cultured in the rotating cell culture system (RCCS) display morphological, phenotypic, and functional properties of EVT-like cell lines that more closely mimic differentiating in utero EVTs, with increased expression of genes mediating invasion (e.g. matrix metalloproteinases (MMPs)) and trophoblast differentiation. The Saint Georges Hospital Placental cell Line-4 (SGHPL-4) (kindly donated by Dr. Guy Whitley and Dr. Judith Cartwright) is an EVT-like cell line that was used for testing in the RCCS. The design of the RCCS culture vessel is based on the principle that organs and tissues function in a three-dimensional (3-D) environment. Due to the dynamic culture conditions in the vessel, including conditions of physiologically relevant shear, cells grown in three dimensions form aggregates based on natural cellular affinities and differentiate into organotypic tissue-like assemblies. The maintenance of a fluid orbit provides a low-shear, low-turbulence environment similar to conditions found in vivo. Sedimentation of the cultured cells is countered by adjusting the rotation speed of the RCCS to ensure a constant free-fall of cells. Gas exchange occurs through a permeable hydrophobic membrane located on the back of the bioreactor. Like their parental tissue in vivo, RCCS-grown cells are able to respond to chemical and molecular gradients in three dimensions (i.e. at their apical, basal, and lateral surfaces) because they are cultured on the surface of porous microcarrier beads. When grown as two-dimensional monolayers on impermeable surfaces like plastic, cells are deprived of this important communication at their basal surface. Consequently, the spatial constraints imposed by the environment profoundly affect how cells sense and decode signals from the surrounding microenvironment, thus implying an important role for the 3-D milieu. We have used the RCCS to engineer biologically meaningful 3-D models of various human epithelial tissues. Indeed, many previous reports have demonstrated that cells cultured in the RCCS can assume physiologically relevant phenotypes that have not been possible with other models. In summary, culture in the RCCS represents an easy, reproducible, high-throughput platform that provides large numbers of differentiated cells that are amenable to a variety of experimental manipulations. In the following protocol, using EVTs as an example, we clearly describe the steps required to three-dimensionally culture adherent cells in the RCCS.

Impact of turbulence on riverine zooplankton: a mesocosm experiment

Summary1. With increases in river discharge over time and space, zooplankton generally encounter increased turbulence, turbidity, hydraulic forces, downstream advection and food limitations, all of which should affect species diversity and densities. Of these factors, the role of turbulence on the distribution of zooplankton is least known along longitudinal and lateral dimensions in river networks.2. We tested the factorial effects of turbulence and grazing level on Ohio River potamoplankton in spring and summer using twelve 1600‐L, outdoor mesocosms. Turbulence was calculated using the Froude number for equal depths but with current velocities of 0.064 and 0.32 m s−1. Grazing levels corresponded to a high density treatment (=ambient river densities of rotifers, copepods and cladocerans) and a low density treatment (initially no zooplankton >64 μm). All tanks had the same water residence time, and hydraulic stress was minimized by circular flow patterns.3. Zooplankton densities and population growth rates were significantly affected by turbulence level and season. In general, rotifer populations grew faster in high turbulence tanks (though Keratella and Brachionus populations flourished in both treatments in summer) and microcrustaceans thrived better in low turbulence environments. The larger, calanoid copepods handled more turbulent conditions much better than cyclopoids or nauplii. Zooplankton had no detectable effects on particulate organic carbon concentrations in either month (values were higher in spring), but rotifers reduced chlorophyll concentrations in both months.4. The relative importance of turbulence in controlling potamoplankton is probably to vary not only on a longitudinal basis in river networks but also with both the hydrogeomorphic complexity of river reaches and the type and amount of river regulation. Plans for river rehabilitation and management should incorporate non‐turbulent habitats in large rivers as a means of enhancing zooplankton populations and providing an important food web component for planktivores.

Effect of small-scale shear on grazing and growth of the dinoflagellate Pfiesteria piscicida

Low turbulence environments have been hypothesized to be necessary for toxic outbreaks of the heterotrophic/mixotrophic dinoflagellate Pfiesteria piscicida. A toxic Pfiesteria outbreak occurred in the shallow waters (the flats) of the lower Pocomoke River, MD, USA, in 1997. During August 1999 and May and August 2000, data were collected with a Shallow Water ADV Turbulence Tripod (SWATT) to estimate turbulent shear at a location monitored for Pfiesteria on the flats. Approximately 78% of the observed shears were ≤1 s −1 and 98% were ≤2 s −1. Densities of Pfiesteria-like dinoflagellates were low in the Pocomoke River during 1999 and 2000 and no toxic outbreaks occurred. In the laboratory, Couette cylinders were used to determine the effect of small-scale shear on feeding and growth of cultured P. piscicida growing on cryptophyte prey. Shear of 1 s −1 had little or no effect on feeding or growth but 3 s −1 reduced feeding and survival/growth of Pfiesteria zoospores. Small, rapidly dividing Pfiesteria cells were most susceptible to negative effects of shear. Pfiesteria appears to be more sensitive to small-scale shear than are most autotrophic dinoflagellates. However, in the lower Pocomoke River, turbulent shear is rarely high enough to inhibit the growth of non-toxic Pfiesteria zoospores. Toxic functional types (TOX-A and TOX-B) may be more sensitive to small-scale shear; it will be important to determine the responses of these types of Pfiesteria in order to predict the affects of wind and tidal mixing on toxic outbreaks.

Limitations on the Use of Impermeable Mesocosms for Ecological Experiments Involving Aurelia sp. (Scyphozoa: Semaeostomeae)

Microcosms permit controlled ecological experiments but the effects of small enclosures on predators, prey, and their interactions, compromise their relevance to field populations. I examined the effects of Aurelia size on the utility of impermeable mesocosms deployed in highly stable water columns. Aurelia of all sizes (5‐29 cm bell diameter) were observed adhered to walls. Individuals larger than 10 cm adhered to walls in disproportionately high numbers, experienced a significant decline in mean size, and incurred physical damage at greater rates, than those less than 10 cm. These results demonstrate that, at least for impermeable walled mesocosms deployed in low turbulence environments, larger enclosures will not necessarily (i) ameliorate wall effects for animals of the size typically manipulated in microcosms and (ii) make enclosures suitable for manipulating Aurelia larger than those normally enclosed in microcosms. The mechanism proposed to explain adhesion suggests that enclosure walls alter the hydrodynamics of fluid flow around Aurelia, which may have implications for estimating the predation impact of these animals since the hydrodynamics of feeding and swimming have co-evolved.

Variable N-Factor Method for Transition Prediction in Three-Dimensional Boundary Layers

Linear amplitude methods are presented for estimating the location of transition caused by crossflow instabilities, intended for moderate- to low-turbulence environments. A linear amplitude-based method combines receptivity, linear growth, and an amplitude correlation for predicting transition. Information about the model surface finish (and/or suction distribution) and the freestream disturbance environment accounted for through the receptivity process. The variable N-factor method is presented as a limiting case, following simplifying assumptions about the receptivity. Transition N factors are presented as a function of the surface roughness

Fossil analogues of present-day Cladocora caespitosa coral banks: Sedimentary setting, dwelling community, and taphonomy (Late Pliocene, W Mediterranean)

Cladocora caespitosa is a common zooxanthellate, ahermatypic, constructional scleractinian coral in shallow waters of the present-day Mediterranean. Extensive coral banks in Upper Pliocene shallow marine deposits of the Almeria-Nijar Basin (SE Spain) contain the same species. These banks occur on debris-flow conglomerates deposited in a fan delta, or on bioclastic accumulations interpreted as storm deposits. Direct relationships of coral beds with coastal facies indicate that C. caespitosa colonized shallow settings near the paleocoast, probably not deeper than 20–30 m. Low turbulence allowed corals to colonize substrates, which remained stable for long periods. Activity of organisms in the coral community, storms, and detritic discharges from the fan delta were the most significant mechanisms disturbing the coral development. The hard substrata provided by coral banks promoted colonization by cemented and epibyssate organisms. Coral banks marked maximum flooding surfaces at the end of transgressive systems tracks. They were suddenly buried by sediment input into the basin. Taphonomic signatures measured on components of the coral bank communities indicate a low turbulence environment, probably a bay. The low hydraulic energy further inhibited post-burial reworking, thus promoting the in situ preservation of a great part of the organisms inhabiting the bioconstructions.

Investigation of the mechanisms of low-frequency wind noise generation outdoors

Simultaneous measurement of wind noise and the instantaneous wind speed were performed for bare and screened microphones outdoors. Analysis of these measurements demonstrates that the dominant source of pressure fluctuations at the microphone outdoors is the intrinsic turbulence in the flow. This is in contrast to the results of measurements performed in low-turbulence environments by Hosier and Donavan [Natl. Bur. Stand. Rpt. NBSIR79-1599 (Jan. 1979)] and by Strasberg [J. Acoust. Soc. Am. 83, 544–548 (1988)]. For low-turbulence conditions the fluctuating wake of the screen is the dominant noise source. This finding has important implications for windscreen design for outdoor measurements since the principles described by Hosier and Donavan apply only to low-turbulence conditions.

An analysis of low-frequency wind noise in turbulent environments.

Simultaneous measurement of wind noise and the instantaneous wind speed were performed for bare and screened microphones outdoors. Analysis of these measurements demonstrates that the dominant source of pressure fluctuations at the microphone outdoors is the intrinsic turbulence in the flow. This is in contrast to the results of measurements performed in low turbulence environments by Hosier and Donavan and by Strasberg. For low turbulence conditions the fluctuating wake of the screen is the dominant noise source. This finding has important implications for windscreen design for outdoor measurements since the principles described by Hosier and Donavan apply only to low turbulence conditions.