Aeolian saltation on Mars at low wind speeds

ABSTRACT Generally, the environmental wind speeds in urban areas are relatively low due to clustered buildings. At low wind speeds, an aerodynamic stall occurs near the blade roots of a horizontal axis wind turbine (HAWT), leading to decay of the power coefficient. The research targets to design canards with optimal parameters for a small-scale HAWT system operated at variable rotational speeds. The design was to enhance the performance by delaying the aerodynamic stall near blade roots of the HAWT to be operated at low wind speeds. For the optimal design of canards, flow fields of the sample blades with and without canards were both simulated and compared with the experimental data. With the verification of our simulations, Taguchi analyses were performed to seek the optimum parameters of canards. This study revealed that the peak performance of the optimized canard system operated at 540 rpm might be improved by ∼35%.

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Dependence of Power Characteristics on Savonius Rotor Segmentation

Energies ◽

10.3390/en14102912 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2912

Author(s):

Krzysztof Doerffer ◽

Janusz Telega ◽

Piotr Doerffer ◽

Paulina Hercel ◽

Andrzej Tomporowski

Keyword(s):

High Wind ◽

Horizontal Axis Wind Turbine ◽

Savonius Rotor ◽

Power Characteristics ◽

Wind Speeds ◽

Single Segment ◽

High Elongation ◽

Low Wind Speeds ◽

Number Of Segments ◽

Rotor Type

Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.

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Traffic Density-Related Black Carbon Distribution: Impact of Wind in a Basin Town

International Journal of Environmental Research and Public Health ◽

10.3390/ijerph18126490 ◽

2021 ◽

Vol 18 (12) ◽

pp. 6490

Author(s):

Borut Jereb ◽

Brigita Gajšek ◽

Gregor Šipek ◽

Špela Kovše ◽

Matevz Obrecht

Keyword(s):

Black Carbon ◽

Carbon Concentration ◽

Ground Level ◽

Traffic Density ◽

Carbon Distribution ◽

Wind Speeds ◽

Black Carbon Concentration ◽

Low Wind Speeds ◽

Temperature Inversions ◽

Carbon Concentrations

Black carbon is one of the riskiest particle matter pollutants that is harmful to human health. Although it has been increasingly investigated, factors that depend on black carbon distribution and concentration are still insufficiently researched. Variables, such as traffic density, wind speeds, and ground levels can lead to substantial variations of black carbon concentrations and potential exposure, which is even riskier for people living in less-airy sites. Therefore, this paper “fills the gaps” by studying black carbon distribution variations, concentrations, and oscillations, with special emphasis on traffic density and road segments, at multiple locations, in a small city located in a basin, with frequent temperature inversions and infrequent low wind speeds. As wind speed has a significant impact on black carbon concentration trends, it is critical to present how low wind speeds influence black carbon dispersion in a basin city, and how black carbon is dependent on traffic density. Our results revealed that when the wind reached speeds of 1 ms−1, black carbon concentrations actually increased. In lengthy wind periods, when wind speeds reached 2 or 3 ms−1, black carbon concentrations decreased during rush hour and in the time of severe winter biomass burning. By observing the results, it could be concluded that black carbon persists longer in higher altitudes than near ground level. Black carbon concentration oscillations were also seen as more pronounced on main roads with higher traffic density. The more the traffic decreases and becomes steady, the more black carbon concentrations oscillate.

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Optimal Control of the Positional Electric Drive and Its Implementation

Machines ◽

10.3390/machines9040070 ◽

2021 ◽

Vol 9 (4) ◽

pp. 70

Author(s):

Vladimir Dotsenko ◽

Roman Prokudin ◽

Alexander Litvinenko

Keyword(s):

Optimal Control ◽

Wind Turbine ◽

Electric Drive ◽

Minimum Energy ◽

Air Gap ◽

Synchronous Generators ◽

Capacitor Discharge ◽

Wind Speeds ◽

Minimum Energy Consumption ◽

Low Wind Speeds

The article deals with the optimal control of the positional electric drive of the stator element of a segment-type wind turbine. The calculation options charts current in the assumption of the minimum energy consumption and the implementation of line chart current using the phenomenon of capacitor discharge. The analysis of the implementation is expressed in a jump-like change in current and a triangular graph of the speed change. This article deals with small capacity synchronous wind turbine generators with a segment type stator. These units have the possibility of intentionally changing the air gap between the rotor and stator. This allows: (1) Reduce the starting torque on the rotor shaft, which will allow the rotor to pick up at low wind speeds. (2) Equivalent to change of air gap in this case is change of excitation of synchronous generators. Thus, the purpose of the article is to consider a method of excitation of generators in a segmented design, by controlling the gap with the electric drive, while providing control should be carried out with minimal losses.

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Comparison of Weibull Estimation Methods for Diverse Winds

Advances in Meteorology ◽

10.1155/2020/3638423 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Ferhat Bingöl

Keyword(s):

Wind Farm ◽

Study Data ◽

Distribution Functions ◽

Likelihood Method ◽

Estimation Methods ◽

Weibull Function ◽

Wind Speeds ◽

Low Wind Speed ◽

Low Wind Speeds ◽

Wind Distribution

Wind farm siting relies on in situ measurements and statistical analysis of the wind distribution. The current statistical methods include distribution functions. The one that is known to provide the best fit to the nature of the wind is the Weibull distribution function. It is relatively straightforward to parameterize wind resources with the Weibull function if the distribution fits what the function represents but the estimation process gets complicated if the distribution of the wind is diverse in terms of speed and direction. In this study, data from a 101 m meteorological mast were used to test several estimation methods. The available data display seasonal variations, with low wind speeds in different seasons and effects of a moderately complex surrounding. The results show that the maximum likelihood method is much more successful than industry standard WAsP method when the diverse winds with high percentile of low wind speed occur.

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Thermal comfort models for outdoor thermal comfort in warm humid climates and probabilities of low wind speeds

Journal of Wind Engineering and Industrial Aerodynamics ◽

10.1016/0167-6105(90)90331-6 ◽

1990 ◽

Vol 36 ◽

pp. 481-488 ◽

Cited By ~ 5

Author(s):

Richard Aynsley ◽

Marcus Spruill

Keyword(s):

Thermal Comfort ◽

Outdoor Thermal Comfort ◽

Wind Speeds ◽

Low Wind Speeds

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The Evaporation of Water from Helix Aspersa

Journal of Experimental Biology ◽

10.1242/jeb.41.4.783 ◽

1964 ◽

Vol 41 (4) ◽

pp. 783-792

Author(s):

JOHN MACHIN

Keyword(s):

Air Flow ◽

Complex Form ◽

Ambient Air ◽

Helix Aspersa ◽

Flat Surfaces ◽

Wind Speeds ◽

Low Wind Speeds ◽

Rate Of Evaporation ◽

Snail Helix Aspersa

1. The construction and use of a wind-tunnel apparatus is described in which measurements of evaporation under controlled conditions of temperature, humidity and air flow can be made. 2. Two mathematical formulae, applicable to evaporation in relatively low wind speeds, are described. It is suggested that a promising approach to evaporation from moist-skinned animals is provided by the application of Leighly's formula: E = K(p0-pd)c(v/x)n, where the rate of evaporation (E) is expressed in terms of the vapour pressure at the evaporating surface (p0) and in the ambient air (pd), the wind speed (v) and the length of the evaporating surface parallel to the wind (x). The constant, K, is calculated independently and the terms n and c are left for empirical determination. 3. Values of n and c for different types of evaporating surface are given together with the method used in their calculation. Those relating to flat evaporators and to the snail, Helix aspersa, are shown to differ significantly. 4. In general n increases and c decreases as the amount of air disturbance caused by the snail increases. 5. The fact that n for flat surfaces is in good agreement with previously established theory is taken as evidence that Leighly's formula may be validly applied. 6. The combined determination of n and c is introduced as a convenient assessment of a complex form in terms of air flow and evaporation.

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Rapid coral mortality following unusually calm and hot conditions on Iriomote, Japan

F1000Research ◽

10.12688/f1000research.12660.2 ◽

2018 ◽

Vol 6 ◽

pp. 1728 ◽

Cited By ~ 2

Author(s):

Andrew H Baird ◽

Sally A. Keith ◽

Erika Woolsey ◽

Ryuta Yoshida ◽

Tohru Naruse

Keyword(s):

Water Movement ◽

Sea Surface ◽

Bleaching Event ◽

Coral Mortality ◽

Average Wind Speed ◽

Common Cause ◽

Wind Speeds ◽

Average Wind ◽

The Mean ◽

Low Wind Speeds

Coral bleaching can be induced by many different stressors, however, the most common cause of mass bleaching in the field is higher than average sea surface temperatures (SST). Here, we describe an unusual bleaching event that followed very calm sea conditions combined with higher than average SST. Patterns of mortality differed from typical bleaching in four ways: 1) mortality was very rapid; 2) a different suite of species were most affected; 3) tissue mortality in Acropora spp. was often restricted to the center of the colony; 4) the event occurred early in summer. The two weeks prior to the event included 8 days where the average wind speed was less than 3 ms-1. In addition, SSTs in the weeks preceding and during the event were 1.0-1.5°C higher than the mean for the last 30 years. We hypothesize that this unusual bleaching event was caused by anoxia resulting from a lack of water movement induced by low wind speeds combined with high SST.

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