Near-surface Flow Research Articles

Partial cavity shedding on a hydrofoil resulting from re-entrant flow and bubbly shock waves

Partial cavity flows forming on a NACA0015 hydrofoil are visualized using high-speed cinematography and time-resolved X-ray densitometry. These observations reveal the underlying flow features that lead to the cloud cavity shedding. Previous studies have reported that both near-surface liquid re-entrant flow and bubbly shock waves can serve as the mechanisms causing cavity pinch-off and cloud shedding. We identify both mechanisms in the current study. The cavity shedding frequency was also examined and related to the underlying flow dynamics. The probability of re-entrant flow or bubbly shock-induced shedding processes are quantified, and the likelihood of each mechanism is shown to be a function of both the cavitation number and the Mach number of the bubbly mixture within the separated region of the cavity. When the Mach number of the two-phase mixture in the cavity exceeds unity, shock waves become the dominant mechanism that lead to large-scale cavity shedding and cloud cavitation.

Dry air intrusions link Rossby wave breaking to large-scale dust storms in Northwest Africa: Four extreme cases

Large dust storms in the Saharan desert and the subsequent transport of airborne dust over large distances are a major meteorological hazard. Several mechanisms associated to dust emission, occurring on a range of scales, have been previously documented, notably involving Rossby wave breaking and a low-level jet. However, the mechanistic link between the different features and actual dust concentrations has not been coherently established. Here, using a Lagrangian approach, and the conceptual view of extratropical cyclone airstreams, the role of the dry intrusion airstream for translating the influence of the upper-tropospheric Rossby wave perturbation to near-surface flow conductive for the highest dust concentrations is examined. To this end, four large-scale dust storms that were accompanied by dry intrusions in west Africa are studied. Data from the Copernicus Atmospheric Monitoring Service (validated against AERONET station data) are combined with atmospheric data from reanalysis and objectively-identified Lagrangian trajectories of dry intrusions. Common, coherent structures highlighting the role of dry intrusions link the upper-tropospheric Rossby wave breaks with the lower-tropospheric dry and cold jets. These conditions favor dust uplift and transport along an arc-shaped cold front trailing from a Mediterranean cyclone. Consequently, the southwest side of the front is characterized by the highest near-surface dust concentrations ahead of the dry intrusion outflow, where the Intertropical Discontinuity shifts equatorward by 3 to 7°. The northeast part of the front is, however, accompanied by southerly, warm conveyor belt-like flow transporting the dust northward to the Mediterranean, Middle East and/or Europe at mid and upper-tropospheric levels. While case-to-case variations exists, the central role of dry intrusions in all cases calls for systematic investigation of its occurrence as a predictive tool for large dust transport events.

Stability Analysis of the Volcanic Cave El Mirador (Galápagos Islands, Ecuador) Combining Numerical, Empirical and Remote Techniques

El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápagos Islands formed due to cooled near-surface lava flows. Since this natural formation is considered a tourist site, a large number of people frequent it daily; however, its safety conditions have not yet been defined by a comprehensive geotechnical study. In this research, a stability analysis was carried out by combining both empirical methodologies based on geomechanical classifications using Barton’s Q Index and the recently created Cave Geomechanical Index (CGI), and numerical modeling through the finite element method. In addition, three-dimensional modelling was performed using the remote photogrammetric technique Structure from Motion (SfM) to create the numerical calculation sections and dimensions of the different critical parts of the cave. The results of the analysis showed that there is evidence of instability and subsidence along the tunnel. Furthermore, the geotechnical parameters obtained from the different methods complemented each other, resulting in more realistic engineering representation of the subsurface environment. Finally, a graph showing the two empirical methodologies Barton’s Q Index and CGI, with the addition of the Factors of Safety (FoS) obtained from the modeling is presented.

Nanoparticle Taylor Dispersion Near Charged Surfaces with an Open Boundary.

The dispersive spreading of microscopic particles in shear flows is influenced both by advection and thermal motion. At the nanoscale, interactions between such particles and their confining boundaries become unavoidable. We address the roles of electrostatic repulsion and absorption on the spatial distribution and dispersion of charged nanoparticles in near-surface shear flows, observed under evanescent illumination. The electrostatic repulsion between particles and the lower charged surface is tuned by varying electrolyte concentrations. Particles leaving the field of vision can be neglected from further analysis, such that the experimental ensemble is equivalent to that of Taylor dispersion with absorption. These two ingredients modify the particle distribution, deviating strongly from the Gibbs-Boltzmann form at the nanoscale studied here. The overall effect is to restrain the accessible space available to particles, which leads to a striking, tenfold reduction in the spreading dynamics as compared to the noninteracting case.

Decomposition of Estuarine Circulation and Residual Stratification under Landfast Sea Ice

Abstract For Arctic estuaries that are characterized by landfast sea ice cover during the winter season, processes generating estuarine circulation and residual stratification have not yet been investigated, although some of the largest estuaries in the world belong to this class. Landfast sea ice provides a no-slip surface boundary condition in addition to the bottom boundary, such that frictional effects are expected to be increased. For this study of estuarine circulation and residual stratification under landfast sea ice, first, a simple linear analytical model is used. To include tidally varying scenarios, a water-column model is applied with a second-moment turbulence closure to juxtapose free-surface and ice-covered estuaries. Well-mixed and strongly stratified tidally periodic scenarios are analyzed by means of a decomposition of estuarine circulation into contributions from gravitational circulation, eddy viscosity–shear covariance (ESCO), surface stress, and river runoff. A new method is developed to also decompose tidal residual salinity anomaly profiles. Estuarine circulation intensity and tidally residual potential energy anomaly are studied for a parameter space spanned by the Simpson number and the unsteadiness number. These are the major results of this study that will support future scenario studies in Arctic estuaries under conditions of accelerated warming: (i) residual surface drag under ice opposes estuarine circulation; (ii) residual differential advection under ice destabilizes the near-surface flow; (iii) reversal of ESCO during strong stratification does not occur under landfast sea ice; (iv) tidal pumping (s-ESCO) contributes dominantly to residual stratification also with sea ice cover. Significance Statement Our work gives a first qualitative and quantitative understanding of how landfast sea ice cover on tidal estuaries impacts on the generation of estuarine circulation and residual stratification. Along the Arctic coasts, where some of the world’s largest estuaries are located, these processes play a significant role for the economy and ecology by means of transports of sediments, nutrients and pollutants. Due to Arctic amplification, the conditions for ice-covered estuaries are strongly changing in a way that the ice-covered periods may be shorter in the future. Our results intend to motivate field observations and realistic model studies to allow for better predicting the consequences of these changes.

A numerical investigation exploring the potential role of porous fencing in reducing firebrand impingement on homes

Firebrand impingement is a leading cause of home ignitions from wildland fire. The use of porous fencing has recently been proposed as a potential method for mitigating firebrand impingement on homes. A porous fence can act as a windbreak to alter the near-surface flow and induce particle deposition, as demonstrated in other applications, such as the use of snow fences to protect roadways from drifting snow. Conservation advocates have proposed the use of fire-resistant vegetation to act as a fence upwind of homes or subdivisions. Porous fences could also be constructed from fire-resistant materials such as metal, rock, or composites. This numerical investigation of the effectiveness of porous fencing to reduce firebrand impingement on homes conducted a series of experiments to explore the effect of porous fencing on the near-surface flow field and firebrand transport downwind of the fence. We also evaluated the sensitivity of the results to various fence, flow, and firebrand properties, including fence height, fence porosity, wind speed, firebrand source location, and firebrand size. To our knowledge, this is the first study to investigate the concept of using a fence to induce firebrand deposition upwind of homes. Our results showed that porous fencing can reduce firebrand impingement on homes by up to 35% under certain conditions; however, fencing can also increase impingement on homes. The mitigation effectiveness depended on the proximity of the firebrand source, distance between the fence and home as a function of fence height, wind speed, and firebrand size. A series of key findings and recommendations are provided.

Effect of Partial Ground and Partial Ceiling on Propeller Performance

Finite extent flat obstacles behind a propeller (“partial ground”) and ahead of the propeller (“partial ceiling”) were examined experimentally for a small-scale fixed-pitch propeller in hover. Cases included circular and annular plates, which can be summed up or superimposed. Near-surface smoke and flow visualization show a projected time-averaged streamline on the ground plate, dividing a swirling flow inboard and a radial flow outboard. The flow pattern was juxtaposed with pressure data on the ground plate. Changes in propeller thrust and power due to ground/ceiling effect were measured by a force balance and correlated with flow visualization. For a plate of diameter equal to that of the propeller, ground effect on thrust and power was comparable to that of an “infinite” plate, while the flowfield also resembles that of the infinite plate. For a plate of less than half of the propeller diameter, ground or ceiling effect was found to be negligible. Thrust and power effects for circular and respective annular plates were superimposed to determine whether the increase in thrust or decrease in power required is itself additive to the respective effects seen with the constituent obstacles. For ceiling effect, this holds but less so for ground effect. A curve fit to thrust and power data resulted in a predictive model accurate to within 6%.

Wind influence on residual circulation in Patagonian channels and fjords

Circulation in estuaries is typically considered to be driven by horizontal density gradients, called gravitational circulation, but can be modified by other forcing such as the wind. Studies have shown that wind influence can either augment or counteract density-driven residual flows in estuaries, but the temporal and spatial extent of this influence remains unknown, particularly in deep and highly stratified fjords. This study aims to fill this gap by investigating the seasonal variability in residual circulation, wind forcing, and stratification in an extensive fjord and channel system in Chilean Patagonia. Observations of current velocity and wind are supplemented by atmospheric and hydrodynamic circulation models in the Moraleda Channel, a system that connects the fjord system of Northern Patagonia to the Pacific Ocean. Results show a marked seasonality, given that the surface outflow is reversed by wind forcing during the winter, a season characterized by strong southward (up-channel) winds. This produces a near-surface flow directed up-channel in the upper ∼40 m of the water column, in opposition to the horizontal pressure gradient. Cross-channel transects revealed that the vertical structure of the along-channel residual velocity was three-layer during the winter. The near-surface (<50 m) along-channel current on the eastern side of the channel followed the wind direction (southward). Between 50 and 100 m depth the flow was out-channel and below 100 m depth the flow was again in-channel. On the western side, the along-channel residual flow was two-layer, with near surface flow directed northward (against the wind) with a return flow below (deeper than 50 m). During the spring, northward (out-channel) winds dominated and the vertical structure of the along-channel residual velocity was two-layer, augmenting the horizontal pressure gradient, which stabilized the water column, enhancing stratification, inhibiting mixing and elevated gravitational circulation.

A CFD study of the effects of combined impurities, ground temperature, and topography upon the consequence distances and plume shapes generated by CO2 release from CCS pipeline failure.

In the carbon capture and storage (CCS) infrastructure, the risk of a high-pressure buried pipeline rupture possibly leads to catastrophic accidents due to the release of tremendous amounts of carbon dioxide (CO2). Therefore, it is crucial to conduct an in-depth study on CO2 atmospheric dispersion when developing CO2 pipeline. In fact, the CO2 captured from diverse industrial processes may contain a variety of impurities. The combined effect of the toxicities of the multiple impurities increases the risk, which has usually been ignored by previous studies. In this paper, computational fluid dynamics (CFD) technology is applied to investigate the influence of hazardous chemicals on CO2 stream dispersion under different meteorological, complex terrain features, and ground temperature condition. In addition, the effect of combined toxic impurities on consequence distance was also investigated comprehensively. It was found that complex conditions affected the near-surface flow field, and obstacles enhanced the lateral dispersion of CO2. Compared to 288K ground temperature, the plume area inside the 50,000 ppmv CO2 boundary decreased by 8.2%. The hazardous effects of combined toxic impurities became significant compared to a single toxic impurity. This study may furnish a viable assessment technique for the risks associated with CCS.

From Macro- to Microscale: A combined modelling approach for near-surface wind flow on Mars at sub-dune length-scales.

The processes that initiate and sustain sediment transport which contribute to the modification of aeolian deposits in Mars' low-density atmosphere are still not fully understood despite recent atmospheric modelling. However, detailed microscale wind flow modelling, using Computational Fluid Dynamics at a resolution of &lt;2 m, provides insights into the near-surface processes that cannot be modeled using larger-scale atmospheric modeling. Such Computational Fluid Dynamics simulations cannot by themselves account for regional-scale atmospheric circulations or flow modifications induced by regional km-scale topography, although realistic fine-scale mesoscale atmospheric modeling can. Using the output parameters from mesoscale simulations to inform the input conditions for the Computational Fluid Dynamics microscale simulations provides a practical approach to simulate near-surface wind flow and its relationship to very small-scale topographic features on Mars, particularly in areas which lack in situ rover data. This paper sets out a series of integrated techniques to enable a multi-scale modelling approach for surface airflow to derive surface airflow dynamics at a (dune) landform scale using High Resolution Imaging Science Experiment derived topographic data. The work therefore provides a more informed and realistic Computational Fluid Dynamics microscale modelling method, which will provide more detailed insight into the surface wind forcing of aeolian transport patterns on martian surfaces such as dunes.

Cutaneous Microcirculatory Flow Sensing for Flap Monitoring in a Porcine Model of Arterial and Venous Occlusion

PURPOSE: Cutaneous devices employing near infrared spectroscopy (NIRS) for continuous free flap tissue oxygenation (StO2) monitoring have several limitations. Confounding factors like skin pigmentation and thickness, ambient light incursion, and inconsistency at the skin-sensor interface can alter StO2 measurements. As an alternative means for peripheral free flap monitoring, we present a novel probe that calculates microvascular blood flow velocity by measuring tissue thermal diffusion. This device is cutaneous, wireless and not subject to the same confounding variables as NIRS. METHOD: The cutaneous perfusion sensor includes 5 thermistors, a Bluetooth chip, and small battery mounted on circuit board. A thermal actuator (4-mm diameter) delivers a small amount of thermal power to the surface of the skin. The device is cutaneously mounted with a silicone acrylate adhesive onto target tissue. The diffusion of heat is measured and analytically converted into a measurement of microcirculatory blood flow velocity. Rapid thermal diffusion occurs in situations of high tissue perfusion, while slower thermal diffusion indicates slower or absent near-surface blood flow. This device was tested alongside Vioptix T.Ox in a porcine rectus abdominus myocutaneous flap model of arterial and venous pedicle occlusion. After flap elevation, the flow device and T.Ox were applied to the skin. Acland clamps were alternately applied to the flap artery and veins to achieve conditions of flap ischemia and congestion, each lasting 15 minutes, with a 15 minute intervening recovery period. In total, 10 devices were tested on 16 flaps in 10 separate pigs over 60 unique vaso-occlusive events. RESULTS: Continuous monitoring was accomplished and no connection loss was observed with either T.Ox or the novel devices. Flow measurements were responsive to both ischemia and congestion, and returned to baseline during recovery periods. Flow measurements corresponded with vascular occlusion and release, and closely followed StO2. Cross-correlation at zero lag showed agreement between these two sensing modalities, ranging from 0.76 to 0.83. Two novel devices tested simultaneously on the same flap showed only minor variations in flow measurements, with a cross-correlation of 0.87. CONCLUSION: This novel probe is capable of detecting changes in tissue microcirculatory blood flow. This device performed well in a swine model of flap ischemia and congestion, and shows promise as a potentially useful clinical tool. Because flow measurements are not affected by the variable lighting and light absorbing properties of tissue, this monitoring strategy has the potential to provide more consistent information than NIRS. Future studies will characterize longevity of the device over a period of several days.

Application of optical velocity measurements including a novel calibration technique for micron-resolution to investigate the gas flow in a model experiment for crystal growth

An important step in the fabrication of many modern semiconductor materials and devices is the crystal growth process. These processes take place in high-temperature furnaces using inert gas and other atmospheres. The flow in the gas phase influences the transport of crystal components, dopants and impurities and hence has a significant impact on the grown crystals. In this work, we study the flow in a simplified model of a crystal growth furnace. This model is made of PMMA filled with a Diesel mixture as a model fluid to match the refractive index of PMMA and to allow for measurements in the complex geometry. The comparability to the flow in a real furnace is ensured by matching the Reynolds number. Two optical measurement methods, Particle Image Velocimetry (PIV) and the Laser Doppler Velocity Profile Sensor (LDV-PS) are used to investigate the global flow field as well as the small-scale flow structures. A calibration model is developed for the LDV-PS to reduce systematic measurement errors caused by the refractive index of the model fluid from up to 1% to less than 0,1%. The results obtained in this study improve the understanding of the gas flow behavior inside a crystal growth furnace and provide reference data for simulation. The first analysis shows a highly unsteady flow with unexpected flow direction along the crystal and melt surfaces. The near-surface flow patterns are of particular relevance in crystal growth because of their large influence on the local heat and mass transport during the crystallization process.

Modeling Active Colloids: From Active Brownian Particles to Hydrodynamic and Chemical Fields

Active colloids are self-propelled particles moving in viscous fluids by consuming fuel from their surroundings. Here, we review the numerical and theoretical modeling of active colloids propelled by self-generated near-surface flows. We start with the generic model of an active Brownian particle taking into account potential forces and effective pairwise interaction, which include hydrodynamic and phoretic interactions. Also, the squirmer as a model microswimmer is introduced. We then discuss the explicit modeling of self-generated fluid flow and the full hydrodynamic-chemical coupling. Finally, we discuss recent advances in selected topics in which modeling of active colloids is used to study motion in crowded and complex environments, microrheology in active baths, active colloidal engines, adaptive responses of active colloids with the help of machine learning techniques, as well as effects of colloid and fluid inertia.

Soft-robotic ciliated epidermis for reconfigurable coordinated fluid manipulation.

The fluid manipulation capabilities of current artificial cilia are severely handicapped by the inability to reconfigure near-surface flow on various static or dynamically deforming three-dimensional (3D) substrates. To overcome this challenge, we propose an electrically driven soft-robotic ciliated epidermis with multiple independently controlled polypyrrole bending actuators. The beating kinematics and the coordination of multiple actuators can be dynamically reconfigured to control the strength and direction of fluid transportation. We achieve fluid transportation along and perpendicular to the beating directions of the actuator arrays, and toward or away from the substrate. The ciliated epidermises are bendable and stretchable and can be deployed on various static or dynamically deforming 3D surfaces. They enable previously difficult to obtain fluid manipulation functionalities, such as transporting fluid in tubular structures or enhancing fluid transportation near dynamically bending and expanding surfaces.

Phreatic volcanic eruption preceded by observable shallow groundwater flow at Iwo-Yama, Kirishima Volcanic Complex, Japan

It is difficult to forecast phreatic eruptions because they are often characterised by an abrupt onset at shallow depths beneath volcanoes. Here we show that temporal changes in the tilt, tremor, and horizontal electric field have occurred repeatedly near the vent of a small phreatic eruption at Iwo-Yama, Kirishima Volcanic Complex, Japan. Such geophysical changes were observed 13 times, with one of these events occurring immediately before the onset of the 2018 phreatic eruption. These observations suggest that shallow hydrothermal intrusions, which are observed as tilt changes with tremors, commonly induce near-surface cold groundwater flow, which is observed as electric-field changes. Near-surface groundwater flows towards the active vent, potentially inhibiting a phreatic eruption. However, explosive phreatic eruptions occur when the intrusion is shallow and cold groundwater flow is depleted. The near-surface groundwater is key in controlling the occurrence of phreatic eruptions and can be monitored using electric-field measurements.

Subinertial flow patterns in a tropical coral reef system of the southwestern gulf of Mexico

One-year subinertial flow profiles and near-bottom temperatures were recorded in a tropical coral reef of the southwestern Gulf of Mexico to determine whether baroclinicity affects flow distributions. The subinertial flow at four sites was predominantly influenced by three empirical modes of variability. The first mode (explaining 78% of the variance) was mostly associated to wind stress (r = 0.62). Its temporal variability had greatest energy during the northerly wind season (October–May), related to atmospheric cold fronts, at periods of 2–10 days and at 20–30 days. Mode 2 (with 6% of the variance) was related to sea-level slopes, linked also to northerly wind events; this mode induced an anticyclonic circulation around the reefs, although a less intense cyclonic circulation was also observed. Mode 3 (with 5% of the variance) was associated to a baroclinic pressure gradient that drove bidirectional flow profiles: Near-surface flows moving in opposite direction to near-bottom flows. Mode 3 dominated in the vertically stratified summer (June–September), the rainy season, but it was also occasionally observed during northerly winds. Near-bottom summer intrusions of relative cold water were baroclinically driven, linked to Mode 3, and unrelated to Ekman dynamics. Modes 2 and 3 of variability described additional flow distributions relative to the behavior already proposed for the reefs on the southwestern continental shelf of the Gulf of Mexico.

Field Observations of Near-Surface Wind Flow Across Expressway Embankment on the Qinghai–Tibet Plateau

Crushed rock layers (CRLs), ventilation ducts (VDs) and thermosyphons are air-cooling structures (ACSs) widely used for maintaining the long-term stability of engineered infrastructures in permafrost environments. These ACSs can effectively cool and maintain the permafrost subgrade’s frozen state under climate warming by facilitating heat exchange with ambient air in cold seasons. As convection is a crucial working mechanism of these ACSs, it is imperative to understand the near-surface wind flow (NSWF) across a constructed infrastructure, such as an embankment. This article describes a yearlong field observation of the NSWF across an experimental expressway embankment, the first of its kind on the Qinghai–Tibet Plateau (QTP). The wind speed and direction along a transect perpendicular to the embankment on both the windward and leeward sides and at four different heights above the ground surface were collected and analyzed. The results showed that the embankment has a considerable impact on the NSWF speed within a distance of up to ten times its height, and in the direction on the leeward side. A power law can well describe the speed profiles of NSWF across the embankment, with the power-law indices (PLIs) varying from 0.14 to 0.40. On an annual basis, the fitted NSWF PLI far away from the embankment was 0.19, which differs substantially from the values widely used in previous thermal performance evaluations of ACSs on the QTP. Finally, the significance of the NSWF to the thermal performance of the ACSs, particularly the CRLs and VDs, in linear transportation infrastructure is discussed. It is concluded that underestimating the PLI and neglecting wind direction variations may lead to unconservative designs of the ACSs. The results reported in this study can provide valuable guidance for infrastructure engineering on the QTP and other similar permafrost regions.

Observations and Parametrization of the Turbulent Energy Dissipation Beneath Non-Breaking Waves

Here, for non-breaking short surface waves, we have experimentally determined the value of the turbulent eddy viscosity νT or its ratio νT*≡νT/ν, where ν is the water kinematic viscosity. The non-breaking wave-generated turbulent eddy viscosity νT was found to depend on the ratio of the wave period, T, to the microscale Kolmogorov time scale, τη. Our observations were consistent with νT*=1.46·(T/τη)−2.6 when (T/τη)&lt;0.9. That implied that the νT*∝ϵ−1.3, where ϵ is the background turbulent energy dissipation rate. The near-surface turbulent flow associated with non-breaking waves was characterized by a short inertial subrange. The background turbulence appears to modulate the amount of energy the non-breaking waves dissipate locally and, consequently, the wave’s decay rate. Our results imply that the background turbulent flow acts as a lubricant, permitting waves to propagate further when traveling over a more energetic turbulent background flow. Our results have implications for the modeling of oceanic wave propagation or the air–sea exchange processes.

Experimental investigation of the near-surface flow dynamics in downburst-like impinging jets

Downbursts are strong downdrafts that originate from thunderstorm clouds and create vigorous radial outflows upon hitting the ground. This study is part of the comprehensive experimental research on downburst outflows produced as large-scale impinging jets in the WindEEE Dome simulator at Western University, Canada. The 2800 tests carried out form the largest database of experimental measurements on downburst winds developed thus far, which is made available to the public in its whole and described in detail in a complementary study. Therefore, the current manuscript merely focuses on the data post-processing outcomes and interpretation of results from a selected subset of measurements. Impinging jets are here simulated as transient phenomena in which velocity time series are characterized by a sudden ramp-up of velocity, followed by the velocity peak, a short statistically stationary region, and the final velocity slowdown, as it is expected to occur in the actual downbursts. A dominant velocity peak that was systematically observed in all velocity records is associated with the radial advection of the primary vortex in the outflow. Depending on the radial distance from the downdraft, the primary vortex was sometimes preceded by a secondary, much smaller, vortex close to the surface. Vertical profiles of mean velocity and turbulence intensity are for the first time characterized through the extent of a downburst-like event in the spatiotemporal domain. Particularly, these profiles rapidly change in relation to the passage of the primary vortex and consequent variation of the surface layer thickness. This study lays out a foundation for an experimental model of non-stationary downburst outflows to come.

Statistical characteristics and complexity of stochastic wind speeds in near-surface flow fields

Statistical characteristics of meteorological elements play an important role in climate assessment. The statistical study of wind speeds in near-surface flow fields is mainly concerned by wind energy. Determinacy and stochasticity of wind speeds are important for wind power generation system. Probability density function (PDF) is the main approach to describe wind speed distribution. Here we show a theoretical evolution pattern of statistical characteristics of stochastic wind speed system was constructed. This is simple and applicable worldwide. Poisson, gamma (or Weibull), and negative binomial distribution corresponds to the timescale of 10 min, less than one year, and many years, respectively. Downscaling functions eliminating a parameter are the distributions of the shape parameter, and statistically are the emergence of each level of system. Variations of the scale parameter characterizing thermal convection are reflected in wind speed distributions through variations of the shape parameter representing forced convection. The emergence of Poisson, gamma, and negative binomial distribution is the result of spatial interaction, spatial interaction that varies with time, and space, time and inheritable instructions, separately. Stochasticity of wind speed system is intrinsic. Static PDFs describe the deterministic statistical characteristics of stochastic wind speeds, which emphasizes that determinacy contains stochasticity. Dynamic relationships among levels of system reflect the evolution of system, which embodies constructivism. From the view of the discontinuous statistical characteristics, stochastic wind speed system is catastrophic. These results provide a new path for cross-level research of complexity science.