Continuous Turbulence Research Articles

A demonstration of 24-hour continuous optical turbulence monitoring in a city

A demonstration of 24-hour continuous optical turbulence monitoring in a city

Numerical Study of Vortex Effect on Splitter Plate under Turbulence Flow over Circular Cylinder

Vortex shedding is commonly observed in both natural and artificial situations. Two key variables, the blockage ratio and the Reynolds number, determine the flow characteristics around a confined bluff body. The goal of the current study was to apply numerical simulation to examine the development of vortices in a continuous turbulence flow at the distanced position of a single splitter plate. As a starting point, the flow around a fixed circular cylinder and plate is examined at various spaced position ratios, where *L ratios are defined as the distance between the cylinder's centre and the plate's front edge. In the wake of the cylinder, when *L is raised, positive and negative vortices are generated. The pressure distribution following the vortex sheddingcore strike is felt at the plate face tip (starting edge). Compared to the other two positions, the CL created by L2 is larger and receives better cortex hits.

Evaluation of the Planetary Boundary Layer Height From ERA5 Reanalysis With MOSAiC Observations Over the Arctic Ocean

AbstractThe planetary boundary layer height (PBLH) is a crucial indicator reflecting the region of the atmosphere characterized by continuous turbulence. Here, we use radiosonde and surface meteorological observations (4–7 times per day, year‐round measurements) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition to derive the PBLH (PBLHMOSAiC), and further evaluate the PBLH from the ERA5 reanalysis (PBLHERA5). Comparisons between PBLHMOSAiC and PBLHERA5 from different perspectives reveal that: (a) The overestimation of PBLHERA5 when the sea ice concentration is >90% is significant with the centered root mean squared error reaching up to 201 m; (b) The difference between the two products is notably pronounced in cold seasons, while it is comparatively diminished in warm seasons; (c) In neutral boundary layers, differences in PBLHERA5 are larger compared with stable and convective boundary layers. In addition, the analysis of error sources indicates that the bias of PBLHERA5 is sensitive to the bias of vertical thermal structure and wind speed profiles in ERA5 data sets in all conditions. Finally, we find a Random Forest model effectively reduces the bias of PBLHERA5 with the index of agreement reaching up to 0.71 in the test data set, while a multiple linear regression demonstrates comparable performance to the Random Forest model.

Turbulence in Indian aviation financing sector: time to understand and implement the Cape Town regime in the true spirit

Abstract India, being a vast country with middle-income population, requires speedy and economic means of transportation for connecting its different parts. With rail and road transportation not having immense success in providing speedy means of transportation, aviation connectivity is of prime importance to India. Unfortunately, the Indian aviation sector is having a disastrous run over the years with several big players ending up in bankruptcy. Added to this, several Indian laws stand as impediments to enforcing the rights of financiers in the aviation sector. Accordingly, the financiers are not willing to take the risk of investing in the Indian aviation sector. This issue has been continuing even after India has become a party to the Cape Town regime relating to aviation financing in 2008. The failure to implement the Cape Town regime is the chief reason for continued turbulence in Indian aviation financing. Hence, a probe into the Cape Town regime relating to aviation financing with a view to implement it in the true spirit attains great significance in India.

A comparison of next-generation turbulence profiling instruments at Paranal

ABSTRACT A six-night optical turbulence monitoring campaign has been carried at Cerro Paranal observatory in 2023 February and March to facilitate the development and characterization of two novel atmospheric site monitoring instruments – the ring-image next-generation scintillation sensor (RINGSS) and 24-h Shack Hartmann image motion monitor (24hSHIMM) in the context of providing optical turbulence monitoring support for upcoming 20–40 m telescopes. Alongside these two instruments, the well-characterized Stereo-SCIDAR and 2016-MASS-DIMM were operated throughout the campaign to provide data for comparison. All instruments obtain estimates of optical turbulence profiles through statistical analysis of intensity and wavefront angle-of-arrival fluctuations from observations of stars. Contemporaneous measurements of the integrated turbulence parameters are compared and the ratios, bias, unbiased root mean square error, and correlation of results from each instrument assessed. Strong agreement was observed in measurements of seeing, free atmosphere seeing, and coherence time. Less correlation is seen for isoplanatic angle, although the median values agree well. Median turbulence parameters are further compared against long-term monitoring data from Paranal instruments. Profiles from the three small-telescope instruments are compared with the 100-layer profile from the stereo-SCIDAR. It is found that the RINGSS and SHIMM offer improved accuracy in characterization of the vertical optical turbulence profile over the MASS-DIMM. Finally, the first results of continuous optical turbulence monitoring at Paranal are presented which show a strong diurnal variation and predictable trend in the seeing. A value of 2.65 arcsec is found for the median daytime seeing.

Control parameter optimization of underwater gliders for turbulence observation

Turbulent mixing plays an important role in shaping the circulation and distribution of heat and carbon within the climate system. Underwater gliders are ideal turbulence observation platforms, but appropriate control parameters are required for them to achieve high-precision and large-scale continuous turbulence measurement, for which speed and endurance are two important indicators. Taking these indicators as the optimization objectives, this study establishes an optimization model for the control parameters of underwater gliders, which integrates two gliding strategy models, a dynamic model, and an energy consumption model. The multi-objective optimization of both conventional gliding strategy and our pitch adjustment strategy is performed with non-dominated sorting genetic algorithm-II to obtain the optimal control parameters. After the optimization, both gliding strategies can achieve an ideal gliding speed for turbulence observation, with the gliding range increased by more than 6% in the diving phase and more than 10% in the climbing phase. The proposed optimization model is verified to be effective with a sea trial performed by Petrel-L underwater glider. After proper modifications, the proposed method is expected to be further applied to other types of gliders.

Experimental and Numerical Study on the Aerodynamic Admittance of Twin-Box Bridge Decks in Sinusoidal Gusts and Continuous Turbulence

Experimental and Numerical Study on the Aerodynamic Admittance of Twin-Box Bridge Decks in Sinusoidal Gusts and Continuous Turbulence

Energy-Harvesting Strategy Investigation for Glider Autonomous Soaring Using Reinforcement Learning

Birds and experienced glider pilots frequently use atmospheric updrafts for long-distance flight and energy conservation, with harvested energy from updrafts serving as the foundation. Inspired by their common characteristics in autonomous soaring, a reinforcement learning algorithm, the Twin Delayed Deep Deterministic policy gradient, is used to investigate the optimal strategy for an unpowered glider to harvest energy from thermal updrafts. A round updraft model is utilized to characterize updrafts with varied strengths. A high-fidelity six-degree-of-glider model is used in the dynamic modeling of a glider. The results for various flight initial positions and updraft strengths demonstrate the effectiveness of the strategy learned via reinforcement learning. To enhance the updraft perception ability and expand the applicability of the trained glider agent, an extra wind velocity differential correction module is introduced to the algorithm, and a strategy symmetry method is applied. Comparison experiments regarding round updraft, the Gedeon thermal model, and Dryden continuous turbulence indicate the crucial role of the further optimized methods in improving the updraft-sensing ability of the reinforcement learning glider agent. With optimized methods, a glider trained in a simplified thermal updraft with a simple training method can have more effective flight strategies.

Intelligent feedforward gust alleviation based on neural network

This paper proposes a neural network-based intelligent feedforward gust alleviation framework, which includes a neural network identification model and a neural network controller. A neural network training dataset is formed by collecting flight data and the gust data encountered during the aircraft flight. A neural network identification model is first trained to accurately predict the aircraft’s output. Then, based on the output of the identification model and the collected flight data, the parameters of the time-delay neural network controller are obtained through a learning process. The simulation results show that the designed intelligent controller has good gust alleviation effects for both continuous turbulence excitation and discrete gust excitation. For example, when the aircraft is 40000 kg and the flight speed is 0.81Ma, the controller achieves a 67.82% reduction in wingtip acceleration and a 35.90% reduction in center of mass acceleration under continuous turbulence excitation. When considering the measurement uncertainties, such as noise existing in the collected data, the trained controller can still achieve an acceptable gust alleviation effect. Finally, considering a flight in which the aircraft mass is constantly changing, the intelligent controller, which continuously learns from new flight data, maintains a good gust alleviation effect throughout the flight.

Analysis of urban turbulence intensity observed by Beijing 325-m tower and comparison with the IEC turbulence model for small wind turbines

The accurate assessment of turbulence intensity is crucial for the effective utilization of urban wind energy. However, the Normal Turbulence Model (NTM) prescribed by the IEC standard has not been adequately evaluated for its applicability in urban environments. To address this gap, we analyze one-year continuous turbulence observations collected at multiple levels on a 325-m meteorological tower in Beijing. The results show that: the turbulence intensity follows the Johnsonsb distribution instead of the Normal distribution in the IEC standard; it has significant diurnal variation and piecewise power-law vertical variation; the NTM underestimates turbulence intensity at most times and heights. A new turbulence intensity model with an exponential form is proposed, which significantly outperforms the NTM. Further, the exponential model fits the observations better than power-law model that outperforms the NTM. In terms of the fitting errors to the measurements, the full-year, monthly, and hourly RMSE (MAE) of this model are reduced on average by 51.81% (54.31%), 33.04% (34.38%) and 29.46% (28.24%) compared to that of the power-law model. These findings will contribute to the revision of the IEC standards governing the safe operation of small wind turbines in complex wind environments such as urban areas.

The characteristics of atmospheric boundary layer height over the Arctic Ocean during MOSAiC

Abstract. The important roles that the atmospheric boundary layer (ABL) plays in the central Arctic climate system have been recognized, but the atmospheric boundary layer height (ABLH), defined as the layer of continuous turbulence adjacent to the surface, has rarely been investigated. Using a year-round radiosonde dataset during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we improve a Richardson-number-based algorithm that takes cloud effects into consideration and subsequently analyze the characteristics and variability of the ABLH over the Arctic Ocean. The results reveal that the annual cycle is clearly characterized by a distinct peak in May and two respective minima in January and July. This annual variation in the ABLH is primarily controlled by the evolution of the ABL thermal structure. Temperature inversions in the winter and summer are intensified by seasonal radiative cooling and warm-air advection with the surface temperature constrained by melting, respectively, leading to the low ABLH at these times. Meteorological and turbulence variables also play a significant role in ABLH variation, including the near-surface potential temperature gradient, friction velocity, and turbulent kinetic energy (TKE) dissipation rate. In addition, the MOSAiC ABLH is more suppressed than the ABLH during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment in the summer, which indicates that there is large variability in the Arctic ABL structure during the summer melting season.

A critical analysis of turbulence modulation in particulate flow systems: a review of the experimental studies

Abstract In multiphase particulate systems, the turbulence of the continuous phase (gas or liquid) is modulated due to interactions between the continuous phase and the suspended particles. Such phenomena are non-trivial in the essence that addition of a dispersed phase to a turbulent flow complicates the existing flow patterns depending on the physical properties of the particles leading to either augmentation or attenuation of continuous phase turbulence. In the present study, this aspect has been comprehensively analysed based on the available experimental data obtained from the well-studied turbulent flow systems such as channel and pipes, free jets and grids. Relevant non-dimensional parameters such as particle diameter to integral length scale ratio, Stokes number, particle volume fraction, particle momentum number, and particle Reynolds number have been utilised to characterise the reported turbulence modulation behavior. Some limitations of these commonly used dimensionless parameters to characterise turbulence modulation are discussed, and possible improvements are suggested.

Deviation from a Continuous and Universal Turbulence Cascade in NGC 6334 due to Massive Star Formation Activity

We use molecular line data from the Atacama Large Millimeter/submillimeter Array, Submillimeter Array, James Clerk Maxwell Telescope, and NANTEN2 to study the multiscale (∼15–0.005 pc) velocity statistics in the massive star formation region NGC 6334. We find that the nonthermal motions revealed by the velocity dispersion function (VDF) stay supersonic over scales of several orders of magnitude. The multiscale nonthermal motions revealed by different instruments do not follow the same continuous power law, which is because the massive star formation activities near central young stellar objects have increased the nonthermal motions in small-scale and high-density regions. The magnitudes of VDFs vary in different gas materials at the same scale, where the infrared dark clump N6334S in an early evolutionary stage shows a lower level of nonthermal motions than other more evolved clumps due to its more quiescent star formation activity. We find possible signs of small-scale-driven (e.g., by gravitational accretion or outflows) supersonic turbulence in clump N6334IV with a three-point VDF analysis. Our results clearly show that the scaling relation of velocity fields in NGC 6334 deviates from a continuous and universal turbulence cascade due to massive star formation activities.

Microstructure Turbulence Measurement in the Northern South China Sea from a Long-Range Hybrid AUV.

This study describes the development of a long-range hybrid autonomous underwater vehicle (AUV) for ocean turbulence measurement. It is a unique instrument, combining the characteristics of the conventional AUV and the buoyancy-driven glider, with a variety of flexible motion modes, such as cruise mode, glider mode, drift mode, and combination of multiple motion modes. The hybrid AUV was used for continuous turbulence measurement in the continental slope of the northern South China Sea in 2020. A total of ten continuous profiles were completed covering a horizontal span of 25 Km and a depth of 200 m. The hybrid AUV was operated in the combined glider and cruise mode. The hybrid AUV's flight performance was stable and satisfied the requirement for turbulence observation. The measured velocity shears from both probes were in good agreement, and the noise-reduced shear spectra were in excellent agreement with the Nasmyth spectrum. The water column in the study area was highly stratified, with a thick thermocline. The dissipation rate (ε) varied from 1.41 × 10-10 to 4.18 × 10-7 W·kg-1. In the surface mixed layer, high values of ε (10-9∼10-8 W·kg-1) were observed toward the water surface. In the thermocline, ε was 10-9.5∼10-9 W·kg-1, which was smaller than the level of the surface mixed layer. This result was mainly because of the strong "barrier"-like thermocline, which damped the transmission of wind and heat energy from the surface mixed layer to the deep layer. Overall, this study demonstrates the utility of hybrid AUVs for collecting oceanic turbulence measurements. They are a powerful addition to traditional turbulence instruments, as they make it possible to survey large areas to obtain high-quality and high-resolution data in both vertical and horizontal directions over long durations.

Evaluation of the controllability of a remotely piloted high-altitude platform in atmospheric disturbances based on pilot-in-the-loop simulations

In the context of the project HAP, the German Aerospace Center (DLR) is currently developing a solar-powered high-altitude platform that is supposed to be stationed in the stratosphere for 30 days. The development process includes the design of the aircraft, its manufacturing and a flight test campaign. Furthermore, a high-altitude demonstration flight is planned. While the high-altitude flight will be performed using a flight control and management system, during take-off and landing and at the beginning of the low-altitude flight test campaign, the aircraft will be remotely piloted. The aircraft has a wing span of 27 m and operates at extremely low airspeeds, being in the magnitude of around 10 m/s equivalent airspeed, and is therefore profoundly susceptible to atmospheric disturbances. This is particularly critical at low altitudes, where the airspeed is lowest. Hence, both time and location for take-off, landing or low-altitude flight test campaigns need to be selected thoroughly to reduce the risk of a loss of aircraft. In this regard, the knowledge about the operational limits of the aircraft with respect to atmospheric conditions is crucial. The less these limits are known, the more conservative the decision about whether to perform a flight on a certain day or not tends to be. On the contrary, if these limits have been adequately investigated, the amount of days and locations that are assessed as suitable for performing a flight might increase. This paper deals with a pilot-in-the-loop simulation campaign that is conducted to assess the controllability of the high-altitude platform in atmospheric disturbances. Within this campaign, the pilots are requested to perform practical tasks like maintaining track or altitude, flying a teardrop turn or performing a landing while the aircraft is subject to different atmospheric disturbances including constant wind, wind shear, continuous turbulence, and discrete gusts of different magnitudes. This paper describes the desktop simulator used for the campaign, outlines the entity of investigated test points and presents the assessment method used to evaluate the criticality of the respective disturbances. Finally, a set of restrictions on the acceptable wind conditions for the high-altitude platform are found. The underlying limits comprise a constant wind speed of 3.0 m/s in any direction, except during landing, maximum wind shear of 0.5 text { m/s}^{2} and gusts with peak speeds of 1.5 to 2.0 m/s, depending on the direction.

COMPARISON OF TWO METHODS TO CALCULATE EXTERNAL LOADS AT FLIGHT IN CONTINUOUS TURBULENCE

The external loads from the continuous turbulence on the elastic high aspect ratio wing of the transport category aircraft are calculated by Dynamics of Turbulence Air (DTA) and Interactive Multidisciplinary Aircraft Design (IMAD) methods. The response to continuous turbulence was determined taking into account the requirements of CS-25.341(b). The model of the aircraft structure is directed by symmetrical spatial beam schematization. Determination of aerodynamic forces and moments was performed using the methods of linear computational aerodynamics: the panel method of Doublet-Lattice and Constant Pressures (DLM/CPM) and the method of circulation. Comparison of the results of load determination showed that, in general, the values of the loads calculated using IMAD are lower than the values calculated using DTA. Therefore, when designing an aircraft, it is advisable to combine these methods: calculate the loads using IMAD, as a more functional method, and then the loads obtained in the critical points of the calculated flight area should be confirmed using the DTA method. Thus, this study determined the difference between the results of the calculation of loads from the continuous turbulence on the elastic wing of the transport category aircraft using DTA and IMAD methods.

Density-based topology optimization of a surface cooler in turbulent flow using a continuous adjoint turbulence model

Density-based topology optimization of a surface cooler in turbulent flow using a continuous adjoint turbulence model

Investigation of load alleviation in aircraft pre-design and its influence on structural mass and fatigue

This work elaborates an aircraft pre-design process that integrates loads analysis, load alleviation, structural optimization and fatigue analysis. The consideration of maneuver and gust load alleviation in early design stages is a promising concept to reduce wing bending moments, structural mass and extend the fatigue life, as shown on two mid-range configurations: one with a backward and another one with a forward swept wing respectively. In the loads analysis, quasi-steady maneuvers and dynamic 1-cos gusts are considered. For the load alleviation, the ailerons are deflected symmetrically. While the maneuver load alleviation reacts to the commanded load factor, the gust load alleviation reacts to fluctuations in the angle of attack. With the selected loads from the simulations, the structure of the wing and horizontal tailplane (HTP) is optimized toward mass minimization. The constraints considered are material strength, buckling stability and static aeroelastic requirements. The steps comprising loads analysis and structure optimization are conducted iteratively until the wing box mass converges. The load alleviation yields a reduction of wing box mass by 2.8% on the backward and 6.1% on the forward swept wing configuration. A subsequent, qualitative fatigue analysis is carried out to compare the fatigue behaviors of the active and passive aircraft (with and without load alleviation). For the reference missions, loads due to continuous turbulence and ground-air-ground cycles are considered, and the fatigue life of the active aircraft is improved by 28% and 12% respectively, on top of the mass benefit. As a conclusion, the proposed process can serve to gain an insight into the effects of load alleviation on the design loads, mass reduction and the resulting change in the fatigue behavior of a given aircraft in the pre-design phase, before it advances to the next design stage.

Effects of zinc and iron on the abundance of Microcystis in Lake Taihu under green light and turbulence conditions.

Trace element is one of the important factors affecting the growth of Microcystis. The effects of zinc (0.4mg/L) and iron (2mg/L) on the abundance of Microcystis in Lake Taihu were investigated under continuous turbulence and green light conditions in a microcosm experiment. The study results showed that the abundance of Microcystis in the zinc treatment and the iron treatment group was 8.30% and 214% of that in the control group at the end of the experiment, respectively. The proportion of Cyanobacteria in the total phytoplankton biomass in the control, iron treatment, and zinc treatment group decreased from 99.99% at the beginning of the experiment to 13%, 18%, and 1% at the end of the experiment, respectively. At the end of the microcosm experiment, the phytoplankton community was dominated by Bacillariophyta in the control group, accounting for 63%, but it was dominated by Chlorophyta in the zinc treatment and the iron treatment group, accounting for 89% and 42%, respectively. The study results showed that under green light and turbulence, 0.4mg/L zinc remarkably decreased the abundance of Microcystis, but 2mg/L iron effectively increased the number of Microcystis and other algae. This research results provided a new idea for controlling Microcystis blooms.

Host-Region: Safe Folklore and the Negotiation of Difference In Post-Socialist Diasporas in Newfoundland

Many studies of diasporas focus on (large) locales where sizable diasporic populations provide room for group formation based on a single ethnicity. Scholars often treat such regions as representative of larger units, defining hostland in broad geopolitical categories of countries and even continents. Based on ethnographic research devoted to immigrants from postSocialist Europe and Asia to the Canadian island of Newfoundland, I propose the concept of host-region to emphasize a regional perspective in diaspora studies. The overall small newcomer population and the unique socio-cultural context of the island result in regionally-specific diasporic group-building dynamics, stimulating new Newfoundlanders to expand the notion of their people beyond likeminded co-ethnics. Safe home-region folklore, namely, select cultural expressions that reinforce a sense of unity and do not cause tensions within a group, offers points of connection. However, contrary to many studies that emphasize the notion of commonality within groups, I show that difference, reinforced by continuous turbulence in the home-region, can be equally important in group-building endeavors.