High Turbulence Levels Research Articles

Comparison of Hemodynamic Performance, Three-Dimensional Flow Fields, and Turbulence Levels for Three Different Heart Valves at Three Different Hemodynamic Conditions.

The hemodynamic performance of different prosthetic heart valves is difficult to compare among studies due to a variety of test conditions and experimental techniques. Existing studies are typically limited to one family of valves (biological or mechanical) and testing conditions of 5l/min and often lack sufficient spatial resolution. To address these limitations, a pulse duplicator with a multi-view imaging system (Tomo-PIV) was employed to investigate the three-dimensional flow field in the aortic root of three different valves: a tri-leaflet mechanical heart valve (TRIFLO, Novostia), a bi-leaflet mechanical heart valve (On-X, Artivion), and a biological heart valve (Perimount, Edwards Lifesciences). The valves were tested at low (3l/min), normal (5l/min), and elevated (7l/min) cardiac output under hypotensive (40/60mmHg), normotensive (80/120mmHg), and moderate hypertensive (105/170mmHg) pressure conditions, respectively. Compared to the Perimount, peak mean velocity was - 33%, - 24%, - 18% for the TRIFLO and - 32%, - 20%, - 11% for the On-X at low, moderate, and elevated , respectively. Corresponding peak values decreased by - 66%, - 57%, - 44% (TRIFLO) and - 60%, - 50%, - 36% (On-X). At low , was lower for Perimount (1.07cm2) than for TRIFLO (1.47cm2) and On-X (1.52cm2), while it increased for elevated to 2.75cm2 (TRIFLO) and 2.16cm2 (Perimount and On-X). For all valves, increasing led to increased flow velocities, higher and higher levels of turbulence, and the spatial influence of the valve on the flow field in the ascending aorta was extended. peaked closer to the STJ than for TRIFLO and Perimount.

Differential diffusion modelling for LES of premixed and partially premixed flames with presumed FDF

Large eddy simulations (LES) with flamelet and presumed filtered density function closure are used to simulate turbulent premixed and partially premixed hydrogen flames. Different approaches to model differential diffusion are investigated and compared. In particular, two existing models are extended to the LES framework to correct the resolved diffusive flux of the controlling variables due to differential diffusion. A lean premixed turbulent hydrogen flame in a slotted burner configuration is simulated first to compare the capability of the considered models in capturing local mixture fraction redistribution, super-adiabatic temperatures and thermo-diffusive instabilities. Results show that both models describe the formation of cellular burning structures. Next, a partially premixed lifted hydrogen flame in vitiated hot coflow is simulated to gain insight on the relevance of differential diffusion modelling at a higher turbulence level, a different combustion mode and in the presence of a complex stabilisation mechanism. Good predictions of the turbulent mixing and temperature fields are observed. Moreover, results show that the flame lift-off height has an appreciable sensitivity to the differential diffusion model. When differential diffusion is included only in the thermochemistry database, only mild effects on the predicted temperature fields, mixing and flame height are observed. On the contrary, a considerable shift of the flame base is observed when corrections are applied in the LES at the resolved level, depending on what controlling variables are considered. Further analyses reveal how the corrections of diffusive fluxes in the thermochemistry and at the LES level affect differently the flame burning mode, whose details are given throughout the paper.

Population synthesis models indicate a need for early and ubiquitous disk substructures

Context. Large millimeter surveys of star-forming regions enable the study of entire populations of planet-forming disks and reveal correlations between their observable properties. The ever-increasing number of these surveys has led to a flourishing of population study, a valuable tool and approach that is spreading in ever more fields. Population studies of disks have shown that the correlation between disk size and millimeter flux could be explained either through disks with strong substructure, or alternatively by the effects of radial inward drift of growing dust particles. Aims. This study aims to constrain the parameters and initial conditions of planet-forming disks and address the question of the need for the presence of substructures in disks and, if needed, their predicted characteristics, based on the large samples of disk sizes, millimeter fluxes, and spectral indices available. Methods. We performed a population synthesis of the continuum emission of disks, exploiting a two-population model (two-pop-py), considering the influence of viscous evolution, dust growth, fragmentation, and transport, varying the initial conditions of the disk and substructure to find the best match with the observed distributions. Disks both with and without substructure have been examined. We obtained the simulated population distribution for the disk sizes, millimeter fluxes, and spectral indices by post-processing the resulting disk profiles (surface density, maximum grain size, and disk temperature). Results. We show that the observed distributions of spectral indices, sizes, and luminosities together can be best reproduced by disks with significant substructure; namely, a perturbation that is strong enough to be able to trap particles, that is formed early in the evolution of the disk, and that is within 0.4 Myr. Agreement is reached by relatively high initial disk masses (10−2.3 M⋆ ⩽ Mdisk ⩽ 10−0.5 M⋆) and moderate levels of turbulence (10−3.5 ⩽ α ⩽ 10−2.5). Other disk parameters play a weaker role. Only opacities with a high absorption efficiency can reproduce the observed spectral indices. Conclusions. Disk population synthesis is a precious tool for investigating and constraining the parameters and initial conditions of planet-forming disks. The generally low observed spectral indices call for significant substructure, like that which planets in the mass range of Saturn to a few Jupiters would induce, to already be present before 0.4 Myr. Our results indicate that substructure, which so far has only been assessed in individual disks, is likely ubiquitous and extends to the whole population, and imply that most “smooth” disks hide unresolved substructure.

THE EVOLUTION OF CZECHIA’S SECURITY POLICY UNDER THE INFLUENCE OF THE RUSSIA-UKRAINE WAR

For now, almost all spheres of international life are in the process of transformation. A particularly high level of turbulence characterizes European security, which has faced numerous challenges over the past decade such as the migration crisis, terrorist acts, the COVID-19 pandemic, information threats, etc. Directly threatening the European Union’s eastern borders, Russia’s full-scale invasion has become one of the most crucial security challenges. In this regard, the EU and NATO member states have to review their approaches to ensuring security and stability. Due to Czechia’s membership in both of these blocs and its geographical proximity to a war zone, its security policy has undertaken changes at the current stage, which this article covered.This article defines the reasons for the evolution of the security policy of the Czech Republic. It is worth noting that due to its geographic proximity to the war zone, Czechia perceives Russia’s aggression as a direct threat to its national security. Apart from Russia’s full-scale invasion of Ukraine, the assessment of Russia’s perception of the country is influenced by the Russian military intelligence services’ involvement in the explosions at Czech weapons warehouses in 2014 and Russia’s espionage activities as well. Thus, the increasing regional tensions and the political crisis in international relations prompted the Czech Republic to revise its key security and defense files, according to which Russia and China have been defined as the main security threats.Moreover, the author concludes that support for Ukraine became part of Czechia’s security policy, where the country demonstrated its clear position and declared its intention to sign a security agreement with Ukraine. Also, it is necessary to commend the importance of Czechia’s artillery shells initiative to Ukraine. The Czech Republic has taken several practical steps to respond to security threats increasing its defense spending to 2% of GDP and investments in the defense industry, along with modernizing the military forces and diversifying energy resources in order to get rid of Russia’s dependence. Accordingly, a comprehensive approach to reacting to new security challenges and threats can minimize their impact on Czechia’s security in the future.

Direct numerical simulation of transition under free-stream turbulence and the influence of large integral length scales

Under the action of free-stream turbulence (FST), elongated streamwise streaky structures are generated inside the boundary layer, and their amplitude and wavelength are crucial for the transition onset. While turbulence intensity is strongly correlated with the transitional Reynolds number, characteristic length scales of the FST are often considered to have a slight impact on the transition location. However, a recent experiment by Fransson and Shahinfar [J. Fluid Mech. 899, A23 (2020)] shows significant effects of FST scales. They found that, for higher free-stream turbulence levels and larger integral length scales, an increase in the length scale postpones transition, contrary to established literature. Here, by performing well-resolved numerical simulations, we aim at understanding why the FST integral length scale affects the transition location differently at low- and high turbulence levels. We found that the integral length scales in Fransson and Shahinfar's experiment are so large that the introduced wide streaks have substantially lower growth in the laminar region, upstream of the transition to turbulence, than the streaks induced by smaller integral length scales. The energy in the boundary layer subsequently propagate to smaller spanwise scales as a result of the nonlinear interaction. When the energy has reached smaller spanwise scales, larger amplitude streaks results in regions where the streak growth are larger. It takes longer for the energy from wider streaks to propagate to the spanwise scales associated with the breakdown to turbulence, than for those with smaller spanwise scales. Thus, there is a faster transition for FST with lower integral length scales in this case.

Building entrepreneurial resilience during crisis using generative AI: An empirical study on SMEs

Recently, Gen AI has garnered significant attention across various sectors of society, particularly capturing the interest of small business due to its capacity to allow them to reassess their business models with minimal investment. To understand how small and medium-sized firms have utilised Gen AI-based tools to cope with the market's high level of turbulence caused by the COVID-19 pandemic, geopolitical crises, and economic slowdown, researchers have conducted an empirical study. Although Gen AI is receiving more attention, there remains a dearth of empirical studies that investigate how it influences the entrepreneurial orientation of firms and their ability to cultivate entrepreneurial resilience amidst market turbulence. Most of the literature offers anecdotal evidence. To address this research gap, the authors have grounded their theoretical model and research hypotheses in the contingent view of dynamic capability. They tested the research hypotheses using cross-sectional data from a pre-tested survey instrument, which yielded 87 useable responses from small and medium enterprises in France. The authors used variance-based structural equation modelling with the commercial WarpPLS 7.0 software to test the theoretical model. The study's findings suggest that Gen AI and EO have a significant influence on building entrepreneurial resilience as higher-order and lower-order dynamic capabilities. However, market turbulence has a negative moderating effect on the path that joins entrepreneurial orientation and entrepreneurial resilience. The results suggest that the assumption that high market turbulence will have positive effects on dynamic capabilities and competitive advantage is not always true, and the linear assumption does not hold, which is consistent with some scholars' assumptions. The study's results offer significant contributions to the contingent view of dynamic capabilities and open new research avenues that require further investigation into the non-linear relationship of market turbulence.

Airborne wind energy systems flying optimal trajectories in turbulent wind using flight path tracking

Airborne Wind Energy Systems (AWES) consist of tethered wings harvesting power from the wind. Rigid-wing (aircraft) pumping-mode AWES are considered here: they generate power during the reel-out phase and consume a fraction of this power during the reel-in phase. Those devices fly complex trajectories that require advanced control strategies. In the present work, we aim to develop a Large Eddy Simulation (LES) framework and improve the fidelity of existing models. The toolbox AWEbox is used for reference trajectories generation and control. Here the device is operated with a closed-loop control using a 6-DOF aircraft model. The aircraft is modeled using an actuator line (AL) for the wing, and the effects of the control surface are incorporated using their geometry and lift slope. The AL-based model is used to assess the robustness of the nonlinear model predictive controller against turbulence and to compare the performance between idealized conditions in AWEbox and turbulent wind conditions in the LES. The controller demonstrates high efficiency in tracking the reference trajectory and extracting the maximum power, even at high turbulence levels.

Investigation of the effect of free-stream turbulence on paired vertical-axis wind turbines using wind tunnel testing and an actuator-line model

The aerodynamic interaction of vertical-axis wind turbines (VAWTs) in paired configurations can be advantageous in wind farms. However, these turbines operate in the atmospheric boundary layer which is characterised by high turbulence and may also face high-turbulence levels associated with downstream wakes. Therefore, the main goal of this study is to explore the impact of turbulence intensity on the efficiency of paired VAWTs, employing a combination of wind tunnel experiments and an actuator-line model (ALM) integrated in a URANS-based OpenFOAM solver. The present ALM employs aerodynamic coefficients derived from experimental dynamic measurements conducted on a pitching aerofoil. The wind tunnel tests suggest that paired VAWTs operating in turbulent inflow can experience advantages arising from both the mutual aerodynamic interaction between them and the effect of turbulence on the aerodynamic conditions on their aerofoils. Additionally, the ALM sheds light on the mechanisms that contribute to the enhanced power output of isolated and paired VAWTs in turbulent inflow conditions.

Unsteady Flows and Component Interaction in Turbomachinery

Unsteady component interaction represents a crucial topic in turbomachinery design and analysis. Combustor/turbine interaction is one of the most widely studied topics both using experimental and numerical methods due to the risk of failure of high-pressure turbine blades by unexpected deviation of hot flow trajectory and local heat transfer characteristics. Compressor/combustor interaction is also of interest since it has been demonstrated that, under certain conditions, a non-uniform flow field feeds the primary zone of the combustor where the high-pressure compressor blade passing frequency can be clearly individuated. At the integral scale, the relative motion between vanes and blades in compressor and turbine stages governs the aerothermal performance of the gas turbine, especially in the presence of shocks. At the inertial scale, high turbulence levels generated in the combustion chamber govern wall heat transfer in the high-pressure turbine stage, and wakes generated by low-pressure turbine vanes interact with separation bubbles at low-Reynolds conditions by suppressing them. The necessity to correctly analyze these phenomena obliges the scientific community, the industry, and public funding bodies to cooperate and continuously build new test rigs equipped with highly accurate instrumentation to account for real machine effects. In computational fluid dynamics, researchers developed fast and reliable methods to analyze unsteady blade-row interaction in the case of uneven blade count conditions as well as component interaction by using different closures for turbulence in each domain using high-performance computing. This research effort results in countless publications that contribute to unveiling the actual behavior of turbomachinery flow. However, the great number of publications also results in fragmented information that risks being useless in a practical situation. Therefore, it is useful to collect the most relevant outcomes and derive general conclusions that may help the design of next-gen turbomachines. In fact, the necessity to meet the emission limits defined by the Paris agreement in 2015 obliges the turbomachinery community to consider revolutionary cycles in which component interaction plays a crucial role. In the present paper, the authors try to summarize almost 40 years of experimental and numerical research in the component interaction field, aiming at both providing a comprehensive overview and defining the most relevant conclusions obtained in this demanding research field.

0/1 and 3 - dimensional cold flow analysis of a diesel engine: A case study

Gas motion in the engine cylinder plays a critical role in diesel engines' air-fuel mixing and combustion processes. Moreover, it influences the engine's performance, emissions, and heat transfer. The intake air motion regulates the main phases of the flow in the cylinder, which is characterized by swirl, squish, and turbulence. Inducing swirl and tumble in the intake process provides high turbulence levels at ignition, resulting in more effective flame speeds and better combustion for lean air-fuel ratios or with EGR. Computational fluid dynamics (CFD) software is used to enhance in-cylinder flow characteristics. In this study, a cold flow simulation of a naturally aspirated, direct injection diesel engine was conducted with different piston bowls using AVL Fire M R2022.2. Swirl, tumble, and TKE parameters were investigated to make a detailed analysis of the in-cylinder flow for the relevant engine. Contrary to the expectation, the swirl ratio for the Piston B configuration is less than that for the original piston configuration. It causes a decrement of swirl ratio compared to the initial piston geometry and the maximum decrement is about 19%. In both cases, the second peak of TKE corresponding to the reverse-squish is around at the -30 CA and the difference between the curves is about ±8%.

Numerical Study on Mixing Characteristics of Circular and Non Circular Jets

The study of non-circular jet flows has become important due to their various applications such as aircraft exhaust, combustion chambers and injectors. The goal of present paper is to examine the impact of elliptical, square, and triangular shaped orifices on the mixing characteristics of a free jet with Mach number 0.8. Numerical simulations using an SST K-ω two-equation turbulence model were conducted with a Reynolds number of 3.46×105 for all cases. The mean velocity, decay rate, half-velocity width, spread rate, and turbulence intensity of the jet were analysed. The results showed that the triangular orifice provided the best mixing efficiency, with a shorter jet core length. The decay rate was found to be lowest for the square jet and highest for the triangular jet, which matches with the previous research. The asymmetric jets experienced two axis-switching points, while the square jet experienced a 450 rotation of its axes but no axis-switching. The core region had lower turbulence levels, while the highest turbulence levels were in the shear layer.

Freestream and shear layer effects in bluff-body-stabilized turbulent premixed flames

The effects of low and high approach flow turbulence levels on a large-scale, confined, premixed bluff-body-stabilized flame are experimentally characterized. The flame and flow are imaged using simultaneous 10-kHz-rate formaldehyde (CH2O) planar laser-induced fluorescence (PLIF), hydroxyl (OH) PLIF, particle image velocimetry (PIV), and OH* chemiluminescence. Elevated approach flow turbulence intensities of 16 % as compared to a lower value of 3 % affects the global and local flame and flow. The elevated approach flow turbulence results in a 22 % reduction in the length of the recirculation zone, despite the mean flame and mean shear layer locations being similar for both approach flow turbulence levels. Increasing the approach flow turbulence intensity does not lead to the mean flame position moving further into the reactant freestream. Both approach flow turbulence levels result in a similar growth of the flame brush thickness moving downstream until approximately 1.5 bluff-body widths, after which the flame brush for the low and high approach flow turbulence case stops growing and continues to linearly increase, respectively. This study describes the mechanisms by which high approach flow turbulence affects the global and local flame and emphasizes that the turbulent flame characteristics are influenced not only by the freestream approach flow turbulence but also by the bluff-body shear layers, recirculation zone, and wake.

Experimental study of the upstream bathymetry effects on a ducted twin vertical axis turbine

Tidal turbines at sea are subject to complex flow conditions. Among that complexity, wide bathymetry obstacles can generate powerful coherent flow structures whose impact on horizontal axis tidal turbines was proved to be highly detrimental. Consequently, the present paper aims at studying the effects of such coherent flow structures on the response of another tidal turbine geometry, namely a bottom-mounted ducted twin vertical axis tidal turbine (2-VATT). We tested a 1/20 scale model of such a 2-VATT in Ifremer’s flume tank either with a flat bed or downstream of a wide bathymetry obstacle at a constant far upstream velocity and we measured the turbine response simultaneously with the flow velocity. These flow measurements make it possible to compute cross-correlations in order to analyse the influence of the velocity fluctuation on the turbine response. The results reveal a strong drop in the average power and loads coefficients of the 2-VATT combined with significantly larger fluctuation. The velocity deficit and the high level of turbulence in the obstacle wake is responsible for a 40% lower average power coefficient and more than 3 times higher standard deviation compared to the flat bed configuration. The loads standard deviations are multiplied by 2 for the drag and by 10 for the lift when the 2-VATT is downstream of the bathymetry obstacle. This behaviour strongly increases the risks of structural fatigue failure, but the turbine drifting or overturning risks under those conditions remain lower than with the flat bed. The power fluctuation increase appears to be mostly due to the flow shear in the obstacle wake whereas the load fluctuation is mostly due to the periodical passing of the coherent flow structures. Thus, a proper characterisation of the flow at each precise turbine locations prior deployment at sea is highly recommended to design their structure accordingly.

Forming giant planets around late-M dwarfs: Pebble accretion and planet–planet collision

We propose a pebble-driven core accretion scenario to explain the formation of giant planets around the late-M dwarfs of M★=0.1– 0.2 M⊙. In order to explore the optimal disk conditions for giant planet, we performed N-body simulations to investigate the growth and dynamical evolution of both single and multiple protoplanets in the disks with both inner viscously heated and outer stellar irradiated regions. The initial masses of the protoplanets are either assumed to be equal to 0.01 M⊕ or calculated based on the formula derived from streaming instability simulations. Our findings indicate that massive planets are more likely to form in disks with longer lifetimes, higher solid masses, moderate to high levels of disk turbulence, and larger initial masses of protoplanets. In the single protoplanet growth cases, the highest planet core mass that can be reached is generally lower than the threshold necessary to trigger rapid gas accretion, which impedes the formation of giant planets. Nonetheless, in multi-protoplanet cases, the cores can exceed the pebble isolation mass barrier aided by frequent planet–planet collisions. This consequently speeds their gas accretion up and promotes giant planet formation, making the optimal parameter space to grow giant planets substantially wider. Taken together, our results suggest that even around very-low-mass stellar hosts, the giant planets with orbital periods of ≲100 days are still likely to form when lunar-mass protoplanets first emerge from planetesimal accretion and then grow rapidly by a combination of pebble accretion and planet–planet collisions in disks with a high supply of a pebble reservoir >50 M⊕ and a turbulent level of αt ~ 10−3−10−2.

Design and Simulation of Double-Nozzle Venturi Bubble Generator for Aeration System

Aquatic organisms rely heavily on oxygen for survival and maintaining adequate dissolved oxygen (DO) levels is crucial for the health and productivity of aquaculture systems. Aeration methods, such as venturi bubble generators, play a vital role in enhancing DO concentrations by facilitating oxygen transfer from the atmosphere to water. This study explores the performance of traditional venturi bubble generators and introduces a novel double-nozzle design for potential improvements in energy efficiency and oxygen transfer. Using computational fluid dynamics (CFD), we compared the performance of conventional half-inch and one- inch venturi bubble generators to a newly proposed double-nozzle design. Pressure profiles, velocity distributions, turbulence characteristics, bubble size distributions, and energy losses were evaluated to assess the effectiveness of each design. Results revealed significant differences in performance among the three venturi bubble generator designs. Compared to traditional designs, the double-nozzle configuration demonstrated superior characteristics, including smaller bubble sizes, more uniform bubble distribution, and higher turbulence levels. However, the double- nozzle venturi bubble generator also exhibited notable power losses due to pressure fluctuations.

Experimental investigation of flame morphology and instabilities in turbulent wind-driven flames

This paper investigates the effect of freestream turbulence on flame profile parameters and streak behavior for boundary layer flames stabilized over a liquid fuel-soaked wick. In contrast to conventional gaseous burners, the study utilized a condensed fuel surface to better emulate realistic burning scenarios, thereby increasing the reliability of the obtained results. This study explores the impact of crossflow velocity (ranging from 1 m/s to 2 m/s) and turbulent intensity (varying between 1.8 % and 16 %) on the dynamic evolution of flame geometry and streak profile. For a given flow velocity, the results indicate a reduction in flame length and flame attachment length with turbulence intensity; in contrast, an increase in tilt angle was observed with increasing turbulence intensity. However, the rate of their increase or decrease was found to vary across different ranges of freestream turbulence intensity. Also, the flame exhibits a curling action in higher turbulence intensity scenarios that influence the global flame structure. The average mass burning rate was also found to be positively related to the flow turbulence in all considered cases. Freestream turbulence induces significant disturbances that amplify and destabilize coherent structures, accelerating the transition to turbulence in the overall flow and resulting in a shorter flame attachment length. Streak spacing experiences accelerated growth with higher turbulence levels, with a sharp surge in the initial region due to the blowing effect caused by the condensed fuel surface. The influence of flow turbulence was also observed by plotting lognormal distribution curves representing streak spacing data. The impact of elevated freestream turbulence on the dispersion of the distribution curve was found to be more pronounced than that of the flow velocity, emphasizing its crucial role in governing the streak dynamics.

Управління бізнесом під час війни

The interaction between business and hostilities represents a complex dynamic, as both of these aspects have a huge impact on each other. When discussing this connection, one should consider not only the challenges, but also the opportunities it opens up for businesses in the face of instability and conflicts. The high level of discordance and geopolitical turbulence creates special conditions for strategic thinking and adaptability of business leaders. Hostilities cause economic instability, reduced production, destruction of infrastructure and loss of jobs, which leads to losses for local enterprises and causes great risks for investors who have to invest in countries with ongoing military conflicts, due to the instability of government structures and doubts about the economic recovery after the end of the certain conflict. The conditions of military conflict require a high level of attention from business organizations to ensure the safety and security of their employees, since this category of assets is one of the most important for the sustainability of the enterprise. Simultaneously, the protection of property assets is of great importance, as enterprises must minimize the possible risks of destruction or damage in the conditions of hostilities. In addition, effective risk management requires the enterprise to develop and implement strategies to adapt to the changing geopolitical environment, which allows it to maintain stability and efficiency of operation during adverse conditions. It is important to note that competent risk management is a crucial factor for maintaining business activity and the successful functioning of the enterprise even in the most complex scenarios of a conflict environment. War, as a complex phenomenon, creates not only challenges but also opportunities for business, especially in the context of certain industries and scenarios. For example, it stimulates the demand for products and services related to the defense industry, which contributes to the development of technology, weapons production, transport and communication systems. Post-conflict recovery markets open up new opportunities for companies in the fields of construction, reconstruction and infrastructure solutions. Thus, military conflicts, although they pose significant challenges to society and the economy, at the same time provide opportunities for the development of new technologies, markets and management strategies that require comprehensive analysis and response on the part of business and politics.

Revisiting the interplay of trust and contracts: The roles of technological turbulence and dependence disadvantage

Drawing on information processing theory, this study revisits the interplay between trust and contracts by comprehensively examining the impact of the interaction of different types of trust (i.e., ability trust and goodwill trust) and contracts (i.e., control contract and coordination contract) under different uncertainties (i.e., technology turbulence and dependence disadvantage) on supplier opportunism. We build a moderated moderation model to test the proposed hypotheses using a combined dataset of a survey of 200 Chinese manufacturers and secondary data. The results show that coordination contract weakens the effectiveness of ability trust but strengthens the effectiveness of goodwill trust. When firms face a high level of technological turbulence, both types of contracts weaken the effectiveness of ability trust in curbing opportunism, while under a high level of dependence disadvantage, contracts weaken ability trust but reinforce goodwill trust in curbing opportunism. Our results are found to be robust after being verified by a variety of statistical specifications and estimations. The results provide nuanced insights for both the literature and practice.

Государственные инвестиции и устойчивость мировой экономики

As history shows, in difficult periods, there is invariably an increase in the state’s involvement in economic life. As of now, there is a number fundamental macrotrends showing that the world fell into a highly dangerous situation of so called polycrisis. These include more and more evident dysfunction of the US-centric model of globalization, the inexorable formation of new independent centers of international power, extremely high level of geopolitical turbulence. The global financial and economic sphere continues to function due to massive debt pumping which translates to its underlying fragility. That is why the formation of an efficient system of sustainable development, as proclaimed in the UN SDG program, is so urgent. In order to overcome the current state of instability the world economy needs to found and engage stable and reliable sources of long-term capital instead of borrowed money. Such capital is available with the institutional investors, primarily the sovereign wealth funds and pension funds. As for the first ones, in recent years, they have noticeably diversified the goals, directions and objects of their operations. The changes are so serious that a term “sovereign wealth funds 3.0” entered into the analytical discourse. In the activities of most state investors, there is a tendency to shift the focus from the external to the internal one, which does not allow capital to completely dissolve in the global financial system. The geographical priorities of investment are changing: if initially the focus of state funds was on the most developed economies of the world, now it is beginning to shift towards the world majority, which in the future should contribute to a more equal distribution of productive forces and wealth and, as a result, to increase the stability of the world economy and improve the quality of its dynamics. “Sovereign wealth funds 3.0” are also characterized by new methods of funding, when it is provided by giving the fund the right to use cash flows generated by the state assets entrusted to it. Some sovereign wealth funds, having reached a certain level of maturity, enter the global private capital market, partially filling the deficit of reliable debt instruments observed there. Due to the peculiarities of financing and a long-term planning horizon, large sovereign wealth funds are able to painlessly absorb temporary financial losses, compensating them in the long-term perspective. This allows them to carry out the most important long-term projects. Thus, the state investment funds make a significant, though not always visible and appreciated, contribution into the stabilization of the financial market and the global economy at large.

NUMERICAL INVESTIGATION OF TURBULENCE CHARACTERISTICS AND SELF-SIMILARITY IN A HIGHLY AERATED STABLE HYDRAULIC JUMP USING LARGE EDDY SIMULATION

This work presents a numerical study of a stable hydraulic jump at Froude number 4.25 and Reynolds number 1.15×105 inside a horizontal and rectangular channel with a length of 3.2 m, a width of 0.5 m and a height of 0.4 m using large eddy simulation (LES). Classical hydraulic jump characteristics are obtained, such as conjugate depths, jump length, void fraction and velocity profiles. The hydraulic jump maximum streamwise velocity decay and shear layer spreading rate are simulated and compared with experimental data. For these parameters, numerical results demonstrate that is possible to stablish an analogy with other shear flows, such as the horizontal plane wall jet. Profiles of streamwise and vertical components of mean velocity are simulated, and self-similarity is observed for cross-sections located at the recirculation region of the jump. Self-similarity is also observed in terms of turbulent fluctuations, insofar as LES simulations indicate a high level of turbulence in the recirculation region. The simulated root mean square of streamwise velocity fluctuations, , ranges from 0.5 to 0.7 of the maximum cross-sections velocity, whereas the root mean square of vertical component of velocity fluctuations, , stays around 0.5 of the maximum cross-sections velocitiy. All validation comparisons show good agreement with the selected experimental data of Kramer and Valero (2020) and Wang (2014), presenting average deviations always lesser than 5%.