Source Of Turbulence Research Articles

"Romanian Ngos’ Efforts to Advocate on Behalf of Marginalized Groups and Prevent Social Turbulence"

While Romania has undergone huge progress during the last 30 years, the situation of marginalized groups hasn’t progressed as well as the country’s rapid economic development. The plight of vulnerable groups such as unhoused people, persons with disabilities, and the LGBTQ community continues to be a source of social turbulence, as they are consistently facing exclusion. Authorities do not prioritize their integration within society and there is a lack of policies to deal with these issues, leading to the appearance of extremely polarizing movements such as the 2018 referendum initiative to ban same-sex unions. This paper aims to analyze three case studies where advocacy organizations championed the cause of the above-mentioned groups, in order to increase visibility, representation, and integration, and pinpoint best practices for organizations advocating on behalf of disadvantaged groups. The three main best practices we have learned regarding advocacy projects targeting public policy for marginalized groups are: a. always put a local group at the center of the project, b. bring outside partners or mentors who can bring advocacy skills to the project, c. look for other, supplemental, positive outcomes, that usually tend to come up in the work with marginalized groups.

A theoretical study of self-soise generation in turbulent jets using one-dimensional turbulence and Lighthill's acoustic analogy

Modeling and simulation of turbulent jet noise is an ongoing numerical challenge relevant to noise pollution control. In the present study, the concept of a novel dimensionally reduced modeling approach based on the so-called one-dimensional turbulence model (ODT) is discussed. ODT aims to resolve source terms due to velocity and kinematic pressure variations in the acoustic near-field at all relevant scales, but only for a single physical coordinate. In the standalone formulation of the model, the physical coordinate taken as a notional line of sight that is pointing in radial cross-stream direction and advected downstream with the axial velocity of the jet while the microscales evolve. Thereby, turbulence is represented by a stochastically sampled sequence of discrete mapping events that punctuate the deterministic molecular diffusive advancement. It is discussed how an ensemble of small-scale resolving independent flow realizations can be used to estimate turbulent noise sources from a range of scales. The main objective is to present an approach for the prediction of broadband self-noise generated by a turbulent jet using ODT and Lighthill's equation. Dedicated experimental measurements are conducted for verification and validation of the numerical modeling approach.

Effect of radius ratio on the instabilities in a vaneless diffuser

The prominent features of the primary instabilities of a turbulent source flow between finite-span parallel rings with spatially modulated inflow conditions rotating at angular rate Ω are investigated. Two different two-dimensional instabilities that occur at large (αQ≳1.00) and low (αQ≲0.65) flow rates have been traced back to two different physical mechanisms related to jet-wake and mean-core flow, respectively. The effect of the radial aspect ratios Γ on the instability characteristics of the flow between parallel rings is also considered in this paper. Numerical URANS simulations are conducted for three different radial aspect ratios, i.e. Γ=1.25, 1.5, and 2, the corresponding cross-sectional aspect ratios Λ=2(Γ−1)×3.325, and two conceptually different inflow conditions. Their impact on the rotating instabilities in terms of instability mode number and instability frequency is the main focus of this study and is analyzed by fast Fourier transform (FFT) and wavelet analysis. Realistic inflow conditions with a leakage flow are found to overtake the instability for small radius ratios and affect the primary instabilities for large radius ratios.

Turbulence in the development of Ukraine and Russian aggression as a destroyer of the agricultural sector

Turbulence acts as a key characteristic of the development of systems, processes, and structures of various natures, and when it increases, their destruction or self-organization occurs at a new level, resulting in transitions from disorder to order and vice versa. Stochastic systems have a state determined by a random combination of its components, both internal and external, at different times, and the final result cannot be clearly predicted or precisely predicted. Therefore, the key problem of modern times is to ensure sustainable development of socio-economic and other multi-sectoral systems under the conditions of increased turbulence. An extremely powerful source of turbulence is the Russian-Ukrainian war, which arose suddenly and avalanche-like destroyed and continues to destroy the existing order and is accompanied by unpredictable and catastrophic consequences. The devastating consequences of military operations on Ukrainian territory caused and continue to cause significant damage to the national economy, including and the agricultural sector, and its restoration requires significant financial, material and human resources and a long time.

Classification of Turbulent Mixing Driven Sources in Marine Atmospheric Boundary Layer With Use of Shipborne Coherent Doppler Lidar Observations

AbstractA method to identify the turbulent mixing sources within the marine atmospheric boundary layer (MABL) based on the shipborne coherent Doppler lidar measurements is introduced in this paper. Combining with the coherent Doppler lidar signal‐to‐noise ratio, vertical velocity skewness, turbulence kinetic energy dissipation rate, and wind shear intensity, the categories of turbulent mixing sources and the specific turbulent mixing sources could be determined. The method is applied into two voyages of MABL observation during May 2021 in the South China Sea and during April 2022 in the Bohai Sea and Yellow Sea. The turbulent mixing processes are captured and the classification of the turbulence driven sources within the MABL are realized. The temporal‐spatial evolution characteristics of the turbulence mixing process in the MABL are investigated under different weather conditions containing clear‐sky day, cloudy‐sky day, and sea‐fog day. The convective mixing process is recognized in the daytime of the clear‐sky day and the intermittent cloud‐driven turbulence exists below the cloud layer. Additionally, the turbulent mixing is weak which could not act as the main driven source during the sea‐fog day. Furthermore, the dominant turbulence scale analyses of different turbulence sources are conducted based on the cospectra of the vertical velocity and the horizontal speed measurements. The turbulence parameters of different turbulence sources are statistical analyzed and compared in different sea areas. The classification method has the broad application prospects on the study of the air‐sea interaction.

Occurrence frequency of subcritical Richardson numbers assessed by global high-resolution radiosonde and ERA5 reanalysis

Abstract. Kelvin–Helmholtz instability (KHI) is most likely to be the primary source for clear-air turbulence, which is of importance in pollution transfer and diffusion and aircraft safety. It is indicated by the critical value of the dimensionless Richardson (Ri) number, which is predicted to be 1/4 from linear stability analysis. However, Ri is fairly sensitive to the vertical resolution of the dataset; a higher resolution systematically leads to a finer structure. The study aims to evaluate the performance of ERA5 reanalysis in determining the spatial–temporal variabilities in subcritical Ri by comparing it against a near-global high-resolution radiosonde dataset during the years 2017 to 2022 and further highlights the global climatology and dynamical environment of subcritical Ri. Overall, the occurrence frequency of Ri<1/4 is inevitably underestimated by the ERA5 reanalysis over all climate zones at all heights from the near-ground atmosphere up to 30 km, compared to radiosonde, due directly to the severe underestimation in wind shears. Otherwise, the occurrence frequency of Ri<1 in ERA5 is climatologically consistent with that from Ri<1/4 in radiosondes in the free troposphere, especially over the midlatitude and subtropics in the Northern Hemisphere and Southern Hemisphere. Therefore, we argue that the threshold value of Ri could be approximated as 1 rather than 1/4 when using ERA5-based Ri as a proxy for KHI. The occurrence frequency of subcritical Ri revealed by both datasets exhibits significant seasonal cycles over all climate zones. In addition, it is positively correlated with the standard derivation of orography at low levels and is exceptionally strong over the Niño-3 region at heights of 6–13 km. Furthermore, a high occurrence of subcritical Ri would likely be accompanied by strong wind speeds and intensive orographic or non-orographic gravity waves.

Investigating Spatial and Temporal Structuring of E‐Region Coherent Scattering Regions Over Northern Norway

AbstractRecently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar Observing Network radar system located in northern Norway is capable of measuring ionospheric E‐region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four different events from June and July of 2022 are examined in the present study, where the coherent scatter measurements are used as a tracer for large‐scale ionospheric phenomena such as plasma density enhancements and ionospheric electric fields. By applying a two‐dimensional Fourier analysis to range‐time‐intensity data, we perform a multi‐scale spatial and temporal investigation to determine the change in range over time of large‐scale ionospheric structures (>3 km) which are compared with line‐of‐sight velocities of the small scale structures (∼5 m) determined from the Doppler shift of the coherent scatter. The spectral characteristics of the large‐scale structures are also investigated and logarithmic spectral slopes for scale sizes of 100–10 km were found to be between −3.0 and −1.5. This agrees with much of the previous work on the spatial spectra scaling for ionospheric electric fields. This analysis aids in characterizing the source of the plasma turbulence and provides crucial information about how energy is redistributed from large to small scales in the E‐region ionosphere.

Kelvin–Helmholtz Instability “Tube” and “Knot” Dynamics. Part II: KHI T&K Dynamics in a Multiscale Gravity Wave Direct Numerical Simulation

Abstract A companion paper by Fritts et al. reviews evidence for Kelvin–Helmholtz instability (KHI) “tube” and “knot” (T&K) dynamics that appear to be widespread throughout the atmosphere. Here we describe the results of an idealized direct numerical simulation of multiscale gravity wave dynamics that reveals multiple larger- and smaller-scale KHI T&K events. The results enable assessments of the environments in which these dynamics arise and their competition with concurrent gravity wave breaking in driving turbulence and energy dissipation. A larger-scale event is diagnosed in detail and reveals diverse and intense T&K dynamics driving more intense turbulence than occurs due to gravity wave breaking in the same environment. Smaller-scale events reveal that KHI T&K dynamics readily extend to weaker, smaller-scale, and increasingly viscous shear flows. Our results suggest that KHI T&K dynamics should be widespread, perhaps ubiquitous, wherever superposed gravity waves induce intensifying shear layers, because such layers are virtually always present. A second companion paper demonstrates that KHI T&K dynamics exhibit elevated turbulence generation and energy dissipation rates extending to smaller Reynolds numbers for relevant KHI scales wherever they arise. These dynamics are suggested to be significant sources of turbulence and mixing throughout the atmosphere that are currently ignored or underrepresented in turbulence parameterizations in regional and global models. Significance Statement Atmospheric observations reveal that Kelvin–Helmholtz instabilities (KHI) often exhibit complex interactions described as “tube” and “knot” (T&K) dynamics in the presence of larger-scale gravity waves (GWs). These dynamics may prove to make significant contributions to energy dissipation and mixing that are not presently accounted for in large-scale modeling and weather prediction. We explore here the occurrence of KHI T&K dynamics in an idealized model that describes their behavior and character arising at larger and smaller scales due to superposed, large-amplitude GWs. The results reveal that KHI T&K dynamics arise at larger and smaller scales, and that their turbulence intensities can be comparable to those of the GWs.

Assessment of Five Wind-Farm Parameterizations in the Weather Research and Forecasting Model: A Case Study of Wind Farms in the North Sea

Abstract To simulate the large-scale impacts of wind farms, wind turbines are parameterized within mesoscale models in which grid sizes are typically much larger than turbine scales. Five wind-farm parameterizations were implemented in the Weather Research and Forecasting (WRF) Model v4.3.3 to simulate multiple operational wind farms in the North Sea, which were verified against a satellite image, airborne measurements, and the FINO-1 meteorological mast data on 14 October 2017. The parameterization by Volker et al. underestimated the turbulence and wind speed deficit compared to measurements and to the parameterization of Fitch et al., which is the default in WRF. The Abkar and Porté-Agel parameterization gave close predictions of wind speed to that of Fitch et al. with a lower magnitude of predicted turbulence, although the parameterization was sensitive to a tunable constant. The parameterization by Pan and Archer resulted in turbine-induced thrust and turbulence that were slightly less than that of Fitch et al., but resulted in a substantial drop in power generation due to the magnification of wind speed differences in the power calculation. The parameterization by Redfern et al. was not substantially different from Fitch et al. in the absence of conditions such as strong wind veer. The simulations indicated the need for a turbine-induced turbulence source within a wind-farm parameterization for improved prediction of near-surface wind speed, near-surface temperature, and turbulence. The induced turbulence was responsible for enhancing turbulent momentum flux near the surface, causing a local speed-up of near-surface wind speed inside a wind farm. Our findings highlighted that wakes from large offshore wind farms could extend 100 km downwind, reducing downwind power production as in the case of the 400-MW Bard Offshore 1 wind farm whose power output was reduced by the wakes of the 402-MW Veja Mate wind farm for this case study. Significance Statement Because wind farms are smaller than the common grid spacing of numerical weather prediction models, the impacts of wind farms on the weather have to be indirectly incorporated through parameterizations. Several approaches to parameterization are available and the most appropriate scheme is not always clear. The absence of a turbulence source in a parameterization leads to substantial inaccuracies in predicting near-surface wind speed and turbulence over a wind farm. The impact of large clusters of offshore wind turbines in the wind field can exceed 100 km downwind, resulting in a substantial loss of power for downwind turbines. The prediction of this power loss can be sensitive to the chosen parameterization, contributing to uncertainty in wind-farm economic planning.

Effects of localized application of porous material on trailing-edge noise of a circulation-controlled wing

This manuscript reports on the effects of localized application of porous material on trailing-edge noise of a circulation-controlled wing. This circulation-controlled configuration consists of a main wing with a droop-nose and a highly deflected flap, where the flow on the flap is attached due to the Coanda effect. The rear 10% of the flap consists of porous material. The numerical investigation was mainly carried out with a High fidelity Zonal Overset-LES method. Due to the strong pressure difference between the pressure and suction side, the flap’s porous inset experiences an enhanced flow through the porous medium as compared to the reference configuration with a non-porous flap. As a result, the boundary layer on the flap’s suction side was considerably thickened. Upon analysing the turbulent sound sources, it became evident that the application of porous material resulted in higher levels of the power spectral density of surface pressure fluctuations across the complete spectrum, related to the aforementioned strong flow through the porous material. However, the turbulent eddies traversing on the porous material were slowed down (observation based on stream-wise correlations), which was a noise reduction mechanism observed in the current study. The far-field sound characteristics revealed that a noise reduction could be seen for certain radiation directions when considering only the flap’s trailing-edge noise as a sound source. Even when the full flap noise is considered, the noise reduction effect of the porous material is evident for frequencies f between 500 Hz and 10 kHz in the forward-downward radiation direction (as defined by the polar angle θ∈ [180∘, 270∘]). To conclude, this study provides novel insights regarding the importance of the flow-through aspect of porous material and the subsequent boundary layer thickening and argues that this phenomenon needs to be kept moderate in order to achieve noise reduction. Furthermore, the study emphasizes on the importance of curvature noise which needs to be the focal point of noise reduction in such circulation-controlled wings.

Россия в современной архитектуре международных отношений: прогнозные сценарии и границы допустимой реструктуризации

Introduction. The article is devoted to the characterization and substantiation of the basic principles and priority areas of the foreign policy activity of the Russian Federation in the context of the transformation of the modern system of international relations. Scenario approaches to the development of the Russian state and its functional role in the context of increased conflict potential between countries of Western and non-Western civilizations that are most frequently articulated within the political science discourse are interpreted. The study's relevance stems from the need to reconsider the dominant grounds for restructuring the contemporary world order, which lacks security and stability, while compromising the development interests of most states and societies at national, regional, and global levels. Methods and materials. The authors rely on the conceptual statements of the political organization of the contemporary world, developed by M.M. Lebedeva within the framework of a system approach. In identifying the sources of global turbulence experienced by the current system of international relations, the theoretical constructions by I. Wallerstein, S. Huntington, G. Kissinger, and O.V. Gaman-Golutvina were used. The elucidation of the functional specifics of Russia as a civilization state in the system of the world order of the past and present is based on a civilizational approach. The empirical base of the article was the normative and legal documents of the Russian Federation and the results of surveys conducted by leading centers: VCIOM, FOM, and Levada Center (this organization is included in the unified register of individuals and organizations recognized as foreign agents in the Russian Federation). Analysis and results. In the course of the study, the dominant factors that contribute to the radicalization of the conflict potential of the existing system of international relations were revealed and interpreted. The relationship between the escalation of the conflict between the Western bloc countries and Russia, the multifaceted objectification of Russophobia in all spheres of life, and the strategic vectors of Russia’s foreign policy formulated in The Concept of the Foreign Policy of the Russian Federation (2023) is traced. At the same time, attention is focused not only on the principles of the new Russian statehood and the place of the Russian Federation in the contemporary world but also on the historical continuity of Russia as a civilization state. Authors’ contribution. S.A. Pankratov developed the theoretical basis of the study, analyzed the dominant trends in the transformation of the modern system of international relations, and carried out the general scientific editing of the article. E.V. Klinshans summarized and analyzed the empirical data related to the priorities of the implementation of the foreign policy of the Russian Federation and formulated the main conclusions of the work.

Energetic Constraints on Ocean Circulations of Icy Ocean Worlds

Globally ice-covered oceans have been found on multiple moons in the solar system and may also have been a feature of Earth’s past. However, relatively little is understood about the dynamics of these ice-covered oceans, which affect not only the physical environment but also any potential life and its detectability. A number of studies have simulated the circulation of icy-world oceans, but have come to seemingly widely different conclusions. To better understand and narrow down these diverging results, we discuss the energetic constraints for the circulation on ice-covered oceans, focusing in particular on Snowball Earth, Europa, and Enceladus. The energy input that can drive ocean circulation on ice-covered bodies can be associated with heat and salt fluxes at the boundaries as well as ocean tides and librations. We show that heating from the solid core balanced by heat loss through the ice sheet can drive an ocean circulation, but the resulting flows would be relatively weak and strongly affected by rotation. Salt fluxes associated with freezing and melting at the ice sheet boundary are unlikely to energetically drive a circulation, although they can shape the large-scale circulation when combined with turbulent mixing. Ocean tides and librations may provide an energy source for such turbulence, but the magnitude of this energy source remains highly uncertain for the icy moons, which poses a major obstacle to predicting the ocean dynamics of icy worlds and remains an important topic for future research.

Velocity field characterization of single-phase flows across a tube bundle through spatial filter velocimetry

This paper presents experimental vector velocity fields of external flows across a tube bundle to characterize the flow structure and elucidate the main mechanisms of turbulence generation. The experiments were conducted in a tube bundle test section composed of 20 rows of 4 tubes with 20 mm O.D. arranged in a normal triangular configuration with a transversal pitch per diameter ratio of 1.25. The experiments were conducted under single-phase flows with Reynolds numbers ranging from 210 to 19560, comprising transitional and turbulent flow regimes. The vector velocity fields were obtained through the Spatial Filter Velocimetry (SFV) technique, resulting in maximum spatial and temporal resolutions of 2.1 samples/mm and 49.6 kHz, respectively. The velocity measurements obtained through SFV enabled the analysis of the flow development, the vector velocity field, the flow turbulence, the velocity fluctuation along the time, and the effects of the mechanism of momentum transport on the pressure gradient. The obtained results indicate that the flow separation and the repeated intersection of opposite flows are the most relevant sources of turbulence. Moreover, the analysis of the terms of the RANS equations reveals that the convective terms are the most relevant terms for the pressure gradient.

Dependency of vertical velocity variance on meteorological conditions in the convective boundary layer

Abstract. Measurements of vertical velocity from vertically pointing Doppler lidars are used to derive the profiles of normalized vertical velocity variance. Observations were taken during the FESSTVaL (Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg) campaign during the warm seasons of 2020 and 2021. Normalized by the square of the convective velocity scale, the average vertical velocity variance profile follows the universal profile of Lenschow et al. (1980). However, daily profiles still show a high day-to-day variability. We found that moisture transport and the content of moisture in the boundary layer could explain the remaining variability of the normalized vertical velocity variance. The magnitude of the normalized vertical velocity variance is highest on clear-sky days and decreases as the absolute humidity increases and surface latent heat flux decreases on cloud-topped days. This suggests that moisture content and moisture transport are limiting factors for the intensity of turbulence in the convective boundary layer. We also found that the intensity of turbulence decreases with an increase in the boundary layer cloud fraction during FESSTVaL, while the latent heating in the cloud layer was not a relevant source of turbulence in this case. We conclude that a new vertical velocity scale has to be defined that would take into account the moist processes in the convective boundary layer.

Sources of Turbulence on an Unswept Wing of a Supersonic Passenger Airplane

Sources of Turbulence on an Unswept Wing of a Supersonic Passenger Airplane

Modeling of the Magnetic Turbulence Level and Source Function of Particle Injection from Multiple SEP Events

Solar energetic particles (SEPs) are produced by solar eruptions and are harmful to spacecraft and astronauts. The four source function parameters of particle injection for SEP events and the magnetic turbulence level can be collectively referred to as key parameters. We reproduce the electron intensity-time profiles with simulations for five SEP events observed by multispacecraft such as ACE, STEREO-A, and STEREO-B, so we can obtain the five fitted key parameters for each of the events. We analyze the relationship among the five fitted key parameters, and also the relationship between these parameters and the observed event features. Thus, the model of key parameters are established. Next, we simulate another 12 SEP events with the key parameters model. Though the predicted electron intensity-time profiles do not fit the observed ones well, the peak flux and event-integrated fluence can be predicted accurately. Therefore, the model can be used to estimate the radiation hazards.

Saturation of the magnetorotational instability and the origin of magnetically elevated accretion discs

ABSTRACT We propose that the strength of angular momentum transport in accretion discs threaded by net vertical magnetic field is determined by a self-regulation mechanism: the magnetorotational instability (MRI) grows until its own turbulent resistivity damps the fastest growing mode on the scale of the disc thickness. Given weak assumptions as to the structure of MRI-derived turbulence, supported by prior simulation evidence, the proposed mechanism reproduces the known scaling of the viscous α-parameter, $\alpha \propto \beta _z^{-1/2}$. Here, $\beta _z = 8\pi p_{\rm g}/B_{z0}^2$ is the initial plasma β-parameter on the disc mid-plane, Bz0 is the net field, and pg is the mid-plane gas pressure. We generalize the argument to discs with strong suprathermal toroidal magnetic fields, where the MRI growth rate is modified from the weak-field limit. Additional sources of turbulence are required if such discs are to become magnetically elevated, with the increased scale heights near the mid-plane that are seen in simulations. We speculate that tearing modes, associated with current sheets broadened by the effective resistivity, are a possible source of enhanced turbulence in elevated discs.

Stress analysis of PWR pressurizer surge-line during single phase and two-phase thermal stratification

Non-uniform temperature distribution at horizontal pipes cross section leads to an asymmetric thermal stress. This condition would be considered as an ageing mechanism due to fatigue effect, known as thermal stratification. To evaluate this ageing mechanism, the stress analysis should be done in horizontal pipelines like surge-line connected the pressurizer to the hot leg of primary loop of NPPs by consideration of operational or transient conditions. During these conditions, the status of surge-line would be single phase or two-phase stratified flow. To estimate the equivalent stress in horizontal section of surge-line, the developed CFD model for both single and two-phase flow is coupled with mechanical structural analysis. In two phase-condition, the heat transfer coefficient is evaluated by employment of turbulent kinetic energy source function. The results show that the maximum stress is almost same for single and two-phase stratification, but the propagation of cold water layer intensifies the asymmetric stress in two-phase condition.

Observations of River Plume Mixing in the Surf Zone

Abstract We use salinity observations from drifters and moorings at the Quinault River mouth to investigate mixing and stratification in a surf-zone-trapped river plume. We quantify mixing based on the rate of change of salinity DS/Dt in the drifters’ quasi-Lagrangian reference frame. We estimate a constant value of the vertical eddy diffusivity of salt of Kz = (2.2 ± 0.6) × 10−3 m2 s−1, based on the relationship between vertically integrated DS/Dt and stratification, with values as high as 1 × 10−2 m2 s−1 when stratification is low. Mixing, quantified as DS/Dt, is directly correlated to surf-zone stratification, and is therefore modulated by changes in stratification caused by tidal variability in freshwater volume flux. High DS/Dt is observed when the near-surface stratification is high and salinity gradients are collocated with wave-breaking turbulence. We observe a transition from low stratification and low DS/Dt at low tidal stage to high stratification and high DS/Dt at high tidal stage. Observed wave-breaking turbulence does not change significantly with stratification, tidal stage, or offshore wave height; as a result, we observe no relationship between plume mixing and offshore wave height for the range of conditions sampled. Thus, plume mixing in the surf zone is altered by changes in stratification; these are due to tidal variability in freshwater flux from the river and not wave conditions, presumably because depth-limited wave breaking causes sufficient turbulence for mixing to occur during all observed conditions. Significance Statement River outflows are important sources of pollutants, sediment, and nutrients to the coastal ocean. Small rivers often meet large breaking waves in the surf zone close to shore, trapping river water and river-borne material near the beach. Such trapped material can influence coastal public health, beach morphology, and nearshore ecology. This study investigates how trapped fresh river water mixes with salty ocean water in the presence of large breaking waves by using high-resolution measurements of waves, salinity, and turbulence. We find that the surf zone is often fresh and stratified, which could have significant implications for the fate of riverine material. Wave breaking provides a constant source of turbulence, and the amount of mixing is limited by the degree of vertical salt stratification; more mixing occurs when stratification is higher.

Hydrodynamic turbulence in disks with embedded planets

The vertical shear instability (VSI) is a source of hydrodynamic turbulence that can drive vigorous vertical mixing and moderate levels of accretion in protoplanetary disks, and it could be observable in the near future. With high-resolution three-dimensional numerical hydrodynamics simulations, we modeled the behavior of the VSI in protoplanetary disks with and without embedded planets. We then measured its accretion and mixing capabilities by comparing the full Reynolds stress, which includes the contribution of nonaxisymmetric features, such as spiral arms and vortices, to the Reynolds stress due to the azimuthally averaged velocity field, which can be attributed to good approximation to the VSI. We verified that the VSI can contribute to the accretion stress and showed that, depending on disk conditions, an embedded planet can coexist with or suppress VSI turbulent stress. Specifically, the presence of spiral shocks launched by a planet or planet-generated vortices can interfere with the VSI near the planet’s vicinity, with the instability recovering at large enough distances from the planet or vortex. Our results suggest that observations of VSI signatures are unlikely in disks that contain massive, nonaxisymmetric features.