Properties of the compressibility and transport motion in wall-bounded turbulent flows at Mach 8

The compressibility effect and transport motion in highspeed turbulent boundary layer (TBL) is a fundamental problem because they dominate the average and statistical characteristics. Using the statistical methods and flow visualization technology, flat-plate TBLs at [Formula: see text] with high- and low-wall temperatures, [Formula: see text] and 1.9, are investigated based on the direct numerical simulation (DNS) datasets. Compared with previous studies, this study considers relative higher Mach number and strong cold wall temperature condition at the same time. First, the turbulent Mach number and turbulent intensity show that the compressibility effects are enhanced by the cooling process. Second, the high-order statistical moments and structure parameters confirm cold wall that causes stronger compressibility and the corresponding increased intensities of local streamwise and wall-normal transport motions. Finally, for uncovering the relationship between the compressibility effect and turbulent transport, more in-depth visualization analyses of velocity streaks are performed. It is found that ‘knot-like’ structures are generated when cooling the wall, and they lead to stronger intermittent, which results in the rapid increase of local compressibility effect and the wall-normal transport motion. Our research sheds light on providing a theoretical basis for further understanding the compressibility effects of TBL at high Mach number.

Stochastic modeling of transient surface scalar and momentum fluxes in turbulent boundary layers

<p>Turbulence is ubiquitous in atmospheric boundary layers and manifests itself by transient transport processes on a range of scales. This range easily reaches down to less than a meter, which is smaller than the typical height of the first grid cell layer adjacent to the surface in numerical models for weather and climate prediction. In these models, the bulk-surface coupling plays an important role for the evolution of the atmosphere but it is not feasible to fully resolve it in applications. Hence, the overall quality of numerical weather and climate predictions crucially depends on the modeling of subfilter-scale transport processes near the surface. A standing challenge in this regard is the robust but efficient representation of transient and non-Fickian transport such as counter-gradient fluxes that arise from stratification and rotation effects.</p><p>We address the issues mentioned above by utilizing a stochastic one-dimensional turbulence (ODT) model. For turbulent boundary layers, ODT aims to resolve the wall-normal transport processes on all relevant scales but only along a single one-dimensional domain (column) that is aligned with the vertical. Molecular diffusion and unbalanced Coriolis forces are directly resolved, whereas effects of turbulent advection and stratification are modeled by stochastically sampled sequence of mapping (eddy) events. Each of these events instantaneously modifies the flow profiles by a permutation of fluid parcels across a selected size interval. The model is of lower order but obeys fundamental conservation principles and Richardson's 1/4 law by construction.</p><p>In this study, ODT is applied as stand-alone tool in order to investigate nondimensional control parameter dependencies of the scalar and momentum transport in turbulent channel, neutral, and stably-stratified Ekman flows up to (friction) Reynolds number <em>Re</em> = <em>O</em>(10<sup>4</sup>). We demonstrate that ODT is able to capture the state-space statistics of transient surface fluxes as well as the boundary-layer structure and nondimensional control parameter dependencies of low-order flow statistics.<br>Very good to reasonable agreement with available reference data is obtained for various observables using fixed model set-ups. We conclude that ODT is an economical turbulence model that is able to not only capture but also predict the wall-normal transport and surface fluxes in multiphysics turbulent boundary layers.</p>

Dunes as palaeo-wind vanes: Investigating palaeowind regimes using semi-automated remote sensing approaches to dunefield mapping and orientation quantification

<p>Many dryland regions of the world are at high risk of desertification from combined human land use and anthropogenic climate change. One symptom of desertification is the reactivation of previously stable dunefields. Since morphologies of stable dunes are thought to reflect wind regimes at the time of their formation, the degree to which dune orientation reflects modern winds may be one way to assess changes in wind regimes and the progression of desertification in a region.</p><p>Here we investigate the relationship between wind dynamics and desert dune orientation in one region at risk of desertification, southeast Kazakhstan in Central Asia, on the basis of open-source software and open-access datasets. Using Google Earth Engine, we map dunes or interdune spaces within six palaeo-dunefields in the Ili-Balkhash area, by performing a multi-layer object-based image analysis (OBIA) on satellite remote sensing data (Sentinel-2 optical imagery and SRTM digital elevation models). A semi-automated GIS approach is used to undertake data cleansing and the quantification of dominant palaeo-dunefield orientations. The resulting orientation trends are concurrent with the region’s topography: The dunefields within the Ili valley show a narrow, mostly E-W oriented trend concurrent with the course of the valley while the orientation ranges become broader towards the open pre-Balkhash area.</p><p>We then predict modern dune orientations by applying the maximum gross bedform-normal transport rule on reanalysed wind data for 2008-2018. This approach by Rubin and Hunter (1987) allows the deduction of sand transport and resulting bedform trends from wind direction frequencies. The predicted modern orientation trends for the dunefields in the Ili-Balkhash area yield only partial consensus with observed palaeo-bedform trends. We therefore propose that modern wind regimes are not exclusively responsible for existing dune morphologies in the region, and that dune orientation may be inherited from earlier wind regimes.</p>

International and national practice for estimating cash expenditures of road replacement, repair and maintenance

The paper considers the importance of the uninterrupted functioning of the transport network, which is the most important condition for eliminating the transport inaccessibility of Arctic territories of the regions, thus excluding transport discrimination of the population living in the Arctic zone of the Russian Federation. Besides, the paper provides a brief overview of international road repair and maintenance experience on the example of Norway, analysis of the standard for repair and maintenance of roads in the Russian Federation, proposals on the method of calculating the cash expenditures of replacement, repair and maintenance of roads in the Russian Federation. The Decree of the Government of the Russian Federation No. 658 dated May 30, 2017 approved the standards of financial expenditures and the rules for calculating the size of federal budget allocations for replacement, repair and maintenance of federal roads. However, at the moment, not all regions have updated the regulatory framework on the norms of financial expenditures and the rules for calculating budget allocations for replacement, repair and maintenance of regional and inter-municipal roads. The existing methodology for calculating the cost of repair and maintenance of roads in the Arctic territory of Russia does not fully provide the need to bring the existing roads into normal transport and operational condition for their safe operation. The analysis shows that there is no systematic work to ensure sustainable financing of the road economy in the republic and the road industry is financed at a level much lower than the actual needs.

Study on Combustion Properties of Aviation Carpet under Low Ambient Pressure

The flame-retardant materials in the cabin of civil aircraft is possible to induce fire accident, which can cause certain threat to the operation safety of aircraft. The cabin pressure of civil aircraft is generally maintained at 75~84 kPa under normal transport condition, and the combustion behavior of aviation carpet will change under this pressure. Combustion properties of an aviation carpet, selected from civil aircraft, were studied at Guanghan City (520 m altitude) and Kangding airport (4290 m altitude), Sichuan province of China in this work, respectively. The results showed that the smoke density of the aviation carpets increased sharply and the decreasing rate of the oxygen volume fraction became more quickly under low pressure. Furthermore, the rising rate of carbon dioxide volume fraction also became rapidly with the decrease of the ambient pressure. The content of the carbon monoxide under low pressure was lower than that under normal pressure at the beginning of the combustion. However, the carbon monoxide production increased sharply when the combustion lasted for 4 minutes. In addition, the ignition time of the aviation carpet was shorter under low pressure.

Yardangs and Dunes: Minimum- and Maximum-Dissipation Aeolian Landforms

Yardangs are ridges formed in soft rock by aeolian erosion in a unidirectional wind environment, and often have a 4 : 1 length : width ratio that is associated with a minimum-drag shape for a given width. Dunes are emergent aeolian landforms formed by accumulation and removal of sand particles. Dunes have a range of morphologies (barchans, stars, linear, transverse etc.) which can be mapped to the sand supply and the diversity of wind directions. The dune pattern that generally emerges is one that maximizes gross bedform normal transport (GBNT). For fixed imposed wind speed, a minimum drag force corresponds to a minimum dissipation, whereas maximum sand transport corresponds to maximum dissipation. These examples illuminate a more general paradox in non-equilibrium thermodynamics, wherein entropy production rates may be maximized or minimized depending, vaguely, on the degrees of freedom in the system. In these geomorphological examples, however, the difference is informatively clear: whereas yardangs emerge simply by removal of material alone and dissipation is minimized, dunes form by the much less constrained removal and accumulation to maximize dissipation.

A mutation in the catalytic domain of cellulose synthase 6 halts its transport to the Golgi apparatus

D395N in the catalytic domain of CESA6 interrupts its normal transport to the Golgi, which hampers its function in cellulose synthesis.

Rényi Entropy Power Inequalities via Normal Transport and Rotation

Following a recent proof of Shannon’s entropy power inequality (EPI), a comprehensive framework for deriving various EPIs for the Rényi entropy is presented that uses transport arguments from normal densities and a change of variable by rotation. Simple arguments are given to recover the previously known Rényi EPIs and derive new ones, by unifying a multiplicative form with constant c and a modification with exponent α of previous works. In particular, for log-concave densities, we obtain a simple transportation proof of a sharp varentropy bound.

Rényi Entropy Power Inequalities via Normal Transport and Rotation

Following a recent proof of Shannon's entropy power inequality (EPI), a comprehensive framework for deriving various EPIs for the Rényi entropy is presented that uses transport arguments from normal densities and a change of variable by rotation. Simple arguments are given to recover the previously known Rényi EPIs and derive new ones, by unifying a multiplicative form with constant c and a modification with exponent α of previous works. In particular, for log-concave densities, we obtain a simple transportation proof of a sharp varentropy bound.