A concept of entropy increment ratio ( s ) is introduced for compressible turbulence simulation through a series of direct numerical simulations (DNS). s represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f s to describe the boundary layer region and propose an entropy-based detached-eddy simulation method (SDES). This approach follows the spirit of delayed detached-eddy simulation (DDES) proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performances are compared in the following flows, namely, pure attached flow with thick boundary layer (a supersonic flat-plate flow with high Reynolds number), fully separated flow (the supersonic base flow), and separated-reattached flow (the supersonic cavity-ramp flow). The Reynolds-averaged Navier-Stokes (RANS) resolved region is reliably preserved and the modeled stress depletion (MSD) phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions. Advances in computer speeds have made it possible to utilize more accurate methods of simulating and modeling turbulent flows. However, grid requirements and time cost typically restrict direct numerical simulation (DNS) and even large eddy simulation (LES) to only low Reynolds numbers. That is, Reynolds-averaged Navier-Stokes (RANS) equations along with a turbulence model seem still to be a powerful tool for engineering aerodynamic analysis nowadays, whereas, traditional RANS approaches do not resolve any turbulent flow structures, but model the effect of turbulence on the mean flow in terms of representative mean turbulence scales. As a result, all spectral effects are lost in the time averaging process. The unsteady variant of this, URANS, although managing to resolve non-stationary mean flows, will produce too much eddy viscosity polluting the predicted fields [1,2]. For many turbulent flows of engineering importance, traditional RANS or URANS modeling may be an awkward approach or may fail to reproduce the relevant flow physics. Hybrid RANS/LES approaches [3] represent a credible alternative improving the description of such flows at a reasonable cost by taking into account most of the flow unsteadiness. The main idea of these methods is to model the turbulent structures in the attached region of the flow and to solve the large length-scale structures elsewhere. One of the most popular RANS/LES methods is the detached-eddy simulation proposed by Spalart et al. in 1997 [4] (termed in the following as DES97), which is based on a modification of the length scale employed by Spalart-Allmaras RANS model (SA) [5]. Since the time it was put forward, DES97 has been applied successfully to numerous engineering flow problems, especially in high-Reynolds number separated

Antibiotics such as Oxytetracycline (OTC) is widely used around the world and it caused serious environmental issues in China, especially in Yangtze delta area. However, its effects on amphibian gut morphology and intestinal microbiota are still unclear. In this study, tadpoles of Pelophylax nigromaculatus was exposed to 0, 5, 90 and 450 μg/L OTC of environmentally relevant concentrations from Gosner (Gs) 26 to Gs 38. The results showed that severe histopathological injuries including cytoplasmic damage, cell arrangement disorganisation and structure deformation were observed in the gut of larvae in 90 and 450 μg/L OTC exposure groups. Moreover, Tunel assay also revealed higher apoptotic ratio in the intestine of tadpoles in 90 and 450 μg/L OTC treatment groups. Furthermore, the relative abundance of dominant phyla and genera of gut microbial community in OTC exposure groups was significantly different from that of control though the richness and species diversity did not show remarkable changes. We concluded that OTC may pose potential health risks to amphibian larvae through inducing gut histopathological injury and intestinal microbiota dysbiosis.

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Implicit LES results of a cylinder flow with high order numerical methods in a coarse and a refined grid were compared. The weighted essentially non-oscillatory (WENO) scheme is employed for convective flux while central differencing schemes are used for viscous terms. Several modifications were made to the high order accuracy scheme. Results show that the high order accurate schemes adopted in this paper is feasible and efficient.

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