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In the summer (July and August) of 2022, unprecedented heat wave occurred along the Yangtze River Valley (YRV) over East Asia while unprecedented flood occurred over western South Asia (WSA), which are located on the eastern and western sides of Tibetan Plateau (TP). Here, by analyzing the interannual variability based on observational and reanalysis data, we show evidences that the anomalous zonal flow over subtropical Tibetan Plateau (TP) explains a major fraction the extreme events occurred in 2022. As isentropic surfaces incline eastward (westward) with altitude on the eastern (western) side of the warm center over TP in summer, anomalous easterly (westerly) flow in upper troposphere generates anomalous descent (ascent) on the eastern side of TP and anomalous ascent (descent) on the western side of TP via isentropic gliding. The anomalous easterly flow is extremely strong to reverse the climatological westerly flow over subtropical TP in 1994, 2006, 2013 and 2022. The easterly flow in 2022 is the strongest since 1979, and it generates unprecedented descent (ascent) anomaly on the eastern (western) side of TP, leading to extreme heat wave over YRV and extreme flood over WSA in 2022. The anomalously strong easterly flow over subtropical TP in 2022 is dominated by atmospheric internal variability related to mid-latitude wave train, while the cold sea surface temperature anomaly over the tropical Indian Ocean increases the probability of a reversed zonal flow over TP by reducing the meridional gradient of tropospheric temperature.

In this paper, the fluid flow of Tesla valve after the change of three structural parameters, such as diverting Angle, bend outlet width and stages, is analyzed, and their effects on the performance of Tesla valve single channel are studied. The results show that the Di value of the Tesla valve presents an upward trend with the increase of the three parameters, that is, the performance of the single pilot pass is getting better and better, but the improvement of its performance will be limited to a certain extent. When the diverting Angle increases, the pressure drop and energy loss caused by the reverse flow of the fluid will be larger, but if the diverting Angle is too large, the forward flow of the fluid in the Tesla valve will be affected. When the width of the bend outlet increases to a certain size, the fluid flowing into the bend pipe is close to the upper limit, and the single pilot performance of the Tesla valve will not be greatly improved. The increase of multiple Tesla valve stages has an effect on both forward and reverse flow of fluid.

We report a general synthetic strategy for highly robust growth of diverse lateral heterostructures, multiheterostructures, and superlattices from two-dimensional (2D) atomic crystals. A reverse flow during the temperature-swing stage in the sequential vapor deposition growth process allowed us to cool the existing 2D crystals to prevent undesired thermal degradation and uncontrolled homogeneous nucleation, thus enabling highly robust block-by-block epitaxial growth. Raman and photoluminescence mapping studies showed that a wide range of 2D heterostructures (such as WS₂-WSe₂ and WS₂-MoSe₂), multiheterostructures (such as WS2-WSe2-MoS2 and WS2-MoSe2-WSe2), and superlattices (such as WS₂-WSe₂-WS₂-WSe₂-WS₂) were readily prepared with precisely controlled spatial modulation. Transmission electron microscope studies showed clear chemical modulation with atomically sharp interfaces. Electrical transport studies of WSe₂-WS₂ lateral junctions showed well-defined diode characteristics with a rectification ratio up to 10⁵.

The unsteady flow separation and wake dynamics around finite wall-mounted circular cylinders fully immersed in a turbulent boundary layer (TBL) are investigated experimentally using a time-resolved particle image velocimetry (TR-PIV) system. The cylinder aspect ratios (h/d = 0.7–7.0, where h and d are the height and diameter of the cylinder, respectively) and the relative boundary layer thickness (δ/d = 8.7, where δ is the boundary layer thickness) were chosen to systematically investigate the effects of submergence ratio (δ/h = 1.2–12.4) using δ/h values much larger than that reported in the literature. With δ/h > 1.0, the cylinders encountered elevated turbulence levels (4%–10 %), reduced mean velocity and strong mean shear in the approach TBL which had profound effects on the attachment length and flapping motion of the reverse-flow region on the top surface of the cylinders. The time-averaged statistics including the mean velocities, Reynolds stresses and production terms were used to characterize the flow field and the large-scale anisotropy. The results showed that the wake structure of the submerged cylinders can be divided into dipoles and quadruples with a critical h/d = 3.5 and δ/h = 2.5. Both categories exhibited strong anisotropy, but the quadruples showed an interesting pattern where the streamwise Reynolds normal stress is less than the other components due to negative production in the wake region. Spectral analysis and joint-probability density functions are used to show that the reverse-flow region behind the cylinder is characterized by low-frequency flapping motions with a Strouhal number that decreases with increasing aspect ratio. The spatio-temporal evolution of the vortices also revealed the occurrence of cellular shedding behaviour where the vortices near the free end are shed discretely while those in the lower span are shed in the form of long streaky structures.

The numerical investigation focuses on the flow patterns around a rectangular cylinder with three aspect ratios ($L/D=5$, $10$, $15$) at a Reynolds number of $1000$. The study delves into the dynamics of vortices, their associated frequencies, the evolution of the boundary layer and the decay of the wake. Kelvin–Helmholtz (KH) vortices originate from the leading edge (LE) shear layer and transform into hairpin vortices. Specifically, at $L/D=5$, three KH vortices merge into a single LE vortex. However, at $L/D=10$ and $15$, two KH vortices combine to form a LE vortex, with the rapid formation of hairpin vortex packets. A fractional harmonic arises due to feedback from the split LE shear layer moving upstream, triggering interaction with the reverse flow. Trailing edge (TE) vortices shed, creating a Kármán-like street in the wake. The intensity of wake oscillation at $L/D=5$ surpasses that in the other two cases. Boundary layer transition occurs after the saturation of disturbance energy for $L/D=10$ and $15$, but not for $L/D=5$. The low-frequency disturbances are selected to generate streaks inside the boundary layer. The TE vortex shedding induces the formation of a favourable pressure gradient, accelerating the flow and fostering boundary layer relaminarization. The self-similarity of the velocity defect is observed in all three wakes, accompanied by the decay of disturbance energy. Importantly, the decrease in the shedding frequency of LE (TE) vortices significantly contributes to the overall decay of disturbance energy. This comprehensive exploration provides insights into complex flow phenomena and their underlying dynamics.

We perform direct numerical simulations of actively controlled laminar separated wakes around low-aspect-ratio wings with two primary goals: (i) reducing the size of the separation bubble and (ii) attenuating the wing tip vortex. Instead of preventing separation, we modify the three-dimensional (3-D) dynamics to exploit wake vortices for aerodynamic enhancements. A direct wake modification is considered using optimal harmonic forcing modes from triglobal resolvent analysis. For this study, we consider wings at angles of attack of $14^\\circ$ and $22^\\circ$, taper ratios $0.27$ and $1$, and leading edge sweep angles of $0^\\circ$ and $30^\\circ$, at a mean-chord-based Reynolds number of $600$. The wakes behind these wings exhibit 3-D reversed-flow bubble and large-scale vortical structures. For tapered swept wings, the diversity of wake vortices increases substantially, posing a challenge for flow control. To achieve the first control objective for an untapered unswept wing, root-based actuation at the shedding frequency is introduced to reduce the reversed-flow bubble size by taking advantage of the wake vortices to significantly enhance the aerodynamic performance of the wing. For both untapered and tapered swept wings, root-based actuation modifies the stalled flow, reduces the reversed-flow region and enhances aerodynamic performance by increasing the root contribution to lift. For the goal of controlling the tip vortex, we demonstrate the effectiveness of actuation with high-frequency perturbations near the tip. This study shows how insights from resolvent analysis for unsteady actuation can enable global modification of 3-D separated wakes and achieve improved aerodynamics of wings.

Pharmaceutical supply chain (PSC) is one of the most important healthcare supply chains and the recent pandemic (COVID-19) has completely proved it. Also, the environmental and social impacts of PSCs are undeniable due to the daily entrance of a large amount of pharmaceutical waste into the environment. However, studies on closed-loop PSCs (CLPSC) are rarely considered real-world requirements such as competition among diverse brands of manufacturers, the dependency of customers’ demand on products’ price and quality, and diverse reverse flows of end-of-life medicines. In this study, a scenario-based Multi-Objective Mixed-Integer Linear Programming model is developed to design a sustainable CLPSC, which investigates the reverse flows of expired medicines as three classes (must be disposed of, can be remanufactured and can be recycled). To study the competitive market and deal with demand uncertainty, a novel scenario-based game theory model is proposed. The demand function for each brand depends on the price and quality provided. Then, a hybrid solution approach is provided by combining the LP-metrics method with a heuristic algorithm. Furthermore, a real case study is investigated to evaluate the application of the model. Finally, sensitivity analysis and managerial insights are provided. The numerical results show that the proposed classification of reverse flows leads to proper waste management, making money, and reducing both disposal costs and raw material usage. Moreover, competition increases PSCs performance and improves the supply of products to pharmacies.

The growth and characteristics of linear, oblique instabilities on a highly swept fin on a straight cone in Mach 6 flow are examined. Large streamwise pressure gradients cause doubly inflected cross-flow profiles and reversed flow near the wall, which necessitates using the harmonic linearized Navier–Stokes equations. The cross-flow instability is responsible for the most-amplified disturbances, however, not all disturbances show typical cross-flow characteristics. Distinct differences in perturbation structure are shown between small ($\\sim$3–5 mm) and large ($\\sim$10 mm) wavelength disturbances at the unit Reynolds number $Re' = 11 \\times 10^6$ m$^{-1}$. As a result, amplification measurements based solely on wall quantities bias a most-amplified disturbance assessment towards larger wavelengths and lower frequencies than would otherwise be determined by an off-wall total-energy approach. A spatial-amplification energy-budget analysis demonstrates (i) that wall-normal Reynolds-flux terms dictate the local growth rate, despite other terms having a locally larger magnitude and (ii) that the Reynolds-stress terms are responsible for large-wavelength disturbances propagating closer to the wall compared with small-wavelength disturbances. Additionally, the effect of free-stream unit Reynolds number and small yaw angles on the perturbation amplification and energy budget is considered. At a higher Reynolds number ($Re' = 22 \\times 10^6$ m$^{-1}$), the most-amplified wavelength shrinks. Perturbations do not behave self-similarly in the thinner boundary layer, and the shift in most-amplified wavelength is due to decreased dissipation relative to the lower-Reynolds-number case. Small yaw angles produce a streamwise shift in the boundary layer and disturbance amplification. The yaw results quantify a potential uncertainty source in experiments and flight.

We investigate Reynolds number effects in strong shock-wave/turbulent boundary-layer interactions (STBLI) by leveraging a new database of wall-resolved and long-integrated large-eddy simulations. The database encompasses STBLI with massive boundary-layer separation at Mach $2.0$, impinging-shock angle $40^{\\circ }$ and friction Reynolds numbers ${\\textit {Re}}_\\tau$ $355$, $1226$ and $5118$. Our analysis shows that the shape of the reverse-flow bubble is notably different at low and high Reynolds number, while the mean-flow separation length, separation-shock angle and incipient plateau pressure are rather insensitive to Reynolds number variations. Velocity statistics reveal a shift in the peak location of the streamwise Reynolds stress from the separation-shock foot to the core of the detached shear layer at high Reynolds number, which we attribute to increased pressure transport in the separation-shock excursion domain. Additionally, in the high Reynolds case, the separation shock originates deep within the turbulent boundary, resulting in intensified wall-pressure fluctuations and spanwise variations associated with the passage of coherent velocity structures. Temporal spectra of various signals show energetic low-frequency content in all cases, along with a distinct peak in the bubble-volume spectra at a separation-length-based Strouhal number $St_{L_{sep}}\\approx 0.1$. The separation shock is also found to lag behind bubble-volume variations, consistent with the acoustic propagation time from reattachment to separation and a downstream mechanism driving the shock motion. Finally, dynamic mode decomposition of three-dimensional fields suggests a Reynolds-independent statistical link among separation-shock excursions, velocity streaks and large-scale vortices at low frequencies.

Hydrogen is a promising fuel for decarbonizing energy production and aeronautical propulsion. Even though hydrogen is a zero-carbon fuel, its unique physical and chemical properties pose significant challenges for use in conventional combustion systems, particularly due to potential issues with combustion stability and increased NOx emissions. This study investigates a 100% H 2 double coaxial swirl burner, adapted from a prior CH 4 / H 2 burner design. The burner features two concentric, co-rotating swirling jets, with a fast H 2 premixing stage positioned just before the nozzle outlet to mitigate flashback risks. We present a preliminary analysis of the isothermal flow generated by two injector geometries, using Stereo PIV to capture detailed flow dynamics. In addition to examining the time-averaged flow field, we apply Proper Orthogonal Decomposition (POD) to identify coherent structures within the flow. Results show that the two geometries produce distinct flow field configurations and varying intensities of reverse flow in the near-injection region (within 1–2 diameters downstream). Although similar patterns emerge further downstream, subtle differences in flow structure remain.