Low Pressure Region Research Articles

Optimal design of a combined Power-Heating-Oxygen system for plateau hotel buildings

The Qinghai–Tibet Plateau of China is a region of low atmospheric pressure and oxygen deficiency, with a high heating demand in the winter; therefore, plateau hotel buildings have a demand for comprehensive power-heating-oxygen loads. Solar energy resources are particularly abundant in plateau areas, where a combined multi-energy system based on solar energy can be designed to meet the demand of plateau hotel buildings for multiple loads. However, currently, there is a relative lack of methods for the optimal design and performance evaluation of combined power-heating-oxygen (CPHO) systems. Thus, this study proposes a CPHO system model for plateau hotels, and provides two operation strategies, i.e., power priority and oxygen priority. Taking the minimum total annual cost of the combined system as the optimization objective, an optimized CPHO system model for plateau hotels has been proposed, followed by a case study of a hotel in Qilian County, Qinghai Province. Results showed that: 1) Compared with the conventional combined power-heating (CCPH) system, the CPHO system saw reductions of 0.8% and 1.3% in its total annual cost under the operation strategies of power priority and oxygen priority, respectively. 2) The energy self-consumption (SC) rates of the CCPH system and CPHO system under the operation strategies of power priority and oxygen priority were 84.8%, 64.2%, and 89.8%, respectively; with power self-sufficiency (PSS) rates of 8.3%, 49.9%, and 29.5%, and oxygen self-sufficiency (OSS) rates of 0.0%, 3.2%, and 4.7%, respectively. 3) The total annual cost of the CPHO system was affected slightly by the cost of photovoltaics (PVs) and energy storage devices, and significantly by the price of oxygen. When the price of oxygen was 8 yuan per normal cubic meter(Nm3) or above, the CPHO system was economically efficient under the operation strategy of oxygen priority. When the price of oxygen was 10yuan/Nm3 or above, the system was economically efficient under both operation strategies.

Enhanced ammonia adsorption-desorption properties of synthesized zeolite-carbon composite with the effect of Si/Al ratio

Effective ammonia (NH3) adsorbent is crucial for removing undecomposed NH3 residue after splitting into N2 and H2 fuel. In this study, a zeolite-activated carbon (AC) hybrid was successfully synthesized with a trace AC amount and different Si/Al ratios via hydrothermal method. The NH3 adsorption–desorption properties and mechanisms were investigated through two major activity tests, employing high pressure adsorption isotherm analyzer and breakthrough set up. Incorporating AC at 1 wt%, effectively shortened the regeneration period of the pure zeolite by ∼50 % due to the AC’s pore-widening effect on zeolite network, reducing the trapping of adsorbed NH3 in the zeolite pores. Interestingly, an optimum Si/Al ratio of 1.6 led to the highest specific surface area of 977.57 m2/g by the formation of zeolite mixture with coexisting NaX (faujasite zeolite with high Al atoms per cell) and NaY (higher crystalline faujasite zeolite with low Al atoms per cell). These improved structural characteristics consequently exhibited the highest NH3 (99.9995 %) storage capacity of 15.6 mmol/g at a partial pressure of 300 kPa in isotherm analysis at 25 °C. Besides, the initial breakthrough adsorption capacity for dilute NH3 (5%/N2 balance) under atmospheric conditions reached 8.9 mmol/g, accurately equivalent to isotherm analysis result at 5 kPa. This reproducibility of consistent adsorption uptake within low pressure region in both tests was credited to the compositional presence of both acidic and alkaline surface functionalities in the optimum zeolite-AC hybrid as stable NH3 adsorption sites. These active sites also provided a uniform dynamic adsorption capacity of ∼4 mmol/g throughout 15 cycles. Conclusively, this work highlighted the importance of zeolite composition and AC-incorporated proportion for the H2 purification aspect.

Surface Pressure Measurement of Truncated, Linear Aerospike Nozzles Utilising Secondary Injection for Aerodynamic Thrust Vectoring

A cold-gas test campaign has been conducted at the DLR’s P6.2 test bench in Lampoldshausen, with the objective of investigating the linear aerospike nozzle flow in interaction with secondary injection thrust vector control (SITVC). In this campaign, the influence of nozzle truncation, injection position and injection pressure on the nozzle surface and base pressure is analysed using pressure probes and Schlieren flow-visualisation techniques. The effects of injection position and truncation on the nozzle surface pressure development are comparable for all geometric variations, resulting in a locally increased static pressure upstream and a locally decreased static pressure downstream of the injection. The magnitude and dimension of these high- and low-pressure regions are correlated with the injection pressure. However, the influence of injection position and truncation on the base pressure is not entirely predictable by the named parameters, indicating an interdependence between both geometric parameters. Finally, the required pressure ratio of injection to the primary flow to ensure sonic injection has been analysed on TUD’s cold-gas test bench. This allows the respective injection position-dependent threshold to be identified. The analysis reveals that these experiments have been conducted under transsonic injection conditions.

Experimental and numerical analysis of cavitator angle effects on artificial cavitation characteristics under low ventilation coefficients, with prediction using optimized random forest and extreme gradient boosting models

Artificial cavitation, a complex two-phase phenomenon, involves cavity formation by injecting air into a low-pressure region behind the cavitator. Influenced by factors like cavitator shape and angle, ventilation coefficient, etc., its understanding is crucial. While past research primarily focused on large ventilation coefficients, this study explores the impact of cavitator angles on ventilated cavity characteristics at low ventilation coefficients. For this purpose, three experimental, numerical and machine learning methods have been used. Initially, three angles (0°, 12.5°, 25°) were experimentally investigated across ventilation coefficients of 0.017–0.085. Additionally, through numerical simulations, the effects of increasing the cavitator angle up to 40° at small ventilation coefficients were explored. By optimizing random forest (RF) and Extreme Gradient Boosting (XGB) using Bayesian Optimization Algoritm (BOA), the cavitation characteristics under varying cavitator angles were predicted. The results show the appropriate accuracy of the BOA-XGB model compared to the RF model in predicting the characteristics of cavitation. Results indicate at very small ventilation coefficients, the shape of the cavity is not affected by the cavitator angle. However, with the increase of the ventilation coefficient, in addition to its value, the cavitator angle also affects the shape of the cavity. Increasing the cavitator angle under constant ventilation coefficient induces asymmetry in the cavity's end, elongates the cavity, and reduces the cavitation number.

Numerical and Experimental Analysis of Vortex Pump with Various Axial Clearances

Axial clearance is a critical parameter affecting the performance of vortex pumps. In this study, numerical simulation and experimental validation methods are employed to establish four different clearance schemes. The analysis focuses on multiple aspects, including the internal flow field, clearance flow field, leakage flow, and recirculation flow, to investigate the impact of axial clearance on the internal flow field and the external characteristics of the vortex pump. The results indicate that under the pressure difference between the inlet and outlet, the main flow leaks from the high-pressure region at the outlet to the clearance flow channel, and the clearance flow returns to the main flow channel at the low-pressure region of the inlet. As the axial clearance increases, the intensity of the vortices inside the pump gradually decreases. This leads to a reduction in intensity of the momentum exchange between the fluid inside and outside the impeller, causing a decline in the pump performance curve. Simultaneously, the increase in clearance reduces the flow resistance in the clearance region, and the clearance flow gradually stabilizes. The interaction between the clearance flow and the main flow intensifies, causing the leakage flow and recirculation flow to increase rapidly, which results in significant energy loss.

Improving the sealing performance of honeycomb seal by drilling double wall-holes

A novel double-wall-hole honeycomb seal (D-WHHCS) is proposed in this paper. D-WHHCS is designed based on a traditional honeycomb seal (HCS) by drilling double holes in the honeycomb sidewalls. The leakage characteristics of D-WHHCS are investigated via the computational fluid dynamics (CFD) method. The sealing performance of D-WHHCS under different seal clearances, wall hole positions, operating pressures and rotating speeds is studied. The sealing mechanism of D-WHHCS is revealed. The results show that D-WHHCS has better sealing performance than HCS under all the considered operating conditions, with a maximum leakage reduction of 3.95%. A fluid concentration effect when the axial cavity number (N) = 14 is observed in D-WHHCS, which causes a 9.16% improvement in the maximum turbulent kinetic energy compared with HCS at the outlet extension. A large vortex in the cavities of D-WHHCS with N = 14 is guided by the jets at the centerlines of the drilling hoes. The average turbulent dissipation in the cavities of D-WHHCS is a maximum increase of 95.30%, even though the vortexes in the cavities with N = 13 are weakened by the counteractive effect of two jets. The leakage reduction performance of D-WHHCS decreases with increasing clearance. An abnormal low-pressure region is produced in the first cavity because the intensive jet covers the first two cavities and suppresses the throttling effect of the first-stage honeycomb cavity. The leakage of D-WHHCS further decreases along with holes closing to rotor surface.

Study on rotating stall characteristics of centrifugal pumps based on gamma transition model

The phenomenon of rotating stall in centrifugal pumps is closely associated with the evolution of the blade boundary layer. Aiming to accurately predict the characteristics of the boundary layer, this study investigates the phenomenon of rotating stall in centrifugal pump impellers using the gamma (γ) transition model. The accuracy of the numerical simulation was confirmed by comparing its conclusions with the results of the testing. In calculations considering transition characteristics, the distribution of low-pressure areas inside the impeller is relatively discontinuous, while the pressure distribution is more uniform. However, in calculations without considering transition, the low-pressure regions in neighboring flow channels exhibit a tendency to be interconnected, resulting in a more variable pressure distribution, and the pressure contour at the outlet is closer to parallel. The dynamic characteristics of the centrifugal pump impeller rotating stall were obtained through the dynamic mode decomposition method, including the frequency, structure, and dynamic evolution process of the stall vortex. Through modal reconstruction, it was discovered that the impeller's rotation causes the stall vortex to undergo periodic fluctuations. The stall vortex is not stationary but moves synchronously with the rotation of the blades. At different time points, the stall vortex exhibits periodic changes. At the blade suction entrance, the stall vortex initially appears. Subsequently, multiple vortex structures resulted in channel blockage. After a period of development, the excess vortex structures merge to generate a typical “8” shaped vortex structure and move toward the exit. Finally, the exit stall vortex disappears, and a new vortex structure is generated at the inlet of the blade suction surface.

The lift enhancement mechanism caused by the deformation of the surface of the wide-speed waverider

The optimization method provides an effective approach to enhance the low-speed lift of the vortex lift waveriders by deforming the aerodynamic shape refinedly. However, the vortex lift enhancement mechanism of the optimized configuration is unclear. In this study, the flow evolutions of the original and the optimized configurations are studied by employing the delayed detached-eddy simulation. Results indicate that the convex deformation of the leeward surface plays a dominant role in enhancing the vortex lift by enhancing the low-pressure suction at the upstream breakdown location and delaying the vortex breakdown. For the enhancement of the low-pressure suction, the convex deformation intensifies the streamwise vorticity below the axis of the primary vortex of the leading-edge vortex, in turn enhancing the downwash effect and causing the primary vortex to move downward. This reduces the pressure coefficient induced by the primary vortex on the leeward surface, thus enhancing the vortex lift. In terms of the delay of the vortex breakdown, the convex deformation compresses and accelerates the flow between the spanwise convex and the leading edge. These intensities enhance the washing effect along the spanwise direction on the outward wing and cause the primary vortex to deflect toward the outboard wing. Subsequently, the primary vortex and the shedding vortices generated by the shear layer instability merge, which increase the primary vortex intensity, and enhance the streamwise velocity in the vortex axis. Correspondingly, the primary vortex breakdown is delayed. Ultimately, the increased low-pressure region caused by the delay of the vortex breakdown enhances the vortex lift.

Hydrogen isotope transport parameters in materials for tritium extraction systems. Focus on the low pressure

This work aims to fill a gap in the H transport database for niobium and vanadium, materials proposed for the fabrication of tritium extraction systems. The permeability, key parameter for this application, has not been properly determined in niobium so far. Values are given for H2 and D2 permeability in two different Nb samples from different suppliers but with similar microstructure from ∼300 °C to 500 °C and tested with loading pressures from 20 mbar to 500 mbar:ϕ(Nb/H2)[mol·m−1·s−1·Pa−0.5]=4.49·exp(−19,258T)ϕ(Nb/D2)[mol·m−1·s−1·Pa−0.5]=1.31·exp(−19,332T)For vanadium, new measurements for material from different suppliers and with very different microstructure allow to confirm values for the permeability recently published (in contrast to the traditionally accepted values indirectly derived from solubility and diffusivity). In this work, the following expression is given for deuterium:ϕ(V/D2)[mol·m−1·s−1·Pa−0.5]=1.31·exp(−11,603T)There are very few documented attempts to measure surface rate constants for either of the two materials under consideration. These parameters are especially important and define the permeation process under certain conditions, in particular at low pressures. Hydrogen and deuterium permeation data in Nb and V has been therefore obtained in a wide range of pressures, with special focus in the low pressure region, the role of the microstructure being also evaluated. Surface rate constants σk1 and σk2, which are fundamental parameters for the modelling of H isotope transport through the materials, have been determined in vanadium and niobium with different surface finishes, this factor resulting determinant of the result.

Humidity-resistant, breathable, waterproof, and bionic triboelectric electronic skins for self-powered haptic sensing and human motion recognition

Researchers have been striving for a long time to create an electronic skin (E-skin) that can rival or surpass human skin in functionality. Herein, inspired by human skin, we developed a bionic triboelectric E-skin (BTE-skin) via a cost-effective method with superior humidity-resistance, breathability and waterproofness. Benefiting from introducing HKUST-1 into silicone rubber as the triboelectric layer significantly enhances the humidity resistance of the triboelectric E-skin, and the output is increased by a factor of 2.15 at 90 % relative humidity. The construction of a fully enclosed electrode structure and a three-dimensional microporous array structure promises BTE-skin excellent breathability (water vapor transmission of 500 g/m2/d and air permeability of 293 mm/s) and waterproofness. In addition, the BTE-skin exhibits a wide sensing range (up to 100 kPa), ultra-high pressure response sensitivity in the low-pressure region (504.60nA/kPa), fast response time (42 ms), and excellent cycling stability over 10,000 cycles. Furthermore, based on the BTE-skin, a self-powered smart home control system and a visual leg motion recognition system have been successfully developed. This work proposes a new strategy for tracking electronic human skin and manifests great potential in the intelligent wearable sensing field, which can help human life move toward a more convenient and intelligent future.

Importance of the semimetallic state for the quantum Hall effect in HfTe5

At ambient pressure, HfTe5 is a material at the boundary between a weak and a strong topological phase, which can be tuned by changes in its crystalline structure or by the application of high magnetic fields. It exhibits a Lifshitz transition upon cooling, and three-dimensional (3D) quantum Hall effect (QHE) plateaus can be observed at low temperatures. Here, we have investigated the electrical transport properties of HfTe5 under hydrostatic pressure up to 3 GPa. We find a pressure-induced crossover from a semimetallic phase at low pressures to an insulating phase at about 1.5 GPa. Our data suggest the presence of a pressure-induced Lifshitz transition at low temperatures within the insulating phase around 2 GPa. The quasi-3D QHE is confined to the low-pressure region in the semimetallic phase. This reveals the importance of the semimetallic ground state for the emergence of the QHE in HfTe5 and thus favors a scenario based on a low carrier density metal in the quantum limit for the observed signatures of the quasiquantized 3D QHE. Published by the American Physical Society 2024

Hydrodynamic Performance Research of Underwater Oscillating Fin With the Compound Locomotion of Two Modes

Abstract The fish-like propulsion robot is becoming a profound intelligent equipment due to its excellent swimming ability and good environmental adaptability. In this paper, we propose the oscillating fin based on the fish swimming mechanism, which is compounded with the locomotion modes of sway and yaw. The kinematic and dynamic models are established to study the locomotion mechanism of the oscillating fin. The hydrodynamic performance of underwater locomotion is investigated to analyze the velocity, the propulsive force, the pressure, the propulsive efficiency, and the vortices property. Finally, the experimental measurements of the robot with oscillating fin propulsion are carried out to analyze the underwater propulsion of the oscillating fin and the unsteady fluid flow with Strouhal number. The results illustrate that the propulsive force is fluctuating, and the velocity is increasing to the maximum value. The underwater propulsion velocity could reach 1.2 m/s in a period of 0.4 s. Besides, the high- and low-pressure regions change alternatively, and the fin deforming process illustrates the vortices property and the locomotion mechanism analyses. The propulsive efficiency of the oscillating fin with compound waves is increased by 11% compared with that of the one without deformation. The experiments of the robot prototype verify the numerical simulation, and the propulsive velocity with a period of 0.4 s is two times larger than that of a period of 0.8 s. The Strouhal number of each motion mode is obtained through theoretical and experimental analyses.

Unraveling thermodynamic anomalies of water: A molecular simulation approach to probe the two-state theory with atomistic and coarse-grained water models.

Thermodynamic and dynamic anomalies of water play a crucial role in supporting life on our planet. The two-state theory attributes these anomalies to a dynamic equilibrium between locally favored tetrahedral structures (LFTSs) and disordered normal liquid structures. This theory provides a straightforward, phenomenological explanation for water's unique thermodynamic and dynamic characteristics. To validate this two-state feature, it is critical to unequivocally identify these structural motifs in a dynamically fluctuating disordered liquid. In this study, we employ a recently introduced structural parameter (θavg) that characterizes the local angular order within the first coordination shell to identify these LFTSs through molecular dynamics simulations. We employ both realistic water models with a liquid-liquid critical point (LLCP) and a coarse-grained water model without an LLCP to study water's anomalies in low-pressure regions below 2 kbar. The two-state theory consistently describes water's thermodynamic anomalies in these models, both with and without an LLCP. This suggests that the anomalies predominantly result from the two-state features rather than criticality, particularly within experimentally accessible temperature-pressure regions.

Numerical study on the influence of riblet yaw-angle on drag reduction rate with different immersion heights

This paper uses the Large-eddy simulation method to investigate the influence of riblet yaw angle on drag reduction rate with different immersion heights, revealing that the vortex structure is gradually transformed from riblet-tip vortex pairs to boundary vortex forms with the increase of yaw angle, and analyzing the influence mechanism of immersion height on the critical yaw angle. The result shows that the drag-reduction rate of riblets decreases as the yaw angle increases, and the critical angle of the riblet varies with the different immersion heights. When the immersion height is 0.7, 0.5, and 0.3, the critical yaw angle is close to 30, 40, and 50°, respectively. As the immersion height increases, the cross-flow velocity at the riblet tip is more accessible to reach the critical velocity at which a boundary vortex can be formed, resulting in a smaller critical yaw angle for larger immersion heights. Furthermore, with the yaw angle increases, the normal diffusivity of normal vorticity and spanwise vorticity increase and decrease, respectively, which indicates that the lateral flow fluctuations decrease beyond a critical yaw angle, while the Reynolds stress component due to energy dissipation induced by the streamwise velocity decreases. Meanwhile, with the formation of a boundary vortex, the ability of the riblet to reduce viscous shear stresses increases due to the reduction of near-wall velocity gradient, and the emergence of a high-pressure region on the windward side of the riblet and a low-pressure region on the leeward side, consequently augmenting the differential pressure drag. This work provides valuable insights for designing riblets with heightened effectiveness at larger yaw angles, thereby extending their applicability under diverse flow conditions.

Drag reduction of Clark-Y hydrofoil by biomimetic fish scale structure under the condition of biomimetic jet

Hydrofoil, as the basic shape of the fluid blade, is widely used in fluid transport and energy conversion. However, friction resistance and pressure differential resistance are generated in the hydrofoil flow process, resulting in substantial energy consumption and negatively affecting the economy. On this basis, we propose two drag-reducing structures based on Clark-Y hydrofoil. In the design process of the jet structure, we considered the bionic jet velocity, jet angle and jet structure position as the design parameters and obtained the optimal jet structure by using Taguchi method. Finally, the two schemes (Clark-Yori and Clark-Yopt) are numerically simulated using large eddy simulation. Results show that when Ujet = 1.44 m/s, θ = 3° and x = 18.6 mm, the jet structure can play a significant drag reduction effect. Compared with Clark-Yori, the drag coefficient of Clark-Yopt is reduced by 26.5%, and the lift drag ratio is increased by 16.4%. Compared with Clark-Yori, Clark-Yopt can reduce the wall shear stress of the leading edge of the hydrofoil, thereby diminishing the frictional resistance. Meanwhile, the jet structure can effectively balance the area of the low-pressure region on the suction side of the hydrofoil, significantly reducing the pressure differential resistance. Clark-Yopt can accelerate the vortex collapse that decreases turbulence intensity and turbulence resistance. Moreover, it can effectively block the near-wall reflux of hydrofoil and reduce the internal friction between the reflux and the main flow.

Energy Characteristics in the Flow Channel of the Shaft-Type Tubular Pumping Station Considering Tides

The shaft-type tubular pumping station has the remarkable characteristics of a large flow rate and high efficiency. It can realize the functions of irrigation, pumping, and drainage through pumping and generating conditions considering tides. Moreover, it is widely used in the plain area of eastern China and the tidal area along the marine region. Due to the different topological features of the airfoil of the impeller, the energy evolution characteristics of the shaft-type tubular pumping station during pumping and generating conditions remain unclear. The entropy generation theory was introduced to numerically simulate the flow pattern and energy characteristics in the shaft-type channel, impeller, and straight channel in operation conditions. The results show that the flow pattern is stable when the shaft-type channel and the straight-type channel are used as the inlet channel under pumping and generating conditions, and a low-pressure region occurs in the contraction section of the shaft-type channel. The velocity of sections of the inlet and outlet and the middle section of the impeller in the generating condition is larger than that in the pumping condition. In addition, the difference in the static pressure on the blade surface nearby the hub is large. With a change in the position of the wingspan, the difference gradually decreases from the small flow condition to the large flow condition. There is a high-entropy production rate zone in the channel contraction section and the shaft-type wall surface of the shaft-type flow channel. When the straight-type channel is used as the outlet flow channel, a high-entropy production region appears near the inlet water surface. In the pumping condition, a high-entropy production area is found at the inlet of the impeller, the blade groove channel, and the inlet of the guide vane. In the generating condition, a high-entropy production area is found at the out-of-impeller outlet, the blade groove channel, and the outlet of the guide vane. These research achievements have some reference value for the design of the shaft-type tubular pumping station considering tides and the study of hydraulic performance, along with the energy characteristics of the channels.

Interdecadal variability of the pre-monsoon cyclone characteristics over the Bay of Bengal

The low-pressure systems intensified to cyclones prior to the onset of the Indian summer monsoon season over the North Indian Ocean are referred to as pre-monsoon season (PMS) cyclones. Climate change is amplifying the pre-monsoon cyclone landscape, fostering more frequent and intense storms with altered tracks, resulting in heightened risks for coastal communities and economies. This study investigates the interdecadal variations in tropical cyclone and key large-scale atmospheric parameters that influence the characteristics of cyclones, including track, frequency over the Bay of Bengal (BoB) during the pre-monsoon season from 60 years of data. The large-scale atmospheric parameters are analyzed by calculating climatological anomalies. It is noted that the frequency of cyclones making landfall over the eastern Indian coastal landmass has increased in the recent decade compared to the past five decades. Compared to the past fifty years, the percentage frequency has increased in the recent ten years by 50%. At the low level, stronger easterlies are dominant and upper-level jet streams shift to lower latitudes, indicating that the path of cyclones has shifted from the north (N)-northeast (NE) to the northwest (NW), i.e. towards the east Indian coastal landmass, over the recent decade. In contrast to the previous five decades, an unusual low-pressure region has emerged over the NW India and Pakistan regions, creating a favorable path for cyclones moving towards the Indian region in recent decade. Cyclones have been more intense in the recent decade than they were in the previous five decades, according to the rise in low- and mid-level specific humidity and temperature over the BoB.

Numerical study of mixing vane spacer grid effect on subchannel mixing in a 5 × 5 rod bundle

Turbulent flow in rod bundle with spacer grid without mixing vanes and with mixing vanes of inclination angles from 10° to 30° was investigated by Reynolds Stress Transportation (RST) model under Reynolds numbers (Re) from 3.96 × 103 to 3.96 × 105. The predicted results were validated by experimental data of lateral velocity field in 5 × 5 rod bundle. The cross-flow velocity was relatively well predicted against experimental data, while lateral Reynolds normal stress was underpredicted near spacer grid and overpredicted far from spacer grid. The mixing vanes in one sub-channel generate high pressure region at the upstream side of mixing vane and low-pressure region at the downstream side of mixing vane, forming secondary flow structures. The lateral velocity increases with inclination angle and Re increasing. The lateral Reynolds stress increases with inclination angle increasing and decreases with Re increasing. The anisotropic turbulent states were studied by Lumley triangle method. The mixing vanes are the main factor dominating the turbulent states in rod bundle. The space grid resistance follows decreasing power function of Re and increases with inclination angle increasing. The secondary flow intensity follows an exponentially decaying function of distance from spacer grid and increases with inclination angle and Re increasing. The turbulent mixing coefficient model is an exponentially decreasing function of the distance from spacer grid, and it increases with inclination angle increasing and decreases with Re increasing. This paper studied the inclination angle and Re effect on the sub-channel mixing in a relatively large range of inclination angle and Re, improving the understandings of the sub-channel mixing phenomena.

Jet-induced vortices of a row of distributed engines at vertical take-off condition

Abstract The aerodynamic performance of a wing model with a row of distributed engines are investigated at the vertical take-off condition. The engines are installed near the trailing edge of the wing. During vertical take-off, the jets exit from the engines and impinge perpendicularly to the ground, providing a thrust for the aircraft. Due to the ground effects, complex vortex structures are induced by the jets. The vortices are categorised into the spanwise vortices and the chordwise vortices. The underwing vortices can lead to low-pressure regions on the lower surface of the wing, resulting in an undesirable downward force. The underwing vortex structures are affected by the ratio of the engine distance to the engine diameter ( $S/D$ ). At a small $S/D$ = 1.10, the flow field is dominated by the spanwise vortices; at a large $S/D$ = 2.78, the flow field is dominated by the chordwise vortices. The range and strength of the spanwise vortices are affected by the vortices interaction. Competition mechanism exists between the range and strength effects, which results in the non-linear variation of the wing lift coefficient with engine spacing. The details of the flow physics underneath the wing and its mechanism on the lift of the wing during take-off are investigated.

Sliding-mediated ferroelectric phase transition in CuInP2S6 under pressure

Interlayer stacking order has recently emerged as a unique degree of freedom to control crystal symmetry and physical properties in two-dimensional van der Waals (vdW) materials and heterostructures. By tuning the layer stacking pattern, symmetry-breaking and electric polarization can be created in otherwise non-polar crystals, whose polarization reversal depends on the interlayer sliding motion. Herein, we demonstrate that in a vdW layered ferroelectric, its existing polarization is closely coupled to the interlayer sliding driven by hydrostatic pressure. Through combined structural, electrical, vibrational characterizations, and theoretical calculations, we clearly map out the structural evolution of CuInP2S6 under pressure. A tendency toward a high polarization state is observed in the low-pressure region, followed by an interlayer-sliding-mediated phase transition from a monoclinic to a trigonal phase. Along the transformation pathway, the displacive-instable Cu ion serves as a pivot point that regulates the interlayer interaction in response to external pressure. The rich phase diagram of CuInP2S6, which is enabled by stacking orders, sheds light on the physics of vdW ferroelectricity and opens an alternative route to tailoring long-range order in vdW layered crystals.