Throat Width Research Articles

Optimising Venturi flume oxygen transfer efficiency using uncertainty-aware decision trees

ABSTRACT This study optimizes standard oxygen transfer efficiency (SOTE) in Venturi flumes investigating the impact of key parameters such as discharge per unit width (q), throat width (W), throat length (F), upstream entrance width (E), and gauge readings (Ha and Hb). To achieve this, a comprehensive experimental dataset was analyzed using multiple linear regression (MLR), multiple nonlinear regression (MNLR), gradient boosting machine (GBM), extreme gradient boosting (XRT), random forest (RF), M5 (Pruned and Unpruned), random tree (RT), and reduced error pruning (REP). Model performance was evaluated based on key metrics: correlation coefficient (CC), root mean square error (RMSE), and mean absolute error (MAE). Among the proposed models, M5_Unprun emerged as the top performer, exhibiting the highest CC (0.9455), the lowest RMSE (0.1918), and the lowest MAE (0.0030). GBM followed closely with a CC value of 0.9372, an RMSE value of 0.2067, and an MAE value of 0.0006. Uncertainty analysis further solidified the superior performance of M5_Unpruned (0.7522) and GBM (0.8055), with narrower prediction bands compared to other models, including MLR, which exhibited the widest band (1.4320). One-way analysis of variance confirmed the reliability and robustness of the proposed models. Sensitivity, correlation, and SHapley Additive exPlanations analyses identified W and Hb as the most influencing factors.

Optimizing Duct Geometry for Micro-Scale VAWTs: Exploring Aerodynamics and Aeroacoustics with URANS and DDES Models

Among several advantages of the Vertical Axis Wind Turbines (VAWTs), such as the low cut-in speed, these turbines have lower efficiency compared to Horizontal Axis Wind Turbines (HAWTs). In order to increase the power of VAWTs, a novel approach is employed to address the aforementioned issue. In this study, a convergent-divergent duct (including three components: nozzle, diffuser, and flange) is used, and in the first step of this study, the angles and lengths of all duct components and throat width are optimized (in 3D configuration). In the optimization process, first, the design points are determined by the Design of Experiment (DOE) method, and for each design point, the flow field inside the duct is modeled by the Reynolds-Averaged Navier-Stokes (RANS) approach. Moreover, the objective function of this optimization problem is to maximize the velocity of the flow inside the duct. In the following, the general treatment of the statistical population is forecasted using the Response Surface Method (RSM), and the optimal duct is obtained using the Genetic Algorithm (GA). It is observed that the optimal duct increases the local wind speed up to 1.99 times (from 5 m/s to 9.94 m/s at the throat). Furthermore, a sensitivity analysis was performed on the duct components, which are the most effective parameters in increasing wind speed, nozzle angle, and nozzle length. In the second step, a Darrieus VAWT (with both 2D and 3D configurations) is numerically validated, and then this turbine is scaled-down and located in the optimal duct. The position and tip-clearance of a turbine within the optimal duct are investigated to find the best configuration for higher power generation. Subsequently, both the bare wind turbine and the ducted wind turbine undergo thorough aerodynamic and aeroacoustic analysis, using unsteady RANS and Delayed Detached Eddy Simulations (DDES) approaches, respectively. The results reveal a remarkable improvement in the aerodynamic efficiency (power coefficient increased up to 2.5 times) with the addition of the optimal duct, while the aeroacoustic performance of the system is compromised, leading to an increase in sound pressure level.

ENGINEERING OF LIQUID-GAS EJECTOR USING NUMERICAL SIMULATION

The article deals with the development and application of the technology of injection of low-pressure associated petroleum gas (APG) into the reservoir through the reservoir pressure maintenance system (RPMS) in connection with the entry into force of the Russian government decree on the mandatory utilization of 95 % of produced APG. The technology under consideration, the key element of which is a liquid-gas ejector (LGE), makes it possible to achieve this level with minimal investment, in the shortest possible time and to stop flaring APG at flares remote from the central oil and gas treatment facilities of oil and gas production facilities. LGEs have a relatively simple and reliable design due to the absence of moving elements.At present, there are known LGEs of classical designs, in which the level of hydrodynamic losses can reach 40–60 %. High hydrodynamic losses make it inexpedient to use such ejectors at small fields operated at a late stage of development, remote from the central oil and gas treatment facilities, due to the limitations of the existing equipment complex and the allowed operation mode of the injection well stock. To ensure the possibility of including LGE in the RPM system it was required to develop a new design of LGE, allowing to reduce hydrodynamic losses up to 30 %, as well as to ensure the maximum possible percentage of APG utilization. The article is devoted to the development, calculation of geometry and operating mode of LGE using numerical modeling in ANSYS environment.Modeling of the flowing part of the main elements of LGE (confuser nozzle, diffuser throat and gas channel width) at different values of parameters directly affecting the level of hydraulic losses is carried out. The results of calculations of numerical simulation of LGE allowed to optimize the dimensions of the internal geometry of LGE, thus it was possible to develop a new device for the required initial data, which will reduce the level of hydraulic losses up to 30 % and ensure the involvement of the maximum volume of gas in the RPM system.

The influences of jet axis switching and aerodynamic focusing on aerosol deposition in converging–diverging slit impactors

The deposition pattern or “linewidth” of an inertial particle deposit from acceleration of an aerosol through a high aspect ratio slit nozzle-substrate system is influenced by particle size-dependent aerodynamic focusing. In addition to this, high aspect ratio jets will eventually undergo downstream “jet-axis switching”, wherein the jet profile shrinks along its major axis and elongates in the direction of the minor axis. Jet axis switching in an aerosol may also lead to “rotated” particle deposits. In this study, we use a converging–diverging slit nozzle system with a major axis length of 8 mm and a throat width (minor axis) of 200 μm to examine the deposition patterns of monodisperse particles in the 100 nm–5 μm diameter range, in air with an upstream pressure of 252 Torr and variable downstream pressure in the 3–50 Torr range. The nozzle-to-substrate distance L∗ is varied from 90 to 248 times longer than the throat width. We find deposition patterns that are strongly dependent on particle size, downstream pressure, and L∗. Depending on particle diameter and operating conditions, we obtain deposits resembling the nozzle dimensions and orientation, deposits which are completely switched (perpendicular to the nozzle), or deposits which are relatively symmetric and focused at a center point. The latter appear to be the result of the combined effects of jet axis switching and aerodynamic focusing. In general, the influence of jet axis switching is more pronounced on smaller particles at higher downstream pressures, and with larger distances to the substrate. The extent of switching and area of the deposit are also both inversely related to the particle Stokes number.

Effect of particle size distribution variability on the permeability of hydrate-bearing sediments: A CFD study

Natural gas hydrates (NGH) are considered as a future clean energy in the era of carbon neutrality. The seepage behaviour of hydrate-bearing sediment (HBS) and its controlling factors are significant for developing effective production strategies. In this study, we aim to elucidate how the heterogeneous spatial distribution of clayey-silty sediment particles, particularly the non-uniform particle size distribution (PSD) affects the permeability of HBS. An algorithm was developed to generate the heterogeneous spatial distribution of sediment particles based on the PSD of hydrate-bearing cores extracted from Japan Nankai Trough (D50 = 122 μm). A series simulation of fluid flow in porous media based on CFD was conducted for the HBS with varying hydrate saturations (SH). The watershed segmentation algorithm was employed for the identification of pore structure, including pore space and pore throat with a detailed analysis on the pore structure evolution with SH. Host sediments with higher uniformity result in initial high permeability but the permeability reduction with increasing SH is more significant compared with that of lower uniformity. Pore throat width reduced to less than 5 μm with SH above 50% compared with its original width of ∼30 μm. Tortuosity exhibits a linear increase with SH, while permeability decreases exponentially with increasing tortuosity. We propose an improved permeability model (KCpro) based on the classical Kozeny-Carman model accounting for the change in specific surface area for non-uniform PSD in HBS with good agreement. This study confirmed the applicability of CFD modelling as a promising tool to study the seepage behaviour of HBS complementary to classical permeability experimental tests. Results of this study provide fundamental understanding on how permeability evolves in HBS with significant PSD variations in natural gas hydrate reservoirs in nature.

Numerical modeling and CFD simulation of diffuser augmented dual vertical axis hydrokinetic Banki-Michell turbine

Hydrokinetic Banki turbines present an affordable, technically feasible, environmentally friendly technology. Their construction without requiring more expensive structures like diversion weirs, canals, forebay, and penstock, makes their initial investment much lower than commonly used horizontal Banki turbine of the same capacity. The possibility to install in the existing canals for Ultra Low Head applications is the additional motivating factor for this research. The system studied includes two Banki runners without internal shafts mounted vertically side by side surrounded by nozzle and diffuser structures. In the first scenario, Nozzle and then the Nozzle-diffuser augmented structures were separately studied to enhance the output of the runner for ultra-low head application, and the effects of each on the speed, pressure, and power output were analyzed. For the case of commonly used Banki, without nozzle and diffuser augmentation the speed for Ultra Low Head was minimum and determined to be 344 rpm, which is far below the recommended value of 800 rpm for safe operation at a flow rate of 1 m^3/s. In view of this, in the present study the enhanced speed on account of improvement was found to be 850 rpm and 1025 rpm for the design without and with diffuser assemblies respectively. Besides, the performance is seen to be improved by 7.6% with the diffuser as compared with the one without diffuser assembly. Detailed simulation results are presented and discussed: 3D ANSYS-FLUENT optimization result provided optimum number of blades for each runner to be 19 and with the optimum throat width in both cases as 202 mm. On account of the lack of any results reported so far for this innovative geometry, validation of the simulated results was carried out with reported results for the dual horizontal axis Banki turbines with good agreement.

Flow Field Simulations Over Reentry Modules at High Speed

Reentry capsule configurations significantly differ from each other due to entry conditions and mission requirements. This paper describes numerical simulations of the viscous flow over the Beagle and the OREX (Orbital Reentry EXperiments) configurations for freestream Mach numbers in the range of 1.2 - 5.0. The flow fields over the reentry modules are obtained by solving time-dependent axisymmetric compressible laminar Navier-Stokes equations. The fluid mechanics equations are discretized in spatial coordinates employing a finite volume method, which reduces the governing equations to semi-discretized ordinary differential equations. Temporal integration is carried out using a two-stage Runge-Kutta time-stepping scheme. A local time-stepping is employed to get the steady state solution. The numerical simulation is performed on a single-block structured grid. The flow field features around the reentry capsules such as bow shock wave, sonic line, expansion fan and recirculation flow in the base-shell region are well captured by the present numerical computation. The effects of the geometrical parameters of the module, such as aspect ratio, frontal segment bluntness, fore body cone angle and shoulder rounding radius on the wake throat width, distance from the wake throat to the base of the model, flow departure angle and aerodynamic drag are analyzed using the numerically simulated flow field.

Numerical Investigation of the Oblique Detonation Waves and Stability in a Super-Detonative Ram Accelerator

This study numerically investigates the effects of diluent gas proportion, the overdrive factor, and throat width on the wave structure and thrust performance of a ram accelerator operating in super-detonative mode. For premixed gas of a high energy density, a typical unstart oblique detonation wave system is observed due to the ignition on the front wedge of the projectile, and the detonation waves move downstream to the shoulder as the energy density decreases. In the start range of the overdrive factor, the wave position also shows a tendency to move downstream as the projectile velocity increases, accompanied by oscillations of the wave surface and thrust. As the throat width increases, the wave standing position changes non-monotonously, with an interval of upstream movement and Mach reflection. The typical wave structure of a ram accelerator in super-detonative mode is identified, as well as the unstart stable wave features and the unstable process for choking, which can provide theoretical guidance for avoiding unstart issues in ram accelerators and optimizing their performance.

Experimental study of strong imbibition in microcapillaries representing pore/throat characteristics of tight rocks

Imbibition pervasively exists in many industrial processes and is fundamental in developing unconventional resources in tight formations. Micromodels have been widely used as powerful tools for real-time observations of imbibition dynamics to support numerical modeling developments and understanding of macroscopic patterns. However, the inherent limitation of 2D micromodels in presenting 3D features in the pores/throats of tight rocks may reduce the reliability of the microfluidic results. Here, we quantitively investigate imbibition dynamics in single pore geometries that consider 2D pore-scale characteristics of tight rocks with an etching depth higher than the critical geometric criteria for including 3D features. We discuss the experimental data based on varying parameters, such as five pore shapes, a wide range of pore-throat aspect ratios (6.25 to 100), two typical throat widths (3 and 8 μm), and local capillary numbers (10-6 to 10-4). The results show that the wetting phase saturations increase linearly with the increasing inlet flow rate, consistent with previous findings in cores and 2.5D micromodels, but only in macropores. Snap-offs are found when the moved meniscus front pressure is higher than the critical capillary pressure of snap-off. An etching depth higher than the critical geometric criteria is necessary but insufficient to mimic imbibition dynamics in tight rocks by 2D micromodels with a pattern that the most pore-throat aspect ratios are less than 30 at a strong imbibition condition.

Comparison of Aerodynamic Loss of a Gas Turbine Vane with Various Trailing Edge Cooling Schemes

In this study, a comparison of aerodynamic loss of gas turbine vane with various trailing edge configurations was experimentally performed. For the trailing edge, three cooling schemes (the cutback slot, the central injection slot, and the pressure side hole) and three levels of trailing edge diameter (7.5, 10.0, and 12.5% of the throat width, respectively) were considered. The total pressure loss was measured in a five-vane linear cascade at the low-speed mainstream condition (20 m/s) using a Kiel probe and a two-axis traversing device. The measurement region was constrained to the near mid-span region, and the measurement step size was 1 mm. The results showed that the distribution of the total pressure loss was strongly affected by cooling schemes. The vane with the pressure side hole showed a similar distribution to that of the baseline in which a cooling scheme was not applied. It was also shown that the total pressure loss increased as the trailing edge diameter increased regardless of the cooling schemes. Except for the cutback slot cases, there was an inflection point at which the tendency of the area-averaged total pressure loss to the blowing ratio was changed. Through the present study, correlation equations for each cooling scheme were derived against the trailing edge diameter and the blowing ratio.

Impact of Slots on the Aerodynamic Performance of the Variable Inlet Guide Vane Cascade of a Centrifugal Compressor

This study reconstructed the flow field of a symmetrical variable inlet guide vane in a centrifugal compressor through the passive control method of vane slots. Based on the high-fidelity numerical simulation model verified by experiments, the influence of different slot forms on the flow field was investigated, and the passive control mechanism was revealed. The results demonstrated that the vane slot method can effectively suppress the suction surface separation and broaden the range of low-loss incidence angles. Overall, the 50_30 slotted vane achieves the best flow field control, with a 65.6% reduction in the total pressure loss coefficient and a 2.3° reduction in the deviation angle, respectively, at a 25° incidence angle. The linear characteristics of the pre-swirl grade variation curve with variable inlet guide vane incidence angles are also improved. Furthermore, changing the slot outlet angle has the most significant influence on the aerodynamic performance as it changes the throat width of the location, thereby affecting the flow rate and momentum of the jet. Finally, the impact of the velocity varies in the first self-similarity region on the slotted vane. The results indicate that, in contrast to the baseline vane, the suppression effect of the slot jet on the flow separation improves with the inlet velocity, whereas the deviation angle of the slotted vane declines with the inlet velocity. Meanwhile, the higher the incoming flow velocity, the better the slotted jet can inhibition of flow separation.

Numerical study on oxygen transport pattern in porous transport layer of proton exchange membrane electrolysis cells

A transient, two-dimensional and two-phase numerical model is established to study the nature of oxygen transport in proton exchange membrane electrolysis cells (PEMEC). Randomly generated circle fibers are used to construct a patterned porous transport layer (PTL), and the volume of fluid (VOF) method is employed to capture accurate gas-liquid interfaces. The patterns of oxygen transport and the relationship between multiple transport paths are analyzed in detail. We propose for the first time the concept of ‘isolation belt’, which is composed of a series of narrow throats, hindering the spontaneous combination of different oxygen transport paths. The influence of PTL perforation and spatially-graded fiber diameters on oxygen transport are explored. The numerical results show that perforation can probabilistically destroy the ‘isolation belt’, forming a transport path with high priority, which helps to reduce oxygen saturation. Moreover, when the porosity of PTL remains unchanged, reducing the fiber diameter in the region near the catalyst layer (CL) can significantly reduce the local oxygen saturation. The pressure variation reveals its consistency with the maximum throat width of the oxygen transport path, which indicates the law of capillary pressure. From the perspective of mathematical probability theory, a novel functional expression of the profile of oxygen saturation with respect to the structural properties of PTL is proposed to make a concise explanation of gas bubble transport in the context of PEMEC or similar gas-liquid porous flow. The highlights in this paper include: • Comprehensive spatiotemporal profile for in the process of oxygen penetration. • The concept of isolation belt for spontaneous merging of oxygen pathways. • A mathematical explanation for probability of oxygen saturation distribution. • Influence of PTL perforation and graded fiber diameters on oxygen saturation.

Residual NAPL Morphology Effects on Electrical Resistivity: Insights From Micromodel Displacement Experiments and Pore Network Simulations

AbstractCharacterizing residual non‐aqueous phase liquids (NAPLs) in porous media is essential for designing contaminated site remediation strategies. The direct current resistivity method is increasingly being used at sites contaminated by NAPLs, which uses the Archie's second law to connect NAPL saturation with the resistivity of porous media. A power‐law relationship connecting the phase morphology measured by Euler characteristic with resistivity has also been observed at the pore‐scale. Because these relationships are limited for porous media with specific wettability, previous research works have demonstrated deviations from Archie's second law in both the laboratory and field experiments. To evaluate the effects of residual NAPL morphology with different wettability on bulk resistivity, we developed two 2D‐micromodels and measured their electrical resistivity and phase morphology during phase displacement under laboratory‐controlled conditions. Furthermore, pore network simulations of a variety of conditions were performed in absence of surface conduction. Results show that NAPL distributed in dead ends of the pore space has limited influence on bulk resistivity since they do not control the current path and voltage distribution. The correlations between resistivity index and Euler characteristic are determined by NAPL ganglia size and pore throat width. A power‐law relationship is found between the Archie's saturation exponent and the average size of the residual NAPL ganglia, indicating that this exponent can be interpreted as the rate of change of the pore water connectivity with saturation. These insights provide a physical framework connecting the morphology and wettability of the NAPL ganglia with the Archie's saturation exponent.

A composite approach towards understanding the mechanisms and driving variables of river mouth variability: A case study of the Da Dien River mouth

ABSTRACT This research aims to present a composite approach to characterizing the intra-annual and interannual variability in inlet throat width and understanding its mechanism (how, when, and why it varies). The techniques used include remote sensing imagery analysis, spectral and cross-spectral analyses, correlation analyses, and random forest variable importance. The Da Dien River mouth (DDRM), which is located in southern Central Vietnam and experiences a strong annual signal of climate regimes, was selected as a case study to demonstrate the applicability of the approach. The results show that the narrowing/widening of the DDRM throat width is highly dynamic and variable under the significant dominant influence of wave height, tide and river flow, which seasonally and interannually vary according to the monsoon regime, El Niño/Southern Oscillation and sunspot number variations (better correlation with ENSO events). The overall throat width decreases during El Niño/the positive QBO phase and increases during La Niña periods/the negative QBO phase. The difference in river flow magnitudes is the main cause for the constriction/expansion of the DDRM throat width. The successful application of the study approach to the DDRM case study demonstrates its usefulness and ability to be applied to other case studies in tropical monsoon regions.

Methane Diffusion Through Nanopore-Throat Geometry: A Molecular Dynamics Simulation Study

SummaryMolecular diffusion dominates over pressure-driven convection as the major mass transport mechanism in nanoporous media with <10-nm pores, which is typical pore size for shale gas recovery. To study fluid behavior at this scale, molecular dynamics (MD) simulation has been widely applied. Nevertheless, classic capillary tube or slit models are of uniform geometry that miss the converging-diverging pore-throat feature, while more realistic models lose simplicity and generality.In this work, we propose a novel geometric model that can reproduce the realistic converging-diverging structure in subsurface porous media without any additional complexity compared to classic slit or capillary models. In this pore-throat model, we are able to identify how nonuniform geometry affects the methane diffusion for both pure methane and for methane mixtures with water, carbon dioxide, and helium.For a pure methane system, we demonstrate the fundamental impact of throat width on diffusion coefficient when the throat width is narrower than 20 Å and identify a critical throat width that determines whether methane can self-diffuse though the throat. This critical throat size is regulated by the energy barrier at the throat rather than by molecular size. We then introduce a semianalytical model to predict self-diffusion coefficient as a function of pressure, temperature, and throat width.For mixtures, we observe the key impact of spatially nonuniform fluid distribution in determining diffusion. Water or carbon dioxide can locally concentrate at the throat, which reduces methane diffusivity, while helium prefers to stay in the pore body, which mildly enhances methane diffusivity. Specifically, although residual water reduces methane diffusion (26% reduction for 20% water molar fraction), it completely blocks the throat and thus prohibits pressure-driven methane convection. By comparison, the dominance of molecular diffusion over convection can be extended to larger pores in presence of residual water. It provides an explanation on shale gas production when connate water is expected to block the flow path.

Implantable double-layer pump chamber piezoelectric valveless micropump with adjustable flow rate function

The piezoelectric valveless micropump with the characteristics of precise liquid delivery is widely utilized in the field of biomedicine. However, the improvement of the flow rate of the piezoelectric micropump relies on the increase in size and driving voltage, which hinders its application in the implantable medical field. This article proposes a double-layer chamber valveless piezoelectric micropump, which has the obvious advantages of small size and adjustable flow rate, and is expected to be applied to the treatment of implantable hydrocephalus. The overall size of the micropump is 10 mm × 10 mm × 4 mm, which can be implanted in the cerebral cortex. Combined with polydimethylsiloxane-polyethylene glycol terephthalate bonding technology, the double-layer chamber micropump solves the contradiction between miniaturization and large flow range. The flow rate generated by micropump under low voltage can be adjusted according to the amount of hydrocephalus. In order to reveal the mechanism of increasing the flow rate, the working efficiencies of the microvalve and micropump are studied in this article. The electric-solid-fluid coupling simulation and experimental tests obtained the optimal structural parameters: the divergence angle is 30°, the throat width is 300 μm, and the upper chamber depth is 100 μm. The proposed micropump can achieve the tunable flow rate of 2.16–51.74 μl min−1.

Simulation and validation of the gas flow in close-coupled gas atomisation process: Influence of the inlet gas pressure and the throat width of the supersonic gas nozzle

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29∙Lo, 0.5∙Lo, 0.77∙Lo and 2∙Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

Portable central baffle flume

This paper investigated the hydraulic characteristics of the triangular central baffle (TCB) flume. Laboratory tests were carried out to determine the flume dimensions. The field applicability of the proposed portable device was examined by on-farm installation. According to the laboratory tests, when the contraction ratio, r, was less than 0.39, the flow capacity was not affected by the ratio between the flume’s floor height and the throat width. The laboratory analysis also showed that there was no significant effect of installing an entrance ramp on the stage-discharge relationship for r<0.39, while the entrance ramp increased the discharge capacity for r>0.39. The stage-discharge curve obtained based on the laboratory tests was verified using field data. The results revealed that the proposed portable flume could be used accurately to determine the flow through an unlined ditch. Practical suggestions were proposed to determine the distinguishing condition curve.

Parametric Research and Aerodynamic Characteristic of a Two-Stage Transonic Compressor for a Turbine Based Combined Cycle Engine

This paper researches the parametric optimization of a two-stage transonic compressor having a large air bypass at partial rotating speed according to flow analysis for a turbine-based combined cycle engine (TBCC). To obtain adequate thrust, the inlet transonic compressor of the turbofan part of the TBCC is required to have a wider frequently used corrected rotating speed range and a larger mass-flow rate at low rotating speed, which is different from a typical transonic compressor. The one-dimensional blade design parameters and flow path of the baseline two-stage transonic compressor are introduced. With the widely used CFD software Numeca, the three-dimensional flow fields of the baseline transonic compressor and effects of the flow path between Stage 1 and Stage 2 on the inlet mass flow rate are analyzed for indicating the further improvement direction. For design speed (NC = 1.0), to improve the efficiency at the design point, parametric research is carried out on Rotor 2 to optimize the shock structure and strength, resulting in enhanced efficiency at the design point due to reduced shock loss of Rotor 2. For partial speed (NC = 0.8 and 0.7), since the flow field analysis indicates that the flow blockage in S1 limits the entire mass flow rate, the parametric redesign of stator S1 aims at obtaining an increased blade throat width to enhance the flow capacity of S1. Simulation confirms the increase in the mass-flow rate and efficiency at partial speed due to the reduction in flow blockage and related viscous losses. Aerodynamic analysis at representative operation points indicates that the modifications of R2 and S1 lead to obvious aerodynamic improvement at all rotating speeds (NC = 1.0 to 0.7), while maintaining sufficient stall margin.

Thermal rectification in nozzle-like graphene/boron nitride nanoribbons: A molecular dynamics simulation

Innovations in manufacture of graphene-based nano-devices are principally the outcome of engineering of the nanostructure, while advanced nano-transistors, thermal logic nano-circuits, and thermal nano-diodes are multi-component tailor-made nanomaterials with precise molecular layout. To achieve such delicate graphene-based nanostructures, it is essential to optimize both materials and geometrical parameters. Herein we introduce nozzle-like graphene (G)/boron nitride (BN) nanostructures with very high unidirectional thermal rectification efficiency applying classical molecular dynamics (MD) simulations using Tersoff potential. A series of nozzle-like G/BN and BN/G nanoribbons with variable throat width, L (5–50 Å) and convergence angle, ϴ (20-90°) under average T = 300 K andΔT = 40 K (temperature differences between the thermal baths) situation were simulated to provide a complete image of thermal rectification for such nozzle-like nanostructures to be intended as thermal nano-diodes. Thermal conductivity and rectification analyses unveiled nozzle-like G/BN devices with a comparatively excellent unidirectional thermal rectification of ∼ 25%, at L = 40 Å and ϴ = 60°, which was conceptualized in view of phonon scattering perspective. We believe that the outcome of this survey would open new avenues in manufacturing tailor-made graphene-based nano-diodes.