Reduced Flow Velocity Research Articles

Investigation of Erying–Powell fluid flow in the elliptical multi‐stenosed artery: Application of perturbation method via polynomial solutions

AbstractIn the current work, we analyzed the non‐Newtonian rheology of blood through a multi‐stenosed artery with a cross‐section of elliptical shape. The blood is regarded as Erying–Powell fluid, and flow is considered to have no slip at the stenotic wall. The mathematical model is processed to a non‐dimensional form, and conditions of mild stenosis are utilized to decrease its nonlinearity. The resulting equations are solved by applying the perturbation technique by considering the fluid characteristic parameter as the perturbation parameter. The solution is completed by using the polynomial of degree four. The solutions of mathematical equations are deeply examined by graphical analysis. The non‐Newtonian impacts are predominant in the surrounding of the stenosed wall along the minor axis of the elliptical artery. The height of stenosis affects the pressure rise and flow resistance. The shear stress at the arterial wall is very high in the stenotic region and has more potent effects in the neighboring boundary point on the minor axis. Progressive stenosis causes a reduction in the blood flow velocity surrounding the arterial wall due to higher resistance to the flow. However, the velocity improves near the center line of the artery. Further, the fluid's velocity is very high in the constricted (stenotic zone) region.

Morphophysiological Responses of the Goat Mammary Gland to Water Scarcity in Arid and Semi-Arid Environments: Are They Enough to Generate Adaptation to New Climatic Challenges?

Due to climate change, diverse territories of the planet will suffer from water restrictions. Goats are perceived as the most resilient ruminants in this scenario. So, various studies have focused on describing how a lower water intake influences milk production, especially in breeds adapted to desert environments. In water-stress situations, goats lose up to 32% of their body weight (BW), the rate of passage is reduced, and the digestibility of the feed increases. When goats consume water again, the rumen prevents hemolysis and osmotic shock from occurring. Regarding milk production, the response varies depending on the breed and the level of water restriction, maintaining the milk volume or reducing it by up to 41%. Systemically, it decreases the urinary volume and glomerular filtration rate, increasing blood osmolality and the vasopressin (ADH) concentration. Studies are scarce regarding changes in blood flow to the mammary gland, but there would be a reduction in blood flow velocity of up to 40% without changing blood pressure. New studies must be undertaken to determine which breeds or crosses are the best adapted to changing environmental conditions and to improve our understanding of the changes that occur at the morphophysiological level of the caprine mammary gland.

Application of a subgrid-scale urban inundation model for a storm surge simulation: Case study of typhoon Haiyan

This study evaluated the individual drag force model (iDFM), a subgrid-scale model for simulating tsunami inundation in coastal urban areas. The iDFM was then applied to characterize Typhoon Haiyan-induced storm surge inundations in 2013. Using a post-typhoon survey dataset containing inundation depths at different survey points with inundation limits, the performance of iDFM was validated, and the results confirmed that iDFM accurately estimates the storm surge inundation depths but overestimates the limit of inundation. In addition, the results revealed that the iDFM flow velocity was a dominant factor, and the inclusion of buildings in the simulated affected the arrival of the leading edge of inundation. Furthermore, the reduction in flow velocity was sensitive to the subgrid-scale parameters, and the spatial distribution pattern of buildings located in the inundated area affected the relative difference in the maximum flow velocity with the regional roughness model. The inundation characteristics of the Typhoon Haiyan storm surge models were compared with a historical tsunami event. The inundation characteristics were similar and model differences were observed mainly in the fluid velocity and momentum flux rather than the inundation depth. However, the magnitudes of relative differences observed in Tacloban were larger for fluid velocity and momentum flux, respectively, than in the tsunami event. The effect of building drag on advection was also substantial in Tacloban due to the differences in the inflow mass and momentum fluxes.

Theoretical study of silver nanoparticle suspension in electroosmosis flow through a nonuniform divergent channel with compliant walls: A therapeutic application

This study explores the effect of silver nanoparticles on heat transfer and flow behavior within the context of the Ellis fluid model. It specifically considers electroosmotic forces in a nonuniform divergent channel with compliant walls. The analysis involves studying thermal transport in silver-blood nanofluid flow, using MATHEMATICA 13.2 software to obtain exact solutions for velocity and temperature distribution. Findings reveal that certain parameters, such as wall damping and wall elastic properties, increase skin friction, while compliant wall parameters generally reduce flow velocity. Additionally, wall rigidity and tension parameters lead to larger trapped boluses. Notably, a 1% concentration of nanoparticles enhances heat transfer by up to 13.75%, offering control over heat transfer rates. This research introduces a novel perspective by examining compliant wall impacts on heat transfer analysis in the context of electroosmotic flow within the Ellis fluid model, incorporating silver nanoparticles with potential therapeutic applications due to their antibacterial properties.

Unconfined fishway design, implementation, and assessment for the emerald Shiner (Notropis atherinoides) in the Upper Niagara River, New York

An engineered seawall in need of repair along the Upper Niagara River in Buffalo, NY, was previously identified as a hydrodynamic barrier to the migration of a small but important prey fish, the emerald shiner (Notropis atherinoides), and its connection to the upstream environs of Lake Erie. This study proposed a novel unconfined fishway design to be incorporated into existing plans for rehabilitation of the seawall at Broderick Park. The proposed fishway was developed using a two-dimensional depth-averaged numerical model, it was explored by placing the target fish into a physical model, and the constructed demonstration project was assessed using field measurements and observations. The numerical model showed that modular baffles attached to the seawall reduced the nearshore flow velocities to about 0.4 to 0.6 m s−1, which was within the acceptable range of velocities for the upstream migration of the emerald shiners. The physical experiments demonstrated that most emerald shiners chose to swim toward, within, or close to the proposed fishway in the presence of higher flow velocities within the main channel region. The proposed fishway design was integrated into the seawall repair as part of a demonstration project supervised by the US Army Corps of Engineers-Buffalo District. Post-construction assessment of the installation showed that (1) the modular baffles reduced time-averaged flow velocities near the seawall and water surface, (2) while very few shiners were observed swimming along the pre-construction seawall, large numbers were observed swimming upstream within this reduced flow velocity corridor created by the baffles, and (3) the structural integrity of the installation proved to be durable and resilient to extremely harsh environmental conditions. This study explored a new approach to fishway design for the passage of relatively small fish in large rivers, and it effectively melded fishway requirements into seawall restoration in concert with the expectations of multiple stakeholders.

Heat Transfer in Magnetohydrodynamic Convective Flow of Hybrid Nanofluid Over a Revolving Cone with Heat Generation/Absorption

The contemporary study’s goal is to investigate the role of the Casson hybrid nanofluid on boundary layer flow and heat transfer over a vertical rotating cone using various base fluids. The dynamic effects of the magnetic field and heat generation/absorption are taken into account in the modeling of hybrid nanofluids. Flow-related PDEs are remodeled to ODEs through use of similarity transmutations. Furthermore, the numerical results are explained using the fourth order Runge-Kutta scheme in conjunction with the shooting technique. The solution depends on a Lorentz force, Casson parameter, heat generation/absorption and spin parameter. The dependency of the skin friction coefficient and local Nusselt number on these four parameters is numerically explored. To the best of the author’s knowledge, the presence of three types of hybrid nanoparticles (Al2O3– TiO2, TiO2–Cu and Al2O3–Cu) with Newtonian/non-Newtonian base fluids has not yet been examined. The findings of the study reveal that increasing the magnetic parameter values reduces flow velocities (tangential and swirl) and increases the tangential velocity profile of Newtonian based hybrid nanofluid. Additionally, the thermal profile and non-Newtonian based hybrid nanofluid indicate a rising trend in heat generation/absorption parameter. Furthermore, the thermal transfer rate of water-based hybrid nanofluid is increased, while the skin friction coefficient reverses.

Smaller optic nerve diameters and reduced flow velocity of ophthalmic artery suggest a history of optic neuritides: Transorbital Ultrasonography and Doppler Ultrasound in multiple sclerosis

Smaller optic nerve diameters and reduced flow velocity of ophthalmic artery suggest a history of optic neuritides: Transorbital Ultrasonography and Doppler Ultrasound in multiple sclerosis

Non-Invasive Evaluation of Retinal Vascular Alterations in a Mouse Model of Optic Neuritis Using Laser Speckle Flowgraphy and Optical Coherence Tomography Angiography.

Optic neuritis, a characteristic feature of multiple sclerosis (MS), involves the inflammation of the optic nerve and the degeneration of retinal ganglion cells (RGCs). Although previous studies suggest that retinal blood flow alterations occur during optic neuritis, the precise location, the degree of impairment, and the underlying mechanisms remain unclear. In this study, we utilized two emerging non-invasive imaging techniques, laser speckle flowgraphy (LSFG) and optical coherence tomography angiography (OCTA), to investigate retinal vascular changes in a mouse model of MS, known as experimental autoimmune encephalomyelitis (EAE). We associated these changes with leukostasis, RGC injury, and the overall progression of EAE. LSFG imaging revealed a progressive reduction in retinal blood flow velocity and increased vascular resistance near the optic nerve head in the EAE model, indicating impaired ocular blood flow. OCTA imaging demonstrated significant decreases in vessel density, number of junctions, and total vessel length in the intermediate and deep capillary plexus of the EAE mice. Furthermore, our analysis of leukostasis revealed a significant increase in adherent leukocytes in the retinal vasculature of the EAE mice, suggesting the occurrence of vascular inflammation in the early development of EAE pathology. The abovechanges preceded or were accompanied by the characteristic hallmarks of optic neuritis, such as RGC loss and reduced visual acuity. Overall, our study sheds light on the intricate relationship between retinal vascular alterations and the progression of optic neuritis as well as MS clinical score. It also highlights the potential for the development of image-based biomarkers for the diagnosis and monitoring of optic neuritis as well as MS, particularly in response to emerging treatments.

Bedform evolution along a submarine canyon in the South China Sea: New insights from an autonomous underwater vehicle survey

ABSTRACTTraditional mapping of bedforms in submarine canyons relied on vessel‐mounted and towed sensors, but their fine‐scale geomorphology and shallow structure requires higher resolution datasets. This study utilizes a high‐resolution dataset obtained from an autonomous underwater vehicle, combined with seismic reflection profiles and sediment cores, to analyse bedform sets within a 25.6 km long submarine canyon (canyon C14) in the northern South China Sea. A train of crescent‐shaped axial steps, indicative of cyclic steps formed by supercritical turbidity currents, is imaged along the canyon. Axial steps in the upper course show erosional truncations and sub‐horizontal reflectors on the lee and stoss sides, respectively, pointing to erosional–depositional cyclic steps formed by confined flows with high erosional capacity. This is facilitated by canyon narrowness and steeper axial gradient. After a transition segment, the lower course widens, with a gentler axial gradient, resulting in increased asymmetry and wavelength of axial steps. Backset bed deposits on the stoss sides of these steps indicate depositional cyclic steps with higher aggradation. Sediment filling, almost padding each cyclic step associated scour suggests the reworking of previously formed bedforms by gravity flows fed by destabilization processes on the canyon sidewalls and upstream lee faces and, possibly, by shelf‐edge and uppermost slope spillover into the canyon. At the lowermost course, cyclic steps transition to a furrow field, likely associated with flow velocity reduction facilitated by canyon floor widening and a further decrease in slope gradient. Flow braiding and re‐convergence, related to the erosion of fine‐grained deposits within the canyon floor, should have played a role to produce furrows under supercritical conditions. This work enhances our understanding of the detailed morphology and shallow relief configuration of bedforms in deep‐water submarine canyons, providing insights into their causative processes and evolution.

The impact of sick sinus syndrome on flow velocity of the left atrial appendage in patients with atrial fibrillation

Abstract Background Sick sinus syndrome (SSS) itself has been suspected as one of potential embolic stroke sources, however, the mechanism remains unclear. Reduced flow velocity of left atrial appendage (LAAFV) plays a major role in thrombus formation in patients with atrial fibrillation (AF). We evaluated the contribution of SSS to LAAFV in patients with AF. Methods We studied 153 consecutive patients (age 69±10, 100 males, 79 paroxysmal AF, CHADS2 score 1.6±1.2) who underwent catheter ablation (CA) for AF at our hospital and our college of medicine. All patients enrolled in this study underwent transesophageal echocardiography (TEE) and transthoracic echocardiography prior to CA. LA global mean voltage and LA activation time were also measured using High-density LA mapping during CA. Clinical characteristics and laboratory data was obtained before CA for AF. SSS was defined as sinus arrest with 3 seconds or more by Holter ECG, or pacemaker implantation due to SSS. Results Reduced LAAFV was associated with old age (R²=0.0783, P=0.0005), female (R²=0.0260, P=0.0285), non-paroxysmal AF (R²=0.1403, P<0.0001), hypertension (R²=0.0226, P=0.0338), history of congestive heart failure (R²=0.0890, P=0.0007), high CHADS2 score (R²=0.1248, P<0.0001), high level of BNP (R²=0.2054, P<0.0001), AF rhythm during TEE (R²=0.1577, P<0.0001), low LV ejection fraction (R²=0.0255, P=0.0488), large LA diameter (R²=0.1544, P<0.0001), high E wave (R²=0.1168, P<0.0001), low LA global mean voltage (R²=0.1775, P<0.0001), long LA activation time (R²=0.1383, P<0.0001) and SSS (n=29, R²=0.0957, P=0.0002). On multiple linear regression analysis, SSS, AF rhythm during TEE, BNP, female was independently related to reduced LAAFV (Table). Conclusion SSS itself might be related to reduced LAAFV in patients with AF.Table

Improving Bendability of 6000-Series Extruded Aluminum Profiles Using Dies through Shear Stress and Flow-Velocity Reduction

Improving Bendability of 6000-Series Extruded Aluminum Profiles Using Dies through Shear Stress and Flow-Velocity Reduction

Analysis of the Exothermic Reaction of Flame Ignition in the Combustion Chamber of a Gas Turbine Unit

This article analyses the exothermic reaction of flame ignition in the combustion chamber of a gas turbine unit, which is characteristic of combustion chambers operating on traditional hydrocarbon fuels. The combustion of gases as an explosive process in confined and semi-enclosed areas remains a poorly understood section of thermal physics. Without a detailed review of the physical and chemical processes taking place in the combustion chamber, it cannot be said whether the gas turbine unit will run sustainably. It is also important to know what combustion modes are in principle possible after a loss of stability in the combustion chamber in order to take action against this in advance. To describe flame ignition and quenching in the flow of the fuel–air mixture through a combustion chamber, a system of differential conservation equations of energy and reactive species supplemented with the equation of state is used. Nonstationary combustion processes in gas-turbine engines were studied, and flame ignition and blow-off were determined by the heat balance and by the continuity of chemical processes. Calculation methodologies for various operating modes of the combustion chamber of a gas turbine unit are developed and realized. The results of the calculations that were carried out are presented with graphical interpretation and with their analysis provided in sufficient detail. Based on this analysis, recommendations are then provided. From the graphs, it can be observed that the combustion chamber of a gas turbine unit reaches its maximum limit of stable operation at the optimum value of the reduced flow velocity in the openings of the air supply to the combustion and the mixing zones of the flame tube (λOC)opt = 0.22 when the fuel–air mixture is at maximum depletion, ensuring that combustion does not stop and flame failure does not occur. The topic of this article relates to the intensification of hydrocarbon fuel combustion and the technological improvement of combustion chambers in gas turbine units. This topic is of exceptional importance and relevance, emphasizing its significance. The purpose of this work is to develop and implement a methodology for calculating various modes of operation of the combustion chamber of a gas turbine unit.

Automatic assessment of collaterals physiology in chronic total occlusions by means of artificial intelligence.

Assessment of collaterals physiology in chronic total occlusions (CTO) currently requires dedicated devices, adds complexity, and increases the cost of the intervention. This study sought to derive collaterals physiology from flow velocity changes (ΔV) in donor arteries, calculated with artificial intelligence- aided angiography. Angiographies with successful percutaneous coronary intervention (PCI) in 2 centers were retro- spectively analyzed. CTO collaterals were angiographically evaluated according to Rentrop and collateral connections (CC) classifications. Flow velocities in the primary and secondary collateral donor arteries (PCDA, SCDA) were automatically computed pre and post PCI, based on a novel deep-learning model to extract the length/time curve of the coronary filling in angiography. Parameters of collaterals physiology, Δcollateral-flow (Δfcoll) and Δcollateral-flow-index (ΔCFI), were derived from the ΔV pre-post. The analysis was feasible in 105 out of 130 patients. Flow velocity in the PCDA significantly decreased after CTO-PCI, proportionally to the angiographic collateral grading (Rentrop 1: 0.02 ± 0.01 m/s; Rentrop 2: 0.04 ± 0.01 m/s; Rentrop 3: 0.07 ± 0.02 m/s; p < 0.001; CC0: 0.01 ± 0.01 m/s; CC1: 0.04 ± ± 0.02 m/s; CC2: 0.06 ± 0.02 m/s; p < 0.001). Δfcoll and ΔCFI paralleled ΔV. SCDA also showed a greater reduction in flow velocity if its collateral channels were CC1 vs. CC0 (0.03 ± 0.01 vs. 0.01 ± 0.01 m/s; p < 0.001). For each individual patient, ΔV was more pronounced in the PCDA than in the SCDA. Automatic assessment of collaterals physiology in CTO is feasible, based on a deeplearning model analyzing the filling of the donor vessels in angiography. The changes in collateral flow with this novel method are quantitatively proportional to the angiographic grading of the collaterals.

Laminar flow over a rectangular cylinder experiencing torsional flutter: Dynamic response, forces and coherence modes

This study investigates the flutter response of a rectangular cylinder model with an aspect ratio of 5 at the Reynolds number Re = 100 via direct numerical simulation. The effects of two key parameters, i.e., the moment of inertia and reduced flow velocity, on the aerodynamic performance and dynamic responses of the cylinder in the state of torsional flutter are investigated. To reveal the flutter mechanism, the high-order dynamic mode decomposition (HODMD) analysis is conducted to decompose the flow field. The results show that both an increase in the moment of inertia and a higher reduced flow velocity lead to a larger torsional amplitude and a corresponding decrease in torque. At the same time, the primary frequency decreases and the size of the shedding vortex gradually enlarges. The vortices shed from the leading edge and the trailing edge of the model form a 2P wake pattern. The leading-edge vortex is significantly larger than the trailing-edge vortex in terms of strength and size. The leading edge plays a dominant role and only contributes to the odd-order HODMD modes while the even-order modes are deemed inconsequential. As the moment of inertia increases, the total energy of the higher-order modes increases, which has the same results as the power spectral density of torque, reflecting increased nonlinearity and complexity of the system. Similarly, increasing the reduced flow velocity at the same moment of inertia has similar excitation effects.

Numerical Prediction of the Streamwise Fluidelastic Instability

Abstract Recent experimental investigations have shown that tube arrays can become unstable in the streamwise direction. This is contrary to the long-held notion that fluidelastic instability is only a concern in the direction transverse to the flow. The possibility of the streamwise fluidelastic instability (SFEI) as a potential threat to the integrity of tube bundles was confirmed by the recent failures of newly installed replacement steam generators. A number of investigations were conducted to uncover the nature of this mechanism. A theoretical framework was developed by Hassan and Weaver (2016, “Modeling of Streamwise and Transverse Fluidelastic Instability in Tube Arrays,” ASME J. Pressure Vessel Technol., 138(5), p. 051304) to model streamwise fluidelastic instability in a bundle of flexible tubes. The model utilized a simple time lag expression for the flow channel area perturbation. The current work aims at developing a numerical model to precisely predict the flow perturbation characteristics in a tube bundle due to streamwise tube motion. Flow simulations were carried out for single phase fluid flow in a parallel triangle tube bundle array with 1.2, 1.5, and 1.7 pitch to diameter ratios. The numerical model was validated against numerical and experimental results available in the fluidelastic instability literature. Simulations were carried out for a range of reduced flow velocities. The model results showed that the upstream flow perturbation magnitude and phase are different from those obtained downstream of the moving tube. The obtained flow perturbation characteristics were implemented in the Hassan and Weaver (2016, “Modeling of Streamwise and Transverse Fluidelastic Instability in Tube Arrays,” ASME J. Pressure Vessel Technol., 138(5), p. 051304) model and the streamwise FEI threshold was predicted.

Prevention Due to Assembled Boulders Against Local Scouring in Low-head Hydraulic Structures

In low-head hydraulic structures, the prevention against local scouring of the river bed downstream of concrete aprons must be required during flood stages. Generally, protection blocks are installed downstream of the apron, but they do not control the flow passing through the blocks to reduce the velocity near the bottom. In most of river fields, the installation of protection blocks may not help protect the river bed. In the case of low drop-structures, hydraulic jump occurs during flood stages just below the drop-structures. The main flow near the bottom continues far downstream, and a local scouring is formed. In the case of the movable weir, a local scouring occurs downstream of the weir during flood stages. There is little information on the countermeasure against the local scouring below the movable weir during flood stages. Recently, the authors proposed the installation of consecutively assembled boulders instead of protection blocks. This paper presents the effect of installing consecutively assembled boulders on the prevention of local scouring for both low drop-structures and movable weirs. The effect of seepage on reducing flow velocity near the bottom has been shown, the comparison between the installation of protection blocks and the installation of consecutively assembled boulders has been discussed. In the case of the movable weir, the flow velocity near the bottom below the protection blocks is always larger than that below the assembled boulders, in which the effect of the deflected flow formation by the support pier is not negligible.

A three-dimensional study of flow characteristics over different forms of stepped–labyrinth spillways in the skimming flow regime

Abstract To improve the performance of stepped spillways, their combination with labyrinth spillways is an interesting topic. In this study, several labyrinth configurations of stepped spillways were presented. Validation of the numerical model was done using the results of the previous physical models. After that, three configurations including: conventional stepped, trapezoidal-labyrinth, and rectangular-labyrinth were modeled using the OpenFOAM model for the skimming flow regime. For simulation, the InterFOAM solver and RNG k–ε turbulence model were used. The results showed an increase of 34.7 and 21.1% in energy dissipation in the trapezoidal and rectangular stepped–labyrinth spillways compared to the conventional stepped type, for dc/h = 1.45 (the range of dc is between 8 and 14.5 cm). The flow velocity in the end step of the trapezoidal- and rectangular-labyrinth configuration is reduced by 50.5 and 31.1%, respectively. Furthermore, in the trapezoidal configuration, a 14.7% reduction in flow velocity has been achieved compared to the rectangular stepped–labyrinth configuration. The results showed that the minimum pressure on the vertical faces of the steps occurred in their upper half and the rectangular configuration has resulted in the highest amount of negative pressure. The turbulence kinetic energy, especially in trapezoidal configuration, has increased toward the downstream.

Sediment transport trend and its influencing factors in coastal bedrock island sea areas-a case study of Chudao island, China

Coastal bedrock islands sea areas have a unique natural environment, frequent human activities, and complex sedimentary dynamic processes. In this paper, we select the Chudao Island sea area off the coast of Shandong Peninsula, China, as a typical research area to investigate the sediment transport trends and influencing factors by means of high-precision bathymetric survey, high-density sediment sampling, grain-size trend analysis and hydrodynamic numerical modeling. Results and analysis indicate that the grain size parameters including mean grain-size, sorting coefficient and skewness are zonal distributed, roughly parallel to the isobaths. While the overall sediment transport trend is from island shore to sea, with several convergence centers near the loop centers of bottom flow and at the edge of the agriculture area. The near-bottom flow velocity is primary factor that controlling the significance of sediment transport trend, while the flow decides the general patterns of sediment transport trend and sediment distribution. Submarine topography can either directly transport sediments down its slope, or indirectly affect the direction of sediment transport by constraining the near-bottom flow from shallow to deep waters. Besides the natural factors of bottom flow and submarine topography, human activities represented by aquaculture also affect the sediment transport trend in coastal bedrock island sea areas. First, the increased sedimentation rate caused by organic matters and the diffusion of scallop fragments may cause sediment coarsening. Second, the artificial aquaculture facilities can reduce flow velocity and therefore hinder the initiation, suspension and transport of sediment near the aquaculture areas. Our methods and findings provide high-resolution details to insight into the sediment transport trends to improve the understanding of the modern sediment dynamics in small-scale coastal bedrock island sea areas and provide reference for corresponding engineering and agriculture activities.

The effect of coupled combustion reaction on conjugate heat transfer in boundary layer of a segregated oxidizer/fuel solid motor

Combustion reaction plays an important role in heat transfer of boundary layer of solid rocket motor. In the present study, a transient numerical model is developed to investigate the influence of coupled combustion reaction on heat transfer in boundary layer of the segregated oxidizer/fuel solid motor (SOFSM). The results show that conjugate heat transfer characteristics of non-reacting flow are distinct from those of the reacting flow with coupled combustion. The reacting flow with coupled combustion renders higher and more homogeneous temperature and velocity compared with the non-reacting flow. Due to the effect of combustion heat release on thermophysical properties of the gas phase species, the heat transfer coefficient and effective thermal conductivity of the reacting flow are much higher than those of the non-reacting flow. When the combustion time increases, the heat transfer coefficients decrease in the reacting and non-reacting flows due to reduced flow velocity and lower O2 concentration. The Nusselt number (Nu) of the reacting flow is also higher than that of the non-reacting flow. Significant decrease of Nu is found in the non-reacting flow with combustion time. However, the Nu varies very slightly along the flow direction in the reacting flow. As pressure increases from 1.5 MPa to 5.0 MPa, the high-temperature area becomes narrower and the flow velocity decreases in the combustion channel. The diffusion and mixing of the oxidizer and fuel gas along the radial direction are thus weakened in the coupled combustion flow. The total heat transfer coefficient decreases from 295.88 W m−2 K−1 to 46.52 W m−2 K−1 and Nu decreases from 36.27 to 16.56 with increase of pressure. The distribution of total heat transfer coefficient is found to be highly synchronous to the distribution of regression rate of coupled combustion process. The distribution of heat transfer coefficient directly affects parallel regression and coupled combustion of the TAGN propellant. The fitting relationship of Nu, i.e., Nu = 0.058Re0.6Pr0.424 is obtained for the coupled combustion flow in the motor, which provides better insight into the heat transfer in the SOFSM system.

Optimal Sewer Network Design for Cities in Hilly Regions

ABSTRACT This paper proposes a method to include drop manholes in the optimal design of sewer networks. These structures dissipate energy and reduce flow velocity, which is important in hilly regions where high slopes induce velocities that exceed the maximum allowable. The methodology proposed here introduces a new type of arc to represent drop manholes in a model that uses graph theory to achieve the minimum cost design of a sewer network. Also, for the estimation of drop manhole costs, a new cost function is developed based on pipe and manhole cost equations proposed in the literature. The methodology was tested in eight different series of pipe configurations, as well as a real sewer network located in Colombia, varying the pipe material and the land slope. The results demonstrated that the proposed methodology allows for the optimal design of sewer networks in hilly regions while satisfying all hydraulic and commercial constraints.