Search Results (26)

Ammonium bisulfate (ABS) fouling in air preheaters has become a critical challenge restricting the safe and efficient operation of coal-fired units. Optimizing the flow field of the outlet of the upstream SCR system is a potentially effective path to mitigate ABS fouling. In this work, CFD simulations were conducted on the SCR De-NO_x system and its succeeding flue ducts connected to the air preheater. The simulation results of the original design show that a significant velocity deviation exists at the inlet of the air preheater (with the CV₁ up to 53.2%), with a portion of the flue gas adhering to the walls, which could induce ABS fouling in the low-temperature region. By adding flow guide plates into the flue duct, the flow uniformity before the air preheater was expected to be effectively improved. Notably, considering the deposition characteristics of ABS and the operating characteristics of the rotary air preheater, this study proposed a novel evaluation indicator, radial variance coefficient (CV₂), which focuses on the velocity uniformity based on the annular sector unit, to indicate the risk of ABS deposition. The influence on velocity uniformity of different flow guide plate layouts was analyzed. Based on the multiple evaluation metrics including pressure drop and flow uniformity, the optimal layout scheme was then selected. After optimization, the radial variance coefficient decreased from 30.7% to 11.7%, with the pressure drop slightly increased from 50 Pa to 80 Pa. This study could help to reduce unit failure frequency and support efficient operation of coal-fired power plants. Full article

A computational study is conducted on shock wave propagation and diffraction in an annular duct. The curved geometry and central obstruction of the annular configuration generate complex wave phenomena not typically observed in linear channels. The evolution of incident shock fronts, their interactions with the inner and outer walls, and the resulting diffraction patterns are analysed in detail. Particular focus is placed on the formation of reflected and transmitted waves, as well as the effects of curvature and channel dimensions on shock strength and propagation speed. High-resolution computational fluid dynamics (CFD) simulations are used to capture transient flow features, and results are validated against available experimental data. Simulations are performed across a range of annular geometries with varying radii of curvature and inlet Mach numbers. Simulations across a range of inlet Mach numbers (1.5–3.0) and radii of curvature show that increasing curvature intensifies shock focusing near the inner wall, raising local pressure peaks by up to 20%, while promoting faster attenuation of the transmitted wave downstream. At higher Mach numbers, the reflected shock transitions from regular to Mach reflection, producing triple-point structures. The comparison of shock structures across configurations shows good agreement with experimental observations. The findings enhance understanding of shock dynamics in non-standard geometries and have implications for the design of detonation engines, pulse detonation systems, and safety analyses in confined environments. Full article

A three-dimensional numerical simulation of hot air anti-icing was conducted on the full-annular realistic model of engine intake components, comprising the intake ducts, intake casing, struts, axial flow casing, and zero-stage guide vanes, based on the intermittent maximum icing conditions and the actual engine operating parameters. The simulation integrated multi-physics modules, including air-supercooled water droplet two-phase flow around components, water film flow and heat transfer on anti-icing surfaces, solid heat conduction within structural components, hot air flow dynamics in anti-icing cavities, and their coupled heat transfer interactions. Simulation results indicate that water droplet impingement primarily localizes at the leading edge roots and pressure surfaces of struts, as well as the leading edges and pressure surfaces of guide vanes. The peak water droplet collection coefficient reaches 4.2 at the guide vane leading edge. Except for the outlet end wall of the axial flow casing, all anti-icing surfaces of intake components maintain temperatures above the freezing point, demonstrating effective anti-icing performance. The anti-icing characteristics of the intake components are governed by two critical factors: cumulative heat loss along the hot air flow path and heat load consumption for heating and evaporating impinging water droplets. The former induces a 53.9 °C temperature disparity between the first and last struts in the heating sequence. For zero-stage guide vanes, the latter factor exerts a more pronounced influence. Notable temperature reductions occur on the trailing edges of three struts downstream of the hot air flow and at the roots of zero-stage guide vanes. Full article

A new lift enhancement scheme is designed for the cruise flight process of a tail-sitter UAV (Unmanned Aerial Vehicle), proposing a fusion configuration with embedded grid channels on the duct wall. The low pressure zone at the lip of the duct is induced to expand through the grid channels, forming a significant force component difference with the non-grid side, thereby generating significant lift effects for the propeller of the ducted fan during level flight. Taking a ducted fan system as an example, a design method for embedding grids into the ducted wall is established. By using the sliding mesh technique to simulate propeller rotation, the effects of annular distribution angle, grid channel width, circumferential and flow direction grid quantity on its aerodynamic performance are evaluated. The results indicate that the ducted fan embedded in the grid can generate a lift about 22.16% of total thrust without significantly affecting thrust and power characteristics. The increase in circumferential distribution angle increases within a reasonable range and benefits the lift of the propeller. However, the larger the grid width, the more it affects the lip and tail of the duct. Ultimately, the overall effect actually deteriorates the performance. The number of circumferential grids has a relatively small impact. As the number of flow grids increases, the aerodynamic characteristics of the entire fusion configuration significantly improves, due to its favorable induction of airflow at the lip and tail of the duct, as well as blocking the dissipation of blade-tip vortices. Full article

Accurate loss prediction since the preliminary design steps is crucial to improve the development process and the aerodynamic performance of turbines. Initial design phases typically employ reduced-order models in which the different loss-generating mechanisms are assessed through correlations. These correlations are often based on the hypothesis of loss linearity, which assumes that losses from different sources can be summed to obtain the total losses. However, this assumption could constitute an oversimplification, as losses occur concurrently and can interact with each other, potentially impacting overall performance, all the more in low aspect ratio turbomachinery. The aim of this paper is to investigate the role of interactions between different phenomena in the generation of loss. 3D RANS simulations are run on two simplified representations of a turbine blade channel, a curved duct and a linear cascade, and on a real turbine vane. Several inlet and wall boundary conditions are employed to examine loss-generating phenomena both separately and simultaneously. This approach enables the analysis of where and how interactions occur and quantifies their influence on the overall losses. Losses caused by boundary layer–vortex interactions are found to be highly sensitive to the relative positions of these two phenomena. It was observed that the loss linearity assumption may be acceptable in certain cases, but it is generally inadequate for off-design conditions and twisted annular configurations. Full article

Autonomous underwater vehicles (AUVs), as primary platforms, have significantly contributed to underwater surveys in scientific and military fields. Enhancing the maneuverability of autonomous underwater vehicles is crucial to their development. This study presents a novel vectored thruster and an optimized blade design approach to meet the design requirements of a specially shaped AUV. Determining the ideal blade characteristics involves selecting a maximum diameter of 0.18 m and configuring the number of blades to be four. Furthermore, the blades of the AUV were set to rotate at a speed of 1400 revolutions per minute (RPM). The kinematics of the thrust-vectoring mechanism was theoretically analyzed. A propulsive force test of the vectored thruster with ductless and ducted propellers was performed to evaluate its performance. A ductless propeller without an annular wing had a higher propulsive efficiency with a maximum thrust of 115 N. Open-loop control was applied to an AUV in a water tank, exhibiting a maximum velocity of 0.98 m/s and a pitch angle of 53°. The maximum rate of heading angle was 14.26°/s. The test results demonstrate that the specially designed thrust-vectoring mechanism notably enhances the effectiveness of AUVs at low forward speeds. In addition, tests conducted in offshore waters for depth and heading control validated the vectored thruster’s capability to fulfill the AUV’s motion control requirements. Full article

Embryological development of the pancreas is a complex phenomenon and, therefore, it can have multiple developmental aberrations. Fortunately, the majority of these pancreatic ductal anomalies are asymptomatic with no clinical relevance and are incidentally detected during diagnostic cross-sectional imaging or endoscopic retrograde cholangiopancreatography (ERCP) or autopsy. Occasionally, pancreatic duct anomalies can result in symptoms like abdominal pain or recurrent pancreatitis. Also, an accurate pre-operative diagnosis of ductal anomalies can prevent inadvertent duct injury during surgery. Conventionally, ERCP had been used for an accurate diagnosis of pancreatic duct anomalies. However, because it is invasive and associated with a risk of pancreatitis, it has been replaced with magnetic resonance cholangiopancreatography (MRCP). MRCP has demonstrated high sensitivity and specificity for the diagnosis of ductal anomalies, which can be further improved with the use of secretin-enhanced MRCP. Endoscopic ultrasound (EUS) is a new diagnostic and interventional tool in the armamentarium of endoscopists and has demonstrated promising results in the detection of pancreatic duct variations and anomalies. Along with the visualization of the course and configuration of the pancreatic duct, EUS can also visualize changes in the pancreatic parenchyma, thereby helping with an early diagnosis of any co-existent pancreatic disease. Absence of the stack sign and crossed duct sign are important EUS features to diagnose pancreas divisum. EUS can also help with the diagnosis of other congenital ductal anomalies like annular pancreas, ansa pancreatica, and anomalous pancreaticobiliary union, although the published experience is limited. Full article

Introduction: Congenital anomalies (CA’s) of most of the gastrointestinal tract have been linked causally with prenatal or community cannabis exposure. Therefore, we studied this relationship in Europe. Methods: CA data were from Eurocat. Drug-use data were sourced from the European Monitoring Centre for Drugs and Drug Addiction. Income data were taken from the World Bank. Results: When countries with increasing rates of daily cannabis use were compared with those which were not, the overall rate of gastrointestinal CA’s (GCA’s) was higher in the former group (p = 0.0032). The five anomalies which were related to the metrics of cannabis exposure on bivariate analysis were bile duct atresia, Hirschsprungs, digestive disorders, annular pancreas and anorectal stenosis or atresia. The following sequence of GCA’s was significantly linked with cannabis metrics at inverse-probability-weighted-panel modelling, as indicated: esophageal stenosis or atresia, bile duct atresia, small intestinal stenosis or atresia, anorectal stenosis or atresia, Hirschsprungs disease: p = 1.83 × 10⁻⁵, 0.0046, 3.55 × 10⁻¹², 7.35 × 10⁻⁶ and 2.00 × 10⁻¹², respectively. When this GCA series was considered in geospatial modelling, the GCA’s were significantly cannabis-related from p = 0.0003, N.S., 0.0086, 6.652 × 10⁻⁵, 0.0002, 71.4% of 35 E-value estimates and 54.3% minimum E-values (mEVv’s) > 9 (high zone) and 100% and 97.1% > 1.25 (causality threshold). The order of cannabis sensitivity by median mEVv was Hirschsprungs > esophageal atresia > small intestinal atresia > anorectal atresia > bile duct atresia. Conclusions: Seven of eight GCA’s were related to cannabis exposure and fulfilled the quantitative criteria for epidemiologically causal relationships. Penetration of cannabinoids into the community should be carefully scrutinized and controlled to protect against exponential and multigenerational genotoxicity ensuing from multiple cannabinoids. Full article

In this paper, planar and the cylindrical broadband non-uniform acoustic absorbers were constructed, both of which use broadband absorption units (BAUs) as their building blocks. The impedance boundary Navier–Stokes equation (IBNSE) method was developed to predict the absorption characteristics of the lined duct with non-uniform acoustic absorbers, in which each small piece of perforated plate is acoustically equivalent to a semi-empirical impedance model through the boundary condition. A total of four semi-empirical impedance models were compared under different control parameters. The full Navier–Stokes equation (FNSE) method was used to verify the accuracy of these impedance models. It was found that the IBNSE method with the Goodrich model had the highest prediction accuracy. Finally, the planar and the cylindrical non-uniform acoustic absorbers were constructed through spatial extensions of the BAU. The transmission losses and the absorption coefficients of the rectangular duct–planar acoustic absorber (RDPAA) and annular duct–cylindrical acoustic absorber (ADCAA) systems under grazing flow were predicted, respectively. The results demonstrated that the broadband absorption of the designed non-uniform acoustic absorbers was achieved. The developed IBNSE method with Goodrich model was accurate and computationally efficient, and can be used to predict the absorption characteristics of an acoustically treated duct in the presence of grazing flow. Full article

Ensuring the proper operation of tunnel firefighting systems in cold regions is a key issue at hand. According to the characteristics of cold region tunnel fire control systems, this paper puts forward a kind of air heat tracing system (AHTS) that is suitable for cold region tunnel firefighting systems. In the AHTS, an annular air duct was used to heat the firefighting pipe and keep it warm, so that the water temperature in the firefighting pipe is above the freezing point, which helps prevent the water in the firefighting pipe from freezing and avoids the failure of the firefighting system. Meanwhile, the finite element software ANSYS was used to simulate the working state of the AHTS under different conditions, and the insulation effect under different conditions was evaluated. The results showed that the AHTS has a good heating and heat preservation function, which can effectively maintain the normal operation of the tunnel firefighting system in cold regions under a low temperature environment (below 0 °C). Furthermore, increasing the air temperature and air speed in the system was beneficial to the working effect of the AHTS, and the “high temperature and low speed” mode was beneficial to reduce the system power consumption. It is recommended that v = 5 m/s and Ta = 50 °C be used as the preset operating parameters. Finally, according to the numerical analysis results, the scientific and reasonable working parameters of the AHTS under different working conditions were optimized. The research content can provide new ideas and theoretical support for the thermal insulation technology of tunnel firefighting systems in cold regions in the future. Full article

Heat transport in rotating processes finds a wide range of application in which academic issues in the fluid mechanics and heat transfer areas are here reported. This paper discusses successive works from the seminal paper of Taylor (1923) to recent numerical results established from a broad range of methods such as DNS, LES, RANS or LB methods. The flow regimes identification is thus reported in Taylor–Couette geometry. The role of the axial flow rates in the apparition, stabilization and destruction of the large-scale of the turbulent structures is depicted in the case of Taylor–Couette–Poiseuille geometry. In a non-isothermal condition, a discussion is held on the various exponent values found in the scaling relationships relying on the Nusselt number as a function of the Rayleigh or Reynolds numbers according to the regimes of thermal convection. Full article

The variable area bypass injector (VABI) plays a crucial role in variable cycle engines by regulating the flow mixing process in complex bypass ducts, and low-dimensional theoretical models are the key to revealing its working mechanism while estimating its aerodynamic performance. An improved VABI model using the control volume method is established, through which the feature parameters that determine the VABI aerodynamic performance are summarized. To acquire an accurate prediction of the injection ratio, a calibration item is introduced to the governing equations to consider the static pressure discrepancy on the mixing plane, and a numerical database is developed to obtain the calibration item. Results show that the aerodynamic parameters that determine the VABI performance include the bypass total pressure ratio, bypass backpressure, and the injection ratio, while the injection angle and the VABI opening area also influence the injection flow characteristics. The injection ratio is increased by reducing the bypass total pressure ratio, decreasing the bypass backpressure, and closing the VABI. Numerical validation shows that the calculation error of the improved model is generally below 3%. The improved VABI model is then validated by a well-arranged experiment, for which the annular flow is simplified into a rectangular duct flow with an error of less than 5%. The experimental validation also proves the accuracy of the model. Full article

In this study, a novel hybrid annular radial magnetorheological damper (HARMRD) is proposed to improve the ride comfort of an electric vehicle (EV) powered by an in-wheel motor (IWM). The model primarily comprises annular-radial ducts in series with permanent magnets. Mathematical models representing the governing motions are formulated, followed by finite element analysis of the HARMRD to investigate the distribution of the magnetic field density and intensity of the magnetorheological (MR) fluid in both the annular and radial ducts. The optimized model generates a damping force of 87.3–445.7 N at the off-state (zero input current) with the excitation velocity ranging between 0 and 0.25 m/s. By contrast, the generated damping force varies from 3386.4 N to 3753.9 N at an input current of 1.5 A with the same velocity range as the off state. The damping forces obtained using the proposed model are 31.4% and 19.2% higher for the off-field and on-field states, respectively, compared with those of the conventional annular radial MR damper. The efficiency of the proposed model is evaluated by adopting two different vehicles: a conventional vehicle powered by an engine and an EV powered by an IWM. The simulation results demonstrate that the proposed HARMRD along with the skyhook controller significantly improves both the ride comfort and road-holding capability for both types of vehicles. Full article

Fuel rod cladding failure in a nuclear reactor produces different phenomena related to vibrations and fluid–structure interaction. The most significant aspect of those phenomena is the creation of a pressure wave at the failure position and its propagation in the coolant fluid flowing around the fuel rod. An accurate understanding of the propagation of the pressure wave around the fuel rod can help us design a method to detect a failure, determine its position, and estimate some of its characteristics with a single and simple sensor, such as a pressure sensor or a piezoelectric acoustic sensor, that can be mounted relatively far from the failure. Such a method can be useful for the monitoring of nuclear fuel rods, where instrumentation possibilities are restricted (because of neutron flux, radiation, high temperature, and available space) as well as for any kind of application involving annular ducts and limited instrumentation possibilities. The current paper is related to the specific application of nuclear fuel rod monitoring. It deals with preliminary numerical simulations that are necessary to know the evolution of a fluid pressure profile along the system containing the rod. They are carried out by finite element methods, using the EUROPLEXUS code. They provide the necessary information about the propagation of pressure waves around the rod to design measurement and signal processing methods as well as properly interpret experimental results from tests in industrial reactors, research reactors, or experimental mock-ups. They also provide some information that could not be experimentally obtained because of the constraints in a nuclear environment. Despite the specific application we show in this article, similar calculation methods, theoretical observations, and results interpretations can be easily adapted to the other mentioned applications. Full article

Pleated membrane filters are widely used to remove undesired impurities from a fluid in many applications. A filter membrane is sandwiched between porous support layers and then pleated and packed into an annular cylindrical cartridge with a central hollow duct for outflow. Although this arrangement offers a high surface filtration area to volume ratio, the filter performance is not as efficient as those of equivalent flat filters. In this paper, we use asymptotic methods to simplify the flow throughout the cartridge to systematically investigate how the number of pleats or pleat packing density affects the performance of the pleated membrane filters. The model is used to determine an optimal number of pleats in order to achieve a particular optimum filtration performance. Our findings show that only the “just right”—neither too few nor too many—number of pleats gives optimum performance in a pleated filter cartridge. Full article