Search Results (164)

Blade tip leakage vortex (TLV) is a critical phenomenon in hydraulic machinery, which can significantly affect the internal flow characteristics and deteriorate the hydraulic performance. In this paper, the blade tip leakage flow and TLV characteristics in a novel dishwasher pump were investigated. The correlation between the vorticity distribution in various directions and the leakage vortices was established within a rotating coordinate system. The results show that the TLV in a composite impeller can be categorized into initial and secondary leakage vortices. The initial leakage vortex originates from the evolution of two corner vortices that initially form at different locations within the blade tip clearance. This vortex induces pressure fluctuations at the impeller inlet; its shedding is identified as the primary contributor to localized energy loss within the flow passage. These findings provide insights into TLVs in complex pump geometries and provide solutions for future pump optimization strategies. Full article

To address the problems of low crushing efficiency and uneven distribution in traditional straw crushing and returning machines for cotton stalk return operations in Xinjiang, a vertical straw crushing and returning machine with large and small dual-blade discs was designed, adapted to Xinjiang’s cotton planting model. The machine employs a differentiated configuration of large and small blade discs corresponding to four and two rows of cotton stalks, respectively, effectively reducing tool workload while significantly improving operational efficiency. A simulation model of the crushing and returning machine was developed using the discrete element method (DEM), and a flexible cotton stalk model was established to systematically investigate the effects of machine forward speed, crushing blade rotational speed, and knife tip-to-ground clearance on operational performance. Single-factor simulation experiments were conducted using crushing qualification rate and broken stalk drop rate as evaluation indicators. Subsequently, a multi-factor orthogonal field experiment was designed with Design-Expert software (13.0.1.0, Stat-Ease Inc, Minneapolis, MN, USA). The optimal working parameters were determined to be machine forward speed of 3.5 m/s, crushing blade shaft speed of 1500 r/min, and blade tip ground clearance of 60 mm. Verification tests demonstrated that under these optimal parameters, the straw crushing qualification rate reached 95.9% with a broken stalk drop rate of 15.5%. The relative errors were less than 5% compared to theoretical optimization values, confirming the reliability of parameter optimization. This study provides valuable references for the design optimization and engineering application of straw return machinery. Full article

This study presented an autonomous shield-cutting end-effector for maize surrounding weeding (SEMSW), addressing the challenges of the low weed removal rate (WRR) and high seedling damage rate (SDR) in northern China’s 3–5 leaf stage maize. The SEMSW integrated seedling positioning, robotic arm control, and precision weeding functionalities: a seedling positioning sensor identified maize seedlings and weeds, guiding XYZ translational motions to align the robotic arm. The seedling-shielding anti-cutting mechanism (SAM) enclosed crop stems, while the contour-adaptive weeding mechanism (CWM) activated two-stage retractable blades (TRWBs) for inter/intra-row weeding operations. The following key design parameters were determined: 150 mm inner diameter for the seedling-shielding disc; 30 mm minimum inscribed-circle for retractable clamping units (RCUs); 40 mm ground clearance for SAM; 170 mm shielding height; and 100 mm minimum inscribed-circle diameter for the TRWB. Mathematical optimization defined the shape-following weeding cam (SWC) contour and TRWB dimensional chain. Kinematic/dynamic models were introduced alongside an adaptive sliding mode controller, ensuring lateral translation error convergence. A YOLOv8 model achieved 0.951 precision, 0.95 mAP50, and 0.819 mAP50-95, striking a balance between detection accuracy and localization precision. Field trials of the prototype showed 88.3% WRR and 2.2% SDR, meeting northern China’s agronomic standards. Full article

As a core component in renewable energy systems for grid regulation, hydropower units are increasingly exposed to flow conditions that elevate the risk of cavitation and erosion, posing significant challenges to the safe operation of flow-passage components. In this study, model testing and computational fluid dynamics (CFD) simulations are employed to investigate the hydraulic performance and cavitation behavior of a bulb turbine operating under rated head conditions and varying cavitation numbers. The analysis focuses on how changes in cavitation intensity affect flow characteristics and efficiency within the runner region. The results show that as the cavitation number approaches its critical value, the generation, growth, and collapse of vapor cavities increasingly disturb the main flow, causing a marked drop in blade hydraulic performance and overall turbine efficiency. Cavitation predominantly occurs on the blade’s suction side near the trailing edge rim and in the clearance zone near the hub, with bubble coverage expanding as the cavitation number decreases. A periodic inverse correlation between surface pressure and the cavitation area is observed, reflecting the strongly unsteady nature of cavitating flows. Furthermore, lower cavitation numbers lead to intensified pressure pulsations, aggravating flow unsteadiness and raising the risk of vibration. Full article

Rotor–stator interaction and the coupling between the clearance flow and main flow amplify the flow complexity in small-scale, high-speed automotive pumps. This degrades the pressure fluctuations, compromising the operational stability of these pumps. To better understand the pressure fluctuation distribution characteristics within such a pump, the Reynolds-averaged Navier–Stokes equations and the shear stress transport k-ω turbulence model were applied to numerically compute the pump. The simulation results were compared with experimental data, and good agreement was achieved. The results show that pressure fluctuations in the main flow region are mainly dominated by the blade passing frequency, and the intensity of pressure fluctuations in the near-field area of the tongue reaches its peak value, showing significant fluctuation characteristics. Significant peak signals are captured in the low-frequency band of pressure fluctuations in the clearance region. The pressure fluctuation characteristics are also affected by the rotor–stator interaction between the impeller front shroud and the volute casing, while the dominant frequency is still the blade passing frequency. In addition, the dominant frequencies of pressure fluctuations in the main and clearance flows show a similar distribution to the flow rate, but the minimum amplitude corresponds to different flow rates. Full article

This paper details the development of a full turbine model and ensuing aero-servo-elastic analysis of the International Energy Agency’s 15MW Reference Wind Turbine. This model provides the means to obtain realistic turbine performance data, of which normal and tangential blade loads are extracted and applied to a simplified drivetrain model developed expressly to quantify the shaft eccentricities caused by aerodynamic loading, thus determining the impact of aerodynamic loading on the generator structure. During this process, a method to determine main bearing stiffness values is presented, and values for the IEA-15MW-RWT obtained. It was found that wind speeds in the region of turbine cut-out induce shaft eccentricities as high as 56%, and that tangential loading has a significant contribution to shaft eccentricities, increasing deflection at the generator area by as much as 106% at high windspeeds, necessitating its inclusion. During a subsequent generator structure optimisation, the shaft eccentricities caused by the loading scenarios examined in this paper were found to increase the necessary mass of the rotor structure by 40%, to meet the reduced airgap clearance. Full article

This study aims to elucidate the mechanisms by which tip seal leakage flow induces steam excitation, thereby enhancing the operational safety of steam turbines. Using numerical simulations, it investigates the detailed characteristics of the flow field in the turbine tip seal cavity. By introducing Boundary Vorticity Flux (BVF) into the tip seal flow field, this research explores the relationship between leakage vortex structures in non-uniform flow fields at the blade tip and the resulting steam excitation forces. The results demonstrate that, during eccentric rotor operation, the extent and intensity of vortices within the seal cavity vary, lead to changes in the BVF distribution along the shroud surface, which in turn alter the tangential forces and induce variations in lateral excitation force at the blade tip. Additionally, the non-uniform flow in the tip seal clearance induces circumferential pressure variations across the shroud, leading to adjustments in radial excitation force at the blade tip. Full article

The mucociliary clearance system is an innate defense mechanism in the human respiratory tract, which plays a crucial role in protecting the airways from infections. The clearance system secretes mucus from the goblet cells, which scatters in the respiratory epithelium to trap foreign particles entering the airway, and then the mucus is removed from the body via the movement of cilia residing under the mucus and above the epithelium cells. The layer containing cilia is called the periciliary layer (PCL). This layer also contains an incompressible Newtonian fluid called PCL fluid. This study aims to determine the velocity of the PCL fluid driven by the cilia movement instead of a pressure gradient. We consider bundles of cilia, rather than an individual cilium. So, the generalized Brinkman equation in a macroscopic scale is used to predict the fluid velocity in the PCL. We apply a mixed finite element method to the governing equation and calculate the numerical solutions in a two-dimensional domain. The numerical domain is set up to be the shape of a fan blade, which is similar to the motion of the cilia. This problem can be applied to problems of fluid flow propelled via moving solid phases. Full article

An inductive clearance measurement sensor has advantages of good anti-interference, fast response speed, and high sensitivity, and it has obvious technical potential in aeroengine turbine tip clearance measurement. In this paper, a rotor dynamic tip clearance measurement experiment system was designed based on a high-resolution inductive measurement system. The high temperature calibration experiment, performance verification experiment, and dynamic clearance measurement experiment under varying operating conditions were used to verify the high-temperature dynamic measurement performance of the measurement system. The resolution was used as the evaluation parameter of measurement performance. The experimental result shows the system has good resolution and dynamic response at 1000 °C, and the dynamic resolution reaches 10 μm in the 3 mm measuring range. The varying condition experiment results show that the blade deformation caused by the speed change of 1000–3000 r/min and the temperature change of 600–1000 °C can be resolved, and the resolution reaches about 10 μm. The research results verify that the inductance clearance measurement system has the characteristics of high temperature resistance and high resolution, and the technical specifications of clearance detection meet the basic requirements of dynamic clearance measurement of turbine tips, which provides an effective detection method for aeroengine health monitoring. Full article

Sediment erosion of hydraulic turbines has gradually become a key factor affecting their long-term stable operation. There are many different factors that can cause erosion in the Francis hydraulic turbine; among them, the vortex occurs in the turbine, which is also a negative factor for the unit. In this paper, the purpose is to study the complex erosion characteristics and specific influencing factor mechanism. The method is based on numerical simulation, combined with the verification data on site. Research results show that the differences in flow patterns among various components correspond to the erosion distribution of the unit at the same location, indicating that local flow patterns affect the unit’s erosion. The highest total erosion rate is on the surface of the runner at 1.08 × 10⁻³ kg·s⁻¹·m⁻². The erosion rate on the guide vane wall is second highest, also at 9.8 × 10⁻⁴ kg·s⁻¹·m⁻². The total erosion rate in the clearance is lower than that on the guide vane wall at 7.03 × 10⁻⁴ kg·s⁻¹·m⁻². The lowest total erosion rate is found in the draft tube at 2.57 × 10⁻⁴ kg·s⁻¹·m⁻². The effect of local vortices not only exacerbate the microscopic damage on the blade surface but also leads to a more obvious nonuniform erosion distribution, especially at the clearance, where erosion is more severe. The vortex in the guide vane passage alters the particle trajectory at the guide vane outlet, increasing the erosion in the guide vane clearance. Similarly, the vortex in the draft tube increases particle rotation, enhancing erosion on the draft tube wall. Research indicates that eliminating vortices is beneficial for reducing sediment erosion within the unit. The research results provide a theoretical basis for the optimization design of Francis hydraulic turbine. Full article

Turbines are rotating machines that generate power by the expansion of a fluid; due to their characteristics, these turbomachines are widely applied in aerospace propulsion systems. Due to the clearance between the rotor blade tip and casing, there is a leakage flow from the blade pressure to the suction sides, which generates energy loss. There are different strategies that can be applied to avoid part of this loss; one of them is the application of so-called desensitization techniques. The application of these techniques on gas turbines has been widely evaluated; however, there is a lack of analyses of hydraulic turbines. This study is a continuation of earlier analyses conducted during the first stage of the hydraulic axial turbine used in the low-pressure oxidizer turbopump (LPOTP) of the space shuttle main engine (SSME). The previous work analyzed the application of squealer geometries at the rotor tip. In the present paper, winglet geometry techniques are investigated based on three-dimensional flowfield calculations. The commercial CFX v.19.2 and ICEM v.19.2 software were used, respectively, on the numerical simulations and computational mesh generation. Experimental results published by the National Aeronautics and Space Administration (NASA) and data from previous works were used on the computational model validation. The parametric analysis was conducted by varying the thickness and width of the winglet. The results obtained show that by increasing the winglet thickness, the stage efficiency is also increased. However, the geometric dimension of its width has minimal impact on this result. An average efficiency increase of 2.0% was observed across the entire turbine operational range. In the case of the squealer, for the design point, the maximum efficiency improvement was 1.62%, compared to the current improvement of 2.23% using the winglet desensitization technique. It was found that the proposed geometries application also changes the cavitation occurrence along the stage, which is a relevant result, since it can impact the turbine life cycle. Full article

Centrifugal pumps are known to efficiently transport water from a certain point. However, they developed great concerns in water supply and distribution applications regarding their operating efficiency, which were caused by the accumulated losses and sudden power consumption growth. Thus, mitigating these concerns is important to improve the performance of the centrifugal pump. This study used ANSYS 2022 R2 for the optimization design process, combining the strengths of Computational Fluid Dynamics (CFD) and Response Surface Method (RSM), to come up with an optimal design for a centrifugal water pump. Splitter blades, with a length of 80% of the main blade, were included in the design to assess their effects on the performance of the pump. Design parameters such as the placement of the splitter blades, their ellipse ratios, and the volute tongue, were also investigated for further improvement. Results indicate that finding a perfect balance between the placement of the splitter blades, the design of the volute tongue clearance and thickness, and configuring the ellipse ratio of the splitter blades improves the pump’s performance. The optimal design results in 27.35%, 15.70%, 28.18%, 16.67%, and 8.36% improvement in total efficiency, total head, static efficiency, static head, and power consumption, respectively. Full article

Rotors have been utilized for aircraft propulsion since the dawn of aviation, but their performance can degrade significantly if not properly designed. This study focuses on developing an accurate design tool and model validation for shrouded rotors. An experimental test rig was designed and manufactured to measure the rotor thrust and total thrust separately as well as the rotor torque. A key aspect was to account for the impact of a test rig on experimental results using computational simulations for the shrouded rotor configuration with and without the test rig. The findings indicate that the effects of the test rig were minimal and could be neglected, ensuring the validity of the experimental data compared to the analytical model. The analytical model employs a hybrid approach combining blade element momentum theory (BEMT) and the sphere-cap model which are used in conjunction with the shrouded rotor inflow ratio, as well as post-stall and tip gap clearance models. BEMT is used to calculate rotor performance, while the sphere-cap model addresses the aerodynamic influence of the shroud. The results demonstrate that the analytical model predicts shrouded rotor performance with considerable accuracy, addressing both the rotor dynamics and the shroud’s contribution to performance. Full article

Tip leakage flow interacts with the mainstream, impacting the energy transmission process within the impeller of the fan and causing a significant flow loss. Understanding the flow characteristics within the impeller is a prerequisite and foundation for achieving efficient operation of the fan. Therefore, numerical simulations and experimental methods were employed to obtain the internal flow field of the mining counter-rotating axial flow fan, and the influence of flow rate on the tip leakage flow pattern was mastered. The spatial trajectory of the leakage vortex was quantified, and the distribution characteristics of the backflow were explored. The mechanism of energy loss caused by the leakage flow was revealed. The research findings indicate that when the flow rate exceeds 1.0 Q_BEP (Q_BEP is flow rate at the best efficiency point), the complex flow field near the blade tip is mainly caused by the tip leakage flow. However, the tip leakage flow and the leading edge overflow are the main factors causing disturbances in the flow field within the impeller at small flow rates. At large flow rates, the starting positions of the tip leakage vortex cores for both the front and rear impellers are located near the middle of the blade tip. As the flow rate decreases, the starting position of the vortex core gradually shifts toward the leading edge point, and the vortex structure evolves from an initial circular shape to an elliptical shape. The tip leakage flow and the leading edge overflow are the main cause of the backflow at the impeller inlet. The helical vortices caused by the tip leakage flow and the leading edge overflow, as well as the backflow in the impeller, are the key factors causing energy loss in the tip clearance flow field. Full article

Small-size turbine drilling tools have better application prospects in small borehole drilling and so on. Based on the SST model, the influence of a Φ73 mm turbine knuckle-shape parameters on the mechanical energy output characteristics was simulated, and the vortex structure of the turbine internal flow field was analyzed to find the law. First, the influence of leading-edge radius on the turbine internal flow field is concentrated on the rotor suction surface. Second, as with the axial clearance, there is a regular effect of the trailing-edge radius on the flow field in the rotor as a whole and in the middle and rear parts of the stator. Third, the change in the installation-staggering angle does not change the turbine output performance. The output performance is optimal when the leading-edge radius of the Φ73 mm turbine blade is 0.8 mm, the trailing-edge radius is 0.4 mm, and axial clearance is 6 mm. At the same time, the effects of rotational speed, displacement, and fluid viscosity on the output performance of the turbine were simulated, and the output performance of the turbine of this size was predicted under the conditions of low rotational speed, small displacement, and high fluid viscosity. Under the working conditions of conventional drilling parameters, the output pressure drop of a single-stage turbine can be up to 0.018 MPa or less, and the torque is more than 1.6 Nm. If 100–200-stage turbines are used as the power, the output torque can reach 150–300 Nm, which can meet the demand of rock-breaking in the mine. Full article