Search Results (158)

Twin-screw compressors (TSCs) are widely used in various industries. Their performance is influenced by several parameters, such as rotor profiles, clearance gaps, operating speed, and thermal effects. Traditionally, optimizing these parameters relied on experimental methods, which are costly and time-consuming. However, advancements in computational tools, such as Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA), have revolutionized compressor analysis. This study presents a CFD analysis of a specific model of a TSC in a 5 male/6 female lobe configuration using the SolidWorks Flow Simulation environment—an approach not traditionally applied to such positive displacement machines. The results visually present internal flow trajectories, fluid velocities, pressure distributions, temperature gradients, and leakage behaviors with high spatial and temporal resolution. Additionally, torque fluctuations and isosurface visualizations revealed insights into mechanical loads and flow behavior. The proposed method allows for relatively easy adaptation to different TSC configurations and can also be a useful tool for engineering and educational purposes. Full article

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

This study examines the labyrinth seal disc of an aero-engine, specifically analysing the radial deformation caused by centrifugal force and heat stress during operation. This distortion may lead to discrepancies in the performance attributes of the labyrinth seal and could potentially result in contact between the labyrinth seal tip and neighbouring components. A numerical analytical model incorporating the rotor and stator cavities, along with the labyrinth seal disc structure, has been established. The sealing integrity of a standard labyrinth seal disc’s flow channel is evaluated and studied at different clearances utilising the fluid–solid-thermal coupling method. The findings demonstrate that, after considering radial deformation, a cold gap of 0.5 mm in the conventional labyrinth structure leads to stabilisation of the final hot gap and flow rate, with no occurrence of tooth tip rubbing; however, both the gap value and flow rate show considerable variation relative to the cold state. When the cold gap is 0.3 mm, the labyrinth plate makes contact with the stator wall. To resolve the problem of tooth tip abrasion in the conventional design with a 0.3 mm cold gap, two improved configurations are proposed, and a stability study for each configuration is performed independently. The leakage and temperature rise attributes of the two upgraded configurations are markedly inferior to those of the classic configuration at a cold gap of 0.5 mm. At a cold gap of 0.3 mm, the two improved designs demonstrate no instances of tooth tip rubbing. 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

Labyrinth seals, extensively used in aerospace and turbomachinery as non-contact sealing devices, undergo accelerated wear and enhanced leakage due to repeated rub-impact between rotating shafts and sealing rings. To address the problem of increased leakage under rub-impact conditions, this research integrates experimental and numerical methods to investigate the deformation mechanisms and leakage characteristics of thermoplastic labyrinth seals. A custom designed rub-impact test rig was constructed to measure dynamic forces and validate finite element analysis (FEA) models with an error of 5.1% in predicting tooth height under mild interference (0.25 mm). Computational fluid dynamics (CFD) simulations further demonstrated that thermoplastic materials, such as PAI and PEEK, displayed superior resilience (with rebound ratios of 57% and 70.3%, respectively). Their post-impact clearances were 4.8–18.3% smaller than those of PTFE and F500. Leakage rates were predominantly correlated with interference, causing a substantial increase compared to the original state; at 0.25 mm interference (reverse flow), increases ranged from 151% (PAI) to 217% (PTFE), highlighting material-dependent performance degradation. Meanwhile, tooth orientation modulated leakage by 0.5–3% through the vena contracta effect. Based on these insights, two optimized inclined-tooth geometries were designed, reducing leakage by 28.2% (Opt1) and 28.1% (Opt2) under rub-impact. These findings contribute to the development of high-performance labyrinth seals suitable for extreme operational environments. Full article

The dynamic response of pump valve motion directly influences the volumetric efficiency of drilling pumps and serves as a critical factor in performance enhancement. This study presents a coupled fluid–structure interaction (FSI) analysis of a novel secondary cushioned pump valve for drilling systems. A validated 3D transient numerical model, integrating piston–valve kinematic coupling and clearance threshold modeling, was developed to resolve the dynamic interactions between reciprocating mechanisms and turbulent flow fields. The methodology addresses critical limitations in conventional valve closure simulations by incorporating a geometrically adaptive mesh refinement strategy while maintaining computational stability. Transient velocity profiles confirm complete sealing integrity with near-zero leakage (<0.01 m/s), while a 39.3 MPa inter-pipeline pressure differential induces 16% higher jet velocities in suction valves compared to discharge counterparts. The secondary cushioned valve design reduces closure hysteresis by 22%, enhancing volumetric efficiency under rated conditions. Parametric studies reveal structural dominance, with increases in cylindrical spring stiffness lowering discharge valve lift by 7.2% and velocity amplitude by 2.74%, while wave spring optimization (24% stiffness enhancement) eliminates pressure decay and reduces perturbations by 90%. Operational sensitivity analysis demonstrates stroke frequency as a critical failure determinant: elevating speed from 90 to 120 rpm amplifies suction valve peak velocity by 59.87% and initial closing shock by 129.07%. Transient flow simulations validate configuration-dependent performance, showing 6.3 ± 0.1% flow rate deviations from theoretical predictions (Q_{t_max} = 40.0316 kg/s) due to kinematic hysteresis. This study establishes spring parameter modulation as a key strategy for balancing flow stability and mitigating cushioning-induced oscillations. These findings provide actionable insights for optimizing high-pressure pump systems through hysteresis control and parametric adaptation. Full article

Alzheimer’s disease (AD) is characterized by amyloid-beta (Aβ) pathology and is closely linked to oxidative stress, which contributes to blood–brain barrier leakage, renal dysfunction, and cognitive decline. We investigated the effects of N-acetyl cysteine (NAC), an FDA-approved antioxidant, on oxidative stress, brain Aβ levels, barrier leakage, renal function, and cognition in 5xFAD mice. Eight-week-old 5xFAD mice were fed a rodent diet supplemented with 600 mg/kg_Diet NAC for 4 weeks; wild-type (WT) mice and control 5xFAD mice were fed a regular rodent diet. We detected elevated brain and renal 4-hydroxynonenal(4-HNE) levels, reduced creatinine clearance, and increased plasma S100β levels in untreated 5xFAD mice compared to WT controls. Untreated 5xFAD mice also had higher capillary leakage, reduced P-gp activity, and impaired cognition compared to WT. NAC treatment of 5xFAD mice reduced brain Aβ40 levels, normalized 4-HNE levels to control levels, improved creatinine clearance, decreased capillary leakage, and lowered S100β plasma levels. NAC improved cognitive performance in 5xFAD mice, as shown by Y-maze. Our findings indicate that Aβ-induced oxidative stress contributes to barrier dysfunction, renal impairment, and cognitive deficits in 5xFAD mice. Notably, NAC treatment mitigates these effects, suggesting its potential as an adjunct therapy for AD and other Aβ-related pathologies by reducing oxidative stress. 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

Premature seal failure induced by the unevenness of interstage pressure distribution in multi-stage brush seals significantly compromises the sealing efficiency of Air-Turbo Rocket (ATR) engines operating under high-pressure (megapascal-level) differential conditions. Conventional pressure equalization designs for such seals often result in significant leakage rate increases. This study addresses the pressure imbalance phenomenon in four-tooth three-stage brush composite seals through a novel fractal–geometric porous-media model, rigorously validated against experimental data. Systematic investigations were conducted to elucidate the effects of structural parameters and operational conditions on both sealing performance and pressure distribution characteristics. Key findings reveal that, under the prototype structure parameter, the first-, second-, and third-stage brush bundles account for 18.3%, 30.0%, and 43.3% of the total pressure drop, respectively, with grate teeth contributing 8.4%, demonstrating an inherent pressure imbalance. Axial brush spacing exhibits a minimal impact on the pressure distribution, while the gradient thickness settings of the brush bundles show limited influence. Radial clearance optimization and gradient backplate height adjustment effectively regulate pressure distribution, albeit with associated leakage rate increases. Structural modifications based on these principles achieved only a 5.8% leakage increment while reducing the maximum bundle pressure drop by 23%, demonstrating effective pressure balancing. A simplified analysis of entropy reveals that the fundamental mechanism governing the pressure imbalance stems from non-uniform entropy generation caused by aerodynamic damping dissipation across sequential brush stages. These findings establish a dampened dissipation-based theoretical framework for designing high-performance multistage brush seals in aerospace applications, providing critical insights for achieving an optimal balance between leakage control and pressure equalization in extreme-pressure environments. Full article

To investigate the performance of high-speed miniaturized screw refrigeration compressors, this study designed rotors with identical theoretical displacement but varying rated speeds. A normalized analysis established quantitative evaluation criteria for geometric performance, while an exergy analysis model assessed leakage exergy losses. Thermodynamic modeling evaluated the impact of different clearances and rated speeds on performance. Computational fluid dynamics (CFD) simulations analyzed the gas forces and torque acting on the rotors. The rate of efficiency improvement with increasing speed follows a non-linear relationship, demonstrating diminishing returns at ultra-high speeds, where further speed elevation provides negligible efficiency gains. This study reveals that, while tip-housing leakage represents the largest volumetric leakage in screw compressors, interlobe leakage contributes the most significantly to power losses. When the rated speed increases from 3000 rpm to 15,000 rpm, interlobe leakage remains the dominant source of power loss, with its relative contribution showing a marked increase. For compressors with identical cylinder dimensions, reducing the number of lobes decreases the discharge pressure fluctuations and power consumption. Larger wrap angles increase the contact line length and discharge port area, reducing the volumetric efficiency while creating a trade-off between leakage and discharge losses, resulting in an optimal wrap angle that maximizes the adiabatic efficiency. Full article

Innovating seal structures and optimizing size parameters are effective ways to enhance the leakage characteristics of labyrinth seals (LSs). Inspired by the ecological fishways with high flow resistance on dam sides, a novel bio-inspired staggered labyrinth seal is proposed. The leakage characteristics of both the curved-edged bio-inspired labyrinth seal (CELS) and the straight-edged bio-inspired labyrinth seal (SELS) at different tooth-incline angles are studied numerically and experimentally. The influence of key geometrical parameters on the leakage characteristics and flow field parameters of the CELSs are investigated, and the leakage control mechanism of bio-inspired LSs is revealed via analyzing flow field parameter distribution. The results indicate that, compared to conventional double-sided staggered straight-tooth labyrinth seals, the leakage rate reduction in CELSs is up to 30% when the incline angle is equal to 25°, outperforming that of the SELS in leakage control. This improvement is mainly attributed to the flow path bending and jet contraction effects at the tooth-tip entrance, along with the thermodynamic effects of the high-turbulence dissipation zone adjacent to the tooth top. The optimum leakage characteristics can be achieved when seal clearance h < 0.5 mm, aspect ratio δ < 0.6, and tooth thickness t < 1.5 mm. This work provides new insights into the structural design of high-resistance and low-leakage labyrinth seals. 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

Hemodialysis (HD) is a critical treatment for patients with end-stage kidney disease (ESKD). The effectiveness of conventional dialyzers used there could be compromised during extended use due to limited blood compatibility of synthetic polymeric membranes and sub-optimal dialyzer design. In fact, blood flow in the hollow fiber (HF) membrane could trigger inflammatory responses and thrombus formation, leading to reduced filtration efficiency and limiting therapy duration, a consequence of flowing the patients’ blood through the lumen of each fiber while the dialysate passes along the inter-fiber space (IOF, inside-out filtration). This study investigates the development of HF membranes for “outside-in filtration” (OIF) in HD. In OIF, blood flows through the inter-fiber space while dialysate flows within the fiber lumens, reducing the risk of fiber clogging and potentially extending treatment duration. For the OIF mode, the membrane should have a blood-compatible outer selective layer in contact with the patient’s blood. We develop HFs for OIF via liquid-induced phase separation using PES/PVP (polyethersulphone/polyvinylpyrrolidone) blends. The fibers’ surface morphology (SEM, scanning electron microscopy), chemistry (ATR-FTIR—attenuated total reflection-Fourier transform infrared spectroscopy, XPS—X-ray photoelectron spectroscopy), transport properties, and uremic toxin removal from human plasma are evaluated and compared to commercial HFs. These membranes feature a smooth, hydrophilic outer layer, porous lumen, ultrafiltration coefficient of 13–34 mL m² h⁻¹ mmHg⁻¹, adequate mechanical properties, low albumin leakage, and toxin removal performance on par with commercial membranes in IOF and OIF. They offer potential for more efficient long-term HD by reducing clogging and systemic anticoagulation needs and enhancing treatment time and toxin clearance. Full article

This paper reviews the current state of dynamic sealing technologies, examining the challenges faced by conventional sealing methods under complex working conditions, such as high temperature, high pressure, and corrosive environments. It also provides a concise overview of the status and developmental trends in sealing inspection technologies. From the perspective of obstruction mechanisms, this study reinterprets the concept of sealing science by redefining the classification of sealing types based on solid-phase medium obstruction, fluid hydrostatic and hydrodynamic obstruction, fluid pumping obstruction, fluid energy dissipation obstruction, and fluid impact obstruction. Comparative analyses of sealing structures across these obstruction mechanisms are presented. The sealing technology based on fluid impact medium obstruction, newly proposed by this paper, represents an innovative sealing approach. It offers distinct advantages such as zero wear, structural simplicity, and high stability, addressing longstanding issues in high-speed, large-clearance non-contact seals, including low leakage suppression efficiency, system complexity, and poor stability. Since its introduction, this novel sealing structure has garnered significant attention and recognition from both the academic and industrial sealing communities. With the potential to revolutionize the field, this groundbreaking sealing design is poised to lead the next wave of technological advancements in sealing science. Full article

This study utilizes numerical calculations and experimental studies to analyze the cavitation characteristic law and performance of an agricultural irrigation axial flow pump with a specific rotational speed of 735 at 0.2Q_opt–1.2Q_opt operating conditions. The external characteristics and constant cavitation performance of the axial flow pump are simulated by using the $SST k-\omega$ turbulence model and $Zwart$ cavitation model, and the corresponding performance curves are obtained. The results show that the highest efficiency point occurs at the 1.1Q_opt condition, and the efficiency reaches 77.07%; the hump phenomenon occurs in the 0.6Q_opt–0.8Q_opt head curve, which is mainly caused by the fluid leakage due to the clearance at the top of the lobe. The critical cavitation margin (${NPSH}_3$) was determined to be 4.48 m, 4.36 m, and 4.09 m at 0.8Q_opt, 1.0Q_opt, and 1.2Q_opt flow conditions, respectively. These findings suggest that cavitation is more probable at lower flow conditions. In circumstances where the inlet pressure is lower than the critical pressure, the phenomenon of cavitation manifests predominantly within the low-pressure region of the suction surface of the blade. This region encompasses the inlet rim and the area surrounding the maximum thickness. This study provides a theoretical basis and practical reference for solving the cavitation problem of axial flow pumps. Full article