Low Flow Research Articles

Improving near-stall performance of axial flow compressors using variable rotor tandem stage. A steady analysis

This paper investigates the idea of substituting the first stage of a conventional axial-flow compressor and its inlet guide vane (IGV) row with a variable rotor tandem (VRT) stage to reduce the size and weight of axial-flow compressors. It is expected that a tandem stage gains higher pressure ratio than a conventional stage, and simultaneously, its variable stagger rotor provides more flexibility in handling unsteady phenomena at low mass flow rates. A three-dimensional numerical model based on Reynolds-Averaged Navier–Stokes equations is developed to conduct this investigation. To validate the numerical model, experimental tests are conducted on a tandem single-stage axial-flow compressor test bench in the Dana laboratory of Amirkabir University of Technology, to compare the performance map with numerical results. The validated numerical model is then employed to simulate the performance of both front and aft variable rotor blades. The proposed tandem stage effectively performs the IGV duty, suppresses instabilities at low mass flow rates, and eventually extends the compressor's stable operational range. This proves that a VRT stage is an efficient active surge-control system tool. The detailed survey of the three-dimensional flow field reveals that the aft tandem rotor blade stagger angle is more effective in increasing the stall margin and decreasing the minimum operational mass flow rate than the front row of blades. It is observed that when the aft blades rotate in the direction of decreasing the tandem blades' gap area, the flow momentum increases and causes the compressor stability at lower mass flow rates.

Season-dependent climate sensitivity of the surface runoff of major rivers in Changbai Mountain

Due to the sensitivity of runoff to changes in seasonal snowpack, the changes in surface runoff within high-latitude and high-elevation areas are more complex than in other areas. However, this sensitivity is often overlooked when correlating changes in runoff with meteorological variables. Here, we analyze changes in surface runoff during snowmelt and snowless periods and their sensitivity to climate change from 1960 to 2019 in the upstream watersheds of the Songhua, Yalu, and Tumen Rivers in Changbai Mountain. Most runoff indices, except for low flow in the Yalu River, exhibited decreasing trends during snowmelt and snowless periods. Precipitation was the primary variable responsible for surface runoff during snowless and snowmelt periods. Notably, rainfall replenished all runoff indices during snowless periods, particularly under high flow conditions. The average and high flows were also primarily supplemented by rainfall during snowmelt periods. However, low flow was positively correlated with snowmelt in the Songhua and Tumen Rivers and with temperature in the Songhua, Yalu and Tumen Rivers during snowmelt periods. Additionally, extreme runoff events were closely associated with extreme precipitation. These findings demonstrate the seasonal and index-dependent climate sensitivity of surface runoff within Changbai Mountain, offering insights into the surface runoff response mechanism to climate change in high-altitude mountainous areas. Under future climate change conditions, frequent and intense extreme precipitation events may increase the risk of flooding, owing to the high sensitivity of high flows to precipitation, posing a serious threat to regional ecological security.

Effect of hills on wind turbine flow and power efficiency: A large-eddy simulation study

This study investigates the influence of topography on wind turbine flow and power efficiency. Specifically, a standalone wind turbine is positioned at the top of idealized two-dimensional hills, and the effects of hill geometry and turbine position are systematically investigated. Various parameters are studied, including hill slope, distance between the leeward side of the hill and the turbine, turbine hub height, and hill size. Overall, it is observed that the turbine wake is consistently stronger in the hill cases compared to the flat case. This is attributed to two characteristics of hill flows: (1) the negative streamwise velocity gradients on the leeward side of the hills and (2) the reduced turbulence above the hilltops and hill wake regions. In addition, it is observed that the turbine induction factor is consistently increased in the hill cases compared to the flat case, while the turbine power and thrust coefficients are reduced. In practice, this means that turbines on the hills produce less power output than those on flat terrain for an equivalent wind potential, with the potential decrease in power output reaching more than 20% for certain cases. Altogether, the results offer new insights into the effect of topography on turbine power efficiency. In addition, the study identifies clear relationships between the turbine power coefficient, the induction factor, the overall maximum deficit, and the base flow pressure gradient. These relationships could potentially be used to predict the change in power efficiency based on the wake flow or the base flow. Overall, the results show a clear connection between the turbine power efficiency and the turbine wake development.

Unsteady characteristics of supersonic base flow influenced by the exhaust jet

The supersonic base flow with an exhaust jet is significantly unsteady, whose characteristics can be influenced by the exhaust jet states. By the exhaust jet, we mean the working fluid produced by the rocket engine and exhausted by the base nozzle in supersonic velocity, which is used to generate thrust. A numerical investigation of the base flow at Mach 1.96 is carried out via the delayed detached eddy simulation. The effects of presence, expanded states, and temperature of the exhaust jet on the unsteady characteristics are analyzed. Compared with the exhaust jet off, the exhaust jet presence causes the base pressure fluctuation intensity to increase in the high-frequency band (SrD > 0.5) and changes the dominant mode from wake oscillation (SrD = 0.12) to the periodically expand-shrink of the exhaust jet diameter (SrD = 0.16). Compared with the underexpanded state, the overexpanded exhaust jet induces the flow separation inside the nozzle, which causes a decrease in the base pressure fluctuation intensity in the high-frequency band (SrD > 1.0), and the separation point movement and exhaust jet oscillation constitute the dominant mode (SrD = 0.13). Compared with the low-temperature jet, the base pressure fluctuation intensity is slightly reduced in the high-frequency band (SrD > 1.0) for the high-temperature jet, and the flapping motion of the jet shear layer becomes the dominant mode (SrD = 1.5).

Flexible non-Brownian filament in intensified shear flow

The behavior of a three-dimensional, non-Brownian flexible filament in a low Reynolds number shear flow was investigated through theoretical and numerical analyses. In the phase plane with Reynolds number Re∈[0.03,8] and flow intensity Z∈[800,35 000], four primary motion modes of the filament were identified: rigid, C-buckling, U-turn, and S-turn. By employing the principle of symmetry, a theoretical model was developed to explain the S-turn mode, and we discovered that the critical flow strength for the transition from U-turn to S-turn was approximately Zc=4900. Our numerical simulations confirmed this transition value. In a system devoid of thermal fluctuations, it was observed that the mode transitions of microscale filament precisely corresponded to the abrupt scale rate changes in the non-Newtonian behavior of the macroscopic solution. Although the polymer stress under different modes has distinct underlying causes, they can all be predicted by the generalized Hooke's law.

Millimeter wave radiation to measure blood flow in healthy human subjects

Objective.Peripheral Artery Disease (PAD) is a progressive cardiovascular condition affecting 8-10 million adults in the United States. PAD elevates the risk of cardiovascular events, but up to 50% of people with PAD are asymptomatic and undiagnosed. In this study, we tested the ability of a device, REFLO (Rapid Electromagnetic FLOw), to identify low blood flow using electromagnetic radiation and dynamic thermography toward a non-invasive PAD diagnostic.Approach.During REFLO radio frequency (RF) irradiation, the rate of temperature increase is a function of the rate of energy absorption and blood flow to the irradiated tissue. For a given rate of RF energy absorption, a slow rate of temperature increase implies a large blood flow rate to the tissue. This is due to the cooling effect of the blood. Post-irradiation, a slow rate of temperature decrease is associated with a low rate of blood flow to the tissue. Here, we performed two cohorts of controlled flow experiments on human calves during baseline, occluded, and post-occluded conditions. Nonlinear regression was used to fit temperature data and obtain the rate constant, which was used as a metric for blood flow.Main results.In the pilot study, (N= 7) REFLO distinguished between baseline and post-occlusion during the irradiation phase, and between baseline and occlusion in the post-irradiation phase. In the reliability study, (N= 5 with 3 visits each), two-way ANOVA revealed that flow and subject significantly affected skin heating and cooling rates, while visit did not.Significance.Results suggest that MMW irradiation can be used to distinguish between blood flow rates in humans. Utilizing the rate of skin cooling rather than heating is more consistent for distinguishing flow. Future modifications and clinical testing will aim to improve REFLO's ability to distinguish between flow rates and evaluate its ability to accurately identify PAD.

Molecular Mechanisms Underlying Intracranial Aneurysm Rupture

Intracranial aneurysms, a major cause of subarachnoid hemorrhage(SAH), pose a significant social burden due to their poor patient outcomes. Recent studies, including those using animal models, have shed light on a new disease concept: intracranial aneurysms as a chronic inflammatory disease. This process is triggered by abnormal hemodynamic forces and mediated by immune cells like macrophages and neutrophils. The initiation of intracranial aneurysms is a two-step process. First, high wall shear stress and mechanical stretch work together to promote macrophage infiltration into the arterial walls. This infiltration is facilitated by endothelial cells and fibroblasts, which are activated to produce chemoattractants. Once the lesions enlarge, low wall shear stress and turbulent flow take over, maintaining macrophage infiltration. As the disease progresses towards rupture, infiltration creates hypoxic conditions that exacerbate the situation. These conditions, in turn, induce the formation of neovessels at the weakest point of the aneurysm and promote specific inflammatory microenvironments rich in neutrophils. The excessive tissue destruction caused by neutrophil-mediated inflammation ultimately leads to lesion rupture. Therefore, intracranial aneurysm rupture requires not only structural changes but also qualitative alterations within the chronic inflammatory environment. This suggests that factors mediating chronic inflammation could be potential targets for predicting or preventing aneurysm rupture.

Competitive flow of bilateral internal thoracic artery Y-graft: Insights from hemodynamics and transit time flow measurement parameters

Recent studies have demonstrated the superior efficacy of bilateral internal thoracic artery (BITA) grafts compared to other graft methods in treating coronary artery disease. Competitive flow (CF) is a primary factor contributing to graft failure in the long term. For the first time, the CF of the BITA-Y graft has undergone rigorous numerical analysis. Through the application of transit time flow measurement (TTFM) and hemodynamic parameters, this study provides a new perspective on graft performance. Simulation results indicate that average flow, TTFM, and hemodynamic parameters fall within the critical range for stenosis severities below 90%. Specifically, at 80% stenosis, the mean graft flow (MGF) and pulsatility index (PI) of the left internal thoracic artery (LITA) were 0.071 cc/s and 27, respectively, while those of the right internal thoracic artery (RITA) were 0.211 cc/s and 11. With increasing stenosis severity, TTFM parameters remained within the clinical permissible limit (MGF > 0.34 cc/s and PI < 5). At 95% stenosis severity, the MGF and PI for LITA were 0.526 cc/s and 1.2, respectively, while those for RITA were 0.790 cc/s and 0.9. The results indicate the presence of competitive flow within the BITA-Y graft for stenosis severities below 90% area reduction, suggesting a potential risk of graft failure in the long term. Additionally, the results indicated that when there are significant differences in stenosis severity between the two native arteries, the BITA-Y graft is not optimal due to CF, characterized by low MGF and high reverse flow.

Failed Thrombus Aspiration and Reduced Myocardial Perfusion in Patients With STEMI and Large Thrombus Burden

BackgroundThrombus aspiration (TA) is used to decrease large thrombus burden (LTB), but it can cause distal embolization. ObjectivesThe aim of this study was to investigate the impact of TA failure on defective myocardial perfusion in patients with ST-segment elevation myocardial infarction (STEMI) and LTB. MethodsIn total, 812 consecutive patients with STEMI and LTB (thrombus grade ≥3) were enrolled, who underwent manual TA during the primary percutaneous coronary intervention. TA failure was defined as the absence of thrombus retrieval, presence of prestenting thrombus residue, or distal embolization. The final TIMI flow grades and other myocardial perfusion parameters of the failed TA group were matched with those of the successful TA group. ResultsThe proportion of final TIMI flow grade 3 was lower (74.6% vs 82.2%; P = 0.011) in the failed TA group (n = 279 [34.4%]) than in the successful TA group (n = 533 [65.6%]). The failed TA group also had lower myocardial blush grade, lower ST-segment resolution, and a higher incidence of microvascular obstruction than the successful TA group. TA failure was independently associated with low final TIMI flow grade (risk ratio: 1.525; 95% CI: 1.048-2.218; P = 0.027). Old age, Killip class ≥III, vessel tortuosity, calcification, and a culprit vessel other than the left anterior descending coronary artery were associated with TA failure. ConclusionsTA failure is associated with reduced myocardial perfusion in patients with STEMI and LTB. Advanced age, hemodynamic instability, hostile coronary anatomy such as tortuosity or calcification, and non–left anterior descending coronary artery status might attenuate TA performance. (Gangwon PCI Prospective Registry [GWPCI]; NCT02038127)

Abstract 58: The 5-HT7 receptor contributes to increased hindquarter blood flow caused by skeletal muscle contraction

Exogenous serotonin (5-hydroxytryptamine, 5-HT) causes a reproducible decrease in blood pressure in normotensive and hypertensive rats. This is associated with dilation of arterioles in skeletal muscle. The 5-HT7 receptor KO rat strain allowed us to test the role of this receptor in both responses as well as the effects of endogenous 5-HT -- acting at 5-HT7 receptors -- on normal circulatory regulation. First, we hypothesized that the 5-HT7 receptor KO rat would have a higher hindquarter (HQ) vascular resistance (HQVR) than wildtype (WT) because of loss of this receptor. In rats anesthetized with isoflurane, instrumented with arterial catheters and flow probes on the terminal aorta, male KO rats had significantly higher resting HQVR [mm Hg/ml/min; KO (16.0±2.0) vs WT (10.8±0.6.0), p = 0.04] and lower HQ blood flow than normal Sprague-Dawley (SD) rats. No differences in resting HQVR or HQ flow were observed in female rats. Intravenous infusion of 5-HT (50 ug/kg/min) reduced systemic blood pressure and HQVR; these parameters were significantly attenuated (~56%) in male KO rats versus WT and SD animals. In females, falls in systemic blood pressure and HQVR were absent in both KO and WT rats. Second, as 5-HT has been implicated in the pathophysiology of heart failure (HF), a left anterior descending artery ligation model of HF was used to investigate the potential role of 5-HT7 regulation of HQ flow in HF-associated exercise intolerance. The ability of hindlimb muscle stimulation to increase blood flow using transdermal neuromuscular electrical stimulation was tested (NMES). M and F KO rats showed a reduced ability to increase HQ flow during muscle contraction vs WT (% over basal: M WT = 118±18 vs KO =14.6±7.1; F WT= 101±12 vs KO = 7.6±6) rats. This was observed in both intact and HF rats (in which flow changes were already impaired). Acute administration of the 5-HT7 receptor antagonist SB269970 abolished the ability of NMES to increase HQ flow in normal SD rats. Importantly, the microcirculatory capacity, visualized by Lectin-594, was not significantly different in the gastrocnemius muscle of WT (arbitrary fluorescence units/area: 946±40) vs KO (914±69). These data support that the 5-HT7 receptor, likely activated by endogenous 5-HT, is an important regulator of skeletal muscle vascular resistance. Thus, 5-HT may have a larger role in normal and pathophysiological regulation of the circulation than has previously been appreciated.

Machine learning and numerical simulation research on specific energy consumption for gradated coarse particle two-phase flow in inclined pipes

In deep-sea mining engineering, accurately predicting the energy required per unit length of pipeline to transport a unit mass of solids (dimensionless specific energy consumption, DSEC) is crucial for ensuring energy conservation and efficiency in the project. Based on our previous work, we utilized the machine learning (ML) and the computational fluid dynamics (CFD)–discrete element method (DEM) method to study the transport characteristics and flow field variations of gradated coarse particles in inclined pipes (gradated particles refer to solid particles mixed in specific size and quantity ratios). First, we collect 1185 sets of data from 13 experimental literature, and after analyzing and processing them, an ensemble model based on four other ML models is developed. Both for pure substance particles (PS) and mixed particles (MP), the prediction accuracy of this ensemble model is relatively higher (PSs are spherical particles with uniform size and density, and MPs are particles with different shapes, sizes, and densities). Then, the CFD-DEM process and the operating conditions include low flow velocity with low volume concentration (2 m/s and 2.5%), low flow velocity with high volume concentration (2 m/s and 7.5%), and high flow velocity with low volume concentration (4 m/s and 2.5%). Under conditions of low flow velocity and low concentrations, as well as high flow velocity and low concentrations, the DSEC hardly changes with the variation of the pipe inclination angle. Under low flow velocity and high-concentration conditions, as the pipe gradually becomes vertical, the value of DSEC gradually increases.

Performance improvement of multi-blade centrifugal fan based on impeller outlet flow control

The impeller of the multi-blade centrifugal fan significantly impacts the fan's internal flow field and aerodynamic performance. To improve the axial flow distribution along the impeller and suppress the blade passage backflow at the impeller outlet of multi-blade centrifugal fans, a method of variable chord length blade design is proposed. Simultaneously, optimization models are established with static pressure and efficiency as objectives. By altering the control points of the Bezier curve, the leading-edge profile of the impeller is optimized. The results indicate that using variable chord length blades can expand the operating range of the multi-blade centrifugal fan. The maximum flow rate improvement reaches 10.6%. Significant enhancements in the aerodynamic efficiency of the multi-blade centrifugal fan are observed at low flow rates, with a maximum improvement of 4.9%. The variable chord length blade design method enables adjustment of the axial flow distribution at the impeller outlet to better match the impeller's flow requirements. This leads to increased outlet flow on both the shroud and hub sides of the impeller, consequently reducing the backflow area on both sides and improving the blade passage backflow phenomenon. Moreover, variable chord length blades facilitate a more uniform circumferential flow distribution at the impeller outlet, reducing the diversion pressure of the volute tongue, mitigating flow separation within the blade passage, weakening the interaction between the impeller and the volute tongue, and lowering energy losses in the impeller–volute tongue regions. Consequently, this enhances the aerodynamic performance of multi-blade centrifugal fans.

Assessing the Potential of Environmental DNA for Monitoring Nature‐Like Bypasses: Erroneous Surveillance Owing to DNA Flow‐Through

ABSTRACTNature‐like bypasses refer to fishways that simulate natural streams. Apart from facilitating fish migrations, bypasses possess the capacity to enhance biodiversity in dammed rivers. Feasibility of environmental DNA (eDNA) as a tool for bypass assessments is unknown. This study investigated fish eDNA in 10 bypasses and their main channels. Initially, the relative DNA flow‐through was estimated in bypasses. Subsequently, the impact of environmental factors and bypasses on fish assemblages was evaluated, and the robustness of the eDNA and electrofishing methods was assessed pertaining to bypass monitoring. The eDNA flow‐through was computed using an equation to estimate the residual DNA at specified distances downstream of the source site. The relative DNA flow‐through was lowest in the longest bypass with low flow rate and highest in the shortest bypass with higher flow rate and was dependent on the DNA decay rate coefficient used. The redundancy analysis revealed significant effects of spatial location, agriculture, catchment area, and bypass length on the species composition. The within‐river analyses indicated significant and nonsignificant bypass effects on species composition and total species richness, respectively. Higher richness and DNA abundance of migratory and threatened species were observed in the bypasses than in the main channels. The eDNA samples displayed higher species richness compared to electrofishing. The species composition of the bypass eDNA samples was intermediate between that of the main channel eDNA and bypass electrofishing samples, which further corroborated performance of eDNA flow‐through in bypasses. Therefore, bypass eDNA samples represented variable mixtures of local and main channel assemblages, indicating relatively low robustness of eDNA for quantitative and spatially accurate bypass assessments. Nevertheless, these results demonstrate practical applicability of eDNA in surveying the presence of desired species and evidence of the benefits of bypasses in supporting biodiversity and species threatened by damming.

Formation of sodium-alginate droplets in an X-microdevice: Characterization of the pinching efficiency

Experiments and simulations are used jointly to gain a comprehensive insight into the pinching mechanism that generates alginate droplets in an X-microdevice operating in a hydrodynamic flow-focusing configuration. The X-microdevice is fed with an aqueous alginate solution into one inlet channel, while sunflower oil and Span80 are fed into the other two inlet channels. The use of the adaptive mesh refinement and volume of fluid method allows accurate tracking of the interface in numerical simulations. The sensitivities of numerical predictions to the contact angle and the surface tension are estimated through dedicated sets of simulations. Subsequently, numerical simulations and experiments are compared for different flow rates with a satisfactory agreement. We observe that the pinch-off mechanism may lead to the formation of several satellite drops in addition to the main droplet. A pinching performance indicator is suggested based on the amount of alginate that is encapsulated in the main droplet. The effect of operating conditions on the pinching efficiency, frequency, and droplet diameter is discussed to provide valuable information to optimize the droplets production. The pinching efficiency is closely related to the length and diameter of the liquid thread. At low flow rates, a short liquid thread is observed. This leads to the formation of few satellites and, thus, to high pinching efficiency but low droplet production. Increasing the dispersed-phase flow rate slightly reduces the efficiency but significantly increases the production.

A comprehensive method for error separation in hydrological modelling

AbstractEvaluation metrics play a pivotal role in the calibration process of hydrological models, serving as objective functions that directly influence the final values of model parameters and significantly affect users' perceptions of model performance. However, the choice and interpretation of evaluation metrics are subjective; therefore, this study provides a more objective framework for assessing model performance. This paper initially explored the applicability of various commonly used evaluation metrics, providing an overview of their limitations. Following this, we decomposed errors by analysing their physical significance and geometric representation in scatter plots, categorizing them into systematic and unsystematic errors. Through the decomposition and derivation of the Nash–Sutcliffe efficiency (NSE) formula, we established the quantitative relationship among various evaluation metrics. The soil and water assessment tool (SWAT) model was utilized to simulate monthly runoff in the Baishan basin (China), for the period 1994–2017, with NSE serving as the objective function for calibration. Our findings are consistent with previous studies, indicating that the model tends to slightly underestimate high flows while significantly overestimating low flows. Further analysis through error decomposition and the examination of relationships among various evaluation metrics revealed that unsystematic errors were dominant during the spring snowmelt runoff period, while systematic errors prevailed in the dry season. By evaluating the runoff series based on the magnitude of runoff or by categorizing it according to seasons and months, a more stringent assessment of the model's performance was achieved. These findings not only highlight the necessity for careful selection of evaluation metrics but also underscore the significance of our methodological advancements in enhancing hydrological model precision and reliability.

A note on Taylor–Couette style flows with two parallel inner cylinders

The flow in the gap between an inner and outer cylinder presents a variety of regimes, which are well explored. In the present work, we attempt to explore a more complex flow, with two parallel co-rotating inner cylinders. The rationale behind this arrangement was the following: in terms of base two-dimensional flow, close to each inner cylinder, the base flow resembles a laminar Couette flow, and close to the outer cylinder, the flow may again resemble a Couette flow, with the two inner cylinders being seen as a single source of momentum, while in the middle point between the inner cylinder, there is stagnation saddle point with two incoming and two out coming streamlines, creating a zone with a high shear where interaction of Taylor–Couette style rolls is expected. The experiment allowed to identify six regimes: for Re<50, presence of the base two-dimensional flow; for 50<Re<70, the first regime of steady rolls, equivalent to Taylor vortices; for 70<Re<110, vortices become unsteady; for 110<Re<170, in the stretched zone, the flow is unsteady while the same fluid parcels are then stabilized when leaving the stagnation point region and slowed down toward the outer wall; when Re>170, there is the onset of turbulent rolls, with loss of spatial periodicity and apparition of turbulence; and finally a second type of steady rolls occurs for a sudden start of cylinders and 50<Re<60.

Effect of Land Use Land Cover on the Hydrology of Rwizi River Catchment located in Southwestern Uganda

Changes in land use and land cover usually affect the hydrological processes of river flows, sediment transport, and water quality on a global scale. Hence, the objective of this paper was to investigate the effect of Land Use Land Cover (LULCC) on the Hydrology of Rwizi River Catchment located in South-western Uganda using appropriate standard techniques and procedures including Soil and Water Assessment Tool (SWAT). Model calibration and validation demonstrated good agreement (R² = 0.76-0.86, NSE = 0.75-0.78). LULC analysis revealed significant increases in built-up areas and forestland, with declines in grazing land and wetlands. These changes were driven by socio-economic factors and hydro-climatic influences. The study found strong correlations between LULC types and sediment yield, highlighting the implications for water quality and erosion control. The results show that urban growth raises surface runoff and peak flows as a result of a rise in impervious surfaces, whereas agricultural intensification raises water demand and lowers base flow, especially during dry spells. Deforestation has led to increased sedimentation rates, degrading water quality. These findings underscore the significant anthropogenic and climatic impacts on LULCC dynamics and hydrological processes in the catchment. The study emphasizes the critical need for integrated watershed management strategies to mitigate these impacts and ensure sustainable water management practices. By advancing understanding in hydrological sciences, this research informs policy and management decisions for sustainable development in tropical river basins globally.

Hepatocyte aquaporin 8-mediated water transport facilitates bile dilution and prevents gallstone formation in mice

Although water channel aquaporin-8 (AQP8) has been implicated in hepatic bile formation and liver diseases associated with abnormal bile flow in human and animal studies, direct evidence of its involvement in bile secretion is still lacking. This study aimed to determine the role of AQP8 in bile secretion and gallstone formation. We generated various transgenic knock-in and knockout mouse models and assessed liver AQP8 expression by immunostaining and immunoblotting, hepatic bile secretion by cannulation of the common bile duct, cholesterol gallstone formation by feeding a high-fat lithogenic diet, and identified regulatory small molecules by screening the organic fractions of cholagogic Chinese herbs and biochemical characterization. We identified a novel expression pattern of AQP8 protein in the canalicular membrane of approximately 50% of the liver lobules. AQP8-deficient mice exhibited impaired hepatic bile formation, characterized by the secretion of concentrated bile with a lower flow rate and higher levels of bile lipids than that of wild-type littermates. AQP8-/- mice showed accelerated gallstone formation, which was rescued by AAV-mediated hepatic expression of AQP8 or AQP1. Moreover, we identified a small molecule, scutellarin, that upregulates hepatocyte AQP8 expression in vitro and in vivo. In AQP8+/+ mice, scutellarin significantly increased bile flow, decreased bile lipid concentrations, and prevented gallstone formation compared to AQP8-/- mice. Molecular studies revealed that scutellarin promoted the ubiquitination and degradation of HIF-1α, a transcriptional negative regulator of AQP8, by disrupting its interactions with HSP90. AQP8 plays a crucial role in facilitating water transport and bile dilution during hepatic bile formation, thereby mitigating gallstone formation in mice. Small-molecule intervention validated hepatocyte AQP8 as a promising drug target for gallstone therapy. The incidence of gallstone disease is high, and current drug treatments for gallstones are very limited, necessitating the identification of novel drug targets for developing new drugs with universal applicability. To our knowledge, this is the first study to provide direct evidence that hepatic water channel AQP8 plays a key role in bile dilution and gallstone formation. Modulation of hepatic water transport may provide a universal therapeutic strategy for all types of gallstone diseases.

Investigation of mechanisms on leading edge vortex generation and suppression in vaned diffuser of a centrifugal compressor

This study numerically investigates the mechanisms for generating and suppressing the leading edge vortex (LEV) in a vaned diffuser of a centrifugal compressor, aiming to enhance the compressor's stable operating range. Detailed analyses focus on the mechanisms of the rotating stall and the initiation process of the LEV. Notably, the end wall contouring method is applied to vaned diffuser to suppress the LEV and improve diffuser stability. The suppression mechanisms of the LEV are examined to deepen the understanding of stability enhancement mechanisms. Results demonstrate that, under stall conditions, the vaned diffuser experiences two-cell rotating stalls moving opposite to the impeller rotation direction, each rotating at approximately 12% of impeller rotation speed. The formation of diffuser stall is attributed to a longitudinal vortex developing from the LEV and causing the passage blockage. The increasing spanwise distortion of leading edge (LE) incidence angles and circumferential distortion of static pressures at the diffuser inlet promote the evolution of the longitudinal vortex from LEV. The end wall contouring of vaned diffuser effectively enhances the compressor's stable operating range by 15.10% and 8.90% toward lower flow rate conditions for machine Mach numbers 1.3 and 1.2, respectively. At near-stall points, the end wall contoured diffuser reduces spanwise distortion of LE incidence angles and circumferential distortion of static pressures at the diffuser inlet, mitigates the LE flow separation and corner separation, suppresses the generation and development of the LEV, delays the onset of rotating stall in vaned diffuser, and thereby improves the stable operating range of centrifugal compressor stage.

Thermal performances of Gyroid-fin heat sink for power chips

As a kind of triply periodic minimal surface (TPMS), the Gyroid-TPMS is utilized for fluid cooling system with good hydraulic and thermal performances. In this study, a special fin structure based on Gyroid-TPMS, referred to as the Gyroid-fin, is designed to replace the plate-fin of the conventional heat sink (HS) for cooling the integrated power chips. The multi-physical simulations are modelled for numerical analysis, and the specific test system is designed to compare the thermal performances of Gyroid-fin HS and plate-fin HS. The numerical simulation indicates that the Gyroid-fin can induce eccentric helical flows and enhance the convective heat transfer significantly. The temperature distributions range from 35.69 to 46 °C on the surface of the plate-fin to 38.5−43.2 °C on that of Gyroid-fin. The temperature difference is reduced from 10.31 °C of plate-fin HS down to less than 4.7 °C of Gyroid-fin HS. Besides, the Gyroid-fin provides an area of 850.3 cm2 for heat dissipation which is almost 3 times of the plate-fin, and the thermal resistance of Gyroid-fin HS is about 15 % less than that of plate-fin HS. The Gyroid-fin HS has a better temperature uniformity in all directions than plate-fin HS. With the flow rate increasing, both the maximum surface temperature and the surface temperature difference of Gyroid-fin HS and plate-fin HS will decrease, and the pressure drops of Gyroid-fin HS and plate-fin HS will increase. For the balance of pressure drop and thermal resistance, the operating point can be set at the flow rate of 6 L/min for both Gyroid-fin HS and plate-fin HS. Moreover, for the same value of thermal resistance, the Gyroid-fin HS requires a lower flow rate than plate-fin HS, and it also means less pump power cost for the liquid cooling system. This work helps to solve the constraint of heat sinks that heat dissipation capacity of electronic devices in high power density applications.