Effect of counter-rotating fan’s speed matching on stall inception and characteristics of tip clearance flow

In order to study the effect of speed matching on behavior of tip clearance flow and its possible link to stall inception in counter-rotating fan, the Reynolds-averaged Navier-Stokes equations are solved by the numerical method in conjunction with a SST turbulence model, the effect of speed matching on performance and stability margin are investigated, so are the difference of the tip clearance flow in different speed matching. Furthermore, the effect of speed matching on behavior of tip clearance flow and its possible link to stall inception are investigated. Research results show that: when the rotational speed of Rotor 2 is less than that of Rotor 1, with the decrease of rotational speed of Rotor 2 has no notable effect on tip clearance flow fields of the two rotors, therefore offset of stalling boundary is minor and strong blockage effect is observed in Rotor 1; when the rotational speed of Rotor 1 is less than that of Rotor 2, decrease of rotational speed of Rotor 1 show significant effect on the two rotors, which leads to major offset of stalling boundary, tip leakage flow performance of Rotor 1 improved, while that of Rotor 2 weakened and large blockage area occurs. By comparison, speed variation of Rotor 1 has more effect on stalling boundary of counter-rotating fan

Influence of axial spacing on stall development of FBCDZ-10-No20 mode contra-rotating fan

The rotating fan is prone to instability such as stall and even surge when operating at low flow rates. In order to study the influence of axial spacings on the stall inception and its development and propagation process of a contra-rotating fan , a Shear Stress Transport(SST) k-ω turbulence model was used to numerically simulate the unsteady flow in the whole passage of a FBCDZ-10-No20 contra-rotating fan. The stall evolution of fan under two axial spacings are investigated. The results show that the axial spacing has significant influence on the inception and development of fan stall.In the stall inception stage, when the axial spacing between the two-stage impellers is 170 mm, the stall inception first occurs within the rear impeller, which locates in the trailing edge area on the suction surface of the blade root. Then stall inception develops from the blade root to the tip area along the radial direction, and accumulates towards a blade passage along the circumferential direction and falls off on the way to form a blocking area, which eventually leads to stall. When the axial spacing is 70 mm, the stall inception successively occurs the tip area of the two-stage impellers. Then stall inception keeps increasing, which eventually leads to stall. During the full stall stage, the axial spacing has a significant effect on the propagation of the stall vortex in the circumferential, axial and radial directions. When the axial spacing is 170 mm, the type of stall vortex shows the single vortex full-blade high stall. The propagation range of the stall vortex in the axial direction is limited to the region of rear impeller, and rotates at 33.3% of the rear impeller speed in the circumferential direction; When the axial spacing is 70 mm, the type of stall vortex shows the multi-vortex partial blade high stall. The stall vortex are successively generated in the tip area of the two-stage impellers, propagating upward and downstream in the axial direction, and are dispersed in the area above 70% of the blade height of each blade channel in the radial direction. Due to the change of the axial distance between the two-stage impellers, the type of stall inception of the fan is changed from “partial surge type” to “Spike-type”

Pressure-induced electronic topological transition and superconductivity in topological insulator Bi2Te2.1Se0.9

Great attention has been drawn to topological superconductivity due to its potential application in topological quantum computing. Meanwhile, pressure is regarded as a powerful tool for tuning electronic structure and even inducing superconductivity in topological insulators. As a well-defined topological insulator, Bi2Te2.1Se0.9 can be a suitable candidate to search for topological superconductivity and study its intrinsic property. In this paper, we report the occurrence of superconductivity and electronic topological transition (ETT) in Bi2Te2.1Se0.9 with applied pressure. Superconductivity can be observed at 2.4 GPa with the Tconset around 6.6 K in Bi2Te2.1Se0.9 by resistance measurement, and the corresponding structure resolved by X-ray diffraction and Raman experiments doesn't change below the pressure of 8.4 GPa. Moreover, at about 3.0 GPa, the abnormal changes of c/a as well as the full width at half maximum (FWHM) of mode indicate the occurrence of electronic topological transition (ETT). These results indicate that superconductivity can be realized in doped topological insulator Bi2Te2.1Se0.9 in the low-pressure rhombohedral phase

Effect of axial spacing on rotating stall performance of FBCDZ-10-No20 contra-rotating fan

Mining contra-rotating fan are prone to rotational stall when it operates at low flow rates, which seriously affects the operational stability. The unsteady flow in the full flow passage of a FBCDZ-10-No20 contra-rotating fan at five axial spacings was numerically simulated by using the SST k-ω turbulence model. The effect of axial spacing on the stall process of contra-rotating fan was studied, and the mechanism of stall inception and development at different axial spacings was revealed. The results shown that the axial spacing had a significant influence on the initial position, type and development of stall inception. For the axial spacings of 70 mm and 100 mm, the stall inception first occurred at the tip of the front stage, and subsequently appeared at the tip of the rear stage due to the rotor-rotor interaction between the two stages. However, compared with the axial spacing of 70 mm, the rotor-rotor interaction at the axial spacing of 100 mm was relatively weak, making it take longer for a stall inception to occur in the rear stage. For all three axial spacings of 140 mm, 170 mm and 225 mm, the stall inception occurred first in the root of rear stage. The difference was that for the axial spacing of 140 mm, the leakage flow at the tip of the front stage cannot completely flow out of the channel with the main flow, and a localized tip blockage area was formed. However, for both spacings of 170 mm and 225 mm, there was almost no blockage area at the tip of the front stage, and eventually only mature stall vortices formed in the rear stage. With the increase of the axial spacing, the blockage area formed by both the leading edge overflow and the trailing edge reverse flow those originated from the leakage flow at the tip of the front stage gradually reduced. In contrast, the blockage area formed by the radial vortex on the suction surface near the root of the rear stage gradually increased. When the leakage flow at the tip of the front stage failed to form blockage area, the stall type changed from the “spike type” induced by the tip leakage flow at the front stage to the “localized surge type” induced by the radial vortex flow at the root of the rear stage

Metagenomic Next-Generation Sequencing in the Diagnosis of HHV-1 Reactivation in a Critically Ill COVID-19 Patient: A Case Report

Background: Secondary infections pose tremendous challenges in Coronavirus disease 2019 (COVID-19) treatment and are associated with higher mortality rates. Clinicians face of the challenge of diagnosing viral infections because of low sensitivity of available laboratory tests. Case Presentation: A 66-year-old woman initially manifested fever and shortness of breath. She was diagnosed as critically ill with COVID-19 using quantitative reverse transcription PCR (RT-qPCR) and treated with antiviral therapy, ventilator and extracorporeal membrane oxygenation (ECMO). However, after the condition was relatively stabled for a few days, the patient deteriorated with fever, frequent cough, increased airway secretions, and increased exudative lesions in the lower right lung on chest X-rays, showing the possibility of a newly acquired infection, though sputum bacterial and fungal cultures and smears showed negative results. Using metagenomic next-generation sequencing (mNGS), we identified a reactivation of latent human herpes virus type 1 (HHV-1) in the respiratory tract, blood and gastrointestinal tract, resulting in a worsened clinical course in a critically ill COVID-19 patient on ECMO. Anti-HHV-1 therapy guided by these sequencing results effectively decreased HHV-1 levels, and improved the patient\u27s clinical condition. After 49 days on ECMO and 67 days on the ventilator, the 66-year-old patient recovered and was discharged. Conclusions: This case report demonstrates the potential value of mNGS for evidence-based treatment, and suggests that potential reactivation of latent viruses should be considered in critically ill COVID-19 patients

Mechanism of crocin I on ANIT-induced intrahepatic cholestasis by combined metabolomics and transcriptomics

Background: Intrahepatic cholestasis (IC) is a disorder of bile production, secretion, and excretion with various causes. Crocin I (CR) is effective in the treatment of IC, but its underlying mechanisms need to be further explored. We aimed to reveal the therapeutic mechanism of crocin I for IC by combining an integrated strategy of metabolomics and transcriptomics.Methods: The hepatoprotective effect of CR against cholestasis liver injury induced by α-naphthylisothiocyanate (ANIT) was evaluated in rats. The serum biochemical indices, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bile acid (TBA), total bilirubin (TBIL), direct bilirubin (DBIL), tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), and interleukin 1β (IL-1β), as well as the liver oxidative stress indexes and the pathological characteristics of the liver were analyzed. In addition, we also performed a serum metabolomics study using UPLC-Q Exactive HF-X technology to investigate the effect of CR on the serum of rats with ANIT-induced IC and screened potential biomarkers. The enrichment analysis of differential expressed genes (DEGs) was performed by transcriptomics. Finally, the regulatory targets of CR on potential biomarkers were obtained by combined analysis, and the relevant key targets were verified by western blotting.Results: CR improved serum and liver homogenate indexes and alleviated liver histological injury. Compared with ANIT group, the CR group had 76 differential metabolites, and 10 metabolic pathways were enriched. There were 473 DEGs significantly changed after CR treatment, most of which were enriched in the retinol metabolism, calcium signaling pathway, PPAR signaling pathway, circadian rhythm, chemokine signaling pathway, arachidonic acid metabolism, bile secretion, primary bile acid biosynthesis, and other pathways. By constructing the “compound-reaction-enzyme-gene” interaction network, three potential key-target regulation biomarkers were obtained, including 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), ATP-binding cassette transporter G5 (ABCG5), and sulfotransferase2A1(SULT2A1), which were further verified by western blotting. Compared with the ANIT group, the CR group significantly increased the expression of ABCG5 and SULT2A1, and the expression of HMGCR significantly decreased.Conclusion: Combined metabolomic and transcriptomic analyses show that CR has a therapeutic effect on IC through regulation of the biosynthesis of bile acids and bilirubin in the bile secretion pathway and regulation of the expression of HMGCR, ABCG5, and SULT2A1

Rolling Bearing Fault Feature Extraction Based on Adaptive Tunable Q-Factor Wavelet Transform and Spectral Kurtosis

The fault feature of the rolling bearing is difficult to extract when weak fault occurs and interference exists. The tunable Q-factor wavelet transform (TQWT) can effectively extract the weak fault characteristic of the rolling bearing, but the manual selection of the Q-factor affects the decomposition result and only using TQWT presents interference. Aiming at the above problems, an adaptive tunable Q-factor wavelet transform (ATQWT) and spectral kurtosis (SK) method is proposed in this paper. Firstly, the method applies particle swarm optimization (PSO) to seek the optimized Q-factor for avoiding manual selection, which uses the kurtosis value of the transient impact component as the particle fitness function. The rolling bearing fault signal is decomposed into continuous oscillation component and transient impact component containing fault feature by the optimized Q-factor. Then, due to the presence of interference in the decomposition result of ATQWT, the SK analysis of the transient impact component is used to determine the frequency band of periodic impact component characterizing fault feature by fast kurtogram. Finally, the band-pass filter established through the above frequency band is employed to filter the interference in the transient impact component. Simulation and experimental results indicate that the ATQWT can highlight the periodic impact component characterizing rolling bearing fault feature, and the SK can filter interference in the transient impact component, which improves feature extraction effect and has great significance to enhance fault diagnosis accuracy of the rolling bearing. Compared with EEMD-TQWT and TQWT-SK, the fault feature extracted by the proposed method is prominent and effective

Evaluation and Optimization of Human Resource Supply in Packaging Design Project

In order to solve the problem of selection of human resource provider for the demander in package design project, firstly, the evaluation index system of provide side is established, and the entropy weight method is used to calculate the objective weight of the evaluation index; secondly, the subjective weight is solved by the five scale valuation method, and the comprehensive weight with subjective and objective significance is obtained; then, with the help of the ideal point method, the provide side is evaluated, which can provide a reference for the choice of the demander; finally, an example is given to verify the effectiveness and practicability of the method