y. wei

The impeller of a double-suction centrifugal fan may be subject to axial offset due to assembly or operational failure. The internal flow is asymmetric about the central disc and deteriorates the fan’s performance. In this work, the characteristics of flow were numerically investigated for the baseline model (Model-BM) and the axially offset impeller model (Model-Offset). The objective and motivation are to provide a detailed assessment and quantification of the effect of offset impeller on the fan’s performance and transient physics of the asymmetric flow. The numerical data reveal that the offset impeller generates highly asymmetric flow. The difference in mean flow rate at the two inlets of Model-Offset is 25.02m³/h, accounting for 6.8% of the total flow rate. The static pressure rise reduces by 2.40% for Model-Offset, and the static pressure efficiency is reduced by 2.11%. The leakage flow gets pronounced in the enlarged clearance with the inward and outward motion of air, while the narrowed clearance blocks it. The reversed flow is significant in the NA-side blade passages, especially close to the impeller end ring, where the leakage flow and the volute tongue confinement dominate. The reversed flow persists throughout the impeller, is still evident as the air first enters the volute, and is significant on the NA-side of the fan outlet.

This study aims to evaluate the therapeutic efficacy of hyperbaric oxygen (HBO) as adjuvant therapy for patients with cerebral small vessel disease (CSVD) related dizziness and to assess the impact of this treatment on diagnostic indicators from both transcranial Doppler (TCD) and computed tomography (CT).

A prospective randomized controlled study was conducted from January 2019 to December 2023, including 200 patients with CSVD related dizziness. They were randomly assigned to either the HBO group or the control group. The control group received betahistine mesylate tablets, while the HBO group received HBO in addition to the control group treatment. Various parameters including Dizziness Handicap Inventory (DHI) scores, cerebral artery blood flow velocity (Vm), resistance index (RI), pulsatility index (PI), cystatin (Cys), homocysteine (HCY), hypersensitive c-reactive protein (hs-CRP) levels, and CT imaging for grading cerebral white matter degeneration were assessed before and after treatment.

After treatment, DHI scores in both groups decreased significantly, with the HBO group showing greater improvement compared to the control group. Hemodynamic parameters (Vm, RI, PI) improved significantly in both groups, with greater improvements seen in the HBO group. White matter lesion grading and levels of Cys, HCY, and hs-CRP were significantly lower in the HBO group post-treatment compared to the control group.

HBO as adjuvant therapy demonstrates significant therapeutic benefits for CSVD related dizziness. It effectively alleviates symptoms, improves hemodynamic parameters, enhances white matter lesion assessment outcomes, and promotes neurological function recovery.

The flow field of a low specific speed centrifugal pump is investigated in the present work based on numerical simulation to establish the effect of circumferential positions of balance holes on cavitation behaviour and cavitation erosion of the centrifugal pump. The distribution of the pressure around balance holes is studied, the initiation and development of cavitation at different balance hole schemes are compared, and the distribution of cavitation erosion for the original pump and the ideal scheme is also predicted. The results show that when the NPSHa is high, there is low pressure zone in balance hole, which leads to cavitation in the pump. The cavitation performance of pump is improved by gradually moving balance holes away from blade suction surface, as this reduces low pressure zones around the balance hole and incipient cavitation. Under critical cavitation conditions, the cavitation shows a tendency to collapse as the angle (φ) of circumferential position of balance holes decreases, and the proportion of the higher vapor volume fraction in cavitation core zones also decreases. The cavitation erosion zones on blade surfaces are predicted by using the Erosive Power Method (EPM). The erosion impact of the original pump is more pronounced in the comparative results.

In this study, numerical simulations of centrifugal compressors are carried out using ANSYS-CFX software. The focus lies in investigating the impact of the inlet tip-clearance (ITC) on the characteristics of the internal complex flow and the aerodynamic performance of centrifugal compressors. Specifically, the paper mainly emphasizes the influence of ITC on the polytropic efficiency and total pressure ratio of a centrifugal compressor, as well as the variations in velocity and pressure at the blade tip, the spatiotemporal evolution of the tip-leakage vortex (TLV), and fluctuations in pressure and velocity downstream of the passage near the blade surface. Analysis of tip-leakage flow (TLF) and TLV motion patterns at rated operating conditions reveals the spatiotemporal evolution within one revolution. Results from Fast Fourier Transform (FFT) spectrum analysis indicate that the TLV motion pattern may be affected by the ITC size. The fluid flow resistance and backflow in the blade tip region are gradually reduced, the flow field stability is effectively enhanced, and the reflux vortex at the volute outlet is eliminated, thereby the working range of the centrifugal compressor is effectively extended by decreasing the ITC. The aerodynamic performance of the centrifugal compressor is effectively increased in the range of the medium and high flow rates by decreasing ITC. Additionally, it is observed that pressure, velocity, and load in the blade tip region do not exhibit a linear relationship with ITC, resulting in a nonlinear change in aerodynamic performance concerning ITC. Pressure and velocity spectrum analysis suggests that the effect of TLF is stronger at the top of the flow passage compared to the middle. Moreover, with the increase of ITC, the effect of TLF decreases at the middle and top of the pressure side (PS) while increasing at the bottom of PS and the suction side (SS).

To explore the diffusion characteristics of the hippocampus injury (HI) in children during the complex acute febrile seizure (CAFS) through multiple b value (1000-2000 s/mm2) of diffusion-weighted imaging (DWI).

This prospective observational study enrolled children with HI during CAFS, and nasopharyngeal and sinus disease (NSD). The multiple b value from DWI of the hippocampus were scanned.

A total of 41 children were included, with 21 of them had HI during CAFS, while the other 20 children were NSD. There was significant difference in apparent diffusion coefficient (ADC) values of the left and right hippocampus between children with HI during CAFS and NSD (r < 0.05). The corresponding ADC graphs were relatively clear at b = 1000 s/mm2 and 1200 s/mm2.

Hippocampal DWI scans at b = 1000 s/mm2 and 1200 s/mm2 might be recommended clinical b value point for diffusion characterization of HI.

This study aims to investigate the pituitary MRI morphological parameters and alterations in 25-hydroxyvitamin D3 [25-(OH) D3], free thyroxine (FT4), and sex hormone levels in female children with central precocious puberty (CPP) and assess their clinical relevance.

From February 2022 to February 2023, 46 female children with CPP and 46 healthy controls were included. Pituitary MRI morphological parameters, 25-(OH) D3, FT4, and sex hormone levels were compared. Diagnostic values of each parameter were assessed.

Patients with CPP exhibited higher pituitary height and altered morphology compared to controls, with a higher proportion in grades 4 and 5 (P < 0.05). Coronal and sagittal dimensions were increased, while coronal width was decreased in the study group (P < 0.05). Levels of E2, LH, FSH, and FT4 were elevated, while 25-(OH) D3 was reduced in CPP patients (P < 0.05). Pituitary height, coronal height, and hormone levels showed high diagnostic value for CPP, with AUC values ranging from 0.811 to 0.886. Combined diagnosis using these indicators improved AUC to 0.909.

In female children with CPP, significant differences exist in pituitary MRI morphological parameters, sex hormones, 25-(OH) D3 and FT4 levels, providing valuable diagnostic insights for CPP.

With the increasing complexity of the industrial production process, the transmission medium of the hydraulic turbine is no longer satisfied, and the gas-liquid two-phase mixed medium has to be considered. The presence of gas in the transmission medium will alters the internal flow structure of the hydraulic turbine and affect its operational stability. Therefore, for the purpose of clarifying the influence of inlet gas content on the internal flow of PAT, the unsteady flow of the PAT is simulated in this paper using numerical simulation. Based on the numerical simulation results, the influence of inlet gas content on the internal flow characteristics, characteristics of pressure fluctuation in impeller and volute, and vortex evolution of flow field are analyzed. The accumulation of gas phase leads to the emergence of vortices, and regions with low pressure values appear at the vortex generation. The major factor of the periodic variation of pressure fluctuation between volute and cut-water is the dynamic and static interference of impeller. The increase of gas content causes more flow disorder in the cut-water region and the volute contraction section. Since the gas in the flow channel is predominantly on the suction side of blades, the flow field on the suction side is more complex than that on the pressure side, and the amplitude of pressure fluctuation increases appropriately. The vortex structure is mainly distributed on balance hole, inlet area of impeller and suction side of blade. As the blade rotates, there are new shedding and growth of vortices, and finally attached to the volute wall. Increasing gas content enhances the influence of blade rotation on the vortex evolution characteristics in the volute and impeller.

Temporal flow characteristics of a 3D centrifugal impeller suction system were numerically studied in vacuum conditions. The blockage of the high-speed rotating impeller appeared, which greatly dropped the suction of the layer suction device. The temporal flow characteristics of the 3D centrifugal impeller suction system were worthy of attention in vacuum conditions. Separation vortices were generated near the blade suction surface. The blocking mechanism of the passage was further analyzed at different extremely low flow rates through the time-space evolution of the streamline. The Q-criteria was introduced to analyze the vortex evolution within the fluid domain of the impeller. Vortex evolution law was captured—the vortices always generated near the suction surface of the blade and moved to the pressure surface of the adjacent blade in the same passage and disappeared. The uniform distribution of three stall cells was captured through the diagram of turbulent kinetic energy. The flow rate increased, and the vortex evolution period gradually decreased. The comparison of pressure fluctuations in different conditions further demonstrated the flow mechanism at the vacuum flow rate was different from that at low flow rates. The sharp increase of pressure fluctuations near the blade pressure surface was consistent with the phenomenon near the suction surface. The pressure fluctuation at extremely low flow was mainly composed of scattered fluctuations caused by fluid separation. The steady and unsteady characteristics described the internal flow characteristics of this suction system at vacuum-flow rates. Theresults provide a profound design for vacuum cleaners.

Multi-wing centrifugal fans are wildly used in the central air-conditioning. The influence of dimensionless clearance of the volute-tongue on aerodynamic performance and noise is studied by numerical simulation and experimental tests in this paper. The complicated internal flow related to unsteady flow in a centrifugal fan with multiple wings is investigated by numerical simulation. Besides, the influence of circumstance on the noise is analyzed. It is testified that the internal flow of centrifugal fans is ameliorated using appropriate volute tongue clearance. Reduced eddy current decreased the local-flow loss near the volute tongue and exit. The experimental results show that the static pressure of model △t/R2=0.12 rose to 7.5 Pa and the aerodynamics noise value reduced to 4 dB compared with that of a reference model. Meanwhile, an obvious reduction of aerodynamics noise by 3.74 dB is obtained for model △t/R2=0.12 installed in the air conditioning unit. The static pressure of centrifugal fan is significantly improved for the model with a cochlear tongue clearance ratio of △t/R2=0.12. It is further demonstrated that the proper dimensionless distance effectively suppresses the aerodynamic noise of forward multi-wing fans.

The steady and unsteady characteristics of the internal flow in a high-speed centrifugal blower are studied by computational fluid dynamics (CFD) approach at low flow rates. It is demonstrated that as the flow rate decreases, the separation of flow in the blade passage becomes serious, and separated vortexes always occur on the suction surface of the blade which gradually expand and block the passage. The stall cells move downstream and generate vortices at the exit of the passage, resulting serious loss to the performance of the blower. Q-criteria is used to analyze the flow field and explore the evolution of the vortex structure in the impeller. It is further found that strong pressure fluctuations are caused by the rotating stall in the impeller. At the stall conditions, the instability characteristics are particularly obvious. At flow rates of 0.65Qn and 0.47Qn, the pressure fluctuation in the blade passage is dominated by the blade passing frequency, while a lower frequency dominates at 0.26Qn. Moreover, the flow on the suction surface of impeller blades fluctuates substantially. The characteristics of steady flow and unsteady flow can clearly explain the internal flow of centrifugal blower for vacuum cleaners at low-flow conditions, which can be widely used in various engineering designs of vacuum cleaners.

Let R be a finite local ring of characteristic a power of 2 with the residue field k. In this paper, we define a generalized orthogonal graph on a module of rank at least 2 over R. Then we study its graph properties via the same graph over k. The number of vertices and the valency of each vertex in this graph over R are computed. We also prove that this graph is arc transitive and find its diameter. Moreover, the first subconstituent of this orthogonal graph is considered. We show that it is a generalized strongly regular graph.

Centrifugal pumps often deviate from its design condi-tion during its operation and work at low mass flow conditions. Under such circumstances, unstable flow phenomena may be generated, affecting the efficient and stable operation of pumps. In this paper, a self-circulating casing treatment in U-tube shape is employed on a centrifugal pump to study its effects on the pump’s performance by computational and experi-mental studies. CFD results show that as the flow rate decreases, the back-flow in the inlet pipe of the studied pump without casing treatment increases in intensity and spreads over an growing distance, interfering with the main flow. CFD results also reveal that the casing treatment has a sucking function to the back-flow due to the blade loading of the pump, and when the inlet bleed of the U-tube is placed above (in front of) the leading edge of the blades, the sucking is the strongest, and the control of the back-flow and the improvement to the head coefficient under low mass flow conditions is the best, as the vortex blockage caused by the sucked back-flow in the U-tube is the smallest; when the bleed is under (after) the leading edge of the blades, the effect of the casing treatment is the second best; and when the bleed is across the leading edge of the blades, the blockage in the U-tube is most severe, and the sucking function is the weakest, so there is little improvement to the back-flow and head coefficient. Finally, the relia-bility of this study was demonstrated employing an open pump experimental system with the original pump and the same pump with the casing treatment whose bleed is located above the leading edge of the impeller.

Numerical simulation was used to investigate the effect of an inclined volute tongue on the complex flow characteristics and the aerodynamic performance of multi-blade centrifugal fans. We focused on the effects of the clearance, the inclination angle and the volute tongue’s on controlling the centrifugal fan’s internal flow characteristics and aerodynamic performance. The results showed that the volute tongue’s reasonable clearance ratio and the inclined volute tongue design were beneficial to improving the flow pattern around the volute tongue and volute outlet of the centrifugal fan, as well as reducing the local flow loss. It is of great significance to increase the centrifugal fan’s static pressure and related efficiency by increasing the radius and inclination angle of the volute tongue. Due to the reduced of vortex, the local flow loss was reduced. Numerical results indicated that model C’s static pressure rose to 12.5Pa, and the related static-pressure efficiency of to 3.8% compared with the reference geometry due to the reduced of flow loss.

Squirrel cage fans are commonly used in HVAC (heating, ventilation, and air conditioning) systems. The single arc blade model is commonly used in this type of fans since it can be shaped simply only by two parameters of inlet and outlet angle of blade. However, the efficiency of the fans is much lower than that we expected. In this paper, the single arc blade is replaced by double-arc blade in order to optimize the blade model and to improve the static pressure efficiency and total pressure efficiency of the fan. Numerical results show that the design with double arc blade is able to improve the internal flow, and to enhance the aerodynamic performance of squirrel cage fans.