b. liu

Investigating the aerodynamic characteristics of an ultrahigh-speed elevator between the car and counterweight during the staggering process is crucial for the development of drag reduction and noise abatement technologies. In this study, an actual operating ultrahigh-speed elevator is selected as the research object, and an unsteady flow numerical simulation model for three-dimensional, has been constructed using the method of dynamic mesh. The aerodynamic behaviours of the elevator at various interleaving operating speeds are analysed. The impacts of the counterweight on the flow velocity, pressure, lateral force, aerodynamic drag, and sound pressure level (SPL) of the car are investigated. The results show that a streamlined counterweight can stabilize airflow between the windward areas of the car and counterweight, reducing turbulence, the lateral lift, surface pressure gradients, and SPL, while also lessening the effects of reduced car-counterweight spacing. At a speed of 6 m/s, a bi-arc counterweight with a radius of 250 mm demonstrates superior performance in reducing lateral lift force and aerodynamic drag compared to a traditional rectangular counterweight, with reductions of 12.2% in lateral lift force and 9.3% in aerodynamic drag. Additionally, the simulation and test errors are within 10%, confirming the accuracy of the numerical calculation method.

The dynamic behavior of a glycerol aqueous droplet impacting on a thin water film was experimentally investigated with a high-speed camera. Numerous splash behaviors with different impact velocities (2.0-4.5 m/s), liquid film thicknesses (140-700 μm) and glycerol solution concentrations (30 wt%, 60 wt% and 80 wt%) were statistically analyzed, and finally classified based on morphological features. The laser-induced fluorescence images illustrate that the prompt splash secondary droplets mainly originated from the thin water film, while the components of delayed splash secondary droplets came from both the glycerol aqueous droplet and the thin water film. The results show that increasing viscosity suppresses prompt splash,  inhibits the crown expansion and accelerates the crown collapse, while decreasing droplet viscosity facilitates prompt splash. The decreasing film thickness promotes passive delayed splash and increases the crown height. A splash morphology regime map was presented based on Weber number, dimensionless film thickness and solution mass concentration, delineating a threshold between prompt splash and coalescence. It also found that the occurrence of crown lamella rupture is sensitive to the film thickness and We.

We perform a thorough numerical analysis of the impact of inflow conditions on the aerodynamic performance of a tandem cascade. In particular, we investigate the effects of the incidence angle and the inlet boundary layer (IBL) thickness on the three-dimensional flow field structure and aerodynamic performance. Our results show that the gap flow strength of the tandem cascade decreases with the increase of incidence angle, and it can effectively reduce the mixing of the wakes of the forward blade (FB) and rear blade (RB). In turn, this prevents the passage vortex (PV) in the RB passage from developing along the circumferential direction. The occurrence of IBL does not modify the effects of the incidence angle on the tandem cascade, however, it reduces the load of the RB and the gap flow strength near the endwall. Under all incidence angles, IBL increases the total pressure loss of the tandem cascade, and decreases the static pressure rise (except for an incidence angle equal to -6°). The maximum loss increment is at 2° incidence angle, and the maximum static pressure rise decrement is at 6° incidence angle (Thick-IBL condition) or 7° incidence angle (Thin-IBL condition). Furthermore, we found that the presence of IBL changes the minimum loss condition from 0° (design condition) to -2° incidence angle. Our results thus indicate that in the practical engineering application of the tandem cascade, the reality that IBL degrades the tandem cascade performance in the full incidence angle range should be considered. And the strong endwall secondary flow effect caused by IBL should be considered in the tandem cascade three-dimensional design, so that the tandem cascade two-dimensional performance advantage can be better played.

To explore the efficacy and optimal modality of three-dimensional (3D) MRI sequences in the preoperative detection of neurovascular compressions (NVCs) in patients with trigeminal neuralgia (TN).

Forty-nine cases of typical unilateral TN had undergone 3D time-of-flight magnetic resonance angiography (3D-TOF MRA), 3D fast imaging employing steady-state acquisition (3D-FIESTA), and contrast-enhanced 3D spoiled gradient-recalled sequence (3D-SPGR) on a 3 Tesla MR scanner. Neurovascular relationships (including neurovascular contact and position and the nature of the offending vessels) on MR images were reviewed by a neuroradiologist who was unaware of the clinical findings. Subsequently, microvascular decompression (MVD) surgery was performed on all patients. Comparison was made between the imaging results and surgical findings.

MVD verified NVC in 48 (98%) symptomatic nerves, while 3D-TOF MRA, 3D-FIESTA, and 3D-SPGR revealed NVC in 38 (78%), 48 (98%), and 47 (96%) cases, respectively. Agreement between the position of NVC, as defined by 3D-FIESTA (κ = 0.86) or 3D-SPGR (κ = 0.83) and surgical findings, was excellent. Moreover, excellent agreement was confirmed between the nature of compressing vessels as defined by 3D-FIESTA in combination with 3D-TOF MRA (κ = 0.95) or contrast-enhanced 3D-SPGR in combination with 3D-TOF MRA (κ = 0.92) and surgical findings.

NVCs were visualized with good sensitivity and specificity with 3D MRI sequences in TN. We propose that 3D-FIESTA combined with 3D-TOF MRA is a safe, convenient, and efficacious MRI sequence for revealing NVCs and is crucial for the preoperative diagnosis and surgical planning of MVD.

Percutaneous biliary drainage (PTBD) is a palliative treatment for malignant biliary obstruction. The present study adopted different methods of fixing the drainage tube, aiming to evaluate the efficacy and complications for patients.

Total 68 patients with malignant biliary obstruction, enrolled from 2015 May to 2018 March, were randomly divided into two groups to perform PTBD. 34 patients in group A were fixed the drainage tube by using the traditional way and 34 patients in group B by using an ameliorated approach. The clinical success rate, level of direct/indirect bilirubin, complications and quality of life of patients were recorded.

PTBD was successfully performed on all 68 patients. The direct and indirect bilirubin levels of all patients were significantly decreased at 1-week and 1-month post-surgery (P<0.001). Compared with group A, the level of direct bilirubin in group B decreased more significantly at 1-month after the operation (P<0.05). The quality of life of patients was improved in the two groups at 1-month after the operation (P<0.001). In addition, the rate of early postoperative complications was 38.24% in group B, which was not significantly different from the rate in group A (41.18%) (P>0.05). However, the complication rate of late postoperative in group B (6/34) was significantly less than complication rate in group A (16/34) (P<0.05).

PTBD is an effective method of treating malignant biliary stricture. The ameliorated fixing method for the drainage tube in PTBD effectively decreases the incidence of late complications, further improving patient quality of life.

Aiming at better controlling the ventilated supercavity flow for drag reduction, the experimental and numerical researches of supercavity by rear gas reflux are proposed in this paper. Several experiments with different test bodies have been carried out to study the formation and collapse conditions of jet-reflux supercavity. An open-circulation water tunnel for ultra-high-speed jet experiment and air jet system is employed to form jet-reflux supercavity around the bodies installed in the forward strut. The experiment results show that the supercavity can be maintained by the reflux of tail jet flow when an initial supercavity covering the jet outlet is formed. However, the supercavity will be destroyed when the jet intensity is further enhanced. Under the same jet coefficient, the scale of jet-reflux supercavity extends as the increase of the body length, while the critical jet coefficient for the collapse of the supercavity decreases as the increase of the body length. The multiphase flow model coupling the VOF model and the level-set method is applied to capture the air-water interface. Then, the flow field characteristics of the jet-reflux supercavity are analyzed and compared with the ventilated supercavity. The streamline inside the cavity presents considerable three-dimensional asymmetry inflating flow characteristics. The variation of the gas reflux coefficient along the axial direction is obtained, which indicates that a handful of reflux gas are required to sustain the head cavity. Therefore, the jet-reflux supercavity can be formed within a certain range of the tail jet intensity. Although jet intensities are not equal to each other, the scale of cavity head is roughly maintained under the same reflux coefficient. When the supercavity gets closed to the nozzle outlet, the maximum scale of cavity is decreased, which leads to a weaker reflux at the outlet. The cavity interface will be impinged by the high-speed gas and mixture liquid, which obviously causes deformation and final collapse. In order to improve the stability of the jet-reflux supercavity, it is necessary to use the gas re-directed structure to control the reflux.

Blade lean has been extensively used in axial compressor stators to control flow separations, but its influence mechanism on transonic compressor rotors remains to be revealed. The aim of this study is to numerically explore the influence of blade lean on the performance and shock wave/tip leakage flow interaction in a transonic compressor rotor. The effects of leaned pattern (positively lean and negatively lean), leaned angle and leaned height were studied. Results showed that, compared with baseline configuration, the efficiency and total pressure ratio of the entire constant rotating speed line of positively leaned rotor were both decreased. The absolute value of peak efficiency was reduced by as much as 4.34% at 20° lean angle, whereas the maximum reduction of peak total pressure ratio was 0.1 at 20° lean angle. The tip leakage flow streamlines of baseline transonic rotor can be divided into two parts, i.e., the primary vortex and secondary vortex which arises after the shock. Due to shock/tip leakage vortex interaction, the primary vortex enlarged and low-momentum region showed up after the shock; under near stall (NS) condition, tip leakage vortex breakdown occurred after interacting with shock. As positively leaned angle increased, the shock and the shock/tip leakage vortex interaction point moved upstream. In addition, the phenomenon of tip leakage vortex breakdown was enhanced. For negatively leaned rotors, as negatively leaned angle increased, the peak efficiency and total pressure ratio showed a tendency of first increasing and then decreasing. At 5° leaned angle, the peak efficiency was increased by 0.8% at most, and the maximum increment of total pressure ratio was 0.05 at 5° leaned angle. Besides, the loading of blade tip reduced and the loading moved toward trailing edge, resulting in the downstream movements of primary vortex, shock front and shock/tip leakage vortex interaction location. The results may help to improve the near tip flow field of transonic compressor rotor with leaned blade technology.

It has been proved that suitable slot structure of compressor slotted blade can generate high-momentum jet flow through pressure difference between the pressure and suction surface, the slot jet flow can reenergize the local low-momentum fluid to effectively eliminate the flow separation. In order to investigate and evaluate the impact of full-span slot and blade-end slot on the performance of the post-loaded blade, which has serious flow separation on the suction surface both near blade midspan and endwall, a diffusion stator cascade with large camber angle is selected as the research object. Firstly, the blade-end slotted scheme and the full-span slotted scheme are set up. Then the performance of datum cascade and two slotted cascades is computed in the wide incidence angle range of -8º to 6º at the Mach number of 0.7, the corresponding blade-chord-based Reynolds number 𝑅𝑒𝐶 is 7.7 × 105 . Finally, the performance of the three cascades is analyzed and compared. The results show that, in the computational incidence angle range, both of the two slotted schemes can reduce the total pressure loss for datum cascade and enhance its pressure diffusing capability. However, compared with the blade-end slot, the full-span slot has a better comprehensive control effect on the corner separation and the boundary layer separation near blade midspan, hence, compared with those of blade-end slotted cascade, the total pressure loss coefficients and the static pressure coefficients of full-span slotted cascade are respectively further decreased and increased. Under the blowing effect of full-span slot jet, the total pressure loss coefficients of datum cascade are significantly decreased, ranging as high as 21.2%, 23.1%, 24.5% and 23.4% under the incidence angles of 0°, 2°, 4° and 6°, respectively. The full-span slotted scheme has a better adaptability to wide incidence angle range, it can effectively broaden the available incidence angle range for datum cascade.

Suitable slot structure of the compressor blade can generate high-momentum jet flow through pressure difference between the pressure and suction surface, it has been proved that the slot jet flow can reenergize the local low-momentum fluid to effectively suppress the flow separation on the suction surface. In order to explore a slotted method for better comprehensive suppressing effects on the boundary layer separation near blade midspan and the three-dimensional corner separation, a diffusion stator cascade with large camber angle is selected as the research object. Firstly, the Slotted_1 and Slotted_2 whole-span slotted schemes are set up, then the Slotted_3 scheme with whole-span slot and blade-end slots is proposed, finally the performance of original cascade and slotted cascades is computed under a wide range of incidence angles at the Mach number of 0.7. The results show that: in the full range of incidence angles, compared with the whole-span slotted cascades, the development of the endwall secondary flow on the suction surface of Slotted_3 cascade is effectively suppressed, the degree of the mutual interference between the secondary flow and the main flow is reduced. Besides, on the suction surface of Slotted_3 cascade, the boundary layer separation near blade midspan and the corner separation are basically eliminated. As a result, compared with those of original cascade, the total pressure losses of Slotted_3 cascade are reduced in the full range of incidence angles, and its operating range of incidence angles is broadened. Moreover, compared with the whole-span slotted schemes, Slotted_3 scheme has a better adaptability to wide range of incidence angles.

The impact of varying the tip clearance of each rotor on the performance of a counter-rotating axial compressor has been investigated based on numerical simulations. The main purpose was to investigate the sensitivity to the tip clearance of each of the two individual rotors and the corresponding aerodynamic mechanisms associated with the performance variation in this compressor. The results indicated that both the total pressure ratio and the efficiency decreased as the tip clearance was increased, and the sensitivity curve for peak efficiency for both rotors was found to be an approximately linear negative relationship with increasing tip clearance. The variations of peak efficiency and stability margin of Rotor 2 were more sensitive to changing tip clearance than Rotor 1. An optimum combination of tip gaps existed for this compressor, i.e. 0.5τ for Rotor 1 and 0.25τ for Rotor 2 (where τ represents the nominal tip clearance value). At this optimum configuration, the peak efficiency and stability margin were improved by 0.63% and 29.4%, respectively. The location of the onset of the tip leakage vortex was found to be shifted downstream when the tip clearance increased. The nature of the tip leakage flow for each rotor was found to be influenced by the variation of tip clearance in the other rotor. Rotor 2 showed a more significant impact on Rotor 1. Additionally, varying the combination of tip clearances changed which of the two rotors was the first to stall.

In order to reduce the adverse effect of the tip leakage flow of cantilever stator on compressor performance, the impact of the axial position of endwall streamwise suction slot on tip leakage flow was numerically studied. The study on the overall performance of the compressor and the details of the flow field near the stator end region with and without suction showed that all suction schemes could weaken the tip leakage flow intensity to a certain extent, and the flow control effect was gradually enhanced with the increase of the suction flow rate. In the case of small suction flow rate, for example, 0.5%, the short slot schemes can improve the overall efficiency of the compressor by about 0.5%, which is more advantageous than the long slot scheme, and the overall efficiency improvement of the latter is about 0.3%. The advantage of the long slot scheme in flow control is reflected in the case of large suction flow rate, that is, 1.0%, which may improve the overall efficiency of the compressor by about 0.96%. The axial position of suction slot has a significant influence on flow control effect of the tip leakage flow. Compared with the downstream suction, which only modified the flow field by reducing the blocking effect generated by tip flow vortex, the upstream suction could better control the tip leakage flow by restraining the development of the initial stage of the leakage vortex. Besides, the endwall suction scheme with a full chord length slot has the greatest impact on the passage vortex, its effect on modifying the flow field near the end zone was determined by the combinatorial action of the enhancement of the passage vortex and the attenuation of the leakage vortex.