One of the important ways of improving axial compressor performance is to control the Tip leakage flow near the endwall region. Numerical computations were conducted to investigate the impact of blade Tip suction on the axial compressor cascade performance in current paper. Three suction schemes located on the blade Tip with different chordwise coverage were investigated in total. The results show that the cascade overall performance can be effectively enhanced by the proper suction scheme on the blade Tip and the best scheme should be arranged at slightly downstream of the onset point of the Tip leakage vortex (TLV). The control effectiveness and mechanisms are different for the different suction schemes. For the suction scheme covering the starting point of TLV, the onset point of TLV is shifted downstream, while an additional induced leakage flow near the blade leading edge is generated resulting in the increase of mixing loss. It is more effective when the structure of the main TLV is destroyed and divided into different parts by applying the blade Tip suction arranged slightly behind the onset point of TLV. In addition, the blade loading is redistributed near the blade Tip after the blade Tip suction and the total pressure loss caused by the suction slots should also be considered in the design process.

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.

Characteristics of rotor blade Tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper contributes to the investigation of Tip leakage flow in a low speed isolated axial compressor rotor blades row. Simulations are carried out on near-stall condition, which is valuable of being studied in detail. In turbomachines, flows are non-isotropic and highly three-dimensional. The reason arises from the complicated structure of bound walls, Tip leakage flows, secondary flows, swirl effects, streamlines curvatures and pressure gradients along different directions. Therefore, accurate studies on Tip leakage flow would be accompanied by many challenges such as adopting suitable turbulence models. So, investigations are carried out numerically utilizing two well-known turbulence models of k-ε and k-ω-SST, separately. It is shown that the k-ε model yields poor results in comparison to the k-ω-SST model. To realize reasons for this discrepancy, turbulence parameters such as turbulent kinetic energy, dissipation and eddy viscosity terms at the Tip clearance region were surveyed in detail. It is found out that estimation for eddy viscosity term is too high in the k-ε model due to excessive growth of turbulent kinetic energy, timescale, and lack of effective damping coefficient. This leads to dissipation of vortical structure of flow and wrong estimation of the flow field at the rotor Tip clearance region. Nevertheless, k-ω-SST turbulence model provides results consistent with reality.

During the operation of a water-jet pump, cavitation generates noise and vibration, causes surface erosion of the hydraulic components, and reduces the performance of the pump. Suppressing the cavitation is beneficial for improving the stability of the energy system of the water-jet pump. In order to investigate the mechanism of cavitation suppression and optimize the cavitation performance of the water-jet pump, the unsteady cavitation flow was studied by numerical simulation and experiment in this paper. Using high-speed photography technology on a closed test platform, the cavitation flow structures in the water-jet pump were captured, and the physical process of cavitation evolution was revealed. Based on this, in order to obtain the cavitation flow characteristics closely related to the cavitation performance, the cavitation flow in the impeller Tip clearance was studied by numerical simulation, the vorticity variation rate in the Tip clearance was analyzed, the effects of different cavitation conditions on the vorticity in the Tip clearance were revealed. Additionally, this paper analyzed the pressure pulsation characteristics of the Tip clearance under different cavitation conditions, and emphatically analyzed the influence of the cavitation flow on the Tip clearance pressure pulsation.

This paper aims to understand the effects of circumferential inlet distortion and Tip injection on a transonic impeller performance and flow field. For distorted inflow, the impeller is subjected to a stationary 120-degrees circumferential total pressure distortion. Full annulus unsteady three-dimensional analysis has been used to study the inlet distortion and Tip injection effects on the impeller performance, stability and flow field. The results show that the circumferential inlet distortion reduces the impeller total pressure ratio and adiabatic efficiency, however, it has no significant impact on the safe operating range. Unlike the inlet distortion, the Tip injection considerably increases the operating range. According to the results, the distortion and Tip injection effect on the compressor performance is mainly due to changes in Tip leakage flow. The inlet distortion has unfavorable influences on the flow field, especially near the impeller Tip, however, the Tip injection ameliorates the flow field in this region. In both the clean and distorted inflow, the Tip injection causes downstream shock transmission, weakening the shock-Tip leakage interaction. Hence, stall inception is postponed, and the impeller stability is improved in the presence of the Tip injection.

To control secondary flow effects and enhance the aerodynamic performance of the compressor, the flow control effects of the flow suction at the endwall with different circumferential positions and at the blade Tip were numerically investigated in the cantilever stator of an axial single-stage transonic compressor. The main purpose was to gain a better understanding of the application of boundary layer suction and the associated control mechanisms in the cantilever stator. The studies show that the optimal position of the endwall suction slot should be located up the stator blade, in terms of the leakage flow structures and the blade Tip unloading effect. In addition, the flow control effects of the suction at the blade Tip on leakage flow upstream is better than that of the endwall flow suction with the same structure. Further, the studies of compressor aerodynamic performance curves illustrate that the efficiency and pressure ratio is increased by 0. 34% and 1. 09% at the peak efficiency point, and are increased by 0. 39% and 0. 14% at the near stall point, respectively.

Systematic Computational Fluid Dynamics (CFD) simulations on incompressible water pipe flow with leakage were conducted in the present study. The aim is to provide the understanding of how different parameters, including the leakage pipe diameter, inlet mass flow rate, and main pipe length, affect the flow phenomena at the vicinity of the leakage location. The present CFD data show that the leakage pipe diameter has dominant effect on the leak mass quantity, pressure change at the vicinity of leak location, total pressure drop and pressure gradient along the main pipe. The effects of both inlet mass flow rate and the main pipe length on leak mass quantity are comparably important. Due to existence of the leakage pipe, larger velocity but lower pressure at upstream, and lower velocity but larger pressure at downstream occur at the vicinity of leakage, which causes adverse pressure at this region. The pressure change resulted from the adverse pressure increases approximately linear with the leak size ratio (ratio of leakage pipe diameter to main pipe diameter) when it is smaller than approximately 40%, at which the maximum pressure change at the leak location occurs. When the leak size ratio is smaller than approximately 5%, the pressure change at the leak location is seen to be approximately zero, implying negligible pressure difference at the two boundary points of leakage pipe. There is sudden change in the pressure gradient along the flow direction at the leak location, which results from a local pressure increase there. When farther away from the leakage, the magnitude of the maximum pressure gradient along the flow direction is reduced due to attenuation of leakage effect. The present study proves that CFD analysis could be an effective and less-costly way to investigate pipe flow with leakage, so as to provide scientific understanding of the physics on pipe flows with leakage.