Search

In order to study the influence of the circumferential position of the balance hole on the cavitation performance of the semiopen impeller centrifugal pump, a low specific speed semiopen impeller centrifugal pump is taken as the object, and 4 kinds of circumferential positions of balance holes are designed. The SST k-ω turbulence model and the Rayleigh–Plesset cavitation bubble dynamics equation are used to calculate the full flow field of the centrifugal pump. Research shows that, under cavitation conditions, as the circumferential position of the balance hole is farther away from the blade working surface, the cavitation performance of the pump is reduced, and the larger θ (the angle of the balance hole and the leading edge of the blade in the direction of rotation) is, the easier the jet cavitation occurs near the balance hole. On the other hand, with the development of cavitation, the axial force of the impeller has also changed greatly. In contrast, the farther the balance hole is arranged in the circumferential direction (i.e., the greater θ), the more limited is the ability of the balance hole to balance the axial force.

In this paper, the influence of the specific area of balancing hole on the cavitation performance of high-speed centrifugal pump is studied by numerical method. The results show that in the initial cavitation stage, with the increase of the specific area, the head and efficiency of the pump decreases, and the shaft power increases in a small range. The specific area of the balance hole can change the magnitude and direction of the rotor axial force. With the increase of the specific area, the anti-cavitation performance of the pump is weakened, especially when the specific area reaches a certain value, the vortex flow appears in the balance hole, which causes serious distortion of the flow condition at the inlet of the centrifugal impeller. Meanwhile, cavitation also occurs in the balance chamber and is mainly concentrated near the hub of the centrifugal impeller.

In order to study the correlation between the internal flow noise of the centrifugal pump and the turbulent pressure pulsation, a single-stage single-suction centrifugal pump was used as the research object by the combination of numerical calculation and experiment. Based on the RNG k-e model and the N-S equation, the model pump was simulated numerically by CFD. A dipole sound source was extracted by the turbulent pulse action of the volute wall surface according to the FW-H equation. The acoustic field of the model pump was solved on the basis of the boundary element method, and the sound pressure distribution of the internal flow field under the action of the dipole sound source of the volute wall and the frequency response of the inlet and outlet fields were obtained. The results show that the distribution of hydrodynamic noise inside the centrifugal pump is related to the pressure pulsation, presenting obvious dipole distribution and disturbance at the tongue. The sound pressure value of the field is mainly concentrated in the blade passing frequency and double frequency, in which the blade passing frequency is the strongest, and the sound pressure value decreases obviously under other double frequency. The main frequency of hydrodynamic noise is the blade passing frequency.

According to the design requirements of a booster centrifugal pump, the full three-dimensional numerical calculation of the model pump is carried out based on the RNG k-ɛ turbulence model and the Rayleigh–Plesset cavitation model to analyze the influence of the axial matching of the inducer and the suction chamber (i.e. the degree of the axial extension of the inducer into the suction chamber) on the cavitation performance of the centrifugal pump. Five sets of centrifugal pump design schemes were selected respectively with the ratio of the axial direction of the inducer into the suction chamber and the axial distance of the inducer hub were 0 (original scheme), 1.6%, 3.2%, 4.8%, and 6.4% to compare the distribution of axial static pressure of the inducer and the suction chamber, the variation of cavitation characteristics, head (energy of a fluid per unit weight obtained by working with a pump expressed in the form of height) and efficiency of the centrifugal pump, the distribution of bubbles in the inducer and the impeller, and the static pressure distribution law of the inducer in the runner. According to the results, what are illustrated are that the cavitation performance of the centrifugal pump can be improved by inserting the inducer into the suction chamber to a certain extent, and the cavitation performance is better with the increase of the axial indentation degree, but it tends to be stable after reaching a certain degree. At the same time, it was found that the vapor bubbles in the inducer and the impeller first appeared in the low pressure region at the inlet rim of the blade.

To suppress the cavitation instability caused by the leakage vortex at the tip clearance of the high-speed inducer, this study establishes a structure (i.e., annular groove) at the upstream boundary of the high-speed inducer that can absorb the leakage vortex, and 6 sets of design projects are determined, including the initial plan and the axial distance of 0 mm, 2.5 mm, 5 mm, 7.5 mm, and 10 mm, respectively. The effects of annular grooves on cavitation performance under different schemes are studied through a combination of experiment and numerical calculation. The results show that cavitation tends to occur at the position where the leading edge of the suction surface of the inducer intersects the shroud and the bubbles volume is distributed in gradient. Vortex belt is formed at the inlet of the inducer. The axial position of the annular groove relative to the inducer is an important parameter suppressing the occurrence of clearance leakage vortex cavitation, asymmetric vortex cavitation and rotating vortex cavitation. In the proper position, annular groove can significantly suppress the bubbles incipient and improve the cavitation performance of the inducer. It can improve the head of the centrifugal pump effectively under the condition of little effect on centrifugal pump efficiency. However, at other positions, the annular groove cannot improve the cavitation performance of the centrifugal pump, indicating the annular groove has an axial optimal position in inhibiting cavitation and improving cavitation performance of the inducer, at this time $${\mathrm{L}}_{1}=0$$ mm.

In order to study the influence of blade outlet cutting width on hydrodynamic excitation noise of the centrifugal pump with low specific speed, five schemes are used to perform V-shaped cutting on the outlet of the impeller blade are studied in this study. Based on Lighthill acoustic analogy, combining computational fluid dynamics and computational acoustics, RNG k-ε turbulence model is used to calculate internal unsteady flow field of the centrifugal pump, and the acoustic solution is based on the flow field calculation. The results show that the pressure pulsation can reflect the sound pressure level to a certain extent; proper cutting of the blade outlet can improve the flow state of the rear cavity of the centrifugal pump and make the flow uniform; the V-shaped cutting of the blade outlet also can reduce the dynamic and static interference between the impeller outlet and the volute tongue, effectively reducing the sound pressure level of the internal sound field, when the blade outlet cutting width is a/ b2 = 33.33%, the inlet sound pressure level and the outlet sound pressure level are decreased by 4.8% and 7.2%, respectively. In terms of internal sound field, the sound pressure level at the outlet of the pump is obviously higher than that at the inlet.

To study the effect of the dip angle of the inducer blade section in the meridian plane on the cavitation performance of the high-speed centrifugal pump, four schemes of the inducer have been considered only by changing the dip angle of the blade section in the meridian plane while keeping the other geometrical parameters unchanged. Based on the RNG k–ɛ turbulence model and Zwart-Gerber-Belamri cavitation model, three-dimensional numerical simulation of a high-speed centrifugal pump is carried out. The results show that the cavitation performance of high-speed centrifugal pump will be improved when the dip angle of the blade section in the meridian plane increases within a certain range, but the cavitation performance will deteriorate when the dip angle exceeds a certain extent. A moderate raise of the blade section dip angle will change the blade inlet angle and blade outlet angle of the shroud and hub of the inducer, improve the matching of the liquid flow angle with the blade inlet angle and restrain the cavitation at the blade leading edge. The change in the dip angle has a weak influence on the external performance of the high-speed centrifugal pump, indicating that there is almost no effect on the capacity of the inducer.

The application of pumps as turbines (PAT) has been developed in several applications for energy recovery schemes. Therefore, establishing a performance correlation between pump mode and turbine mode is essential for selecting the proper machine. However, slip phenomenon is the challenges of head prediction for PAT. In this paper, the slip phenomenon of pump and PAT was revealed, and the slip factor was studied using CFD. The effect of slip on head prediction for PAT was analyzed, and a theoretical prediction model was presented considering slip factors. In order to validate the head prediction model, six centrifugal pumps with specific speed (ns) from 9 to 54.8 were tested as turbines. Results showed that the predicted head by the proposed method was in good agreement with the experimental data, and it is more accurate than Stepanoff, Alatorre-Frenk, Sharma, and Derakhshan models. This method can be applied in head prediction for low specific speed PAT ( ns

Compared with the general centrifugal pump, the screw centrifugal pump has a spiral radial impeller and opening flow passage. The impeller inlet is a spiral blade and outlet of blade looks like to mixing-flow pump blade. Its special structure made the screw pump not only having spiral propelling effect but also having centrifugal effect, therefore the screw centrifugal pump has both the merits of screw pump and centrifugal pump. According to the structure characteristics of screw centrifugal pump, character of flow-field inside the pump and projection drawing on foundation with one-dimension, the regularity for change of pitch in the variable-pitch parametric equation group is given in this paper. And the variable-pitch parameter equation group of the screw centrifugal pump is perfected. Using the parametric equation, to segment streamline dots on axial plane for designing screw centrifugal pump blade is facilitated, which has important meaning to the CAD, numerical simulation of three-dimension flow-field and improve performances of screw centrifugal pump