Performance Of Mixed-flow Pump Research Articles

Study on passive suppression method of rotating stall in mixed-flow pump: Using different impeller rim structures

Tip leakage flow (TLF) is not only an important factor causing hydraulic loss in mixed-flow pump, but also one of the inceptions of rotating stall. At present, limiting the stall of rotating machinery by restraining the TLF has gradually become a research hotspot of rotating machinery. However, in the field of mixed-flow pump, it is still in the initial stage of exploration. With the development of hydraulic machinery towards large-scale and high-speed, it is necessary to study its rotating stall suppression methods and expand its efficient operation range. Therefore, based on the idea of passive suppression of rotating stall, four new impeller rim structures are proposed in this study to optimize the performance of mixed-flow pump and to suppress or delay the occurrence of stall. The research results show that the geometric structure of the rim clearance has a significant impact on the energy performance of the mixed-flow pump, Bulge_Tip structure and Double_Rib_Tip structure make the critical stall and deep stall operating points shift to the low flow rate operating points, which improves the “saddle area” performance of the mixed-flow pump to a certain extent. However, there are two stall segments in the performance curve of Groove_Tip and Single_Rib_Tip structures, which worsens the pump performance in the “saddle area”. From the analysis of flow mechanism, it can be seen that Bulge_Tip structure and Double_Rib_Tip structure can restrain the loss of turbulent kinetic energy in the gap under stall condition to a certain extent, and limit the position and strength of unsteady secondary vortex (SV) structure at the impeller outlet, so as to shorten the stall range of mixed-flow pump without deteriorating the stall flow field in the impeller. Therefore, Bulge_Tip structure and Double_Rib_Tip structure has a light application prospect in stall suppression of hydraulic machinery.

Influence of different blade numbers on the performance of “saddle zone” in a mixed flow pump

In order to study the effect of different numbers of impeller blades on the performance of mixed-flow pump “saddle zone”, the external characteristic test and numerical simulation of mixed-flow pumps with three different impeller blade numbers were carried out. Based on high-precision numerical prediction, the internal flow field and tip leakage flow field of mixed flow pump under design conditions and stall conditions are investigated. By studying the vorticity transport in the stall flow field, the specific location of the high loss area inside the mixed flow pump impeller with different numbers of blades is located. The research results show that the increase in the number of impeller blades improve the pump head and efficiency under design conditions. Compared to the 4-blade impeller, the head and efficiency of the 5-blade impeller are increased by 5.4% and 21.9% respectively. However, the increase in the number of blades also leads to the widening of the “saddle area” of the mixed-flow pump, which leads to the early occurrence of stall and increases the instability of the mixed-flow pump. As the mixed-flow pump enters the stall condition, the inlet of the mixed-flow pump has a spiral swirl structure near the end wall for different blade numbers, but the depth and range of the swirling flow are different due to the change in the number of blades. At the same time, the change in the number of blades also makes the flow angle at 75% span change significantly, but the flow angle at 95% span is not much different because the tip leakage flow recirculates at the leading edge. Through the analysis of the vorticity transport results in the impeller with different numbers of blades, it is found that the reasons for the increase in the values of the vorticity transport in the stall condition are mainly impacted by the swirl flow at the impeller inlet, the tip leakage flow at the leading edge and the increased unsteady flow structures.

Energy characteristics of mixed-flow pump under different tip clearances based on entropy production analysis

In order to investigate the effect of impeller tip clearance on the internal flow fields and the hydraulic losses in mixed-flow pump, the entropy production method with computational fluid dynamics (CFD) is employed to analyze the energy losses in a low specified number mixed-flow pump with guide vane. The results show that the size of tip clearance is closely related to the external characteristic performance of mixed-flow pump, and the effect of tip clearance on the flow fields of mixed-flow pump is obvious at design flow rate condition. When the tip clearance raises from 0.2 mm to 1.1 mm, the head drop loss coefficient increases 1.62 times in the impeller. As the tip clearance augments from 0.2 mm to the 1.1 mm, the total entropy production in impeller increases by 142%. Whereas, the total entropy production in guide vane descends by 21.8% slightly. It indicates that the increase of tip leakage flow (TLF) may increase the energy losses in impeller but the hydraulic losses in guide vane is suppressed to some extent as a result of an existence of TLF. Therefore, for the sake of improving the energy performance of mixed-flow pump, it is necessary to take the scale of blade tip clearance into account and consider optimizing the hydraulic design structure of guide vanes comprehensively to match the tip clearance.

Multi-Parameter Optimization and Analysis on Performance of a Mixed Flow Pump

A mixed flow pump with guide vanes was chosen as research model in this study, and eight parameters of the impeller were selected as optimization variables, including blade outlet inclination angle, blade wrap angle at hub, blade inlet angle and outlet angle at middle stream line, blade outlet width, front shroud inclination angle, hub inclination angle and vane number. Firstly, orthogonal experimental method and CFD numerical simulation method were used to produce samples, then the RBF neural network was adopted to establish the performance prediction model as the objective function, multi-island genetic algorithm was used for solving the objective function at last. Based on all the above, a method of multi-parameter optimization method on energy performance of mixed flow pump without changing the nominal diameter of impeller outlet was proposed and then verified by experiments. By this method, the pump head and efficiency at the design point of the model pump were increased by 11.5% and 4.32%, respectively. Meanwhile, the peak value of pressure pulsation coefficient at pump inlet, impeller outlet, guide vane outlet and pump outlet all decreased obviously, by a maximum decrease of 62.9%. Compared to the original model, the static pressure in the optimization model increased by 30kPa and the gradient of static pressure distribution after optimization becomes larger and more uniform. The turbulent energy intensity at the impeller outlet was reduced by 0.2m2/s2. The pressures at the 60% blade position and 80% blade position both increased by nearly 65kPa and the pressure decreased by 50kPa at the blade pressure side.

Influence of impeller and guide vane hub size on hydraulic performance of mixed-flow pump

Because of the beneficial properties of the mixed flow pump, it is widely used in the fields of irrigation and drainage. Our research team designed a mixed-flow pump, which with maximum efficiency more than 87%. However, its maximum operating efficiency range is biased towards large flow areas. In order to find the reasons for deviation from the design head, we have a three-dimensional modeling of the pump system and numerical simulation to analyze the internal flow. The numerical simulation results agree well with the experimental results and the experimental results verified the accuracy of the numerical simulation. When Q = 288 L/s, 360 L/s and 432 L/s, poor flow conditions appear near the hub. We refer to change the impeller and guide vane hub ratio method which only change the impeller and guide vane hub radius as blade shape remains unchanged. The result of this approach shows that it is possible to shift the highest efficiency point to the design point, but this can result in poor impeller performance. So we try to only change the guide vane hub radius and numerical simulation results show that it is effective. Finally, in the design head point, experimental test proved that when the guide vane hub radius is increased by 11 mm, pump system efficiency is increased by about 2.3%. This article can provide some references for the design of a mixed-flow pump.

PERFORMANCE IMPROVEMENT OF MIXED FLOW PUMP IMPELLER THROUGH CFD ANALYSIS

Centrifugal pumps are the largest used hydraulic machine. However, the performance of centrifugal pump is generally not very good. Making them more efficient is a major challenge. The performance of the centrifugal pump greatly depends on its geometrical parameters and the vane profile. Computation fluid dynamics (CFD) has been found to be very good tool for numerical analysis of flow through complex system including centrifugal pumps. The present study deals with the performance analysis of a mixed flow type centrifugal pump designed centrifugal pump to deliver 0.25 m 3 /s water at a head of 20 m running at 1450 rpm using ANSYS CFX 14.0 software. Modeling of the pump unit has been done using PTC Cre-o 2.0 software. The performance of the pump was first determined using the initially obtained vane angles. The inlet vane angle and outlet vane angle are then varied to analyses the improvement in pump performance .The results shows that for an initial inlet angle 20.08 and outlet angle 16.28 , the efficiency of the pump is 83 %.however, for an optimized angles at inlet and outlet as 20.16 and 16.62 respectively, the efficiency of pump raised to 88 % thus showing an improvement in the performance of mixed flow pump.

Experimental study of the effect of blade tip clearance and blade angle error on the performance of mixed-flow pump

The hydraulic performance test of the mixed-flow pump has been carried out through selecting different blade tip clearances and various blade angle errors. The ratio of the mixed-flow pump efficiency reduction and the blade tip clearance variation (Δη/Δδ) varies with the flow rate coefficient ϕ revealing a parabolic trend. An empirical equation has been developed for the mixed-flow pump model by parabolic fitting. For the same blade tip clearance variation Δδ, the mixed-flow pump efficiency reduction Δη increases rapidly as the flow rate rises. For any given flow rate, the efficiency, the head and the shaft power of the mixed-flow pump all decrease with the increase of the blade tip clearance. Among them, the efficiency reduction Δη varies approximately linearly with the blade tip clearance variation Δδ. When the angle of an individual blade of the mixed-flow pump has a deviation, the performance curves will move and change. These curves have consistent change directions with the performance curves under the condition of all the blades rotated at the same time, but have smaller offset and lower range of variation. When an individual blade angle error changes to ±2°, the optimal efficiency of the mixed-flow pump will have no significant difference. When the individual blade angle error increases to ±4°, the optimal efficiency will decrease by 1%.

Hydraulic Performance of a Mixed-Flow Pump: Unsteady Inviscid Computations and Loss Models

The hydraulic performance of an industrial mixed-flow pump is analyzed using a three-dimensional potential flow model to compute the unsteady flow through the entire pump configuration. Subsequently, several additional models that use the potential flow results are employed to assess the losses. Computed head agrees well with experiments in the range 70 percent–130 percent BEP flow rate. Although the boundary layer displacement in the volute is substantial, its effect on global characteristics is negligible. Computations show that a truly unsteady analysis of the complete impeller and volute is necessary to compute even global performance characteristics; an analysis of an isolated impeller channel and volute with an averaging procedure at the interface is inadequate.