Research On Internal Flow And Cavitation Characteristics Of A Centrifugal Pump In Slit-laden Water

Pumps play an important role in many irrigations and Drainage &Water project. However, natural rivers entrain suspended different degrees sediment, solid particles and other impurities. when the pumps operate in this muddy water conditions, the internal flow state of pump presents typical solid-liquid two-phase flow and its core over component of flow must be subjected to certain degree of damage, including wear and cavitation. However, research on cavitation of the hydraulic machinery is less, under the existing condition of silt-laden water, Cavitation research mostly uses the test method, the cavitation internal flow characteristic is not totally understood. In order to assure the safe,stable and efficient operation of centrifugal pump, the research on internal flow characteristics of hydraulic machinery under the condition of silt laden water is significant and innovative.This study selects a specific speed of 190 Horizontal single-stage single suction centrifugal pump as the research object. Used RANS method, based on Mixture model and Schnerr-Sauer cavitation mode. Regarded the fresh water and sand-laden water as medium, both non-cavitation internal flow and cavitation internal flow are simulated in a centrifugal pump. The aim is to analyze the effect of solid particles on the internal flow characteristics and cavitation performance of a centrifugal pump. The main research contents and results are as follows:1. By using the Fluent software, the steady numerical calculation of the whole flow passage of the centrifugal pump is carried out under the fresh water condition, and the curve of the external characteristic of the centrifugal pump is obtained. By comparing it to the performance curve obtained from the test, the result whose error is less than 3% verifies the reliability of the calculation model and numerical algorithm in this paper.2.Based on Mixture model, the steady non-cavitation multiple loading conditions(0.4Q、0.6Q、0.8Q、1.0Q、1.2Q) under the condition of the silt-laden water are numerically calculated. By comparing the calculation results to the fresh water condition results, we analyze the similarities and differences of external characteristics under condition of two different medium and the effect of solid particles on characteristics of internal flow in a centrifugal pump.3.Based on mixture model, the RNG k-ε turbulence model and Schnerr-Sauer cavitation model, we numerically simulate steady cavitation flow of a centrifugal pump both in the fresh water and the silt-laden water conditions. Combined with the theoretical derivation of the basic equation of pump cavitation, we analyze the variation of cavitation performance in a centrifugal pump, the process of cavity development in a passage, the velocity distribution and the static-pressure load distribution of blade in a passage.4. Under the conditions of the two kinds of medium, the pump head change trend is basically the same, the head increases with the increase of the flow rate. The change trend of pump efficiency is basically consistent, the efficiency is increased with the increase of flow rate. When the flow rate increases to the optimum operating condition of the near 1.0Q, efficiency reaches a maximum value. And then, the efficiency decreases with the increase of flow rate. In addition, the efficiency of the fresh water single-phase medium is higher than that of the silt-laden water.5. Under the same flow rate, two different kinds of medium conditions, the static-pressure distribution is basically the same, but the overall pressure of the silt-laden water is higher than that of the fresh water and the flow velocity distribution is more disordered than the fresh water. Additionally, the pump optimal operating point shifts to the small flow rate in the silt-laden water.6. Under the condition of silt-laden water, the critical cavitation margin is higher than that of the fresh water and pump is prone to cavitation. With the increase of sediment concentration, degree of cavitation intensified. Under the condition of two kinds of medium, the cavity distribution is basically same in a passage. But under the same net positive suction head, cavity volume fraction is higher and cavitation is more serious under the silt-laden water, two medium conditions of cavitation respectively belong to different cavitation stages.7. Solid particles have certain impact on cavitation pressure characteristic, the cavitation pressure of the silt-laden water medium is higher than that of the fresh water medium. When carrying out numerical simulation of cavitating flows, we should consider the impact of water quality on cavitation pressure characteristics and correct saturation vapor pressure moderately.