Performance Prediction And Internal Flow Of Than Single-stage Singlesuction Centrifugal Pump With Medium Specific Speed

Normally the centrifugal pump with specific speed of 80-150 were defined as medium specific speed centrifugal pump.Due to the advantages of high head and small flow,it was widely applied to fields such as energy generation,rural water conservancy and circulating water treatment etc.However,China started late on pump study.Thus,the industrial foundation was relatively weak.The produced pumps were low efficient and high energy consumption and the stability remains to improve.For purpose of improving working performance of pumps,the internal flow characteristics of pumps shall be studied in details.This paper regards four medium specific speed centrifugal pumps as the studied models.By the means of numeric calculation and experiment verification,the internal flow characteristic distributing situation and prediction curve of external characteristics of medium specific speed centrifugal pumps in different situations were eventually obtained and the experiment verification was also obtained.Meanwhile,the analysis and study on cutting values of impeller were conducted,which shall have practical significance on the improvement of medium specific speed centrifugal pump performance in the future.The study and conclusions of this paper was as follows:1.The three-dimensional water data model of full flow field of fluid domain of the four medium specific speed centrifugal pumps was rendered utilizing commercial three-dimensional modeling software Pro/E and the medium specific speed centrifugal pumps were assembled.The software Gambit was applied to classify the networks,where the fluid domains of impeller and volute adopt unstructured networks and the inlet and outlet pipelines adopt structured network.2.The steady numeric calculation of full flow filed of the four medium specific speed centrifugal pumps was conducted with RNG k-? Turbulent Model and the result indicates:(1)From impeller inlet to outlet,the static pressure of rotary surface of impeller presents step increase along the radial direction.With the reducing of flow,diffusing tube pressure of volute gradually increases and the scope also expands gradually.Under the working condition of small flow,the impeller exists obvious backflow phenomenon and the internal flow state in the runner was poor.With the increase of flow,the relative velocity distribution was gradually homogeneous.It was known by streamline chart that the streamlines of four medium specific speed centrifugal pumps were smooth under the working condition of design and with flow reduction,the streamlines occur disorders.At 0.2Q,the outlet of volute occurs swirl.Under working condition of high flow,the internal flow state of volute was still poor and backflow also occurs.(2)To conduct experiment on the four medium specific speed centrifugal pumps and by collected data,the result shows that the peak efficiencies of four medium specific speed centrifugal pumps all deviate from the design working condition in different degrees.Meanwhile,to verify the reliability of numerical method,contrastive analysis between performance parameter obtained from experiment and performance parameter obtained from numeric calculation were conducted and the result was quite close.3.Two centrifugal pumps with the separate specific speed 126 and 133 were conducted impeller cut for five times and each model was conducted numerical simulation in six different working condition points.The simulated internal flow distribution situation and performance parameters in the pumps were obtained.According to performance parameters,external characteristic curve charts were rendered.It was known by contrastive analysis:Impeller cut has greater influence on both internal flow characteristics and external characteristics of the centrifugal pumps.When the cutting values of impeller were small,the distribution of flow field has no change basically.With further increase of the cutting values of impeller,the flow field was in disorder and the flow state was poor;the head,shaft power and efficiency after impeller cut all reduce.Basically,with the increase of cutting values,the reduction was more.Thus,impeller cut shall be controlled in the limited scope.In addition,not only shall the influence of impeller cut on performance of centrifugal pumps be emphasized,but also the undesirable phenomena such as the impact shock of the centrifugal pumps caused by impeller cut shall be emphasized.