Three-Dimensional Laser Measurement Of Flow Field In Box Passage And Pump Impeller Inlet

As an important part of the large and middle low-lift pumping stations, the inlet passage is the transition section of the forebay and the impeller chamber whose purpose is10divert the water in forebay smoothly into the impeller room and to provide a better flow pattern for the pump. Among these passages, box passage wins widespread concern in the engineering application for saving cost and ease of construction, which has a simple structure, single cross section shape change, low flow channel height and small foundation excavation depth. But if its size selection is unreasonable, poor internal flow patterns may result in flow separation and vortex which will directly affect the flow pattern at pump impeller inlet, increase pump hydraulic losses and reduce pump efficiency.The international advanced PIV (Particle imaging velocimetry), non-contact measurement technology, was adopted in this paper to measure the three dimensional flow fields within the horn tube of box culvert inlet passage. The measurements of three typical flow condition show that, during small flow rate (17.02l/s) condition, flow pattern disorders such as vortex and secondary reflux occurs in horn tube. Water conditions at impeller inlet are much poor. Then at design flow rate (34.57l/s) condition, in trumpet tube and pump impeller inlet is good, flow field follows a symmetrical distribution with no bad flow patterns such as eddy happening. However during high flow rate (42.26l/s) condition, submerged vortex occurs and inlet flow pattern is not good in passage. So vortex rectification measures must be taken to improve the flow pattern within the flow, and to improve pump unit operation efficiency.CFD numerical simulation was also adopted to simulate the flow field of inlet passage under the same conditions of PIV measurement. Comparison of calculation results and experimental results indicates that both results match and could very well reveal the flow field characteristics within inlet passage. Three-dimensional laser measurement results can be good to verify the results of numerical simulation. Moreover, on the basis of the original design, three-dimensional flow field for PIV measurement was made after the rectifier by setting a vortex canceling cone below the trumpet tube. The results show that, after adding vortex canceling cone, it successfully eliminated the submerged vortex in trumpet tube when running under high flow rate conditions. Internal flow pattern has been greatly improved and flow field at pump impeller inlet is basically a symmetrical distribution. The flow pattern in box passage is pretty good, So it is necessary to adopt vortex rectification measures to improve flow pattern in the box passage.