Internal Flow Analysis Of Contra-rotating Axial Fan And Low Flow Condition Performance Optimization

Turbo-machinery occupies a very important position in the national economy and it has been widely used in the industrial production, agricultural irrigation, energy mining and defense industry. The internal flow in turbo-machinery is very complicated. The object of this paper is contra-rotating axial flow fan. Firstly, axial fan theory is introduced, and then the numerical simulation model and steady flow field of the axial fans model. The results of internal axial flow fan show that with the reduction in flow, vortex generated from leakage flow at the tip increases, which disrupt the internal flow in fan. Also by analyzing the test results also verify that with the reduction in flow, pressure mutation at the tip of the blade occurred, and flow is also disorder. Finally, we propose two optimization plans, one is to reduce the axial fan duct, and the other is install static ring respectively at the top of impeller. Through numerical simulation we found that the two plans are able to optimize the internal flow when in small flow. The main work is as follows:1?This paper introduces the method of turbo-machinery study, states the classic model and status of tip clearance, and explains the internal structure and internal loss of axial fans.2?In this paper, we establish three-dimensional model of the contra-rotating axial fan, and take numerical simulation for the three-dimensional model. Through the results of velocity, pressure and vortex we found that with the reduction in flow, flow disturbance occurred in the fan. By the results of the analysis carried out by the research group, we also found that with the reduction in flow, pressure mutation at the tip of the blade occurred. By comparing the test results and numerical simulation results we have also found that with the reduction in flow,the flow at the blade tip is disorder.3?Though the study we found that with the reduction in flow, the flow at the blade tip is disorder. Which is mainly due to the leakage flow at the tip of the blade causes the vortex at the tip and then influence mainstream in fans, it is necessary to control the leakage flow. In this paper, through reducing the tip clearance we can improve internal flow when in low flow conditions.4?This paper optimizes the internal flow in fan through two methods. One is to reduce the axial fan duct, from 510 mm diameter to 506 mm. The other one is to install2 mm duct static ring at the cylinder wall of the first-stage or the second-stage impeller.We take numerical simulation analysis for the two methods, and compare with the original fan speed, pressure situations and vortex and find that the two methords are able to optimize the internal flow when in small flow.5?Through the analysis of the above optimization plan we found that the best way is to change the duct diameter. The installation of the static ring will influence the internal flow in fan, especially in the larger flow, local resistance loss increases,but its impact is still relatively small. Through comparing two methods of installing static ring, installation of static ring at the cylinder wall of the first-stage is better in low flow conditions and the optimization effect is more obvious.