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Study Of Mechanism Of The Internal Flow Loss And Optimization Design Of A High Specific-speed Centrifugal Fan

Posted on:2020-09-15Degree:MasterType:Thesis
Country:ChinaCandidate:X LiFull Text:PDF
GTID:2392330596479392Subject:Water Resources and Hydropower Engineering
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Centrifugal fans are widely used in various sectors of the national economy and are important equipment for many industries.And they are also the main energy-consuming equipments.With the continuous improvement of national environmental protection requirements,the high specific speed centrifugal fan with large flow and low pressure rise characteristics has become an urgent need for industrial production.However,using the traditional series of centrifugal fans to operate under large flow conditions will cause the fan operating efficiency to drop sharply and increase energy consumption.Therefore,in order to meet the needs of energy saving and environmental protection,it is necessary to develop a high specific speed centri fugal fan with better performance and higher cfficiency to meet the specific needs in actual production.Also,the mechanism of internal flow is the key to optimal design the centrifugal fan.In this paper,a high specific speed centrifugal fan based on the traditional model was designed.The three dimensional unsteady numerical model was established and verified by experiments.The Internal flow loss mechanism was revealed through analyzing unsteady flow field and pressure pulsation signal of high specific speed centrifugal fan.Besidcs,the high specific speed centrifugal fan was optimized designed based on using different types of impeller blades,adding anti-vortex rings and bafflcs,and redesigning the front plate of impeller.The main work completed and conclusions are as folllows:(1)Design of high specific speed centrifugal fan.Due to the ccentrifugal fan needs to operate under large mass flow condition sometimes.high secific speed centrifugal fan was designed by adjusting some parameters of Y4-73 centrifugal fan,such as impeller diameter,impeller outlet width,impcller shape of front plate,et al.Compared to the original fan,the high specific speed centrifugal fan has a specific speed of 120,and maximum operating efficiency of high specific speed centrifugal fan moves to large flow conditions.Both total pressure and efficiency have been improved under the new large mass flow design condition,and the efficiency has increased by about 10%.(2)The flow loss mechanism of high specific speed centrifugal fan.The main loss of high specific speed centrifugal fan comes from the impeller and volute,and the loss at the volute is about 11.9%.Through the analysis of internal flow field and pressure pulsation signal of centrifugal fan under different mass flow conditions,it is found that the flow separation phenomenon occurs at the impeller channel.The flow separation is more obvious at the front plate of impeller and extends into volute diffuser cavity,resulting in the decrease of volute efficiency.Especially under the condition of small mass flow,the leakage vortex inside the impeller seriously blocks the flow channel and the impeller function is greatly reduced.At the same time,the pressure fluctuation amplitude of the fan reaches the maximum.(3)Effect of different optimized schemes on performance of high specific speed centrifugal fan.Due to the serious flow loss of the impeller and the volute,the flow separation phenomenon in the impeller and the large scale vortex in the volute are reduced by the modification of the impeller and the volute.On the impeller,the effects of three different blade types on the performance of the fan were analyzed.The results show that the plate type blade of the fan has the highest total pressure and efficiency under the design mass flow condition.On the volute,The internal flow loss of the volute was expected to be reduced by adding a vortex ring and different types of baffle.The results show that this method is not suitable for the fan model selected in this paper.The impact of this method on the performance of different types of centrifugal fan still needs further study.(4)The flow loss mechanism at front plate of impeller and optimal design of the front plate profile.The flow condition at the front plate of the impeller has a great influence on the overall performance of the centrifugal fan.The aerodynamic performance test was carried out for the taper plate and the arc plate which are usually designed for the fan impeller.With the enhancement of the specific speed,the influence of impeller shrouds was increased.When the specific speed was 73 and 120,the efficiency of front arc plate impeller was increased by 5%and 14.5%,respectively compared with front taper plate impeller.The flow separation phenomenon at the flow channel of taper plate impeller appears too early and extend to the impeller outlet.So that the efficiency of the fan is decreased,at the same time,the pressure pulsation is increased.The flow condition at arc plate impeller outlet is stable,the efficiency was improved by 1%under the design condition after further optimization of the arc plate impeller.
Keywords/Search Tags:centrifugal fan, numerical simulation, high specific speed, loss mechanism, optimization design
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