Research On Combined Compressor Of Miniature Turbojet Engine

In the new century,contemporary wars are dominated by local conflicts and various weapons and equipment are also developing toward unmanned,low-cost,and efficient trends.As the main power of various unmanned equipment,the micro-turbojet engine's operating performance of the compressor determines the performance index of the entire equipment.At present,most of micro-turbojets adopt single-stage centrifugal or multi-stage axial flow,and the problems of efficiency,manufacturing cost,design cycle and flow loss have been plagued by the development of micro-turbojet engines.In order to improve the short board brought by single-stage centrifugal and multi-stage axial flow and integrate its advantages,under the premise of controlling the axial and radial dimensions,this paper proposes to use a combined compressor to improve the operating index of the micro turbojet engine.The design index of the combined compressor is 3.2kg / s,pressure ratio 4.8,speed 44000 r / min and isentropic efficiency 80%.It is mainly composed of self-designed axial compressor,centrifugal compressor and bladeless diffuser.The core content is as follows:First,the self-designed axial compressor was numerically calculated at 100% design speed and the characteristic curve was drawn.The typical flow field structure at the design point was analyzed and the operating performance under non-design point was compared.The results show that: the flow rate at the design point is 3.229 kg / s,the pressure ratio is 1.39 and the isentropic efficiency is 84.12%;the flow field structure at the design point is well distributed,and the flow loss is mainly concentrated in the tip area and root area;the operating performance under unsteady conditions Poor,the flow loss is large,and the isentropic efficiencies near the clogging point and near-stall point are 66.05% and 82.41%,respectively.Secondly,with the self-designed centrifugal compressor as the object,the purpose is to study and analyze the flow mechanism and loss of the centrifugal compressor.The numerical calculation of the 100% design speed is performed and the operating performance of the design point and the non-design point are analyzed.The research shows that: The calculated value of the centrifuge under the design conditions is a flow rate of 3.363 kg / s,a pressure ratio of 3.678,and an isentropic efficiency of 84.15%.The flow field of the centrifugal compressor under the design conditions is better and the operating efficiency is high;the centrifugation under unstable conditions The operating efficiency of the compressor has decreased,mainly due to the decrease and increase of the outlet back pressure,which has caused changes in the angle of attack and shock wave of the airflow.Finally,based on the flow characteristics of the axial compressor and the centrifugal compressor,a new combination compressor is obtained by combining them.Take this as the final research object of this paper,the full working point of 90%,100%,and 110% rotational speeds were calculated respectively,and the characteristic curves of the combination compressor at different rotational speeds speeds are drawn.Through calculation and analysis,we know that the flow rate at the design point is 3.131 kg / s,the pressure ratio is 4.822,and the isentropic efficiency is 81.85%.The calculated value is basically consistent with the design index,which is in accordance with the design plan;the flow field structure under each typical operating condition at 100% design speed The distribution is different,the design point and the highest efficiency point are running well,and there is no obvious loss at the height of the middle leaf,and the flow condition near the clogging point and the near-stall point is extremely bad.The main reason is that it deviates from the design conditions and the outlet back pressure The change of the airflow angle with the inlet causes changes in centrifugal force,pressure difference between the suction surface and the pressure surface,shock wave and Coriolis force.The coupling effect between the four is unbalanced,resulting in the combination compressor under non-design conditions.The flow loss in the blade tip and root area is increased;the operation at the highest efficiency point at 90% and 110%design speed is better,the isentropic efficiency is 84.24% and 80.45% respectively,the main difference comes from the increase in speed,causing shock waves As the strength and load increase,the flow loss gradually increases.