Optimization Of Aerodynamic Performance And Analysis Of Acoustic Field Characteristics Of Turbine Exhaust Diffuser

The turbocharger as an important part of the internal combustion engine power plant,its performance is often able to a large extent influence the performance of internal combustion engine,exhaust diffuser as the core components in turbine exhaust volute,its aerodynamic performance indirectly affects the working state of the turbine components,therefore,to exhaust diffuser optimized design to reduce exhaust volute flow loss of energy conservation and emissions reduction has important engineering significance.This article selects has practical application in ship host of axial flow axially symmetric volute exhaust section as the research object,by using the method of numerical simulation reveals the internal flow field characteristics and the reasons for the loss,in order to reduce the loss,the exhaust diffuser study on geometric structure parameters,and the case for the optimization design,in order to further enhance the diffuser performance.The main research work of this thesis includes the following parts:(1)The internal flow law of the exhaust volute section was preliminarily studied.The structure parameters of the object studied in this thesis are introduced,the CFD grid of the computational model is built,and the grid independence is verified.By analyzing the internal flow field of the original volute exhaust section,the main cause of flow loss is pointed out.The results show that the poor performance of the original diffuser results in a large flow loss in the whole volute section,and the main loss is caused by the eddy current inside the volute,the mixing of the air flow from different directions in the exhaust passage and the separation of the fluid inside the diffuser.(2)Study on the influence of structural parameters of the exhaust diffuser on its performance parameters.The total pressure loss coefficient of the volute decreases first and then increases with the increase of the inner wall Angle.With the continuous increase of the inner wall Angle,the air flow and the inner wall of the diffuser begin to separate.With the increase of the relative axial length of the diffuser,the total pressure loss coefficient of the volute exhaust section increases slowly at first and then rapidly,and obvious jet flow appears at the outlet of the diffuser.When the inner wall of the diffuser is set as a circular arc,the total pressure loss coefficient of the exhaust section of the volute decreases greatly,and the static pressure recovery coefficient of the diffuser increases greatly.Therefore,compared with the inner wall of the linear circular arc,the performance of the exhaust diffuser is better improved.(3)Based on the response surface optimization method,the geometric structural parameter optimization design of the diffuser was developed.The response surface optimization Design of exhaust diffuser was carried out by using the Design Expert software,and the flow field simulation calculation was carried out for different schemes.Results show that the accuracy is higher,the response surface optimization method can be predicted,the response surface optimization,the optimized exhaust diffuser improved performance,installation,spiral case of the optimized diffuser flow loss is reduced greatly,the whole of the volute exhaust flow field is improved,the static pressure recovery coefficient at the design condition from 0.474 to 0.683,the export of volute from 0.474 to 0.283,the total pressure loss at the bottom of the volute area of the turbulent kinetic energy has fallen dramatically,diffuser inlet pressure drop is more advantageous to the expansion of the turbine power.(4)Analysis of the interaction between the turbine and the volute exhaust section and analysis of the turbine noise characteristics.The unsteady calculation is carried out on the whole cycle model of the turbine,and the aerodynamic noise of the turbine is calculated with the acoustical calculation software.The results show that compared with the original diffuser,the optimized diffuser is more conducive to the expansion work of the turbine.Dipole source is the main noise sources of the turbine,mainly in the low frequency under the action of a single blade aerodynamic noise,when more than 300 Hz noise attenuation,rapid and high noise level near the turbines first-order shaft frequency,harmonic response analysis through the turbine,the turbine first six levels of sound power level,found that the turbines are mainly distributed in the high frequency noise.To sum up,this thesis systematically studied the influence of structural parameters of turbine exhaust diffuser on the performance of volute exhaust section,carried out the optimization design of geometric structural parameters,studied the characteristics of sound source and sound field distribution of turbine noise,and provided a method support for the improvement of turbine performance.