| The kinetic energy of the airflow at the outlet of the centrifugal compressor impeller accounts for 30%?40%of the impeller's amount of work.It is necessary to use this part of the energy reasonably to convert the kinetic energy into pressure energy to prevent a large amount of energy loss.As centrifugal compressors move toward high efficiency,high load and wide operating conditions,the role of diffusers becomes even more important.The tandem cascade diffuser has the characteristics of high efficiency,low loss and wide operating range.Based on the above knowledge,this paper studies the influence of the geometric parameters of the tandem cascade diffuser on the performance of the centrifugal compressor.In this paper,the centrifugal compressor of a gas turbine is taken as the research object,and the wedge-shaped diffuser is modified by tandem cascade,and the circumferential and radial positions of the rear row of the tandem cascade diffuser and the front and rear rows of blades are modified.The chord length ratio is studied,and the tentative optimization of adding small blades to the tandem cascade diffuser is also carried out.In the research process,the numerical simulation method is mainly used in the research process,and the commercial software NUMECA is used for numerical calculation and pre-and post-processing,main tasks as follows:1 Study the influence of the performance of the centrifugal compressor stage on the downstream position of the tandem cascade diffuser in different circumferential positions.The results show that the circumferential position of the rear row of blades has a significant impact on the overall performance of the centrifugal compressor and the tandem cascade diffuser.When the rear row of blades is in a suitable circumferential position,the tapered passage formed by the low-speed fluid of the front row of blades through the front and rear rows of blades can be accelerated,the fluid energy in the boundary layer of the rear row of blades is increased,and the rear surface of the rear row of blades is delayed or eliminated.Layer separation reduces losses.Centrifugal compressors perform best when the RCP is 30%.2.The influence of the performance of the centrifugal compressor stage on the rear radial blades of the tandem cascade diffuser is studied.The results show that the working range of the centrifugal compressor stage is greatly affected when the rear row of blades is at different radial positions.Due to the thickness of the blade,when the radial position of the rear row of blades changes,the geometry of the gap channel formed between the front and rear rows of blades is also affected,and the role of the slit channel is also different.When the radial distance is 0,the centrifugal compressor has the best overall performance.3.Based on the determination of the circumferential position and radial position of the rear row of the cascade,the series cascade of the centrifugal diffuser of the centrifugal compressor is modified to greatly improve the aerodynamic performance of the original centrifugal compressor.And optimize the exploration by adding small blades on the basis of suitable chord length ratio tandem cascade diffusers.The results show that the performance of the modified cascade diffuser is better than the original wedge diffuser.Within a certain range,the shorter chord length of the front row of the tandem cascade diffuser,between the front and rear rows of blades the acceleration effect provided by the tapered channel is more obvious for the development of the front blade boundary layer,thereby reducing the front row diffusing loss and improving the performance of the compressor.Adding a small blade with a suitable chord length near the leading edge of the tandem cascade diffuser can increase the total pressure ratio without substantially reducing the efficiency and working margin of the centrifugal compressor,while broadening its maximum flow capacity.The chord length of the small blade should be between 7%and 10%of the total chord length. |
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