Effect Of The Blade Diffuser On The Performance Of Model Stage

Centrifugal compressors are key equipments in petrochemicals,metallurgy and many other industries.The efficiency and stability of the centrifugal compressors are crucial for the long-period and full load safe operation of the whole production line.Experiences indicate that the efficiency of the compressor with blade diffuser is higher than that of with non-blade diffuser,but the pressure disturbance caused by the blade diffuser may propagate upstream thus affect the flow in the impeller and ultimately cause resonance stress and the fatigue failure of the impeller blade.So that in some industry fields especially in chemical industry, non-blade diffuser are generally used instead of the blade diffuser for safety reasons and the benefit of high efficiency of the blade diffuser has to be sacrificed.The design method of the blade diffuser that will not cause impactive force on the impeller is an imperative key technique in centrifugal compressor industry.The model stage studied in this thesis was designed by Nuovo Pignone in the 70s last century but is still in use in manufacturing factory in China.The efficiency of such a model stage is usually 10%lower than the modern state-of-art products in current market. Significant improvement had been done by DUT following many numerical experiments and a series of structure modifications.The adoption of the blade diffuser was the key approach. But before the modifications being used in the real design,the impactive force caused by the blade diffuser must be studied.Steady and unsteady numerical analysis were carried out in this paper to analysis the pressure disturbance and its impact on the impeller.Base on the CFD software NUMACA,a numerical analytic system for the model stage was developed.Based on the blade diffuser of the prototype design model stage with small flow rate,numerical analysis was performed to study the effect of the orientation and the blade chord of the blade diffuser relative to the impeller on the performance of the model stage.Simulations results were analyzed to study the influences of the blade diffuser on the stage performance and the optimal design of the blade diffuser.Unsteady state flow analyses were performed to study the interaction between the blade diffuser and the impeller.The unsteady pressure fields were obtained to observe the impactive effects of the blade diffuser on the impeller.The results obtained may provide an analytic base for the detailed mechanics analysis of the impeller to decide the scope of the impactive effects.