Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it ...Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it is possible to obtain higher pressure ratios compared to conventional compressors. However, it must be noted that imposing higher aerodynamic loads results in higher loss coemcients and deteriorates the overall performance. To avoid the loss increase, the boundary layer quality must be studied carefully over the blade suction surface. Employment of advanced shaped airfoils （like CDAs）, slotted blades or other boundary layer control methods has helped the de- signers to use higher aerodynamic loads on compressor blades. Tandem cascade is a passive boundary layer control method, which is based on using the flow momentum to control the boundary layer on the suction surface and also to avoid the probable separation caused by higher aerodynamic loads. In fact, the front pressure side flow momentum helps to compensate the positive pressure gradient over the aft blade＇s suction side. Also, in compari- son to the single blade stators, tandem variable stators have more degrees of freedom, and this issue increases the possibility of finding enhanced conditions in the compressor off-design performance. In the current study, a 3D design procedure for an axial flow tandem compressor stage has been applied to design a highly loaded stage. Following, this design is numerically investigated using a CFD code and the stage characteristic map is reported. Also, the effect of various stator stagger angles on the compressor performance and especially on the compressor surge margin has been discussed. To validate the CFD method, another known compressor stage is presented and its performance is numerically investigated and the results are compared with available experimental results.展开更多
This study proposed a design and optimization strategy for a tandem arranged cascade using the Non-dominated Sorting Genetic Algorithm(NSGA) Ⅱ multi-objective optimization algorithm and Back Propagation(BP) neural ne...This study proposed a design and optimization strategy for a tandem arranged cascade using the Non-dominated Sorting Genetic Algorithm(NSGA) Ⅱ multi-objective optimization algorithm and Back Propagation(BP) neural network technology. The NASA Stage 35 was employed as the initial bench mark in the present study and five geometric control parameters were working as the optimization parameters aiming to enhance the aerodynamic performance in terms of total pressure rise and efficiency. Results showed that the feasibility and capability of the proposed optimization strategy was successfully examined. In view of the fact that the initial tandem cascade(directly scaling down from NASA Stage 35) cannot guarantee the aerodynamic performance, first optimization trial was conducted to optimize the initial design. Results showed that the optimum can improve the flow quality whereas the separation on the blade is decayed or even eliminated particularly at the tip and root regions. However, compared with the initial tandem design, the enhancement in total pressure ratio(0.47%) and efficiency(1%) are too small to be noticed. Second investigation was particularly emphasizing on a high turning tandem compressor with an increment by 28°. The pressure rise and efficiency were augmented by 1.44% and 2.34%(compared to the initial tandem design), respectively. An important conclusion can be drawn that the optimization strategy is worthy to be used in high turning compressors with a considerable performance improvement.展开更多
Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explore...Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explored for various tip clearance levels,axial spacings and circumferential clockings.Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle,meridional gas passage and camber distributions in order to have a true comparison with conventional design.Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance.Linear-equation models for correlating stage characteristics with tip clearance are proposed.Comparing two designs,it is clearly evident that the conventional design shows better performance at moderate flow rates.However;near choke flow,tandem design gives better results primarily because of the increase in throat area.Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.展开更多
文摘Increasing the aerodynamic load on compressor blades helps to obtain a higher pressure ratio in lower rotational speeds. Considering the high aerodynamic load effects and structural concerns in the design process, it is possible to obtain higher pressure ratios compared to conventional compressors. However, it must be noted that imposing higher aerodynamic loads results in higher loss coemcients and deteriorates the overall performance. To avoid the loss increase, the boundary layer quality must be studied carefully over the blade suction surface. Employment of advanced shaped airfoils （like CDAs）, slotted blades or other boundary layer control methods has helped the de- signers to use higher aerodynamic loads on compressor blades. Tandem cascade is a passive boundary layer control method, which is based on using the flow momentum to control the boundary layer on the suction surface and also to avoid the probable separation caused by higher aerodynamic loads. In fact, the front pressure side flow momentum helps to compensate the positive pressure gradient over the aft blade＇s suction side. Also, in compari- son to the single blade stators, tandem variable stators have more degrees of freedom, and this issue increases the possibility of finding enhanced conditions in the compressor off-design performance. In the current study, a 3D design procedure for an axial flow tandem compressor stage has been applied to design a highly loaded stage. Following, this design is numerically investigated using a CFD code and the stage characteristic map is reported. Also, the effect of various stator stagger angles on the compressor performance and especially on the compressor surge margin has been discussed. To validate the CFD method, another known compressor stage is presented and its performance is numerically investigated and the results are compared with available experimental results.
基金financially supported by the National Natural Science Foundation of China(No.51376150)
文摘This study proposed a design and optimization strategy for a tandem arranged cascade using the Non-dominated Sorting Genetic Algorithm(NSGA) Ⅱ multi-objective optimization algorithm and Back Propagation(BP) neural network technology. The NASA Stage 35 was employed as the initial bench mark in the present study and five geometric control parameters were working as the optimization parameters aiming to enhance the aerodynamic performance in terms of total pressure rise and efficiency. Results showed that the feasibility and capability of the proposed optimization strategy was successfully examined. In view of the fact that the initial tandem cascade(directly scaling down from NASA Stage 35) cannot guarantee the aerodynamic performance, first optimization trial was conducted to optimize the initial design. Results showed that the optimum can improve the flow quality whereas the separation on the blade is decayed or even eliminated particularly at the tip and root regions. However, compared with the initial tandem design, the enhancement in total pressure ratio(0.47%) and efficiency(1%) are too small to be noticed. Second investigation was particularly emphasizing on a high turning tandem compressor with an increment by 28°. The pressure rise and efficiency were augmented by 1.44% and 2.34%(compared to the initial tandem design), respectively. An important conclusion can be drawn that the optimization strategy is worthy to be used in high turning compressors with a considerable performance improvement.
基金the Deanship of Scientific Research,Research Center of College of Engineering, King Saud University for the financial support
文摘Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explored for various tip clearance levels,axial spacings and circumferential clockings.Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle,meridional gas passage and camber distributions in order to have a true comparison with conventional design.Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance.Linear-equation models for correlating stage characteristics with tip clearance are proposed.Comparing two designs,it is clearly evident that the conventional design shows better performance at moderate flow rates.However;near choke flow,tandem design gives better results primarily because of the increase in throat area.Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.
