The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the...The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the two or three stage pressure ratio is analyzed in two cases of constant heat transfer rate for the inter cooler or constant inter stage inlet temperature, based on the minimum of the sum of theoretical compression power at each stage about a multi stage reciprocating compressor. Furthermore, with an example of two stage compressor the influence on the sum of the power of each stage is analyzed when practical pressure ratio deviates from the optimum value. It is obtained that under different cooling conditions the optimum pressure ratio distribution of the multi stage compression is various, and the change of the optimum pressure ratio within a small range has little influence on the sum of the power each stage. For the two stage compression, this range can be represented as ε 1=(0 96～1 06)ε 1j .展开更多
This study numerically investigated a single stage centrifugal compressor "Radiver" with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and th...This study numerically investigated a single stage centrifugal compressor "Radiver" with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance.The results demonstrate that tandem design and clocking fraction(ks)significantly affects the compressor performance.The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller.The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary.In order to restrain the inducer wake and exducer shock losses,parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained.The modified tandem impeller with 25%clocking arrangement shows an 8.45%stall margin increase and maintains the total pressure ratio and efficiency as the conventional design,which proves the potential of tandem impeller to improve compressor stage performance.It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.展开更多
The resistance torque of a piston stage II com- pressor generates strenuous fluctuations in a rotational period, and this can lead to negative influences on the working performance of the compressor. To restrain the s...The resistance torque of a piston stage II com- pressor generates strenuous fluctuations in a rotational period, and this can lead to negative influences on the working performance of the compressor. To restrain the strenuous fluctuations in the piston stage II compressor, a variable duty-cycle control method based on the resistance torque is proposed. A dynamic model of a stage II com- pressor is set up, and the resistance torque and other characteristic parameters are acquired as the control tar- gets. Then, a variable duty-cycle control method is applied to track the resistance torque, thereby improving the working performance of the compressor. Simulated results show that the compressor, driven by the proposed method, requires lower current, while the rotating speed and the output torque remain comparable to the traditional vari- able-frequency control methods. A variable duty-cycle control system is developed, and the experimental results prove that the proposed method can help reduce the specific power, input power, and working noise of the compressor to 0.97 kW.m-3.min-1, 0.09 kW and 3.10 dB, respectively, under the same conditions of discharge pressure of 2.00 MPa and a discharge volume of 0.095 m3/rain. The proposed variable duty-cycle control method tracks the resistance torque dynamically, and improves the working performance of a Stage II Compressor. The pro- posed variable duty-cycle control method can be applied to other compressors, and can provide theoretical guidance for the compressor.展开更多
To investigate the control effect and flow mechanism of the L-shaped endwall groove on corner separation in the real compressor stage,a single stage axial flow compressor is selected as the research object and the L-s...To investigate the control effect and flow mechanism of the L-shaped endwall groove on corner separation in the real compressor stage,a single stage axial flow compressor is selected as the research object and the L-shaped grooves are introduced on the stator casing side.First,the experimental measurement is conducted on the optimal L-shaped groove obtained through a full factorial experimental design,and the results demonstrate that the optimal groove has a great control over the endwall flow.Moreover,the peak efficiency is improved by 0.9%and the stall margin is increased by 4.46%.Then,the flow field visualization of numerical results and analysis of variance method are employed to analyze the control mechanism and parameter control law of the L-shaped groove.It is found that the L-shaped groove can guide the skewed inlet endwall boundary layer towards the streamwise direction due to its confinement effect,thereby delaying the onset of corner separation and reducing the size of ring vortex.As a result,the aerodynamic performance of the compressor is enhanced.Furthermore,the groove depth and groove width play a significant role in controlling endwall flow among the three L-shaped groove design parameters.The larger groove depth and smaller groove width enhance the capability of the streamwise groove to constrain the endwall boundary layer,leading to a greater reduction in endwall loss.展开更多
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
文摘The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the two or three stage pressure ratio is analyzed in two cases of constant heat transfer rate for the inter cooler or constant inter stage inlet temperature, based on the minimum of the sum of theoretical compression power at each stage about a multi stage reciprocating compressor. Furthermore, with an example of two stage compressor the influence on the sum of the power of each stage is analyzed when practical pressure ratio deviates from the optimum value. It is obtained that under different cooling conditions the optimum pressure ratio distribution of the multi stage compression is various, and the change of the optimum pressure ratio within a small range has little influence on the sum of the power each stage. For the two stage compression, this range can be represented as ε 1=(0 96～1 06)ε 1j .
基金financial support from the National Natural Science Foundation of China(Nos.51876022 and 51836008)
文摘This study numerically investigated a single stage centrifugal compressor "Radiver" with a wedge diffuser and several tandem-designed impellers to explore the flow phenomena within the tandem impeller and the potential to enhance compressor performance.The results demonstrate that tandem design and clocking fraction(ks)significantly affects the compressor performance.The compressor stage with tandem impellers of Series A of boundary layer growth interruption alone are observed to have a widely operating range but efficiency and total pressure ratio penalty compared with that of conventional impeller.The tandem impeller with at least the same impeller efficiency as the conventional design is considered as a critical design criteria so that further modification process based on the flow characteristic of tandem impeller is necessary.In order to restrain the inducer wake and exducer shock losses,parameters modification of blade angle and thickness distributions are necessary and the modified tandem impeller of Series B is obtained.The modified tandem impeller with 25%clocking arrangement shows an 8.45%stall margin increase and maintains the total pressure ratio and efficiency as the conventional design,which proves the potential of tandem impeller to improve compressor stage performance.It is noteworthy that the tandem impellers of Radiver have not shown obviously balanced exit flow field and the fundamental mechanism of stall margin extending of tandem impeller lies on the improved impeller/diffuser matching performance resulting from the incidence angle variation at diffuser inlet.
基金Supported by National Natural Science Foundation of China(Grant No.51275452)Zhejiang Provincical Natural Science Foundation of China(Grant No.LY14E050021)Commonweal Technology Project of Science and Technology Department of Zhejiang Province,China(Grant No.2015C31071)
文摘The resistance torque of a piston stage II com- pressor generates strenuous fluctuations in a rotational period, and this can lead to negative influences on the working performance of the compressor. To restrain the strenuous fluctuations in the piston stage II compressor, a variable duty-cycle control method based on the resistance torque is proposed. A dynamic model of a stage II com- pressor is set up, and the resistance torque and other characteristic parameters are acquired as the control tar- gets. Then, a variable duty-cycle control method is applied to track the resistance torque, thereby improving the working performance of the compressor. Simulated results show that the compressor, driven by the proposed method, requires lower current, while the rotating speed and the output torque remain comparable to the traditional vari- able-frequency control methods. A variable duty-cycle control system is developed, and the experimental results prove that the proposed method can help reduce the specific power, input power, and working noise of the compressor to 0.97 kW.m-3.min-1, 0.09 kW and 3.10 dB, respectively, under the same conditions of discharge pressure of 2.00 MPa and a discharge volume of 0.095 m3/rain. The proposed variable duty-cycle control method tracks the resistance torque dynamically, and improves the working performance of a Stage II Compressor. The pro- posed variable duty-cycle control method can be applied to other compressors, and can provide theoretical guidance for the compressor.
基金financially supported by the National Natural Science Foundation of China(No.52176045)the National Science and Technology Major Project of China(No.J2019-I-0011-0011)。
文摘To investigate the control effect and flow mechanism of the L-shaped endwall groove on corner separation in the real compressor stage,a single stage axial flow compressor is selected as the research object and the L-shaped grooves are introduced on the stator casing side.First,the experimental measurement is conducted on the optimal L-shaped groove obtained through a full factorial experimental design,and the results demonstrate that the optimal groove has a great control over the endwall flow.Moreover,the peak efficiency is improved by 0.9%and the stall margin is increased by 4.46%.Then,the flow field visualization of numerical results and analysis of variance method are employed to analyze the control mechanism and parameter control law of the L-shaped groove.It is found that the L-shaped groove can guide the skewed inlet endwall boundary layer towards the streamwise direction due to its confinement effect,thereby delaying the onset of corner separation and reducing the size of ring vortex.As a result,the aerodynamic performance of the compressor is enhanced.Furthermore,the groove depth and groove width play a significant role in controlling endwall flow among the three L-shaped groove design parameters.The larger groove depth and smaller groove width enhance the capability of the streamwise groove to constrain the endwall boundary layer,leading to a greater reduction in endwall loss.
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.
