Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until no...Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until now.To conquer this issue,unsteady full-annulus simulations were conducted to investigate the stall mechanism of a mixed-flow compressor with and without axial slot casing treatment(ASCT).The circumferential propagating speed of spike inception resolved by the numerical approach is 87.1%of the shaft speed,which is identical to the test data.The numerical results confirmed that the mixed-flow compressor fell into rotating stall via spike-type with and without ASCT.The flow structure of the spike inception was investigated at 50%design rotational speed.Instantaneous static pressure traces extracted upstream of the leading edge had shown a classic spiky wave.Furthermore,it was found that with and without ASCT,the mixed-flow compressor stalled through spike with the characteristic of tip leakage spillage at leading edge and tip leakage backflow from trailing edge,which is different from a fraction of the centrifugal compressor.The resultant phenomenon provides conoborating evidence for that unlike in axial-flow compressor,the addition of ASCT does not change the stall characteristics of the mixed-flow compressor.The flow structure that induced spike inception with ASCT is similar to the case with smooth casing.In the throttling process,tip leakage flow vortex had been involved in the formation of tornado vortices,with one end at the suction side,and the other end at the casing-side.The low-pressure region relevant to the downward spike is caused by leading-edge separation vortex or tornado vortex.The high-pressure region relevant to the upward spike is induced by blockage from the passage vortex.These results not only can provide guidance for the design of casing treatment in mixed-flow compressor,but also can pave the way for the stall waring in the highly-loaded compressors of next-generation aeroengines.展开更多
Casing treatments(CT) can effectively extend compressors flow ranges with the expense of efficiency penalty. Compressor efficiency is closely linked to loss. Only revealing the mechanisms of loss generation can design...Casing treatments(CT) can effectively extend compressors flow ranges with the expense of efficiency penalty. Compressor efficiency is closely linked to loss. Only revealing the mechanisms of loss generation can design a CT with high aerodynamic performance. In the paper, a highly-loaded mixed-flow compressor with tip clearance of 0.4 mm was numerically studied at a rotational speed of 30,000 r/min to reveal the effects of axial slot casing treatment(ASCT) on the loss mechanisms in the compressor. The results showed that both isentropic efficiency and stall margin were improved significantly by the ASCT. The local entropy generation method was used to analyze the loss mechanisms and to quantify the loss distributions in the blade passage. Based on the axial distributions of entropy generation rate, for both the cases with and without ASCT, the peak entropy generation rate increased in the rotor domain and decreased in the stator domain during throttling the compressor. The peak entropy generation in rotor was mainly caused by the tip leakage flow and flow separations near the rotor leading edge for the mixed-flow compressor no matter which casing was applied. The radial distributions of entropy generation rate showed that the reduction of loss in the rotor domain from 0.4 span to the rotor casing was the major reason for the efficiency improved by ASCT. The addition of ASCT exerted two opposite effects on the losses generated in the compressor. On the one hand, the intensity of tip leakage flow was weakened by the suction effect of slots, which alleviated the mixing effect between the tip leakage flow and main flow, and thus reduced the flow losses;On the other hand, the extra losses upstream the rotor leading edge were produced due to the shear effect and to the heat transfer. The aforementioned shear effect was caused by the different velocity magnitudes and directions, and the heat transfer was caused by temperature gradient between the injected flow and the incoming flow. For case with smooth casing(SC), 61.61% of the overall loss arose from tip leakage flow and casing boundary layer. When the ASCT was applied, that decreased to 55.34%. The loss generated by tip leakage flow and casing boundary layer decreased 20.54% relatively by ASCT.展开更多
The influence of Axial-Slot Casing Treatment(ASCT)on the performance and stability enhancement mechanisms of ASCT were experimentally and numerically investigated in a highspeed mixed-flow compressor under three diffe...The influence of Axial-Slot Casing Treatment(ASCT)on the performance and stability enhancement mechanisms of ASCT were experimentally and numerically investigated in a highspeed mixed-flow compressor under three different tip clearances.Unsteady simulations showed the compressor stalled through end-wall stall route,i.e.the spike stall inception originating from rotor tip region,which was validated by dynamical measurements.When the ASCT was applied,greater than 20%of Stall Margin Improvement(SMI)could be achieved for the compressor under each tip clearance size.The streamwise velocity contours and flow structures in the tip region and axial slots were deeply analyzed to explore how the so called‘‘suction and injection effects"generated by the ASCT manipulate tip clearance flow and enhance the stability of compressor under different tip clearances.It was found that the dominant stability enhancement mechanisms of ASCT varies with tip clearance size for the mixed-flow compressor.(A)For the small tip clearance,the dominant mechanism of stability enhancement is the blockage reduction generated in the blade passage by the suction effect of ASCT.(B)For the large tip clearance,the injection effect of the ASCT is the dominant mechanism of stability enhancement with ASCT,which plays the leading role in delaying the spillage of incoming/tip leakage flow interface at the rotor Leading Edge(LE)plane.展开更多
A series of steady and unsteady numerical calculations of the internal flow in mixed-flow pumps with three different specific speeds were carried out based on the N-S equation coupled with the standard k-εturbulence ...A series of steady and unsteady numerical calculations of the internal flow in mixed-flow pumps with three different specific speeds were carried out based on the N-S equation coupled with the standard k-εturbulence model under different operating conditions to investigate the relationship between the impeller specific speed and the pump performance as well as pressure pulsations.Meanwhile,the pump performance and pressure pulsations inside the mixed-flow pump with three different specific speeds were also analyzed and compared with the corresponding test data.From the results,the averaged deviations between the predicted and tested head among different impellers are below 5%,and with respect to the equivalent impeller specific speeds of 280 and 260,the values are 4.30%and 3.69%,respectively.For all the impeller schemes,the best efficiency point of the mixed-flow pump is found at the flow rate of 1.2 Q_(d) and the higher head deviation occurs at lower flow rates.Especially,it can be found that the specific speed has a slight effect on the pressure fluctuation in the impellers.Eventually,it is determined that the pump performance curves calculated by numerical simu-lations have good agreement with the relevant experimental results,which verifies that the numerical methods used in the present study are accurate to a certain extent.Furthermore,the results also provide some references to the pressure pulsation analysis and the performance improvement of the mixed-flow pump design.展开更多
Accurate and efficient prediction of the aerodynamic performance and flow details of axial-flow com-pressors is of great engineering application value for the aerodynamic design and flow control of axial-flow compres-...Accurate and efficient prediction of the aerodynamic performance and flow details of axial-flow com-pressors is of great engineering application value for the aerodynamic design and flow control of axial-flow compres-sors.In this work,a delayed detached eddy simulation method is developed and applied to numerically simulate the tur-bulent channel flow and the aerodynamic performance of NASA Rotor 35.Several acceleration techniques including parallel implementation are also used to speed up the iteration convergence.The mean velocity distribution and Reyn-olds stress distribution in the boundary layer of turbulent channel flow and the aerodynamic performance curve of NASA Rotor 35 are predicted.The good agreement between the present delayed detached eddy simulation results and the available direct numerical simulation results or experimental data confirms the effectiveness of the developed meth-od in the accurate and efficient prediction of complex flow in turbomachinery.展开更多
基金The authors are grateful for the support of National Natural Science Foundation of China for the grant with Project No.51636001,No.51790510,and No.51922098the National Science and Technology Major Project(2017-11-0004-0017,2017-H-005-0018)The authors would also appreciate the kind help of Prof.Seume,and the German Research Foundation(DFG)for supporting the experiments as part of the Collaborative Research Centre 880(Sonderforschungsbereich SFB 880).
文摘Casing treatment is an effective technique in extending stall margin of axial and centrifugal compressor.However,its impacts on the stall behaviour of mixed-flow compressor are still not completely understood until now.To conquer this issue,unsteady full-annulus simulations were conducted to investigate the stall mechanism of a mixed-flow compressor with and without axial slot casing treatment(ASCT).The circumferential propagating speed of spike inception resolved by the numerical approach is 87.1%of the shaft speed,which is identical to the test data.The numerical results confirmed that the mixed-flow compressor fell into rotating stall via spike-type with and without ASCT.The flow structure of the spike inception was investigated at 50%design rotational speed.Instantaneous static pressure traces extracted upstream of the leading edge had shown a classic spiky wave.Furthermore,it was found that with and without ASCT,the mixed-flow compressor stalled through spike with the characteristic of tip leakage spillage at leading edge and tip leakage backflow from trailing edge,which is different from a fraction of the centrifugal compressor.The resultant phenomenon provides conoborating evidence for that unlike in axial-flow compressor,the addition of ASCT does not change the stall characteristics of the mixed-flow compressor.The flow structure that induced spike inception with ASCT is similar to the case with smooth casing.In the throttling process,tip leakage flow vortex had been involved in the formation of tornado vortices,with one end at the suction side,and the other end at the casing-side.The low-pressure region relevant to the downward spike is caused by leading-edge separation vortex or tornado vortex.The high-pressure region relevant to the upward spike is induced by blockage from the passage vortex.These results not only can provide guidance for the design of casing treatment in mixed-flow compressor,but also can pave the way for the stall waring in the highly-loaded compressors of next-generation aeroengines.
基金financial support from National Key R&D Program of China under Grant NO.2018YFB0606100the National Natural Science Foundation of China under Grant NO. 51790510 and NO. 51727810
文摘Casing treatments(CT) can effectively extend compressors flow ranges with the expense of efficiency penalty. Compressor efficiency is closely linked to loss. Only revealing the mechanisms of loss generation can design a CT with high aerodynamic performance. In the paper, a highly-loaded mixed-flow compressor with tip clearance of 0.4 mm was numerically studied at a rotational speed of 30,000 r/min to reveal the effects of axial slot casing treatment(ASCT) on the loss mechanisms in the compressor. The results showed that both isentropic efficiency and stall margin were improved significantly by the ASCT. The local entropy generation method was used to analyze the loss mechanisms and to quantify the loss distributions in the blade passage. Based on the axial distributions of entropy generation rate, for both the cases with and without ASCT, the peak entropy generation rate increased in the rotor domain and decreased in the stator domain during throttling the compressor. The peak entropy generation in rotor was mainly caused by the tip leakage flow and flow separations near the rotor leading edge for the mixed-flow compressor no matter which casing was applied. The radial distributions of entropy generation rate showed that the reduction of loss in the rotor domain from 0.4 span to the rotor casing was the major reason for the efficiency improved by ASCT. The addition of ASCT exerted two opposite effects on the losses generated in the compressor. On the one hand, the intensity of tip leakage flow was weakened by the suction effect of slots, which alleviated the mixing effect between the tip leakage flow and main flow, and thus reduced the flow losses;On the other hand, the extra losses upstream the rotor leading edge were produced due to the shear effect and to the heat transfer. The aforementioned shear effect was caused by the different velocity magnitudes and directions, and the heat transfer was caused by temperature gradient between the injected flow and the incoming flow. For case with smooth casing(SC), 61.61% of the overall loss arose from tip leakage flow and casing boundary layer. When the ASCT was applied, that decreased to 55.34%. The loss generated by tip leakage flow and casing boundary layer decreased 20.54% relatively by ASCT.
基金the National Science Foundation of China(Nos.51676184,51636001 and 51922098)the National Science and Technology Major Project(Nos.2017-II-00040017 and 2017-II-0005-0018)the National Key R&D Program of China(No.2018YFB0606100)。
文摘The influence of Axial-Slot Casing Treatment(ASCT)on the performance and stability enhancement mechanisms of ASCT were experimentally and numerically investigated in a highspeed mixed-flow compressor under three different tip clearances.Unsteady simulations showed the compressor stalled through end-wall stall route,i.e.the spike stall inception originating from rotor tip region,which was validated by dynamical measurements.When the ASCT was applied,greater than 20%of Stall Margin Improvement(SMI)could be achieved for the compressor under each tip clearance size.The streamwise velocity contours and flow structures in the tip region and axial slots were deeply analyzed to explore how the so called‘‘suction and injection effects"generated by the ASCT manipulate tip clearance flow and enhance the stability of compressor under different tip clearances.It was found that the dominant stability enhancement mechanisms of ASCT varies with tip clearance size for the mixed-flow compressor.(A)For the small tip clearance,the dominant mechanism of stability enhancement is the blockage reduction generated in the blade passage by the suction effect of ASCT.(B)For the large tip clearance,the injection effect of the ASCT is the dominant mechanism of stability enhancement with ASCT,which plays the leading role in delaying the spillage of incoming/tip leakage flow interface at the rotor Leading Edge(LE)plane.
基金National Natural Science Foundation of China(51976078)Senior Personnel Scientific Research Foundation of Jiangsu University:(15JDG073)Open Research Subject of Key Laboratory of Fluid and Power Machinery,Ministry of Education(szjj2016-065)。
文摘A series of steady and unsteady numerical calculations of the internal flow in mixed-flow pumps with three different specific speeds were carried out based on the N-S equation coupled with the standard k-εturbulence model under different operating conditions to investigate the relationship between the impeller specific speed and the pump performance as well as pressure pulsations.Meanwhile,the pump performance and pressure pulsations inside the mixed-flow pump with three different specific speeds were also analyzed and compared with the corresponding test data.From the results,the averaged deviations between the predicted and tested head among different impellers are below 5%,and with respect to the equivalent impeller specific speeds of 280 and 260,the values are 4.30%and 3.69%,respectively.For all the impeller schemes,the best efficiency point of the mixed-flow pump is found at the flow rate of 1.2 Q_(d) and the higher head deviation occurs at lower flow rates.Especially,it can be found that the specific speed has a slight effect on the pressure fluctuation in the impellers.Eventually,it is determined that the pump performance curves calculated by numerical simu-lations have good agreement with the relevant experimental results,which verifies that the numerical methods used in the present study are accurate to a certain extent.Furthermore,the results also provide some references to the pressure pulsation analysis and the performance improvement of the mixed-flow pump design.
基金National Science and Technology Major Project of China(No.2017-II 0006-0020)National Key Research and Development Project of China(2016YFB0200901)National Natural Science Foundation of China(51776154)。
文摘Accurate and efficient prediction of the aerodynamic performance and flow details of axial-flow com-pressors is of great engineering application value for the aerodynamic design and flow control of axial-flow compres-sors.In this work,a delayed detached eddy simulation method is developed and applied to numerically simulate the tur-bulent channel flow and the aerodynamic performance of NASA Rotor 35.Several acceleration techniques including parallel implementation are also used to speed up the iteration convergence.The mean velocity distribution and Reyn-olds stress distribution in the boundary layer of turbulent channel flow and the aerodynamic performance curve of NASA Rotor 35 are predicted.The good agreement between the present delayed detached eddy simulation results and the available direct numerical simulation results or experimental data confirms the effectiveness of the developed meth-od in the accurate and efficient prediction of complex flow in turbomachinery.
