The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses...The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000.Two slotted schemes for the boundary layer of the endwall were designed(Plan A and Plan B),and the effects of suction mass flow on secondary flow were studied.The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed.The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids.Plans A and B significantly reduced the secondary kinetic energy by 44.2%and 36.9%,respectively,compared with the baseline cascade at the suction mass flow ratios of 1%.With an increase in the mass flow ratio of suction,the secondary flow was gradually reduced in both Plans A and B.It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex.Under unsteady wakes,the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2%for Plan A,because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.展开更多
Experiment measurement is adapted to study the secondary flow of turbine.The subsonic stator experiment flow tunnel is set up.Two different inlet velocities and three different stator heights are applied.The method of...Experiment measurement is adapted to study the secondary flow of turbine.The subsonic stator experiment flow tunnel is set up.Two different inlet velocities and three different stator heights are applied.The method of a rotating slanted hotwire is introduced to measure the stator outlet three-dimensional flow field.The procedure for solving the mean three-dimensional velocity component involving the least-squares technique can be accomplished via the LSQNONLIN optimization function of Matlab.Under different work conditions,the stator outlet secondary flow is more intense at higher inlet flux.Moreover,the shortest stator height will lead to the most intense secondary flow,which gains the largest axial velocity component(w) and radial velocity component (u),but the smallest circumferential velocity component(v).展开更多
The nature of the three-dimensional transition arising in the flow past a cylinder is investigated by apply- ing the Lifschitz-Hameiri theory along special Lagrangian trajectories existing in its wake. Results show th...The nature of the three-dimensional transition arising in the flow past a cylinder is investigated by apply- ing the Lifschitz-Hameiri theory along special Lagrangian trajectories existing in its wake. Results show that the yon K^rm^n street is unstable with regard to short-wavelength perturbations. The asymptotic analysis predicts the possible existence of both synchronous （as modes A and B） and asynchronous （as mode C） instabilities, each associated to specific Lagrangian orbits. The proposed study provides useful qualitative information on the origin of the different modes but no quantitative agreement between the growth rates predicted by the asymptotic analysis and by a global stability analysis is observed. The reasons for such mismatch are briefly discussed and possible improvements to the present analysis are sug- gested.展开更多
基金support for this work was provided by the National Natural Science Foundation of China(No.52206060)the National Science and Technology Major Project of China(Nos.J2019-Ⅱ-0021-0042 and J2019-Ⅱ-0002-0022).
文摘The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000.Two slotted schemes for the boundary layer of the endwall were designed(Plan A and Plan B),and the effects of suction mass flow on secondary flow were studied.The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed.The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids.Plans A and B significantly reduced the secondary kinetic energy by 44.2%and 36.9%,respectively,compared with the baseline cascade at the suction mass flow ratios of 1%.With an increase in the mass flow ratio of suction,the secondary flow was gradually reduced in both Plans A and B.It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex.Under unsteady wakes,the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2%for Plan A,because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.
文摘Experiment measurement is adapted to study the secondary flow of turbine.The subsonic stator experiment flow tunnel is set up.Two different inlet velocities and three different stator heights are applied.The method of a rotating slanted hotwire is introduced to measure the stator outlet three-dimensional flow field.The procedure for solving the mean three-dimensional velocity component involving the least-squares technique can be accomplished via the LSQNONLIN optimization function of Matlab.Under different work conditions,the stator outlet secondary flow is more intense at higher inlet flux.Moreover,the shortest stator height will lead to the most intense secondary flow,which gains the largest axial velocity component(w) and radial velocity component (u),but the smallest circumferential velocity component(v).
文摘The nature of the three-dimensional transition arising in the flow past a cylinder is investigated by apply- ing the Lifschitz-Hameiri theory along special Lagrangian trajectories existing in its wake. Results show that the yon K^rm^n street is unstable with regard to short-wavelength perturbations. The asymptotic analysis predicts the possible existence of both synchronous （as modes A and B） and asynchronous （as mode C） instabilities, each associated to specific Lagrangian orbits. The proposed study provides useful qualitative information on the origin of the different modes but no quantitative agreement between the growth rates predicted by the asymptotic analysis and by a global stability analysis is observed. The reasons for such mismatch are briefly discussed and possible improvements to the present analysis are sug- gested.
