High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model c...High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model considering the difference of wedge transmission's radial deformation between low-speed stage and medium-to-high-speed stage,the friction forces of chuck transmission,and the compressibility of hydraulic oil in rotary hydraulic cylinders.A corrected model of gripping force loss is also established for power chucks with asymmetric stiffness.The model is verified by experiment results.It is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping force increases with the rotational speed increasing at medium and high speed stages.Besides,the loss coefficients of gripping force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed.For wedge power chucks with small wedge angel(α<20°) and ordinary lubrication(μ0>0.06),the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed stage.For wedge power chucks with larger wedge angel(α>20°) or low friction coefficient(μ0<0.06),the wedge transmissions cannot self-lock at high speed stage,and the gripping force loss at the high speed stage is related to the hydraulic lock and hydraulic oil in the rotary hydraulic cylinder;the local loss coefficients of gripping force at the third stage is about 1.75 to 2.13 times that at the second stage.This work is helpful to understand the mechanism of the gripping force loss thoroughly and to optimize power chucks.展开更多
The effects of the vortex generator jet(VGJ)attached at the endwall on the corner separation/stall control are investigated by numerical simulation in a high-turning linear compressor cascade. The results show that th...The effects of the vortex generator jet(VGJ)attached at the endwall on the corner separation/stall control are investigated by numerical simulation in a high-turning linear compressor cascade. The results show that the corner separation could be reduced significantly, which results in a wider operation range as well as a more uniform exit flow angle and total pressure profile. At the near-stall operation point, the maximum relative reduction of the total pressure loss is up to 32.5%,, whereas the jet mass ratio is less than 0.4%,. Based on the analysis of the detailed flow structure, three principal effects of the VGJ on the endwall cross flow and corner separation are identified. One is to increase the tangential velocity component opposite to cross flow, thus inhibiting the endwall secondary flow near the jet exit. The second is to suppress the pitchwise extension of the passage vortex as an air fence. The third is to sweep the low energy fluids towards the mainstream on the up-washed side and to transport the mainstream fluids to the endwall to reenergize the boundary layer on the down-washed side.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 50875234)the National Science and Technology Support Program of China (Grant No. 2006BAF01B09-7)
文摘High speed power chucks are important function units in high speed turning.The gripping force loss is the primary factor limiting the rotational speed of high-speed power chucks.This paper proposes a piecewise model considering the difference of wedge transmission's radial deformation between low-speed stage and medium-to-high-speed stage,the friction forces of chuck transmission,and the compressibility of hydraulic oil in rotary hydraulic cylinders.A corrected model of gripping force loss is also established for power chucks with asymmetric stiffness.The model is verified by experiment results.It is helpful to use the piecewise model to explain the experimental phenomenon that the overall loss coefficient of gripping force increases with the rotational speed increasing at medium and high speed stages.Besides,the loss coefficients of gripping force at each stage during speeding up and the critical rotational speed between two adjacent stages are discussed.For wedge power chucks with small wedge angel(α<20°) and ordinary lubrication(μ0>0.06),the local loss coefficient of gripping force at the low speed stage is about 70% of that at the medium to high speed stage.For wedge power chucks with larger wedge angel(α>20°) or low friction coefficient(μ0<0.06),the wedge transmissions cannot self-lock at high speed stage,and the gripping force loss at the high speed stage is related to the hydraulic lock and hydraulic oil in the rotary hydraulic cylinder;the local loss coefficients of gripping force at the third stage is about 1.75 to 2.13 times that at the second stage.This work is helpful to understand the mechanism of the gripping force loss thoroughly and to optimize power chucks.
基金Supported by the National Natural Science Foundation of China(No.51306042)
文摘The effects of the vortex generator jet(VGJ)attached at the endwall on the corner separation/stall control are investigated by numerical simulation in a high-turning linear compressor cascade. The results show that the corner separation could be reduced significantly, which results in a wider operation range as well as a more uniform exit flow angle and total pressure profile. At the near-stall operation point, the maximum relative reduction of the total pressure loss is up to 32.5%,, whereas the jet mass ratio is less than 0.4%,. Based on the analysis of the detailed flow structure, three principal effects of the VGJ on the endwall cross flow and corner separation are identified. One is to increase the tangential velocity component opposite to cross flow, thus inhibiting the endwall secondary flow near the jet exit. The second is to suppress the pitchwise extension of the passage vortex as an air fence. The third is to sweep the low energy fluids towards the mainstream on the up-washed side and to transport the mainstream fluids to the endwall to reenergize the boundary layer on the down-washed side.
