Consider a foliate Rn-action on a compact connected foliated manifold (M,F). Let mand r be the codimension of F and the (transverse)rank of (M,F)respectively. Suppose r<m.In this paper we prove that either there ex...Consider a foliate Rn-action on a compact connected foliated manifold (M,F). Let mand r be the codimension of F and the (transverse)rank of (M,F)respectively. Suppose r<m.In this paper we prove that either there exists an orbit of the Rn-action of transverse dimension< (m + r)/2 or F can be arbitrarily approached by foliations with rank≥r+1. Moreover weshow that this kind of orbits exists in the following three cases: if F is Riemannian ;when all itsleaves are closed or if X(M)≠0(then r=0).On the other hand all foliate Rn-action on (S3,F) has a fixed leaf if dimF=1.Our result generalies a well known Lima's theorem about Rn-actions on surfaces.展开更多
This study investigates the effects of blade tip geometry on the flow field of a turbine cascade at the incidence angle of 0 degree experimentally. The tests were performed in a low-speed turbine cascade wind tunnel. ...This study investigates the effects of blade tip geometry on the flow field of a turbine cascade at the incidence angle of 0 degree experimentally. The tests were performed in a low-speed turbine cascade wind tunnel. The Reynolds number based on the blade chord was about 172300 at the exit. Traverses of the exit flow field were made in order to measure the overall performance. The effects of using fiat tip and grooved tip with a chord-wise channel were studied. The case with the flat tip is referenced as the baseline. The tip clearances are all 1 mm measuring 0.84 percent of the blade span. The depth of channel is 2mm.The flow field at 10% chord downstream from the cascade trailing edge was measured at 38 span-wise positions and 26 pitch-wise positions using a mini five-hole pressure probe. The static pressure distribution on the tip end wall is measured at 16 pitch-wise stations and 17 chord-wise stations. Results show that there exists great pressure gradient in the pressure side for the fiat tip and the pressure side squealer tip, which means strong leakage flow. The pressure gradient from the pressure side to the suction side is greatly decreased for the grooved tip, and the resulting leakage flow is weaker. The core of the leakage vortex moves closer to the suction side for the pressure side squealer tip and farther away from the suction side for the suction side squealer tip. The pressure side squealer has little advantages over the fiat tip in improving the flow capacity and reducing the overall losses. The suction side squealer tip and grooved tip can effectively decrease the intensity of the tip leakage vortex, improve the flow capacity and reduce loss of the turbine cascade passage and the grooved tip performs the best.展开更多
文摘Consider a foliate Rn-action on a compact connected foliated manifold (M,F). Let mand r be the codimension of F and the (transverse)rank of (M,F)respectively. Suppose r<m.In this paper we prove that either there exists an orbit of the Rn-action of transverse dimension< (m + r)/2 or F can be arbitrarily approached by foliations with rank≥r+1. Moreover weshow that this kind of orbits exists in the following three cases: if F is Riemannian ;when all itsleaves are closed or if X(M)≠0(then r=0).On the other hand all foliate Rn-action on (S3,F) has a fixed leaf if dimF=1.Our result generalies a well known Lima's theorem about Rn-actions on surfaces.
基金funded by the National Natural Science Foundation of China, Grant No. 51161130525 and 51136003supported by the 111 Project, No. B07009
文摘This study investigates the effects of blade tip geometry on the flow field of a turbine cascade at the incidence angle of 0 degree experimentally. The tests were performed in a low-speed turbine cascade wind tunnel. The Reynolds number based on the blade chord was about 172300 at the exit. Traverses of the exit flow field were made in order to measure the overall performance. The effects of using fiat tip and grooved tip with a chord-wise channel were studied. The case with the flat tip is referenced as the baseline. The tip clearances are all 1 mm measuring 0.84 percent of the blade span. The depth of channel is 2mm.The flow field at 10% chord downstream from the cascade trailing edge was measured at 38 span-wise positions and 26 pitch-wise positions using a mini five-hole pressure probe. The static pressure distribution on the tip end wall is measured at 16 pitch-wise stations and 17 chord-wise stations. Results show that there exists great pressure gradient in the pressure side for the fiat tip and the pressure side squealer tip, which means strong leakage flow. The pressure gradient from the pressure side to the suction side is greatly decreased for the grooved tip, and the resulting leakage flow is weaker. The core of the leakage vortex moves closer to the suction side for the pressure side squealer tip and farther away from the suction side for the suction side squealer tip. The pressure side squealer has little advantages over the fiat tip in improving the flow capacity and reducing the overall losses. The suction side squealer tip and grooved tip can effectively decrease the intensity of the tip leakage vortex, improve the flow capacity and reduce loss of the turbine cascade passage and the grooved tip performs the best.
