Abstract:This paper describes unsteady flow phenomena of a two-stage transonic axial compressor, especially the flow field in the first stator. The stator blade with highly loaded is likely to cause a flow separation on the hub, so-called hub-corner separation. The flow mechanism of the hub-corner separation in the first stator is investigated in detail using a large-scale detached eddy simulation (DES) conducted for its full-annulus and full-stage with approximately 4.5 hundred million computational cells. The detaile… Show more
“…The cross flow which accumulated in the SS-corner downstream of focus F1 (colored by orange) also spined around the centerline of the CSV, inducing the climb flow on the SS. The similar vortical structure was also observed in numerical results obtained by Saito et al 27 Figure 11.Formation mechanism of the corner separation vortex on the SS-side.…”
Section: Resultssupporting
confidence: 85%
“…Since the limited region of detached reverse flow appeared inside the vortical flow, which is usually regarded as a feature of the vortex breakdown, it can be inferred that under the adverse pressure gradient in the blade passage, the SS-side CSV might suffer the vortex breakdown like the observation in numerical results of Saito et al 27…”
Section: Resultsmentioning
confidence: 83%
“…The horn-like vortex has the similar appearance with ring-like vortex mentioned in studies of Schulz et al 17 and Yu et al, 19 but sheds downstream periodically, leading to the pressure fluctuation in the machine. By means of an in-house vortex identification algorithm, Saito et al 27 extracted the vortex centerlines in a compressor stator with a partial hub clearance. They found that the corner separation flow was characterized by a streamwise corner separation vortex with one end attached on the hub and another one stretched downstream.…”
In aero-engine compressors, corner separations cause blockage, loss generation, and flow instabilities. The aim of the current study is to gain better knowledge of the vortical structures in corner separation flows and their resultant blockage and loss. Numerical simulations at different incidences have been performed for a high-speed linear compressor cascade. First, vortical structures have been visualized with the help of the Q-criterion and eigenvector method, and those associated with the corner separation have been focused on. It was found that the corner separation occurring on either the pressure surface or suction surface corner region was characterized by a large-scale streamwise vortex, named as the corner separation vortex in this paper. The pressure-side corner separation vortex is observed at a great negative incidence initiated from a focus point on the pressure surface, while the suction-side corner separation vortex observed at all concerned incidences originated from a focus on the endwall near the suction surface. Then, the mechanism by which corner separation vortices resulted in blockage and loss has been uncovered. The results showed that low-momentum fluids inside the core region of corner separation vortices led to the flow blockage and the viscous friction between them, and mainstream was responsible for the entropy generation. One major contributor of low-momentum fluids in the suction-side corner region was an off-wall reversed-flow region which was attributed to the breakdown of the suction-side corner separation vortex. Finally, multi-vortex structures in the leading region of the suction-side corner separation at two high positive incidences have been analyzed. It was found that the horseshoe vortex influenced the formation of the suction-side corner separation vortex, which induced a multi-vortex structure, and prevented the onset location of suction-side corner separation vortex from moving upstream with the increased incidence.
“…The cross flow which accumulated in the SS-corner downstream of focus F1 (colored by orange) also spined around the centerline of the CSV, inducing the climb flow on the SS. The similar vortical structure was also observed in numerical results obtained by Saito et al 27 Figure 11.Formation mechanism of the corner separation vortex on the SS-side.…”
Section: Resultssupporting
confidence: 85%
“…Since the limited region of detached reverse flow appeared inside the vortical flow, which is usually regarded as a feature of the vortex breakdown, it can be inferred that under the adverse pressure gradient in the blade passage, the SS-side CSV might suffer the vortex breakdown like the observation in numerical results of Saito et al 27…”
Section: Resultsmentioning
confidence: 83%
“…The horn-like vortex has the similar appearance with ring-like vortex mentioned in studies of Schulz et al 17 and Yu et al, 19 but sheds downstream periodically, leading to the pressure fluctuation in the machine. By means of an in-house vortex identification algorithm, Saito et al 27 extracted the vortex centerlines in a compressor stator with a partial hub clearance. They found that the corner separation flow was characterized by a streamwise corner separation vortex with one end attached on the hub and another one stretched downstream.…”
In aero-engine compressors, corner separations cause blockage, loss generation, and flow instabilities. The aim of the current study is to gain better knowledge of the vortical structures in corner separation flows and their resultant blockage and loss. Numerical simulations at different incidences have been performed for a high-speed linear compressor cascade. First, vortical structures have been visualized with the help of the Q-criterion and eigenvector method, and those associated with the corner separation have been focused on. It was found that the corner separation occurring on either the pressure surface or suction surface corner region was characterized by a large-scale streamwise vortex, named as the corner separation vortex in this paper. The pressure-side corner separation vortex is observed at a great negative incidence initiated from a focus point on the pressure surface, while the suction-side corner separation vortex observed at all concerned incidences originated from a focus on the endwall near the suction surface. Then, the mechanism by which corner separation vortices resulted in blockage and loss has been uncovered. The results showed that low-momentum fluids inside the core region of corner separation vortices led to the flow blockage and the viscous friction between them, and mainstream was responsible for the entropy generation. One major contributor of low-momentum fluids in the suction-side corner region was an off-wall reversed-flow region which was attributed to the breakdown of the suction-side corner separation vortex. Finally, multi-vortex structures in the leading region of the suction-side corner separation at two high positive incidences have been analyzed. It was found that the horseshoe vortex influenced the formation of the suction-side corner separation vortex, which induced a multi-vortex structure, and prevented the onset location of suction-side corner separation vortex from moving upstream with the increased incidence.
“…Many scholars [1][2][3][4][5][6] have made unremitting efforts to reduce the flow loss and increase the compressor stability margin, such as optimization design, 7,8 blade/end-wall structure optimization, [9][10][11] and flow control technology. 12,13 The application of these methods improves the compressor performance. Flow control technology is widely used and developed because of its remarkable effect in improving the compressor performance, although the technology usually increases the weight of compressor.…”
The axial location of full-span boundary layer suction is studied to explore the influences of suction slot on the cascade performance. At the design condition, the slot with 50% axial location shows a superior capability to reduce the total pressure loss. At the near stall condition, the more upstream of the suction slot is moved, the more total pressure loss is reduced, and the suction slot with a location of 0.7 axial chord length cannot effectively reduces the total pressure loss in all conditions. Moreover, a rearranged segmented suction slot according to the distribution characteristics of the flow reversal region is developed and compared with full-span boundary layer suction. The segmented suction slot shows significant advantages in delaying the stall occurrence, and the stall point is delayed from 7.9° to 10.0° compared with the baseline. According to a quantitative analysis method selected to measure the performances of flow control technologies, the wake loss is significantly reduced by the segmented suction slot. Finally, a set of micro-vortex generator is introduced in the cascade with a segmented suction slot, and the conclusion indicates that the portion near the end-wall is very effective to reduce the flow loss.
“…Many scholars [4][5][6][7] have made unremitting efforts to reduce the flow loss and extend the compressor stability margin by some active and passive flow control devices. [8][9][10][11] Although the application of these methods improves the compressor performance, most of the flow control methods usually increase the weight of compressor and depend on external energy, [12][13][14] which brings a certain economic burden on the aeroengine. Therefore, it is necessary to develop more economical flow control device based on the analysis of the three-dimensional flow structure and the development of vortices in compressors at different conditions.…”
The development of boundary layer affects the compressor cascade performance to a certain extent. Therefore, the compound lean and little blades are selected to redistribute the boundary layer, and the influences of these two flow control technologies on the axial compressor cascade performance are further studied. The calculated results showed that appropriate high pressure region on the blade suction surface near the end-wall is helpful to reduce the total pressure loss of compressor cascade, which can be achieved by positive lean technique. Meanwhile, the maximum stable operation boundary can be expanded by the application of positive leaned blade. On the other hand, the introduction of negative lean angle not only increases the total pressure loss of cascade, but reduces the stable operation range. As the little blades are introduced in the negative lean compressor cascade, the stable operation range is significantly improved by the introduction of little blades. Especially the cascade with −10° lean angle, the maximum stable operation boundary is increased from 1° to 6°. In the positive lean compressor cascade, although more low-energy fluid is accumulated on the blade suction surface near the mid-span, the little blades still show an active role in reducing the total pressure loss and expending the stable operation range, because the influence range of induced vortex reaches 30%span. The results provide a reference for improving the aerodynamic performance of compressor stator, especially when more low-energy fluid is blocked in the range near the mid-span.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
