The evolution of the flow topologies of 3D separations in the stator passage of an axial compressor stage

Proceedings of the Institution of Mechanical Engineers, Part A:

2015

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Complicated flows featuring with highly three-dimensionality and intense rotation/curvature in turbomachines have made the steady Reynolds-averaged Navier-Stokes (RANS) simulation very difficult. In this paper, based on the widely used xbased shear stress transport (SST) model, two modifications (one is denoted as shear stress transport model with curvature correction (SST-CC), the other is denoted as shear stress transport model with reattachment modification (SST-RM)) are assessed in predicting the tip leakage flow in the rotor passage and the three-dimensional separating flow in the stator passage of a low-speed axial compressor. Based on the comprehensive experimental data, including the compressor characteristics lines, inter-blade-row velocity profiles, and also detailed three-dimensional flows inside both rotor and stator passages, the abilities for capturing both compressor performance characteristics and specific flow details for simulations with different turbulence models were analyzed. The results indicate that the SST-CC model could simulate an approximate operating line with the one simulated by the SST model, which is very close to the experimental results, while the SST-RM model over-predicted the compressor pressure rise characteristics at all mass-flow-rate conditions. For the tip leakage flow inside the rotor passage and the three-dimensional separating flow inside the stator passage, the SST-RM model predicts a more accurate result, while for the outlet flow profile of the rotor and the stator passage the SST-CC model could simulate a more anastomotic result. In conclusion, the SST-RM model has advantage in predicting the flow fields within the blade rows, while the SST-CC model is adept in predicting the inter-row flow profiles. However, neither of them could simulate great comprehensive results in the investigated axial compressor.

Section: Stator Outletsupporting

confidence: 76%

Section: Experimental Setup and Layoutmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Assessment of curvature correction and reattachment modification into the shear stress transport model within the subsonic axial compressor simulations

Proceedings of the Institution of Mechanical Engineers, Part A:

2015

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“…In real compressors, some important influencing factors on the endwall 3D separation cannot be ignored, such as the rotor-stator interacting flow [8,9], the upstream cavity flow [10], the clocking effects [11], and the local flow bleeding [12]. Moreover, the behaviors of the endwall 3D separation flow could vary significantly as the operating conditions change, including mass-flow rate and rotating speed [1,[13][14][15]. Among the varied influencing factors in multistage environments, the rotor tip clearance flow always plays the most important role in compressor blade row matching [16].…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of the effect of rotor tip gaps on 3D separating flows inside the stator of a highly loaded compressor stage

Experimental Thermal and Fluid Science

et al. 2016

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Flow separations in compressor blade passages are common and can cause significant flow blockage and loss production. This paper investigates experimentally the three-dimensional (3D) flow separations in a highly loaded low-speed large-scale compressor facility. Oil flow visualizations, stereoscopic particle image velocimetry (SPIV), and five-hole probe measurements are conducted at certain conditions from the near-chock to near-stall condition along the compressor operating line. The 3D separation and vortex flow structures in the stator at different operating conditions are analyzed. By changing the size of the rotor tip gap, six groups of oil-flow pictures are obtained to study the effect of the rotor gaps on the 3D separating flows in the downstream stator. The variation of the corner separation scale is almost linear with the rotor tip gap size. Along the compressor operating line, four typical 3D flow structures are found inside the stator passage. Between the second typical 3D flow structure and the third typical 3D flow structure, an unstable stage exists on the compressor operating line; during this stage, the hub corner separation becomes an open separation from the closed type. A smaller rotor tip gap corresponds to an earlier unstable stage. Finally, a critical rotor tip blockage state usually existed for the transform of corner separation types at a certain rotor tip gap configuration. This discovery is valuable for the study of multistage compressor matching problems at off-design conditions.

“…Detailed experimental results also showed that the low efficiency and even stall limit of Stage-A should be determined by the serious near-hub corner separation that appeared in the stator passage. [33][34][35] In Stage-C, in order to achieve the high design loading coefficient, the rotor was designed with a diffusion factor of about 0.52 at the mid-span at the design condition; however, the diffusion factor at the two ends of the rotor blade was reduced to ensure high flow efficiency could be obtained. As for the stator in Stage-C, the diffusion factor is about 0.48 at the mid-span at the design condition.…”

Section: Radial Variation In Through-flow Parametersmentioning

confidence: 99%

Research on three-dimensional blade designs in an ultra-highly loaded low-speed axial compressor stage: Design and numerical investigations

Advances in Mechanical Engineering

2016

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To realize whether the rules for controlling the blade three-dimensional stacking line in a compressor with conventional loading level could be used for the design of a highly loaded compressor, the effects of three-dimensional bladings in an ultra-highly loaded compressor stage were studied numerically. A low-speed compressor stage (Stage-C) with ultra-high loading coefficient (=0.52) was designed at first. Due to the well-chosen through-flow design parameters accompanied using controlled diffusion airfoil with spikeless leading edge, Stage-C achieved the design goal of loading level with high peak efficiency of about 0.89. However, all the blades in Stage-C were designed with radial stacking lines. And then, Stage-C-three-dimensional was redesigned with non-radial stacking blades based on Stage-C, after which 1-point compressor efficiency profit was achieved. Based on the numerical simulations, the performance change in the two compressors and also the effects of blade three-dimensional stacking were discussed in depth. It was found that the endwall corner separation and secondary flows could be suppressed effectively using endwall bending; however, the blade forward sweep design at the rotor tip failed due to strong rotor-stator coupling effects in the highly loaded compressor stage.