Abstract:Numerical simulation has been conducted on a transonic contra-rotating axial compressor to investigate the shock wave and flow characteristics under various operation conditions. Results indicate that the shock-wave structure in the downstream rotor (Rotor 2) of transonic contra-rotating axial compressor is more complex than that in the upstream rotor (Rotor 1). Under the choke condition, a double shock-wave structure appears in the Rotor 2 leading to serious loss. Moving to the design condition, a single shoc… Show more
“…As shown on the left side of Figure 10, the high EGR zone, which also represents losses due to the separation bubble, vanishes as the compressor operates at lower mass flow rates. 48 Figure 10.Separation-induced transition and high EGR region.…”
Section: Resultsmentioning
confidence: 99%
“…As shown on the left side of Figure 10, the high EGR zone, which also represents losses due to the separation bubble, vanishes as the compressor operates at lower mass flow rates. 48 For in-depth study of the leading-edge boundary layer, the line integral values of the EGR and the spanwise averaged values of streamwise velocity us, flow angle, β 0 , static pressure p, and de-Haller number 12 were measured at was measured using the same directions for the blade angle β 1s (see Figure 2). β 0 is used to approximate the size of the dead-air zone.…”
This study compares the local losses of a radial compressor in the range from surge to choke considering shock phenomena, boundary layer separation, and mixing mechanisms. For this purpose, formulation of the local entropy generation rate (EGR) is added to the computational fluid dynamics (CFD) solver, which models the turbulent flow field of the compressor through the RANS approach. For validation, the numerical pressure rise curve of the compressor is compared with the experimental data. The results indicate that at the design point, the impeller, diffuser, and the volute account for approximately 50.8%, 30.0%, and 12.3% of the EGR, respectively, with approximately 5% in the impeller backspace, 1% in the diffuser cavity, and less than 0.5% in the inlet duct. Approaching the surge condition, local losses due to mixing and shock waves decline while boundary layer losses increase. Based on comprehensive analysis of the leading-edge boundary layer, the largest dead-air zone is found at the design point, resulting in a lower diffusion entrance loss and a higher mixing loss. Furthermore, the EGR variation in the diffuser channel is investigated by shedding light on mixing dynamics and classification of the channel flow regime into three different zones based on mixing ratio (MR). The outcomes show that the flow regime tends to mix more quickly at a higher MR, resulting in a slight decrease in EGR, which benefits compressor performance. We demonstrate that the mixing rate of flow regimes decreases in both the leading-edge boundary layer and the radial diffuser approaching the surge margin.
“…As shown on the left side of Figure 10, the high EGR zone, which also represents losses due to the separation bubble, vanishes as the compressor operates at lower mass flow rates. 48 Figure 10.Separation-induced transition and high EGR region.…”
Section: Resultsmentioning
confidence: 99%
“…As shown on the left side of Figure 10, the high EGR zone, which also represents losses due to the separation bubble, vanishes as the compressor operates at lower mass flow rates. 48 For in-depth study of the leading-edge boundary layer, the line integral values of the EGR and the spanwise averaged values of streamwise velocity us, flow angle, β 0 , static pressure p, and de-Haller number 12 were measured at was measured using the same directions for the blade angle β 1s (see Figure 2). β 0 is used to approximate the size of the dead-air zone.…”
This study compares the local losses of a radial compressor in the range from surge to choke considering shock phenomena, boundary layer separation, and mixing mechanisms. For this purpose, formulation of the local entropy generation rate (EGR) is added to the computational fluid dynamics (CFD) solver, which models the turbulent flow field of the compressor through the RANS approach. For validation, the numerical pressure rise curve of the compressor is compared with the experimental data. The results indicate that at the design point, the impeller, diffuser, and the volute account for approximately 50.8%, 30.0%, and 12.3% of the EGR, respectively, with approximately 5% in the impeller backspace, 1% in the diffuser cavity, and less than 0.5% in the inlet duct. Approaching the surge condition, local losses due to mixing and shock waves decline while boundary layer losses increase. Based on comprehensive analysis of the leading-edge boundary layer, the largest dead-air zone is found at the design point, resulting in a lower diffusion entrance loss and a higher mixing loss. Furthermore, the EGR variation in the diffuser channel is investigated by shedding light on mixing dynamics and classification of the channel flow regime into three different zones based on mixing ratio (MR). The outcomes show that the flow regime tends to mix more quickly at a higher MR, resulting in a slight decrease in EGR, which benefits compressor performance. We demonstrate that the mixing rate of flow regimes decreases in both the leading-edge boundary layer and the radial diffuser approaching the surge margin.
“…However, the mechanisms of the TCV unsteadiness are not clear yet. Many researchers [4][5][6][7][8][9][10][11] noticed that there was a strong oscillation related to TCV in the rotor tip for some compressors, especially under the near-stall (NS) conditions. By the means of Fourier transformation (FT), it was found that the frequency of the oscillation was approximately half of the blade passage frequency (BPF).…”
The unsteady characteristic in the tip region of an axial compressor has been numerically studied with the help of the dynamic mode decomposition analysis. The characteristics of frequency and dynamic modes are compared and discussed under different operating points and different parameters, such as tip clearance and rotating speeds. For the flowfield structures in the tip region, such as tip leakage flow, separation flow and shock wave, their relationships with the unsteadiness are studied in detail. Except for the unsteadiness caused by the interaction between rotating rotor and the stationary boundaries, it is found that the unsteadiness is attributed to the moving of the low-velocity cell. Based on the generation and the development of the low-velocity cell, the unsteady characteristics in tip region are divided into 4 types: BPF-dominated, shedding-dominated, self-induced and separation-dominated. When the tip leakage flow is weak, the unsteadiness in the tip region is only triggered by the blade sweeping. As the tip leakage flow gets stronger to a certain extent, the low-velocity cell is shed into the flow passage and mixed with the main-flow. When the main-flow is weaker under the low flowrate condition, the interaction between the low-velocity cell and the pressure side occurs and generates a new low-velocity cell near the leading-edge of the neighboring blade. The frequency of the new cell generation is actually the self-induced frequency. In the zero and small clearance model, the low-velocity is shed by the separation in the leading-edge and the casing-suction corner. By understanding these unsteady characteristics, the change tendency of the leading frequency in the rotor tip is easily explained and forecasted. Furthermore, under the transonic operation condition, the low-velocity cell is decelerated and eliminated by the shock wave in the unsteadiness of the self-induced type and the separation-dominated type, respectively. Thus, the leading frequency in the tip flow field is moderated.
The aerodynamic stability of an axial compressor stage depends on the rotor and stator. However, due to the specific design requirements, the evolving flow field and the resulting secondary flow structures are different in both components. This study investigates the evolution of dominant secondary flow structures occurring in the rotor and stator of a tip-critical transonic compressor stage at the near-stall condition using unsteady numerical analysis and validates performance characteristics with the experimental data. The investigation reveals that the presence of rotor tip shock creates a large difference in the pressure gradient across the pressure surface and the suction surface, intensifying tip leakage flow and shock-induced boundary layer separation. The higher incidence angle near the hub leading edge creates a local separation and reattachment zone. The radial pressure gradient causes the low momentum flow from this local separation zone to migrate radially upward. This migrated flow interacts with the tip leakage flow and separated blade boundary layer, eventually creating a colossal recirculation zone and subsequent rotor blockage of around 46%. The increasing streamwise adverse pressure gradient pushes the tip shock upstream, and at the onset of the stall, the flow directly separates from the rotor leading edge avoiding the shock formation. The stator flow field is dominated by the asymmetric hub corner separation induced by the streamwise adverse pressure gradient and the tip corner separation caused by the vortex structures convected downstream from the rotor tip region leading to stator blockage of around 48%. Along with the blade passing frequency, four other dominating frequencies (0.06×BPF, 0.12×BPF, 0.44×BPF, and 0.84×BPF) related to the aerodynamic instabilities are observed at the inception of stall.
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.
