The main reason for limiting the working flow range of the compressor is the unstable flow phenomenon of the compressor working at a small flow rate, including stall, surge, and rotational instability. Among them, the rotating stall phenomenon is particularly prone to occur during the operation of centrifugal compressors. In this paper, a three-stage nitrogen centrifugal compressor is taken as the research object, and the dynamic development process of rotating stall in the diffuser is captured by full-channel numerical calculation. After research, the leading-edge vortex at the diffuser inlet is the cause of rotating stall. In the throttling process, the backflow in the diffuser causes the channel blockage and the stall phenomenon triggered by the leading-edge overflow. There are six stall channels in the first-stage diffuser and nine stall channels in the second-stage diffuser. The propagation direction is the same as the rotation direction of the blade, and the propagation speeds are 4.348% and 5.26%, respectively.
Centrifugal pumps account for a significant share of global industrial energy consumption. Optimizing the shape of all components is the main goal in the design process to improve operating efficiency and reduce environmental impact. However, centrifugal pumps often operate under off-design conditions, where the flow is characterized by large separations. The stall process of the impeller of a centrifugal pump is investigated in this work with high-fidelity simulations, considering all channels of the impeller instead of the reduced domain used in the literature under the assumption of a periodic flow behavior, in order to assess whether this assumption holds throughout the evolution of the stall process and whether the non-periodic behavior reported in the literature is phenomenological or related to the numerical setup. In particular, the goal is the description of the flow phenomena with different inlet flow rates, with a focus on the configuration of the vortices and the non-periodic behavior of the flow between the channels of the impeller. The setup of the simulations—e.g., the spatial accuracy of the meshes, the numerical schemes, and the formulation of the turbulence models—is assessed to avoid numerical errors that lead to poor accuracy and a deviation from the periodic behavior of the results. A large number of simulations are carried out, and the results are compared with experiments and other high-fidelity simulations available in the literature. The flow phenomena in the evolution of the stall process are progressive, where the increase in the dimensions of vortices is proportional to the decrease in the inlet flow rate. The stall is steady at each inlet flow rate, and the configuration of the vortices is periodic between all channels at the design and pre-stall conditions, and periodic between alternate stall and non-stall channels at the off-design conditions, confirming the periodic behavior assumed in most of the literature at the deep off-design conditions. All the non-periodic behavior of the flow can be ascribed to the spatial accuracy and turbulence model and decreases with high spatial accuracy, suggesting that it is more related to the numerical setup than to the flow phenomena. The proposed formulation of the turbulence model for high-fidelity simulations demonstrates the best compromise between accuracy and computational efficiency.
A. Fracassi, A. Ghidoni, M. Ghisalberti et al.· The Physics of Fluids· 0 citations
Research has shown that rotating detonation turbine engines have the potential to enhance aero-engine performance. However, the rotating back-propagation pressure wave (RBPW) generated by the detonation-based combustor can adversely affect the upstream compressor. In this study, this unsteady backpressure was simulated using a user-defined function (UDF), and its impact on a centrifugal compressor was numerically investigated. The results show that, under single-wave RBPW, both the total pressure ratio and isentropic efficiency declined at the same mass flow rate compared to steady-state conditions. Variations in the characteristic parameters of the RBPW resulted in shifts of the compressor's operating point. A higher-pressure distortion index caused a greater deviation from the original characteristic line. Increasing the propagation frequency or using a multi-wave configuration mitigated these adverse effects. Under four-wave excitation, compressor performance exceeded that of steady operation. Finally, the stability boundaries of the compressor under RBPW were defined in terms of constant flow rate and constant power constraints.
Y. Qi, Cha Xiong, Yining Zhang et al.· Journal of Engineering For G...· 0 citations
High-speed rotating cooling passages in aero-engine turbine blades experience significant centrifugal compression, leading to strong coupling between thermodynamic states and flow structures, which challenges the validity of incompressible assumptions. In this study, large eddy simulations are performed to investigate the flow evolution induced by rotational compressibility effects in an adiabatic rotating square duct. The results demonstrate that rotational compressibility does not act as an independent additional force term but instead modifies the balance among centrifugal force, Coriolis force, and pressure gradient through density redistribution. The density variation induces a streamwise centrifugal-buoyancy effect, which drives high-momentum fluid toward the trailing side and generates an intensified adverse pressure gradient near the leading side, resulting in progressive boundary-layer thickening and large-scale flow separation. With increasing rotational compressibility, the cross-sectional secondary-flow topology evolves from the classical four-vortex structure to a six-vortex configuration and eventually develops into an eight-vortex topology. This transition may be associated with the expansion of the leading side separated reverse-flow region, which reverses the local Coriolis-force direction and disrupts the original secondary-flow balance. Furthermore, a separation prediction model based on centrifugal work number (CW) and rotation number (Ro) is established to identify the dominant parameters governing rotational-compressibility-induced separation in finite-length rotating ducts. These findings suggest strong coupling among centrifugal compression, flow separation, and secondary-flow topology transition, providing insight for advanced turbine blade cooling design.
Yujie Liu, Ruquan You, Runzhou Liu et al.· The Physics of Fluids· 0 citations
Future jet engine compressors are expected to feature overall pressure ratios (OPR) that approach 70:1. The core of the compressor will downsize with higher OPR, increasing the importance of managing blade-tip clearance. This clearance is influenced by compressor rotor expansion, which is dictated by the flow structure and heat transfer inside the cavities between co-rotating discs. This unstable flow structure is induced by buoyancy under centrifugal acceleration at high Grashof numbers. Further, the flow is destabilised by the enthalpy and momentum exchange with an axial throughflow of cooler air at low radius. The throughflow forms part of the secondary air system and inherently features swirl from rotating components within the compressor. In some cases, the swirl relative to the rotating discs an exceed unity (over-swirl). This paper presents an experimental study of the influence of entrained fluid into the rotating compressor cavity over a range of Rossby numbers and axial throughflow swirl. The University of Bath Compressor Cavity Rig was used to measure the radial distribution of air temperature in the throughflow, the radial distribution of temperature on the discs inside the cavity, the shroud heat flux, and the resultant flow structure from unsteady pressure. The data produces universal Grashof-number correlations for shroud Nusselt number and the radial mass flow within the buoyancy-induced structures that form in the cavity. Swirl is shown to be a fundamental governing non-dimensional parameter determining the slip of the structures and the number of vortex pairs in the cavity. A theoretical model based on first principles is coupled to the data and supports the practical thermal-mechanical design of compressor rotors in industry.
Sebastian Syncerz, Dominic W. A. Lafone-Ward, Mai Mohamed et al.· Journal of turbomachinery· 0 citations
Non-periodic leading-edge wear near the impeller tip is investigated with respect to the aerodynamic performance, steady flow organization, and near-stall unsteady evolution of a centrifugal compressor. A full-annulus three-dimensional impeller–vaned-diffuser model is established for a baseline configuration (O-M) and a non-periodically worn configuration (W-M). The two configurations are compared in terms of performance characteristics, near-tip pressure coefficient, static pressure, entropy, relative Mach number, three-dimensional vortical structures, and pressure fluctuation signals. The W-M generally produces a lower total pressure ratio than the O-M, with a maximum reduction of approximately 0.7%. Nevertheless, the isentropic efficiency is slightly improved over the main operating range, with a peak increase of about 0.6%, and the near-stall flow rate shifts toward a lower value. Pressure coefficient distributions at 95% span show that leading-edge wear weakens both the pressure-side pressure peak and the suction-side suction peak of the worn blades, redistributing the near-tip loading from a highly leading-edge-concentrated form to a broader chordwise distribution. The steady flow fields indicate that wear does not eliminate local low-pressure or high-entropy regions; rather, it reorganizes their circumferential arrangement, converting originally synchronized low-pressure zones, high-entropy bands, and high-speed shear layers into a non-uniform pattern with alternating strong and weak passages. Near-stall unsteady results further reveal that pressure cells, high-entropy zones, and large-scale vortical structures in the O-M exhibit clear cross-passage propagation, whereas the corresponding disturbances in the W-M remain predominantly localized, dispersed, and asynchronous. These results demonstrate that, for the wear location and blade-to-blade distribution considered here, non-periodic leading-edge wear affects stability primarily by weakening the circumferentially coherent amplification of disturbances, rather than by simply reducing all local loss sources.
Hong Xie, Zhibiao Cai, Bo Yang et al.· Aerospace· 0 citations
To suppress the flow-induced vibration of a single-stage single-suction centrifugal pump (rated head 5 m, flow rate 30 m
3
/h, rotational speed 1000 r/min), the key impeller parameters were taken as design variables and screened via the parameter sensitivity analysis method in this study. The internal flow field was solved using the Reynolds-Averaged Navier–Stokes (RANS) approach with the SST k–ω turbulence model, implemented in the commercial CFD code ANSYS Fluent. With pump efficiency and the sample standard deviation of circumferential tangential velocity uniformity at all nodes of the impeller outlet set as the optimization objectives, and pump head as the constraint condition, the Kriging surrogate model combined with the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was adopted to conduct the optimal design of the impeller structure. The results show that the head and efficiency of the optimized pump are increased by 10.8% and 2.7%, respectively. The pressure pulsation amplitudes associated with the blade-passing frequency (BPF) at the volute tongue are significantly reduced, with a 36.1% decrease at the volute tongue and a 22% decrease inside the volute, which effectively mitigates the rotor-stator interaction (RSI). Comparisons of the internal flow fields confirm the suppressed secondary flows, reduced turbulent kinetic energy, weakened jet-wake effects, and improved unsteady performance of the optimized pump, thus verifying the feasibility and effectiveness of the proposed optimization strategy.
Jiafu Guo, Xinxiang He, Abdul Mutalib bin Leman et al.· Proceedings of the Instituti...· 0 citations