Jun 2026· International Journal of Turbo & Jet-Engines· 0 citations· 22 references
Abstract
Abstract To investigate the effects of rainfall on the aerodynamic performance and internal flow of transonic compressors, this study focuses on the NASA Stage 35 single-stage axial compressor. Using an Euler-Lagrange multiphase flow approach, the analysis accounts for both droplet aerodynamic breakup and evaporation effects. Aerodynamic performance and spatial flow fields were evaluated under dry conditions at 70 % of the design speed and wet conditions with varying water contents (3 %, 6 %, and 9 %). The results indicate that, in terms of compression performance, rainfall generally reduces the total pressure ratio and isentropic efficiency of the compressor while narrowing the stable operating range. Near-stall conditions show that droplet evaporation mitigates the rise in total temperature. Regarding the internal flow, momentum exchange between phases weakens the main flow acceleration and pressurization, leading to noticeable decreases in total pressure and axial velocity in the mid-to-upper blade height regions, thereby intensifying radial non-uniformity. Locally, droplet breakup and dispersion increase entropy generation, especially near the blade tip, enhancing mixing losses. Furthermore, the supersonic region on the suction side at 50 % span expands and the relative Mach number increases, altering the transonic flow field structure.
To address the low efficiency and unclear internal loss mechanisms of azimuth waterjet propulsion (AWP) systems operating under shallow and complex flow conditions, this study investigates an AWP unit at 950 rpm with a thrust of 1.63 kN. Steady numerical simulations are conducted under mooring and low-speed conditions, focusing on thrust coefficient, impeller efficiency, pump efficiency, and diffuser flow characteristics, with comparisons to a conventional mixed-flow pump. The results show that the propeller hydraulic efficiency at the design condition is approximately 52%, significantly lower than the 80–93% typical of mixed-flow pumps. The diffuser contributes nearly 80% of the total hydraulic loss, dominated by secondary flow effects. From the perspective of radial equilibrium in the guide vanes, secondary flow development is closely linked to spanwise momentum non-uniformity and deviation from equilibrium. The inclined outflow from the impeller induces strong spanwise imbalance, while the nearly 180° turning in the diffuser suppresses conventional force terms and establishes a pressure-gradient-dominated inertial balance associated with streamline curvature. This mechanism drives transverse migration and entrainment, promoting the formation of counter-rotating vortex pairs and secondary flows. Four major vortex concentration regions are identified, where interactions between secondary flow and recirculation generate complex three-dimensional vortex structures, including induced and spiral separation vortices. These vortices locally block the flow passage, causing pressure fluctuations and energy dissipation. The mid-span region of the guide vanes is identified as the primary location of loss accumulation. These findings provide theoretical and engineering guidance for diffuser optimization in AWP systems. It should be noted that the present study is based solely on numerical simulations, and no experimental validation for the investigated AWP configuration is currently available. Future experimental studies are needed to further verify the predicted hydraulic performance and flow structures.
The exhaust flow at the outlet of modern lean-burn combustors, which offer reduced NOx emissions for gas turbines, is characterized by hot streaks (HS) and residual swirl that affect the aerothermal performance of downstream high-pressure (HP) turbine nozzle guide vanes (NGVs). Although leaned blades are widely employed in turbomachinery design to mitigate secondary flow losses and improve aerodynamic efficiency, the combined influence of straight and compound lean configurations under residual swirl conditions remains comparatively less investigated. The objective of this study is therefore to numerically investigate the effect of blade lean on secondary flows and aerodynamic losses in axial turbine NGVs operating under simplified combustor-exit swirl conditions. The investigations are conducted on the NGV annular cascade developed at the NASA Lewis Research Center. Steady compressible flow simulations are performed by solving the Reynolds-Averaged Navier–Stokes equations using the Shear Stress Transport turbulence model. Three-dimensional vane geometries are generated by stacking the 2D blade profile along linear positive and negative lean axes with respect to the radial direction, with lean angles ranging from α = −8° to +8°. A total of sixteen configurations are first analyzed under axial inflow conditions to evaluate the influence of blade lean on aerodynamic performance. Based on the obtained performance trends, the baseline configuration together with the optimum straight-lean and compound-lean cases are subsequently investigated under two inlet swirl orientations (positive and negative) applied at the leading edge, with a swirl intensity of |Sn| = 0.4.The results show that the negative straight lean configuration NSL02 reduces the total pressure loss coefficient by approximately 3% under axial inflow conditions and by about 14% under negative swirl compared with the baseline case. Under positive swirl conditions, the negative compound lean configuration NCL08 achieves the best performance, reducing the loss coefficient from 2.274 to 1.914, corresponding to an improvement of approximately 16%.
Aissaoui Mohammed Islem, Salaheddine Azzouz, Z. Mansouri· Turkish Journal of Engineeri...· 0 citations
The flow and pressure fields around a harmonically oscillating NACA 0015 airfoil undergoing dynamic stall are investigated at varying reduced frequencies ([Formula: see text]) and Reynolds numbers ([Formula: see text]). Refractive index matching enables simultaneous Stereo Particle Image Velocimetry measurements on both sides of the transparent airfoil. Assuming two-dimensional flows, the pressure is estimated by spatial integration of the material acceleration. The lift, pressure (form) drag, and moments are calculated by integration of the surface pressure, providing a comprehensive picture of the relationship between the flow structure and loading. Results confirm that the migrating broad low-pressure region induced by the dynamic stall vortex along the suction surface delays the stall onset and increases the maximum lift and drag. The vortex detachment time is a constant fraction (0.3) of the oscillation period, and its migration speed is [Formula: see text] of the freestream velocity for all [Formula: see text] and [Formula: see text]. When time scales are shifted by the vortex detachment times, all the lift and drag curves collapse. Vortex fragmentation near the trailing edge weakens the lift and drag, but entrainment of vorticity originating from the pressure side creates a pressure minimum that increases the leading-edge moment. Low-amplitude heaving at low [Formula: see text] and [Formula: see text], mostly at the end of the downstroke, causes lift oscillations.
J. Jose, Yuhui Lu, Karuna Agarwal et al.· AIAA Journal· 0 citations
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.
Zhuhai Zhong, Xiaodan Zhang, Kunlun Bai et al.· Fluids· 0 citations
To address the aerodynamic challenges associated with low-Reynolds-number operation typical of high-altitude cruise conditions in aero-engines, this paper presents an experimental investigation—conducted on a large-scale, low-speed, multi-stage axial turbine facility—in which both the velocity triangles and the reduced wake-passing frequency were held constant. Synchronized hot-film measurements were conducted on the blade surface, and the dynamic flow field at the second-stage stator (S2) exit plane was acquired using a triple- and hot-wire probe. The study examines the effects of Reynolds number (Re = 7.4 × 104 and Re = 8.5 × 104) on the attached-flow transition and wake mixing characteristics of the S2 suction surface. The results indicate that at the lower Reynolds number, the thickened boundary layer and enhanced viscous effects lead to shear sheltering of external disturbances, resulting in a delayed transition onset and attenuated wall shear stress fluctuations. Consequently, the merging and evolution of turbulent spots are restricted, causing the calmed regions at the trailing edge to exhibit stronger intermittency. This process leads to wake broadening, an elevation of global turbulence levels, and a significant increase in velocity deficit magnitude (>1.5%), ultimately resulting in a significantly deeper and wider exit wake profile, indicative of increased aerodynamic loss.
Yingqiang Zhang, Xiao-Dan Zhang, Miaoyi Zhu et al.· The Physics of Fluids· 0 citations
In this study, two passive geometric modifications, namely, slotting and rib addition on the sidewall of the front blunt body, are proposed. Numerical simulations are conducted to investigate the effects of these modifications on the flow and combustion characteristics of an advanced vortex combustor under atmospheric pressure conditions, with an inlet velocity of 80 m/s and inlet total temperatures of 300 and 800 K. Results show that both slotting and rib addition promote fuel/air mixing and improve combustion performance at the cost of decreased total pressure recovery coefficient. As the slot depth increases from 0 to 9 mm, the total pressure recovery coefficient exhibits a non-monotonic trend, first decreasing from 97.96% to 97.56% and then increasing to 97.75%. In contrast, increasing rib height from 0 to 6 mm leads to a monotonic decrease from 97.96% to 97.22%. In addition, increasing slot depth from 0 to 9 mm increases the combustion efficiency from 81.64% to 86.87% and decreases the outlet temperature distribution factor (OTDF) from 1.245 to 1.125. A similar improvement is observed with increasing rib height. As the rib height increases from 0 to 6 mm, combustion efficiency increases from 81.64% to 92.60%, with OTDF decreasing from 1.245 to 0.984. These findings provide design guidance for passive geometric modifications of advanced vortex combustors.
Qian Wang, W. Fan· The Physics of Fluids· 0 citations