Jul 2026· Turkish Journal of Engineering· Vol 10, pp. 1138-1154· 0 citations
Abstract
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%.
Aerothermal interaction between the combustor and the high-pressure turbine is critical for engine efficiency. Standard steady-state methods fail to capture the highly unsteady flow features at the combustor-turbine interface, leading to uncertainties in thermal load prediction. This study investigates the influence of combustor unsteadiness and scale-resolving simulation methods on the aerodynamic performance and thermal load of an engine-representative high-pressure turbine rotor. Numerical investigations utilize RANS, URANS, and Stress-Blended Eddy Simulations. To prescribe realistic unsteadiness, inlet boundary conditions derived from a combustor Large Eddy Simulation are applied via a one-way unsteady coupling method. Results demonstrate that unsteady inlet conditions substantially impact predicted mixing in the stator. This unsteadiness homogenizes the temperature distribution at the stator outlet, significantly increasing temperatures in the end wall regions. While combustor unsteadiness drives turbulent mixing in the stator, rotor passage flow physics are dominated by the choice of the turbulence model. The scale-resolving approach predicts deeper hot gas penetration into the rim seal cavity compared to URANS. Combined with the altered stator exit traverse, this results in higher thermal loads on the rotor blade suction side, particularly in the critical hub and tip regions. Furthermore, the study highlights the significance of inlet unsteadiness for predicting physically consistent flow fields in scale-resolving simulations. Consequently, high-fidelity, transient methods are shown to be essential for accurately predicting thermal loads, relevant for robust cooling design.
Nico Rademacher, Anton Hilfrich, K. Lehmann et al.· Journal of turbomachinery· 0 citations
Aiming at the core issue of flow separation on vertical-axis wind turbine (VAWT) blades under high angles of attack during periodic rotation—which degrades aerodynamic performance and energy capture efficiency—this paper proposes a VAWT blade configuration equipped with double-slotted flaps, drawing on mature high-lift technology from aircraft wings. Numerical simulations are conducted using the Unsteady Reynolds-Averaged Navier–Stokes method with the Shear Stress Transport k–ω turbulence model, covering static aerodynamic characteristics of a single airfoil as well as two-dimensional and three-dimensional full-turbine models. Optimal design parameters of the double-slotted flaps are identified via the control variable method, and the aerodynamic performance and flow-field characteristics of passive vs active controlled double-slotted flap VAWTs are compared. The underlying flow mechanism of unsteady separation control is revealed: flap deflection increases airfoil camber, while high-pressure airflow from the pressure side is injected through the primary and secondary slots into the suction-side boundary layer, re-energizing the stalling boundary layer, and thereby delaying dynamic stall and flow separation. Results show that the optimally configured single airfoil achieves a significantly improved lift-to-drag ratio and delayed flow separation within the 0°–20° angle-of-attack range. Under active control, the power coefficient of the double-slotted flap VAWT at a tip-speed ratio λ = 2.33 is 32% higher than that of the reference wind turbine. Its wake is laterally wider with an extension length reduced to 7R, and both the intensity and spatial extent of vortex shedding on blade surfaces in the three-dimensional flow field are effectively suppressed. This study elucidates the inherent mechanism by which double-slotted flaps enhance VAWT aerodynamic performance—namely, through active unsteady separation control leading to energy capture improvement—and provides theoretical guidance for small vertical-axis wind turbines in distributed and building-integrated wind energy applications.
Shuyan Jing, Huahao Ou, Zhou Ye et al.· The Physics of Fluids· 0 citations
For coupling a transonic high-pressure turbine vane with a rotating detonation combustor, several integration approaches have been considered. Endwall diffusion in the vane row can facilitate coupling by enabling a higher turbine inlet Mach number operating range. Nonetheless, the introduction of diffusive axisymmetric endwalls may promote flow separation and enlarged secondary flows, leading to an overall reduction in turbine stage efficiency. To address this, the present study introduces a shape optimization framework based on computational fluid dynamics for designing diffusive non-axisymmetric endwalls in a transonic vane downstream of a rotating detonation combustor. The reference geometry is a transonic vane with diffusive axisymmetric endwalls, previously analyzed in numerical studies. Both hub and shroud endwalls are parameterized using 20 design variables, and a random sampling approach generates 1000 distinct geometrical configurations. Each design undergoes geometry generation, meshing, and steady Reynolds-averaged Navier–Stokes computation under transonic conditions using a three-dimensional commercial solver. Aerodynamic performances are assessed, and a genetic aggregation method is employed to construct a response surface. A gradient-based optimization algorithm identifies the optimal non-axisymmetric endwall configuration, which is then simulated. Comparative analysis shows that the optimized non-axisymmetric endwall significantly mitigates hub and shroud vortex effects, enhancing aerodynamic efficiency and supporting integration within turbine systems equipped with rotating detonation combustors.
Panagiotis Gallis, Sergio Grasa, G. Paniagua et al.· International Journal of Tur...· 0 citations
Preliminary aerodynamic assessment provides an efficient means of investigating internal flow organization in aircraft gas turbine combustors before more computationally demanding three-dimensional and reactive-flow simulations are undertaken. This study presents a preliminary CFD investigation of cold-flow phenomena in the annular combustion chamber of the F100-PW-229 low-bypass turbofan engine. A two-dimensional planar model was intentionally adopted to identify dominant flow structures and assess their response to representative engine operating conditions at reduced computational cost. Numerical simulations were performed in ANSYS Fluent using a pressure-based coupled solver and the k-ω SST turbulence model for idle, cruise, and maximum rotational speed conditions. Additional simulations were performed at cruise conditions for an altitude of 11 km to examine the influence of reduced ambient pressure and air density on the internal flow field. The results show that increasing engine rotational speed primarily changes the intensity of the aerodynamic field while preserving its dominant spatial organization. The maximum velocity at idle was approximately 55% lower than that at maximum rotational speed, while the corresponding value at cruise was 20.1% lower. Similarly, the maximum stagnation pressure at idle was approximately 67.1% lower than that at maximum rotational speed, while the difference between cruise and maximum speed was 24.2%. A distinct vortex structure was identified in the outer annular passage between the liner and casing, with its location shifting downstream as the operating condition changed. At 11 km altitude, the calculated pressure level was approximately 81% lower and the characteristic flow velocity approximately 9% lower than under corresponding ground-level conditions, while the dominant flow topology remained similar. These results highlight the role of combustor geometry and secondary-air distribution in governing global pressure redistribution, velocity development, and recirculation behavior. Within the scope of the adopted two-dimensional non-reacting formulation, the obtained flow patterns provide an initial aerodynamic reference for identifying regions of interest for subsequent high-fidelity simulations. The proposed approach is therefore intended as a computationally efficient preliminary engineering tool rather than a substitute for validated three-dimensional combustor modelling.
Adam Kozakiewicz, Aleksandra Ludwiczak, B. Ciupek et al.· Applied Sciences· 0 citations
Rotating Detonation Engines (RDEs) offer a promising path toward more efficient and compact propulsion and power systems. However, the highly unsteady and transonic outlet flow generated by the detonation process, characterized by oblique shock wave patterns, introduces significant challenges for turbine integration and overall performance. The present work focuses on the impact of the oblique shock waves exiting the rotating detonation combustor (RDC) on a supersonic inlet high-pressure turbine stage. The analysis examines how the shock pattern, the number of detonation fronts, and their rotation direction affect the unsteady aerodynamics and the overall turbine performance. In addition, the effect of shock waves on the stator and rotor unsteady loads is investigated to provide a preliminary aeromechanical assessment of the supersonic turbine. Full-annulus unsteady simulations were performed to capture the complex RDC–turbine interaction and its effects on blade loading and flow structures. The numerical framework has been validated against a previous Large Eddy Simulation (LES) analysis of the turbine stage under RDC-representative conditions. The comparisons highlight the key mechanisms driving shock–turbine interactions, showing how shock synchronization and rotation direction affect turbine efficiency and power extraction. These findings provide valuable insights into the design configurations and coupling scenarios of turbines operating under detonation-based flow conditions.
L. Pinelli, Pietro Biagini, M. Marconcini et al.· Journal of turbomachinery· 0 citations
The common phenomena in vertical-axis turbines arise from the continuously changing angle of attack (AoA), which results in; flow separation, dynamic stall, unsteady hydrodynamics, complex wake and vortex structures, and Cyclic structural loading. Devices such as vortex generators (VGs) are used to mitigate flow separation and dynamic stall, thereby significantly improving turbine performance. Numerical simulations investigate the effect of VG addition on turbine performance in general, specifically the NACA 0021 blades in the H-type Darrieus turbine. The single-blade model was equipped with rectangular VGs of specific dimensions, arranged in a single row and contra rotating. Computational Fluid Dynamics (CFD) simulation using ANSYS-FLUENT was employed as the numerical approach to compare the performance of an NACA 0021 blade with and without rectangular VGs. The VGs were placed at chordwise positions of 20%c, 25%C, and 30%c. The simulation results show that the most effective VG placement is at 25%c, where the drag coefficient is reduced by up to 38.0% at an AoA of 15°, and by 17.3% at AoA = 20°, compared to the clean airfoil without VGs. This study shows that the addition of VGs reduces drag and enhances turbine performance. The reduction in drag influences the flow separation behavior, thereby delaying stall.
D. Rahuna, I. Utama, Erwandi Erwandi et al.· Engineering power· 0 citations
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