1,721,151 research outputs found
Study of geometric parameters for the design of short intakes with fan modelling
Full text linkThe flow over a short intake is characterised by a strong interaction with the fan, that can only be captured when the rotor blades are modelled in the numerical simulations. In this paper, we use a coupled methodology to derive indications about relevant geometric variables affecting the high-incidence operation of an ultra-high bypass ratio turbofan intake with a length-to-diameter ratio of 0.35. By reproducing the effect of the fan through a body force model, we carry out a parametric study of the influence of the contraction ratio and the scarf angle at take-off conditions for a grid of 28 different three-dimensional shapes. The analysis of the selected performance metrics distributions at three angles of attack of 16°, 24°, and 28° reveals that a contraction ratio higher than 1.20 is needed to avoid separation at high incidence. While for an attached inlet the best performance is found with a moderate scarf angle, in presence of a developed separation the distortion level reduces as the scarf decreases up to negative values. We discuss the correspondence between the distortion indexes and the flow field, highlighting the origin of the detachment for the different geometries, according to the operating condition, and analysing the fan operation in the most distorted case. Finally, we assess the influence of modelling the rotor in the simulations, showing that its suppression effect on the separation at a given incidence depends on the intake geometric features
Aerodynamic Optimization of a Morphing Leading Edge Airfoil with a Constant Arc Length Parameterization
No full textThe paper presents the aerodynamic optimization of a morphing leading edge airfoil using a parameterization based on the class/shape transformation (CST) technique associated with a dedicated procedure to keep the arc length of the curve constant in order to limit the axial stress of the deformed shapes. The optimization is performed with a standard methodology based on genetic algorithms, comparing the results for three different aerodynamic models. Whereas the solutions obtained with the third model are standard droop nose shapes, those found via transitional models show an uncommon deformation with an upward leading edge deflection. A metamodel-assisted optimization loop is used to solve a known problem, showing that an artificial neural network is able to provide a reduction of the convergence effort when approximating the highly nonlinear relationship between the constant arc length parameterization and the aerodynamic behavior predicted with two of the models
Aeropropulsive assessment of engine installation at cruise for UHBPR turbofan with body force fan modelling
No full textThe overall propulsive performance of an aircraft with podded nacelles depends on the interaction occurring between the wing body and the propulsor. With the tight installation required for Ultra-High Bypass Ratio (UHBPR) turbofans, the engine and airframe flows are more coupled, resulting in a mutual interference that can affect the working condition of the turbomachinery and the wing flow. In the paper, we employ a fully coupled fan stage model based on a body force method to evaluate the performance of an ultra-high bypass ratio turbofan in a nominal and closely-coupled installation position, along the cruise phase of a long-haul flight at Mach number 0.85. By comparing the results obtained with a standard powered-on representation based on one-dimensional static boundary conditions, we assess the effect of the engine/airframe coupling on the aerodynamics and propulsive forces. The major differences occur on the discharge flow, on the internal fan nozzle duct and on the jet/wing interaction, due to the nonuniform fan stage outlet status in the body force simulations. The net vehicle force deviates from 1% to 1.6%, according to the position and the cruise phase. The sensitivity of the propulsive forces to the change of installation position, instead, is in general consistent for the two methods. The discrepancy can be much larger if the 1D boundary conditions are not corrected for true engine operating points arising under installation, exceeding 8% in the tighter assembly for the net vehicle force
Wall-Modeled Large-Eddy Simulation of a Transonic Gas Turbine Vane - Part I: Model Setup and Assessment of Turbulent Length Scales
No full textThe implementation of a wall-modeled large eddy simulation (WMLES) model combined with an immersed boundary method (IBM) to investigate the detailed aerodynamics of a gas turbine stator operating in a transonic regime is introduced in this study. In Part I, the potential of scale-resolved simulations within the WMLES framework is exploited by analyzing length scales and coherent structures within the wake. After a validation of the numerical model against experimental data and the identification of the optimal computational grid for balancing cost and accuracy, the presence of coherent vortices within the wake is underscored by the findings, characterized by sizes approximately 0.05 times the chord length and exhibiting primarily isotropic behavior in the cascade plane. Moreover, analysis of velocity fluctuations' probability density functions reveals that the turbulence released is predominantly two-dimensional. Concurrently, examination of pressure signals shows the persistence of a stabilization frequency well beyond the trailing edges of the cascade contrasting with the shedding frequency. Finally, it is demonstrated that as the flow traverses the cascade, its average turbulent content escalates by roughly three orders of magnitude compared to the inflow turbulence levels
Scale-Resolved Modeling of Gas Turbine Vanes: A Wall-Modeled LES and Immersed Boundary Approach
No full textThis study presents a novel methodology for investigating and analyzing the aerothermal dynamics of high-loaded gas turbine vanes. The approach integrates an advanced Wall-Modeled Large Eddy Simulation (WMLES) technique with an Immersed Boundary Method (IBM), enabling the treatment of complex geometries on Cartesian grids, while accurately handling high Mach and Reynolds number flows. A notable strength of the method, as compared to others discussed in the literature, is its compatibility with high-order numerical schemes and explicit algorithms. This enables efficient computation on modern GPU-based architectures, allowing for scale-resolved simulations to be conducted within a time frame comparable to that of standard unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations. The effectiveness and accuracy of the methodology are validated in canonical configurations, including channel flow, spatially developing boundary layers, and shock-boundary layer interactions. The present discussion introduced the method's ability to replicate renown experimental data associated with a gas turbine nozzle in the transonic regime [1] demonstrating alignment between the numerical and the experimental results
EFFECTS OF WALL TEMPERATURE ON TRANSONIC GAS TURBINE AEROTHERMODYNAMICS: A WALL-MODELED LES STUDY
No full textThis paper explores the impact of wall temperature on the performance of transonic gas turbine stators. Wall-modeled Large Eddy Simulations (LES) combined with the immersed boundary method are used in conjunction with modern multiGPU acceleration of Navier-Stokes equations. Six wall-to-recovery temperature ratios are analyzed, from adiabatic to highly cooled conditions, and the time-varying behavior of the system, including low-frequency components, is examined. Findings show that cooler walls affect flow dynamics, particularly by reducing turbulence intensity and increasing aerodynamic losses. Stronger cooling is found to lower energy transfer from the outer flow to the blade boundary layer, altering wake behavior and turbulence length scales. Consequently, cooler wall conditions expand the wake region, impact the stability of the boundary layer, and contribute to greater aerodynamic inefficiencies. Through the use of advanced scale-resolved simulations, such as wall-modeled LES, the research sheds light on the physics of these devices, offering valuable insights that can inform the optimization of cooling strategies in gas turbine technology
PV-PCM integration in glazed buildings. Numerical study through Matlab/Trnsys linked model
No full textThe paper describes the implementation of a 1-dimensional transient model based on the enthalpy method to analyse the thermal behaviour of a Phase Change Material (PCM) layer integrated in a window. The model and algorithm have been validated by comparison with experimental data. The model has then been expanded to couple a PV layer with the PCM layer. The complete model is implemented in MATLAB and linked to TRNSYS in order to estimate the dynamic thermal energy demand of a building equipped with a double skin façade with a PVPCM layer in a ventilated cavity. A parametric study was carried out, investigating three different cavity ventilation strategies for two European cities (Venice and Helsinki). The results show that, when the PCM layer is coupled with the PV layer, in Venice the cooling energy demand is 60 % lower, while in Helsinki the heating demand during the winter season is 36 % lower
TOWARDS NEW INSIGHTS IN GAS TURBINE AEROTHERMODYNAMICS WITH WALL-MODELED LES AND IMMERSED BOUNDARY METHOD
No full textThis paper introduces a novel methodology for investigating and analyzing the aerothermal dynamics of high-loaded gas turbine vanes. The method combines an advanced wall-modeled Large Eddy Simulation technique with an immersed boundary method, allowing for treating complex geometries on Cartesian grids and accurately handling high Mach and Reynolds flows. Compared to other similar solutions available in the literature, the method’s significant strength is its high compatibility with high-order numerical schemes and explicit algorithms. This allows efficient computing on modern GPU-based architectures, enabling scale-resolved simulations within a reasonable time frame, mainly comparable to more standard unsteady Reynolds-Averaged Navier-Stokes simulations. The effectiveness and accuracy of the method are demonstrated through testing and validation in various canonical scenarios, typical of wall turbulence studies. Here, for the first time, its ability to replicate experimental data associated with a gas turbine nozzle in the transonic regime is verified, testing numerical results compatibility with a precursor and well-established experimental campaign
Wall-Modeled Large-Eddy Simulation of a Transonic Gas Turbine Vane-Part II: Mach Number Effect and Losses Prediction
No full textThis is Part II of a companion article which introduced the implementation of a wall-modeled large-eddy simulation (WMLES) model combined with the immersed boundary method to analyze transonic flow in a gas turbine nozzle guide vane. In particular, Part I focused on a fully transonic configuration, validating the model against experimental data, identifying the most cost-effective model in terms of accuracy and computational effort, and demonstrating the benefits of scale-resolved approaches by characterizing the primary scales of wake motion. Part II expands on this by investigating the effects of flow compressibility and comparing high subsonic and fully transonic cases within the same environment. In particular, after initial verification of the numerical model robustness, the instantaneous, near-wall, and averaged flow dynamics are investigated as a function of the cascade expansion ratio. Steady Reynolds-Averaged Navier-Stokes solutions are also compared with the current WMLES, showing the latter with a superior ability to capture transitional behaviors of the boundary layers, turbulent kinetic energy production/convection and dissipation. Such initial stages of the analysis pave the way for characterizing the vane's momentum and thermal losses. Consequently, the local heat transfer characteristics of the cascade are analyzed using a dedicated coefficient designed to quantify the thermal exchange. Finally, Lagrangian statistics within the scale-resolved framework are presented, underscoring the role of compressibility in the wake turbulent behavior and primary frequencies of the system
Robust Design Optimisation of S-ducts
No full textOver the past years, robust optimisations have become very popular and necessary. The aim of this type of optimisation is to consider the sensitivity of the output results to small variations in the operating conditions and manufacturing tolerances. To study such sensitivities, an accurate and efficient method to quantify the uncertainties in physical processes is necessary. We present here the study and design of an S-duct, suitable for distributed propulsion configurations, and we address practical considerations of the application of robust optimisation to real-world design problems under multiple uncertainties. Two different non-intrusive Polynomial Chaos techniques have been chosen to quantify the input and output uncertainties, namely the non-intrusive point collocation and the non-intrusive spectral projection. These two techniques were implemented in two different robust optimisation problems (R1D and R2D) and their optima designs were analysed. To demonstrate the effectiveness of the robust optimisation problem formulation and analysis we compared the newly discovered optimum designs with previous non-robust optimum configurations. The results are discussed in detail and have shown a clear reduction in swirl values at the AIP, without affecting the pressure recovery of the diffuser when uncertainty properties were considered. In addition, robust codes have found S-duct shapes with swirl standard deviation values that are an order of magnitude smaller than the NON-Robust optimized designs and the baseline geometry
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