A CFD Based Throughflow Method With Three-Dimensional Flow Features Modelling

The paper describes the development and validation of a novel computational fluid dynamics (CFD)-based throughflow model. It is based on the axisymmetric Euler equations with tangential blockage and body forces and inherits its numerical scheme from a state-of-the-art CFD solver (TRAF code). Secondary and tip leakage flow features are modelled in terms of Lamb–Oseen vortices and a body force field. Source and sink terms in the governing equations are employed to model tip leakage flow effects. A realistic distribution of entropy in the meridional and spanwise directions is proposed in order to compute dissipative forces on the basis of a distributed loss model. The applications are mainly focused on turbine configurations. First, a validation of the secondary flow modelling is carried out by analyzing a linear cascade based on the T106 blade section. Then, the throughflow procedure is used to analyze the transonic CT3 turbine stage studied in the framework of the TATEF2 (Turbine Aero-Thermal External Flows) European program. The performance of the method is evaluated by comparing predicted operating characteristics and spanwise distributions of flow quantities with experimental data

unsteady methods applied to a transonic aeronautical gas turbine stage

Abstract The importance of considering the unsteady effects in aeronautical engine design has brought to the implementation of simplified unsteady CFD models to respect the temporal restrictions of design cycles. A comparison among steady, Non-Linear Harmonic (NLH) and Full-Annulus (FA) methods has been carried out analyzing the transonic turbine stage CT3, experimentally studied at von Karman Institute for Fluid Dynamics. The understanding of the unsteady phenomena is fundamental to increase the engine efficiency and is precluded in steady calculations. As the computational cost of NLH calculations is of the same order of magnitude of steady ones, it represents a valid and competitive option in a turbine design process

Secondary flow and radial mixing modelling for CFD-based Through-Flow methods: an axial turbine application

Abstract The paper presents the theoretical bases and an application of a CFD-based Through-Flow model. The code solves the axisymmetric Euler equations and takes into account the effect of tangential blockage and body force. It inherits its numerical scheme from a state-of-the-art CFD solver (TRAF code). Blade body forces are calculated directly from the tangency condition to the meridional flow surface, which is iteratively adapted during the time-marching procedure. Dissipative forces are computed through a realistic distribution of entropy along streamlines. Both secondary flow and tip leakage effects on the meridional flow-field are included through the adoption of a concentrated vortex model, while the corresponding loss contributions are evaluated from correlations. Also, a radial mixing model considering both turbulent diffusion and spanwise convection is implemented. The accuracy of the method is assessed by comparison with CFD calculations and experimental data on the transonic CT3 turbine stage tested in the framework of the TATEF2 European project. A good agreement in terms of overall performance and radial distributions is achieved for both design and off-design operating conditions

Validation of an URANS approach for direct and indirect noise assessment in a high pressure turbine stage

Abstract In response to the continuous increase in aircraft noise pollution, computational aeroacoustic analyses are mandatory during the aero-engine design loop. In order to investigate the acoustic generation and propagation phenomena within a multi-stage turbomachinery, an experimental campaign on direct and indirect noise coming from a high pressure axial turbine stage has been carried out by Politecnico di Milano in the context of the European research project RECORD. The purpose of this work is to numerically predict both the direct noise produced by stator/rotor interactions and the indirect noise generated by the non-acoustic fluctuations coming from an annular combustor that impinge on the HPT stage by using URANS analyses. The computational results are in good agreement with experimental measures, confirming the possibility to include the numerical method during the engine design loop to assess noise emissions and suggest low noise design solutions

Reducing Secondary Flow Losses in Low-Pressure Turbines: The "Snaked" Blade

This paper presents an innovative design for reducing the impact of secondary flows on the aerodynamics of low-pressure turbine (LPT) stages. Starting from a state-of-the-art LPT stage, a local reshaping of the stator blade was introduced in the end-wall region in order to oppose the flow turning deviation. This resulted in an optimal stator shape, able to provide a more uniform exit flow angle. The detailed comparison between the baseline stator and the redesigned one allowed for pointing out that the rotor row performance increased thanks to the more uniform inlet flow, while the stator losses were not significantly affected. Moreover, it was possible to derive some design rules and to devise a general blade shape, named 'snaked', able to ensure such results. This generalization translated in an effective parametric description of the 'snaked' shape, in which few parameters are sufficient to describe the optimal shape modification starting from a conventional design. The "snaked" blade concept and its design have been patented by Avio Aero. The stator redesign was then applied to a whole LPT module in order to evaluate the potential benefit of the 'snaked' design on the overall turbine performance. Finally, the design was validated by means of an experimental campaign concerning the stator blade. The spanwise distributions of the flow angle and pressure loss coefficient at the stator exit proved the effectiveness of the redesign in providing a more uniform flow to the successive row, while preserving the original stator losses

Assessment of a Neural-Network-Based Optimization Tool: a Low Specific-Speed Impeller Application

This work provides a detailed description of the fluid dynamic design of a low specific-speed industrial pump centrifugal impeller. The main goal is to guarantee a certain value of the specific-speed number at the design flow rate, while satisfying geometrical constraints and industrial feasibility. The design procedure relies on a modern optimization technique such as an Artificial-Neural-Network-based approach (ANN). The impeller geometry is parameterized in order to allow geometrical variations over a large design space. The computational framework suitable for pump optimization is based on a fully viscous three-dimensional numerical solver, used for the impeller analysis. The performance prediction of the pump has been obtained by coupling the CFD analysis with a 1D correlation tool, which accounts for the losses due to the other components not included in the CFD domain. Due to both manufacturing and geometrical constraints, two different optimized impellers with 3 and 5 blades have been developed, with the performance required in terms of efficiency and suction capability. The predicted performance of both configurations were compared with the measured head and efficiency characteristics

Acercándose a la investigación

Nota de prensa en la que trata de impulsar el interés por la investigación. El Instituto de Salud Carlos III colabora en el programa “INVESTIGA I+D+i”, puesto en marcha por la Fundación San Patricio, para promover el interés de los adolescentes por la cienci

Estimation of the Aerodynamic Force Induced by Vaneless Diffuser Rotating Stall in Centrifugal Compressor Stages

Abstract Rotating stall in centrifugal compressors not only adversely affects the performance before surge, but also can generate high subsynchronous vibrations, marking the minimum flow limit of a machine. Recent works presented an experimental approach to estimate the stall force induced by the unbalanced pressure field in a vaneless diffuser using dynamic pressure measurements. In this study, the results of a 3D-unsteady simulation of a radial stage model were used to estimate the stall force and to compare it with the approximation obtained with an "experimental-like" approach. Results showed that: a) the experimental approach, using an ensemble average approach for transposing data between time and space domains provides sufficiently accurate results; b) the momentum contribution, neglected in experiments, gives negligible contribution to the final intensity of the stall force

A PATH TOWARDS THE AERODYNAMIC ROBUST DESIGN OF LOW PRESSURE TURBINES

ABSTRACT Airline companies are continuously demanding lower-fuelconsuming engines and this leads to investigating innovative configurations and to further improving single module performance. In this framework the Low Pressure Turbine (LPT) is known to be a key component since it has a major effect on specific fuel consumption (SFC). Modern aerodynamic design of LPTs for civil aircraft engines has reached high levels of quality, but new engine data, after first engine tests, often cannot achieve the expected performance. Further work on the modules is usually required, with additional costs and time spent to reach the quality level needed to enter in service. The reported study is aimed at understanding some of the causes for this deficit and how to solve some of the highlighted problems. In a real engine, the LPT module works under conditions which differ from those described in the analyzed numerical model: the definition of the geometry cannot be so accurate, a priori unknown values for boundary conditions data are often assumed, complex physical phenomena are seldom taken into account, operating cycle may differ from the design intent due to a non-optimal coupling with other engine components. Moreover, variations are present among different engines of the same family, manufacturing defects increase the uncertainty and, finally, deterioration of the components occurs during service. Research projects and several studies carried out by the authors lead to the conclusion that being able to design a module whose performance is less sensitive to variations (Robust LPT) brings advantages not only when the engine performs under strong off-design conditions but also, due to the abovementioned unknowns, near the design point as well. Concept and Preliminary Design phases are herein considered, highlighting the results arising from sensibility studies and their impact on the final designed robust configuration. Module performance is afterward estimated using a statistical approach

Improved reference genome of the arboviral vector Aedes albopictus

Background: The Asian tiger mosquito Aedes albopictus is globally expanding and has become the main vector for human arboviruses in Europe. With limited antiviral drugs and vaccines available, vector control is the primary approach to prevent mosquito-borne diseases. A reliable and accurate DNA sequence of the Ae. albopictus genome is essential to develop new approaches that involve genetic manipulation of mosquitoes. Results: We use long-read sequencing methods and modern scaffolding techniques (PacBio, 10X, and Hi-C) to produce AalbF2, a dramatically improved assembly of the Ae. albopictus genome. AalbF2 reveals widespread viral insertions, novel microRNAs and piRNA clusters, the sex-determining locus, and new immunity genes, and enables genome-wide studies of geographically diverse Ae. albopictus populations and analyses of the developmental and stage-dependent network of expression data. Additionally, we build the first physical map for this species with 75% of the assembled genome anchored to the chromosomes. Conclusion: The AalbF2 genome assembly represents the most up-to-date collective knowledge of the Ae. albopictus genome. These resources represent a foundation to improve understanding of the adaptation potential and the epidemiological relevance of this species and foster the development of innovative control measures