1,720,978 research outputs found
Laminar to Turbulent Boundary Layer Transition Investigation on a Supercritical Airfoil Using the γ−θ Transitional Model
No full textNonparametric Fitting of Aerodynamic Data Using Smoothing Thin Plate Splines
No full text.This paper introduces a nonparametric fitting method for the interpolation of aerodynamic observations over a large range of multiple angles of attack. The method is based on the employment of smoothing thin-plate spline class functions, a well-renewed mathematical tool for multivariate data mining based on the generalization of the univariate natural cubic splines, in which a roughness penalty criterion is used to produce very smooth predictive hypersurfaces. Compared with other methods, such as parametric or even conventional nonparametric methods, the use of a smoothing thin-plate spline is more effective, in that the predictive surface comes directly from the observed points, thus minimizing any intervention of the analyst aimed at introducing model parameters. This forms the basis for a very reliable fitting technique, in which model construction can be relatively easy to implement. An application of the method is carried out on a case study representative of some experimental data coming from a wind-tunnel campaign on a typical three-dimensional fuselage-shaped body, aimed at the acquisition of its aerodynamic coefficients over a rather extensive attitude range. Specifically, the application is focused on the body lift coefficient as a function of both angle of attack and sideslip angle. The data set is also interpolated using concurrent responsesurface methods: namely, a linear model, a bivariate spline, a radial basis function network, a support vector regression technique, a regression kriging, and a moving-least-squares approach, alternatively known as local polynomial regression. Results of data fitting are assessed using a cross-validation approach and reveal a clear superiority of smoothing thin-plate spline over the other methods, leading to a more regular fitted surface and a more reliable prediction tool, even when some observations are omitted. This is important per se, but acquires even more significance when an aerodynamic test campaign is to be planned with the minimum number of experimental observation
Numerical vs. Experimental assessment of optimization effects on aerodynamic performance of erica tiltrotor fuselage
No full textThe results of a CFD-based optimization over a 1/8-scaled model of the ERICA tiltrotor fuselage are compared against experimental data obtained from an extensive wind tunnel campaign carried out at the RUAG facilities, as part of the DREAm-Tilt project funded by the Joint Technology Initiative Clean-Sky program. In particular, the effects of optimized geometries of nose, wing/fuselage junction, sponsons and empennages for drag reduction are investigated. The assessment proved the consistency of the optimization approach and the optimized ERICA geometries as experimental validation was successfully obtained
Efficiency and stall margin enhancement in transonic compressor rotors using synthetic jets: A numerical investigation
No full textSeveral passive and active techniques were studied and developed by compressor designers with the aim of improving the aerodynamic behavior of compressor blades by reducing, or even eliminating, flow separation. Fluidic-based methods, in particular, were investigated for a long time, including both steady and unsteady suction, blowing and oscillating jets. Recently, synthetic jets (zero mass flux) have been proposed as a promising solution to reduce low momentum fluid regions inside turbomachines. Synthetic jets, with the characteristics of zero net mass flux and non-zero momentum flux, do not require a complex system of pumps and pipes. They could be very efficient because at the suction part of the cycle the low momennim fluid is sucked into the device, whereas in the blowing part a high-momentum jet accelerates it. To the authors' knowledge, the use of synthetic jets has never been experimented in transonic compressor rotors, where this technique could be helpful (i) to reduce the thickness and instability of blade suction side boundary layer after the interaction with the shock, and (ii) to delay the arising of the low momentum region which can take place from the shock-tip clearance vortex interaction at low flow operating conditions, a flow feature which is considered harmful to rotor stability. Therefore, synthetic jets could be helpful to improve both efficiency and stall margin in transonic compressor rotors. In this paper, an accurate and validated CFD model is used to simulate the aerodynamic behavior of a transonic compressor rotor with and without synthetic jets. Four technical solutions were evaluated, different for jet position and velocity, and one was investigated in detail. Copyright © 2010 by ASME
Multi-criteria Multi-constrained Aerodynamic Optimization of Civil Tiltrotor Empennage Surfaces
No full textThe present work describes the overall optimization strategy that has been adopted for the enhancement of the aerodynamic performance of a civil tiltrotor empennage surfaces. The optimization process has been designed around GeDEA-II, a Multi-Objective Evolutionary Algorithm developed at University of Padua. The optimization algorithm has been used in two different cases: A two-dimensional optimization of the empennage airfoil and a three-dimensional optimization of the empennage winglets, patented by Leonardo Helicopters under the name of finlets. Results demonstrate the effectiveness of the optimization strategies for both the cases. A parametric study of the empennage planform has also been conducted with the aid of an artificial neural network, in order to assess the variations in aerodynamic performance for different geometries
ERICA tiltrotor airframe wake characterization
No full textIn the framework of the European JTI CleanSky GRC2 project devoted to drag reduction of airframe and non-lifting rotating systems of the Green Rotorcraft ITD, a CFD-based optimization was performed on the ERICA tiltrotor configuration and validated by wind tunnel tests. Previous work dealt with the shape optimization of different parts of the tiltrotor fuselage (nose, sponsons, wing/fuselage fairings, empennages) for drag reduction and efficiency improvement purposes, using CFD coupled with innovative design methodologies based on multi-objective evolutionary algorithms. In this paper, a characterization of the ERICA tiltrotor aft fuselage wake is presented based on experimental stereo PIV and numerical investigations. The flow structures are analyzed in relation to the drag reduction observed for the optimized sponsons in comparison to the baseline configuration
Numerical and experimental studies on BLI propulsor architectures
Full text linkAn increasing awareness about the impact of civil air transportation emissions is currently driving a low-carbon technology transition, towards more sustainable propulsion strategies. Boundary layer ingesting systems are one of the most promising solutions, as a closer integration between fuselage and propulsors is considered a key in the achievement of more sustainable architectures. Such architecture is characterized by a high level of integration between the airframe and propulsors, making the design process become a major challenge. The present work deals with a complete CFD based design and optimization of a propulsive fuselage concept, both in terms of airframe shape and fan design
Fullscale Optimization and Fan Design of a Rear BLI Shrouded Propulsor
Full text linkThe environmental concern on the impact of civil air transportation has become a primary driving force for the research and development towards new technologies that could provide a reduction in the emissions. In the context of civil aircraft transportation, Boundary Layer Ingestion (BLI) is among the most promising solutions. Such architecture is characterized by a high level of integration between the airframe and propulsors, making the design process becomes a major challenge. The present work deals with a complete CFD based design and optimization of a propulsive fuselage concept, both in terms of airframe shape and fan design
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