Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Pressure fluctuations from large-scale PIV over a serrated trailing edge

Abstract: Measurements of distributed surface pressure fluctuations over trailing-edge serrations at a Reynolds number Re θ = 4900 are performed with time-resolved 3D particle imaging velocimetry using helium filled soap bubbles as flow tracers. The sparse velocity vector field obtained with Lagrangian particle tracking is densely reconstructed using VIC+, a data assimilation technique based on the vortex-in-cell method. The instantaneous pressure distribution is inferred by invoking the momentum equation. Experiments are performed first over a flat plate, as assessment of the technique, where the properties of the convecting turbulent boundary layer are assessed and surface pressure fluctuations are validated against synchronous surface microphone measurements. The analysis of the flow over the trailing-edge serration focuses on the characterization of the spatial distribution and spectral coherence of surface pressure fluctuations, i.e. the flow features responsible for the acoustic scattering. Present results indicate that the measurement technique is suited to describe the spatio-temporal development of the pressure fluctuations over the serration surface at the proposed scale of the experiments. Graphic abstract: [Figure not available: see fulltext.].Wind EnergyAerodynamics, Wind Energy & Propulsio

A parametric study of serration design for trailing–edge broadband noise reduction

This work discusses the physics of noise reduction achieved from serrated trailing–edges and its impact by the serration design. An experimental campaign is carried out with a benchmark 2D model based on a NACA 633–018 airfoil. Different trailing-edge serrations are tested under several flow speeds and angles of attack conditions to build a complete dataset of acoustic measurements. Systematic modifications of a reference sawtooth serration design are made to its scale and geometry. Scale modifications are based on sawtooth serrations and comprehend carefully considered variations of the serration height (2h), wavenumber (λ), and aspect ratio (2h/λ). Geometric shape modifications are represented by concave–shaped and combed–sawtooth serrations. This study represents a unique sensitivity–based parametric analysis on the scaling and geometric properties of trailing–edge serrations where the impacts of each modification are studied separately. The results obtained are used to provide guidelines for serration design choices and their impact on broadband noise reduction.Wind EnergyAerodynamic

Aeroacoustics of sawtooth trailing-edge serrations under aerodynamic loading

The impact of aerodynamic loading on a serrated trailing edge is studied experimentally. Aerodynamic and acoustic measurements are conducted on a sawtooth-shaped trailing edge, retrofitted to a flat plate featuring a trailing-edge flap, and placed at incidence to the free-stream flow. The turbulent flow across the trailing edge is inspected by time-resolved three-dimensional velocity field measurements obtained from 4D-PIV, while the wall-pressure fluctuations are measured with surface-embedded microphones. Results discuss the relation between the velocity fluctuations over the serrations, the surface pressure fluctuations, and the far-field noise spectra. The aerodynamic analysis discusses the effect of counter-rotating vortex pairs, generated by the pressure imbalance across the edges of the serrations under loading. It is shown that the interaction of these vortices with the incoming turbulence affects the intensity of the wall-pressure spectrum at the outer rim of the serration surface. On the suction side, the intensity of the pressure fluctuations from the incoming boundary layer dominates over that induced by the vortex pairs. On the pressure side, instead, the velocity gradient prescribed by the vortex pairs produces a significant increase of the pressure fluctuations around the edges. The resulting spatial distribution of the wall-pressure fluctuations directly affects the far-field noise. Scattering predictions carried out with the wall-pressure fluctuations in the centre and root (on the suction side) exhibit good agreement with the measured noise in the low-frequency range, whereas using the surface pressure data at the tip of the serration (on the pressure side) yields a better prediction in the high-frequency range.Wind EnergyAerospace EngineeringAerodynamic

A physics-based description and modelling of the wall-pressure fluctuations on a serrated trailing edge

A physical description of the flow mechanisms that govern the distribution of the wall-pressure fluctuations over the surface of a serrated trailing edge is proposed. Three main mechanisms that define the variation of turbulent pressure fluctuations across the serrated edge are discussed and semi-empirical models are formulated accordingly. It is shown that the intensity of the wall-pressure fluctuations increases at the tips under the effect of an increased convective velocity as a result of sidewise momentum diffusion. Furthermore, the change of impedance across the edge causes a local reduction of the pressure fluctuations in the vicinity of the trailing edge. Finally, aerodynamic loading over the serrations due to the non-symmetric flow created at different angles of attack establishes secondary flow patterns that induce higher wall-pressure fluctuations over the serration edges. The latter effect is present only for serrations under high aerodynamic loading, while the former ones are observed under any conditions. Semi-empirical models are formulated for predicting the variation of the wall-pressure fluctuations over the serration surface based on the three physical mechanisms described. These models are calibrated and compared against experiments conducted on a symmetric airfoil model at high Reynolds numbers.Wind EnergyAerodynamic

Wall pressure fluctuations over a serrated trailing edge at different angles of attack

iew Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2179.vidThe unsteady surface pressure fluctuations over trailing-edge serrations retrofitted to the benchmark NACA 633-018 profile are experimentally measured. Miniaturized unsteady pressure transducers installed on the serration surface are used to describe the temporal and spatial distribution of the wall pressure fluctuations over the trailing-edge add-on. The measured spectra, convection velocity, and correlation lengths of the surface pressure fluctuations are presented for the most upstream sensor and compared against the data at different locations along the serration surface. Different angles of attack are tested in a Reynolds number of 2,000,000 (based on the airfoil chord) in order to describe the properties of the wall pressure fluctuations at a range of representative conditions for wind turbine applications. The study details the characteristics of the wall-pressure fluctuations on the serration surface. In particular, the distribution of the wall-pressure fluctuations with and without aerodynamic loading caused by the variation of the airfoil angle of attack is shown, highlighting the impact of the vortex pairs formed around the edges of the serrations under loading on the wall-pressure fluctuations. The experimental results focus on the modifications of the wall-pressure fluctuations over the serration surface. Results show that, at small angles of attack, the amplitude of the wall-pressure fluctuations is higher at the serration root for low frequencies and at the serration tip for high frequencies. As the angle of attack increases, the aerodynamic loading over the serrations causes an increase in the wall pressure fluctuations around the edges of the serrations. This increase depends on the incoming fluctuations from the boundary layer and is related to the degradation of serration acoustic performance at angle. Furthermore, the experimental results corroborate to the benchmark activities for trailing-edge serration noise carried out in collaboration with DTU and DLR, providing information about the pressure fluctuations measured near the edges of the serration.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Wind Energ

Electric flight scheduling with battery-charging and battery-swapping opportunities

With the current advances in aircraft design and Lithium-Ion batteries, electric aircraft are expected to serve as a replacement for conventional, short-range aircraft. This paper addresses the main operational challenges for short-range flights operated with electric aircraft: determining the investment needs for a fleet of electric aircraft, and the logistics of charging stations and swap batteries required to support these flights. A mixed-integer linear program with two phases is proposed. In the first phase, a schedule for flight and battery recharge is developed for a fleet of electric aircraft. In the second phase, optimal times for battery charging are determined, together with an optimal sizing of the number of charging stations and swap batteries. We illustrate our model for short-range flights to and from an European airport and for an electric aircraft designed based on the operational characteristics of a conventional, narrow-body aircraft.Aerospace Transport & OperationsFlight Performance and Propulsio

World heritage mapping in a standard-based structured geographical information system

This research aims at the study of the (dynamic) relationship between the World Heritage sites and the related human settlements development. Geographical Information Systems (GIS) can be useful to represent the involved information and to analyze such relationship. However, an effective harmonized structure and unique storage of possibly heterogeneous datasets is necessary to enable it. This initial step is the focus of this paper. First, the description of the structure of the related datasets and the assessment of the availability, quality, and consistency of the available information about the Heritage sites and properties is presented. Among those requirements, the quality of the associated spatial information is critical (e.g. kind of shape, accuracy, georeferencing). Second, considering the structure of the available datasets concerning the world heritage, together with the HERILAND research requirements, a global world heritage GIS is designed. The classification and data model to manage the WH list falls within the wider issue of structuring the cultural heritage documentation, involving both the definition of the semantic content and the geometric representation. In order to comply with the important requirement of data interoperability in science and to strengthen the outcomes of the research, some standardized data models and classifications are considered. Heritage & ValuesUrban Data ScienceArchitectural Engineering +Technolog

Wavefront measurement for EUV lithography system through Hartmann sensor

Accurate wavefront aberration measurement are essential for next-generation Extreme Ultraviolet (EUV) Lithography. During the past years several accurate interferometric techniques have been developed, but these techniques have limitation. In this work we discuss a different technique based on the Hartmann Wavefront Sensor that requires no interferometry. We present a mathematical model of this system and describe our experimental setup which demonstrates the feasibility and advantages in terms of dynamic range and accuracy compared to interferometric techniquesImaging Science and TechnologyApplied Science

Correction: Aeroacoustic Benchmarking of Trailing-edge Noise from a NACA 633–018 Airfoil with Trailing-edge Serrations: Aeroacoustic Benchmarking of Trailing-Edge Noise from a NACA 63 ₃ –018 Airfoil with Trailing-Edge Serrations (which has been published in the AIAA Journal Vol. 61, No. 1, and can be accessed online via https://doi.org/10.2514/1.J061630)

Correction Notice The authors would like to provide the following corrections and clarifications to the article titled “Aeroacoustic Benchmarking of Trailing-edge Noise from a NACA 633–018 Airfoil with Trailing-edge Serrations” which has been published in the AIAA Journal Vol. 61, No. 1, and can be accessed online via https://doi.org/10.2514/1.J061630. The first correction provides clarity in the abstract. Although the main text and Appendices A and B of the original paper provide a thorough analysis of the varying signal-to-noise levels and clearly state that some data points with inherently high noise levels should be excluded in further analysis, the statement in the abstract could lead to misunderstanding that all data points will directly be included in the benchmark activities. It indeed is up to a broader benchmarking team, after considering results among different institutions, to decide which parts of the present dataset will eventually be included. Therefore, for clarity, the text “ ::: The present data are to be included in the framework of the Benchmark Problems for Airframe Noise Computation ::: ” should be replaced by “ ::: The present data are to be considered among participating institutions and may partially be included in the framework of the Benchmark Problems for Airframe Noise Computation ::: ”. The second correction pertains to the manufacturer of the so-called High-Reynolds Model (HRM) airfoil and a reference mentioned in the second paragraph of Sec. II.A. The text “ ::: manufactured by Deharde ::: [23]” should be “ ::: manufactured by RIVAL ::: [23]”. The part of the model considered in this paper was manufactured by RIVAL and Deharde later produced the spanwise extensions for this model to fit in other larger wind tunnels. The authors apologize for this miscommunication. Besides, Ref. [23] in the original paper should be replaced by Ref. [1] of this correction. During the publication process of our paper, this new reference was published and the original Ref. [23] was updated. Therefore, Ref. [1] of this correction provides up-to-date information about the model and is therefore worth referring to. (Figures Presented) The final correction pertains to the plots in Figs. 13 and 15 in the original article. The legends went missing during the production process. Figures 13 and 15 in the original article should appear as Figs. 1 and 2 in this correction, respectively, with the legends on the right side. The authors apologize for this error.Control & SimulationReflection & LifestyleWind EnergyControl & Operation