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Applied Sciences
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Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft
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Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Aerospace Science and Engineering".

Deadline for manuscript submissions: closed (20 June 2022) | Viewed by 17429

Special Issue Editor

Prof. Dr. Giovanni Bernardini

E-Mail Website
Guest Editor
Department of Engineering, Roma Tre University, Via della Vasca Navale, 79, 00144 Roma, Italy
Interests: unsteady aerodynamics; structural dynamics; aeroelasticity; aeroacoustics; controls; multidisciplinary optimization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

A modern rotorcraft is a complex system, whose design involves a surprisingly high number of disciplines and technologies. Breakthroughs in the rotorcraft field during recent years led to increasingly safe, maneuverable, clean, and quiet vehicles. New configurations, ranging from compound helicopters and tiltrotors to multi-copters, have been designed and are now under certification to comply with specific requests of the market. This progress has been essentially led by new technologies, theoretical advances made in understanding the phenomena governing the physics of rotorcraft, and the development of reliable and efficient computational tools that can be effectively used in their design process. However, several issues in the fields of aerodynamics, aeroservoelasticity, and aeroacoustics remain open, calling for further advances in theory and technology. This progress will be of paramount importance to design ever more efficient, green, and silent rotorcraft, and will become crucial for the development of the urban-mobility aircraft envisaged in the near future.

This Special Issue calls for high-quality papers in the fields of aerodynamics, aeroservoelasticity, and aeroacoustics of rotorcraft, and on all related technologies. We are particularly interested in receiving manuscripts from researchers of both academia and industry, dealing with recent experimental and theoretical/computational advances.

Prof. Giovanni Bernardini
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Applied Sciences is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Near and far field noise
  • vibrations and dynamic loads
  • aeroservoelasticity
  • stability
  • structures and materials
  • active controls
  • multirotor configurations
  • structural health monitoring
  • interactional aerodynamics
  • innovative rotorcraft design

Published Papers (7 papers)

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Research

15 pages, 6052 KiB  
Article
Scalability of Mach Number Effects on Noise Emitted by Side-by-Side Propellers
by Caterina Poggi, Giovanni Bernardini, Massimo Gennaretti and Roberto Camussi
Appl. Sci. 2022, 12(19), 9507; https://doi.org/10.3390/app12199507 - 22 Sep 2022
Cited by 7 | Viewed by 1128
Abstract
This paper presents a numerical investigation of noise radiated by two side-by-side propellers, suitable for Distributed-Electric-Propulsion concepts. The focus is on the assessment of the variation of the effects of blade tip Mach number on the radiated noise for variations of the direction [...] Read more.
This paper presents a numerical investigation of noise radiated by two side-by-side propellers, suitable for Distributed-Electric-Propulsion concepts. The focus is on the assessment of the variation of the effects of blade tip Mach number on the radiated noise for variations of the direction of rotation, hub relative position, and the relative phase angle between the propeller blades. The aerodynamic analysis is performed through a potential-flow-based boundary integral formulation, which is able to model severe body–wake interactions.The noise field is evaluated through a boundary-integral formulation for the solution of the Ffowcs Williams and Hawkings equation. The numerical investigation shows that: the blade tip Mach number strongly affects the magnitude and directivity of the radiated noise; the increase of the tip-clearance increases the spatial frequency of the noise directivity at the two analyzed tip Mach numbers for both co-rotating and counter-rotating configurations; for counter-rotating propellers, the relative phase angle between the propeller blades provides a decrease of the averaged emitted noise, regardless the tip Mach number. One of the main results achieved is the scalability with the blade tip Mach number of the influence on the emitted noise of the considered design parameters. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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43 pages, 13154 KiB  
Article
Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow
by Nikos Spyropoulos, George Papadakis, John M. Prospathopoulos and Vasilis A. Riziotis
Appl. Sci. 2021, 11(24), 12097; https://0-doi-org.brum.beds.ac.uk/10.3390/app112412097 - 19 Dec 2021
Cited by 7 | Viewed by 2141
Abstract
In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is [...] Read more.
In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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23 pages, 5377 KiB  
Article
Aeroelastic Optimization Design of the Global Stiffness for a Joined Wing Aircraft
by Xuyang Li, Zhiqiang Wan, Xiaozhe Wang and Chao Yang
Appl. Sci. 2021, 11(24), 11800; https://0-doi-org.brum.beds.ac.uk/10.3390/app112411800 - 12 Dec 2021
Cited by 3 | Viewed by 2042
Abstract
Due to the complexity and particularity of the joined wing layout, traditional design methods for the global stiffness of a high-aspect wing are not applicable for a joined wing. Herein, a beam-frame model and a three-dimensional wing-box model are built to solve the [...] Read more.
Due to the complexity and particularity of the joined wing layout, traditional design methods for the global stiffness of a high-aspect wing are not applicable for a joined wing. Herein, a beam-frame model and a three-dimensional wing-box model are built to solve the global stiffness aeroelastic optimization design problem for a joined wing. The goal is to minimize the weight, and the constraints are the overall aeroelastic requirements. Based on a genetic algorithm, two methods for the beam-frame model and one method for the three-dimensional model are used for comparative analysis. The results show that the optimization method for a diagonal beam section and the optimization method for an exponential/linear combination function fit are adequate for optimizing and designating the joined wing global stiffness. The distributions obtained using the two methods have good consistency and are similar to the distribution of the three-dimensional model. The stiffness distribution data and the beam section parameters can be converted from each other, which is convenient for redesigning the structure parameters using the stiffness distribution data, and is valuable for engineering applications. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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26 pages, 6506 KiB  
Article
Experimental and Computational Aeroacoustic Investigation of Small Rotor Interactions in Hover
by Austin David Thai, Elisa De Paola, Alessandro Di Marco, Luana Georgiana Stoica, Roberto Camussi, Roberto Tron and Sheryl Marie Grace
Appl. Sci. 2021, 11(21), 10016; https://0-doi-org.brum.beds.ac.uk/10.3390/app112110016 - 26 Oct 2021
Cited by 16 | Viewed by 2759
Abstract
This paper investigates the aeroacoustic interactions of small hovering rotors, using both experiments and computations. The experiments were conducted in an anechoic chamber with arrays of microphones setup to evaluate the azimuthal and polar directivity. The computational methodology consists of high fidelity detached [...] Read more.
This paper investigates the aeroacoustic interactions of small hovering rotors, using both experiments and computations. The experiments were conducted in an anechoic chamber with arrays of microphones setup to evaluate the azimuthal and polar directivity. The computational methodology consists of high fidelity detached eddy simulations coupled to the Ffowcs-Williams and Hawkings equation, supplemented by a trailing edge broadband noise code. The aerodynamics and aeroacoustics of a single rotor are investigated first. The simulations capture a Reynolds number effect seen in the performance parameters that results in the coefficient of thrust changing with the RPM. The acoustic analysis enables the identification of self-induced noise sources. Next, dual side-by-side rotors are studied in both counter-rotating and co-rotating configurations to quantify the impact of their interactions. Higher harmonics appear due to the interactions and it is verified that the counter-rotating case leads to more noise and a less uniform azimuthal directivity. Difficulties that arise when trying to validate small rotor calculations against experiments are discussed. Comparisons of computational and experimental results yield further insight into the noise mechanisms that are captured by each methodology. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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17 pages, 4141 KiB  
Article
Revising of the Near Ground Helicopter Hover: The Effect of Ground Boundary Layer Development
by Theologos Andronikos, George Papadakis, Vasilis Riziotis and Spyros Voutsinas
Appl. Sci. 2021, 11(21), 9935; https://0-doi-org.brum.beds.ac.uk/10.3390/app11219935 - 24 Oct 2021
Cited by 2 | Viewed by 2425
Abstract
The interaction of a helicopter rotor with the ground in hover flight is addressed numerically using a hybrid Eulerian–Lagrangian CFD model. When a helicopter takes off or lands, its wake interferes with the ground. This interaction, depending on the height-to-rotor diameter ratio, causes [...] Read more.
The interaction of a helicopter rotor with the ground in hover flight is addressed numerically using a hybrid Eulerian–Lagrangian CFD model. When a helicopter takes off or lands, its wake interferes with the ground. This interaction, depending on the height-to-rotor diameter ratio, causes the altering of the rotor loading and performance as compared to the unconstrained case and gives rise to the development of a complex outwash flow field in the surrounding of the helicopter. The present study aims to characterize the interactional phenomena occurring in the early stages of the rotor wake development and in particular the interference of the starting vortex with the ground boundary layer and the effect of this interaction in the motion of the vortex in the rotor outwash flow. The hybrid CFD method employed combines a standard URANS compressible finite volume solver, the use of which is restricted to confined grids around solid bodies, and a Lagrangian approximation of the entire flow field in which conservation equations are solved in their material form, disctretized using particle representation of the flow quantities. The two methods are strongly coupled to each other through an appropriate iterative scheme. The main advantage of the proposed methodology is that it can conveniently handle complex configurations with several bodies that move independently from one another, with affordable computational cost. In this paper, thrust coefficient predictions of the hybrid model are compared to predictions of a free wake code and to experimental data indicating that consistent prediction of the rotor load requires the inclusion of the ground boundary layer in the analysis. Moreover, detailed comparisons of the rotor wake evolution predicted by the hybrid model are presented. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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34 pages, 12416 KiB  
Article
Assessment of a Mid-Fidelity Numerical Approach for the Investigation of Tiltrotor Aerodynamics
by Alex Zanotti, Alberto Savino, Michele Palazzi, Matteo Tugnoli and Vincenzo Muscarello
Appl. Sci. 2021, 11(8), 3385; https://0-doi-org.brum.beds.ac.uk/10.3390/app11083385 - 09 Apr 2021
Cited by 17 | Viewed by 3786
Abstract
The study of the complex aerodynamics that characterise tiltrotors represents a challenge for computational fluid dynamics tools. URANS numerical solvers are typically used to explore the aerodynamic features that characterise the different flight conditions of these aircraft, but their computational cost limits their [...] Read more.
The study of the complex aerodynamics that characterise tiltrotors represents a challenge for computational fluid dynamics tools. URANS numerical solvers are typically used to explore the aerodynamic features that characterise the different flight conditions of these aircraft, but their computational cost limits their applications to a few vehicle configurations. The present work explores the capabilities of a new mid-fidelity aerodynamic code that is based on the vortex particle method, DUST, to investigate the performance and flow physics of tiltrotors. With this aim, numerical simulations were performed in DUST while considering XV-15 tiltrotor configurations with increasing complexity. The study started with the investigation of a simpler configuration made up of a single wing and a proprotor. Subsequently, the full aircraft was studied in steady-level flights and its major operating flight conditions were explored—i.e., hover, conversion phase, and cruise. A thorough assessment of the code capabilities was performed by the comparison of the numerical results with high-fidelity Computational Fluid Dynamics (CFD) data. This thorough comparison showed that the mid-fidelity numerical approach implemented in DUST is suitable for capturing the flow physics related to the complex aerodynamic interactions between the proprotors and the wing along with the entire flight envelope of the tiltrotor. Moreover, a good representation of the aerodynamic performance of the vehicle was obtained, particularly for the flight conditions that are characterised by limited flow separations. The good accuracy obtained for both the performance and flow physics, combined with the relatively lower computational costs required by the mid-fidelity solver with respect to the URANS simulations, indicates that DUST could be considered a valuable tool for use in the preliminary design of novel tiltrotor configurations. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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21 pages, 10367 KiB  
Article
Aerodynamic Simulation of Helicopter Based on Polyhedron Nested Grid Technology
by Chenglong Zhou and Ming Chen
Appl. Sci. 2020, 10(22), 8304; https://0-doi-org.brum.beds.ac.uk/10.3390/app10228304 - 23 Nov 2020
Cited by 3 | Viewed by 2023
Abstract
In this paper, a computational fluid dynamics (CFD) simulation method based on the polyhedral nested grid is developed. By comparing the simulation and test results of the hovering flow field of the Caradonna–Tung rotor, the forward flight flow field of the AH-1G rotor, [...] Read more.
In this paper, a computational fluid dynamics (CFD) simulation method based on the polyhedral nested grid is developed. By comparing the simulation and test results of the hovering flow field of the Caradonna–Tung rotor, the forward flight flow field of the AH-1G rotor, the interference flow field of the Robin rotor/fuselage, and the hovering and forward flight flow field of a coaxial rotor, it is proven that the method proposed in this paper can achieve high calculation accuracy under various working conditions. The dual time-stepping method is used for the transient simulation, and the Spalart–Allmaras (S-A) turbulence model, which is widely used in aviation, is adopted in the simulation. Full article
(This article belongs to the Special Issue Aerodynamic Aeroelasticity and Aeroacoustics of Rotorcraft)
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