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Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation

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A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 29548

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Dr. Hasan Kamliya Jawahar

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Guest Editor

Department of Aerospace Engineering, University of Bristol, Bristol BS8 1TH, UK
Interests: aerodynamics; aeroacoustics; high-lift device; hydrodynamics; propellers; turbulence; jets; experimentalfluid dynamics; flow-control; noise-control; wall-bounded flows; surface-treatments; computational fluid dynamics; large eddy simulation

Dr. Stefano Meloni

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Guest Editor

Department of engineering, University of Roma Tre, 00154 Roma RM, Italy
Interests: aeroacoustics; fluid dynamics; wall pressure fluctuations; turbulence
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Special Issue Information

Dear Colleagues,

Future civil air transport concepts such as supersonic aircrafts for long-range air routes and propeller-driven electric aircrafts for regional transports are continuously developing to reduce air pollution. However, their societal acceptance is key to their success, and it may be severely restricted in densely populated areas due to noise emissions.

A common denominator of these upcoming aircraft concepts is the formidable complexity of the highly unsteady aerodynamic and acoustic interactions with the adjacent propulsion systems and aircraft structures, affecting both the aerodynamic performance and noise emissions. The prediction of the aerodynamic performance and noise emission remains challenging, especially for the innovative non-conventional air transport concepts such as Blended Wing Body and Urban Air Mobility aircrafts.

This Special Issue of Fluids calls for high-quality papers in the fields of aerodynamics and aeroacoustics related to future aircraft technologies for greener aviation. We are very interested in receiving manuscripts from researchers from both academia and industry dealing with recent experimental, theoretical, and computational advances, as well as reviews showcasing the current state-of-the-art and all the perspectives related to a greener aviation.

Dr. Hasan Kamliya Jawahar
Dr. Stefano Meloni
Guest Editors

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Keywords

aerodynamics
aeroacoustics
greener aviation
noise emissions
aircraft technologies

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Published Papers (10 papers)

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22 pages, 34917 KiB

Open AccessArticle

Unsteady Subsonic/Supersonic Flow Simulations in 3D Unstructured Grids over an Acoustic Cavity

by Guillermo Araya

Fluids 2024, 9(4), 92; https://doi.org/10.3390/fluids9040092 - 17 Apr 2024

Viewed by 1406

Abstract

In this study, the unsteady Reynolds-averaged Navier–Stokes (URANS) equations are employed in conjunction with the Menter Shear Stress Transport (SST)-Scale-Adaptive Simulation (SAS) turbulence model in compressible flow, with an unstructured mesh and complex geometry. While other scale-resolving approaches in space and time, such as direct numerical simulation (DNS) and large-eddy simulation (LES), supply more comprehensive information about the turbulent energy spectrum of the fluctuating component of the flow, they imply computationally intensive situations, usually performed over structured meshes and relatively simple geometries. In contrast, the SAS approach is designed according to “physically” prescribed length scales of the flow. More precisely, it operates by locally comparing the length scale of the modeled turbulence to the von Karman length scale (which depends on the local first- and second fluid velocity derivatives). This length-scale ratio allows the flow to dynamically adjust the local eddy viscosity in order to better capture the large-scale motions (LSMs) in unsteady regions of URANS simulations. While SAS may be constrained to model only low flow frequencies or wavenumbers (i.e., LSM), its versatility and low computational cost make it attractive for obtaining a quick first insight of the flow physics, particularly in those situations dominated by strong flow unsteadiness. The selected numerical application is the well-known M219 three-dimensional rectangular acoustic cavity from the literature at two different free-stream Mach numbers,

M_{\infty}

(0.85 and 1.35) and a length-to-depth ratio of 5:1. Thus, we consider the “deep configuration” in experiments by Henshaw. The SST-SAS model demonstrates a satisfactory compromise between simplicity, accuracy, and flow physics description. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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58 pages, 9670 KiB

Open AccessArticle

Parametrization Effects of the Non-Linear Unsteady Vortex Method with Vortex Particle Method for Small Rotor Aerodynamics

by Vincent Proulx-Cabana, Guilhem Michon and Eric Laurendeau

Fluids 2024, 9(1), 24; https://doi.org/10.3390/fluids9010024 - 15 Jan 2024

Viewed by 1795

Abstract

The aim of this article is to investigate the parameter sensitivity of the (Non-Linear) Unsteady Vortex Lattice Method-Vortex Particle Method [(NL-)UVLM-VPM] with Particle Strength Exchange-Large Eddy Simulations (PSE-LES) method on a lower Reynolds number rotor. The previous work detailed the method, but introduced parameters whose influence were not investigated. Most importantly, the Vreman model coefficient was chosen arbitrarily and was not suitable to ensure stability for this lower Reynolds number rotor simulation. In addition, the previous work presented a consistency study where geometry and time discretization were refined simultaneously. The present article starts with a comparative literature review of potential methods used to solve the aerodynamics of an isolated hovering rotor. This review highlights the differences in modeling, discretizations, sensitivity analysis, validation cases, and the results chosen by the different studies. Then, a transparent and thorough parametric study of the method is presented alongside discussions of the observed results and their physical interpretation regarding the flow. The sensitivity analysis is performed for the three free parameters of UVLM, namely Vatistas core size, the geometry and the temporal discretizations, and then for the three additional parameters introduced by UVLM-VPM, which are the Vreman model coefficient, the particle spacing, and the conversion time. The effect of different databases in the non-linear coupling is also shown. The method is shown to be consistent with both geometry and temporal refinements. It is also consistent with the expected behavior of the different parameters change, including the numerical stability that depends on the strength of the LES diffusion controlled by the Vreman model coefficient. The effect of discretization refinement presented here not only shows the integrated coefficients where different errors can cancel each other, but also looks at their convergence and where relevant, the distributed loads and tip singularity position. Finally, the aerodynamics results of the method are compared for different databases and with higher fidelity Unsteady Reynolds Averaged Navier–Stokes (URANS) 3D results on a lower Reynolds number rotor. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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12 pages, 4086 KiB

Open AccessArticle

Numerical Study of the Influence of the Critical Reynolds Number on the Aerodynamic Characteristics of the Wing Airfoil

by Anna Utkina, Andrey Kozelkov, Roman Zhuchkov and Dmitry Strelets

Fluids 2023, 8(10), 276; https://doi.org/10.3390/fluids8100276 - 13 Oct 2023

Cited by 1 | Viewed by 1563

Abstract

The paper reports the results of a study concerned with the influence of the size of the leading edge laminar bubble on the aerodynamic characteristics of the HGR01 airfoil. The completely turbulent and transient flows are considered. The mechanism of the appearance and interaction of laminar and turbulent flow separation near the leading and trailing edges of the airfoil is studied in detail. In the paper, the dependence of aerodynamic forces on the critical Reynolds number for the HGR01 airfoil is discussed. It has been established that the separation bubble at the leading edge can only be obtained using the laminar–turbulent transition model. Fully turbulent models are not able to show this feature of the airfoil flow. Graphs of the lift coefficient as a function of the critical Reynolds number, as well as the pressure distribution as a function of the size of the laminar bubble, are shown. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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18 pages, 15091 KiB

Open AccessArticle

Efficient Scale-Resolving Simulations of Open Cavity Flows for Straight and Sideslip Conditions

by Karthick Rajkumar, Eike Tangermann and Markus Klein

Fluids 2023, 8(8), 227; https://doi.org/10.3390/fluids8080227 - 8 Aug 2023

Cited by 1 | Viewed by 1825

Abstract

This study aims to facilitate a physical understanding of resonating cavity flows with efficient numerical treatments of turbulence. It reinforces the efficiency and affordability of scale-adaptive numerical techniques for simulating open cavity flows with a separated shear layer consisting of a wide range of flow scales. Visualization of the resonant modes occurring due to the acoustic feedback loop aids in a better understanding of large-scale flow oscillations. Under this scope, scale-adaptive simulation (SAS) based on the k-

ω

SST RANS model with different turbulence treatments has been studied for an open cavity configuration with a length-to-depth

(L / D)

ratio of

5.7

featuring Mach number (

M a

)

0.8

and Reynolds number (

R e

)

12 \times 10^{6}

. It is shown that the essential cavity flow physics has been captured using the SAS approach with more than

90 %

improved computational efficiency compared to commonly used hybrid RANS-LES approaches. In addition, wall-modeled SAS when supplemented with an artificial forcing concept to trigger the model provides very good spectral estimates comparable with hybrid RANS-LES results. Following the validation of numerical approaches, the directional dependence of the cavity resonance is investigated under asymmetric flow conditions, and spanwise interference of waves due to the lateral walls of the cavity has been observed. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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20 pages, 14723 KiB

Open AccessArticle

An Affordable Acoustic Measurement Campaign for Early Prototyping Applied to Electric Ducted Fan Units

by Stefan Schoder, Jakob Schmidt, Andreas Fürlinger, Roppert Klaus and Maurerlehner Paul

Fluids 2023, 8(4), 116; https://doi.org/10.3390/fluids8040116 - 31 Mar 2023

Viewed by 2337

Abstract

New innovative green concepts in electrified vertical take-off and landing vehicles are currently emerging as a revolution in urban mobility going into the third dimension (vertically). The high population density of cities makes the market share highly attractive while posing an extraordinary challenge in terms of community acceptance due to the increasing and possibly noisier commuter traffic. In addition to passenger transport, package deliveries to customers by drones may enter the market. The new challenges associated with this increasing transportation need in urban, rural, and populated areas pose challenges for established companies and startups to deliver low-noise emission products. The article’s objective is to revisit the benefits and drawbacks of an affordable acoustic measurement campaign focused on early prototyping. In the very early phase of product development, available resources are often considerably limited. With this in mind, this article discusses the sound power results using the enveloping surface method in a typically available low-reflection room with a reflecting floor according to DIN EN ISO 3744:2011-02. The method is applied to a subsonic electric ducted fan (EDF) unit of a 1:2 scaled electrified vertical take-off and landing vehicle. The results show that considerable information at low costs can be gained for the early prototyping stage, despite this easy-to-use, easy-to-realize, and non-fine-tuned measurement setup. Furthermore, the limitations and improvements to a possible experimental setup are presented to discuss a potentially more ideal measurement environment. Measurements at discrete operating points and transient measurements across the total operating range were conducted to provide complete information on the EDF’s acoustic behavior. The rotor-self noise and the rotor–stator interaction were identified as primary tonal sound sources, along with the highest broadband noise sources located on the rotor. Based on engineering experience, a first acoustic improvement treatment was also quantified with a sound power level reduction of 4 dB(A). In conclusion, the presented method is a beneficial first measurement campaign to quantify the acoustic properties of an electric ducted fan unit under minimal resources in a reasonable time of several weeks when starting from scratch. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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17 pages, 2828 KiB

Open AccessArticle

Aerodynamic Shape Optimization of a Symmetric Airfoil from Subsonic to Hypersonic Flight Regimes

by Bernardo Leite, Frederico Afonso and Afzal Suleman

Fluids 2022, 7(11), 353; https://doi.org/10.3390/fluids7110353 - 15 Nov 2022

Viewed by 5922

Abstract

Hypersonic flight has been the subject of numerous research studies during the last eight decades. This work aims to optimize the aerodynamic performance of a two-dimensional baseline airfoil (NACA0012) at distinct flight regimes from subsonic to hypersonic speeds. A mission profile has been defined, where four points representing the subsonic, transonic, supersonic, and hypersonic flow conditions have been selected. A framework has been implemented based on high-fidelity RANS computational fluid dynamics simulations. Gradient-based optimizations have been conducted with the objective of minimizing the drag. The optimization results show an overall improvement in aerodynamic performance, including a decrease in the drag coefficient of up to 79.2% when compared to the baseline airfoil. In the end, a morphing strategy has been laid out based on the optimal shapes produced by the optimization. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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17 pages, 8628 KiB

Open AccessArticle

An Experimental Study of the Aeroacoustic Properties of a Propeller in Energy Harvesting Configuration

by Paolo Candeloro, Edoardo Martellini, Robert Nederlof, Tomas Sinnige and Tiziano Pagliaroli

Fluids 2022, 7(7), 217; https://doi.org/10.3390/fluids7070217 - 27 Jun 2022

Cited by 6 | Viewed by 2635

Abstract

The aim of the present manuscript is to investigate the noise footprint of an isolated propeller in different flight configurations for the propulsion of a hybrid-electric aircraft. Experimental tests were performed at the Low-Turbulence Tunnel located at Delft University of Technology with a powered propeller model and flush-mounted microphones in the tunnel floor. The propeller was investigated at different advance ratios in order to study the noise impact in propulsive and energy harvesting configurations. For brevity, this work only reports the results at the conditions of maximum efficiency in both propulsive and energy harvesting regimes, for a fixed blade pitch setting. Comparing these two configurations, a frequency-domain analysis reveals a significant modification in the nature of the noise source. In the propulsive configuration, most of the energy is related to the tonal noise component, as expected for an isolated propeller; however, in energy harvesting configuration, the broadband noise component increases significantly compared to the propulsive mode. A more detailed analysis requires separation of the two noise components and, for this purpose, an innovative decomposition strategy based on proper orthogonal decomposition (POD) has been defined. This novel technique shows promising results; both in the time and in the Fourier domains the two reconstructed components perfectly describe the original signal and no phase delays or other mathematical artifices are introduced. In this sense, it can represent a very powerful tool to identify noise sources and, at the same time, to define a proper control strategy aimed at noise mitigation. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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14 pages, 2599 KiB

Open AccessArticle

Evaluation of Turbulent Jet Characteristic Scales Using Joint Statistical Moments and an Adaptive Time-Frequency Analysis

by Anderson R. Proença and Stefano Meloni

Fluids 2022, 7(4), 125; https://doi.org/10.3390/fluids7040125 - 25 Mar 2022

Cited by 1 | Viewed by 2821

Abstract

This paper presents an analysis of turbulence characteristic scales and eddy convection velocity of jet flows computed using joint statistical moments, digital filters, and a modified version of the empirical mode decomposition (EMD). The ongoing aim of this study is to develop semi-empirical space-time cross-correlation models based on stationary statistics and jet physical lengths. Multivariate statistics are used to correlate jet properties to one-dimensional time series. The data available to this study were recorded from single-point and two-point hot-wire anemometry experiments carried out for a range of jet Mach numbers (

0.2 \leq M \leq 0.8

). Firstly, the jet eddy convection velocity, turbulence length, and time scales are computed using space-time cross-correlation functions. Isotropic flow and frozen turbulence hypothesis are then used to estimate the joint moments from single-point statistics in the fully developed turbulence region. An EMD-based decomposition method is presented and assessed in both the Gaussian and non-Gaussian signal regions. It is demonstrated that the artificially filtered signal reconstructs the physical properties of single and multi-point jet statistics. The relationship between central moments and joint moments presented here focuses on the region of high turbulence levels, which generates the vast majority of jet mixing noise produced by turbofan engines. Further analysis is required to extend this investigation to intermittent zones and other jet noise sources, such as jet-surface installation noise. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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17 pages, 18894 KiB

Open AccessArticle

A Wavelet-Based Time-Frequency Analysis on the Supersonic Jet Noise Features with Chevrons

by Stefano Meloni and Hasan Kamliya Jawahar

Fluids 2022, 7(3), 108; https://doi.org/10.3390/fluids7030108 - 16 Mar 2022

Cited by 13 | Viewed by 2519

Abstract

A detailed investigation of the statistical properties of the near-field pressure fluctuations induced by an under-expanded jet, by varying the nozzle exit shapes has been presented. Experiments using different convergent Chevron nozzles were carried out in the anechoic chamber at the University of Bristol to assess the importance of the Chevron shape on the near pressure field emitted by a single stream under-expanded jet. Measurements were carried out through an axial microphone array traversed radially to various positions for jet in an under-expanded condition at Mach number M = 1.3. The intermittent behavior is investigated considering the standard statistical indicators and a wavelet-based conditional approach, including the phase angle. The intermittent degree of various features related to different scales, such as Screech tones and broadband shock associate noise were estimated. A series of recently developed wavelet-based tools were assessed as a viable approach to investigate the noise emitted by under-expanded jets. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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Review

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24 pages, 1294 KiB

Open AccessReview

Recent Advances in Passive Acoustic Localization Methods via Aircraft and Wake Vortex Aeroacoustics

by Arnav Joshi, Mustafa M. Rahman and Jean-Pierre Hickey

Fluids 2022, 7(7), 218; https://doi.org/10.3390/fluids7070218 - 29 Jun 2022

Cited by 5 | Viewed by 4262

Abstract

Passive acoustic aircraft and wake localization methods rely on the noise emission from aircraft and their wakes for detection, tracking, and characterization. This paper takes a holistic approach to passive acoustic methods and first presents a systematic bibliographic review of aeroacoustic noise of aircraft and drones, followed by a summary of sound generation of wing tip vortices. The propagation of the sound through the atmosphere is then summarized. Passive acoustic localization techniques utilize an array of microphones along with the known character of the aeroacoustic noise source to determine the characteristics of the aircraft or its wake. This paper summarizes the current state of knowledge of acoustic localization with an emphasis on beamforming and machine learning techniques. This review brings together the fields of aeroacoustics and acoustic-based detection the advance the passive acoustic localization techniques in aerospace. Full article

(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)

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