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Symmetry
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Symmetry in Aerospace Sciences and Applications
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Symmetry in Aerospace Sciences and Applications

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Engineering and Materials".

Deadline for manuscript submissions: 30 November 2024 | Viewed by 7193

Special Issue Editors

Dr. Xi Xia

E-Mail Website
Guest Editor
Associate Professor, Institute of Aerospace Propulsion, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Interests: vortical flows; aerodynamics; combustion
Dr. Yi Gao

E-Mail Website
Guest Editor
Associate Professor, School of Mechanical Engineering, Shanghai Jiao Tong University, 800 Dong Chuan Rd, Minhang, Shanghai 200240, China
Interests: laser fine imaging and spectrum technology for aeroengine and gas turbine combustion chamber; study on ignition characteristics and flame instability mechanism under extreme conditions; study on combustion structure and pollutant formation mechanism of low-emission combustion chamber

Special Issue Information

Dear Colleagues,

Symmetry is an intrinsic connection between mathematics and physics, serving as a cornerstone in developing mathematical principles and physical laws that allow modern aerospace sciences and technologies to thrive. This Special Issue intends to offer featured research on symmetry/asymmetry in aerospace sciences and applications. We invite contributions of theoretical, experimental, and numerical studies on all relevant topics, with emphasis on but not limited to newly proposed symmetry theories, findings of symmetry/asymmetry phenomena or patterns, novel applications of symmetry theories or concepts, technical innovations of symmetry/asymmetry devices, symmetry/asymmetry in numerics and modeling, symmetry and reduction, and symmetry breaking. Through this Special Issue, we aim to demonstrate how symmetry can advance our understanding of scientific problems and promote state-of-the-art technologies in aerospace research.

Dr. Xi Xia
Dr. Yi Gao
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. Symmetry is an international peer-reviewed open access monthly 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

  • fluid dynamics
  • gas dynamics
  • aerodynamics
  • combustion
  • propulsion
  • flow control
  • autonomous systems

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Further information on MDPI's Special Issue polices can be found here.

Published Papers (6 papers)

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Research

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15 pages, 4062 KiB  
Article
Hypergolic Ignition by Off-Center Binary Collision of Monoethanolamine-NaBH4 and Hydrogen Peroxide Droplets
by Dawei Zhang, Siduo Song, Dehai Yu, Yueming Yuan, Hongmei Liu, Xuedong Liu and Xuejun Fan
Symmetry 2024, 16(6), 682; https://doi.org/10.3390/sym16060682 - 2 Jun 2024
Viewed by 618
Abstract
Hypergolic ignition of H2O2 and MEA-NaBH4 by off-center collision of their droplets was experimentally studied, focusing on the characteristics and mechanism of droplet mixing, droplet heating and evaporation, and gas-phase ignition. The whole collision ignition process was divided into [...] Read more.
Hypergolic ignition of H2O2 and MEA-NaBH4 by off-center collision of their droplets was experimentally studied, focusing on the characteristics and mechanism of droplet mixing, droplet heating and evaporation, and gas-phase ignition. The whole collision ignition process was divided into five stages, which were compared, respectively, with that of head-on collision. Under the condition of a slightly off-center collision (for cases where B < 0.35), H2O2 droplets penetrate MEA-NaBH4 droplets after the collision and coalesce with it, but the internal H2O2 drop inside the MEA-NaBH4 droplet does not form a stable sphere. Instead, it rotates and expands inside the mixed droplet. With B increasing to 0.59, the droplets no longer coalesce after collision but separate away, forming satellite droplets. In such cases, multi-ignition mode is observed. When B increases to a certain extent, specifically, 0.85, a grazing collision is observed such that no mass transfer exists during the interaction of droplets, which leads to ignition failure. A theoretical model quantifying droplet swelling rate was established to calculate the volume change of the droplet. It was found that the swelling can be attributed to the flash boiling of superheated internal H2O2 fluid. Meanwhile, the ignition delay time was found to linearly decrease with B at various Wes until the extent where the chemical reaction takes over control, leading to an almost constant time delay defined as RDT. Additionally, the regime of ignition modes corresponding to different droplet mixing features is summarized in the We-B parametric space. Full article
(This article belongs to the Special Issue Symmetry in Aerospace Sciences and Applications)
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23 pages, 24085 KiB  
Article
An ONIOM-Based High-Level Thermochemistry Study on Hydrogen Abstraction Reactions of Large Straight-Chain Alkanes by Hydrogen, Hydroxyl, and Hydroperoxyl Radicals
by Yicheng Chi, Hao Pan, Qinghui Meng, Lidong Zhang and Peng Zhang
Symmetry 2024, 16(3), 367; https://doi.org/10.3390/sym16030367 - 18 Mar 2024
Viewed by 1098
Abstract
Accurate thermochemical data are of great importance in developing quantitatively predictive reaction mechanisms for transportation fuels, such as diesel and jet fuels, which are primarily composed of large hydrocarbon molecules, especially large straight-chain alkanes containing more than 10 carbon atoms. This paper presents [...] Read more.
Accurate thermochemical data are of great importance in developing quantitatively predictive reaction mechanisms for transportation fuels, such as diesel and jet fuels, which are primarily composed of large hydrocarbon molecules, especially large straight-chain alkanes containing more than 10 carbon atoms. This paper presents an ONIOM[QCISD(T)/CBS:DFT]-based theoretical thermochemistry study on the hydrogen abstraction reactions of straight-chain alkanes, n-CnH2n+2, (n = 1–16) by hydrogen (H), hydroxyl (OH), and hydroperoxyl (HO2) radicals. These reactions, with n ≥ 10, pose significant computational challenges for prevalent high-level ab initio methods. However, they are effectively addressed using the ONIOM-based method. One notable aspect of this study is the consideration of the high symmetry of straight-chain alkanes. This symmetry allows us to study half of the reactions, employing a generalized approach. Therefore, a total of 216 reactions are systematically studied for the three reaction systems. Our results align very well with those from the widely accepted high-level QCISD(T)/CBS method, with discrepancies between the two generally less than 0.10 kcal/mol. Furthermore, we compared large straight-chain alkanes (n-C16H34 and n-C18H38) with large methyl ester molecules (C15H31COOCH3 and C17H33COOCH3) to elucidate the impact of functional groups (ester group and C=C double bond) on the reactivity of the long-chain structure. These findings underscore the accuracy and efficiency of the ONIOM-based method in computational thermochemistry, particularly for large straight-chain hydrocarbons in transportation fuels. Full article
(This article belongs to the Special Issue Symmetry in Aerospace Sciences and Applications)
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24 pages, 10039 KiB  
Article
Dynamical Behavior of Small-Scale Buoyant Diffusion Flames in Externally Swirling Flows
by Tao Yang, Yuan Ma and Peng Zhang
Symmetry 2024, 16(3), 292; https://doi.org/10.3390/sym16030292 - 2 Mar 2024
Viewed by 1256
Abstract
This study computationally investigates small-scale flickering buoyant diffusion flames in externally swirling flows and focuses on identifying and characterizing various distinct dynamical behaviors of the flames. To explore the impact of finite rate chemistry on flame flicker, especially in sufficiently strong swirling flows, [...] Read more.
This study computationally investigates small-scale flickering buoyant diffusion flames in externally swirling flows and focuses on identifying and characterizing various distinct dynamical behaviors of the flames. To explore the impact of finite rate chemistry on flame flicker, especially in sufficiently strong swirling flows, a one-step reaction mechanism is utilized for investigation. By adjusting the external swirling flow conditions (the intensity R and the inlet angle α), six flame modes in distinct dynamical behaviors were computationally identified in both physical and phase spaces. These modes, including the flickering flame, oscillating flame, steady flame, lifted flame, spiral flame, and flame with a vortex bubble, were analyzed from the perspective of vortex dynamics. The numerical investigation provides relatively comprehensive information on these flames. Under the weakly swirling condition, the flames retain flickering (the periodic pinch-off of the flame) and are axisymmetric, while the frequency nonlinearly increases with the swirling intensity. A relatively high swirling intensity can cause the disappearance of the flame pinch-off, as the toroidal vortex sheds around either the tip or the downstream of the flame. The flicker vanishes, but the flame retains axisymmetric in a small amplitude oscillation or a steady stay. A sufficiently high swirling intensity causes a small Damköhler number, leading to the lift-off of the flame (the local extinction occurs at the flame base). Under the same swirling intensity but large swirling angles, the asymmetric modes of the spiral and vortex bubble flames were likely to occur. With R and α increasing, these flames exhibit axisymmetric and asymmetric patterns, and their dynamical behaviors become more complex. To feature the vortical flows in flames, the phase portraits are established based on the velocity information of six positions along the axis of the flame, and the dynamical behaviors of various flames are presented and compared in the phase space. Observing the phase portraits and their differences in distinct modes could help identify the dynamical behaviors of flames and understand complex phenomena. Full article
(This article belongs to the Special Issue Symmetry in Aerospace Sciences and Applications)
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16 pages, 7442 KiB  
Article
Experimental Investigation on the Symmetry and Stabilization of Ethanol Spray Swirling Flames Utilizing Simultaneous PIV/OH-PLIF Measurements
by Meng Wang, Chen Fu, Xiaoyang Wang, Kunpeng Liu, Sheng Meng, Man Zhang, Juan Yu, Xi Xia and Yi Gao
Symmetry 2024, 16(2), 205; https://doi.org/10.3390/sym16020205 - 8 Feb 2024
Viewed by 892
Abstract
A detailed experimental study of ethanol spray swirling flames was performed in an axial bluff body stabilized burner. The characteristics of the non-reacting and reacting sprays were recorded by particle imaging velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical. A [...] Read more.
A detailed experimental study of ethanol spray swirling flames was performed in an axial bluff body stabilized burner. The characteristics of the non-reacting and reacting sprays were recorded by particle imaging velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical. A few typical flames with different structures (outer-side-flame-lifting, stable, and near-blow-off) were compared and analyzed. The parameters of the spray, including the spray half-angle (α) and droplet number density (nd), are quantified, and it has been found the flame structure and stability were strongly correlated with the droplet distribution. Several parameters of the flow field, such as velocity magnitude (|U| vorticity (ωz), and turbulent kinetic energy (TKE), are quantitively analyzed, and it is observed that the local strain rate rose as the air flow rate increased, which is not conducive to local flame stability. Regarding the flame, quantities such as progress variable (<c>), flame height (Lf), lift–off height (hlf), and symmetry factor (Snd and S<c>) are calculated, and it can be observed that the flame symmetry keeps worsening when approaching blow–off, and the inner flame branch exhibits a worse stabilization than the outer one. Our comprehensive investigations offer a deeper understanding of stable combustion in such two–phase flames. Full article
(This article belongs to the Special Issue Symmetry in Aerospace Sciences and Applications)
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15 pages, 14813 KiB  
Article
Plane Cascade Aerodynamic Performance Prediction Based on Metric Learning for Multi-Output Gaussian Process Regression
by Lin Liu, Chunming Yang, Honghui Xiang and Jiazhe Lin
Symmetry 2023, 15(9), 1692; https://doi.org/10.3390/sym15091692 - 4 Sep 2023
Cited by 1 | Viewed by 1278
Abstract
Multi-output Gaussian process regression measures the similarity between samples based on Euclidean distance and assigns the same weight to each feature. However, there are significant differences in the aerodynamic performance of plane cascades composed of symmetric and asymmetric blade shapes, and there are [...] Read more.
Multi-output Gaussian process regression measures the similarity between samples based on Euclidean distance and assigns the same weight to each feature. However, there are significant differences in the aerodynamic performance of plane cascades composed of symmetric and asymmetric blade shapes, and there are also significant differences between the geometry of the plane cascades formed by different blade shapes and the experimental working conditions. There are large differences in geometric and working condition parameters in the features, which makes it difficult to accurately measure the similarity between different samples when there are fewer samples. For this problem, a metric learning for the multi-output Gaussian process regression method (ML_MOGPR) for aerodynamic performance prediction of the plane cascade is proposed. It shares parameters between multiple output Gaussian distributions during training and measures the similarity between input samples in a new embedding space to reduce bias and improve overall prediction accuracy. For the analysis of ML_MOGPR prediction results, the overall prediction accuracy is significantly improved compared with multi-output Gaussian process regression (MOGPR), backpropagation neural network (BPNN), and multi-task learning neural network (MTLNN). The experimental results show that ML_MOGPR is effective in predicting the performance of the plane cascade, and it can quickly and accurately make a preliminary estimate of the aerodynamic performance and meet the performance parameter estimation accuracy requirements in the early stage. Full article
(This article belongs to the Special Issue Symmetry in Aerospace Sciences and Applications)
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Review

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13 pages, 4083 KiB  
Review
Symmetry-Breaking-Induced Internal Mixing Enhancement of Droplet Collision
by Yupeng Leng, Chengming He, Qian Wang, Zhixia He, Nigel Simms and Peng Zhang
Symmetry 2024, 16(1), 47; https://doi.org/10.3390/sym16010047 - 29 Dec 2023
Viewed by 1304
Abstract
Binary droplet collision is a basic fluid phenomenon for many spray processes in nature and industry involving lots of discrete droplets. It exists an inherent mirror symmetry between two colliding droplets. For specific cases of the collision between two identical droplets, the head-on [...] Read more.
Binary droplet collision is a basic fluid phenomenon for many spray processes in nature and industry involving lots of discrete droplets. It exists an inherent mirror symmetry between two colliding droplets. For specific cases of the collision between two identical droplets, the head-on collision and the off-center collision, respectively, show the axisymmetric and rotational symmetry characteristics, which is useful for the simplification of droplet collision modeling. However, for more general cases of the collision between two droplets involving the disparities of size ratio, surface tension, viscosity, and self-spin motions, the axisymmetric and rotational symmetry droplet deformation and inner flow tend to be broken, leading to many distinct phenomena that cannot occur for the collision between two identical droplets owing to the mirror symmetry. This review focused on interpreting the asymmetric droplet deformation and the collision-induced internal mixing that was affected by those symmetry breaking factors, such as size ratio effects, Marangoni Effects, non-Newtonian effects, and droplet self-spin motion. It helps to understand the droplet internal mixing for hypergolic propellants in the rocket engineering and microscale droplet reactors in the biological engineering, and the modeling of droplet collision in real combustion spray processes. Full article
(This article belongs to the Special Issue Symmetry in Aerospace Sciences and Applications)
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