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1 – 10 of 20Mengxia Du, Qiao Wang, Yan Zhang, Yu Bai, Chunqiu Wei and Chunyan Liu
As to different angles of attack and nonlinear problems caused by high temperatures in coexisting hypersonic aircraft, people mainly rely on fluid software for research but lack…
Abstract
Purpose
As to different angles of attack and nonlinear problems caused by high temperatures in coexisting hypersonic aircraft, people mainly rely on fluid software for research but lack analysis of flow mechanisms. Owing to computational difficulties, few people use numerical algorithms to combine them for discussion. Hence, this study aims to make a deep inquiry into the laminar flow and heat transfer of compressible Newtonian fluid in hypersonic aircraft with small attack angles.
Design/methodology/approach
In this paper, on the basis of mass, momentum and energy conservation laws, the governing equations of the hypersonic boundary layer are established. Viscosity, specific heat capacity and thermal conductivity are considered nonlinear functions concerning temperature. In virtue of the MacCormack finite difference method, the stationary numerical solutions are solved directly, and the validity of the algorithm is verified.
Findings
The results demonstrate that at Mach number 5, compared to the 0° attack angle, the maximum temperature near-wall at the 3° attack angle increases by about 25%. An enjoyable phenomenon is discovered, where the position corresponding to the maximum wall shear force shifts back as the attack angle and Mach number increase. The relationship between the near-wall maximum temperature versus attack angle and Mach number is fitted through numerical calculation results.
Originality/value
Empirical formulas can be used to estimate heat transfer characteristics at small attack angles, which will guide the design of aircraft thermal protection systems.
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Keywords
For a thermal protection system (TPS) of long endurance hypersonic flight vehicle (HFV), its thermal insulation property not only determines by the manufactured morphology but…
Abstract
Purpose
For a thermal protection system (TPS) of long endurance hypersonic flight vehicle (HFV), its thermal insulation property not only determines by the manufactured morphology but also changes along time. A thermal conductivity prediction model for aerogel considering heat treatment effect is carried out and applied to solve the heat conduction problem of a TPS. The aim of this study is to provide theoretical and numerical references for further development of aerogels applying to TPSs.
Design/methodology/approach
A thermal conductivity prediction model for aerogel is established considering treatment effect. The heat conduction problem of a TPS is derived and solved by combining the differential quadrature method and the Runge–Kutta method. The prediction results of aerogel thermal conductivities are verified by comparing with those in literature, while the calculated temperature field of TPS is verified by comparing with that by ABAQUS.
Findings
Numerical results show that when applying the current prediction model, the calculated high temperature area in the aerogel layer is narrowed due to the decrease of the thermal conductivity during heat treatment process.
Originality/value
This study will be beneficial to carry out the precise design of TPS for long endurance HFVs.
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Kathiravan Balusamy, Vinothraj A. and Suresh V.
The purpose of this study is to explore the effects of aerospike and hemispherical aerodisks on flow characteristics and drag reduction in supersonic flow over a blunt body…
Abstract
Purpose
The purpose of this study is to explore the effects of aerospike and hemispherical aerodisks on flow characteristics and drag reduction in supersonic flow over a blunt body. Specifically, the study aims to analyze the impact of varying the length of the cylindrical rod in the aerospike (ranging from 0.5 to 2.0 times the diameter of the blunt body) and the diameter of the hemispherical disk (ranging from 0.25 to 0.75 times the blunt body diameter). CFD simulations were conducted at a supersonic Mach number of 2 and a Reynolds number of 2.79 × 106.
Design/methodology/approach
ICEM CFD and ANSYS CFX solver were used to generate the three-dimensional flow along with its structures. The flow structure and drag coefficient were computed using Reynolds-averaged Navier–Stokes equation model. The drag reduction mechanism was also explained using the idea of dividing streamline and density contour. The performance of the aero spike length and the effect of aero disk size on the drag are investigated.
Findings
The separating shock is located in front of the blunt body, forming an effective conical shape that reduces the pressure drag acting on the blunt body. It was observed that extending the length of the spike beyond a specific critical point did not impact the flow field characteristics and had no further influence on the enhanced performance. The optimal combination of disk and spike length was determined, resulting in a substantial reduction in drag through the introduction of the aerospike and disk.
Research limitations/implications
To predict the accurate results of drag and to reduce the simulation time, a hexa grid with finer mesh structure was adopted in the simulation.
Practical implications
The blunt nose structures are primarily employed in the design of rockets, missiles, and re-entry capsules to withstand higher aerodynamic loads and aerodynamic heating.
Originality/value
For the optimized size of the aero spike, aero disk is also optimized to use the benefits of both.
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Kajal Vinayak and Shripad P. Mahulikar
In recent years, increased use of all-aspect infrared (IR)-guided missiles based on the long-wave infrared (LWIR; 8–12 µm) band has lowered the probability of aircraft survival in…
Abstract
Purpose
In recent years, increased use of all-aspect infrared (IR)-guided missiles based on the long-wave infrared (LWIR; 8–12 µm) band has lowered the probability of aircraft survival in warfare. The lock-on of these highly sensitive missiles is difficult to break, especially from the front. Aerodynamically heated swept-back leading edges (SBLE), because of their high temperature and large area, serve as a prominent LWIR source for aircraft detection from the front. This study aims to report the influence of sweep-back angle (Λ, based on the Mach number [M∞]) on aerodynamic heating and the LWIR signature of SBLE.
Design/methodology/approach
The temperature along SBLE is obtained numerically as radiation equilibrium temperature (Tw) by discretizing the SBLE length into “n” number of segments, and for each segment, emission based on Tw is evaluated. IR radiance due to reflected external sources (sky-shine and Earthshine) and radiance due to Tw are collectively used to determine the IR contrast between SBLE and its replaced background in the LWIR band (icont-SBLE,LWIR).
Findings
The results are obtained for low subsonic turboprop aircraft (Λ = 3°, M∞ = 0.44); high subsonic strategic bombers (Λ = 35°, M∞ = 0.8); fifth-generation stealth aircraft (Λ = 40°, M∞ = 1.6); and aircraft with supercruise/supersonic capability (Λ = 50°, M∞ = 2.5). The aircraft with supersonic capability (Λ = 50°, M∞ = 2.5) reports the maximum LWIR signatures and hence the highest visibility from the front. The results obtained are compared with values at Λ = 0° for all cases, which shows that increasing Λ significantly reduces aerodynamic heating and LWIR signatures.
Originality/value
The novelty of this study comes from its report on the influence of Λ on the LWIR signatures of aircraft SBLE in the frontal aspect for the first time.
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Tugrul Oktay and Yüksel Eraslan
The purpose of this paper is to improve autonomous flight performance of a fixed-wing unmanned aerial vehicle (UAV) via simultaneous morphing wingtip and control system design…
Abstract
Purpose
The purpose of this paper is to improve autonomous flight performance of a fixed-wing unmanned aerial vehicle (UAV) via simultaneous morphing wingtip and control system design conducted with optimization, computational fluid dynamics (CFD) and machine learning approaches.
Design/methodology/approach
The main wing of the UAV is redesigned with morphing wingtips capable of dihedral angle alteration by means of folding. Aircraft dynamic model is derived as equations depending only on wingtip dihedral angle via Nonlinear Least Squares regression machine learning algorithm. Data for the regression analyses are obtained by numerical (i.e. CFD) and analytical approaches. Simultaneous perturbation stochastic approximation (SPSA) is incorporated into the design process to determine the optimal wingtip dihedral angle and proportional-integral-derivative (PID) coefficients of the control system that maximizes autonomous flight performance. The performance is defined in terms of trajectory tracking quality parameters of rise time, settling time and overshoot. Obtained optimal design parameters are applied in flight simulations to test both longitudinal and lateral reference trajectory tracking.
Findings
Longitudinal and lateral autonomous flight performances of the UAV are improved by redesigning the main wing with morphing wingtips and simultaneous estimation of PID coefficients and wingtip dihedral angle with SPSA optimization.
Originality/value
This paper originally discusses the simultaneous design of innovative morphing wingtip and UAV flight control system for autonomous flight performance improvement. The proposed simultaneous design idea is conducted with the SPSA optimization and a machine learning algorithm as a novel approach.
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This paper aims to provide a case study of complex conflict management within the arms race on the Korean Peninsula. Exploring the complex nexus of nuclear weapons, asymmetry and…
Abstract
Purpose
This paper aims to provide a case study of complex conflict management within the arms race on the Korean Peninsula. Exploring the complex nexus of nuclear weapons, asymmetry and a qualitative arms race, the study explains how the arms race between Seoul and Pyongyang has promoted stability on the Korean Peninsula.
Design/methodology/approach
Presenting the limits of arguments that the US security guarantee is the factor that saved the two Koreas from going to war again, this paper explores the utility of the inter-Korean arms race as a stabilizer that promotes indirect negotiations. While presenting Korean anomalies, this paper analyzes the three stages of the inter-Korean arms race – especially its nuclear weapons, its asymmetry and the nature of arms races – and provides extant explanations on the causes and consequences of the qualitative arms race. These key elements drive the states’ strategic motives.
Findings
Using the case of the inter-Korean qualitative arms race and US extended nuclear deterrence on the Korean Peninsula, the study shows the complexities of conflict management today. This paper identifies three contributing factors – US nuclear weapons, asymmetry and the qualitative characteristic of the arms race – to explain the enduring stability on the peninsula despite the arms race’s intensification. The paper finds that although US nuclear-extended deterrence plays a critical role, it does not capture the full context of the ongoing, dynamic inter-Korean arms race; a prolonged arms race between the two Koreas has become a new regularity; the qualitative characteristic of the inter-Korean arms race, which is driven by technological advancement, contributes to stability in the arms race; and as the constant mismatch in priority technologies becomes more severe, the changes to the existing asymmetry could increase instability.
Originality/value
This paper offers a diverse perspective to the literature on conflict management and captures the complexities of 21st-century conflict management. Through a thorough examination of the inter-Korean arms race, it brings readers’ attention to the nested dynamics within the arms race and shows how an intensifying arms race can promote stability. Furthermore, the paper explains the implications for potential instability – fueled by the comprehensive mix of a dynamic qualitative arms race and the US extended nuclear deterrence – in the Indo-Pacific region.
Details
Keywords
NORTH KOREA: Further provocations likely
Details
DOI: 10.1108/OXAN-ES286189
ISSN: 2633-304X
Keywords
Geographic
Topical
RUSSIA: Military will expand further this year
Kishida and Biden hailed a historic upgrade in defence ties and announced a record volume of around 70 agreements, spanning various sectors.
Details
DOI: 10.1108/OXAN-DB286581
ISSN: 2633-304X
Keywords
Geographic
Topical
Although the comments formed a small section of a wide-ranging campaign speech, they have increased fears that US security guarantees will become unreliable if Trump wins back the…