Abstract Characterized by the quasi-conically symmetric flow field, λ shock wave system, and highly three-dimensional separation structures, the swept shock-wave/boundary-layer interaction (SBLI) induced by sharp fins is one of the most important phenomena in supersonic flights. An aerothermoelastic analysis is conducted on the interactions between thin-walled panels and swept SBLIs. The results of rigid wall condition, aeroelastic analysis and aerothermoelastic analysis are compared to highlight the significant influence of fluid-thermal-structural interactions on the structure and the flow field of swept SBLIs. The results show that in the aeroelastic analysis, for the material applied to the panel, although a dynamic structural response is observed, the deformation is minor and has a limited influence on the flow field. However, in the aerothermoelastic analysis, the consideration of aerodynamic heating has a significant impact on the structural response and the flow field. The deformation is an order of magnitude larger than that in the aeroelastic analysis with high vibration frequency and various main frequencies at different locations. As a result, the flow field is no longer quasi-conically symmetric. The λ shock wave system and separation structures are completely disrupted by multiple shock and expansion waves induced by the large structural deformation and become much more complex with highly three-dimensional features. This research highlights the significance of investigations on complex three-dimensional aerothermoelastic problems for supersonic flight vehicles.

Abstract Current research on active flutter suppression considering time delays tends to focus on fixed time delays. To address situations where the control loop may experience time-varying delays with uncertainty, a time-varying-delay Active Disturbance Rejection Control (TVD-ADRC) is proposed. First, a parameterized unsteady aerodynamic reduced-order model (ROM) based on a long short-term memory network is introduced into the aeroservoelastic modeling. This model is applied to predict unsteady aerodynamic forces and aeroservoelastic (ASE) behaviors across a wide range of Mach numbers. Its effectiveness in capturing the characteristics of unsteady aerodynamics is validated through comparisons with the high-fidelity computational fluid dynamics (CFD) simulations. Second, the proposed method integrates ADRC with a delayed input and a time-delay identification module in the controller design. Specifically, the time-varying delay is identified using the cross-correlation function method with a moving window, and this method dynamically updates the time-delay compensation module. Additionally, a genetic algorithm is employed to optimize controller parameters, and the integral of the time-weighted absolute error is selected as the performance evaluation index for the control system. Finally, a three-degree-of-freedom aeroservoelastic system of an airfoil with a trailing-edge control surface is studied for flutter suppression. Flutter control under uncertain time-varying delays during flutter occurrence is investigated, and the impact of the magnitude of the time delay on the effectiveness of the flutter control is analyzed. Simulation results indicate that the proposed TVD-ADRC controller could effectively suppress the aeroelastic instabilities across a wide range of Mach numbers and effectively counteract the negative effects of time-varying delays.

The prediction of three-dimensional boundary layer transition has long been an important issue in aircraft design. The eN method based on one-dimensional stability theories (LST-eN) is widely used in transition prediction, yet fails to capture transition features of large-scale vortical structures commonly present on the vehicle surface. The vortical structures cause substantial spanwise variations of the base flow and thereby render the one-dimensional stability theories invalid. We in the present study modulate the eN method by exploiting multi-dimensional stability theories, especially the plane-marching parabolized stability equations (PSE3D), to predict the windward transition front of a lifting body under a high-speed flight condition (FLT) and a wind-tunnel condition with two angles of attack (WT1 with 2-degree angle of attack and WT2 with 4-degree angle of attack). The modal instability characteristics for the centerline vortex region in these three cases are similar, featuring the upstream Mack-mode instability and the downstream vortex instabilities. The transition N-factor front qualitatively aligns well with direct numerical simulation (DNS) results for the flight case and the experimental measurements for the wind-tunnel cases. The transition N-factor is correlated to be around 2 for the flight case (based on the DNS data), around 4 for the wind-tunnel case WT1 and around 2 for the wind-tunnel case WT2. Intriguingly, the WT2 case experiences an earlier transition than the WT1 case although the former turns out to be more stable as predicted by the modal stability analysis. Preliminary non-modal analysis shows that non-modal growth is stronger in the WT2 case than in the WT1 case, implying that non-modal disturbances may play a role in the transition process. The cross-flow instability is also addressed for the flight case, focusing on the comparison of results from the one- and multi-dimensional stability analyses.

Scramjets are considered one of the important propulsion systems for realizing hypersonic flights and have attracted a lot of research interest over the past few decades. The present study focuses on conducting a comprehensive numerical investigation on a scramjet inlet-isolator at Mach 5 with the motivation to improve efficiency. The study investigates a two-dimensional scramjet inlet-isolator, analyzing both external and internal flow characteristics by using the commercially available tool Ansys-Fluent. Numerical simulation is the first step to incorporate the passive bleed mechanism into the inlet design features with alterations aimed at improving airflow regulation. The subsequent investigation is the analysis of the effect of a number of cowl deflection angles on performance of the positions. An extensive evaluation is presented on the effect of varying cowl deflection angles on the inlet isolator efficiency. A combined approach is also adopted in the study whereby the most promising configurations from the bleed mechanism and cowl deflection angle studies are incorporated into a single geometry. This aims at increasing the inlet isolator efficiency and the pressure recovery. The aim of this integrated strategy is to develop an inlet geometry that is optimal for performance of the engine and pressure recovery capability enhancement. The study analyzes ten different cases, and it is noted that out of these, the 4-degree cowl deflection angle is the most efficient in enhancing the total pressure efficiency.

This study explores how hydrophobic coating influences the structure of the flow separation at the rear end of 3D bluff bodies. Two 3D representative bluff bodies, namely the standard Ahmed body (SAB), which features flow separation and reattachment at its slant surface, and the elliptical Ahmed body (EAB), which exhibits fully separated flow, are employed. The bluff bodies were coated with Ultra Ever Dry hydrophobic paint. Experiments were carried out on pairs of coated and uncoated SABs and EABs in a water tunnel utilizing time-resolved and standard particle image velocimetry (PIV) at a Reynolds number of 4.3 × 104 based on the model height. The results show that hydrophobic coatings influence the flow features of these bluff bodies. For the SAB, the coating alters the slant separation bubble, increasing the reattachment length by 80% and reducing the shear stress. The Strouhal number on the slant surface of the SAB also increases, with a dominant value of St = 0.24. Proper orthogonal decomposition (POD) analysis shows dominant Strouhal numbers of St = 0.36 and St = 0.48 for the first and second POD modes, respectively. Additionally, dynamic mode decomposition (DMD) analysis identifies a dominant Strouhal number of St = 0.3 in the wake. Conversely, the EAB, which already has a fully separated flow, is less affected by the coating. The wake recirculation length is reduced by 6%. Strouhal numbers on the coated EAB’s slant surface range from 0.40 to 0.55, and those in the wake vary from 0.25 to 0.85. The POD analysis does not reveal dominant Strouhal numbers in the EAB’s wake, while the DMD analysis indicates a dominant Strouhal number of St = 0.013, pointing to energetic modes due to the fully separated flow. These findings demonstrate that hydrophobic coatings affect the flow characteristics of 3D bluff bodies differently, depending on their inherent flow separation properties.

Abstract The infrared radiation characteristics of aircraft are a key focus in attack-defense confrontation and early warning detection. A rapid simulation method for calculating the infrared characteristics of targets is proposed by combining the discrete transfer method. By constructing the aerodynamic shape of a Su-27-like aircraft, the flow field parameters and skin temperature under cruise conditions were calculated. The proposed method was used to generate infrared images and calculate infrared radiation intensity at various detection angles, and perform speed tests. The results indicate that this method has high accuracy; the generated infrared image is clear, accurate, and can be used to identify the characteristic attributes of the target. In the pitch detection plane, the total infrared radiation intensity of the aircraft exhibits a “8” distribution, with the fuselage contributing the most (approximately 50%). In the yaw plane, the vertical stabilizer’s infrared radiation intensity shows a lobed distribution, with peaks at 60° and 120°. The method can achieve a calculation speed of four times per second for a single detection angle, meeting real-time processing requirements and providing valuable data for infrared target recognition algorithms.

Steady-state numerical simulations were conducted to capture the aerodynamic characteristics and flow patterns resulting from a tubercled and non-tubercled wing subjected to various combined pitch and yaw conditions at Re=1.8×105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Re=1.8 \ imes 10^{5}$$\\end{document}. Pitch angle ranged from 0∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0^{\\circ }$$\\end{document} to 25∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$25^{\\circ }$$\\end{document}, while two different yaw angles of 10∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{\\circ }$$\\end{document} and 30∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$30^{\\circ }$$\\end{document} were used. Results show that 10∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{\\circ }$$\\end{document} yaw angle does not impact upon the lift and drag characteristics significantly, while a 30∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$30^{\\circ }$$\\end{document} yaw angle leads to substantial lift and drag losses. Additionally, the tubercled wing continues to confer favourable stall-mitigating characteristics even for the larger yaw angle. Finally, despite skewing the flow structures significantly, the 30∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$30^{\\circ }$$\\end{document} yaw angle also reduces the formations of bi-periodic flow structures, flow separations and recirculating regions along the leading-edge tubercles, suggesting potentially better flow stability and controllability.

Existing studies about wind pressure on agricultural greenhouse buildings concentrate on the mean wind pressure while ignoring the systematic research on fluctuating wind pressure characteristics and the influence of roof shape on the wind pressure characteristics, which are closely associated with the wind-induced damage mechanism. In this study, two typical agricultural greenhouse buildings on tropical islands are selected as prototypes to conduct pressure measurement experiments in the wind tunnel. Based on the wind pressure time series for the two greenhouses, the mean and fluctuating wind pressure distribution pattern and the localized high-pressure generation mechanism are analyzed. Then, the shape coefficient of the two greenhouses is compared in depth to the standards from four countries. Besides, wind pressure non-Gaussian determination criteria for agricultural greenhouse buildings considering the roof shape and wind directions are proposed. Lastly, the differences in wind pressure spectra on the roofs and walls of the two greenhouses are summarized. The results indicate the roof shape has a significant influence on the wind pressure characteristics. Compared with the pitched roof, the vaulted roof will increase the suction effect on the windward front zone and the middle area, mitigate the suction impact on the leeward roof, and weaken the wind pressure non-Gaussian characteristics. The experimental shape coefficient of the pitched-roof greenhouse is basically consistent with the standard from the U.S., while that of the vaulted-roof greenhouse has some deviation from the existing standards. The results provide a theoretical basis for the wind-resistant design of agricultural greenhouse buildings on tropical islands.

The present study introduces a Gauss-Seidel fluid-structure interaction (FSI) method including the flow solver, structural statics solver and a fast data transfer technique, for the research of structural deformation and flow field variation of rotor blades under the combined influence of steady aerodynamic and centrifugal forces. The FSI method is illustrated and validated by the static aeroelasticity analysis of a transonic compressor rotor blade, NASA Rotor 37. An improved local interpolation with data reduction (LIWDR) algorithm is introduced for fast data transfer on the fluid-solid interface of blade. The results of FSI calculation of NASA Rotor 37 show that when compared with the radial basis function (RBF) based interpolation algorithm, LIWDR meets the interpolation accuracy requirements, while the calculation cost can be greatly improved. The data transmission time is only about 1% of that of RBF. Moreover, the iteration step of steady flow computation within one single FSI has little impact on the converged aerodynamic and structural results. The aerodynamic load-caused deformation accounts for nearly 50% of the total. The effects of blade deformation on the variations of aerodynamic performance are given, demonstrating that when static aeroelasticity is taken into account, the choke mass flow rate increases and the peak adiabatic efficiency slightly decreases. The impact mechanisms on performance variations are presented in detail.

One of the main issues concerning the standard Vortex Lattice Method is its application to partially or fully detached flow conditions, where non-linear aerodynamic characteristics appear as the angle of attack increases and/or the aspect ratio decreases. In order to solve such limitations, a pure numerical approach based entirely on the Vortex Lattice Method concepts has been developed. The so-called steady “Full Multi-wake Vortex Lattice Method” comes from the main hypothesis that each discretized element on the body’s surface detaches their own wakes downstream. The obtained results match for lift, drag and moment coefficients for the entire aspect ratio range configurations (under straight wakes and inviscid assumptions). Future unsteady versions of such a multi-wake approach could improve the current results obtained through Vortex Element Methods (as vortons or isolated vortex filaments).