Aerospace Systems最新文献

Multi-annular jets are derived from coaxial jets, which are used to improve the mixing of fuel and air before ignition in a gas turbine combustor and it is essential to achieving stable and effective combustion. In the present work, a multi-annular jet comprising two co-annular and one central jet has been used to understand the flow characteristics and mixing of jets in non-expanded and expanded confinement with different angular outlets. A computational investigation has been performed with different swirl combinations in three air jets inlet under non-combustion conditions. After validation from existing experimental results, parametric studies have been investigated with different expansion ratios, different swirl combinations, and different angular outlets. Using the realizable k–ε turbulence model and commercial software ANSYS FLUENT, results were obtained in the form of streamlines plots, axial velocity contours, and center line axial velocity. Following a comprehensive analysis of the computational output, it is found the mixing process in confinement depends on expansion ratios, swirl combinations, and angular outlets. Results show that the mixing of jets is enhanced in expanded confinement at particular swirl combinations and at certain angular outlets.

The objective of this paper is to enhance the combustion efficiency of a scram jet engine by varying the design parameters. The two dimensional numerical analysis is carried out with four different strut model using the k epsilon method for this study with the Mach number of 2 to evaluate the combustions efficiency and pressure loss. The results shows that strut model design 4 is providing the maximum efficiency of 99% with the total pressure loss of 3.08043 × 10⁵ Pa compare to other strut model. The novelty of the model is to vary the two parameter like strut configuration along with fuel injection locations to enhance the combustion efficiency with minimum increment of pressure loss at supersonic conditions. This proposed method can be used for scramjet and supersonic related applications.

The processing and application of time series are widespread, including tasks like weather forecasting, traffic flow prediction and intention recognition. However, in reality, missing data often occurs due to target occlusion or sensor failures. Many deep learning models are designed for uniformly sampled complete data and cannot be directly applied to scenarios with missing values. Traditional data preprocessing methods, such as imputation and interpolation, introduce additional noise. To address these challenges, we propose an end-to-end model with Learnable Embedding and capture Multidimensional Features (LEMF). LEMF can directly handle real-world time series with missing values. We utilize the LE module to extract richer temporal information, compensating for the limitations of missing data. The MF module can extract features related to the relationships between variables. We leverage these hidden representations for intention recognition, which is the time series classification task. We thoroughly evaluate our model on a self-constructed intention dataset. Compared to baseline model, the LEMF model achieved an average of 10% higher accuracy at each missing ratio. Additionally, we validate the model’s generalization capabilities on two real-world datasets. Our model also shows optimal or suboptimal performance.

A highly efficient combustion chamber is always desired for high performance from jet engines/rocket engines. This paper presents the novel numerical analysis method for optimizing the combustion characteristics of methane (CH₄) in an annular combustion chamber, achieving a maximum exit velocity nearly Mach 5. The velocity achieved is 1650 m/s, which is approximately 5 times of Mach number. The dimension of combustion chamber, length is 100 mm, diameter is 60 mm. Pre-combustion and post-combustion chamber length is 30 mm and 45 mm respectively. The port diameter is 16.5 mm and 4 injectors are used in this case. The main purpose of this paper is to investigate the optimize the combustion of solid fuel and air and justify the numerical model by using a 3D RANS simulation.

This paper is the first part of article series devoted to the computational study of thick composite panels buckling under compressive and shear loads taking into account through-the-thickness shear strains. In the first part of the study, an approximation is carried out taking into account the numerical solutions of the buckling problem. The first part presents a numerical study of orthotropic composite panels of a wide-body aircraft wing of large thicknesses, during which analytical dependencies are derived that determine the critical force for buckling under compressive and shear loads, taking into account through-the-thickness shear strains.

To determine the critical forces at which the panel buckles, the authors used a numerical modeling approach using the Finite Element Method (FEM) and Bubnov-Galerkin method (a method of aircraft structural mechanics). For this purpose, shell models of wing skin panels with orthotropic composite lay-up were made using a layer-by-layer modeling approach. A review of existing analytical dependencies for determining the critical forces for buckling of composite panels taking into account the through-the-thickness shear strains during compression was also carried out.

After validating the computational models, the authors conducted a series of virtual tests and analytical calculations for panels with different aspect ratios and thicknesses ranging from 1.8 mm to 24 mm in 2 mm increments. Based on the data obtained, the influence of through-the-thickness shear strains under compressive and shear loads was studied empirically, and an analytical relationship was obtained for assessing buckling of composite panels of large thicknesses under shear load.

The scientific novelty of this study is the identification of an empirical relationship for problems of composite panels of large thicknesses buckling under the influence of shear load, taking into account through-the-thickness shear strain.

The paper presents three-body interception simulation model, to study the survivability of airborne target against an interceptor, by launching a repeater-type countermeasure system termed as deceiver. State space representation of interceptor, target dynamic states along with autopilot, RF seeker is developed for three-dimensional engagement scenario. The trajectory of deceiver released from target is presented by propagating the discrete-state translational equations of motion. Classical proportional navigation guidance steers the interceptor towards the airborne moving target (or deceiver) based on the echo power received computed using Friis transmission formula. Effective jamming capability of deceiver on interceptor at different seeker acquisition ranges is indicated by ratio of power received from deceiver and target known as jammer-to-signal ratio. Numerical simulations are conducted to study the survivability chances of platform, when the deceiver is deployed from the target aircraft with interceptor approaching from side, head-end, tail-end, top. Miss distances of interceptor from platform and deceiver, interceptor lateral acceleration limits are presented. Monte carlo simulation studies are performed, and probability of platform survival when deceiver is released at different homing ranges of interceptor, as well as for deceiver amplifier gain variations are presented. This study also provides important system design parameters such as deceiver operation time to decide the battery specifications for electronics, and subsequently the overall system design.

In this paper, a series of low-Reynolds number airfoils were explored in application to the Long-Endurance Mars Exploration Flying Vehicle (LEMFEV) project. The end goal of the study was twofold:

• to identify the most effective airfoil or airfoil-boundary layer trip combination for the given aircraft in cruise and unveil the underlying physical mechanism for this effectiveness;

• to determine if the operating range of angles of attack for the selected airfoil could be expanded by placing the boundary layer trips in a relatively aft position such that they affected the boundary layer at a higher angle of attack.

The paper presented two sample specifications for the LEMFEV project; discussed the effect of turbulence on the performance of airfoils under the given conditions; justified the selection of an amplification factor for simulations; developed and justified the measure of merit for airfoil selection and optimization; as well as considered boundary layer trips as a means of enhancing the performance of the selected airfoil. For design and analysis, MATLAB and X-FOIL were used. The analysis showed that for the given design conditions, both considered sample mission profiles were performed better by an airplane with the SD7037-092-88 airfoil. Furthermore, for this airfoil and design conditions, boundary layer trips would only increase drag at lift coefficients where they forced transition, and the boundary layer trips didn’t expand the airfoil's operating range of angles of attack. In other words, eliminating the bubble had a detrimental effect on the lift-to-drag ratio of the airfoil. The friction drag increase due to early transition by far outweighed the pressure drag produced by the laminar bubble.

The need for revolutionary techniques to augment aerodynamic efficiency is paramount for achieving substantial reductions in drag and consequent fuel consumption. This paper revolves around exploiting zinc oxide nanostructures to increase boundary layer adhesion and delay stall in airfoils. Zinc oxide nanostructures are employed to induce vortices, re-energize the airflow and function as nano flow control device. The work on this paper commenced with the proof of concept by means of comprehensive computational simulation utilizing COMSOL software and ended with experimental lab tests. A meticulous two-step process involving the sol–gel method and dip coating was employed to grow nanorods on the wing’s surface. Initial prototyping utilized 3D printing, and subsequent aluminum samples were produced using sand casting techniques. The coated wing specimen underwent rigorous wind tunnel testing to assess its aerodynamic performance under controlled airflow conditions. This thorough approach facilitated a profound understanding of the coated wing's behavior, enabling insights for further optimization. The results revealed a significant 16% delay in stall and an average 4% reduction in drag. This pioneering approach not only optimizes aircraft aerodynamics but also mitigates fuel costs and environmental impact. Moreover, the study's observations offer avenues for future exploration, including the fine-tuning of coating parameters and exploring diverse applications of ZnO nanorods in aerospace engineering.

Tight formation flight, as a significant way for fixed-wing unmanned aerial vehicle (UAV) to execute missions, generates synergistic aerodynamic effects that significantly influence the motion decision-making and control of UAVs. In aerial refueling missions, this is manifested as complex aerodynamic effects such as vortices affecting the path planning of the refueling UAV. This paper proposes a path-planning method for fixed-wing UAVs to conduct aerial refueling under the constraints of synergistic aerodynamics. Firstly, an environment constraint model for vortex distribution is obtained from aerodynamic experimental data of the refueling formation. Subsequently, by utilizing the differential flatness property of fixed-wing UAVs, the nonlinear system states and control variables are mapped to linear functions of flat outputs. This allows the establishment of segment constraints for the path, enabling the use of a key-point heuristic algorithm in the flat output space to generate the aerial refueling flight path. Furthermore, a flat output minimum snap algorithm is applied for multi-constraint optimization of the flight path, resulting in a smooth and feasible optimal path. Simulation experiments demonstrate the effectiveness and advancement of the proposed path-planning method under the influence of vortices.

A numerical analysis has been conducted to study the role of hindfoil initial pitch angle on aerodynamic performance of dragonfly hovering flight. The inclined oscillation of two elliptic airfoils with tandem arrangment at (:Re=157) is analysed using 2D numerical simulation. The pitch amplitude ((:{alpha:}_{m})) is kept constant for both foils and hindfoil initial pitch angle ((:{alpha:}_{{o}_{h}})) is varied from (:{15}^{o}) to (:{75}^{o}) for three different phase oscillations: (:varphi:=:{0}^{o}), (:{90}^{o}) and (:{180}^{o}). The results indicate, for (:{alpha:}_{{o}_{h}}) < (:{45}^{o}), the lower (:{alpha:}_{{o}_{h}}) reduces total lift for all phase differences. It occurs due to the detrimental wake capture and downward dipole jet encountered by hindfoil during downstroke, resulting in less hindfoil (:stackrel{-}{{C}_{V}}). However, for (:{alpha:}_{{o}_{h}}) > (:{45}^{o}), lift enhancement of up to (:46:%) is observed with increase in (:{alpha:}_{{o}_{h}}) during (:varphi:=:{180}^{o}). Also, the higher thrust is obtained during lower (:{alpha:}_{{o}_{h}}) and it reduces with increase in (:{alpha:}_{{o}_{h}}).