Explore the vast range of titles available.

Unmanned Combat Aerial Vehicles (UCAVs) are designed to be lightweight and compact, which can impact their overall lift and aerodynamic capabilities. This study focuses on enhancing the Coefficient of Lift (CL) by optimising the Back Sweep Angle in the Lambda wing-UCAV. The model's baseline geometry remains unchanged during the experimental and numerical analysis, while different back sweep angles ranging from δ=00 to δ=500 are investigated at varied free-stream velocities and angles of attack. This helps to understand the generation of induced lift in the intricate shapes of the Lambda Wing. The results indicate a 5% to 10% increase in the lift for every 100 increments of the Back Sweep Angle, and the vortices' strength increases and reaches a maximum at δ=400. At greater angles (δ >400), the lift drops gradually with the Reynolds number. The stagnation point shifts from 25% to 35% along the chord towards the pressure surface as the angles of attack increase from α=50 to α=100. The angle of attack α>100.

Scombrid fish lunate caudal fins are characterized by a wide range of sweep angles. Scombrid that have small sweep-angle caudal fins move at higher swimming speeds, suggesting that smaller angles produce more thrust. Furthermore, scombrids occasionally use high angles of attack (AoA) suggesting this also has some thrust benefit. This work examined the hypothesis that a smaller sweep angle and higher AoA improved thrust in swimmers by experimentally analyzing a robophysical model. The robophysical model was tested in a water tunnel at speeds between 0.35 and 0.7 body lengths per second. Three swept caudal fins were analyzed at three different AoA, three different freestream velocities, and four different Strouhal numbers, for a total of 108 cases. Results demonstrated that the fin with the largest sweep angle of 50° resulted in lower thrust production than the 40° and 30° fins, especially at higher Strouhal numbers. Larger AoA up to 25° increased thrust production at the higher Strouhal numbers, but at lower Strouhal numbers, produced less thrust. Differences in thrust production due to fin sweep angle and AoA were attributed to the variation in spanwise flow and leading edge vortex dynamics.

The diagonal shear variable-sweep wing changes the relative thickness of the airfoil while changing the sweep angle, which effectively improves the aerodynamic performance of the aircraft for complex flight conditions. In order to explore the problem of maintaining the optimal flight performance of the diagonal shear variable-sweep wing under different flight conditions, five NACA airfoil assemblies with different relative thicknesses are established, and the numerical simulation of the perturbed flow field in a wide speed domain is carried out to analyze the aerodynamic performance under different angles of attack (AoA) and speeds.

Robust optimization design is significant and urgently required for the fly wings, owing to its unique characteristics. However, there is a lack of efficient tools for performing shape optimization which considers multiple uncertainties. This is in part because implementing robust design in the widely used and very efficient adjoint-based optimization method is challenging. This paper addresses this need by developing an uncertainty-based optimization design framework where the gradient-enhanced polynomial chaos expansion and discrete, adjoint-based optimization framework are coupled to perform shape optimization under multiple uncertainties. The gradient information from adjoint equation is applied to improve the computation efficiency. The objective function is the statistic moment, consisting of mean and standard deviation. The gradients of the statistic moment are computed using the adjoint-based system and reconstructing a regression algorithm. A flying wing configuration with deterministic and two uncertainty-based optimizations is performed. The first uncertainty-based optimization considers flight conditions, Mach and angle of attack, and the second one added the planform uncertainty parameters, i.e., inner and outer wing sweep angle. The uncertainty-based optimizations gain reductions of statistic moments by 8.58% and 5.3%, respectively. Compared with the deterministic optimization, the uncertainty-based optimizations behave much better in robustness but sacrifice a small aerodynamic performance. The successful uncertainty-based optimization enables acceptable risks of fly wing design in the development process and indicates that our established framework can be applied for future aircraft robust optimization design.

In response to the current advanced rotor configuration with complex three-dimensional shapes, this configuration effectively improves aerodynamic performance, reduces noise, and greatly increases helicopter flight speed, while also having a certain impact on helicopter ground resonance stability. However, there is still limited research in this area. On the basis of modeling the coupled dynamics model of a three-dimensional shaped rotor and the body, this article studies the influence of the three-dimensional shaped rotor configuration (forward and backward sweep angle, upper and lower reversal angle) on ground resonance. The results indicate that the forward sweep angle and upward thrust angle of the propeller tip have adverse effects on ground resonance, while the backward sweep angle and downward thrust angle increase the stability margin. Reasonable design of complex three-dimensional blade tip configurations can improve ground resonance stability boundary. However, the influence of the three-dimensional shape of the propeller tip configuration is minimal and not significant in general, mainly reflected in the small contribution of the aerodynamic effects brought by the propeller tip to ground resonance.

We reveal the effects of sweep on the wake dynamics around NACA 0015 wings at high angles of attack using direct numerical simulations and resolvent analysis. The influence of sweep on the wake dynamics is considered for sweep angles from $0^\\circ$ to $45^\\circ$ and angles of attack from $16^\\circ$ to $30^\\circ$ for a spanwise periodic wing at a chord-based Reynolds number of $400$ and a Mach number of $0.1$. Wing sweep affects the wake dynamics, especially in terms of stability and spanwise fluctuations with implications on the development of three-dimensional (3-D) wakes. We observe that wing sweep attenuates spanwise fluctuations. Even as the sweep angle influences the wake, force and pressure coefficients can be collapsed for low angles of attack when examined in wall-normal and wingspan-normal independent flow components. Some small deviations at high sweep and incidence angles are attributed to vortical wake structures that impose secondary aerodynamic loads, revealed through the force element analysis. Furthermore, we conduct global resolvent analysis to uncover oblique modes with high disturbance amplification. The resolvent analysis also reveals the presence of wavemakers in the shear-dominated region associated with the emergence of 3-D wakes at high angles of attack. For flows at high sweep angles, the optimal convection speed of the response modes is shown to be faster than the optimal wavemakers speed suggesting a mechanism for the attenuation of perturbations. The present findings serve as a fundamental stepping stone to understanding separated flows at higher Reynolds numbers.

We perform direct numerical simulations of laminar separated flows over finite-aspect-ratio swept wings at a chord-based Reynolds number of $Re = 400$ to reveal a variety of wake structures generated for a range of aspect ratios (semi aspect ratio $sAR=0.5\\text {--}4$), angles of attack ($\\alpha =16^{\\circ }\\text {--}30^{\\circ }$) and sweep angles ($\\varLambda =0^{\\circ }\\text {--}45^{\\circ }$). Flows behind swept wings exhibit increased complexity in their dynamical features compared to unswept-wing wakes. For unswept wings, the wake dynamics are predominantly influenced by the tip effects. Steady wakes are mainly limited to low-aspect-ratio wings. Unsteady vortex shedding takes place near the midspan of higher-$AR$ wings due to weakened downwash induced by the tip vortices. With increasing sweep angle, the source of three-dimensionality transitions from the tip to the midspan. The three-dimensional midspan effects are responsible for the formation of the stationary vortical structures at the inboard part of the span, which expands the steady wake region to higher aspect ratios. At higher aspect ratios, the midspan effects of swept wings diminish at the outboard region, allowing unsteady vortex shedding to develop near the tip. In the wakes of highly swept wings, streamwise finger-like structures form repetitively along the wing span, providing a stabilizing effect. The insights revealed from this study can aid the design of high-lift devices and serve as a stepping stone for understanding the complex wake dynamics at higher Reynolds numbers and those generated by unsteady wing manoeuvres.

The purpose of this study is to investigate the effects of the Reynolds number and the bend sweep angle on the blood flow patterns of S-shaped bends. The numerical simulations of steady flows in S-shaped bends with sweep angles of 45°, 90°, and 135° are performed at Reynolds numbers of 125, 500, and 960. Hemodynamic characteristics such as secondary flows, vorticity, and axial velocity profiles are analyzed in detail. Flow patterns in S-shaped bends are strongly dependent on both Reynolds number and bend sweep angle, which can be categorized into three groups based on the first bend secondary flow effects on the transverse flow of the second bend. For low Reynolds numbers and any sweep angles, secondary flows in the second bend eliminate the first bend effects in the early sections of the second bend and therefore the axial velocity profile is consistent with the bend curvature, while for high Reynolds numbers depending on the bend sweep angles the secondary vortex pattern of the first bend may persist partially or totally throughout the second bend leading to a four-vortex secondary structure. Moreover, an interesting flow feature observed at the Reynolds number of 960 is that the secondary flow asymmetrical behavior occurred around the second bend exit and along the outflow straight section. This symmetry-breaking phenomenon which has not been reported in the previous studies is shown to be more pronounced in the 90° S-shaped bend as compared to other models considered here. The probability of flow separation as one of the important flow features contributing to the onset and development of arterial wall diseases is also studied. It is observed that the second bend outer wall of gentle bends with sweep angles from 20° to 30° at high enough Reynolds numbers are prone to flow separation.

We perform direct numerical simulations of actively controlled laminar separated wakes around low-aspect-ratio wings with two primary goals: (i) reducing the size of the separation bubble and (ii) attenuating the wing tip vortex. Instead of preventing separation, we modify the three-dimensional (3-D) dynamics to exploit wake vortices for aerodynamic enhancements. A direct wake modification is considered using optimal harmonic forcing modes from triglobal resolvent analysis. For this study, we consider wings at angles of attack of $14^\\circ$ and $22^\\circ$, taper ratios $0.27$ and $1$, and leading edge sweep angles of $0^\\circ$ and $30^\\circ$, at a mean-chord-based Reynolds number of $600$. The wakes behind these wings exhibit 3-D reversed-flow bubble and large-scale vortical structures. For tapered swept wings, the diversity of wake vortices increases substantially, posing a challenge for flow control. To achieve the first control objective for an untapered unswept wing, root-based actuation at the shedding frequency is introduced to reduce the reversed-flow bubble size by taking advantage of the wake vortices to significantly enhance the aerodynamic performance of the wing. For both untapered and tapered swept wings, root-based actuation modifies the stalled flow, reduces the reversed-flow region and enhances aerodynamic performance by increasing the root contribution to lift. For the goal of controlling the tip vortex, we demonstrate the effectiveness of actuation with high-frequency perturbations near the tip. This study shows how insights from resolvent analysis for unsteady actuation can enable global modification of 3-D separated wakes and achieve improved aerodynamics of wings.

Through triglobal resolvent analysis, we reveal the effects of wing tip and sweep angle on laminar separated wakes over swept wings. For the present study, we consider wings with semi-aspect ratios from $1$ to $4$, sweep angles from $0^\\circ$ to $45^\\circ$ and angles of attack of $20^\\circ$ and $30^\\circ$ at a chord-based Reynolds number of $400$ and a Mach number of $0.1$. Using direct numerical simulations, we observe that unswept wings develop vortex shedding near the wing root with a quasi-steady tip vortex. For swept wings, vortex shedding is seen near the wing tip for low sweep angles, while the wakes are steady for wings with high sweep angles. To gain further insights into the mechanisms of flow unsteadiness, triglobal resolvent analysis is used to identify the optimal spatial input–output mode pairs and the associated gains over a range of frequencies. The three-dimensional forcing and response modes reveal that harmonic fluctuations are directed towards the root for unswept wings and towards the wing tip for swept wings. The overlapping region of the forcing–response mode pairs uncovers triglobal resolvent wavemakers associated with self-sustained unsteady wakes of swept wings. Furthermore, we show that for low-aspect-ratio wings optimal perturbations develop globally over the entire wingspan. The present study uncovers physical insights on the effects of tip and sweep on the growth of optimal harmonic perturbations and the wake dynamics of separated flows over swept wings.