Search Results (11)

This study investigates the numerical prediction of the sonic boom phenomenon in supersonic aircraft by evaluating the near-field pressure signatures of three different aeroshapes. Two computational fluid dynamics (CFD) solvers, the open-source SU2 Multiphysics code and ANSYS Fluent, were employed to assess their effectiveness in modeling the aerodynamic flow field. A preliminary validation of numerical methods was conducted against numerical data available from the Sonic Boom Prediction Workshops (SBPW) organized by NASA, ensuring simulation reliability. Particular attention is paid to the topology of the mesh grid, exploring hybrid approaches that combine structured and unstructured grids to optimize the accuracy of pressure wave transmission. In addition, different numerical schemes were analyzed to determine the best practices for sonic boom simulations. The proposed methodology was finally applied to three supersonic aircraft developed within the European project MORE&LESS, demonstrating the capability of the model to estimate shock wave generation, evaluate the aeroacoustic performance of different supersonic aeroshapes from Mach 2 to Mach 5, and provide predictions to support ground-level noise assessment. The findings of this study contribute to the definition of a comprehensive workflow for sonic boom evaluation, providing a reliable methodology for exploring future supersonic aircraft designs. Full article

Three-dimensional (3D) computational fluid dynamic (CFD) simulations have been performed to investigate the complex flow features and stripping of fluid materials from a cylindrical water drop at the late-stage in a Shock Liquid Drop Interaction (SLDI) process when the drop’s downstream end experiences compression after it is impacted by a supersonic shock wave ($Ma$ = 1.47). The drop trajectory/breakup has been simulated using a Lagrangian model and the unsteady Reynolds-averaged Navier–Stokes (URANS) approach has been employed for simulating the ambient airflow. The Kelvin–Helmholtz Rayleigh–Taylor (KHRT) breakup model has been used to capture the liquid drop fragmentation process and a coupled level-set volume of fluid (CLSVOF) method has been applied to investigate the topological transformations at the air/water interface. The predicted changes of the drop length/width/area with time have been compared against experimental measurements, and a very good agreement has been obtained. The complex flow features and the qualitative characteristics of the material stripping process in the compression phase, as well as disintegration and flattening of the drop are analyzed via comprehensive flow visualization. Characteristics of the drop distortion and fragmentation in the stripping breakup mode, and the development of turbulence at the later stage of the shock drop interaction process are also examined. Finally, this study investigated the effect of increasing $Ma$ on the breakup of a water drop by shear stripping. The results show that the shed fluid materials and micro-drops are spread over a narrower distribution as $Ma$ increases. It illustrates that the flattened area bounded by the downstream separation points experienced less compression, and the liquid sheet suffered a slower growth. Full article

This article investigates the continuity of derivatives of real-valued functions from a topological perspective. This is achieved by the characterization of their sets of discontinuity. The same principle is applied to Gateaux derivatives and gradients in Euclidean spaces. This article also introduces a generalization of the derivatives from the perspective of the modulus of continuity and characterizes their sets of discontinuities. There is a need for such generalizations when dealing with physical phenomena, such as fractures, shock waves, turbulence, Brownian motion, etc. Full article

The uncertainty of the turbulence/transition model is a problem with relatively high attention in the CFD area. Wall distance is an important physical parameter in turbulence/transition modeling, and its accuracy has a large effect on numerical simulation results. As most CFD solvers use the solving strategy to calculate the nearest distance to the wall based on mesh topology, this makes wall distance one important source of the uncertainty of the simulation results. To investigate the role of wall distance in turbulence/transition simulations, we have conducted simulations for various aerodynamic shapes, such as the plate with zero pressure gradient (ZPG), RAE2822 supercritical airfoil and ONERA M6 transonic wing. Further, the prediction abilities on turbulence/transition and shock wave phenomena of several physical models, including SA, SST and Wilcox-k-ω turbulence models as well as the γ-Re_θt-SST transition model, are analyzed with different degrees of mesh orthogonality. The results imply that the numerical solution of wall distance in the boundary layer has a relatively large error when the mesh orthogonality is bad, having a large effect on the accuracy of the turbulence/transition model. In detail, the Wilcox-k-ω turbulence model is unaffected by mesh orthogonality; under the condition of mesh non-orthogonality, the SA model leads to a substantially larger friction drag and change in the location of shock wave; the SST model also leads to a larger friction drag under the condition of mesh non-orthogonality, whose effect is much less than that for SA model; and the γ-Re_θt-SST model leads to a substantial upstream shift of transition location. Full article

Shock waves and shock-shock interaction are typical phenomena in supersonic or hypersonic flows that have significant impacts on aerodynamic performance. To obtain a comprehensive understanding of the mechanism of shock wave interaction, shock wave detection (SWD) methods are required. However, it is often challenging for most current SWD methods to identify the relationship between shock waves (also known as shock topology). To address this issue, this paper proposes a novel three-dimensional shock topology detection method based on the tomographic reconstruction strategy. This method involves extracting parallel slices from the flow field, then utilizing a two-dimensional shock topology recognition algorithm to obtain shock lines. Shock bands are obtained by connecting shock lines for every two adjacent slices, and shock surfaces are generated by assembling shock bands. Interaction lines are also formed by connecting interaction points. The detected shock wave is a structure composed of “point-line-band-surface”, and the topology relationship with other shock waves is obvious. Numerical results show that the shock waves detected by the proposed method can be categorized into families. Moreover, the shock surfaces generated by this method are free of gaps, holes, and un-physical fragments, which is an improvement over existing SWD methods. Full article

In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data. Full article

In previous work, we considered a four-quadrant Riemann problem for a $2\times 2$ hyperbolic system in which delta shock appears at the initial discontinuity without assuming that each jump of the initial data projects exactly one plane elementary wave. In this paper, we consider the case that does not involve a delta shock at the initial discontinuity. We classified 18 topologically distinct solutions and constructed analytic and numerical solutions for each case. The constructed analytic solutions show the rich structure of wave interactions in the Riemann problem, which coincide with the computed numerical solutions. Full article

In this paper, a four-quadrant Riemann problem for a $2\times 2$ system of hyperbolic conservation laws is considered in the case of delta shock appearing at the initial discontinuity. We also remove the restriction in that there is only one planar wave at each initial discontinuity. We include the existence of two elementary waves at each initial discontinuity and classify 14 topologically distinct solutions. For each case, we construct an analytic solution and compute the numerical solution. Full article

The results of the experimental research on the symmetry of supersonic flow in a symmetric convergent-divergent nozzle are presented. The investigations were focused on the fact that for some flow conditions the flow in a precisely symmetric nozzle becomes asymmetric. Starting from a specific value of Mach number, the flow becomes asymmetric in terms of shock wave λ-foot geometry on both sides of a symmetric nozzle. The evolution of the abovementioned asymmetry has been analysed for Mach number value ranging from M = 1.26 to M = 1.59 with the nozzle opening angle of up to 6.5° on each side. The presented results indicate that for the same flow parameters as Mach number and Reynolds number, and for the same geometry of the nozzle, different λ-foot size is formed at each wall. This unexpected behaviour is responsible for the flow asymmetry. Numerical simulations carried out earlier confirm the appearance of shock wave asymmetry. The side in which the asymmetry takes place is accidental, as the full symmetry of simulation mesh and experiment setup was secured. In numerical simulation the asymmetry follows always the same direction. In experiments the direction of asymmetry happens alternatively without any apparent reason. The explanation of the phenomena is provided in this paper. Full article

The most promising mechanisms for producing and accelerating relativistic jets, and maintaining collimated structure of relativistic jets involve magnetohydrodynamical (MHD) processes. We have investigated the magnetic dissipation mechanism in relativistic jets via relativistic MHD simulations. We found that the relativistic jets involving a helical magnetic field are unstable for the current-driven kink instability, which leads to helically distorted structure in relativistic jets. We identified the regions of high current density in filamentary current sheets, indicative of magnetic reconnection, which are associated to the kink unstable regions and correlated to the converted regions of magnetic to kinetic energies of the jets. We also found that an over-pressured relativistic jet leads to the generation of a series of stationary recollimation shocks and rarefaction structures by the nonlinear interaction of shocks and rarefaction waves. The differences in the recollimation shock structure due to the difference of the magnetic field topologies and strengths may be observable through mm-VLBI observations and space-VLBI mission. Full article

This review discusses several computational methods used on different length and time scales for the simulation of material behavior. First, the importance of physical modeling and its relation to computer simulation on multiscales is discussed. Then, computational methods used on different scales are shortly reviewed, before we focus on the molecular dynamics (MD) method. Here we survey in a tutorial-like fashion some key issues including several MD optimization techniques. Thereafter, computational examples for the capabilities of numerical simulations in materials research are discussed. We focus on recent results of shock wave simulations of a solid which are based on two different modeling approaches and we discuss their respective assets and drawbacks with a view to their application on multiscales. Then, the prospects of computer simulations on the molecular length scale using coarse-grained MD methods are covered by means of examples pertaining to complex topological polymer structures including star-polymers, biomacromolecules such as polyelectrolytes and polymers with intrinsic stiffness. This review ends by highlighting new emerging interdisciplinary applications of computational methods in the field of medical engineering where the application of concepts of polymer physics and of shock waves to biological systems holds a lot of promise for improving medical applications such as extracorporeal shock wave lithotripsy or tumor treatment. Full article