Compressible Flow Research Papers - Academia.edu (original) (raw)

2025, Computers & Mathematics with Applications

Lagrangian shock hydrodynamics simulations will fail to proceed past a certain time if the mesh is approaching tangling. A common solution is an Arbitrary Lagrangian Eulerian (ALE) form, in which the mesh is improved (remeshing) and the solution is remapped onto the improved mesh. The simplest remeshing techniques involve moving only the nodes of the mesh. More advanced remeshing techniques involve altering the mesh connectivity in portions of the domain in order to prevent tangling. Work has been done using Voronoi-based polygonal mesh generators and 2D quad/triangle mesh adaptation. This paper presents the use of tetrahedral mesh adaptation methods as the remeshing step in an otherwise Lagrangian finite element shock hydrodynamics code called Alexa.

2025, 46th AIAA Aerospace Sciences Meeting and Exhibit

ALEGRA is an arbitrary Lagrangian-Eulerian (multiphysics) computer code developed at Sandia National Laboratories since 1990. The code contains a variety of physics options including magnetics, radiation, and multimaterial flow. The code has been developed for nearly two decades, but recent work has dramatically improved the code's accuracy and robustness. These improvements include techniques applied to the basic Lagrangian differencing, artificial viscosity and the remap step of the method including an important improvement in the basic conservation of energy in the scheme. We will discuss the various algorithmic improvements and their impact on the results for important applications. Included in these applications are magnetic implosions, ceramic fracture modeling, and electromagnetic launch.

2025, Shock Waves

Although several mechanisms have been suggested as explanations for the low-frequency unsteadiness in shock wave/turbulent boundary layer interactions, questions remain on causes and effects. In this effort, we examine the observed asymmetry in large-scale shock motions to highlight which of the suggested mechanisms is most consistent with shock-speed observations and accompanying separation dynamics. The analysis is based on a flowfield obtained from a validated large eddy simulation of a fully separated interaction. A statistical analysis is used to determine the speed of bubble collapse relative to dilation. The low-pass filtering required to separate upstream from downstream motions in the presence of higher-frequency jitter is accomplished with a relatively new technique, empirical mode decomposition, that is very appropriate for this purpose. The dynamics of bubble dilation versus collapse are then elaborated with conditional dynamic mode decomposition (DMD) analyses on the respective pressure fields. Bubble breathing is shown to have a different structure during dilation than during collapse-larger structures are observed during collapse when fluid is expelled from the bubble. The nature of the DMD mode associated with Kelvin-Helmholtz (K-H) shedding in the mixing layer also differs between dilation and collapse: When the bubble is dilating, the structures at the dominant K-H frequency are larger than when the bubble is collapsing. Additionally, a link is established between the convecting K-H structures and corrugation observed along the reflected shock. Some aspects of the nature of the asymmetry are linked to the ease of eddy formation (K-H structures), which plays an important role in the collapse of the bubble. Shock unsteadiness • SWBLI • LES • Conditional analysis • Bubble breathing • Kelvin-Helmholtz shedding • Dynamic mode decomposition • Empirical mode decomposition Communicated by H. Olivier and A. Higgins.

2025, Bulletin of the American Physical Society

Shock-wave / boundary layer interactions usually exhibit unsteadiness with strong low frequency content. The present work aims at analyzing the low frequency shock motion using high resolution data from long-time large-eddy simulations. Three different flow configurations are considered yielding incipient to full separation of the boundary layer in the interaction region. Filtered cross-correlation are used to identify the flow regions being able to influence the shock at low-frequency. It is demonstrated that the information paths deduced from the cross-correlations coincide with the pressure characteristic lines. A theoretical computation of the phase velocity along the shock of perturbations induced by the "breathing" of the interaction region is derived. For all the three flow configurations, two different velocities are found, depending on the location of the sources along the boundary of the decelerated zone. These velocities match quite accurately velocities along the shock computed from the LES data by means of cross-correlations.

2025, Zenodo (CERN European Organization for Nuclear Research)

Large-eddy simulations (LES) of transitional shock wave boundary layer interactions (TrSBLIs) are carried out and results are compared with available experimental databases from the TFAST project. The separated region is characterised by low-frequency breathing and it is associated with a fluidic feedback originating from the vicinity of the reattachment point, in agreement with previous investigations. The non-linear spectral analysis reveled a quadratic coupling between the lowfrequency feedback and the linear unstable modes developing within the mixing layer.

2025, Proceeding of Eighth International Symposium on Turbulence and Shear Flow Phenomena

2025, Shock Waves

2025

2025, Communications of the ACM

This algorithm uses a rational variant of the QR transformation with explicit shift for the computation of all of the eigenvalues of a real, symmetric, and tridiagonal matrix. Details are described in Ill. Procedures tredl or tred3 published in [2] may be used to reduce any real, symmetric matrix to tridiagonal form. Turn the matrix end-for-end if necessary to bring very large entries to the bottom right-hand corner.

2025, The Astrophysical Journal

This series of papers investigates the dynamic interior of a quiescent prominence revealed by recent Hinode and SDO/AIA high-resolution observations. This first paper is a study of the static equilibrium of the Kippenhahn-Schlüter diffuse plasma slab, suspended vertically in a bowed magnetic field, under the frozenin condition and subject to a theoretical thermal balance among an opticallythin radiation, heating, and field-aligned thermal conduction. The everywhereanalytical solutions to this nonlinear problem are an extremely restricted subset of the physically admissible states of the system. For most values of the total mass frozen into a given bowed field, force-balance and steady energy-transport cannot both be met without a finite fraction of the total mass having collapsed into a cold sheet of zero thickness, within which the frozen-in condition must break down. An exact, resistive hydromagnetic extension of the Kippenhahn-Schlüter slab is also presented, resolving the mass-sheet singularity into a finite-thickness layer of steadily-falling dense fluid. Our hydromagnetic result suggests that the narrow, vertical prominence H α threads may be falling across magnetic fields, with optically-thick cores much denser and ionized to much lower degrees than conventionally considered. This implication is discussed in relation to (i) the recent SDO/AIA observations of quiescent prominences that are massive and yet draining mass everywhere in their interiors, (ii) the canonical range of 5 -60 G determined from spectral-polarimetric observations of prominence magnetic fields over the years and (iii) the need for a more realistic multi-fluid treatment.

2025

Adjoint Analysis of a Compressible Channel Flow LAIA MORET-GABARRO, PATRICIA CATHALIFAUD, CHRISTOPHE AIRIAU, IMFT -We present an adjoint analysis of a compressible channel flow using Direct Numerical Simulation. The final aim of this study is to build a tool to perform control of the aerodynamic noise. The adjoint equations are derived from the 2D unsteady compressible Navier-Stokes equations, and are computed backward in time. Both systems are discretized using a 6th order compact scheme in space and 4th order Runge-Kutta scheme in time. Appropriate wall boundary conditions are derived and validated for the adjoint system. We perform sensitivity analysis by applying different kinds of forcing to the adjoint equations, where the resulting field shows the forcing of the direct system required to obtain a given effect. In this study, we are interested in finding which perturbation creates higher noise levels at the core flow (i.e. in a position far from the wall) and how to reduce it. This test case is the first step to perform adjoint analysis of more complex wall-bounded flows, and to perform optimal open-loop control to reduce noise.

2025, European Journal of Engineering Research and Science

This study attempts to illustrate the behavior of a fully developed turbulent flow by using k-ε turbulence model. A two dimensional smooth bend channel is adopted for this experiment and water was chosen as working fluid. The Reynolds number was gradually increased to predict the diversity in turbulent kinetic energy (TKE), turbulent dissipation rate, turbulent intensity and eddy viscosity. Primarily the flow has been solved by employing three distinct k-ϵ turbulence models namely, Standard, Renormalization-group (RNG) and Realizable model. After experimenting with ten different sample (from 74E03 to 298E03) of Reynolds numbers, each of these analyses explicitly showed that Standard k-ε model gives much higher value of any aforementioned turbulent properties with respect to other two equation turbulence models. Later it’s been discovered that TKE obtained from Standard k-ω model is almost same as Realizable k-ε model (for Re=298E03, the difference is about 1.8%). It has been observe...

2025, Journal of Hyperbolic Differential Equations

We consider supersonic vortex sheets for the Euler equations of compressible inviscid fluids in two space dimensions. For the problem with constant coefficients, Morando et al. recently derived a pseudo-differential equation that describes the time evolution of the discontinuity front of the vortex sheet. In agreement with the classical stability analysis, the problem is weakly stable if [Formula: see text], and the well-posedness holds in standard weighted Sobolev spaces. Our aim in this paper is to improve this result, by showing the existence in functional spaces with additional weighted anisotropic regularity in the frequency space.

2025, Coupled systems mechanics

In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.

2025, Physics of Fluids

Turbulence developed from Rayleigh-Taylor instability between two compressible miscible fluids in an unbounded domain is addressed in this paper. It is demonstrated that the turbulent Mach number in the turbulent core has an upper bound, independent of the density ratio under a broad range of initial mean configurations. The initial thermodynamic state of the system determines the amount of potential energy per unit mass involved in the turbulent mixing stage, and thus the characteristic level of turbulent fluctuations that is achievable is linked to the characteristic speed of sound such that the turbulent Mach number is limited. For the particular case of an ideal gas, this bound on the turbulent Mach number is found to be between 0.25 and 0.6, depending on the particular initial thermodynamic state. Hence, intrinsic compressibility effects (those owing to large Mach number) are likely to be limited in the turbulent stage of a pure Rayleigh-Taylor problem. This result is confirmed...

2025, Journal of Computational Physics

In this paper, a class of finite difference schemes which achieves low dispersion and controllable dissipation in smooth region and robust shock-capturing capabilities in the vicinity of discontinuities is presented. Firstly, a sufficient condition for semi-discrete finite difference schemes to have independent dispersion and dissipation is derived. This condition enables a novel approach to separately optimize the dissipation and dispersion properties of finite difference schemes and a class of schemes with minimized dispersion and controllable dissipation is thus obtained. Secondly, for the purpose of shock-capturing, one of these schemes is used as the linear part of the WENO scheme with symmetrical stencils to constructed an improved WENO scheme. At last, the improved WENO scheme is blended with its linear counterpart to form a new hybrid scheme for practical applications. The proposed scheme is accurate, flexible and robust. The accuracy and resolution of the proposed scheme are tested by the solutions of several benchmark test cases. The performance of this scheme is further demonstrated by its application in the direct numerical simulation of compressible turbulent channel flow between isothermal walls.

2025, Quarterly of Applied Mathematics

The steady two-dimensional flow of a compressible fluid past a flat plate inclined to the uniform stream is studied on the basis of the Oseen approximation. The use of the momentum equations written in distributions allows us to obtain in a straight-forward fashion the integral equations of the skin friction and of the lift. These equations are integrated for various values of the Reynolds and Mach numbers. The values obtained for the lift in the limit case of the inviscid fluid coincide with those known in conventional aerodynamics for the subsonic and for supersonic flow.

2025, Int. J. Numer. Meth. Fluids 53:1585–1611

Numerical solutions of 2D magneto-hydrodynamic (MHD) equations by means of a fluctuation splitting (FS) scheme (with a new wave model and dual time stepping technique) is presented. The FS scheme, essentially based on the model explained in

2025, vvJournal of Computational Physics 153, 437–466

This paper describes a two-dimensional (2D) upwind residual distribution or fluctuation splitting (FS) scheme (MHD-A) for the numerical solutions of planar magnetohydrodynamics (MHD) equations on structured or unstructured triangular meshes. The scheme is second order in space and time, and utilizes a consistent 2D wave model originating from the eigensystem of a 2D jacobian matrix of the MHD flux vector. The possible waves existing in this wave model are entropy, magnetoacoustic, and (numerical) magnetic monopole waves; however, Alfven waves do not exist since the problem is planar. One of the important features of the method is that the mesh structure has no influence on propagation directions of the waves. These directions are dependent only on flow properties and field gradients (for example, it is shown that the magnetoacoustic waves propagate in the directions of maximum and minimum magnetic strain rates). The other feature is that no flux evaluations and no information from the neighboring cells are needed to obtain a second order, positive, and linearity preserving scheme. A variety of numerical tests carried out by the model on structured and unstructured triangular meshes show that MHD-A produces rather encouraging numerical results even though it is the first FS wave model ever developed for multidimensional MHD.

2025, Journal of Discrete Mathematical Sciences and Cryptography

Let R be a ring with identity and S be a unitary left module over R. In this paper, we give the concepts of semismall compressible and semismall retractable modules. Also, we

2025, Industrial & Engineering Chemistry Research

2025

Convergence of a finite volume scheme for immiscible compressible twophase flow in porous media (Mladen Jurak, Ivana Radišić) . . . . . . Regularity result for 3D incompressible fluid-rigid body interaction problem (Ana Radošević

2025

In this paper we study the existence and uniqueness of the solution of the Stokes system, describing the flow of a viscous fluid, in case of pressure dependent viscosity.

2025, Journal of Turbulence

Compressible flow over a flat plate with two localized and well-separated roughness elements is analyzed by global frequency-response analysis. This analysis reveals a sustained feedback loop consisting of a convectively unstable shear-layer instability, triggered at the upstream roughness, and an upstream-propagating acoustic wave, originating at the downstream roughness and regenerating the shear-layer instability at the upstream protrusion. A typical multi-peaked frequency response is recovered from the numerical simulations. In addition, the optimal forcing and response clearly extract the components of this feedback loop and isolate flow regions of pronounced sensitivity and amplification. An efficient parametric-sensitivity framework is introduced and applied to the reference case which shows that first-order increases in Reynolds number and roughness height act destabilizing on the flow, while changes in Mach number or roughness separation cause corresponding shifts in the peak-frequencies. This information is gained with negligible effort beyond the reference case and can easily be applied to more complex flows.

2025, J Fluid Mech

We consider the interaction of free-stream disturbances with the leading edge of a body and its effect on the transition point. We present a method which combines an asymptotic receptivity approach, and a numerical method which marches through the Orr-Sommerfeld region. The asymptotic receptivity analysis produces a three-deck eigensolution which in its far downstream limiting form produces an upstream boundary condition for our numerical parabolized stability equation (PSE). We discuss the advantages of this method compared to existing numerical and asymptotic analysis and present results which justify this method for the case of a semi-infinite flat plate, where asymptotic results exist in the Orr-Sommerfeld region. We also discuss the limitations of the PSE and comment on the validity of the upstream boundary conditions. Good agreement is found between the present results and the numerical results of Haddad & Corke (1998).

2025

Gas turbine engine simulation program has been developed. In compressor and turbine, 2-D NS implicit code is used with k-ω SST turbulent model. In combustor, 0-D lumped method chemical equilibrium code is adopted under the limitations, the products are only 10 species of molecular and air-fuel is perfectly mixed state with 100% combustion efficiency at constant pressure. Fluid properties are shared on interfaces between engine components. The outlet conditions of compressor have been used as the inlet condition of combustor. The inlet condition of turbine comes from the compressor The back pressure in compressor outlet is transferred by the inlet pressure of turbine. Unsteady phenomena at rotor-stator in compressor and turbine is covered by mixing-plane method. The state of engine can be determined only by given inlet condition of compressor, outlet condition of turbine, equivalence ratio and rotating speed. 초 록 가스터빈 엔진을 모사하기 위한 프로그램을 2차원 CFD 코드를 기반으로 개발 하였다. 압축기와 터 빈은 k-ω SST 난류 모델의 2차원 NS(Navier Stokes) 코드를 이용하였고, 연소기는 lumped method 화

2025, Journal of Aerospace Technology and Management

In order to simulate compressible shear fl ow stability and aeroacoustic problems, a numerical code must be able to capture how a basefl ow behaves when submitted to small disturbances. If the disturbances are amplifi ed, the fl ow is unstable. The linear stability theory (LST) provides a framework to obtain information about the growth rate in relation to the excitation frequency for a given basefl ow. A linear direct numerical simulation (DNS) should capture the same growth rate as the LST, providing a severe test for the code. In the present study, DNS simulations of a two-dimensional compressible mixing layer and of a two-dimensional compressible plane jet are performed. Disturbances are introduced at the domain infl ow and spatial growth rates obtained with a DNS code are compared with growth rates obtained from LST analyses, for each basefl ow, in order to verify and validate the DNS code. The good comparison between DNS simulations and LST results indicates that the code is able to simulate compressible fl ow problems and it is possible to use it to perform numerical simulation of instability and aeroacoustic problems.

2025, Physics of Fluids

We present a two-way coupled fluid–structure interaction scheme for rigid bodies using a two-population lattice Boltzmann formulation for compressible flows. An arbitrary Lagrangian–Eulerian formulation of the discrete Boltzmann equation on body-fitted meshes is used in combination with polynomial blending functions. The blending function approach localizes mesh deformation and allows treating multiple moving bodies with a minimal computational overhead. We validate the model with several test cases of vortex induced vibrations of single and tandem cylinders and show that it can accurately describe dynamic behavior of these systems. Finally, in the compressible regime, we demonstrate that the proposed model accurately captures complex phenomena such as transonic flutter over an airfoil.

2025, International Journal of Multiphase Flow

We present continuum-scale modeling of multiphase compressible flow in porous media with applications to hydrocarbon reservoir engineering. A new black-oil model is developed and compared with a fully compositional simulator to model the thermodynamic phase behavior. In the context of black-oil modeling, where components are lumped into a gas and liquid pseudocomponent with only the gas transferring between liquid and gas phases, we allow for a variable bubble point pressure (e.g., when gas enters an undersaturated zone). Traditionally, a primary variable switching strategy has been used, which is known to be prone to convergence and phase identification issues. Instead, we adopt an overall molar composition-based framework that can robustly model phase appearance or disappearance. Phase properties across a broad range of pressures for different black-oil compositions are constructed from compositional phase split calculations to correctly model the phase transition. Mass transport is updated explicitly by a locally mass conserving multilinear discontinuous Galerkin method. Globally continuous pressure and velocity fields are obtained through an implicit mixed hybrid FE scheme. The robustness and accuracy of our FE simulator are demonstrated in several problems, where we have attained considerable speed-up and maintained the accuracy with the new black-oil model.

2025, HAL (Le Centre pour la Communication Scientifique Directe)

Une procédure d'identification de propriétés élastiques adaptée à un domaine non borné est proposée. Il s'agit d'exploiter un champ de déplacement mesuré au voisinage du point d'application d'une force normale sur la frontière. A partir d'une formulation par potentiels élastiques complexes bi-dimensionnels, les constantes élastiques d'un milieu homogène isotrope sont déterminées. Une analyse de la sensibilité au bruit de mesure est présentée.

2025, All Days

Streamline methods are gaining popularity in the industry by providing fast desktop simulation of large reservoir models or multiple realizations. Traditionally, streamline simulation has been associated with simplified physics, but recent advances have demonstrated its potential also for compressible three-phase or component flows. However, streamline simulation is still most efficient for two-phase incompressible flow, for which one can utilize a particularly efficient front-tracking method to solve 1-D transport equations along streamlines that is unconditionally stable and independent of the strongly irregular time-of-flight grid. In a recent paper (Nilsen and Lie 2008), we presented, for the first time, front-tracking methods for simulating 1-D compressible two-phase flow. We also developed two methods that were particularly efficient for solving compressible flow in which one phase is incompressible, motivated by the simulation of CO 2 injection. Here we apply these methods to streamline simulation of 3-D models, including a real-life model of a North Sea formation, which is under consideration as a potential target for CO 2 deposition. Our numerical results demonstrate that streamlines and front tracking together give very efficient simulation of compressible flow. Similar ideas can also be applied for dual-porosity models, but this is not investigated in great detail herein.

2025, Acta Acustica United With Acustica

Approximate boundary equations for fluid-loaded thin poroelastic layers are derived for time harmonic conditions. The layer is modeled according to Biot theory and both open and closed pores conditions at the fluid-porous interfaces are considered. Series expansions in the thickness variable are used to replace the porous field variables at the boundaries by their values at the center-plane of the layer. When truncated, this yields a system of equations with the fluid pressures at the surfaces and the porous field variables at the center-plane as unknowns. The problem is split into separate symmetric and antisymmetric cases and is solved by utilizing the governing equations for the porous medium. The result is two 2D differential equations in the plane of the layer which relates the fluid pressures to their normal derivatives at the surfaces. Numerical comparisons are made with 3D Biot theory for two material configurations and two thicknesses. The agreement was found to be better than expected. A thin porous layer may then in some cases be replaced by the approximate boundary conditions and thereby simplify the analysis of fluid-porous coupled problems.

2025, Physical Review E

The Layzer model for the nonlinear evolution of bubbles in the Rayleigh-Taylor instability has recently been generalized to the case of spherically imploding interfaces [D. S. Clark and M. Tabak, to appear, PRE (2005).]. The spherical case is more relevant to, e.g., inertial confinement fusion or various astrophysical phenomena when the convergence is strong or the perturbation wavelength is comparable to the interface curvature. Here, the model is further extended to the case of bubble growth during the deceleration (stagnation) phase of a spherical implosion and to the growth of spikes during both the acceleration and deceleration phases. Differences in the nonlinear growth rates for both bubbles and spikes are found when compared with planar results. The model predictions are verified by comparison with numerical hydrodynamics simulations.

2025, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

The early nonlinear phase of Rayleigh-Taylor (RT) growth is typically described in terms of the classic model of Layzer [1955] in which bubbles of light fluid rise into the heavy fluid at a constant rate determined by the bubble radius and the gravitational acceleration. However, this model is strictly valid only for planar interfaces and hence ignores any effects which might be introduced by the spherically converging interfaces of interest in inertial confinement fusion. The work of G. I. Bell [1951] and M. S. Plesset [1954] introduced the effects of spherical convergence on RT growth but only for the linear regime. Here, a generalization of the Layzer nonlinear bubble rise rate is given for a spherically converging flow of the type studied by Kidder [1974]. A simple formula for the bubble amplitude is found showing that, while the bubble initially rises with a constant velocity similar to the Layzer result, during the late phase of the implosion, an acceleration of the bubble rise rate occurs. The bubble rise rate is verified by comparison with full, 2-D hydrodynamics simulations.

2025, Научная визуализация

The approximation of the tensor appearing at a discretization of the multidimensional function is considered from the viewpoint of storing and treating of the results of parametric computations obtained in computational aerogasdynamics. The new algorithm for the computation of the canonical decomposition using gradient descent and approximately decomposable goal functional is described. This algorithm applies the random set of points on the hyperplane orthogonal to the computed core of the canonical decomposition ("umbrella") that ensures its flexible application for an approximation of the tensors with a priori unknown rank and may be naturally transferred on such tensor decomposition as the tensor train. The results of the numerical tests are presented for the model six-dimensional functions and for an ensemble of the numerical solutions for the two-dimensional Euler equations. These equations describe the flow of the compressible gas with two crossing shock waves. The Mach number and angles of the flow deflection serve as the flow parameters. The results are provided for the dimensionality 3 (simple numerical solution) and 4 (the ensemble of the numerical solutions in dependence on the Mach number).

2025, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES

An unstructured grid CFD code capable of handling arbitrary polyhedra, named ''LS-FLOW,'' is developed for aerodynamic analyses of complex geometries. Through a series of numerical test cases, it is demonstrated that LS-FLOW can handle both structured and body-fitted/Cartesian hybrid unstructured grids successfully. Then, the code is validated by comparison with experimental data and theoretical solutions. In addition, it is shown that when a Baldwin-Lomax algebraic turbulence model is employed on the body-fitted/Cartesian grid, the portion of the body-fitted grid should be large enough to contain the whole boundary-layer. Finally, LS-FLOW is applied to a rocket configuration, and its future prospects are addressed.

2025, Bulletin of the American Physical Society

2025, IOP Conference Series: Materials Science and Engineering 642 (1), 012006

The present study investigates the use of various wingtip devices to analyse the parameters of lift and drag for an aircraft wing. The coefficients of lift and drag are investigated in this research to optimize the wing design for enhancing the aircraft performance. A reduction in the drag produced due to wingtip vortices leads to reduced fuel consumption which contributes to the reduction in fuel emissions. The two-dimensional analysis is carried out for the selection of an apposite aerofoil by comparing the lift/drag characteristics of NACA 0012, 2415 and 23015 respectively at the velocity of 79.16 m/s at the angles of attack of 0°,4°,8°,12°,16°and 20°. The aerofoil section NACA 2415 is used to design the threedimensional aircraft wing. For the analysis of the various wing tip devices the threedimensional wing is incorporated with the spiroid winglet, blended winglet, wingtip fence and a mini-winglet. The CFD analysis for the wing designs is carried out for the takeoff and landing phases of an aircraft's flight because the effect of vortices is the highest during these flight phases. The angles of attack range from 0°to 20°. The CFD results reveal that for the wing designs, the plain wing produced the highest drag and the blended winglet proved to be the wingtip device with the most beneficial design. The results obtained for the 30°cant angled blended winglet and 60°cant angled wingtip fence produces additional lift when compared to the results obtained for the counterpart designs. The results obtained from the analysis are in close correlation to the established use of the wingtip devices.

2025, Science China Physics, Mechanics and Astronomy

At the late stage of transitional boundary layers, the nonlinear evolution of the ring-like vortices and spike structures and their effects on the surrounding flow were studied by means of direct numerical simulation with high order accuracy. A spatial transition of the flat-plate boundary layers in the compressible flow was conducted. Detailed numerical results with high resolution clearly represented the typical vortex structures, such as ring-like vortices and so on, and induced ejection and sweep events. It was verified that the formation of spike structures in transitional boundary layers had close relationship with ring-like vortices. Especially, compared to the newly observed positive spike structure in the experiments, the same structure was found in the present numerical simulations, and the mechanism was also studied and analyzed.

2025

Over the past few years, we developed a mathematically rigorous method to study the dynamical processes associated to nonlinear Forchheimer flows for slightly compressible fluids. We have proved the existence of a geometric transformation which relates constant mean curvature surfaces and timeinvariant pressure distribution graphs constrained by the Darcy-Forchheimer law. We therein established a direct relationship between the CMC graph equation and a certain family of equations which we call g-Forchheimer equations. The corresponding results, on fast flows and their geometric interpretation, can be used as analytical tools in evaluating important technological parameters in reservoir engineering.

2025

The aerodynamic performance of an aircraft can be enhanced by incorporating wingtip devices, or winglets, which primarily reduce lift-induced drag created by wingtip vortices. This study outlines an optimization procedure for implementing winglets on a Class I fixed-wing mini-UAV to maximize aerodynamic efficiency and performance. After the Conceptual and Preliminary design phases, a baseline UAV was developed without winglets, adhering to specific layout constraints (e.g., wingspan, length). Various winglet designs-plate and blended types with differing heights, cant angles, and sweep angles-were then created and assessed. A Computational Fluid Dynamics (CFD) analysis was conducted to evaluate the flow around both the winglet-free UAV and configurations with each winglet design. The simulations employed Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the Spalart-Allmaras turbulence model, targeting the optimal winglet configuration for enhanced aerodynamic characteristics during cruise. Charts of lift, drag, pitching moment coefficients, and lift-to-drag ratios are presented, alongside flow contours illustrating vortex characteristics for both baseline and optimized configurations. Additionally, dynamic stability analyses examined how winglets impact the UAV's stability and control. The results demonstrated a significant improvement in aerodynamic coefficients (C Lmax , L/D max , C La , C ma), leading to an increase in both range and endurance.

2025

It is well known that openFoam has become a very popular tool for research work in different fields and particularly, in fluid dynamics. But, it is also known its lack of detailed documentation supporting solvers made using the set of libraries provided by openFoam. Therefore, it becomes necessary to establish appropriate verifications that can be useful to users going for instance, through the selection of equations discretization schemes from fvSchemes libraries and of solution solvers from fvSolutions libraries, to be later applied in the simulation of a given specific problem. With this purpose, executable solvers available in openFoam 1.7 version to solve supersonic air flow problems are tested. Two different approaches have been taken in developing numerical methods to solve problems in transport phenomena at all Mach numbers and traditionally, they have been referred to as pressure-based and density-based methods. In this work, the advantages or disadvantages in applying any ...

2025, Biotechnology Progress

A one-dimensional model of mechanical deformation of compressible chromatography columns is presented. The model is based on linear elasticity and continuum mechanics and is compared to a more complete two-dimensional model and one-dimensional porosity profiles measured by NMR imaging methods. The model provides a quantitative description of compression and the effects of wall support during scale-up. A simple criterion for the significance of wall support as a function of both diameter and length is also developed. Although the model accounts only for mechanical deformation, flow compression can be included, and validation presented here suggests that a more complete model may be valuable for anticipating the effects of scale and aspect ratio on pressure-flow behavior of compressible columns.

2025, Physics of Fluids

Numerical simulations of the unsteady, two-dimensional, incompressible Navier–Stokes equations are performed for a Newtonian fluid in a channel having a symmetric constriction modeled by a two-parameter Gaussian distribution on both channel walls. The Reynolds number based on inlet half-channel height and mean inlet velocity ranges from 1 to 3000. Constriction ratios based on the half-channel height of 0.25, 0.5, and 0.75 are considered. The results show that both the Reynolds number and constriction geometry have a significant effect on the behavior of the post-constriction flow field. The Navier–Stokes solutions are observed to experience a number of bifurcations: steady attached flow, steady separated flow (symmetric and asymmetric), and unsteady vortex shedding downstream of the constriction depending on the Reynolds number and constriction ratio. A sequence of events is described showing how a sustained spatially growing flow instability, reminiscent of a convective instability...

2025

In this paper, the entropy generation of a fully developed laminar flow in annular sector ducts with constant wall heat flux is investigated. Entropy generation is obtained for various aspect ratio (e), various sector angels (2φ), various wall heat flux and various Reynolds number. It is found that with the increasing aspect ratio (e) and sector angels (2φ) values, total entropy generation and pumping power at fixed Reynolds number increases and with increasing wall heat flux values, total entropy generation increases, however, pumping power decreases.

2025

In this paper, the entropy generation of a fully developed laminar flow in annular sector ducts with constant wall heat flux is investigated. Entropy generation is obtained for various aspect ratio (ε), various sector angels (2φ), various wall heat flux and various Reynolds number. It is found that with the increasing aspect ratio (ε) and sector angels (2φ) values, total entropy generation and pumping power at fixed Reynolds number increases and with increasing wall heat flux values, total entropy generation increases, however, pumping power decreases.

2025, International Journal of Mechanical Sciences

The present article aims to implement and investigate a different preconditioning method based in a threedimensional in-house compressible CFD code that ensures the robustness and numerical stability to determine the flowfield considering low Mach number flow. The present preconditioning method involve two different methodologies developed by references . The CFD solver was developed to calculate the Euler and Navier-Stokes equations, numerically, for steady-state regime based on the cell-centered finite volume method (FVM) using Reynolds Averaged Navier-Stokes equations (RANS). The centered second-order scheme was used for the discretization of convective terms from momentum equations. The explicit second-order five-step Runge-Kutta scheme was employed for the time-marching procedure, using an implicit residual smoothing technique to enhance the numerical stability. A local preconditioning method was implemented due to its robustness in predicting low Mach number flows in a compressible CFD code environment. However, for low Mach number flows, near stagnation points, numerical perturbations were amplified generating a stiffness in the convergence rate, which provided an inaccurate solution and numerical stability degradation. Aiming to improve the preconditioning robustness, a flux function and a new limiter were applied to operate with the preconditioning technique based on a pressure sensor. Those corrections re-scale the eigenvectors and ensure the locality of the algorithm, which improves the numerical stability and guarantees the convergence for low-speed flows. The inviscid flow over a NACA 0012 airfoil for compressible and incompressible cases shown accurate and robust solutions. For a viscous flow over a flat plate case in the compressible and incompressible cases, the preconditioning technique purposed in this work supplied good numerical solution in agreement with the analytical solution.

2025, Bulletin of the American Physical Society

based direct numerical simulations (WDNS) of compressible, miscible, and single mode Rayleigh Taylor instability (RTI) with a stratified background density have been completed in 2 and 3 dimensions. As the instability grows, vorticity dynamics are largely responsible for the self-propagation and growth of the bubble and spike. However, in the presence of a background stratification, the vortex interactions are significantly altered. In the case of low Atwood number RTI, this leads to previously unseen regimes, namely, the exaggeration of bubble and spike asymmetries for a weakly stratified background state and the complete suppression of RTI growth in the strongly stratified scenario. To better understand these results, the vorticity transport equation budget was compared to the simplified scenarios of vortex pairs (2D) and vortex rings (3D) moving in a stratified medium.

2025, Bulletin of the American Physical Society

University -Fully resolved adaptive wavelet-based direct numerical simulations (WDNS) of the single-mode, compressible, and miscible Rayleigh-Taylor instability (RTI) have been performed at Reynolds numbers significantly larger than those previously attained. To ensure that WDNS properly captures the full extent of the length and time scales, an exhaustive resolution study was completed. The ensuing results explore the effects of compressibility and background stratification on the vortex generation and interaction that serves as the driver behind the RTI development beyond the early stages. To better understand the eventual suppression that arises at large background stratification, the simplified cases of a pair of counter rotating vortices (2D) and a vortex ring (3D) in stratified media are also presented for the purpose of isolating and explaining the physics behind these effects on RTI growth.