Ivan But

Wave attractors in viscous media exhibit laminar or turbulent behavior, dictated by the intensity of the external forcing. Laminar attractors are often assumed to behave as linear systems. However, existing studies typically focus on fully developed flows, neglecting the dynamic formation process of these attractors. This simplification overlooks crucial transient phenomena that govern their emergence and stability. In this paper, first, we investigate unconventional wave attractor configurations subjected to forcing with a complex spectrum, which lead to early nonlinearity demonstration. Next, we focus on the transient processes of attractor formation and destruction, providing insights into their dynamic evolution. Furthermore, we identify temporal and velocity scaling relationships across various viscosity parameters, revealing the self-similar behavior inherent in these wave-attractor systems.

This study investigates the flow structures and acoustic properties of supersonic jets that release various gases into quiescent air. Numerical simulations are performed on air, hydrogen, and argon jets discharging into an air-filled domain at a Mach number of 2.1 and a Reynolds number of 70 000. The reactingQGDFoam solver is used, which implements quasi-gasdynamic (QGD) equations for homogeneous ideal gas mixtures. This solver is coupled with the libAcoustics library for aeroacoustic analysis. The influence of gas composition on the mean, instantaneous, and acoustic characteristics of the flow is quantified, including the length of the potential jet core, peak acoustic radiation directivity, and turbulent mixing mechanisms. Although all gases demonstrate universal power-law expansion behavior, hydrogen exhibits delayed self-similarity because of competing inertial and turbulent diffusion effects. Additionally, decay law exponents are determined for the mean streamwise velocity of all fluids.

One of the principle conditions of a wave attractor appearance is a periodic external forcing. Real forcing in natural basins caused by tidal interaction is more complex than a monochromatic which is usually used in internal wave attractors investigations. Multi-frequency forcing may lead to the multiple wave attractor formation, some of them may be of low energy, which affects their detection. In the article we simulate a mixed forcing for an internal wave attractor flow and visualize subattractor formed due to this forcing type using several methods, including Proper Orthogonal Decomposition. It is shown that the latter method reveals sub-attractor even in case of highly turbulent flow.

The paper presents an improved approach for modeling multicomponent gas mixtures based on quasi‐gasdynamic equations. The proposed numerical algorithm is implemented as a reactingQGDFoam solver based on the open‐source OpenFOAM platform. The following problems have been considered for validation: the Riemann problems, the backward facing step problem, the interaction of a shock wave with a heavy and a light gas bubble, the unsteady underexpanded hydrogen jet flow in an air. The stability and convergence parameters of the proposed numerical algorithm are determined. The simulation results are found to be in agreement with analytical solutions and experimental data.

Introduction . We present a novel adaptive mesh refinement (AMR) solver, SWqgdAMR, based on the open software platform AMReX. The new solver is grounded in regularized shallow water equations. This paper details the equations, their discretization, and implementation features within AMReX. The efficacy of SWqgdAMR is demonstrated through two test cases: a two-dimensional circular dam break (collapse of a liquid column) and the collapse of two liquid columns of different heights. Materials and Methods . The SWqgdAMR solver is developed to extend the applicability of regularized equations in problems requiring high computational power and adaptive grids. SWqgdAMR is the first solver based on the quasigas dynamic (QGD) algorithm within the AMReX framework. The implementation and validation of SWqgdAMR represent a crucial step towards the further expansion of the QGD software suite. Results . The AMReX-based shallow water equations solver SWqgdAMR with adaptive mesh refinement is described and tested in detail. Validation of SWqgdAMR involved two-dimensional problems: the breach of a cylindrical dam and the breach of two cylindrical dams of different heights. The presented solver demonstrated high efficiency, with the use of adaptive mesh refinement technology accelerating the computation by 56 times compared to a stationary grid calculation. Discussion and Conclusions . The algorithm can be expanded to include bathymetry, external forces (wind force, bottom friction, Coriolis forces), and the mobility of the shoreline during wetting and drying phases, as has been done in individual codes for regularized shallow water equations (RSWE). The current implementation of the QGD algorithm did not test the potential for parallel computing on graphical cores.

The influence of the viscosity on a wave attractor flow has been previously studied, particularly in relation to the widening of the hydrodynamical structures. In this work, we simulate an attractor flow with a peculiar bottom shape that includes an underwater hill. During the simulation, we discovered a side structure appearing beyond the wave attractor. We determined that the appearance of this structure is connected to viscosity. In this article, we consider the behavior of this newly found structure. Additionally, we discuss the challenges of energy accumulation and the estimation of the Reynolds number, which is a non-trivial problem in the context of wave attractor flows.

We consider a steady submerged laminar jet of viscous incompressible fluid flowing out of a tube and propagating along a solid plane surface. The numerical solution of Navier–Stokes equations is obtained in the stationary three-dimensional formulation. The hypothesis that at large distances from the tube exit the flowfield is described by the self-similar solution of the parabolized Navier–Stokes equations is confirmed. The asymptotic expansions of the self-similar solution are obtained for small and large values of the coordinate in the jet cross-section. Using the numerical solution the self-similarity exponent is determined. An explicit dependence of the self-similar solution on the Reynolds number and the conditions in the jet source is determined.