Supercomputing Frontiers and Innovations

Numerical Simulation of Supersonic Free-Flow Stationary Disturbances Caused by Two-Dimensional Roughness in a Turbulent Boundary Layer

Thu, 22 Feb 2024 00:00:00 +0500

Stationary disturbances in a free supersonic flow caused by two-dimensional roughness in a turbulent boundary layer on a wall were investigated using numerical simulation in the FlowVision software package. Calculations were performed for cases where the roughness heights were significantly smaller than the thickness of the boundary layer. In order to reduce the numerical oscillations, the computational grid has been adapted to the perturbation fronts by means. It was found that a disturbance in the form of a small amplitude N-wave is formed in the flow above the boundary layer. The effect of roughness height on disturbances formed in a free flow was studied. It was found that as the roughness height increases, there is an observed increase in the amplitude and spatial scale of the disturbance. It was also found that the gradient of the flow parameters between the disturbance fronts remains practically unchanged for all roughness heights considered. The numerical results were verified with experimental data. A strong agreement was achieved between the simulation and experimental result.

2D Simulation of Micro-Jet Excitation by Heat Source

Aleksandr A. Firsov — Thu, 22 Feb 2024 00:00:00 +0500

Excitation of a laminar gas micro-jet by acoustic impact and by pulse-periodic heat source was simulated using the FlowVision software package in 2D formulation at normal conditions. Heat source imitates an electrical discharge. Air jet was formed by channel with inner size of 0.7 mm with the Poiseuille velocity profile at inlet boundary, the maximum profile velocity was varied in a range of 2.5–10 m/s. Influence of heat source frequency and power on the large-scale vortex formation was described. In the case of a jet with a speed of 5 m/s, the natural oscillations of the jet in response to a single pulse had a frequency fres = 1380 Hz, so excitation of the jet was possible at close frequencies of 1190 Hz and 1500 Hz. At the same time, at a frequency of 1000 Hz (approximately equal to 2/3 fres), every second impulse acted in antiphase and the oscillations developed poorly. Dependence of flow structure from the jet velocity was obtained. The results obtained show the possibility of exciting a micro-jet using low-power electrical discharges such as spark, DBD or corona.

String-Wave Direct Parallel Solver for Sparse System of Linear Equations

Alexey Y. Likhosherstnyy, Yana G. Velikaya — Thu, 22 Feb 2024 00:00:00 +0500

The article discusses a parallel algorithm of solving linear algebraic equations systems for symmetric sparse matrices, which allows to split a large task into many small subtasks, thereby both increasing performance and reducing memory consumption. It is based on a method of simultaneous calculation of intermediate values during matrix factorization with maintaining load balancing on processors so that when the final result of the left parts of the factorization is obtained, the right parts of the factorization do not depend on them. This approach allows the initial stiffness matrix to be represented as a product of a large number of simple matrixes and solve a system of linear algebraic equations in the form of a sequence of solutions by substitution. To reduce the filling of sparse factorization matrices, an approximate minimum degree method was used, which, in addition to being one of the most efficient and fastest ones existing at the moment, allows the developed algorithm to distribute the load of calculations more evenly. The developed method is implemented in APM Ltd. software products for systems with shared memory, but it can also be performed for distributed memory systems.

Three-dimensional Numerical Model of Kerosene Evaporation in Gas Turbine Combustors

Thu, 22 Feb 2024 00:00:00 +0500

A three-dimensional model of the multiphase flow based on the Eulerian–Eulerian approach was implemented using the FlowVision CFD package and, on this basis, a numerical algorithm for study of evaporation of liquid fuel was developed. The created high-performance complex for the carrier and dispersed phases interaction simulation was validated against the well-studied experimental problem of the evaporation and mixing of kerosene emerging from a flat pre-filming airblast atomizer for gas turbine combustors. In this work, the carrier phase is supposed to be air and kerosene vapors, and the dispersed phase is selected as liquid kerosene. Based on the calculated kerosene evaporation drops distributions, an important parameter that characterizes the spray fineness, Sauter mean diameter, is determined. Numerically calculated in the developed model the evaporation rate and Sauter mean diameter of fuel droplets agreed well with the experimental data. In famous works, the air temperature and pressure varied during the experiments. At the same time, in comparison with the calculated data, a stronger influence on the kerosene evaporation was obtained by air temperature than pressure. The dependence on pressure can be seen in the case of taking into account the corresponding changes in the liquid fuel properties. It is also noted that the initial fuel temperature is an important parameter for evaporation. This can be seen in the results of the kerosene evaporation numerical simulation carried out in this study.

Analysis and Optimization of Output Operations in the INM RAS Earth System Model

Maria A. Tarasevich, Ivan V. Tsybulin, Evgeny M. Volodin, Andrey S. Gritsun — Thu, 22 Feb 2024 00:00:00 +0500

The modern development of complex Earth system models forces developers to take into account not only the computational efficiency, but also the performance of the data input and output. This work evaluates the data output performance of the INM RAS Earth system model and optimizes its weak points. The output operations were found to be surprisingly slow on the Cray XC40-LC supercomputer compared to the results obtained on the INM RAS cluster. To identify the bottleneck, the computational time, the distributed data gathering time, and the file system output time were measured separately. The distributed data gathering time was the cause of the slowdown on the Cray XC40-LC, so optimizations were made to the gathering routines without any additional rework of the existing output code. The optimizations resulted in a significant reduction in the overall model running time on the Cray XC40-LC, while the gathering time itself was reduced by a factor of 10²–10³. The results highlight the importance of optimizing the output performance in Earth system models.

High-Performance Computing of Microtubule Protofilament Dynamics by Means of All-Atom Molecular Modeling

Thu, 22 Feb 2024 00:00:00 +0500

Molecular dynamics (MD) simulation is a useful tool for understanding biological systems at the level of individual molecules and atoms. However, studying such massive biological systems as microtubules and even their constituent components (tubulin protofilaments) takes an enormous amount of processing power. In this paper, using MD calculations of individual microtubule protofilaments, we demonstrate how computational architecture and calculation options affect computing performance. When using the “GPU-resident” option in the GROMACS MD package, you may gain a fantastic computation acceleration by using the newest high-end graphics processing unit (GPU), even in conjunction with a rather outdated central processing unit (CPU). For instance, MD of the biomolecular system containing a tubulin protofilament in an explicitly specified solvent consisting of more than 300 thousand atoms can be investigated with performance of 171 ns/day at time step 2 fs when using a single-node computer with the latest CPU and GPU generation architecture (Intel Core i9-13900K and Nvidia RTX4090 respectively). Nevertheless, high performance computing platforms (e.g., the volta2 partition of "Lomonosov-2" supercomputer) can be very suitable for simulation experiments with a large number of independent calculations, such as the umbrella sampling technique. Obtained results allow one to choose the best price-performance solution to study molecular dynamics of biological systems.