Search

Scalability of computations in the FlowVision CFD software on the Angara-C1 cluster equipped with the Angara interconnect is studied. Different test problems with 260 thousand, 5.5 million and 26.8 million computational cells are considered. Computations in FlowVision are performed using a new solver of linear systems based on the algebraic multigrid (AMG) method. It is shown that the the special FlowVision’s Dynamic balancing technology significantly improves performance of computations if features of the problem lead to the non-uniform loading of CPUs. The Angara-C1 cluster demonstrates excellent performance and scalability characteristics comparable with its analogues based on the 4X FDR Infiniband interconnect.

This work presents the model of heat wall functions FlowVision (WFFV), which allows simulation of nonisothermal flows of fluid and gas near solid surfaces on relatively coarse grids with use of turbulence models. The work follows the research on the development of wall functions applicable in wide range of the values of quantity y+. Model WFFV assumes smooth profiles of the tangential component of velocity, turbulent viscosity, temperature, and turbulent heat conductivity near a solid surface. Possibility of using a simple algebraic model for calculation of variable turbulent Prandtl number is investigated in this study (the turbulent Prandtl number enters model WFFV as parameter). The results are satisfactory. The details of implementation of model WFFV in the FlowVision software are explained. In particular, the boundary condition for the energy equation used in high-Reynolds number calculations of non-isothermal flows is considered. The boundary condition is deduced for the energy equation written via thermodynamic enthalpy and via full enthalpy. The capability of the model is demonstrated on two test problems: flow of incompressible fluid past a plate and supersonic flow of gas past a plate (M = 3). Analysis of literature shows that there exists essential ambiguity in experimental data and, as a consequence, in empirical correlations for the Stanton number (that being a dimensionless heat flux). The calculations suggest that the default values of the model parameters, automatically specified in the program, allow calculations of heat fluxes at extended solid surfaces with engineering accuracy. At the same time, it is obvious that one cannot invent universal wall functions. For this reason, the controls of model WFFV are made accessible from the FlowVision interface. When it is necessary, a user can tune the model for simulation of the required type of flow. The proposed model of wall functions is compatible with all the turbulence models implemented in the FlowVision software: the algebraic model of Smagorinsky, the Spalart-Allmaras model, the SST $k-\omega$ model, the standard $k-\varepsilon$ model, the $k-\varepsilon$ model of Abe, Kondoh, Nagano, the quadratic $k-\varepsilon$ model, and $k-\varepsilon$ model FlowVision.

Flow of gas mixture around and inside a scale model of hypersonic vehicle is simulated with use of the FlowVision software. The model is placed in a wind tunnel. All the solid surfaces present in the experiments are taken into account in the calculations. Calculation results are compared with experimental data obtained in two runs: without burning hydrogen in the combustion chamber (cold run) and with burning hydrogen (hot run). The computational grids are built automatically with use of different adaptation options available in FlowVision. The agreement of numerical results with experimental data is good.

Numerical investigation of mixing non-isothermal streams of sodium coolant in a T-branch is carried out in the FlowVision CFD software. This study is aimed at argumentation of applicability of different approaches to prediction of oscillating behavior of the flow in the mixing zone and simulation of temperature pulsations. The following approaches are considered: URANS (Unsteady Reynolds Averaged Navier Stokers), LES (Large Eddy Simulation) and quasi-DNS (Direct Numerical Simulation). One of the main tasks of the work is detection of the advantages and drawbacks of the aforementioned approaches. Numerical investigation of temperature pulsations, arising in the liquid and T-branch walls from the mixing of non-isothermal streams of sodium coolant was carried out within a mathematical model assuming that the flow is turbulent, the fluid density does not depend on pressure, and that heat exchange proceeds between the coolant and T-branch walls. Model LMS designed for modeling turbulent heat transfer was used in the calculations within URANS approach. The model allows calculation of the Prandtl number distribution over the computational domain. Preliminary study was dedicated to estimation of the influence of computational grid on the development of oscillating flow and character of temperature pulsation within the aforementioned approaches. The study resulted in formulation of criteria for grid generation for each approach. Then, calculations of three flow regimes have been carried out. The regimes differ by the ratios of the sodium mass flow rates and temperatures at the T-branch inlets. Each regime was calculated with use of the URANS, LES and quasi-DNS approaches. At the final stage of the work analytical comparison of numerical and experimental data was performed. Advantages and drawbacks of each approach to simulation of mixing non-isothermal streams of sodium coolant in the T-branch are revealed and formulated. It is shown that the URANS approach predicts the mean temperature distribution with a reasonable accuracy. It requires essentially less computational and time resources compared to the LES and DNS approaches. The drawback of this approach is that it does not reproduce pulsations of velocity, pressure and temperature. The LES and DNS approaches also predict the mean temperature with a reasonable accuracy. They provide oscillating solutions. The obtained amplitudes of the temperature pulsations exceed the experimental ones. The spectral power densities in the check points inside the sodium flow agree well with the experimental data. However, the expenses of the computational and time resources essentially exceed those for the URANS approach in the performed numerical experiments: 350 times for LES and 1500 times for ·DNS.

In order to make a correct choice of the artificial heart valve for curing patients with cardio vascular disorder it is very important to know in detail the blood flow in the heart of the specific patient. In this book chapter, two separate approaches are presented on how to model the blood flow within the real human heart. The first approach is based on Magnetic Resonance Imaging/Tomography to get shape (“geometry”) of internal heart volumes in time (tens or hundreds of frames for one heartbeat), and applies a Computational Fluid Dynamics (CFD) tool for simulating and visualizing a blood flow. The second approach is based on the SIMULIA Abaqus LHHM model, combining the structural heart Finite Element Model (FEM) with the CFD simulation to solve the fluid structure interaction problem. The blood flow circulation through the heart is numerically simulated with a modern FlowVision code that has a fully automatic mesh generation using arbitrary cell shapes for dynamic mesh refinement and taking into account the motion of the heart surface, applying the Euler coordinates. The second approach solves the bidirectional fluid-structure interaction problem applying the general purpose CFD code FlowVision and the SIMULIA Living Heart Human Model (LHHM), a dynamic, anatomically realistic, 4-chamber heart model with mechanical valves that considers the interplay and coupling of electrical and mechanical fields, which are acting simultaneously to regulate the heart filling, ejection, and overall like pump functions. LHHM natively includes a 1D fluid network model capable of representing dynamic pressure/volume changes in the intra- and extra-cardiac circulation. In the current work, this network model is first replaced with a full 3D blood model (solved in FlowVision) that provides detailed spatial and temporal resolution of cardiac hemodynamic driven by motions of the beating heart and constrained with appropriate time-varying boundary conditions derived from the literature. After validating this approach, the bidirectional coupling between the blood flow CFD model and the LHHM electromechanical model is activated by using the SIMULIA co-simulation engine and in conclusion the modelling details and results of interest are discussed. Using the real heart MRI/MRT has tested the described approaches of simulating the blood flow and SIMULIA Abaqus LHHM and the simulation results are presented.

The article provides a development of recently published turbulence model KEFV. The submitted version of this model allows modeling transition in a separated flow. The model includes an adjustable mechanism for specifying generation of turbulence in laminar zones with high velocity gradients. The model is implemented in the FlowVision CFD software. Simulation of the air flow around low-Reynolds airfoil Eppler-387 is discussed in the article. The flow conditions are characterized by the Reynolds number Re = 200 000.

Results of numerical simulation of complex conjugate heat transfer in a high power electric transformer are presented. Simulation of the flow and heat transfer inside a transformer with static blast protection was carried out. Analysis of test calculations performed in the FlowVision software suit was carried out. Comparison of the performance of created numerical model against the real experimental data from the thermal tests of the transformer was made.

Simulation of the water flow around a ship hull and a marine propeller operation are considered in this paper as popular problems of ship propulsion, which are frequently investigated through CFD approach now. CFD technologies are used for determination of ship hull resistance as well as the open water curves of the propeller according to usual methods of ship design. FlowVision CFD software is used for simulations based on solving RANS equations. The software was used together with supercomputer “HPC 2” of National Research Center “Kurchatov Institute”. The original features of the numerical models and technologies, software algorithms and the supercomputer’s hardware are submitted and discussed. There are the method of grid formation based on Cartesian initial grid and chimerical overlapping boundary layer grid, special versions of turbulence models, modified method of free surface simulation and many other things among them. Governing equations for water flow, which are integrated using an implicit numerical method, are given as well. The generated systems of linear equations are solved by an aggregative algebraic multigrid method. The scalability of this method on the supercomputer has been studied and analyzed.

A kinetic model for air-carbon surface interaction is suggested. The model is based on the langmuir approach to the kinetics of catalytic reactions. It yields a reasonable agreement with published experimental data on graphite oxidation. A viscous shock-layer code has been developed to simulate hypersonic flows of the 19-species mixture containing air and carbon products. Numerical analysis of ablation and strong ionization processes is carried out with different ablation and ionization models. Calculations show that 1) the maximal drop of the heat flux because of ablation, compared with that obtained for the fully catalytic (chemical-equilibrium) wall in the 11-species air, is within 26% under the conditions discussed; 2) mass loss rate strongly depends on the adsorption type (mobile/immobile); 3) ionization model may have a substantial influence on the shock thickness in the case of re-entry with a hyperbolic velocity; and 4) the effect of the wall catalycity with respect to charged particles on the heating rate is small

A prospective hypersonic HEXAFLY aircraft is considered in the given paper. In order to obtain the aerodynamic characteristics of a new construction design of the aircraft, experiments with a scaled model have been carried out in a wind tunnel under different conditions. The runs have been performed at different angles of attack with and without hydrogen combustion in the scaled propulsion engine. However, the measured physical quantities do not provide all the information about the flowfield. Numerical simulation can complete the experimental data as well as to reduce the number of wind tunnel experiments. Besides that, reliable CFD software can be used for calculations of the aerodynamic characteristics for any possible design of the full-scale aircraft under different operation conditions. The reliability of the numerical predictions must be confirmed in verification study of the software. The given work is aimed at numerical investigation of the flowfield around and inside the scaled model of the HEXAFLY-CIAM module under wind tunnel conditions. A cold run (without combustion) was selected for this study. The calculations are performed in the FlowVision CFD software. The flow characteristics are compared against the available experimental data. The carried out verification study confirms the capability of the FlowVision CFD software to calculate the flows discussed.

A new implicit velocity-pressure split method is discussed in the given presentation. The method implies using conservative velocities, obtained at the given time step, for integration of the momentum equation and other convection-diffusion equations. This enables simulation of super- and hypersonic flows with account of motion of solid boundaries. Calculations of known test cases performed in the FlowVision software are demonstrated. It is shown that the method allows one to carry out calculations at high Mach numbers with integration step essentially exceeding the explicit time step.

A new dissociation model accounting for equilibrium excitation of rotational modes of the molecules and nonequilibrium excitation of vibrational modes is presented. The model has no unknown empirical parameters, and the uncertainty of the model is determined only by uncertainty of the physical quantities characterizing collisions of the particles. The model can be approximated by a simple expression, convenient in gas-dynamic applications. Numerical calculations within the scope of the multi-component nonequilibrium full viscous shock layer model with the use of suggested formulas for dissociation rate constants show that the data of this complex model fit well with experimental data for the shock detachment distance. A comparison of various models accounting for the influence of vibrational nonequilibrium on dissociation rates is carried out. The comparison has shown that the “T u , T” model of Park gives underestimated values of the vibrationally nonequilibrium dissociation rate constants.