Large Scale GPU Based Simulations of Turbulent Bubbly Flow in a Square Duct

In this paper, we present the results of a numerical study of air-water turbulent bubbly flow in a periodic vertical square duct. The study is conducted using a novel numerical technique which leverages Volume of Fluid method for interface capturing and Sharp Surface Force method for accurate representation of the surface tension forces. A three-dimensional geometry construction method is employed during solution of interface equation which gives absolute conservation of mass and sharp interface between gas and liquid phases. The entire algorithm has been implemented on a data parallel mode on multiple graphics processing units (GPU) taking advantage of the large number of available cores. We have studied the dynamics of a swarm of spherical bubbles co-flowing with the upward turbulent flow and compared results with an unladen turbulent flow. The frictional Reynolds number of the unladen $Re_{\tau}$ is 360, which is sufficient to sustain a turbulent flow. We observe the turbulence-driven secondary flows in the mean flow, with complex instantaneous turbulent vortical structures. The interaction of these secondary flows with the upwards rising bubbles is very complex and leads to significant changes in the instantaneous and time-averaged flow field. We present the results of mean void fraction distribution, mean velocities, longitudinal and transverse turbulence intensities along the wall, corner bisector, and wall bisector. A peak in the void fraction distribution near the walls is observed representing the migration of bubbles to a preferred section of the duct. The effects of turbulence-driven secondary flows and instantaneous large eddies on preferential concentration of the bubbles are discussed. The dispersed bubbles are seen to break the long elongated turbulent structures commonly observed in the unladen turbulent flow

STREAmS: a high-fidelity accelerated solver for direct numerical simulation of compressible turbulent flow

We present STREAmS, an in-house high-fidelity solver for large-scale, massively parallel direct numerical simulations (DNS) of compressible turbulent flows on graphical processing units (GPUs). STREAmS is written in the Fortran 90 language and it is tailored to carry out DNS of canonical compressible wall-bounded flows, namely turbulent plane channel, zero-pressure gradient turbulent boundary layer and supersonic oblique shock-wave/boundary layer interactions. The solver incorporates state-of-the-art numerical algorithms, specifically designed to cope with the challenging problems associated with the solution of high-speed turbulent flows and can be used across a wide range of Mach numbers, extending from the low subsonic up to the hypersonic regime. The use of cuf automatic kernels allowed an easy and efficient porting on the GPU architecture minimizing the changes to the original CPU code, which is also maintained. We discuss a memory allocation strategy based on duplicated arrays for host and device which carefully minimizes the memory usage making the solver suitable for large scale computations on the latest GPU cards. Comparison between different CPUs and GPUs architectures strongly favor the latter, and executing the solver on a single NVIDIA Tesla P100 corresponds to using approximately 330 Intel Knights Landing CPU cores. STREAmS shows very good strong scalability and essentially ideal weak scalability up to 2048 GPUs, paving the way to simulations in the genuine high-Reynolds number regime, possibly at friction Reynolds number $Re_{\tau} > 10^4$. The solver is released open source under GPLv3 license and is available at https://github.com/matteobernardini/STREAmS.Comment: 11 pages, 11 figure

Numerical study of turbulent flow in eccentric annular pipe

An eccentric annular duct is a prototype element in many applications, for example in close-packed tubular heat exchangers and coolant channels of nuclear reactors. From a fundamental viewpoint, turbulent flow in eccentric annular ducts is an ideal model for investigating inhomogeneous turbulence. It is also a convenient model to study the laminar and turbulent interface and may serve as a test case for turbulence modelling of flows with partly turbulent regimes. Based on the approach of direct numerical simulation, numerical investigations of turbulent flow in eccentric annular pipes are carried out in this thesis. We first investigated the case of fully turbulent flow. A detailed statistical analysis of turbulent flow and heat transfer was performed. Simulation results, such as friction factors, mean velocity profiles and the secondary-motion pattern, are in overall qualitative and quantitative agreement with the existing experimental data. The components of the Reynolds stress tensor, temperature-velocity correlations and some others were obtained for the first time for such kind of a flow. The study of the partly turbulent flow case was then carried out. Three approaches for detecting interfaces between laminar and turbulent regimes in partly turbulent flow in rotating eccentric pipes were compared and discussed. Positions of laminar-turbulent and turbulent-laminar interfaces obtained from profiles of perturbation enstrophy are the same as those obtained from production terms of enstrophy. Using patterns of streaks defined by wall shear stresses to determine the locations of interfaces showed similar results. The growth rate of a small disturbance in partly turbulent flow case was also analyzed. Small perturbations were introduced into the initial flow field in two different ways. Both cases show that the global growth rate of the small disturbance normalized by the global viscous time scale is constant. This constant value is in a good agreement with that obtained in channel flows and tube flows. A new approach was proposed to distinguish the interface between laminar and turbulent flow by introducing the global and local disturbance growth rate

Numerical study of turbulent flow in eccentric annular pipe

An eccentric annular duct is a prototype element in many applications, for example in close-packed tubular heat exchangers and coolant channels of nuclear reactors. From a fundamental viewpoint, turbulent flow in eccentric annular ducts is an ideal model for investigating inhomogeneous turbulence. It is also a convenient model to study the laminar and turbulent interface and may serve as a test case for turbulence modelling of flows with partly turbulent regimes. Based on the approach of direct numerical simulation, numerical investigations of turbulent flow in eccentric annular pipes are carried out in this thesis. We first investigated the case of fully turbulent flow. A detailed statistical analysis of turbulent flow and heat transfer was performed. Simulation results, such as friction factors, mean velocity profiles and the secondary-motion pattern, are in overall qualitative and quantitative agreement with the existing experimental data. The components of the Reynolds stress tensor, temperature-velocity correlations and some others were obtained for the first time for such kind of a flow. The study of the partly turbulent flow case was then carried out. Three approaches for detecting interfaces between laminar and turbulent regimes in partly turbulent flow in rotating eccentric pipes were compared and discussed. Positions of laminar-turbulent and turbulent-laminar interfaces obtained from profiles of perturbation enstrophy are the same as those obtained from production terms of enstrophy. Using patterns of streaks defined by wall shear stresses to determine the locations of interfaces showed similar results. The growth rate of a small disturbance in partly turbulent flow case was also analyzed. Small perturbations were introduced into the initial flow field in two different ways. Both cases show that the global growth rate of the small disturbance normalized by the global viscous time scale is constant. This constant value is in a good agreement with that obtained in channel flows and tube flows. A new approach was proposed to distinguish the interface between laminar and turbulent flow by introducing the global and local disturbance growth rate

ICASE

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in the areas of (1) applied and numerical mathematics, including numerical analysis and algorithm development; (2) theoretical and computational research in fluid mechanics in selected areas of interest, including acoustics and combustion; (3) experimental research in transition and turbulence and aerodynamics involving Langley facilities and scientists; and (4) computer science

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is operated by the Ohio Aerospace Institute (OAI) and the NASA Lewis Research Center in Cleveland, Ohio. The purpose of ICOMP is to develop techniques to improve problem-solving capabilities in all aspects of computational mechanics related to propulsion. This report describes the accomplishments and activities at ICOMP during 1993

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) was formed to develop techniques to improve problem-solving capabilities in all aspects of computational mechanics related to propulsion. ICOMP is operated by the Ohio Aerospace Institute (OAI) and funded via numerous cooperative agreements by the NASA Lewis Research Center in Cleveland, Ohio. This report describes the activities at ICOMP during 1997, the Institute's twelfth year of operation

NASA high performance computing and communications program

The National Aeronautics and Space Administration's HPCC program is part of a new Presidential initiative aimed at producing a 1000-fold increase in supercomputing speed and a 100-fold improvement in available communications capability by 1997. As more advanced technologies are developed under the HPCC program, they will be used to solve NASA's 'Grand Challenge' problems, which include improving the design and simulation of advanced aerospace vehicles, allowing people at remote locations to communicate more effectively and share information, increasing scientist's abilities to model the Earth's climate and forecast global environmental trends, and improving the development of advanced spacecraft. NASA's HPCC program is organized into three projects which are unique to the agency's mission: the Computational Aerosciences (CAS) project, the Earth and Space Sciences (ESS) project, and the Remote Exploration and Experimentation (REE) project. An additional project, the Basic Research and Human Resources (BRHR) project exists to promote long term research in computer science and engineering and to increase the pool of trained personnel in a variety of scientific disciplines. This document presents an overview of the objectives and organization of these projects as well as summaries of individual research and development programs within each project

PetIGA: A framework for high-performance isogeometric analysis

We present PetIGA, a code framework to approximate the solution of partial differential equations using isogeometric analysis. PetIGA can be used to assemble matrices and vectors which come from a Galerkin weak form, discretized with Non-Uniform Rational B-spline basis functions. We base our framework on PETSc, a high-performance library for the scalable solution of partial differential equations, which simplifies the development of large-scale scientific codes, provides a rich environment for prototyping, and separates parallelism from algorithm choice. We describe the implementation of PetIGA, and exemplify its use by solving a model nonlinear problem. To illustrate the robustness and flexibility of PetIGA, we solve some challenging nonlinear partial differential equations that include problems in both solid and fluid mechanics. We show strong scaling results on up to 4096 cores, which confirm the suitability of PetIGA for large scale simulations

The first ICASE/LARC industry roundtable: Session proceedings

The first 'ICASE/LaRC Industry Roundtable' was held on October 3-4, 1994, in Williamsburg, Virginia. The main purpose of the roundtable was to draw attention of ICASE/LaRC scientists to industrial research agendas. The roundtable was attended by about 200 scientists, 30% from NASA Langley; 20% from universities; 17% NASA Langley contractors (including ICASE personnel); and the remainder from federal agencies other than NASA Langley. The technical areas covered reflected the major research programs in ICASE and closely associated NASA branches. About 80% of the speakers were from industry. This report is a compilation of the session summaries prepared by the session chairmen