Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q49: ExtremeScale Computational Science Discovery in Fluid Dynamics and Related Disciplines IFocus Recordings Available

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Sponsoring Units: DCOMP DFD Chair: P. K. Yeung, Georgia Tech Room: McCormick Place W471B 
Wednesday, March 16, 2022 3:00PM  3:36PM 
Q49.00001: From Turbulence Simulations to Petascale Interactive Numerical Laboratories Invited Speaker: Alex S Szalay Scientists in many disciplines would like to compare the results of their experiments or theoretical hypotheses to data emerging from numerical simulations based on first principles. This requires not only that we can run sophisticated simulations and models, but that at least a selected subset of the results of these simulations are available publicly, through an easytouse portal. We have to turn our simulations into open numerical laboratories in which anyone can perform their own experiments. For a scalable analysis we must have an inherently scalable data access. Flat files violate this principle: the user cannot do anything until a very large file has been physically transferred. 
Wednesday, March 16, 2022 3:36PM  3:48PM 
Q49.00002: Towards DNS of Turbulent Combustion at the Exascale Jacqueline Chen, Martin Rieth, Swapnil Desai, Hessam Babaee, Andrea Gruber, Marc Day Direct numerical simulation methodology and computing power have progressed to the point where it is feasible to perform DNS in representative of flow configurations encountered in practical combustors. These complex flows encompass effects of mean shear, flow recirculation, and wall boundary layers together with turbulent fluctuations which affect entrainment, mixing, ignition and combustion. Examples of recent DNS studies with complex flows relevant to gas turbine and internal combustion engines will be presented. These include turbulent premixed combustion with hydrogen/ammonia blends at elevated pressure as a dropin zero carbon fuel replacement for natural gas in stationary gas turbines and multiinjection autoignition of ndodecane jets at diesel conditions. These cases involve complex kinetic interactions with shear flows at elevated temperature and pressure relevant to practical energy applications, and their computational feasibility is dependent on a capable software stack, adaptive mesh refinement and a dynamic taskbased programming model tailored for upcoming heterogeneous exascale machines. Prospects for onthefly dimension reduction of complex chemistry to reduce the exorbitant cost of large hydrocarbon chemistry evaluation in DNS will also be described as part of a holistic computational workflow including machine learning enabled by asynchronous task based programming on GPUs. 
Wednesday, March 16, 2022 3:48PM  4:00PM 
Q49.00003: Computational Physics on the new Frontier Reuben D Budiardja The Oak Ridge Leadership Computing Facility (OLCF) at Oak Ridge National Laboratory (ORNL) is home to the first exascale supercomputer in the nation, Frontier. Powered by AIOptimized AMD EPYC CPUs with Radeon Instinct GPUs, Frontier enables extremescale simulations in computational physics, including ones involving complex fluid flow, at unprecedented resolutions and performance. In this talk, we share early results of applications with fluid dynamics components and discuss the computational techniques to achieve them on Frontier. We consider how machine learning techniques may be used to accelerate parts of computations, and describe how a leadership computing facility enables access to the massive data sets produced by these simulations. 
Wednesday, March 16, 2022 4:00PM  4:12PM 
Q49.00004: Simulation of extremescale homogeneous turbulence on a new leadership Exascale GPU platform PuiKuen Yeung, Kiran Ravikumar, Stephen Nichols, Rohini UmaVaideswaran Fluid turbulence is a major domainscience problem where highresolution simulations with trillions of grid points are a powerful research tool. We focus on Exascaleready GPU algorithm development based on Fourier pseudospectral methods suitable for homogeneous turbulence in threedimensional space. The overall goal is to push the envelope in simulation size while optimizing aggressively for reasonable time to solution. Fast computation on GPUs, efficient data movement between host and device, as well as highlyscalable communication are all crucial for best performance. Use of the latest OpenMP standard promotes interplatform portability, although machine characteristics still have a strong influence on key programming strategies. Specific issues include the dimensionality of the domain decomposition, collective messagepassing via the host or device, efficient host and device memory utilization and opportunities for asynchronism. We shall provide a status report on both the full turbulence simulation code and a 3D FFT kernel of more general interest, on hardware similar to one of the world's first Exascale machines. 
Wednesday, March 16, 2022 4:12PM  4:24PM 
Q49.00005: NekRS: A Spectral Element Code for Exascale Paul Fischer We describe NekRS, which is an open source spectral element thermal/fluids code designed for exascale platforms. NekRS supports both incompressible and lowMach formulations, ALEbased moving meshes, uRANS, and numerous boundary conditions of relevance to engineering flows. Second and thirdorder timesteppers are provided, using either standard (CFLlimited) semiimplicit methods or characteristicsbased subcycling for advection. A variety of scalable multilevel preconditioners for the pressure Poisson problem have been implemented to ensure optimal performance across a large application space. Several simulation results are presented, including turbulent flow in the full core of a pebble bed reactor that features 352,000 spherical pebbles in an annular domain. The mesh features 98.8 million elements of order N=8, for a total of n=50.5 billion gridpoints. Using 27648 NVIDIA V100s on the OLCF supercomputer, Summit, the wallclock time for this case is 0.25 seconds per step, corresponding to 6 hours for an entire flowthrough time. 
Wednesday, March 16, 2022 4:24PM  4:36PM Withdrawn 
Q49.00006: Supersonic Reacting Flows Alexei Y Poludnenko Reacting flows are pervasive both in our daily lives on Earth and in the Universe. Such flows are fundamental to systems ranging from astrophysical Type Ia supernovae explosions to novel propulsion applications such as scramjets or detonationbased engines. Despite this ubiquity in Nature, turbulent reacting flows still pose a number of fundamental questions concerning their structure and dynamics often exhibiting surprising behavior. In recent years, the advent of massively parallel highperformance computing has enabled the use of largescale direct numerical simulations (DNS) for the exploration of the reacting flow dynamics in extreme, previously inaccessible regimes. This talk will discuss the computational requirements and challenges associated with such extremescale DNS. Furthermore, we will present an overview of a range of phenomena recently discovered in DNS of highspeed reacting flows characterized by high flow speeds, significant compressibility effects, and strong coupling between exothermic reactions and the flow. Such phenomena include intrinsic instabilities of reacting turbulence, onset of catastrophic transitions, e.g., spontaneous detonation formation, and the qualitative changes in the nature of the turbulent cascade in the presence of exothermic reactions. 
Wednesday, March 16, 2022 4:36PM  4:48PM 
Q49.00007: Direct numerical simulation of decaying stratified turbulence with extreme scale separation Gavin Portwood, Stephen de Bruyn Kops Stably stratified turbulence (SST) is a model flow for understanding fluid flows that are highly intermittent and anisotropic at large scales. The understanding derived from SST is important for applications ranging from climate modeling, to pollution mitigation, to deep sea mining, to military operations over cold land or ice. SST is also valuable for enhancing fundamental turbulence theory on turbulent/nonturbulent interfaces, internal intermittency, and anisotropic multiscale energetics. In all turbulent flows, dynamic range, or the ratio of the largest the smallest length scales, has a profound effect on the fluid dynamics. Dynamic range is characterized by the Reynolds number, Re. SST, though, is at least a two parameter problem with Re characterizing the overall dynamic range and Froude number Fr describing the range of comparatively large length scales strongly affected by buoyancy. In direct numerical simulations (DNSs), at least four decades of scale separation is required to resolve the horizontal scales in the strongly stratified regime. Here we present results from simulations using up to 24000×24000×6000 grid point and generating about 55 TB per snapshot of the flow field in time. We show the dynamics when there is sufficient dynamic range for how the flow to be fully turbulent. 
Wednesday, March 16, 2022 4:48PM  5:00PM 
Q49.00008: Direct Numerical Simulations of Turbulent, Multiphysics Hypersonic Flows at Extreme Scales Daniel J Bodony At enthalpies of tens of MJ/kg, the fluid dynamics of highspeed flows past aerodynamicallyshaped objects is characterized by shockturbulencematerial interactions. We seek to understand the details of these interactions through the use of direct numerical simulations of the compressible turbulent reactive flow coupled with material response simulations of the adjacent structure. Our approach utilizes multiple domainspecific codes built for heterogeneous computing architectures that are coupled through a data exchange and time integration framework. The presentation will describe these tools through their application on a Mach 6 flow interacting with a 35 degree compression ramp with an embedded compliant panel. The conditions and model geometry match experiments conducted in the NASA Langley 20inch Mach 6 tunnel, including a simulated incoming sound field due to tunnel wall boundary layer noise. 
Wednesday, March 16, 2022 5:00PM  5:12PM 
Q49.00009: Numerical simulation of the RichtmyerMeshkov instability evolving from broadband initial perturbations Michael Groom, Ben Thornber This talk presents results from both implicit large eddy simulations (ILES) and direct numerical simulations (DNS), performed using the finitevolume code FLAMENCO, of a mixing layer induced by the RichtmyerMeshkov instability (RMI) and evolving from amplitude perturbations containing a broad bandwidth of initial modes. In particular, two different broadband perturbations are analysed, defined by their initial radial power spectra P(k)=Ck^{m} where m=1,2. The amplitudes of individual modes are defined such that either (i), the total standard deviation of the two perturbations are the same or (ii), the amplitudes of the highest wavenumber mode are the same. In both cases all modes are initially linear. 
Wednesday, March 16, 2022 5:12PM  5:24PM 
Q49.00010: Geometry dynamics of turbulent flow structures via tracking Ivan BermejoMoreno, Jonas Buchmeier, Alexander Bussmann, Xiangyu Gao We present a methodology for the analysis of the temporal evolution of flow structures and their mutual interactions based on tracking. The structures, defined as closed surfaces from instantaneous snapshots of the flow, are characterized by areabased joint PDFs of differential geometry pointwise quantities (curvedness and shape index). A hybrid region and attributebased tracking algorithm finds realizable correspondences between structures at consecutive time frames, constructing a directed graph that describes the structure evolution and interaction events (e.g., merging and splitting). Common patterns of structure evolution are extracted by graph querying and subgraph mining conditioned on geometric attributes. Ensemble statistics for structures with common geometries are obtained to study their dynamics through trajectories in parameter spaces that combine geometry and flow physics. We show application of the methodology to numerical datasets obtained from direct numerical simulation of turbulent flows in several canonical configurations, including decaying homogeneous isotropic compressible turbulence and shockturbulence interaction (at different Reynolds, shock and turbulence Mach numbers), compressible mixing layers (at different convective Mach numbers), and the multiphase flow interaction of a droplet breakup in homogeneous isotropic incompressible turbulence. 
Wednesday, March 16, 2022 5:24PM  5:36PM 
Q49.00011: The Challenges of Modeling Astrophysical Reactive Flows Michael Zingale Energy production in stellar environments is dominated by thermonuclear energy release, which can take place in quiet convective flows or explosive environments. Multidimensional models of astrophysical reactive flows have many challenges: capturing the relevant length and timescales, and keeping the different physics inputs coupled together over the course of the simulation. We will show applications to Xray bursts, thermonuclear supernovae, and massive star evolution and discuss how algorithmic improvements and harnessing the power of GPUs has allowed us to make significant progress on understanding these astrophysical events, using our open source AMReXAstrophysics suite of simulation codes. 
Wednesday, March 16, 2022 5:36PM  5:48PM 
Q49.00012: Asynchronous exascale PDE solvers: exploiting extreme parallelism for turbulence simulations Diego A Donzis Future exascale computing systems will be available to study 
Wednesday, March 16, 2022 5:48PM  6:00PM 
Q49.00013: Fluid Dynamics of Supernova Remnants Snezhana I Abarzhi, W. David Arnett, Desmond Hill, Bruce Remington, Kurt Williams, J. Tony Li Supernovae – explosions of stars – are a central problem in astrophysics since they encapsulate the entire process of stellar evolution and nucleosynthesis. RayleighTaylor (RT) and RichtmyerMeshkov (RM) instabilities, developing during the supernova blast, lead to intense mixing of the star’s materials and couple astrophysical to atomic scales. We handle fluid dynamics challenges of RT/RM problem by directly linking the conservation laws governing RT/RM dynamics to symmetrybased momentum model, by precisely deriving the model parameters in the scaledependent and scaleinvariant regimes, and exactly integrating the model equations for variable acceleration in the scaledependent linear and nonlinear regimes and in selfsimilar mixing regime. The theory outcomes explain the observations of supernova remnants, yield the design of scaled laboratory experiments for quantification of RT/RM dynamics in high energy density settings, and find that supernovae can indeed be regarded as an astrophysical initial value problem. 
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