Technical program

  • Timetable and detailed program (Final version, July 18).
  • Notes:
    1. Keynote lectures are given in real-time online.
    2. General presentations are made with pre-recorded videos (10-12 minutes). The details on the video (preparation and upload) has been informed to the authors on June 1.
    3. In each presentation slot, the video is played real-time by the organizer, followed by a live discussion. Therefore, the presenters are advised to be present online at their session as much as possible.
    4. The pre-recorded videos are available to the registered participants for on-demand view during the conference.
    5. The links to the papers, the Zoom rooms, and the view-only folders containing the pre-recorded videos is available from the Registrant zone of the NTA website.

Invited lectures

Bharath Ganapathisubramani, University of Southampton, UK
Turbulent Flows over Heterogeneous Rough Surfaces
Rough surfaces are considered heterogeneous when their surface topography/morphology exhibit large-scale spatial variations. There are several examples of such heterogeneities in engineering applications and the natural environment. When the size/scale of these spatial variations are comparable to the large scales features that are present in the flow, then, they generate secondary flows that alter the characteristics of the turbulent flow. In this talk, I will present results from our recent studies where we examined the impact of different topographical heterogeneities (from smooth ridges to multiscale roughness) on wall-turbulence.

Pino Martin, University of Maryland, USA
Reduced Order Model for Low-frequency Dynamics Inshock Separated Flow
(Co-authors: Hannah Neuenhoff (UMD), Jared Callaham (U Washington) and Steve Brunton (U Washington))
Hypersonic flow environments are characterized by high-dimensional, nonlinear dynamical systems with structures across a large range of scales. Despite the apparent complexity of such flow persistent behaviors are often determined by the balance of a few dominant physical processes and the governing equations can be dramatically simplified. A low order model is developed for the low frequency dynamics in the large eddy simulation of a Mach 7 shock wave/turbulent boundary layer interaction. Dynamic mode decomposition (DMD) is applied to three dimensional snap shots of the flow to isolate modes in the frequency range of interest. The evolution of the temporal coefficients of the low-frequency DMD mode and its com-plex conjugate closely resemble the time series of a stochastic Stuart Landau oscillator. A Langevin regression algorithm is applied to obtain a model for the time evolution of the modal coefficients consistent with this form.

Makoto Tsubokura, Kobe University, Japan
Turbulence Simulation on Massively Parallel Environments toward Next-Generation Computer-Aided Engineering
Development of Large-Eddy Simulation frameworks on massively parallel environments represented by the supercomputer "K" and "Fugaku", and their applications to industrial problems are mentioned. One of the frameworks is based on the unstructured finite volume method to reproduce the complicated geometries typically required for industrial applications. The validity of the method on the applied aerodynamics such as golf balls and road vehicles on the supercomputer "K" and its limit to High Performance Computing are discussed from two points: tuning on the new hardware architectures on many-core processors with lower memory bandwidth, and total turn-around time including the mesh generation. To overcome the problem, new complex unified simulation framework based on the hierarchically structured finite volume method and its applications on the supercomputer "Fugaku" is introduced. In addition to the world-largest vehicle aerodynamics simulation utilizing tens of billions of numerical cells, these applications include direct feedback noise prediction emitted from a gap on the vehicle's surface, and coupling aerodynamics and vehicle's six-degrees-of-freedom motion simulation, as examples of "capability computing" on engineering problems. It should be noted that these simulations are realized on very complicated geometries equivalent to actual vehicles. Finally, airborne infection risk assessment based on droplet/aerosol dispersion simulation in indoor environment and proposal of the countermeasures is introduced as a response of the framework on "Fugaku" to the COVID-19 pandemic. (ACM Gordon Bell Special Prize for HPC-Based COVID-19 Research Awarded) In this simulation more than 50 infection scenes over 1,000 test cases were able to be evaluated in a short period of one year, by drastically decreasing the total turn-around time of the simulation. The scenes include public transportations like a bus, a taxi, an airplane, and a commuter train, and pubic locations like an office, a school, a hospital, a concert hall, a live music club and so on. In fact, "capacity computing" like this is also becoming important applications on the massively parallel environment from the viewpoint of "big data" analysis. Thus, perspective of coupling of data science and HPC turbulence simulation for computer aided engineering is discussed to end the talk.

Michael Wilczek, University of Bayreuth, Germany
Statistics and Geometry of Lagrangian Turbulence
(Co-authors: Lukas Bentkamp (U Bayreuth), Theodore D. Drivas (Stony Brook U), Cristian C. Lalescu (Max Planck Computing and Data Facility))
Fundamental aspects of turbulence can be studied either from an Eulerian or a Lagrangian perspective. Since particles advected with the flow sample turbulence in space and time, the Lagrangian approach is particularly well suited to investigate spatio-temporal fluctuations of turbulence as well as turbulent mixing. In this contribution, we focus on two aspects of Lagrangian turbulence. In the first part, we discuss how the analysis of simulation data can provide insights into the dynamics and statistics of turbulence to develop new models for the single-particle statistics of Lagrangian turbulence. We then focus on geometric aspects of turbulent mixing in the second part of the contribution by characterizing the stretching and folding of material lines.

Tamer Zaki, Johns Hopkins University, USA
Observation-Infused Simulations of Turbulence
High-fidelity simulations of turbulence provide non-intrusive access to all the resolved flow scales and any quantity of interest. However, simulations often invoke idealizations that compromise realism (e.g. truncated domains and modelled boundary conditions). Experiments, on the other hand, examine the true flow with less idealizations, but they continually contend with limited spatio-temporal sensor resolution and the challenge of directly measuring quantities of interest. By assimilating observations, however scarce, in simulations, we can leverage the advantages of both approaches and mitigate their respective deficiencies. The simulations thus achieve higher level of realism by tracking the true flow state, and we can probe any flow quantity of interest at higher resolution than the original measurements. The data-assimilation problem is formulated as a nonlinear optimization, where we seek the flow field that satisfies the Navier-Stokes equations and optimally reproduces available data. In this framework, measurements are no longer mere records of instantaneous, local flow quantities, but rather an encoding of the antecedent flow events that we decode using the governing equations. Chaos plays a central role in obfuscating the interpretation of the data. Measurements that are infinitesimally close may be due to entirely different earlier conditions --- a dual to the famous butterfly effect. We will examine several data-assimilation problems in wall turbulence and establish the minimum resolution of measurements for which we can accurately reconstruct all the missing flow scales. We will highlight the roles of the Taylor microscale and the Lyapunov timescale and discuss the fundamental difficulties of predicting turbulence from limited observations.

TSFP12 Nobuhide Kasagi Award lecture

Dennice Gayme, Johns Hopkins University, USA
A Coherent Structure Based Approach to Modeling Wall-bounded Turbulence