Turbulence at the exascale: application to wind energy, green aviation, air quality and net-zero combustion

该提案汇集了来自英国湍流联盟（UKTC）和英国反应流联盟（UKCRF）的社区，以确保顺利过渡到百亿亿次计算，目的是为致力于湍流研究的生产模拟软件生态系统开发面向未来的变革性技术。理解、预测和控制湍流是至关重要的，也是许多行业的限制因素。如果不能更好地理解湍流，我们今天面临的许多环境和能源相关问题就不可能得到解决。英国正在通过ExCALIBUR计划为百亿亿次计算机时代做准备，以开发百亿亿次计算机的算法和软件。根据设计和开发工作组（DDWG）关于百亿亿级湍流的研究结果，该项目将联合英国七个HEC联盟中的两个，即UKTC和UKCTRF，重新设计或扩展其四个百亿亿级计算生产和研究流求解器的功能：XCOMPACT3D， OPENSBLI， UDALES和SENGA+。这些开源的、完善的、社区流求解器基于结构化网格的有限差分方法，并将开发以满足与百亿亿级计算相关的挑战，同时利用百亿亿级系统提供的重要机会。该项目的一个关键目标是利用完善的领域特定语言（DLS）框架OPS和2DECOMP&FFT库，允许XCOMPACT3D、OPENSBLI、UDALES和SENGA+在大型异构计算机上运行。OPS是近十年来在英国开发的，它针对多块结构网格的应用。它目前可以使用CUDA、OPENACC/OPENMP5.0、OPENCL、SYCL/ONEAPI、HIP及其与MPI的组合来生成代码。OPS dsl的能力将在该项目中得到扩展，特别是其代码生成工具链，用于健壮、故障安全的并行代码生成。相关的工作链将使用2DECOMP&FFT，一个基于fortran的基于二维域分解的库，用于单块结构网格上的空间隐式数值算法。该库包括一个高度可扩展和高效的接口来执行快速傅里叶变换（fft），并依赖于MPI提供一个用户友好的编程接口，该接口向应用程序开发人员隐藏通信细节。2DECOMP&FFT将完全重新设计，以便在使用混合策略的异构超级计算机（来自不同供应商的cpu和gpu）上使用。该项目还将结合exascale-ready耦合接口、UQ功能、I/O和可视化工具到我们的流量求解器，以及基于机器学习的算法，以解决DDWG在exascale湍流中确定的一些关键挑战和机遇。这将与最近资助的几个ExCALIBUR交叉项目合作完成。该项目将重点关注四个高优先级用例（每个求解器一个），定义为通过模拟性能的逐步变化实现高质量，高影响的研究。用例将侧重于风能、绿色航空、空气质量和净零燃烧。百亿亿次计算将改变这些领域的游戏规则，并将有助于使英国成为一个更环保的国家（英国承诺到2050年实现净零碳排放）。这些用例将用于展示基于OPS和2DECOMP&FFT的重新设计的流求解器的潜力，适用于各种硬件和并行范例。

This proposal brings together communities from the UK Turbulence Consortium (UKTC) and the UK Consortium on Reacting Flows (UKCRF) to ensure a smooth transition to exascale computing, with the aim to develop transformative techniques for future-proofing their production simulation software ecosystems dedicated to the study of turbulent flows. Understanding, predicting and controlling turbulent flows is of central importance and a limiting factor to a vast range of industries. Many of the environmental and energy-related issues we face today cannot possibly be tackled without a better understanding of turbulence.The UK is preparing for the exascale era through the ExCALIBUR programme to develop exascale-ready algorithms and software. Based on the findings from the Design and Development Working Group (DDWG) on turbulence at the exascale, this project is bringing together communities representing two of the seven UK HEC Consortia, the UKTC and the UKCTRF, to re-engineer or extend the capabilities of four of their production and research flow solvers for exascale computing: XCOMPACT3D, OPENSBLI, UDALES and SENGA+. These open-source, well-established, community flow solvers are based on finite-difference methods on structured meshes and will be developed to meet the challenges associated with exascale computing while taking advantage of the significant opportunities afforded by exascale systems. A key aim of this project is to leverage the well-established Domain Specific Language (DLS) framework OPS and the 2DECOMP&FFT library to allow XCOMPACT3D, OPENSBLI, UDALES and SENGA+ to run on large-scale heterogeneous computers. OPS was developed in the UK in the last ten years and it targets applications on multi-block structured meshes. It can currently generate code using CUDA, OPENACC/OPENMP5.0, OPENCL, SYCL/ONEAPI, HIP and their combinations with MPI. The OPS DSLs' capabilities will be extended in this project, specifically its code-generation tool-chain for robust, fail-safe parallel code generation. A related strand of work will use the 2DECOMP&FFT a Fortran-based library based on a 2D domain decomposition for spatially implicit numerical algorithms on monobloc structured meshes. The library includes a highly scalable and efficient interface to perform Fast Fourier Transforms (FFTs) and relies on MPI providing a user-friendly programming interface that hides communication details from application developers. 2DECOMP&FFT will be completely redesigned for a use on heterogeneous supercomputers (CPUs and GPUS from different vendors) using a hybrid strategy.The project will also combine exascale-ready coupling interfaces, UQ capabilities, I/O & visualisation tools to our flow solvers, as well as machine learning based algorithms, to address some of the key challenges and opportunities identified by the DDWG on turbulence at the exascale. This will be done in collaboration with several of the recently funded ExCALIBUR cross-cutting projects.The project will focus on four high-priority use cases (one for each solver), defined as high quality, high impact research made possible by a step-change in simulation performance. The use cases will focus on wind energy, green aviation, air quality and net-zero combustion. Exascale computing will be a game changer in these areas and will contribute to make the UK a greener nation (The UK commits to net zero carbon emissions by 2050). The use cases will be used to demonstrate the potential of the re-designed flow solvers based on OPS and 2DECOMP&FFT, for a wide range of hardware and parallel paradigms.