Towards Exascale CFD Simulations Using the Discontinuous Galerkin Solver FLEXI

Modern high-order discretizations bear considerable potential for the exascale era due to their high fidelity and the high, local computational load that allows for computational efficiency in massively parallel simulations. To this end, the discontinuous Galerkin (DG) framework FLEXI was selected to demonstrate exascale readiness within the Center of Excellence for Exascale CFD (CEEC) by simulating shock buffet on a three-dimensional wing segment at transsonic flight conditions. This paper summarizes the recent progress made to enable the simulation of this challenging exascale problem. For this, it is first demonstrated that FLEXI scales excellently to over 500 000 CPU cores on HAWK at the HLRS. To tackle the considerable resolution requirements near the wall, a novel wall model is proposed that takes compressibility effects into account and yields decent results for the simulation of a NACA 64A-110 airfoil. To address the shocks in the domain, a finite-volume-based shock capturing method was implemented in FLEXI, which is validated here using the simulation of a linear compressor cascade at supersonic flow conditions, where the method is demonstrated to yield efficient, robust and accurate results. Lastly, we present the TensorFlow-Fortran-Binding (TFFB) as an easy-to-use library to deploy trained machine learning models in Fortran solvers such as FLEXI.Comment: 15 pages, 5 figure

Aptamer chemistry

International audienceAptamers are single-stranded DNA or RNA molecules capable of tightly binding to specific targets. These functional nucleic acids are obtained by an in vitro Darwinian evolution method coined SELEX (Systematic Evolution of Ligands by EXponential enrichment). Compared to their proteinaceous counterparts, aptamers offer a number of advantages including a low immunogenicity, a relative ease of large-scale synthesis at affordable costs with little or no batch-to-batch variation, physical stability, and facile chemical modification. These alluring properties have propelled aptamers into the forefront of numerous practical applications such as the development of therapeutic and diagnostic agents as well as the construction of biosensing platforms. However, commercial success of aptamers still proceeds at a weak pace. The main factors responsible for this delay are the susceptibility of aptamers to degradation by nucleases, their rapid renal filtration, suboptimal thermal stability, and the lack of functional group diversity. Here, we describe the different chemical methods available to mitigate these shortcomings. Particularly, we describe the chemical post-SELEX processing of aptamers to include functional groups as well as the inclusion of modified nucleoside triphosphates into the SELEX protocol. These methods will be illustrated with successful examples of chemically modified aptamers used as drug delivery systems, in therapeutic applications, and as biosensing devices