Extreme responses of a coupled scalar-particle system during turbulent mixing

Extreme responses of a droplet ensemble during an entrainment and mixing process as present at the edge of a cloud are investigated by means of three-dimensional direct numerical simulations in the Euler–Lagrangian framework. We find that the Damköhler number Da, a dimensionless parameter which relates the fluid time scale to the typical evaporation time scale, can capture all aspects of the initial mixing process within the range of parameters accessible in this study. The mixing process is characterized by the limits of strongly homogeneous (Da > 1) regimes. We explore these two extreme regimes and study the response of the droplet size distribution to the corresponding parameter settings through an enhancement and reduction of the response constant K in the droplet growth equation. Thus, Da is varied while Reynolds and Schmidt numbers are held fixed, and initial microphysical properties are held constant. In the homogeneous limit minimal broadening of the size distribution is observed as the new steady state is reached, whereas in the inhomogeneous limit the size distribution develops strong negative skewness, with the appearance of a pronounced exponential tail. The analysis in the Lagrangian framework allows us to relate the pronounced negative tail of the supersaturation distribution to that of the size distribution

Introduction to Performance Analysis

The complexity of modern High-Performance-Computing systems impose great challenges on running parallel applications efficiently on them. Performance analysis is therefore a key issue to identify bottlenecks and efficiency problems in HPC applications in order to improve and optimize the performance of these applications. We start with an overview of different performance problems whichfrequently occur in parallel applications and give an introductions to the concepts of performance analysis. In the second part we will discuss selected performance analysis tools in more detail and show how to use them in order to identify bottlenecks

Message-Passing Interface - Selected Topics and Best Practices

The Message-Passing Interface (MPI) is a widely-used standard library for programming parallel applications using the distributed-memory model. In the first part of this talk we will give a short overview over concepts and properties of modern HPC hardware architectures as well as basic programming concepts. A brief introduction into a design strategy for parallel algorithms is presented.The focus of the second part will be on the Message-Passing interface. After a short overview over general MPI properties and features we will present selected MPI topics including Derived Datatypes, MPI_Info objects and One-sided Communication and discuss best practices for their usage