Use this search facility to find out more about the profile of our HPC-Europa2 visitors, the type of work they have been doing, and their project achievements.

Abstract
Objectives
Two-dimensional (2D) turbulence is characterized by the conservation of two quadratic invariants, energy and enstrophy. Unlike classical three-dimensional turbulence where only energy is conserved, the extra invariant implies that there exists two inertial ranges with energy flowing to large scales and enstrophy to small scales. When considered in a finite box, energy is forced to accumulate at the largest scale, i.e. at the scale of the box-size.

If the system is continuously forced, then a large scale coherent structure or condensate can form which contains the majority of the energy in the system. In a doubly periodic box, this condensate consists of either a vortex dipole or zonal flow. Little is known how the appearance of a condensate effects the turbulence in the system. Some preliminary results on the flow profile of the condensate in the form of a vortex dipole have already been analysed, however there is still much more than needs to be considered.

Our objectives are to investigate how the appearance of a condensate effects the turbulent flow. We do this by performing high resolution numerical simulations of the 2D Naiver-Stokes equations and to examine the fluxes of energy and momentum in physical space using single-point, second and third order, velocity moments to gain insight into how turbulence leads to the formation and growth of a condensate. Then we will consider the two-point velocity moments to study the behavior of the energy flux in Fourier space and consequently the turbulent spectra. Subsequently, we will be able to study the degree of anisotropy in the turbulence with respect to spatial coordinate and scale associated with the presence of a condensate.

Achievements
So far we have been able to perform several high performance numerical simulations of the 2D Naiver-Stokes equations in various parameter regimes. We have been able to compare the second and third order, single-point, velocity moments between the numerical simulations and theoretical predictions. This has enabled us to verify the behavior of these statistics with parameter variability and, more importantly, uncover new physics related to the interaction between coherent structures and the turbulent background. For instance, we have discovered that the power-law profile of the vortex dipole is robust with regards to different dissipation (viscous and hyper-viscous) mechanisms at small scales, although the vortex core radius is not. Moreover, we find that the vorticity concentrated in the coherent structure scales with the inverse square root of the friction dissipation coefficient.

Abstract
Objectives
The main goal of our project is to maintain the level of performance of the suite, extending the pure message passing paradigms with mixed parallelism using MPI and OpenMP (where possible). In particular, we will start working on one of the most relevant algorithms of the suite: an ad-hoc 3D Fast Fourier Transform. We try 2 approaches to ibridize the code: an implicit approach linking native multi-thread library provided by third-part vendors and an explicit one using OpenMP directly into the code. If the experimental hybrid/mixed paradigm with the FFT is successful, we will try to extend it to other relevant and heavy computational cores of the suite, particularly in the iterative diagonalization of Hamiltonian, which is the second algorithm into suite in order of importance.

Achievements

We implemented two test programs for a detailed performance analysis of the parallel ad-hoc hybrid 3D FTT. Both programs share the same main modules of Quantum ESPRESSO and are able to initialize the FFT grid like a real simulation using a real input parameters. We devoted a large part of the time to design a test program that shares the same structure of the main modules of Quantum ESPRESSO in order to simplify the procedure of integrating the modifications into the main package. This point is very important because Quantum ESPRESSO has fixed data structures that cannot be changed. Both master-only and funneled approach have been developed. We have test the modified algorithm using different combination of MPI and threads number.

After the testing phase, we have transferred all the modifications into the main code of Quantum ESPRESSO and our improvements have been committed into the official repository. We have had the possibility to work on CRAY XT4 (HECToR) and IBM POWER5 (HPCx) clusters hosted by Edinburgh Parallel Computing Centre and, also, IBM BladeCenter LS21 (BCX) in CINECA. Now we are able to run Quantum ESPRESSO using MPI and OpenMP together.

Abstract
Objectives
Numerical study of the unsteady aerodynamics of finite-span flapping rigid wings. Specifically, finite-span rigid wings undergoing pure heaving and root-flapping motions are studied. The numerical simulations are performed at a Reynolds number of Re = 250 and at different values of Strouhal number and reduced frequency.

Achievements
The results were partially achieved. We didn't achieve all of our goals basically due to time constrains and some minors bugs in our applicatios. Adittionally to this, we managed to conduct an aditional study on drag reduction by using biomimetics winglets.