A GPU-based incompressible Navier–Stokes solver on moving overset grids

In pursuit of obtaining high fidelity solutions to the fluid flow equations in a short span of time, graphics processing units (GPUs) which were originally intended for gaming applications are currently being used to accelerate computational fluid dynamics (CFD) codes. With a high peak throughput of about 1 TFLOPS on a PC, GPUs seem to be favourable for many high-resolution computations. One such computation that involves a lot of number crunching is computing time accurate flow solutions past moving bodies. The aim of the present paper is thus to discuss the development of a flow solver on unstructured and overset grids and its implementation on GPUs. In its present form, the flow solver solves the incompressible fluid flow equations on unstructured/hybrid/overset grids using a fully implicit projection method. The resulting discretised equations are solved using a matrix-free Krylov solver using several GPU kernels such as gradient, Laplacian and reduction. Some of the simple arithmetic vector calculations are implemented using the CU++: An Object Oriented Framework for Computational Fluid Dynamics Applications using Graphics Processing Units, Journal of Supercomputing, 2013, doi:10.1007/s11227-013-0985-9 approach where GPU kernels are automatically generated at compile time. Results are presented for two- and three-dimensional computations on static and moving grids.     

Effect of draw ratio on the microstructure, thermal, tensile and dynamic rheological properties of insitu microfibrillar composites

Microfibrillar composites (MFCs) were prepared using different draw/stretch ratios [viz. 2, 5, 8 and 10] from polypropylene/polyethylene terephthalate (PP/PET) blends. Scanning electron microscopy [SEM] images revealed that PET microfibrils were highly oriented after melt blending and drawing. After the conversion of drawn (stretched) blends to MFCs the PET microfibrils were found to be randomly distributed in the PP matrix. The tensile strength and modulus of the MFCs were found to be higher for the samples drawn at stretch ratios 5 and 8 on account of the long PET microfibrils they possessed. The non isothermal crystallization behaviour of the neat blend (as extruded), stretched blend and the MFC was compared. The oriented PET fibrils in the stretched blend were found to have a greater nucleating effect for the crystallization of PP than the spherical PET particles in the neat blend and randomly oriented short PET fibrils in the MFC. Dynamic rheology studies indicated the storage modulus and loss modulus of MFCs were enhanced as draw ratio increases up to an optimized level beyond which they decrease. When the draw ratio increased up to the optimized level the MFCs tended to be more viscous, especially at low frequency, whereas further increasing the draw ratio resulted in a decrease in the complex viscosity. The microfibrils of PET in the MFC were found to perturb the relaxation of molten PP matrix.     

Parallel domain connectivity algorithm for unsteady flow computations using overlapping and adaptive grids

This paper describes the algorithms and functionality of a new module developed to support overset grid assembly associated with performing time-dependent and adaptive moving body calculations of external aerodynamic flows using a multi-solver paradigm (i.e. different CFD solvers in different parts of the computational domain). We use the term “domain connectivity” in this paper to denote all the procedures that are involved in an overset grid assembly, and the module developed is referred henceforth as the domain-connectivity module. The domain-connectivity module coordinates the data transfer between different solvers applied in different parts of the computational domain – body fitted structured or unstructured to capture viscous near-wall effects, and Cartesian adaptive mesh refinement to capture effects away from the wall. The execution of the CFD solvers and the domain-connectivity module are orchestrated by a Python-based computational infrastructure. The domain-connectivity module is fully parallel and performs all its operations (identification of grid overlaps and determination of data interpolation strategy) on the partitioned grid data. In addition, the domain connectivity procedures are completely automated such that no user intervention or manual input is necessary. The capabilities and performance of the package are presented for several test problems, including flow over a NACA 0015 wing and an AGARD A2 slotted airfoil, hover simulation of a scaled V-22 rotor, and dynamic simulation of a UH-60A rotor in forward flight. A modification to the algorithm for improved domain connectivity solutions in problems with tight tolerances as well as heterogeneous grid clustering is also presented.