Parallel Navier-Stokes Research Articles

Virtual Flight Navier-Stokes Solver and its Application

A multi-purpose CFD software VFNS (Virtual Flight Navier-Stokes solver) is developed for aerodynamic and flight dynamic applications. The software is specifically designed to support the research works on coupling problems between aerodynamics and flight dynamics. It employs 6-DOF capability for simulating forced or free moving problems and chimera capability for simulating moving body dynamics including control laws. These challenging applications are enabled by coupling an unsteady, parallel Navier-Stokes flow solver with flight dynamics in sub-iterations of dual-time stepping algorithm. This paper will introduce the numeric methods used in this software and give some applications in free-to-pitch simulations for a square cross-section missile.

NUMERICAL SIMULATION OF UNSTEADY FLOW FIELD AROUND HELICOPTER IN FORWARD FLIGHT USING A PARALLEL DYNAMIC OVERSET UNSTRUCTURED GRIDS METHOD

A parallel Navier-Stokes solver based on dynamic overset unstructured grids method is presented to simulate the unsteady turbulent flow field around helicopter in forward flight. The grid method has the advantages of unstructured grid and Chimera grid and is suitable to deal with multiple bodies in relatively moving. Unsteady Navier-Stokes equations are solved on overset unstructured grids by an explicit dual time-stepping, finite volume method. Preconditioning method applied to inner iteration of the dual-time stepping is used to speed up the convergence of numerical simulation. The Spalart-Allmaras one-equation turbulence model is used to evaluate the turbulent viscosity. Parallel computation is based on the dynamic domain decomposition method in overset unstructured grids system at each physical time step. A generic helicopter Robin with a four-blade rotor in forward flight is considered to validate the method presented in this paper. Numerical simulation results show that the parallel dynamic overset unstructured grids method is very efficient for the simulation of helicopter flow field and the results are reliable.

Prediction of aerodynamic forces on a helicopter fuselage

This paper presents a critical analysis of the aerodynamic loads created by the airframe of a conventional helicopter. The airframe is modelled and computed with an implicit, multi-block, multi-grid parallel Navier-Stokes solver. The flow solver has been optimised and run on up to 200 parallel processors. The cases reported include the effects of angle-of-attack (positive and negative), the effects of yaw (starboard and port) and side flow. Finally, the effects of the support strut in the wind tunnel experiments have been evaluated. Data are shown for the lift, drag and side force coefficients at flight Reynolds numbers (Re = 30m). A case of 30 degrees yaw at a flight Reynolds number is shown. We conclude that with the use of top-end computer resources it is possible to calculate the aerodynamic coefficients with a good degree of accuracy if the flow is mostly attached.

Parallel Large Scale High Accuracy Navier-Stokes Computations on Distributed Memory Clusters

We present a highly scalable parallelization of a high-accuracy 3D serial multiblock Navier-Stokes solver. The code solves the full Navier-Stokes equations and is capable of performing large-scale computations for practical configurations in an industrial enviroment. The parallelization strategy is based on the geometrical domain decomposition principle, and on the overlapped communication and computation concept. The important advantage of the strategy is that the suggested type of message-passing ensures a very high scalability of the algorithm from the network point of view, because, on the average, the communication work per processor is not increased if the number of processors is increased. The parallel multiblock-structured Navier-Stokes solver based on the parallel virtual machine (PVM) routines was implemented on 106-processors distributed memory cluster managed by the MOSIX software package. Analysis of the results demonstrated a high level of parallel efficiency (speed up) of the computational algorithm. This allowed the reduction of the execution time for large-scale computations employing 10 million of grid points, from an estimated 46 days on the SGI ORIGIN 2000 computer (in the serial single-user mode) to 5–6 hours on 106-processors cluster. Thus, the parallel multiblock full Navier-Stokes code can be successfully used for large-scale practical aerodynamic simulations of a complete aircraft on millions-points grids on a daily basis, as needed in industry.

Flutter Computation of Turbomachinery Cascades Using a Parallel Unsteady Navier-Stokes Code

A quasi-three-dimensional multigrid Navier-Stokes solver on single- and multiple-passage domains is presented for solving unsteady flows around oscillating turbine and compressor blades. The conventional direct store method is used for applying the phase-shifted periodic boundary condition over a single blade passage. A parallel version of the solver using the message passing interface standard is developed for multiple-passage computations. In parallel multiple-passage computations, the phase-shifted periodic boundary condition is converted to a simple in-phase periodic condition. Euler and Navier-Stokes solutions are obtained for unsteady flows through an oscillating turbine cascade blade row with both the sequential and the parallel codes. It is found that the parallel code offers almost linear speedup with a slope close to 1 on multiple CPUs. In addition, significant improvement is achieved in convergence of the computation to a periodic unsteady state in the parallel multiple-passage computations due to the use of the in-phase periodic boundary conditions compared with that in the single-passage computations with phase-shifted periodic boundary conditions via the direct store method. The parallel Navier-Stokes code is also used to calculate the flow through an oscillating compressor cascade. Results are compared with experimental data and computations by other authors.

Simulation of plasma flux detachment in Alcator C-Mod and ITER

Understanding the physics of divertor detachment is important since detached operation in ITER could reduce the target heat flux drastically, while aiding helium ash removal. In order to model detachment properly we have incorporated a parallel Navier-Stokes neutral model in UEDGE. In simulations of Alcator C-Mod we reproduce the partial detachment observed in experiments. A bifurcation to a MARFE has been found, similar to experiments. Volume recombination is a very important effect in removing the ion current to the target and we observe strong plasma flux detachment. Similar results have been found for ITER, with an order of magnitude decrease of the peak heat flux and a strong reduction of the target ion flux. Detachment has been induced with both neon and carbon.

An interactive engineering tool for parallel HPC applications

Typical applications of the so-called Grand Challenges need massively parallel computer system architectures. Tools like parallel debuggers, performance analysers and visualizers help the code designer to develop efficient parallel algorithms. Such tools merely support the development cycle. But technical and scientific engineers who make use of parallel high-performance computing applications, e.g. numerical simulation algorithms in computational fluid dynamics (CFD), must be supported in their engineering work by another kind of tool. A tool for the application cycle is required because old, conventional suggestions regarding the arrangement for the application cycle rely on strictly sequential procedures. They are due to the heritage of traditional work on former vector computers. That formative influence is still felt in today's arrangements for the application cycle, prevents a more efficient engineering work and, therefore, must be overcome. New tool conceptions have to be introduced to enable on-line interaction between the technical and scientific engineers and their running parallel simulation. VIPER stands for Visualization of Parallel numerical simulation algorithms for Extended Research and offers physical parameters of the mathematical model and parameters of the numerical method as objects of a graphical user tool interface for online observation and online modification. A special client-server-client process architecture implementation enables technical and scientific engineers who are sitting at their graphic workstation to interact with their parallel simulation algorithms running on a remote parallel computer system. The VIPER prototype is applied on ParNsflex which is a parallel Navier-Stokes solver for real world aero-dynamic problems. A Paragon XP S was selected as test parallel computer system. A first evaluation indicates the superiority of the VIPER conception against conventional procedures.

VIPER - A Tool Concept To Control Parallel CFD Applications

Typical applications in the fields of the so-called Gmrzcf CWW#e5 need massive parallel computer system architectures. Tools like parallel debuggers, performance analysers and visualizers help the code designer to develop efficient parallel algorithms. Such tools merely support the development cycle. But the engineer who makes use of parallel high-performance computing applications, e.g. numerical simulation algorithms in Computational Fluid Dynamics (CFD), must be supported in his engineering work by another kind of tool. A user tool for the production cycle is required because conventional suggestions rely on serial batch-oriented procedures which have significant drawbacks, and therefore, they are not suitable to make use in nowadays High-Performance Computing (HPC). This paper presents the principal idea of the VIPER tool concept which enables the engineer who is sitting at his graphic workstation to interact with the parallel simulation algorithm which is running on a remote parallel computer system. Parameters of theoretical model and of the numerical method are considered as objects and available for Wme observation and Wme modification via the graphical user tool interface. First performance results are shown with the VIPER tool prototype implementation applied on the parallel Navier-Stokes solver PARNSFLEX which was running on an Intel Paragon XP/S multiprocessor system.