摘要:

AbstractCalculations of unsteady turbulent flow around and behind triangular‐shaped flameholders using a finite volume code with ak‐ε model of turbulence are presented.The flow behind the flameholders is found to be unsteady (a von Kármán vortex street appears) with a well defined Strouhal frequency (predictedSr=0·27 compared with an experimental value of 0·25). The predicted profiles of velocity and fluctuating kinetic energy agree well with experiments. The periodic motions in the vortex street are shown to be far more important than the turbulent stochastic motions in exchanging momentum in the transversal direction.The pressure‐velocity coupling is handled with the SIMPLEC pressure correction procedure. The discretization in time is fully implicit and 90 times steps are used to resolve one time cycle. It was found that to capture the vortex street it is very important that the grid spacing is sufficiently fine (

ISSN:0271-2091    

DOI:10.1002/fld.1650161002

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWe describe the implementation of a new 3D vortex algorithm for the computation of the drag and flow field around parachutes. Among its novel features, the algorithm couples large eddy simulation methodology with the vortex method, away from the wall region. Furthermore, boundary conditions for a wall (no‐slip) and compliant boundaries were implemented. The results of several simulations using this algorithm are analysed and discussed. The spectral contents of the vortex method are also considere

ISSN:0271-2091    

DOI:10.1002/fld.1650161003

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe primary aim of this work was to determine the simplest and most effective parallelization strategy for control‐volume‐based codes solving industrial problems. It has been found that for certain classes of problems, the coarse‐grain functional decomposition strategy, largely ignored due to its limited scaling capability, offers the potential for significant execution speed‐ups while maintaining the inherent structure of traditional serial algorithms. Functional decomposition requires only minor modification of the existing serial code to implement and, hence, code portability across both concurrent and serial computers is maintained. Fine‐grain parallelization strategies at the ‘DO loop’ level are also easy to implement and largely preserve code portability. Both coarse‐grain functional decomposition and fine‐grain loop‐level parallelization strategies for the SIMPLE pressure correction algorithm are demonstrated on a Silicon Graphics 4D280S eight CPU shared memory computer system for a highly coupled, transient two‐dimensional simulation involving melting of a metal in the presence of thermal‐buoyancy‐driven laminar convection. Problems requiring the solution of a larger number of transport equations were simulated by including further scalar variables in the calculation. While resulting in slight degradation of the convergence rate, the functional decomposition strategy exhibited higher parallel efficiencies and yielded greater speed‐ups relative to the original serial code. Initially, this strategy showed a significant degradation in convergence rate due to an inconsistency in the parallel solution of the pressure correction equation. After correcting for this inconsistency, the maximum speed‐up for 16 dependent variables was a factor of 5·28 with eight processors, representing a parallel efficiency of 67%. Peak efficiency of 76% was achieved using five processors to so

ISSN:0271-2091    

DOI:10.1002/fld.1650161004

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes flow around a pair of cylinders in tandem arrangement with a downstream cylinder being fixed or forced to oscillate transversely. A sinusoidal parietal velocity is applied to simulate cylinder oscillation. Time‐dependent Navier‐Stokes equations are solved using finite element method. It is shown that there exist two distinct flow regimes: ‘vortex suppression regime’ and ‘vortex formation regime’. Averaged vortex lengths between the two cylinders, pressure variations at back and front stagnant points as well as circumferential pressure profiles of the downstream cylinder are found completely different in the two regimes and, thus, can be used to identify the flow regimes. It is shown that frequency selection in the wake of the oscillating cylinder is a result of non‐linear interaction among vortex wakes upstream and downstream of the second cylinder and its forced oscillation. Increasing cylinder spacing results in a stronger oscillatory incident flow upstream of the second cylinder and, thus, a smaller synchro

ISSN:0271-2091    

DOI:10.1002/fld.1650161005

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractConventional high‐order schemes with reduced levels of numerical diffusion produce results with spurious oscillations in areas where steep velocity gradients exist. To prevent the development of non‐physical oscillations in the solution, several monotonic schemes have been proposed. In this work, three monotonic schemes, namely Van Leer's scheme, Roe's flux limiter and the third‐order SHARP scheme, are compared and evaluated against schemes without flux limiters. The latter schemes include the standard first‐order upwind scheme, the second‐order upwind scheme and the QUICK scheme. All the above schemes are applied to four two‐dimensional problems: (i) rotation of a scalar ‘cone’ field, (ii) transport of a scalar ‘square’ field, (iii) mixing of a cold with a hot front and (iv) deformation of a scalar ‘cone’ field. These problems test the ability of the selected schemes to produce oscillation‐free and accurate results in critical convective situations. The evaluation of the schemes is based on several aspects, such as accuracy, economy and complexity. The tests performed in this work reveal the merits and demerits of each scheme. It is concluded that high‐order schemes with flux limiters can significantly improve

ISSN:0271-2091    

DOI:10.1002/fld.1650161006

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650161007

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

ISSN:0271-2091    

DOI:10.1002/fld.1650161001

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY