Shock Reflection Hysteresis in an Underexpanded Jet: a CFD Study. Department of Aerospace Engineering Report no. 9808

Shock reflection hysteresis in a low density, axisymmetric underexpanded air jet is examined using a Navier-Stokes flow solver. Jets of this type are found in a number of applications e.g. rocket exhausts. The existence of a dual solution domain where either regular or Mach reflection may occur within the complex plume structure is predicted. This is in agreement with experiment where the same phenomenon has been observed for a nitrogen jet. The results of the computational study are used to examine the structure of the plume, and are compared with experimental data where available. The plume structure is complex, involving the interaction of several flow features, making this a demanding problem. A quasi-steady approach is employed in order to calculate the entire hysteresis loop. Included in this report is a review of the two dimensional shock reflection hysteresis problem. Some recommendations are made for further study of this type of flow

Towards Automatic Multiblock Topology Generation. G.U. Aero Report 9826

The need for automation of the multiblock grid generation process is discussed. A new approach to automatically process a multiblock topology in order to prepare it for the grid generation process is described. The method is based on a cost function which attempts to model the objectives of the skilled grid generation software user who at present performs the task of block positioning and shaping in an interactive manner. A number of test cases are examined. It is also suggested that an existing unstructured mesh generation method could be adopted as an initial topology generation tool. Further work towards creating a fully automatic grid generation tool and extension into three dimensions are discussed briefly

Application of PMB2D to Axisymmetric Flows. Department of Aerospace Engineering report 9812

This report describes how the two-dimensional planar flow solver PMB2D has been modified for axisymmetric flows. The equations describing axisymmetric flows are derived. The issue of conservation is discussed. The modified linear system arising at each implicit time step is detailed. Finally, results for inviscid, laminar and turbulent flow test cases are presented

Parallel Aerodynamic Simulation on Open Workstation Clusters. Department of Aerospace Engineering Report no. 9830

The parallel execution of an aerodynamic simulation code on a non-dedicated, heterogeneous cluster of workstations is examined. This type of facility is commonly available to CFD developers and users in academia, industry and government laboratories and is attractive in terms of cost for CFD simulations. However, practical considerations appear at present to be discouraging widespread adoption of this technology. The main obstacles to achieving an efficient, robust parallel CFD capability in a demanding multi-user environment are investigated. A static load-balancing method, which takes account of varying processor speeds, is described. A dynamic re-allocation method to account for varying processor loads has been developed. Use of proprietary management software has facilitated the implementation of the method

Affordable High Powered Clustered Computing for Aerospace Simulation. G.U. Aero Report 9911

Motivated by a lack of sufficient local and national computing facilities for computational fluid dynamics simulations, the Affordable Systems Computing Unit (ASCU) was established to investigate low cost alternatives. The options considered have all involved cluster computing, a term which refers to the grouping of a number of components into a managed system capable of running both serial and parallel applications. Past work by the Unit has demonstrated the significant improvement in the efficiency of a Network of Workstations when management software is employed to scavenge spare cycles and schedule tasks, and has also investigated the use of a managed network for parallel CFD. The present work aims to extend this effort to a higher performance cluster based on commodity processors used for dedicated batch processing. The performance of the cluster has proved to be extremely cost effective, producing a 3 Gigaflops plus peak performance for less than 25K U.K. pounds sterling at current market prices. The experience gained on this system in terms of single node performance, message passing and parallel performance will be discussed. In particular, comparisons with the performance of other systems will be made. A large scale CFD simulation achieved using the new cluster will be presented to demonstrate the potential of commodity processor based parallel computers for aerodynamic simulation

Application of PMB2D to Axisymmetric Flows. Department of Aerospace Engineering report 9812

This report describes how the two-dimensional planar flow solver PMB2D has been modified for axisymmetric flows. The equations describing axisymmetric flows are derived. The issue of conservation is discussed. The modified linear system arising at each implicit time step is detailed. Finally, results for inviscid, laminar and turbulent flow test cases are presented

Towards Automatic Multiblock Topology Generation. G.U. Aero Report 9826

The need for automation of the multiblock grid generation process is discussed. A new approach to automatically process a multiblock topology in order to prepare it for the grid generation process is described. The method is based on a cost function which attempts to model the objectives of the skilled grid generation software user who at present performs the task of block positioning and shaping in an interactive manner. A number of test cases are examined. It is also suggested that an existing unstructured mesh generation method could be adopted as an initial topology generation tool. Further work towards creating a fully automatic grid generation tool and extension into three dimensions are discussed briefly

Parallel Aerodynamic Simulation on Open Workstation Clusters. Department of Aerospace Engineering Report no. 9830

The parallel execution of an aerodynamic simulation code on a non-dedicated, heterogeneous cluster of workstations is examined. This type of facility is commonly available to CFD developers and users in academia, industry and government laboratories and is attractive in terms of cost for CFD simulations. However, practical considerations appear at present to be discouraging widespread adoption of this technology. The main obstacles to achieving an efficient, robust parallel CFD capability in a demanding multi-user environment are investigated. A static load-balancing method, which takes account of varying processor speeds, is described. A dynamic re-allocation method to account for varying processor loads has been developed. Use of proprietary management software has facilitated the implementation of the method

Shock Reflection Hysteresis in an Underexpanded Jet: a CFD Study. Department of Aerospace Engineering Report no. 9808

Shock reflection hysteresis in a low density, axisymmetric underexpanded air jet is examined using a Navier-Stokes flow solver. Jets of this type are found in a number of applications e.g. rocket exhausts. The existence of a dual solution domain where either regular or Mach reflection may occur within the complex plume structure is predicted. This is in agreement with experiment where the same phenomenon has been observed for a nitrogen jet. The results of the computational study are used to examine the structure of the plume, and are compared with experimental data where available. The plume structure is complex, involving the interaction of several flow features, making this a demanding problem. A quasi-steady approach is employed in order to calculate the entire hysteresis loop. Included in this report is a review of the two dimensional shock reflection hysteresis problem. Some recommendations are made for further study of this type of flow

Affordable High Powered Clustered Computing for Aerospace Simulation. G.U. Aero Report 9911

Motivated by a lack of sufficient local and national computing facilities for computational fluid dynamics simulations, the Affordable Systems Computing Unit (ASCU) was established to investigate low cost alternatives. The options considered have all involved cluster computing, a term which refers to the grouping of a number of components into a managed system capable of running both serial and parallel applications. Past work by the Unit has demonstrated the significant improvement in the efficiency of a Network of Workstations when management software is employed to scavenge spare cycles and schedule tasks, and has also investigated the use of a managed network for parallel CFD. The present work aims to extend this effort to a higher performance cluster based on commodity processors used for dedicated batch processing. The performance of the cluster has proved to be extremely cost effective, producing a 3 Gigaflops plus peak performance for less than 25K U.K. pounds sterling at current market prices. The experience gained on this system in terms of single node performance, message passing and parallel performance will be discussed. In particular, comparisons with the performance of other systems will be made. A large scale CFD simulation achieved using the new cluster will be presented to demonstrate the potential of commodity processor based parallel computers for aerodynamic simulation