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

CFD Analysis of Rotor-Fuselage Aerodynamics based on a Sliding Mesh Algorithm

Rotor-fuselage interaction is central to the design and performance analysis of helicopters. However, regardless of its significance this problem is not well-studied and few CFD works have so far been published. In this paper, a method is put forward to allow CFD computations of rotor-fuselage problems using a sliding mesh to interface the rotor and fuselage regions. A sliding plane forms a boundary between a CFD mesh around the fuselage and a rotor-fixed CFD mesh which has to be rotated to account for the motion of the rotor blades. CFD meshes adjacent to a sliding plane do not necessarily have matching nodes or even the same number of cell-faces. This poses a problem of interpolation between CFD meshes and, in addition, the employed algorithms should have small CPU overhead. The properties of this method are assessed and validation results are presented for several flow case

Solution of the Euler Equations in Three Dimensional Complex Geometries Using a Fully Unfactored Method. Aerospace Engineering Report 9907

An unfactored implicit time-marching method for the solution of the three dimensional Euler equations on multiblock curvilinear grids is presented. For robustness the convective terms are discretised using an upwind TVD scheme. The linear system arising from each implicit time step is solved using a Krylov subspace method with preconditioning based on an block incomplete lower-upper (BELU(O)) factorisation. Results are shown for the ONERA M6 wing, a wing/body configuration and the NLR-F5 wing with launcher and missile. It was found that the simulation cost is relatively independent of the number of blocks used and their orientation. Comparison is made with experiment where available and good agreement is obtained

Approximate Jacobians for the Solution of the Euler and Navier-Stokes Equations. G.U. Aero Report 9705

This paper describes a method for efficiently solving the steady-state Euler and Navier-Stokes equations. Robustness is achieved through the use of an upwind TVD scheme for discretising the convective terms. The approximate solution is advanced in time implicitly and the linear system arising at each implicit step is solved using a Conjugate Gradient type method. The main emphasis of this paper is on the use of Jacobian matrices associated with a simpler spatial discretisation. This leads to better conditioned linear systems. The resulting method has lower memory and CPU-time requirements when compared with the one using exact Jacobians

NUMERICAL SIMULATION OF FILM COOLING IN HYPERSONIC FLOWS

Abstract In this paper, a numerical study of film cooling in both laminar and turbulent hypersonic flows has been performed. The aim of this computational work was to investigate the mechanism and effectiveness of film cooling in hypersonic flows. The coolant fluid was found to affect the primary boundary layer in two ways: 1) a separate boundary layer established by the coolant fluid itself, 2) a mixing layer between the primary and coolant flow streams. According to the analysis of the film cooling effectiveness, it has been revealed that under the same primary flow conditions the flow field of film cooling could be recognized as two separate regions. These two regions are divided by the point of the cooling length x A . For laminar flow, film cooling effectiveness was observed to obey a second-order curve in the log-log coordinates against log 10 η = f (log 10 x hṁ ) 2 . For turbulent flow, a linear relation was found suitable to describe the relation between log 10 η and log 10 x hṁ

Direct generation of linearly polarized single photons with a deterministic axis in quantum dots

We report the direct generation of linearly polarized single photons with a deterministic polarization axis in self-assembled quantum dots (QDs), achieved by the use of non-polar InGaN without complex device geometry engineering. Here, we present a comprehensive investigation of the polarization properties of these QDs and their origin with statistically significant experimental data and rigorous k·p modeling. The experimental study of 180 individual QDs allows us to compute an average polarization degree of 0.90, with a standard deviation of only 0.08. When coupled with theoretical insights, we show that these QDs are highly insensitive to size differences, shape anisotropies, and material content variations. Furthermore, 91% of the studied QDs exhibit a polarization axis along the crystal [1–100] axis, with the other 9% polarized orthogonal to this direction. These features give non-polar InGaN QDs unique advantages in polarization control over other materials, such as conventional polar nitride, InAs, or CdSe QDs. Hence, the ability to generate single photons with polarization control makes non-polar InGaN QDs highly attractive for quantum cryptography protocols