Harmen van der Ven

A family of large eddy simulation (LES) filters with nonuniform filter widths

In this Brief Communication a family of filters for large eddy simulation (LES) with nonuniform filter widths is constructed that commute with differentiation up to any given order.

X-LES Simulations Using a High-Order Finite-Volume Scheme

This paper focuses on numerical aspects for hybrid RANS–LES computations using the X-LES method. In particular, the impact of using a high-order finite-volume scheme is considered. The finite-volume scheme is fourth-order accurate on non-uniform, curvilinear grids, has low numerical dispersion and dissipation, and is based on the skew-symmetric form of the compressible convection operator, which ensures that kinetic energy is conserved by convection. A limited grid convergence study is performed for the flow over a rounded bump in a square duct. The fourth-order results are shown to depend only mildly on the grid resolution. In contrast, second-order results require at least half the mesh size to become comparable to the fourth-order results. Additionally, the high-order method is extended with shock-capturing capability in such a way that interference with the subgrid-scale model is avoided. The suitability of this extension is demonstrated by means of a supersonic flow over a cavity.

A provably stable MoT scheme based on quadratic spline basis functions

Computational methods are widely used in the engineering community for the analysis of electromagnetic scattering phenomena. To achieve the robustness required for industrial application the numerical scheme has to be provably stable. The existing stability proof of the space-time Galerkin scheme will be augmented such that it can be used for the more popular marching-on-in-time scheme. These extensions lead to a provably stable scheme that is easy to implement in existing marching methods.

Experiences with Advanced CFD Algorithms on NEC SX-4

In this paper three topics related to parallel CFD simulations are discussed. The first topic is the shared memory parallelization of the unstructured adaptive flow solver Hexadap. The second topic discusses the performance results of this parallelization on a 16 processor NEC SX-4. The third topic combines the first two and concerns the CFD working environment ISNaS as developed by the National Aerospace Laboratory NLR.

The Influence of the Exact Evaluation of Radiation Fields in Finite Precision Arithmetic on the Stability of the Time Domain Integral Equation Method

Transient electromagnetic scattering phenomena can effectively be simulated with time domain integral equation methods. The stability and accuracy of the marching on in time scheme is usually established with exact evaluation of the radiation fields. Due to singularities in their analytical expressions, straightforward evaluation in finite precision arithmetic can jeopardize the accuracy of the radiation fields. Computational experiments confirm this and show that it can even lead to late-time instability of the numerical model. Hence, a reformulation is necessary to remove the singular behavior and obtain the robustness required for industrial application. To this end, highly accurate and well-behaved expressions for the quasi-exact integration method in finite precision arithmetic will be derived in this paper. Numerical experiments confirm the robustness and stability of the improved Marching on in Time scheme.

A NICE HPNC Centre for Flow Simulation

The Netherlands Initiative in CFD for Engineering with HCPN (NICE) aims at increasing the competitiveness of Dutch industry by making available competence in the area of flow simulation on HPCN platforms. The know-how and know-why that is developed is disseminated via a metacomputer for CFD, called HCS. This metacomputer also supports the ability to apply the developed know-how and know-why in industrial engineering problems. The paper sets the outline of the NICE application areas, and presents HCS. The presentation includes a highlight of present experiences with HCS, ongoing developments and finishes with concluding remarks.

Stability analysis of the marching-on-in-time boundary element method for electromagnetics

The Time Domain Integral Equation method for electromagnetics is an appealing computational method for many applications in industry. However, its applicability has long been suffering from instabilities. A rigorous analysis of the variational formulation is imperative to the successful design of stable and robust numerical schemes. In this paper, an established functional framework and stability theorem will be extended to the differentiated version of the electric field integral equations, which can be discretized more efficient and is more often used in engineering literature. The extended stability theorem, combined with efficiency requirements, will give guidelines on the choice of test and basis functions of the space-time Petrov-Galerkin scheme. A discrete equivalence with the collocation method results in the recommendation to choose the quadratic spline basis function in the standard Marching-on-in-Time scheme. Computational experiments confirm that the quadratic spline basis functions have superior stability characteristics compared to the conventional quadratic Lagrange basis functions in time.

Real-Time Visualization of Large Data Sets on NLR's NEC SX-4

Visualization is an integral part of the simulation process. With the increase of computing power for simulation, visualization has lagged behind. This paper will present a real-time visualization system, RVSLIB, which is developed to supply simulation engineers with a visualization tool which performs at the same rate as their simulation packages. RVSLIB is developed and optimized on the NEC SX-4, and applies the client-server model. The compute server, a NEC SX-4 parallel vector computer, serves also as a visualization server: both mapping and rendering of the image is performed on the NEC SX-4. In this way, users not connected through a high-speed network to the supercomputer can use the NEC SX-4 as both compute and visualization server. The system is illustrated for a real-life application within the HPCN project NICE.

Uncertainty Quantification of Aeroelastic Systems with Structural or Aerodynamic Nonlinearities

In this work, various aeroelastic approaches are used in the uncertainty quanti cation of a generic UAV wing. The di erent methods that are employed investigate varying levels of model delity, representing methods that could be used for low-order, rst-case studies, up to much higher delity methodologies. Results consider geometrically-exact structural and aerodynamic nonlinearities, and investigates the validity of using low-order simulations to predict deterministic and uncertainty bounds versus those of higher-order approaches. It is shown how correlated loads envelopes comparing strip theory aerodynamics show good agreement with higher order panel methods, even for very exible wings, but it is also seen how di erences in aerodynamic modelling (which would be equivalent in a structurally linear analysis) can e ect the results, particularly torque. It is also shown how aerodynamic delity can potentially a ect the uncertainty bounds of the computed aerodynamic loads, suggesting that low-order potential ow solvers signi cantly underestimate the uncertainty bounds compared to higher-order RANS approaches.