Verification of a Specialized Hydrodynamic Simulation Code for Modeling Deflagration and Detonation of High Explosives

A specialized hydrodynamic simulation code has been developed to simulate one-dimensional unsteady problems involving the detonation and deflagration of high explosives. To model all the relevant physical processes in these problems, a code is required to simulate compressible hydrodynamics, unsteady thermal conduction and chemical reactions with complex rate laws. Several verification exercises are presented which test the implementation of these capabilities. The code also requires models for physics processes such as equations of state and conductivity for pure materials and mixtures as well as rate laws for chemical reactions. Additional verification tests are required to ensure these models are implemented correctly. Though this code is limited in the types of problems it can simulate, its computationally efficient formulation allow it to be used in calibration studies for reactive burn models for high explosives.

D6.4 Report on stochastic optimisation for unsteady problems

This report brings together methodological research on stochastic optimisation and work on benchmark and target applications of the ExaQute project, with a focus on unsteady problems. A practical, general method for the optimisation of the conditional value at risk is proposed. Three different optimisation problems are described: an oscillator problem selected as a suitable trial and illustration case; the shape optimisation of an airfoil, chosen as a benchmark application in the project; the shape optimisation of a tall building, which is the challenging target application set for ExaQUte. For each problem, the current developments and results are presented, the application of the proposed method is discussed, and the work to be done until the end of the project is laid out.

Correction for non-stationary of hydrodynamic fields in the rheological relationship of liquid

Эксплуатация различного рода технических устройств, в которых реализуются течения жидкости в каналах и трубах, всегда сопровождается нестационарными гидродинамическими процессами. Однако решение задач нестационарных течений жидкостей и газов зачастую приводит к существенных погрешностям, что дает основание исследователям основание сомневаться в справедливости реологических соотношений, учитывающих только неоднородность гидродинамических полей, но не учитывающих их нестационарность. Для устранения этих погрешностей при решении нестационарных задач течения жидкости в каналах и трубах в работах под руководством профессора С.К.Матвеева в выражение для касательного напряжения введена поправка, содержащая производную по времени скорости жидкости. Однако обобщение этой поправки на общий случай течения в тензорном виде оказывается невозможным. Поэтому в данной работе предлагается запись выражения для всего тензора напряжений в жидкости с поправкой на нестационарность, содержащей производную скорости, которая пригодна для описания пространственных течений жидкости. Рассмотрен частный случай нестационарного течения жидкости в плоском канале в одномерной постановке при использовании этой поправки. Показано, что такая модификация реологического соотношения приводит к решениям, согласующимися с решениями С.К.Матвеева. Также эта модификация может привести к уточнениям результатов решения для некоторых задач нестационарных течений. The operation of various technical devices in which fluid flows in channels and pipes are realized is always accompanied by non-stationary hydrodynamic processes. However, the solution of problems of unsteady flows of liquids and gases often leads to significant errors, which gives reason to researchers to doubt the validity of rheological relations, taking into account only the heterogeneity of the hydrodynamic fields, but not taking into account their unsteadiness. To eliminate these errors in solving unsteady problems of fluid flow in channels and pipes, in the work under the guidance of Professor S.K. Matveev, a correction containing the time derivative of the fluid velocity is introduced into the expression for shear stress. However, this correction is generalized to the general case of flow in tensor form turns out to be impossible. Therefore, in this paper, we propose writing an expression for the entire stress tensor in a fluid, adjusted for non-stationarity, containing the derivative of velocity, which is suitable for describing spatial fluid flows. A special case of unsteady fluid flow in a flat channel in a one-dimensional formulation using this correction is considered. It is shown that such a modification of the rheological relation leads to solutions matching the decisions of S.K. Matveev. Also, this modification can lead to more precise results of the solution for some problems of unsteady flows.

Scalability of OpenFOAM Density-Based Solver with Runge–Kutta Temporal Discretization Scheme

Compressible density-based solvers are widely used in OpenFOAM, and the parallel scalability of these solvers is crucial for large-scale simulations. In this paper, we report our experiences with the scalability of OpenFOAM’s native rhoCentralFoam solver, and by making a small number of modifications to it, we show the degree to which the scalability of the solver can be improved. The main modification made is to replace the first-order accurate Euler scheme in rhoCentralFoam with a third-order accurate, four-stage Runge-Kutta or RK4 scheme for the time integration. The scaling test we used is the transonic flow over the ONERA M6 wing. This is a common validation test for compressible flows solvers in aerospace and other engineering applications. Numerical experiments show that our modified solver, referred to as rhoCentralRK4Foam, for the same spatial discretization, achieves as much as a 123.2% improvement in scalability over the rhoCentralFoam solver. As expected, the better time resolution of the Runge–Kutta scheme makes it more suitable for unsteady problems such as the Taylor–Green vortex decay where the new solver showed a 50% decrease in the overall time-to-solution compared to rhoCentralFoam to get to the final solution with the same numerical accuracy. Finally, the improved scalability can be traced to the improvement of the computation to communication ratio obtained by substituting the RK4 scheme in place of the Euler scheme. All numerical tests were conducted on a Cray XC40 parallel system, Theta, at Argonne National Laboratory.

Preliminary Parameter Characterization for Numerical Optimisation of Ducted Propellers

In this paper, a preliminary parameter characterization for the numerical optimisation of ducted propellers was performed. The ENSTA Bretagne in-house solver used is based on the potential flow theory. Although the potential flow solver is able to solve unsteady problems, in this preliminary study only steady state flow problems are considered. Different parameters were analysed, such as the gap between the propeller tip and the inner duct surface as well as the propeller location in the duct tube. The analyses were carried out on a standard advance coefficient range. A quick study showed that a neutral NACA profile for the duct section could provide higher performance predictions than the classical accelerating Kort nozzle 19A.