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This paper focuses on the effects of external geometrical modifications on the aerodynamic characteristics of the MQ-1 predator Unmanned Combat Aerial Vehicle (UCAV) using computational fluid dynamics. The investigations are performed for 16 flight conditions at an altitude of 7.6 km and at a constant speed of 56.32 m/s. Two models are analysed, namely the baseline model and the model with external geometrical modifications installed on it. Both the models are investigated for various angles of attack from −4° to 16°, angles of bank from 0° to 6° and angles of yaw from 0° to 4°. Due to the unavailability of any experimental (wind tunnel or flight test) data for this UCAV in the literature, a thorough verification of calculations process is presented to demonstrate confidence level in the numerical simulations. The analysis quantifies the loss of lift and increase in drag for the modified version of the MQ-1 predator UCAV along with the identification of stall conditions. Local improvement (in drag) of up to 96% has been obtained by relocating external modifications, whereas global drag force reduction of roughly 0.5% is observed. The effects of external geometrical modifications on the control surfaces indicate the blanking phenomenon and reduction in forces on the control surfaces that can reduce the aerodynamic performance of the UCAV.

During the sport of wave surfing, the fins on a surfboard play a major role in the overall performance of the surfer. This article presents the optimisation of a surfboard fin shape, using coupled genetic algorithms with the FLUENT®solver, aiming at the maximisation of the lift per drag ratio. The design-variable vector includes six components namely the chord length, the depth and the sweep angle of the fin as well as the maximum camber, the maximum camber position and the thickness of the hydrofoil (the four-digit NACA parametrization). The Latin hypercube sampling technique is utilised to explore the design space, resulting in 42 different fin designs. Fin and control volume models are created (using CATIA®V5) and meshed (unstructured using ANSYS®Workbench). Steady-state computations were performed using the FLUENT SST k−ω(shear stress transport k−ω) turbulence model at the velocity of 10 m/s and 10° angle of attack. Using the obtained lift and drag values, a response surface based model was constructed with the aim to maximise the lift-to-drag ratio. The optimisation problem was solved using the genetic algorithm provided by the MATLAB®optimisation toolbox and the response surface based model was iteratively improved. The resultant optimal fin design is compared with the experimental data for the fin demonstrating an increase in lift-to-drag ratio by approximately 62% for the given angle of attack of 10°.

The article offers information a concert by the Stadtmusik Stockach conducted by music director Helmut Hubov and the Stockach Chamber Choir and the Nellenburg Kantorei conducted by Stefan Gräsle to be held on December 17, 2022 in the Jahnhalle Stockach, Germany.

In the present study, we develop a generalised Godunov-type multi-directional characteristics-based (MCB) scheme which is applicable to any hyperbolic system for modelling incompressible flows. We further extend the MCB scheme to include the solution of the local Riemann problem which leads to a hybrid mathematical treatment of the system of equations. We employ the proposed scheme to hyperbolic-type incompressible flow solvers and apply it to the Artificial Compressibility (AC) and Fractional-Step, Artificial Compressibility with Pressure Projection (FSAC-PP) method. In this work, we show that the MCB scheme may improve the accuracy and convergence properties over the classical single-directional characteristics-based (SCB) and non-characteristic treatments. The inclusion of a Riemann solver in conjunction with the MCB scheme is capable of reducing the number of iterations up to a factor of 4.7 times compared to a solution when a Riemann solver is not included. Furthermore, we found that both the AC and FSAC-PP method showed similar levels of accuracy while the FSAC-PP method converged up to 5.8 times faster than the AC method for steady state flows. Independent of the characteristics- and Riemann solver-based treatment of all primitive variables, we found that the FSAC-PP method is 7–200 times faster than the AC method per pseudo-time step for unsteady flows. We investigate low- and high-Reynolds number problems for well-established validation benchmark test cases focusing on a flow inside of a lid driven cavity, evolution of the Taylor–Green vortex and forced separated flow over a backward-facing step. In addition to this, comparisons between a central difference scheme with artificial dissipation and a low-dissipative interpolation scheme have been performed. The results show that the latter approach may not provide enough numerical dissipation to develop the flow at high-Reynolds numbers. We found that the inclusion of a Riemann solver is able to overcome this shortcoming. Overall, the proposed generalised Godunov-type MCB scheme provides an accurate numerical treatment with improved convergence properties for hyperbolic-type incompressible flow solvers. Program Title: unified2D-C Program Files doi: http://dx.doi.org/10.17632/8m3dw6zkgc.1 Licensing provisions: CC BY NC 3.0 Programming language: C++ Nature of problem: Incompressible flow solver have generally a non-hyperbolic type and thus the method of characteristics and Riemann solvers cannot be used without modifications for low speed flows. In the framework of compressible flows, the Riemann problem – and the method of characteristics which is closely related to it – is an essential part of the solution procedure. The Riemann solver is able to preserve the conservativeness and, through the evaluation of the eigenstructure of the system, introduces transportiveness into the spatial reconstruction schemes. The characteristics-based scheme allows to couple the pressure and velocity in a physical manner which, together with the Riemann solver, presents a new multi-directional Godunov framework for incompressible flows. Solution method: We show a generalised description of a multi-directional characteristics-based schemes which may be used with any incompressible and hyperbolic system of equations. The Finite Volume approach is used where inter-cell fluxes are reconstructed through a simple but higher-order polynomial interpolation scheme which only adds numerical dissipation proportional to its Taylor-series truncation error. We use the Rusanov Riemann solver which provides the needed conservativeness and transportiveness. It also adds just enough numerical dissipation for cases where the dissipation of the numerical scheme is not sufficient while retaining a high level of accuracy. [ABSTRACT FROM AUTHOR]

In this paper the assessment and the enhancement of the computational performance of a high-order finite volume CFD code is presented. Weighted Essentially Non-Oscillatory (WENO) schemes are considered to be from the most computationally expensive numerical frameworks, in the context of high-resolution schemes particularly on hybrid unstructured grids. The focus of this study is to assess the computational bottlenecks of the solver for the WENO schemes for Implicit Large Eddy Simulation (ILES) and optimise the performance and efficiency through a series of code modifications e.g. formula rewriting, reduction of number operations, inclusion of linear systems libraries, non-blocking communications amongst others. The code is assessed on five different HPC systems; significant speed-up is achieved ranging from 1.5 to 8.5, with very high-order schemes benefiting the most. Good scalability is also obtained up to 10 4 number of cores, demonstrating viability and affordability of WENO type schemes for scale resolving simulations. [ABSTRACT FROM AUTHOR]

This paper presents an enhancement of the Nimrod/O optimization tool by interfacing DEMO, an external multiobjective optimization algorithm. DEMO is a variant of differential evolution - an algorithm that has attained much popularity in the research community, and this work represents the first time that true multiobjective optimizations have been performed with Nimrod/O. A modification to the DEMO code enables multiple objectives to be evaluated concurrently. With Nimrod/O's support for parallelism, this can reduce the wall-clock time significantly for compute intensive objective function evaluations. We describe the usage and implementation of the interface and present two optimizations. The first is two-objective mathematical function in which the Pareto front is successfully found after only 30 generations. The second test case is the three-objective shape optimization of a rib-reinforced wall bracket using the Finite Element software, Code_Aster. The interfacing of the already successful packages of Nimrod/O and DEMO yields a solution that we believe can benefit a wide community, both industrial and academic.

• The Implicit LES approach with 2nd and 3nd order WENO scheme is applied to square cylinder flow at R e = 22000. • The near wall performance of 3rd order WENO ILES is comparable to conventional LES with WALE model and out-performs LES with dynamic Smagorinsky model. • Both LES and ILES face challenge in terms of small quantities such as shear wall stress. • The 2nd-order WENO scheme can also give a fair prediction over the averaged statistics such as drag coefficient, Strouhal number, recirculation length and stream-wise velocity profile with less computational time than a 3rd-order WENO scheme. In this paper, the Implicit Large-Eddy Simulation (ILES) is investigated on the flow around a square cylinder incorporating an unstructured Weighted Essential Non-Oscillatory (WENO) reconstruction method for a Reynolds number of 22,000. Simulations are undertaken in the framework of open-source package OpenFOAM and additional implicit 2nd/3rd-order WENO scheme on the convective term of the viscous incompressible Navier-Stokes Equations. A 2nd-order Euler implicit time integration and Pressure-Implicit Splitting-Operator (PISO) algorithm is used to for the pressure-velocity coupling. Conventional LES with Wall Adapting Local Eddy Viscosity (WALE) model is also carried out as a baseline. The results are compared to high fidelity experiment, DNS data and conventional LES with dynamic Smagorinsky model from previous work. Results show favorable performance for ILES with 3rd-order WENO scheme compared with the conventional LES with dynamic Smagorinsky model and similar performance against LES with WALE model. Results also show acceptable predictions over time-averaged statistics with less computational effort for the ILES of 2nd-order WENO scheme. Shear layer flow analysis suggests that both ILES and LES face similar challenges with small quantities, such as shear stress. Finally, simulations are capturing von Kármán vortex, Kelvin-Helmholtz instability and induced frequency changes. [ABSTRACT FROM AUTHOR]