Aeronautical Problems Research Articles

An Effective Arbitrary Lagrangian-Eulerian-Lattice Boltzmann Flux Solver Integrated with the Mode Superposition Method for Flutter Prediction

An Effective Arbitrary Lagrangian-Eulerian-Lattice Boltzmann Flux Solver Integrated with the Mode Superposition Method for Flutter Prediction

Development of three-dimensional rotated lattice Boltzmann flux solver for the simulation of high-speed compressible flows

A three-dimensional (3D) Rotated Lattice Boltzmann Flux Solver (RLBFS) is proposed and analyzed with matrix-based linear stability theory for simulating compressible flows in a wide range of Mach numbers. The 3D RLBFS applies the finite volume method to discrete the Navier-Stokes equations and evaluates its fluxes at each cell interface. To improve numerical stability, the convective fluxes are obtained in a hybrid way by using the D1Q4 lattice Boltzmann model in two perpendicular directions decomposed by the outer normal vector of each cell interface. The viscous fluxes are computed in a conventional way using the second-order central scheme. The stability performance and order accuracy of the proposed 3D RLBFS are examined by using the matrix-based stability theory and L2 errors on different meshes respectively. It is shown that the 3D RLBFS is stable even at high Mach number and has the second-order accuracy in space. The reliability and capability of the proposed method is further evaluated by simulating several challenging compressible flow problems, including subsonic flow over the DLR-F4, transonic flow over the ONERA M6 wing, supersonic flow around NACA0012 wing, hypersonic flow over the Viking lander capsule, hypersonic flow over a hemisphere and hypersonic flow around a blunt nose double cone. The obtained numerical results are in good agreement with experimental and/or numerical data published in the literature, indicating that the present method provides a reliable and effective tool for simulating practical three-dimensional compressible flow problems in aeronautics and astronautics.

Assessment of turbulence models and mesh types for the simulation of multi-body separation by coupling the CFD and rigid body dynamics

Turbulence models are considered one of the most important sources of numerical errors in the CFD studies on different aeronautical problems. The mesh type can also affect the numerical accuracy and computational efficiency. In this paper, various simulations on the store separation from an aircraft model in the transonic flow have been carried out by coupling the CFD and the rigid body dynamics on the overset mesh. The influence of S-A model, Standard k-epsilon model, SST k-omega model and inviscid model on the simulation results is examined. Different mesh types of both unstructured mesh and structured mesh as component part in overset are also considered. Grid-independence study are first carried out. The effects of different turbulence models and mesh types are then examined by comparing the trajectories, velocities and Eulerian angles. Recommendations are given to get better results for the simulation of multi-body separation problem.

The task of increasing the number of training situations as one of the areas for improving the ergatic software and hardware systems “Aviation simulator”

Currently, the ergatic software and hardware complex, called the “flight simulator”, is used worldwide for professional training of crew members in piloting an aircraft in special flight conditions. Flight and integrated flight simulators include a visual environment simulator that synthesizes for a pilot a three-dimensional image of the external environment behind the simulator’s cabin, which allows pilots to be trained in visual landing on a runway model, while solving aeronautical problems. Simulators of the visual environment developed earlier could not synthesize recognizable areas of the area more than 400 × 400 km in size necessary for training in solving problems of self-driving. Therefore, simulators for the training of navigators were separately developed, teaching the determination of the location of the model of an aircraft in the model of the environment according to the models of radio engineering means of aircraft. Modern optical-technical-software systems for the synthesis of three-dimensional models of the external environment allow us to develop new and modernize existing flight and complex flight simulators by adding training to the crew of the aircraft in solving problems of aircraft navigation. The analysis carried out by the authors of this article showed that for this it is necessary to solve the problem of selecting objects that should become benchmarks and their placement according to the model of a large area. Solutions are proposed that allow us to solve the tasks and develop a model of a recognizable piece of the earth’s surface that is sufficient to solve the problems of piloting and self-driving training on an aircraft simulator.

An Investigation into Neighbouring Search Techniques in Meshfree Particle Methods: An Evaluation of the Neighbour Lists and the Direct Search

Meshfree particle methods are being increasingly employed in solving problems in automotive, aeronautics and oil industries, environmental and geophysical problems, biomechanics and medicine, hydraulic erosion, sediment transport, physics and astronomy, among other areas. Regardless of the application of the particle method, the search for neighbour particles must be done at each numerical iteration (especially in dynamic cases). In 2-D studies, the neighbour lists (linked and Verlet) are techniques commonly used in simulations. This paper presents an investigation of the computational efficiency of the linked list technique through comparison with results of simulations of the direct search (the simplest neighbour search technique). Different numbers of particles and interpolation functions have been used in the tests. By using a simple matrix in the storage of neighbour particles, an improvement in the computational efficiency (in comparison with the direct search’s time processing) has not been seen when the linked list algorithm has been utilised. A similar performance between linked list and direct search has been achieved when the neighbour particles have been stored in pairs (even though the cell-linked list has been updated at each numerical iteration). From the analyses of the CPU processing times found in the problems simulated in this work, in which the efficiency of the linked list was only similar to the direct search, it was concluded that is necessary the implementation of a optimisation technique for computational time saving. The Verlet list is a linked list optimisation proposal in which the neighbour list is not update at each numerical iteration. Through an appropriate choice of the cutoff radius, it is ensured that there is no loss in accuracy in the location of neighbouring particles. Optimisation attempts using the Verlet list have been performed but the improvement in the computational efficiency are not satisfactory in all cases.

A new Nash optimization method based on alternate elitist information exchange for multi-objective aerodynamic shape design

Traditionally, it is considered that Nash equilibrium is based on the symmetric elitist information exchange. This paper presents a new Nash optimization method based on alternate elitist information exchange, it makes the information exchange and decision-making more convenient. Moreover, the subsequent decision-making can get the reward from the decision of the previous one, so the new method is more flexible in numerical implementation than that of the traditional symmetric elitist information exchanged algorithm. The equivalence of the solution of the new algorithm with the Nash optimization problem is proved in the paper. Then it is combined with evolutionary algorithms and/or adjoint methods to solve not only unconstrained but also constrained multi-objective optimization problems in aerodynamics. Numerical results show the potential efficiency and flexibility of new algorithms in solving complex multi-objective/disciplinary optimization problems in aeronautics.

Pitot sensor air flow measurement accuracy: Causal modelling and failure risk analysis

Industrial sensors efficiency is commonly determined by the ability to provide accurate indications during a mission. In addition, several techniques and methods are incorporated to increase sensors measurement accuracy. These examinations are classified into experimental and theoretical classes. Experimental examinations focus on determining the flow coefficient variation, which results from the installation effect and flow characteristics. Theoretical proposals deal principally with formulation of the instrument reliability function. These formulations integrate different parameters which affect the sensor measurement accuracy during a given mission. This paper discusses the failure risk and effect analysis for the Pitot sensors system measurement accuracy during a given mission. In addition, a set of factors is used to determine the causal diagram and to model the corresponding hazard function. These factors are subject to statistical analysis in the second part of this paper. The current study is also driven by a practical need to well manage aeronautical problems linked to Pitot sensors system malfunctioning during a flight.

Numerical Techniques For Future Applications In Termo-Fluid-Dinamic Projects Of VHTGR Reactors: Viscous Case

The present work consisted in solving the Navier-Stokes equations, in conservative and structured forms, in the two-dimensional space, employing a finite difference formulation for spatial discretization. It was implemented the Jameson and Mavriplis algorithm to perform the numerical experiments, as well the isotropic scalar linear and nonlinear models of Pulliam, aiming to provide numerical stability to the algorithm. The Backward Euler method for explicit marching in time was also implemented to accelerate the convergence process. The physical problem of subsonic internal flow to a rectangular channel with obstacle configuration was studied. A spatially variable time step is employed aiming to accelerate the convergence to the steady state solution. The main objective was to implement computational tools to the future application in the nuclear sector of numerical techniques widely applied in aeronautical problems, due to the common employed governing equations of the fluid motion, for preliminary studies of density, velocity, pressure, Mach number and energy contours to the flow of gas helium coolant present in the core of the Very High Temperature Gas-cooled Reactor, the VHTGR. A study involving the algorithm's characteristics in relation to the overall quality of the solution is also accomplished. After the simulations, it was found good behavior of Jameson and Mavriplis algorithm, as well as satisfactory performance of the nonlinear Pulliam operator in scheme convergence, showing the nonlinear model as providing better treatment to the numerical solutions obtained.

Simultaneous Optimization: Sectorization and Congolese Air Traffic Assignment by the Method of Preferential Reference of Dominance

Air controllers encounter aeronautical problems everyday. Those problems complexity is growing as the latter problems emerge in aerial navigations sectors at the time of the air traffic assignment. As a long time as the number of aircraft in a sector is high, the controller-related load will increase in a nonlinear way. Currently, one counts, on the congolese territory, and especially in the vicinity of areas with wars, many planes movements. This would represent in a near future a difficult bulk of control for controllers. In order to avoid saturation in sectors, the congolese airspace must be divided in increasingly small sectors while distributing the workloads. To clarify the analysis, one is interested in the multicriteria optimization which deals with the case of the simultaneous presence of several objectives by the preferential reference of dominance method proposed by Joseph Okitonyumbe and Berthold Ulungu (2014). The latter method is based on a new characterization of the efficient solutions by building the probable assignments in order to minimize the load of control in the sector.

Ship underwater noise assessment by the acoustic analogy. Part I: nonlinear analysis of a marine propeller in a uniform flow

The aim of this work is to analyze the hydroacoustic behavior of a marine propeller through the acoustic analogy and to test the versatility and effectiveness of this approach in dealing with the many (and relatively unexplored) issues concerning the underwater noise and its numerical prediction. In particular, a propeller in a noncavitating open water condition is examined here by coupling a Reynolds averaged Navier–Stokes hydrodynamic solver to a hydroacoustic code implementing different resolution forms of the Ffowcs Williams–Hawkings (FWH) equation. The numerical results suggest that unlike the analogous aeronautical problem, where the role played by the nonlinear quadrupole sources is known to be relevant just at high transonic or supersonic regime, the pressure field underwater seems to be significantly affected by the flow nonlinearities, while the contribution from the linear terms (the thickness and loading noise components) is dominant only in a spatially very limited region. Then, contrary to popular belief and regardless of the low blade rotational speed, a reliable hydroacoustic analysis of a marine propeller cannot put aside the contribution of the nonlinear noise sources represented by the turbulence and vorticity three-dimensional fields and requires the computation of the FWH quadrupole source terms.

Optimal design of tonal noise control inside smart-stiffened cylindrical shells

This paper deals with the abatement of noise inside cylindrical cavities bounded by stiffened shells that are impinged by external tonal sound waves. The problem is analysed in a multidisciplinary context, involving interactions among exterior noise field, elastic shell dynamics, interior acoustics and control system. The actuation in the noise control process is performed through piezoelectric patches embedded in the stiffened shell, driven by a control law obtained from an optimal LQR cyclic control formulation, coupled with a genetic optimization algorithm (GA). A modal approach is applied to describe the smart shell dynamics and the interior acoustics that are coupled in the acoustoelastic plant model, while the exterior acoustic scattering is predicted through a boundary element method formulation. Numerical results deal with an aeronautical problem concerning a general aviation aircraft cabin impinged by the pressure disturbances emitted by a pair of propellers; in particular, the effectiveness and robustness of the active control law synthesized through the GA is investigated.

외부 유동 해석에 대한 오픈 소스 코드, OpenFOAM의 검증

This paper aims to verify the applicability of OpenFOAM, the widely recognized open source CFD code, to external flows commonly found in aeronautical problems. To this end, several representative flow cases are selected first from subsonic to supersonic flow fields. Then, the computational results obtained from OpenFOAM are systematically compared against available data from experiments and other numerical codes. It was found that the strength and location of shock are well predicted and the effects of boundary conditions on the computed results are reviewed. Subsonic flow with massive separation is selected to validate the prediction capability of OpenFOAM. Based on the current results, the limitation and possibility of OpenFOAM was confirmed and for future study using OpenFOAM was suggested.

Reduction environmental effects of civil aircraft through multi-objective flight plan optimisation

With rising environmental alarm, the reduction of critical aircraft emissions including carbon dioxides (CO2) and nitrogen oxides (NOx) is one of most important aeronautical problems. There can be many possible attempts to solve such problem by designing new wing/aircraft shape, new efficient engine, etc. The paper rather provides a set of acceptable flight plans as a first step besides replacing current aircrafts. The paper investigates a green aircraft design optimisation in terms of aircraft range, mission fuel weight (CO2) and NOx using advanced Evolutionary Algorithms coupled to flight optimisation system software. Two multi-objective design optimisations are conducted to find the best set of flight plans for current aircrafts considering discretised altitude and Mach numbers without designing aircraft shape and engine types. The objectives of first optimisation are to maximise range of aircraft while minimising NOx with constant mission fuel weight. The second optimisation considers minimisation of mission fuel weight and NOx with fixed aircraft range. Numerical results show that the method is able to capture a set of useful trade-offs that reduce NOx and CO2 (minimum mission fuel weight).

Hans Wolfgang Liepmann

Hans Wolfgang Liepmann

Numerical and analytical models for high speed train pantograph radiated noise prediction

The present work deals with the development and comparison of an analytical and numerical models for the evaluation of the noise radiated from a pantograph of an high speed train. Under the numerical point of view, a simplified model has been developed for the pantograph; the model that substructures the problem approaching a complex structure as a combination of simple components, has been derived from a similar aeronautical problem (landing gear noise) but has been self‐modified to adapt the formulation to the specific problem. The output of the model is the radiated noise level and spectra as a function of the pantograph speed. The CFD numerical model has been developed for the pantograph based upon a commercial code; only the upper part of the system has been herein simulated because it was addressed as the main noise source during previous laboratory acoustic tests. As an output of the model, the radiated noise has been derived with special reference to two main speed to which experimental data could be referred. Analytical and numerical results will be within the paper discussed and compared to highlight the single approach's advantage and drawbacks. At the and of the paper, some line experimental results will be also introduced and discussed.

Comparison between a centered and a flux difference split schemes using unstructured strategy

Products developed at industries, institutes and research centers are expected to have high level of quality and performance, having a minimum waste, which require efficient and robust tools to numerically simulate stringent project conditions with great reliability. In this context, Computational Fluid Dynamics (CFD) plays an important role and the present work shows two numerical algorithms that are used in the CFD community to solve the Euler equations applied to typical aerospace and aeronautical problems. Particularly, unstructured discretization of the spatial domain has gained special attention by the international community due to its ease in discretizing complex spatial domains. This work has the main objective of illustrating some advantages and disadvantages of a centered algorithm and an upwind one using an unstructured spatial discretization of the flow governing equations. Numerical methods include a finite volume formulation and the Euler equations are applied to solve a supersonic flow over a ramp problem, a hypersonic flow over a blunt body problem, a hypersonic flow over a double ellipsoid problem and a supersonic flow over a simplified configuration of VLS problem. Convergence acceleration is obtained using a spatially variable time stepping procedure.

Inexact information aided, low‐cost, distributed genetic algorithms for aerodynamic shape optimization

AbstractDespite its robustness, the design and optimization of aerodynamic shapes using genetic algorithms suffers from high computing cost requirements, due to excessive calls to Computational Fluid Dynamics tools for the evaluation of candidate solutions. To alleviate this problem, either the use of distributed genetic algorithms or the implementation of surrogate evaluation models have separately been proposed in the past. A distributed genetic algorithm relies on the handling of population subsets that evolve in a semi‐isolated manner by regularly exchanging their best individuals. It is known that distributed schemes generally outperform single‐population ones. On the other hand, the implementation of less costly surrogate evaluation tools, such as the autocatalytic radial basis function networks developed by the authors for the purpose of getting rid of most of the ‘useless’ exact evaluations, reduces considerably the computational cost. The aim of the present paper is to employ a surrogate evaluation model in the context of a distributed genetic algorithm and to demonstrate that the combination of both results in maximum economy in CPU cost. In addition, whenever a multiprocessor system is available, the gain is much more pronounced, since the new optimization method maximizes parallel efficiency. The proposed method is used to solve inverse design and optimization problems in aeronautics and turbomachinery. Copyright © 2003 John Wiley & Sons, Ltd.

Solution of aerospace problems using structured and unstructured strategies

Products developed at industries, institutes and research centers are expected to have high level of quality and performance, having a minimum waste, which require efficient and robust tools to numerically simulate stringent project conditions with great reliability. In this context, Computational Fluid Dynamics (CFD) plays an important role and the present work shows two numerical algorithms that are used in the CFD community to solve the Euler and Navier-Stokes equations applied to typical aerospace and aeronautical problems. Particularly, unstructured discretization of the spatial domain has gained special attention by the international community due to its ease in discretizing complex spatial domains. This work has the main objective of illustrating some advantages and disadvantages of numerical algorithms using structured and unstructured spatial discretization of the flow governing equations. Numerical methods include a finite volume formulation and the Euler and Navier-Stokes equations are applied to solve a transonic nozzle problem, a low supersonic airfoil problem and a hypersonic inlet problem. In a structured context, these problems are solved using MacCormack’s implicit algorithm with Steger and Warming’s flux vector splitting technique, while, in an unstructured context, Jameson and Mavriplis’ explicit algorithm is used. Convergence acceleration is obtained using a spatially variable time stepping procedure.

Optimization of Time Saving in Navigation Through an Area of Variable Flow

In planning routes between well-defined points of departure and arrival, both aircraft and ships can take into account forecast values of certain geophysical parameters so that the route chosen is in some sense optimized. For aircraft flying the North Atlantic, the methods used are described in the papers by Attwooll, Bennett, and Monk (all 1982). There have been a number of papers on ship-routeing; they were reviewed by Motte and Calvert (1988). It should be noted that whereas for aircraft the dominant consideration is the wind (for which the maritime equivalent is the current), ship-routeing on the trans-oceanic scale is dominated by considerations of waves. However, on smaller scales, currents can be the dominant consideration: for example, see the paper by Fales (1991). That paper does not make use of the basic theory that was applied to the aeronautical problem in the 1940s. Although the work reported here is orientated to aeronautical applications, it clearly has ramifications for certain maritime problems.

Real Flow Limitations in Supersonic Airplane Design

Real Flow Limitations in Supersonic Airplane Design