Aircraft Modeling and Simulation

Various aerodynamics, structural dynamics, and control design and experimental studies are presented with the aim of advancing green and morphing aircraft research. The results obtained with an in-house CFD code are compared and validated with those of two NASA codes. The aerodynamical model of the UAS-S45 morphing wing as well as the structural model of a morphing winglet are presented. A new design methodology for oleo-pneumatic landing gear drop impact dynamics is presented as well as its experimental validation. The design of a nonlinear dynamic inversion (NDI)-based disturbance rejection control on a tailless aircraft is presented, including its validation using wind tunnel tests

On a Cartesian cut-cell methodology for simulating atmospheric ice accretion on aircraft

Atmospheric in-flight ice accretion has been a significant operational hazard in aviation for decades. Super-cooled water droplets impinge on exposed surfaces such as wings and rotor blades. These droplets may freeze on the surface thereby changing lift characteristics and disturb weight and aerodynamic balances. The multiple length scales involved prevent designing dynamically similar flows making traditional aeronautical engineering tools such as wind tunnel experiments not suitable. Therefore, computational fluid dynamics (CFD) methods have proved an attractive alternative to study atmospheric icing effects. However, most approaches are based on simple incompressible models and are only suited for small ice heights due to the difficulty of dynamically tracking the ice accretion. This thesis aims to develop novel mathematical models to capture more relevant phenomena and to improve the numerical methods to allow dynamic tracking of the air-ice interface. The initial chapter presents an augmented air and droplet model which tracks droplet temperatures thereby producing more accurate heat fluxes for the phase transition calculation. Firstly, we validate our novel model for common ice accretion test cases and find excellent agreement with literature. The advantage of the augmented system is demonstrated by applying it to an experimental setup that studies the heat exchange between water droplets and air for various flow conditions. We find excellent agreement between our model and the experiment for all presented cases whereas constant-temperature approaches match only for short interaction times. Finally, we apply the new system to study the droplet temperatures around various aerofoil and find significant temperature differences compared with conventional models. The following chapter studies the freezing process on the wing geometry. Presently, the most advanced model is based on lubrication theory, however, linear terms are truncated. We extend the series expansion to include first order terms and demonstrate that the additional order is necessary to accurately capture the thin film flow on a cylinder. Furthermore, we extend the lubrication-theory- based approach which was limited to simple geometries. The extended model is valid on arbitrary wing shapes making it more relevant for engineers studying real-world problems. The penultimate chapter combines the previous two to give a simulation of the full icing process. We integrate it with a Cartesian cut-cell method which can cope dynamically with moving interfaces. The robustness and performance of the cut-cell techniques allow us to simulate ice growth on real-world geometries. We demonstrate this capability by presenting results of the dynamic ice growth on a NACA 0012 aerofoil - making this the first such numerical experiment.EPSR

New strategies for the aerodynamic design optimization of aeronautical configurations through soft-computing techniques

Premio Extraordinario de Doctorado de la UAH en 2013Lozano Rodríguez, Carlos, codir.This thesis deals with the improvement of the optimization process in the aerodynamic design of aeronautical configurations. Nowadays, this topic is of great importance in order to allow the European aeronautical industry to reduce their development and operational costs, decrease the time-to-market for new aircraft, improve the quality of their products and therefore maintain their competitiveness. Within this thesis, a study of the state-of-the-art of the aerodynamic optimization tools has been performed, and several contributions have been proposed at different levels: -One of the main drawbacks for an industrial application of aerodynamic optimization tools is the huge requirement of computational resources, in particular, for complex optimization problems, current methodological approaches would need more than a year to obtain an optimized aircraft. For this reason, one proposed contribution of this work is focused on reducing the computational cost by the use of different techniques as surrogate modelling, control theory, as well as other more software-related techniques as code optimization and proper domain parallelization, all with the goal of decreasing the cost of the aerodynamic design process. -Other contribution is related to the consideration of the design process as a global optimization problem, and, more specifically, the use of evolutionary algorithms (EAs) to perform a preliminary broad exploration of the design space, due to their ability to obtain global optima. Regarding this, EAs have been hybridized with metamodels (or surrogate models), in order to substitute expensive CFD simulations. In this thesis, an innovative approach for the global aerodynamic optimization of aeronautical configurations is proposed, consisting of an Evolutionary Programming algorithm hybridized with a Support Vector regression algorithm (SVMr) as a metamodel. Specific issues as precision, dataset training size, geometry parameterization sensitivity and techniques for design of experiments are discussed and the potential of the proposed approach to achieve innovative shapes that would not be achieved with traditional methods is assessed. -Then, after a broad exploration of the design space, the optimization process is continued with local gradient-based optimization techniques for a finer improvement of the geometry. Here, an automated optimization framework is presented to address aerodynamic shape design problems. Key aspects of this framework include the use of the adjoint methodology to make the computational requirements independent of the number of design variables, and Computer Aided Design (CAD)-based shape parameterization, which uses the flexibility of Non-Uniform Rational B-Splines (NURBS) to handle complex configurations. The mentioned approach is applied to the optimization of several test cases and the improvements of the proposed strategy and its ability to achieve efficient shapes will complete this study

New strategies for the aerodynamic design optimization of aeronautical configurations through soft-computing techniques

Premio Extraordinario de Doctorado de la UAH en 2013Lozano Rodríguez, Carlos, codir.This thesis deals with the improvement of the optimization process in the aerodynamic design of aeronautical configurations. Nowadays, this topic is of great importance in order to allow the European aeronautical industry to reduce their development and operational costs, decrease the time-to-market for new aircraft, improve the quality of their products and therefore maintain their competitiveness. Within this thesis, a study of the state-of-the-art of the aerodynamic optimization tools has been performed, and several contributions have been proposed at different levels: -One of the main drawbacks for an industrial application of aerodynamic optimization tools is the huge requirement of computational resources, in particular, for complex optimization problems, current methodological approaches would need more than a year to obtain an optimized aircraft. For this reason, one proposed contribution of this work is focused on reducing the computational cost by the use of different techniques as surrogate modelling, control theory, as well as other more software-related techniques as code optimization and proper domain parallelization, all with the goal of decreasing the cost of the aerodynamic design process. -Other contribution is related to the consideration of the design process as a global optimization problem, and, more specifically, the use of evolutionary algorithms (EAs) to perform a preliminary broad exploration of the design space, due to their ability to obtain global optima. Regarding this, EAs have been hybridized with metamodels (or surrogate models), in order to substitute expensive CFD simulations. In this thesis, an innovative approach for the global aerodynamic optimization of aeronautical configurations is proposed, consisting of an Evolutionary Programming algorithm hybridized with a Support Vector regression algorithm (SVMr) as a metamodel. Specific issues as precision, dataset training size, geometry parameterization sensitivity and techniques for design of experiments are discussed and the potential of the proposed approach to achieve innovative shapes that would not be achieved with traditional methods is assessed. -Then, after a broad exploration of the design space, the optimization process is continued with local gradient-based optimization techniques for a finer improvement of the geometry. Here, an automated optimization framework is presented to address aerodynamic shape design problems. Key aspects of this framework include the use of the adjoint methodology to make the computational requirements independent of the number of design variables, and Computer Aided Design (CAD)-based shape parameterization, which uses the flexibility of Non-Uniform Rational B-Splines (NURBS) to handle complex configurations. The mentioned approach is applied to the optimization of several test cases and the improvements of the proposed strategy and its ability to achieve efficient shapes will complete this study

Investigation of thermal loads onto a cooled strut injector inside a scramjet combustion chamber

For future aviation or space transportation systems, scramjets could provide a complement or even an alternative to conventional propulsion systems. However, due to the high-enthalpy flow environment, scramjet development still implies considerable technical challenges. One of the most relevant issues is the need for an efficient fuel injection and mixing system. It has to guarantee a stable and reliable combustion process, as the flow residence time inside the engine is only in the order of several milliseconds. Strut-based injection systems have proven to be a suitable choice due to their ability to provide fuel directly into the center of the flow. In contrast to wall-based injection systems, however, struts are exposed to the complete aerodynamic heat loads of the flow, which necessitates active cooling to avoid structural damages. As experimental facilities are hardly able to reproduce flight conditions over a long period of time, a numerical approach is inevitable to assess the heat loads onto a strut and to evaluate the internal cooling mechanism. Within the present thesis, a numerical solver for the conjugate simulation of heat transfer in supersonic flows was developed and integrated into the OpenFOAM software package. A thorough validation for a variety of data from both literature and in-house studies was conducted. The accurate prediction of different phenomena relevant for supersonic flows could be verified. The solver was then applied to the evaluation of an internally cooled strut injector. In a first step, the injector was investigated at moderate flow temperatures. Experimental data for different flow temperatures and coolants was obtained using infrared thermography of the injector surface. A comparison to numerical simulations led to the identification of characteristic well and poorly cooled zones along the injector surface, which could be explained by features of either the external or the internal flow field. Finally, the lobed strut injector was studied numerically at hot gas conditions representative for the ITLR model combustor, where no experimental data of the surface is available. Besides the leading edge, a second hot zone was identified towards the trailing edge of the strut, which was attributed to the impact of the reflected leading edge shock wave onto the surface. Activation of internal air cooling was found to lower the general temperature level, but to have only a small effect on the leading edge. Instead, heat conduction towards the cooled combustor side walls provided a considerable part of the cooling in this area. Switching to hydrogen as coolant led to a further reduction of the injector temperature at a considerably lower coolant mass flux, without changing the overall characteristics of the cooled injector. Changing to more realistic, hotter combustor side walls for a hydrogen-cooled strut caused a generally higher injector surface temperature. While the hottest injector regions were found to be near the side walls, the leading edge could still be partially cooled by the internal hydrogen flow

Rotary Wing Aerodynamics

This book contains state-of-the-art experimental and numerical studies showing the most recent advancements in the field of rotary wing aerodynamics and aeroelasticity, with particular application to the rotorcraft and wind energy research fields