The present work focuses on the prediction of pollutant emissions in gas turbine engines by means of a reactor network considering chemical kinetics. The network was developed based on the CFM56 -7B27/B1F aviation engine, calibrated with the pollutant emission data (EINOx, EICO and EIHC) provided by ICAO at maximum power and compared to other operating conditions. A study of local species formation in every reactor was carried out to analyze the differences and similarities between the model and experimental data.

El presente trabajo se centra la predicción emisiones contaminantes en motores turbina de gas. Para ello, se ha desarrollado una red de reactores químicos, en la que cada reactor modela el comportamiento de cada zona de la cámara de combustión en 0D/1

The analysis of the risk from re-entry objects has become an important topic. Concerning the uncertainties and different flow regimes, the object-oriented tools have been developed and used for various re-entry mission scenarios because of the simplified computation process and low calculation burden, which allow a probabilistic analysis. In this study, the heat flux correlations that are used in the object-oriented tools are investigated and compared to better understand the heat flux predictions with respect to re-entry survivability. Often these tools calculate the continuum stagnation-point heat flux using the correlation formulae of Lees and Fay–Riddell, which usually assume local thermo-chemical equilibrium with a fully-catalytic wall condition in the shock layer. Based on this observation, heat flux measurements were conducted in a hypersonic wind tunnel, and validated with the theory of Fay–Riddell considering the equivalent velocity gradient. For the comparison, in total, 11 different heat flux correlations were examined. It is shown that, based on the formula of Fay–Riddell, the differences in the final integrated heat flux were less than 16% which led to a large discrepancy in the survivability estimations for the cases of small spheres made of aluminum. This shows the importance of considering the heat flux correlation as well as the velocity gradient effect for such re-entry analysis.

Space debris that re-enter the Earth's atmosphere can be partially or fully ablated along the trajectory path after hitting the atmosphere layers, once these become denser (approximately below 82 km). This paper combines reentry survival analysis to by-product generation analyses according to specific trajectory analysis and different levels of modelling within the re-entry simulation tool. Particular attention is made on metallic alloy decomposition and metallic oxides formation from the debris' materials ablation. Generic alloys present within satellite constructions are considered. The flow field in the induced shock layer is considered to be in non-equilibrium and the trajectory tool is based on a 3DOF object-oriented approach. The by-product analyses give important information on emitted species in the atmosphere at different altitudes, and the risk of substances reaching the ground is evaluated as a function of the initial break-up altitude. The non-equilibrium atmospheric chemistry within the shock layer has a significant impact for the re-entry analysis.

The concern caused by the rising population of space debris has increased. One of the recommended mitigation measures is the safe re-entry disposal either in a controlled or uncontrolled manner. Performing a controlled re-entry, where the spacecraft is guided down to impact in a designated zone such as the ocean or a non-populated area, complies with the mitigation standards. However, it has limitations in terms of the cost of developing and ensuring reliability of a system. Therefore, an uncontrolled re-entry can be preferred as a simpler and cheaper alternative for the disposal of space debris. To reduce the casualty area of the surviving fragments, design-for-demise techniques have been proposed. From the point of view of the design-for-demise techniques, it is significant to identify and investigate the critical components that are directly related to the casualty risk. In this paper, re-entry survivability analysis of critical components has been conducted to identify the most critical ones and to understand the effects of uncertainties on casualty risk. The material properties within elements such as the propellant tanks, balance masses and payloads that can be critical components are crucial parameters. The initial conditions, relative sizes, and aerodynamic forces are also significant. In the view of engineering design, either a change of the material or a mass/size reduction is recommended to demise the components. Monte Carlo simulations are performed to evaluate the sensitivity. (C) 2021 COSPAR. Published by Elsevier B.V.

This study presents calibrated vacuum ultraviolet spectroscopic measurements and filtered cyanogen violet band images for steel, cold graphite, and preheated graphite models at three reentry-relevant conditions in the X2 Expansion Tube. An analysis of these experiments concluded that there were no unique radiating species in the boundary layer of an ablating model within the spectral range of 120-180nm. Spectral measurements showed an increase in atomic carbon emission in the boundary layer with preheated graphite models. Filtered images revealed significant cyanogen emission in the boundary layer of the preheated graphite models. A comparison with spectral measurements concluded that the production of cyanogen in the boundary layer did not reduce the nitrogen line emission relative to the shock layer. The increase in the cyanogen boundary-layer emission relative to the shock-layer emission was found to vary with freestream conditions.

The mechanisms that should be considered for separation flow control applications of nanosecond pulsed dielectric barrier discharge (DBD) actuators were investigated on a NACA 0015 profile for velocities of 10 m / s ( R e = 100,000 ) and 20 m / s ( R e = 200,000 ) in ambient wind tunnel conditions. Near and post-stall angles of attack were considered ( 16 ∘ and 24 ∘ ). The dominant frequencies existing in the flow were measured. Moderate voltage levels were applied (4 and 7 kV ) and the actuator was operated at these identified dominant frequencies and compared with known effective frequencies from literature. In all cases, influences by the actuator on the flow structures were observed and the operation of the actuator at the dominant flow frequencies of a stalled airfoil was shown to give control authority.

The majority of problems in aircraft production and operation require decisions made in the presence of uncertainty. For this reason, aerodynamic designs obtained with traditional deterministic optimization techniques seeking only optimality in a specific set of conditions may have very poor off-design performances or may even be unreliable. In this work, a novel approach for robust and reliability-based design optimization of aerodynamic shapes based on the combination of single-and multi-objective evolutionary algorithms and a continuation multilevel Monte Carlo methodology is presented, to compute objective functions and constraints that involve statistical moments or statistical quantities, such as quantiles, also called value at risk and conditional value at risk, without relying on derivatives and meta-models. Detailed numerical studies are presented for the RAE 2822 transonic airfoil design affected by geometrical and operational uncertainties.

In this chapter, we describe the Continuation Multi-Level Monte Carlo (C-MLMC) algorithm proposed in Collier et al. [1] and apply it to efficiently propagate operating and geometric uncertainties in internal and external aerodynamic simulations. The key idea of MLMC, presented in the previous chapter, is that one can draw MC samples simultaneously and independently on several approximations of the problem under investigation on a hierarchy of nested computational grids (levels). In the continuation algorithm (C-MLMC) the parameters that prescribe the number of levels and simulations per level are computed on the fly to further reduce the overall computational cost.

The effects of phenolic decomposition on shock layer radiation in air were investigated in the X2 expansion tube. By subjecting a carbon phenolic aeroshell to a flow with a velocity of 9.81 km · s, decomposing resin on the model surface was allowed to react with the boundary-layer gases. Emission spectroscopy was used to measure radiation emitted by the gas in parts of the ultraviolet, visible, and near-infrared spectrum and then compared with control measurements taken with a steel model. With the composite model in place, measured spectral radiance was seen to increase for CN violet band radiation but remained unchanged for atomic emissions in the visible and near-infrared spectrum. Recorded data were then compared with spectra produced by two-dimensional axisymmetric computational fluid dynamics simulations parsed to the NEQAIR radiation solver. Both the applied chemistry models overpredicted CN violet Δν = 0 band radiation, but excellent comparison was found for the Δν = +1 band. Good comparisons were also achieved for the O triplet (777 nm) and atomic N line intensities, between 740 and 750 nm. However, peak intensities were underestimated by the numerical simulations in the visible spectrum. Background radiation and broadening of the spectral wings were not accurately accounted for by simulations.

The effects of phenolic decomposition on shock-layer radiation were investigated experimentally in X2 expansion tube for a Venus entry flow. A carbon-phenolic composite aeroshell was subjected to a flow with a flight equivalent velocity of 9.35 km . s(-1) . Emission spectroscopy was used to measure boundary-layer radiation in parts of the ultraviolet (380-480 nm) and visible (620-700 nm) spectrum, and it was compared to control measurements taken with a cold steel model. With the composite model in place, the calibrated spectral radiance measured was seen to increase for the O (645.598 nm) atomic line and the N-2(+) (391.22 nm) band head, but it decreased for the C-2 Swan band (420-480 nm). The recorded data were then compared to numerical spectra produced by two-dimensional axisymmetric computational fluid dynamic simulations coupled to a radiation solver. Both of the applied chemistry models overpredicted CN violet Delta v = 0 band radiation, which demonstrated strong self-absorption at these conditions. Better comparisons were achieved for the C-2 Swan band radiation. At visible wavelengths, peak intensities were underestimated by the numerical simulations. Several possible reasons were hypothesized for these discrepancies.

The present section will focus on the applicability issues of Monte Carlo-based methods, as well as those methods based on sampling techniques. Special focus will be put on the Multi-Level Monte Carlo method and the two implementations developed during the UMRIDA project, namely the Continuous MLMC and MLMC. All named methods have been described in the above sections of this book.

In this chapter, we present a general introduction to Monte Carlo (MC)-based methods, sampling methodologies, stratification methods, and variance reduction techniques. In the first part, we will discuss the theoretical basis and the convergence proprieties of MC methods. The next part is devoted to pseudorandom and quasi-random number generation, the generation of random variables and the application of stratification. It is followed by techniques for correlation and discrepancy control. The third part presents the concept of Latin Hypercube Sampling (LHS). The last part introduces the concept of Multi-Level Monte Carlo (MLMC).

In this chapter, we present a robust optimization approach based on the combination of evolutionary algorithms and the Continuation Multi-Level Monte Carlo (C-MLMC) methodology, presented in Chap. https://doi.org/Continuation Multi-level Monte Carlo , to estimate robust designs, without relying on derivatives and meta-models. We present numerical studies for the 2D RAE-2822 transonic airfoil design affected by operating uncertainties. The performance of a robust optimal designs is compared to the deterministic optimal solutions to underline the improvements in robustness that can be achieved.

Plasma wind tunnel experiments have been performed simulating a Hayabusa reentry trajectory point at 78.8km altitude with a velocity of 11.7km/s corresponding to a local mass-specific enthalpy of 68.4MJ/kg and a stagnation pressure of 2.44kPa. Ablation-radiation coupling is investigated using a carbon preform sample, a lightweight carbon phenolic ablator sample, and cooled copper. Optical emission spectroscopic measurements in the vacuum ultraviolet (VUV) regime (116-197nm) have been conducted through a bore hole in the stagnation point of the different samples. Optical emission spectroscopic measurements in the UV/VIS spectral range (320-810nm) have been conducted viewing the plasma from the side. The stagnation point VUV radiation to the carbon preform sample is strongest, whereas it is weakest for the carbon phenolic sample. In the UV/VIS both carbon-based material samples lead to stronger plasma radiation than copper. Atomic number densities in front of the samples are largest for the carbon preform sample and lowest for the carbon phenolic sample. Rotational and vibrational temperatures are lower for both the carbon-based materials compared with copper. The measurements show for the first time experimentally the radiative heat flux mitigation by carbon phenolic materials.

This work evaluates the changes in radiative properties of two decomposing carbonaceous porous materials, each composed of two semi-transparent, homogeneous and isotropic phases. The understanding of the complex dependence of macroscopic optical behaviour on material microstructure, bulk phase properties and the wavelength of incoming radiation is paramount for modelling, design and optimisation of systems incorporating such media. Experimental and numerical techniques were combined to solve the homogenised radiative transfer equations using Monte Carlo ray tracing in the limit of geometrical optics. Effective radiative properties required by these equations were determined by Monte Carlo techniques using the exact 3D microstructures of the samples, obtained through high-resolution synchrotron computed tomography. This methodology is applied to a medium density carbon phenolic and a high density graphite reinforced polymer composite, each composed of semi-transparent solid and fluid phases. The extent of material decomposition is seen to affect the absorption behaviour of both samples. This effect is more obvious in the lower density carbon phenolic, where an 18% increase in absorptance is observed due to decomposition, compared to an increase of just 2% for the graphite. A library of absorption data is presented for use in continuum heat transfer modelling of similar chemically reacting macroporous carbon composites.

The majority of problems in aircraft production and operation require decisions made in the presence of uncertainty.For this reason aerodynamic designs obtained with traditional deterministic optimization techniques seeking only optimality in a specific set of conditions may have very poor off-design performances or may even be unreliable.In this work we present a novel approach for robust optimization of aerodynamic shapes based on the combination of single and multi-objective Evolutionary Algorithms and a Continuation Multi Level Monte Carlo methodology to estimate robust designs, without relying on derivatives and meta-models.Detailed numerical studies are presented for a transonic airfoil design affected by geometrical and operational uncertainties.

In this work we present an efficient Multi Level Monte Carlo (MLMC) algorithm capable of propagating operational uncertainties, due to atmospheric variability of external aerodynamics flows and geometrical uncertainties due to manufacturing tolerances and fatigue. The technique is tested on the NACA 0012 airfoil in transonic conditions and a two compression ramps hypersonic scramjet intake configuration. The efficiency of the proposed MLMC algorithm in terms of accuracy versus overall computational cost is compared to a standard MC method.