Uncertainty quantification of leakages in a multistage simulation and comparison with experiments

The present paper presents a numerical study of the impact of tip gap uncertainties in a multistage turbine. It is well known that the rotor gap can change the gas turbine efficiency but the impact of the random variation of the clearance height has not been investigated before. In this paper the radial seals clearance of a datum shroud geometry, representative of steam turbine industrial practice, was systematically varied and numerically tested. By using a Non-Intrusive Uncertainty Quantification simulation based on a Sparse Arbitrary Moment Based Approach, it is possible to predict the radial distribution of uncertainty in stagnation pressure and yaw angle at the exit of the turbine blades. This work shows that the impact of gap uncertainties propagates radially from the tip towards the hub of the turbine and the complete span is affected by a variation of the rotor tip gap. This amplification of the uncertainty is mainly due to the low aspect ratio of the turbine and a similar behavior is expected in high pressure turbines

The Economic Growth Debate - Geography versus Institutions: Is There Anything Really New?

International analysis of economic growth has confirmed the theoretical assumption that international variations in per capita income can to a large extent be explained by differences in the accumulation of capital and human capital and by differing rates of technological progress. However, these results do not provide an answer to the question as to what causes trans-national variations in accumulation rates and technological progress. In searching for the ultimate drivers of economic growth, three competing lines of explanation have emerged: ? The geography-hypothesis which assumes that economic growth is ultimately determined by geographical characteristics ? The institutions-hypothesis which views the quality of institutions as a fundamental driver of growth ? The policy-hypothesis which emphasises the importance of economic policy This paper provides an overview over these three hypotheses and revisits the debate over their empirical relevance. Comparing the three approaches leads to the conclusion that none of them is really new and that many of their findings have already been incorporated into the strategies for international development assistance. Furthermore, the three hypotheses are not as exclusive as the debate on geography versus institutions would suggest but are indeed interconnected and complementary. --

Ausländische Direktinvestitionen in Entwicklungsländern: Eine überschätzte Wachstumsdeterminante?

Ziel dieses Beitrags ist es, eine unvoreingenommene und systematische Überprüfung der Wachstumswirkungen ausländischer Direktinvestitionen in Entwicklungsländern vorzunehmen. Zu diesem Zweck werden zunächst die theoretischen Wirkungskanäle dargestellt, über die Direktinvestitionen auf das Wirtschaftswachstum Einfluss nehmen. Anschließend wird eine Auswertung der verfügbaren empirischen Studien vorgenommen und in einer eigenen empirischen Untersuchung der Gesamteinfluss von FDI auf das Wirtschaftswachstum ermittelt. Dazu wird eine Paneldatenuntersuchung auf Makroebene durchgeführt, die einem Ansatz von Borensztein, de Gregorio und Lee (1998) folgt und diesen um die Betrachtung verschiedener Ländergruppen erweitert. --

Assessment of inhibited alveolar-capillary membrane structural development and function in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of extreme prematurity and is defined clinically by dependence on supplemental oxygen due to impaired gas exchange. Optimal gas exchange is dependent on the development of a sufficient surface area for diffusion. In the mammalian lung, rapid acquisition of distal lung surface area is accomplished in neonatal and early adult life by means of vascularization and secondary septation of distal lung airspaces. Extreme preterm birth interrupts secondary septation and pulmonary capillary development and ultimately reduces the efficiency of the alveolar-capillary membrane. Although pulmonary health in BPD infants rapidly improves over the first few years, persistent alveolar-capillary membrane dysfunction continues into adolescence and adulthood. Preventative therapies have been largely ineffective, and therapies aimed at promoting normal development of the air-blood barrier in infants with established BPD remain largely unexplored. The purpose of this review will be: (1) to summarize the histological evidence of aberrant alveolar-capillary membrane development associated with extreme preterm birth and BPD, (2) to review the clinical evidence assessing the long-term impact of BPD on alveolar-capillary membrane function, and (3) to discuss the need to develop and incorporate direct measurements of functional gas exchange into clinically relevant animal models of inhibited alveolar development

SAMBA: Sparse Approximation of Moment-Based Arbitrary Polynomial Chaos

A new arbitrary Polynomial Chaos (aPC) method is presented for moderately high-dimensional problems characterised by limited input data availability. The proposed methodology improves the algorithm of aPC and extends the method, that was previously only introduced as tensor product expansion, to moderately high-dimensional stochastic problems. The fundamental idea of aPC is to use the statistical moments of the input random variables to develop the polynomial chaos expansion. This approach provides the possibility to propagate continuous or discrete probability density functions and also histograms (data sets) as long as their moments exist, are finite and the determinant of the moment matrix is strictly positive. For cases with limited data availability, this approach avoids bias and fitting errors caused by wrong assumptions. In this work, an alternative way to calculate the aPC is suggested, which provides the optimal polynomials, Gaussian quadrature collocation points and weights from the moments using only a handful of matrix operations on the Hankel matrix of moments. It can therefore be implemented without requiring prior knowledge about statistical data analysis or a detailed understanding of the mathematics of polynomial chaos expansions. The extension to more input variables suggested in this work, is an anisotropic and adaptive version of Smolyak's algorithm that is solely based on the moments of the input probability distributions. It is referred to as SAMBA (PC), which is short for Sparse Approximation of Moment-Based Arbitrary Polynomial Chaos. It is illustrated that for moderately high-dimensional problems (up to 20 different input variables or histograms) SAMBA can significantly simplify the calculation of sparse Gaussian quadrature rules. SAMBA's efficiency for multivariate functions with regard to data availability is further demonstrated by analysing higher order convergence and accuracy for a set of nonlinear test functions with 2, 5 and 10 different input distributions or histograms

Der Beitrag der Geography vs. Institutions-Debatte zur Erklärung von Good oder Bad Governance

In den letzten Jahren haben sich im Bereich der Entwicklungsökonomie zwei Debatten entwickelt, die im folgenden Beitrag verknüpft werden sollen. Zum einen wird im Rahmen der Geography vs. Institutions Debatte darüber diskutiert, in welchem Ausmaß geographische oder institutionelle Charakteristika fundamentale Entwicklungsursachen darstellen können, zum anderen hat die Diskussion um Good und Bad Governance die Bedeutung der Regierungsführung für den Entwicklungsprozess deutlich gemacht. Dieser Beitrag analysiert, inwieweit die Erkenntnisse der Geography vs Institutions Debatte zur Erklärung von Governance-Strukturen herangezogen werden können. Die Analyse erfolgt an Hand eines einfachen Entscheidungsmodells, mit dem der Einfluss verschiedener geographischer und institutioneller Faktoren auf das Verhalten von Politikern untersucht werden kann. Eine anschließende empirische Überprüfung der gewonnenen Hypothesen zeigt zwar, dass geographische Charakteristika offenbar tatsächlich zur Erklärung der Governance-Qualität beitragen können. Diese Ergebnisse müssen jedoch auf Grund von Unzulänglichkeiten bei der Messung der Governance-Qualität mit äußerster Vorsicht interpretiert werden. --

Uncertainty quantification for fat-tailed probability distributions in aircraft engine simulations

Rare event simulation is vital for industrial design because some events, so-called black swans, can have fatal consequences despite their low probability of occurrence. Finding low-probability events far off the mean design is a challenging task for realistic engineering models because they are characterized by high computational demands, many input variables, and often insufficient statistical information to build parametric probability distributions. Therefore, an adaptive and arbitrary polynomial chaos method, called sparse approximation of moment-based arbitrary polynomial chaos, is suggested in this work. Sparse approximation of moment-based arbitrary polynomial chaos creates custom polynomial basis functions and grids based on statistical moments to avoid incorrect statistical assumptions. The contribution of this work is that it is derived how rare event simulation can conveniently be integrated into adaptive sparse grid methods by calculating polynomial chaos expansions based on the statistical moments of truncated fat-tailed distributions. Moreover, the use of tempered alpha-stable distributions is suggested to avoid discontinuous tail cutoffs. Sparse approximation of moment-based arbitrary polynomial chaos is compared to other statistical methods in two industrial aircraft engine simulations: a simulation of transient cycle temperature in a turbine cavity and hot-gas ingestion in the interwheel region. In both cases, sparse approximation of moment-based arbitrary polynomial chaos agrees with previous results but obtains them with lower computational effort

Stochastic Variation of the Aero-Thermal Flow Field in a Cooled High-Pressure Transonic Vane Configuration

In transonic high-pressure turbine stages, oblique shocks originated from vane trailing edges impact the rear suction side of each adjacent vane. High-pressure vanes are usually cooled to tolerate the combustor exit temperature levels, which would reduce dramatically the residual life of a solid vane. Then, it is highly probable that shock impingement will occur in proximity of one of the coolant rows. It has already been observed that the presence of an adverse pressure gradient generates non-negligible effects on heat load due to the increase in boundary layer thickness and turbulence level, with a detrimental impact on the local adiabatic effectiveness values. Furthermore, the generation of a tornado-like vortex has been recently observed that could further decrease the efficacy of the cooling system by moving cold flow far from the vane wall. It must be also underlined that manufacturing deviations and in-service degradation are responsible for the stochastic variation of geometrical parameters. This latter phenomenon greatly alters the unsteady location of the shock impingement and the time-dependent thermal load on the vane. Present work starts from what is shown in literature and provides a highly-detailed description of the aero-thermal field that occurs on a model that represents the flow conditions occurring on the rear suction side of a cooled vane. The numerical model is initially validated against the experimental data obtained by the University of Karlsruhe during TATEF2 EU project, and then an uncertainty quantification methodology based on the probabilistic collocation method and on Padè's polynomials is used to consider the probability distribution of the geometrical parameters. The choice of aleatory unknowns allows to consider the mutual effects between shock-waves, trailing edge thickness and hole diameter. Turbulence is modelled by using the Reynolds Stress Model already implemented in ANSYS® Fluent®. Special attention is paid to the description of the flow field in the shock/boundary layer interaction region, where the presence of a secondary effects will completely change the local adiabatic effectiveness values