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PrefaceIt is no wonder that Uncertainty Quantification has become more and more of an actuality in the last decade as the modelling capability jointly with computational power has increased a lot. In the past, the capability to predict flow field and performance in aero engines as well as in turbomachinery was of great support to the design. However, the range of errors in such results was so large as to suggest the use of CFD, mainly to understand the direction of trends and improvements more than the exact evaluation of thermo-fluid-dynamic parameters, which could affect performance, reliability and life of the engine components.Recently, we have seen two different but relevant matters:

In computational fluid dynamics (CFD), it is possible to identify namely two uncertainties: epistemic, related to the turbulence model, and aleatoric, representing the random-unknown conditions such as the boundary values and or geometrical variations. In the field of epistemic uncertainty, large eddy simulation (LES and DES) is the state of the art in terms of turbulence closures to predict the heat transfer in internal channels. The problem is still unresolved for the stochastic variations and how to include these effects in the LES studies. In this paper, for the first time in literature, a stochastic approach is proposed to include these variations in LES. By using a classical uncertainty quantification approach, the probabilistic collocation method is coupled to numerical large eddy simulation (NLES) in a duct with pin fins. The Reynolds number has been chosen as a stochastic variable with a normal distribution. The Reynolds number is representative of the uncertainties associated with the operating conditions, i.e., velocity and density, and geometrical variations such as the pin fin diameter. This work shows that assuming a Gaussian distribution for the Reynolds number of ±25%, it is possible to define the probability to achieve a specified heat loading under stochastic conditions, which can affect the component life by more than 100%. The same method, applied to a steady RANS, generates a different level of uncertainty. New methods have been proposed based on the different level of aleatoric uncertainties which provides information on the epistemic uncertainty. This proves, for the first time, that the uncertainties related to the unknown conditions, aleatoric, and those related to the physical model, epistemic, are strongly interconnected. This result, which is idealized for this specific issue, can be extrapolated, and has direct consequences in uncertainty quantification science and not only in the gas turbine world.

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The main role of the intake is to provide a sufficient mass flow to the engine face and a sufficient flow homogeneity to the fan. Intake-fan interaction off design represents a critical issue in the design process because intake lines are set very early during the aircraft optimization. The offdesign operation of an aero-engine, strictly related to the intake flow field, can be mainly related to two different conditions. When the plane is in near ground position, vorticity can be ingested by the fan due to crosswind incidence. During the flight, distortions occur due to incidence. In these conditions, the windward lip is subjected to high acceleration followed by strong adverse pressure gradients, high streamline curvature, and cohabitation of incompressible and transonic flow around the lip. All these features increase the risk of lip stall in flight at incidence or in crosswind near ground operation and increase the level of forcing seen by the fan blades because of the interaction with nonuniform flow from the intake. This work deals with the study of two sources of distortions: ground vortex ingestion and flight at high incidence conditions. A test case representative of a current installation clearance from the ground has been investigated and the experimental data available in open literature validated the computational fluid dynamics (CFD) calculations. An intake, representative of a realistic civil aero-engine configuration flying at high incidence, has been investigated in powered and aspirated configurations. Distortion distributions have been characterized in terms of total loss distributions in space and in time. The beneficial effect of the presence of fan in terms of distortion control has been demonstrated. The mutual effect between fan and incoming distortion from the intake has been assessed in terms of modal force and distortion control. CFD has been validated by means of comparisons between numerical results and experimental data which have been provided. Waves predicted by CFD have been compared with an actuator disk approach prediction. The linear behavior of the lower disturbance frequency coming from distortion and the waves reflected by the fan has been demonstrated.