Experimental investigation of a vibrating axial turbine cascade in presence of upstream generated aerodynamic gusts

An experimental investigation has been conducted in the non-rotating annular test facility of the "Laboratoire de Thermique Appliquée et de Turbomachines" (LTT), "École Polytechnique Fédérale de Lausanne" (EPFL). During this investigation, the unsteady aerodynamic response of a turbine cascade was investigated for three different cases: (1) the clamped blades subjected to periodic, upstream generated aerodynamic gusts, (2) the cascade forced to vibrate in the travelling wave mode in a uniform flow, and (3) the cascade forced to vibrate in the presence of the upstream generated aerodynamic gusts, with a common excitation frequency and a constant gust-vibration phasing. These measurements were aimed at identifying important aspects of the unsteady aeroelastic behavior of the blades. Particular attention was focused on the relationship between the time-dependent flows of (1) and (2) and that of (3) in an effort to better understand aerodynamic forced response phenomena in turbomachinery The experimental tasks detailed above have been performed in a non-rotating annular test facility using a test rig composed of rotating wake generators and a fixed turbine cascade. There are two rotating wake generators: one possesses 13 elliptical struts and the other has 22. Each one is designed to generate wake profiles similar to a blade row. The turbine cascade consist of 20 blades attached to separate torsion suspension system, with a magnetic excitation feature, allowing the control of the cascade's vibration mode. Several blades are instrumented to measure the resulting surface steady pressures, unsteady pressures and blade vibration mode The specific objectives of this investigation were: measure the unsteady aerodynamic blade response to: (1) imposed cascade vibration modes (travelling wave mode), (2) upstream generated aerodynamic gusts, and (3) combinations of these two effects. using the above experimental results, address the local validity of the assumptions inherent in linearized treatments of the forced response problem. Specifically, can the local unsteady blade loading be considered as a linear superposition of the unsteady forces derived individually from the cascade's vibration mode and from the aerodynamic gusts? The final conclusions of this work were: the simultaneous measurements have demonstrated the important influence of the gust-vibration phase angle Φ on the blade surface time-dependent pressure distribution and has identified it as the key parameter. For a given test configuration and flow condition, the selection of the gust-vibration phase angle allows a local constructive or destructive interaction between the main harmonics of both excitation sources. Generally, this suggest that the gust-vibration phase angle has an important effect on the excitation levels and excited modes of the cascade. The practical implication of this phenomenon is that the judicious choice of a gust-vibration phase angle can diminish significantly the aerodynamic excitation levels for a given cascade vibration mode, flow condition and test configuration of a single stage. It is even possible that certain periodic variations of this phase angle produces another excitation source in turbomachinery. the simultaneous vibrating cascade and upstream generated aerodynamic gusts excitations can be accurately predicted by the linear superposition of the individual gust-induced and vibration-induced unsteady flow fields. This principle was shown to be applicable locally for various test configurations, including different engine orders, inter-blade phase angles, gust-vibration phase angles, and flow conditions. The only significant discrepancies were observed in the presence of shocks, but these were limited to a localized region reducing their importance in terms of the overall unsteady aerodynamic loading of the blade. It has been shown that these discrepancies were mainly due to the variation of the shock's mean location between gust-response only, controlled-vibration only and simultaneous measurements. The main practical advantage of this linear superposition principle is that the numerical and experimental investigation of the aerodynamic forced response problem can be separated into: (1) the identification of the local forcing-function due to upstream generated gusts only, (2) a local aerodynamic stability analysis of the cascade alone. The simultaneous measurements have shown that measurement errors vary significantly as the local pressure disturbance contributions due to the gusts and the cascade's vibration mode interact constructively or destructively. Particular attention is needed in simultaneous measurements in order to separate measurement error effects and physical phenomena

Eine Klassifizierung von mediendidaktischen Unterstützungsangeboten als Ansatz für die Fokussierung von Austausch und Professionalisierung

An vier unterschiedlich ausgerichteten Hochschulen in Deutschland wurden im Zuge der Förderprogramme der letzten Jahre Maßnahmen rund um die Digitalisierung der Lehre entwickelt. Alle verfolgten das Ziel, die mediendidaktischen Kompetenzen der Lehrenden weiterzuentwickeln. In einem ersten Schritt wurden aufgrund vergleichbarer Ausgangslagen unabhängig voneinander Unterstützungsangebote mit einem Fokus auf toolorientierte Workshops und E-Teaching Programme entwickelt. Eine intensive Auseinandersetzung mit den bisherigen Erfahrungen und den Bedarfen der Lehrenden führte zu einer Weiterentwicklung mit unterschiedlichen Schwerpunktsetzungen. Wesentlich waren dabei sowohl die gewählte Sozialform (Gruppe versus Individuum) als auch die inhaltliche Ausrichtung (Informationsvermittlung versus Begleitung von Entwicklungsvorhaben Lehrender). Aus Perspektive der hochschul- und mediendidaktisch Beratenden beschreibt jedes der vier – durch die Kombination dieser beiden Dimensionen – definierten Felder einer Matrix eine spezifische Rolle und damit auch ein Bündel relevanter Anforderungen und zu entwickelnder Kompetenzen. Diese wurden in zwei Workshops genutzt, um den kollegialen Austausch im Sinne einer Community of Practice zu fokussieren

Local Yield Measurement with GPS in Serial Combine Harvesters 1990

Nach ersten Untersuchungen zur lokalen Ertragsermittlung in Mähdreschern konnten 1990 erstmals GPS-gestützte Ertragsmessungen mit zwei Serienmähdreschern unter Praxisbedingungen durchgeführt werden. Nach Entwicklung und Integration der Messtechnik wurden damit lokale Ertragsermittlungen auf zwei Standorten in Bayern und auf einem Feld in Österreich durchgeführt. Trotz unzureichender Abdeckung der Satellitenkonfiguration und zeitaufwendigem Datentransfer verlief die gesamte Ertragsmessung problemlos und störungsfrei. Dargestellt wird der gesamte Ablauf der Messkampagne mit den erstellten Ertragskarten.Following first investigations of local yield determination in combine harvesters in 1990 very first GPS-based series of measurements with two serial combine harvesters were realized on farm level. After developing and integrating the data acquisition equipment local yield measurement was executed at two sites in Bavaria and another one in Austria. Although the coverage of the satellite configuration was poor and the data transfer from the mobile harvesting technology was time consuming the yield measurement was free of problems and interruptions. The whole process of the measurement campaign and first yield maps are presented

Design and dynamic optimization of a tristable x-ray attenuator mechanism for the STIX instrument

The STIX (Spectrometer/Telescope for Imaging X-rays) instrument on the ESA Solar Orbiter satellite is designed to study the Sunrays emissions. The wide energy range of incident X-ray fluxes, expected during the solar flares, requires the incorporation of a moveable X-ray attenuator covering and uncovering the instrument detectors depending on X-ray fluxes intensity. In the frame of the STIX Detector Module Prime Contract with ESA, Almatech has designed an attenuator mechanism provided with 2 end-strokes and 1 neutralmid- stroke stable positions. In particular, the two stable end-stroke positions avoid the use of a dedicated launchlock device to reduce complexity, lower the total mass while increasing the system reliability, all in the same time. Flexures as well as end-position switches are used as accelerator/decelerator devices in the mechanism. A cam-shaped switch trigger design allows the optimization of their dynamic contributions in the system. This article first presents the design of the STIX Attenuator Mechanism and then focuses on presenting the optimization of its dynamic response that plays a major role in the limitation of exported force, micro vibrations and torque to the spacecraft on one hand, as well as on the required actuation power on the other hand

Development and preliminary testing of a high precision long stroke slit change mechanism for the SPICE instrument

In the frame of ESA’s Solar Orbiter scientific mission, Almatech has been selected to design, develop and test the Slit Change Mechanism of the SPICE (SPectral Imaging of the Coronal Environment) instrument. In order to guaranty optical cleanliness level while fulfilling stringent positioning accuracies and repeatability requirements for slit positioning in the optical path of the instrument, a linear guiding system based on a double flexible blade arrangement has been selected. The four different slits to be used for the SPICE instrument resulted in a total stroke of 16.5 mm in this linear slit changer arrangement. The combination of long stroke and high precision positioning requirements has been identified as the main design challenge to be validated through breadboard models testing. This paper presents the development of SPICE’s Slit Change Mechanism (SCM) and the two-step validation tests successfully performed on breadboard models of its flexible blade support system

Policy-Based Composition and Embedding of Extended Virtual Networks and SFCs for IIoT

The autonomic composition of Virtual Networks (VNs) and Service Function Chains (SFCs) based on application requirements is significant for complex environments. In this paper, we use graph transformation in order to compose an Extended Virtual Network (EVN) that is based on different requirements, such as locations, low latency, redundancy, and security functions. The EVN can represent physical environment devices and virtual application and network functions. We build a generic Virtual Network Embedding (VNE) framework for transforming an Application Request (AR) to an EVN. Subsequently, we define a set of transformations that reflect preliminary topological, performance, reliability, and security policies. These transformations update the entities and demands of the VN and add SFCs that include the required Virtual Network Functions (VNFs). Additionally, we propose a greedy proactive heuristic for path-independent embedding of the composed SFCs. This heuristic is appropriate for real complex environments, such as industrial networks. Furthermore, we present an Industrail Internet of Things (IIoT) use case that was inspired by Industry 4.0 concepts, in which EVNs for remote asset management are deployed over three levels; manufacturing halls and edge and cloud computing. We also implement the developed methods in Alevin and show exemplary mapping results from our use case. Finally, we evaluate the chain embedding heuristic while using a random topology that is typical for such a use case, and show that it can improve the admission ratio and resource utilization with minimal overhead