128 research outputs found
The flexible asymmetric shock tube (FAST): A Ludwieg tube facility for wave propagation measurements in high-temperature vapours of organic fluids
No full textThis paper describes the commissioning of the flexible asymmetric shock tube (FAST), a novel Ludwieg tube-type facility designed and built at Delft University of Technology, together with the results of preliminary experiments. The FAST is conceived to measure the velocity of waves propagating in dense vapours of organic fluids, in the so-called non-ideal compressible fluid dynamics (NICFD) regime, and can operate at pressures and temperatures as high as 21 bar and 400 ?C, respectively. The set-up is equipped with a special fast-opening valve, separating the high-pressure charge tube from the low-pressure plenum. When the valve is opened, a wave propagates into the charge tube. The wave speed is measured using a time-of-flight technique employing four pressure transducers placed at known distances from each other. The first tests led to the following results: (1) the leakage rate of 5×10?4mbarl s?1 for subatmospheric and 5×10?2mbarl s?1 for a superatmospheric pressure is compatible with the purpose of the conceived experiments, (2) the process start-up time of the valve has been found to be between 2.1 and 9.0 ms, (3) preliminary rarefaction wave experiments in the dense vapour of siloxane D6 (dodecamethylcyclohexasiloxane, an organic fluid) were successfully accomplished up to temperatures of 300?C, and (4) a method for the estimation of the speed of sound from wave propagation experiments is proposed. Results are found to be within 2.1 % of accurate model predictions for various gases. The method is then applied to estimate the speed of sound of D6 in the NICFD regime.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin
Working Fluid Design for Organic Rankine Cycle (ORC) Systems
No full textThe Organic Rankine Cycle is an energy conversion cycle similar to the conventional Rankine cycle which runs on a working fluid other than water. The selection of a working fluid is a critical part of designing an Organic Rankine Cycle (ORC) system. The number of fluid types actually used in commercial ORC power plants do not justify the number of fluid selection studies present in scientific literature. Hence the objective of this work is to develop a tool which simultaneously optimizes the energy conversion process and selects the optimum working fluid for a given heat source. It is based on a framework that uses a continuous-molecular targeting approach which allows for an integrated working fluid and system design. The process is modeled in Cycle Tempo, a modern graphical tool for thermodynamic analysis and optimization of systems for the production of electricity, heat and refrigeration. The system is simultaneously optimized with the pure component parameters of PCP-SAFT equation of state using a state-of-the-art optimization suite. The working fluid is selected by comparison of the pure component parameters of the PCP-SAFT equation of state with real fluids. A preliminary turbine model implemented directs the tool to generate suitable fluids for practically realistic systems. The tool has been tested for a waste heat recovery system for heavy-duty truck engines based on an ORC turbogenerator. The choice of working fluid is restricted to only the siloxane class which not only adheres to the technical, environmental, and toxicological requirements typical of the automotive sector but also allows for the implementation of a preliminary radial turbine model, whose shaft can be lubricated by the working fluid itself. The turbine has been modeled by applying the methodology of using non-dimensional parameters. Future work will be devoted to implement detailed component models and extending the scope of fluid selection to other organic fluid classes.Energy TechnologyProcess and EnergyMechanical, Maritime and Materials Engineerin
Working fluid design for organic rankine cycle systems (ORC)
No full textThe Organic Rankine Cycle is an energy conversion cycle similar to the conventional Rankine cycle which runs on a working fluid other than water. The selection of a working fluid is a critical part of designing an Organic Rankine Cycle (ORC) system. The number of fluid types actually used in commercial ORC power plants do not justify the number of fluid selection studies present in scientific literature. Hence the objective of this work is to develop a tool which simultaneously optimizes the energy conversion process and selects the optimum working fluid for a given heat source. It is based on a framework that uses a continuous-molecular targeting approach which allows for an integrated working fluid and system design. The process is modeled in Cycle Tempo, a modern graphical tool for thermodynamic analysis and optimization of systems for the production of electricity, heat and refrigeration. The system is simultaneously optimized with the pure component parameters of PCP-SAFT equation of state using a state-of-the-art optimization suite. The working fluid is selected by comparison of the pure component parameters of the PCP-SAFT equation of state with real fluids. A preliminary turbine model implemented directs the tool to generate suitable fluids for practically realistic systems. The tool has been tested for a waste heat recovery system for heavy-duty truck engines based on an ORC turbogenerator. The choice of working fluid is restricted to only the siloxane class which not only adheres to the technical, environmental, and toxicological requirements typical of the automotive sector but also allows for the implementation of a preliminary radial turbine model, whose shaft can be lubricated by the working fluid itself. The turbine has been modeled by applying the methodology of using non-dimensional parameters. Future work will be devoted to implement detailed component models and extending the scope of fluid selection to other organic fluid classes.Energy TechnologyProcess & EnergyMechanical, Maritime and Materials Engineerin
Experimental Observation of Non-Ideal Compressible Fluid Dynamics: with Application in Organic Rankine Cycle Power Systems
No full textFlight Performance and PropulsionEnergy Technolog
An Experimental Study on Supersonic Panel Flutter Using Simultaneous Digital Image Correlation and Schlieren
No full textSupersonic panel flutter is a self-excited vibration, where energy is transferred into thin flexible panels, such as skin panels in supersonic vehicles, from the (supersonic) flow around them, which can lead to their rapid fatigue failure. Relevant examples of this include the failure of skin panels in the X-15 vehicle, or violent oscillations in non-adaptable nozzles during start-up, such as the space shuttle main booster. With the contemporary trends of decreasing weight and increasing operational speeds in the design of next generation aircraft and launch vehicles, such structures will become more common, and flutter needs to be inherently accounted for in the design.In recent years, advancements in numerical techniques, such as Computational Fluid Dynamics (CFD) and the Finite Element Method (FEM), have led to numerous studies that address the effect of non-linearities, such as flutter behaviour in the transonic and hypersonic regime. In spite of that, experimental data needed to validate these studies is limited, based on coarse pointwise measurement techniques, and only focused on the structural response of the panel rather than on the entire Fluid Structure Interaction (FSI). The use of simultaneous, full-field and non-intrusive measurements can be used to address these issues. To this extent, panel designs were developed and an experimental campaign was proposed where Digital Image Correlation (DIC) and Schlieren are simultaneously used by means of high speed cameras to study classical panel flutter at Mach 2 inside the ST-15 wind tunnel at the Delft University of Technology. Additionally, a Laser Doppler Vibrometer (LDV) was used to validate the DIC measurements. The experiment allowed for a comparison with well understood theory, such that the setup can be proven to be robust, and can therefore later be used to assess the effect of panel flutter non-linearities or other supersonic FSIs.Synchronisation between DIC and schlieren was demonstrated through a matching frequency spectrum, and maximum correlation inside corresponding pixel windows between panel displacement and schlieren grey-scale fluctuations with a zero time-lag. One finding was that during the panel down-stroke phase, a travelling wave character was observed which has previously been found only under transonic conditions. Furthermore, at moderate dynamic flutter pressures, a typical second bending panel flutter mode shape was observed, which grew into a single bending mode again with increasing higher dynamic flutter pressures. From the spectral analysis it was found that all configurations fluttered at the same frequency of 770 [Hz], independent of dynamic flutter pressure or edge conditions. This was higher than expected from analysis. These combined observations led to the conclusion that, in the current facility, a frequency lock-in occurs due to merging of the flutter phenomenon with a wind tunnel resonance vibration.These observations provide an insight into combining these experimental techniques to study supersonic FSI behaviour, and particularly into certain unexpected behaviour encountered at the TU Delft ST-15 wind tunnel. This can be used to further tune future experiments and guide researchers to obtain a better understanding in the non-linearities found in panel flutter.Aerospace Engineerin
Stereoscopic PIV on a delta wing in supersonic flow
No full textEver since the 1950s delta wings are being used as an efficient planform for supersonic flight. Over time extensive research on the aerodynamics of this type of wings has been performed using many different measurement techniques. Due to technical difficulties, measurements on delta wings in a supersonic flow are still scarce and often limited to qualitative data only. The addition of PIV as a diagnostic tool in aerodynamics opened doors for new measurements. Nowadays PIV is a well-established non-intrusive measurement method that is being applied in large scale subsonic industrial facilities on a regular basis and in research facilities in all flow regimes. Stereoscopic PIV measurements on delta wings are done previously in sub- and transonic flow, and one 2C-PIV experiment has been done on a delta wing in supersonic flow at moderate angle of attack. The motivation of the current investigation is to perform stereo-PIV measurements around a sharp-edged delta wing in a supersonic flow at high angle of attack using the latest advances in PIV. Furthermore an extension is made to a similar setup in the industrial facility of DNW-SST on the EUROSUP model. The flow around a delta wing is succesfully described at different Mach numbers and for several angles of attack. A spanwise scan using individual measurement planes in streamwise orientation has been made, which are combined to construct a mean flow field in the complete volume. The response of the tracer particles is measured by an oblique shock test, from which the slip velocity with respect to the flow and the drift from the flow path, due to their inertia, is determined. Schlieren, shadowgraphy and oil flow visualisation are applied to give additional information on the flow. Several flow features have been measured by PIV. As expected a vortex is present on the leeward surface of the wing. Due to the large deflection of the flow on the windward surface, a detached shock is present before the leading edge extending to the expansion side of the wing. Attached to the vortex an inboard shock wave has been measured. Furthermore the flow field appeared to be conical, i.e. the flow variables are constant on rays emerging from the apex. A similar stereo-PIV setup has been succesfully applied in the industrial supersonic facility SST at DNW using a high-repetition acquisition system including a model sliding mechanism to increase data production. However, due to the large size of the seeding particles in this campaign, the data generated in this tunnel remains questionable, and a thorough investigation on the seeding production is necessary to acquire reliable PIV data in this facility.AerodynamicsAerospace Engineerin
Modelling horizontal soil deformations
No full textMany cities around the world are located in deltaic areas, these areas have a major economic potential due to their strategic location close to seas and waterways. On the other hand, these deltaic regions are generally covered with very compressible soils. When embankments are constructed on such soils large vertical deformations will occur, but also a significant amount of horizontal deformations can be expected at the outer sides of the embankment. These deformations can have an adverse effect on nearby structures, for instance pile foundations, cables and ducts. This research concentrates on the horizontal deformations, which are most prominent at the outer sides of the embankment. A case where horizontal deformations have resulted in damage is reported by Fellenius and Johansson (1972). They presented a case where several piles of a building in Huddinge near Stockholm buckled due to excessive horizontal movements. More recently the HSL railway track near The Hague was damaged due to horizontal soil deformations (Maas and Wuite, 2006). The horizontal deformations slightly deformed the piles under the concrete railway track.Geo-EngineeringGeotechnologyCivil Engineering and Geoscience
Validation of PLAXIS Embedded Piles For Lateral Loading
No full textIn recent years, the embedded pile model has been successfully implemented in PLAXIS 3D. The embedded pile consists of beam elements connecting to the surrounding soil by means of special interfaces (skin interface and foot interface). Although the embedded pile doesn’t take into account volume, a particular elastic region around the pile whose dimension is equivalent to the pile diameter is assumed in which plastic behavior is neglected. This makes the embedded pile almost behave like the volume pile. Therefore, it may be said that the embedded pile model is considered as a ‘simplified’ model of the volume pile. Although the embedded pile is a relatively new feature, it has been validated by comparisons with the volume pile as well as with measurements from real tests. The finding shows that the embedded pile is not only in good agreement with the volume pile, but also able to resemble the real pile behavior. However these validations are only considered in terms of axial loading (compression loading and tension loading). Therefore it’s questionable whether the embedded pile also shows a good performance in the situation of being subjected to lateral loading. In order to answer this question, this thesis is aimed to give a validation of the embedded pile for lateral loading caused by external forces as well as soil movements in embankment applications. This validation is firstly made in PLAXIS imaginary models (a ‘simplified’ model as considered in Chapter 3 and ‘advanced’ models as considered in Chapter 4) and then in a PLAXIS model of a real case study as considered in Chapter 5.Geo-EngineeringGeotechnologyCivil Engineering and Geoscience
Design of a Weather Balloon Alternative
No full textWeather balloons have been used for decades as a means of measuring atmospheric properties. Balloons are launched twice a day from almost 900 locations worldwide, carrying measurement instruments called radiosondes. Along with data from ground-based sensors, aircraft, and remote-sensing satellites, the collected meteorological data is fed into numerical weather forecasts and climate models. The weather balloons typically burst at altitudes of around 33 km, after which the radiosonde falls back with a parachute but without any control. This leads to large amounts of waste scattered over land and sea. While the balloon material itself is fully biodegradable, the loss of radiosondes and their associated electronics can be an environmental threat. Furthermore, the loss of the filling gases such as helium and hydrogen also poses a threat to the environment – helium is a non-renewable resource and hydrogen indirectly causes warming effects when released in the upper atmosphere. These factors present the need to develop sustainable and reusable alternatives to current weather balloons. In response to this pressing need, the BRAVO family of gliders has been developed, which is short for “Balloon-Released Aerial Vehicle for weather Observation”. This report provides a comprehensive overview of the design process of creating these gliders. It introduces the detailed final design and outlines the logistical and operational procedures associated with their usage. Furthermore, the report encompasses meticulous analyses of cost and market factors, technical risks, and sustainability considerations. To ensure reliability, the gliders undergo thorough verification and validation processes. Finally, the report concludes with gained insights, recommendations, and directions for future work.FAE3200 - Design Synthesis ExerciseAerospace Engineerin
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