Strömungsmaschinen in der Energietechnik

The Allam Cycle is one of the most promising concepts in thermal power generation, especially due to its high thermal efficiency (> 60 %) and near zero emissions while being fossil fueled. In view of a global shift towards renewable energies and the imminent scarcity of fossil energy sources, the transition of thermal power generation to hydrogen as fuel becomes increasingly relevant. This raises questions about the performance, design and operational challenges associated with switching to hydrogen. Although various combinations of working fluids and fuels have been discussed before, a thorough design and a thermodynamic analysis of the H2-fired Allam Cycle has yet to be carried out. This work presents an Aspen HYSYS-based first thermodynamic analysis of the H2-fueled Allam Cycle and compares it with the fossil-fueled cycle. Preventing and compensating the inevitable CO2 release via the condensate becomes the key challenge, for the solution of which three methods are proposed and evaluated. The resulting, newly proposed LSM-model allows a net zero emission H2-Allam Cycle. Based on the lower heating value (LHV) the thermal efficiency of the H2-Allam Cycle is 5 % higher than for the NG-Allam Cycle. This is primarily due to the higher specific turbine work resulting from the increased specific isobaric heat capacity of the steam-enriched working fluid and secondarily due to the higher LHV of hydrogen. When accounting for the energy requirements of hydrogen processing and losses via turbine cooling, the thermal efficiency of the new cycle drops significantly but remains competitive with the NG-Allam Cycle.

There are various mechanisms through which water droplets can be present in compressor flows, e.g. rain ingestion in aeroengines or overspray fogging used in heavy duty gas turbines to boost power output. For the latter, droplet evaporation within the compressor leads to a cooling of the flow as well as to a shift in the fluid properties which is beneficial to the overall process. However, due to their inertia, the majority of droplets is deposited in the first stages of a multistage compressor. While this phenomenon is generally considered in CFD-computations of droplet-laden flows, the subsequent re-entrainment of collected water, the formation of new droplets and the impact on the overall evaporation is mostly neglected because of the additional computational effort required, especially with regard to the modeling of films formed by the deposited water. The work presented here shows an approach which allows to integrate the process of droplet deposition and re-entrainment based on relatively simple correlations and experimental observations from literature. Thus, the two-phase flow in multistage compressors can be modelled and analyzed very efficiently. In this paper, the models and assumptions used are described first, then the results of a study performed based on a generic multistage compressor are presented, whereby the various models are integrated step by step to allow an assessment of their impact on the droplet evaporation throughout the compressor and overall performance. It can be shown that evaporation becomes largely independent of droplet size when deposition on both rotor and stator and subsequent re-entrainment of collected water is considered. In addition, open issues with regard to a future improvement of models and correlations of two-phase flow phenomena are highlighted based on the results of the current investigation.

As drone technology evolves, modular drones are increasingly central, offering rapid adaptability through the interchange of sensors, motors, and structural battery modules. However, this flexibility also introduces complex control challenges that traditional Proportional-Integral-Derivative (PID) controllers often struggle to address, particularly under dynamic reconfigurations and nonlinear responses. In this paper, we propose a novel approach integrating Invertible Neural Networks (INNs) and Reinforcement Learning (RL) to enhance adaptability and effectiveness in modular drone control. INNs facilitate precise, reversible command mapping via bijective transformations, ensuring robust handling of changing drone weight, geometry, and functionality. When combined with RL, these networks further enable real-time optimization of flight performance, dynamically responding to shifts in operational conditions. We outline a comprehensive research agenda employing the PX4 simulation framework to benchmark INN- and RL-based methods against standard PID controllers, focusing on improved response times, reduced error rates, and better system resilience. The anticipated findings aim to substantiate the potential of these advanced control systems – particularly in conjunction with emerging structural battery designs – to significantly expand the capabilities and operational scope of next-generation unmanned aerial vehicle (UAVs) in real-world applications.

Thin shear stress-driven water films can be found in a wide variety of applications, such as heat exchangers,low-pressure stages of steam turbines or in compressors in the case of high fogging. In aviation, sheardriven water films are of interest in icing phenomena and heavy rain events, among others, as they pose aserious safety risk. The challenge in researching these films is the complex relationship between the turbulent boundary layer and the three-dimensional wavy film, as they influence each other. However, available literature mostly features time resolved but localized pointwise measurements of film behavior. Moreover, experimentsare often done in low-speed gas flows, which are not characteristic for turbomachinery applications. In thispaper, shear-driven water films are investigated in a new experimental test rig, which allows temporal andspatial resolution of films under turbomachinery-like conditions. The test rig can be operated at gas velocities exceeding 100 m/s and has a measuring section consisting of a 0.3 m wide rectangular duct with variableheight. Optical access to the measuring section is provided from both top and bottom side. Flow velocity profiles and turbulence intensities were obtained using 3D Laser Doppler Anemometry (LDA). The sheardriven water films were investigated with a novel light absorption measurement technique that allows films tobe recorded both temporally and spatially resolved, allowing to identify and investigate the wavy film structure.The technique is based on the light absorption of a water-ink mixture, which is illuminated by a white lightsource. The light intensity attenuation, which increases with film thickness and ink concentration, is recordedby a high-speed camera. The measurement technique was used to investigate the films behavior for variousair velocities and film Reynolds numbers.

The paper aims to investigate the system behavior of a solar hybrid microturbine through dynamic simulation, relying on experimental data from existing literature. The focus of this evaluation is on assessing the systems response to changes in solar heat flow from the solar receiver to simulate dynamic operation. By evaluating various simulated operational scenarios, the systems performance was assessed by comparing the minimum, average, and maximum solar heat flow from the solar receiver during regular operation. The main objective of these evaluations is to determine the optimal configuration to ensure safe and efficient system operation. The study shows that the parallel configuration outperforms the serial configuration. Specifically, the parallel configuration achieves a peak thermal efficiency of 37%, while the serial configuration reaches 33%. Additionally, the fuel conversion rate for both configurations rises to over 90% at maximum Direct Normal Irradiance (DNI) and decreases to below 40% at minimum DNI. This studies provide valuable insights into the dynamic behavior and performance of the solar hybrid microturbine system, guiding the selection of the most suitable configuration for optimized operational outcomes. Moreover, the study underscores the importance of dynamic analysis in ensuring efficient and reliable power generation.

Dust testing of vehicles on unpaved roads is crucial in the development process for automotive manufacturers. These tests aim to ensure the functionality of locking systems in dusty conditions, minimize dust concentration inside the vehicle, and enhance customer comfort by preventing dust accumulation on the car body. Additionally, deposition on safety-critical parts, such as windshields and sensors, can pose threats to driver vision and autonomous driving capabilities. Currently, dust tests are primarily conducted experimentally at proving grounds. In order to gain early insights and reduce the need for costly physical tests, numerical simulations are becoming a promising alternative. Although simulations of vehicle contamination by dry dust have been studied in the past, they have often lacked detailed models for tire dust resuspension. In addition, few publications address the specifics of dust deposition on vehicles, especially in areas such as door gaps and locks. Many authors focus primarily on the environmental impact of vehicles due to non-exhaust emissions, such as tire and road wear particles (TRWP) and brake wear on paved roads. To close this gap, this paper presents an experimental test in which a vehicle drives through a dry dust track. Using special dust measurement techniques positioned in the wheelhouse, we determine the number and size distribution of the dust particle field around the tire circumference. The results of this experiment provide a deeper understanding of the dust dispersion patterns generated by tires on unpaved surfaces and serve as valuable data for boundary conditions and for the validation of CFD (computational fluid dynamics) simulations.

Vast progress has been achieved in the last decades on understanding the phenomena related to the onset of condensation in steam flows, both experimentally and especially numerically. Nevertheless, there is still a considerable disagreement between the various numerical models used. Unfortunately, the available experimental validation data is not sufficiently detailed to allow for a proper validation of CFD simulations. Hence, further experiments are necessary to close this gap. This paper presents new experimental data of a condensing steam flow, acquired in a supersonic nozzle according to Barschdorff, at the Institute of Thermal Turbomachinery Laboratory (ITSM) in the University of Stuttgart. In previous experiments done at the ITSM, steam was throttled and cooled down using a controlled water injection. However, the stability of inlet conditions, in particular the inlet temperature, was not satisfactory. Moreover, evidence of larger droplets was detected during the post-processing of data. Consequently, this paper also introduces novel modifications to the ITSM nozzle test-rig, which consist of adding a water bath steam cooling vessel system to accomplish steady inlet conditions and improve control of the operating points in the nozzle. With this scheme it is possible to maintain stable and dry inlet conditions, yielding in having sufficient time to measure the flow features and droplet spectra repeatedly, generating new and reliable experimental data. Similar to the experiments done by Barschdorff, a steady inlet pressure of 784 mbar was set at various inlet temperatures down to 100.2°C. Condensation onset is accurately captured across the nozzle for all operating conditions using up to 1 mm spatial resolution for both pneumatic and droplet size measurements. Droplet light spectra are measured using the light extinction method. CFD simulations were performed using the commercial solver ANSYS CFX; Sauter diameters, droplet numbers, wetness and its correspondent condensation onset locations were calculated. Nonetheless, the droplet diameters are numerically overestimated by approximately a factor of 2. Thus, it is evident that further understanding and development of the numerical droplet growth model, especially at lower expansion rate nozzles, is still obligatory. The validity and accuracy of this work is demonstrated by the extremely high reproducibility of the results. It is concluded that there is a good agreement pneumatically, between experimental and numerical results.

Considerable progress has been achieved in recent decades in understanding the phenomena related to the onset of condensation in steam flows, both experimentally and especially numerically. Nevertheless, there is still a certain disagreement between the different numerical models used. Unfortunately, the available experimental validation data are not sufficiently detailed to allow for proper validation of computational fluid dynamics (CFD) simulations. Therefore, this paper presents new experimental data for condensing steam flows, acquired in a supersonic nozzle according to Barschdorff, at the Institute of Thermal Turbomachinery Laboratory (ITSM) at the University of Stuttgart. A steady inlet pressure of approximately 784 mbar was set for three inlet temperatures down to 100.2 ∘C. Condensation onset is accurately captured across the nozzle, using down to 1 mm spatial resolution for both pneumatic and light spectra measurements. CFD simulations were performed using the commercial solver ANSYS CFX. The droplet diameters are numerically overestimated by approximately a factor of 1.5. Disagreement has been found between original Barschdorff’s experiments and measurements at ITSM. However, there is a good agreement in terms of the pressure distribution along the nozzle axis between experimental and numerical results. The reproducibility of the results is excellent.

To face the challenge regarding reconversion of stored green hydrogen into electricity, zero emission oxyfuel hydrogen cycles with steam as a working fluid are very promising in both thermal efficiency and large-scale applicability. Previous studies suggest that with Turbine Inlet Temperatures (TIT) of 1700 °C thermal efficiencies in excess of 70% based on Lower Heating Value (LHV) can be reached. This work starts with a historical review, from the early 80s until today, of the processes proposed in the literature which can be categorized in partly condensing and fully condensing cycles. Also, since the calculations in the literature are based on different assumptions of cycle parameters, component efficiencies and material limitations, a selection of state-of-the-art process and component parameters in the turbomachinery and power plant industry will be established to help identify the technically realizable and promising cycles. Those parameters will also be used as a common base for thermodynamic simulations of the selected cycles and can serve as a reliable reference for further calculations. The simulations show that thermal efficiencies up to 73% are achievable under conditions reflecting the present state-of-the-art and 75% in the near future, considering current development. Mitsubishi’s intercooled topping recuperation cycle shows the highest thermal efficiency with 75% based on LHV. Moreover, a higher TIT goes along with increased cooling demand and thus higher losses in the turbine, counteracting the efficiency increase due to the elevated temperature. A parametric analysis will identify the optimum operating point of each cycle regarding TIT with consideration of the cooling efficiency.