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High-resolution turbofan intake flow characterization by automated stereoscopic-PIV in an industrial wind tunnel environment
No full textUnsteady inlet flow distortion can influence the stability and performance of any propulsion system, in particular for more novel, short and slim intakes of future aero-engine configurations. As such, the requirement for measurement methods able to provide high spatial resolution data is important to aid the understanding of these flow fields. This work presents flow field characterisations at a crossflow plane within a short aeroengine intake using stereoscopic particle image velocimetry (SPIV). A series of tests were conducted across a range of crosswind and high angle of attack conditions for a representative short and slim aspirated intake configuration at two operating points in terms of mass flow rate. The velocity maps were measured at a crossflow plane within the intake at an axial position L/D = 0.058 from where a fan is expected to be installed. The diameter of the measurement plane was 250 mm, and the final spatial resolution of the velocity fields had a vector pitch of 1.5 mm which is at least two orders of magnitude richer than conventional pressure-based distortion measurements. The work demonstrates the ability to perform robust non-intrusive flow measurements within modern intake systems in an industrial wind tunnel environment across a wide range of operating conditions; hence, it is suggested that SPIV can potentially become part of standard industrial testing. The results provide rich datasets that can notably improve our understanding of unsteady distortions and influence the design of novel, closely coupled engine-intake systems.Aerodynamic
Polarimetric Calibration of an FMCW Doppler Radar with Dual-Orthogonal Signals
No full textIn this paper, the full calibration chain of FMCW radar with simultaneous transmission of two orthogonally polarized orthogonal waveforms is considered. Specifically for this type of polarimetric radar, compensation of signals’ biases and equalization of the amplification gains of the parallel polarimetric channels in the receiver are jointly performed using the noise measurements. The calibrations of the absolute complex gains of the transmitter’s polarimetric channels together with complex antenna gains are done using the model-based fit of the measurements of the rotating dihedral reflector. Phase relations between polarimetric channels are treated in the Doppler domain using the unfolded velocity of the target. The performed calibration results in high-accurate measurements of the radar targets’ polarimetric scattering matrix (PSM) in the Doppler domain. All the proposed calibration steps are illustrated using real radar data.Microwave Sensing, Signals & System
Assessment of immersed boundary methods for hypersonic flows with gas–surface interactions
No full textThe efficacy of immersed boundary (IB) methods with adaptive mesh refinement (AMR) techniques is assessed in the context of atmospheric entry applications, including effects of chemical nonequilibrium (CNE) and gas–surface interactions (GSI). We scrutinize a conservative cut-cell IB method and two non-conservative IB methods, comparing their results with analytical solutions, data from the literature, and results obtained with a reference solver that operates on body-fitted grids. All solvers employ the same external thermochemistry library, ensuring that all observed differences can be attributed solely to differences in the underlying numerical methodologies. We present results for eight benchmark cases. Four verification cases verify the implementation of chemistry, transport properties, catalytic boundary conditions, and shock capturing. Four validation cases encompass blunt geometries with adiabatic and isothermal, as well as inert, catalytic and ablative boundary conditions. Overall, the results obtained with the IB solvers are in very good agreement with the reference data. Discrepancies arise in cases with large temperature or concentration gradients at the wall, and these are linked to conservation errors inherent to ghost-cell and interpolation-based IB methods. Only a strictly conservative cut-cell IB method is on par with body-fitted grid methods.Aerodynamic
Swept Transition Experimental Platform (STEP)
No full textA new experimental facility named Swept Transition Experimental Platform (STEP) has been designed and built for detailed studies of crossflow instability and its interaction with surface irregularities and varying wall temperature conditions. The STEP is designed for use in the anechoic low-turbulence wind tunnel facility at the Delft University of Technology (TU Delft). The new facility consists of a swept flat-plate model with a movable leading edge capable of precisely translating to create forward/backward-facing step irregularities. In addition, the plate’s wall temperature can be adjusted to study the potential of thermal laminar flow control. An adjustable pressure body provides the favorable pressure distribution required to enhance the development of crossflow instability. Static pressure measurements are conducted to characterize the nominal pressure distribution. In addition, detailed hot-wire measurements and theoretical stability calculations reveal that the combination of discrete roughness elements, pressure distribution, and experimental facility allows for a detailed study of the development of crossflow instability in the linear and non-linear growth regime. Consequently, the STEP enables further fundamental research on laminar flow control at TU Delft.AerodynamicsShip Hydromechanics and Structure
Parametric study of a switchable vortex generator for load alleviation in transonic conditions
No full textThis paper investigates the impact of introducing a switchable vortex generator (SVG), acting as a mini-tab, on the aerodynamic performance of a high-aspect-ratio wing's outer section in transonic regime. A parametric study is conducted employing computational fluid dynamics 2D simulations, focusing on the aerodynamic effects of changing the chord-wise position and height of the vane of a SVG located on the airfoil upper surface in both nominal cruise conditions and for varying angles of attack. The analysis reveals that mini-tabs can strongly affect the aerodynamic forces produced by the wing section, showing great potential for load alleviation and control, but also emphasising the need for a careful parameter selection to reduce undesirable effects such as the generation of shock waves. In cruise conditions, lift reduction increases with the vane height and has its maximum for chord-wise positions at 60% of the chord-length. However, SVGs located in the first half of the chord-length yield more robust performance for varying angle of attack, without sharp lift variations or generated shock waves, and a delayed stall onset. High SVGs (≥3% chord-length) can also lead to strong shock waves on the airfoil lower surface at small or negative angle of attack, while small SVGs (Group Sodj
Sparse Temporal Convolutional Neural Networks for Keyword Spotting
No full textKeyword spotting (KWS) is an essential component of voice recognition services on smart devices. Its always-on characteristic requires high accuracy and real-time response. Also, low power consumption is another key demand for KWS devices. In previous research, neural networks have become popular for KWS tasks for their accuracy compared to traditional machine learning technologies. Among classical neural networks like recurrent neural networks (RNNs) and convolutional neural networks (CNNs), temporal convolutional networks (TCNs) have begun to catch attention recently. Moreover, studies related to sparsity are always an efficient method to deal with the growing model size issue for modern neural network designs. As a potential solution, in this work, a TCN model is trained for KWS on the Google Speech Command V2 dataset and achieves an accuracy of 94.1\%. Based on that, two different sparsity are applied to the TCN model. One is temporal sparsity. By creating a Delta convolution layer, the Delta temporal convolutional network (DeltaTCN) achieves an accuracy of 93.6\% with a 72\% reduction in floating-point operations (FLOPS) compared to the original TCN model. Another is structural weight sparsity. By creating sparsity on the weight matrix of each convolution layer, the structural sparse temporal convolutional network (SSPTCN) achieves 93.6\% accuracy with a 70\% reduction in FLOPs and a 39\% reduction in parameters.Electrical Engineerin
Design guidelines to protect stakeholders’ values in AI systems: Based on a use case situated in the Japanese life insurance industry
No full textIntegrating artificial intelligence (AI) into Japan's life insurance sector marks a significant move towards data-centric precision, reflecting the nation's shift towards Society 5.0. In this domain, AI is revolutionizing decision-making processes and enhancing operational efficiency, with applications ranging from fraud detection in credit card systems to predictive underwriting. While AI offers notable benefits, it also introduces risks, including privacy breaches, algorithmic biases, and inadequate human supervision. To tackle these risks, the Japanese government has initiated guidelines for societal protection, but gaps remain in the insurance industry's implementation, especially in translating social norms into the industry's context to protect stakeholders' values.The industry needs a guide for safely designing, developing, and deploying AI systems, considering stakeholders' perspectives. This guide fills two knowledge gaps: a framework for translating high-level values into Japanese life insurance industry requirements and an initial process for converting these high-level values into organizational guidelines.An empirical study on predictive underwriting informed the research, identifying 13 values and four informal social institutions for the AI design process. It involved eight experts who defined 54 norms, which were later refined and categorized into process and assessment norms focusing on data and AI. The result is ten design guidelines for AI system developers, which are validated by experts, addressing the full AI lifecycle. These guidelines contribute scientifically by introducing an initial process combining design for values with system safety concepts, reporting standardization, and AI governance frameworks.Future research should replicate this process in various contexts, reevaluate the value framework with broader stakeholder inputs, investigate the dynamics between Japanese society and AI in more detail, and delve deeper into system theoretic hazards analysis. This approach promises to strengthen the value framework and process applicability in different organizational settings.Systems Engineering, Policy Analysis and Management (SEPAM
Blade Element Theory Model for UAV Blade Damage Simulation
No full textFrom fault-tolerant control to failure detection, blade damage simulation is integral for developing and testing failure-resilient modern unmanned aerial vehicles. Existing approaches assume partial loss of rotor effectiveness or reduce the problem to centrifugal forces resulting from the shift in the propeller centre of gravity. In this study, a white-box blade damage model based on Blade Element Theory is proposed, integrating both mass and aerodynamic effects of blade damage. The model serves as plug-in to the nominal system model, enables the simulation of any degree of blade damage and does not require costly experimental data from failure cases. A complementary methodology for the identification of the airfoil lift and drag coefficients is also presented. Both contributions were demonstrated with the Bebop 2 drone platform and validated with static test stand wrench measurements obtained at 3 levels of blade damage (0%, 10%, 25%) in a dedicated wind tunnel experimental campaign with velocities up to 12 m/s. Results indicate high accuracy in simulating a healthy propeller. In the presence of blade damage, the model exhibits a relative error between 5% and 24% at high propeller rotational speeds and between 15% and 75% at low propeller rotational speeds.Control & Simulatio
Effect of struts and central tower on aerodynamics and aeroacoustics of vertical axis wind turbines using mid-fidelity and high-fidelity methods
No full textThis study investigates the impact of struts and a central tower on the aerodynamics and aeroacoustics of Darrieus Vertical Axis Wind Turbines (VAWTs) at chord-based Reynolds numbers of 8.12 × 104. A 2-bladed H-Darrieus VAWT is used, featuring a 1.5m diameter, a solidity of 0.1 and a blade cross-section of symmetrical NACA 0021. The turbine design is kept simple and straight-bladed which is essential for isolating and analyzing the specific effects of struts and a tower. The high-fidelity Lattice Boltzmann Method (LBM) in PowerFLOW 6-2020 and the mid-fidelity Lifting Line Free Vortex Wake (LLFVW) method in QBlade 2.0 are employed, with the mid-fidelity method providing a faster analytical tool for insights into the turbine performance. Firstly, both the LLFVW (mid-fidelity) and LBM (high-fidelity) methods effectively capture the general trends observed in VAWT power performance. However, the former predicts mean thrust values that are approximately 10% higher, and mean torque values that are approximately 19% higher, in comparison to the latter. Subsequently, the former predicts lower streamwise wake velocities relative to those predicted by the latter. These differences increase in configurations that include struts and a tower (to 30% - 31%). Secondly, the presence of struts and a tower leads to a reduction in both mean power (by 15% to 55%) and thrust (by 3% to 3.6%), with a further small decrease observed when doubling the tower diameter (power and thrust both by 0.5% to 3%). The struts predominantly affect the spanwise distribution of blade loading, while the tower impacts the azimuthal variation of blade loading. Additionally, the addition of struts and a tower reduces low-frequency noise (50-200 Hz) while increasing high-frequency noise (> 300 Hz). The observed decrease in mean blade loading results in reduced low-frequency noise, while the increase in high-frequency noise is ascribed to the increased intensity of BWI/BVI leading to higher unsteady loading fluctuations on blades.Wind Energ
Hydrogen Peroxide as an Oxidiser for Medium-Lift Launch Vehicles: A Performance and Integration Analysis
No full textCryogenic and semi-cryogenic propellants are the most commonly used liquid propellants for applications in medium-lift launch vehicles. Despite their high performance, the storage requirements for these propellants often lead to complex, heavy, and voluminous structures. The only storable propellant used in medium-lift launch vehicles, UDMH/NTO, comes with its own problems of high toxicity and reduced performance. A promising alternative to this could be storable fuels with highly concentrated hydrogen peroxide (HTP) as an oxidiser. Despite a shorter history of dedicated development, HTP has proved itself an effective oxidiser for in-space applications and small-lift launch vehicles. Therefore, the question could be raised towards the potential of this oxidiser for applications in medium-lift launch vehicles. In this study, the application potential of an HTP-based storable bi-propellant for medium-lift expendable launch vehicles was investigated. To this extent, a large selection of green storable fuels was considered to find the most suitable propellant for this application.Both the integration and compatibility potential of the propellants and the propulsive and mass performance potential were investigated. The integration and compatibility potential were evaluated through a qualitative assessment based on non-performance-related propellant characteristics. Furthermore, eight fuels were subjected to a more detailed assessment covering the criteria of handling toxicity, environmental toxicity, material compatibility, handling and storage, development level, and coolant qualities. RP-1 was found to be the most suitable fuel with respect to the specific criteria, while ethanol, methanol, isooctane, and isopropanol were also found to be promising alternatives. A launch vehicle model was created to evaluate the propulsive and mass potential of twelve fuels proposed based on earlier findings. This model included a propulsion model, a mass and sizing model, and an aerodynamics and trajectory model, which were all connected through a global optimisation model. In terms of propulsive potential, the cryogenic propellant hydrolox was predicted to have a 25% higher vacuum specific impulse than the best-performing HTP-based propellant DMAZ/HTP. In terms of the specific impulse density, kerosene-derivative fuels in combination with HTP were predicted to have a better performance than hydrolox and than that other conventional storable propellant UDMH/NTO. The optimised gross lift-off mass for the launch vehicle concepts employing HTP was found to be 42-61% higher than the gross lift-off mass of Ariane 6 predicted through the model. Separately, the payload capability of the HTP-based launch vehicle concepts was predicted to be at least 38% lower. In both cases, RP-1/HTP was reported to be the HTP-based propellant with the best performance, while DMAZ, isooctane, and isopropanol could be regarded as suitable alternatives. All of these propellants also outperformed UDMH/NTO. Through a sensitivity analysis, it was discovered that up to 270kg additional payload could be taken to GTO upon considering elevated chamber pressures in the HTP-based engine design. In the end, the high potential and promise of HTP were confirmed as it was concluded that increased development efforts towards HTP-based storable bi-propellant rocket engines could not only lead to a promising alternative to cryogenic propellants but could also allow for the complete replacement of toxic hydrazine-derivative fuels.Aerospace Engineerin