ALBERT

Description: Aerospace, Vol. 5, Pages 100: Experimental Validation of an Onboard Transient Luminous Events Observation System for VisionCube via Ground Simulation Environment Aerospace doi: 10.3390/aerospace5040100 Authors: Seho Kim Taehyung Nam Dongwon Jung The VisionCube is a 2-unit CubeSat developed in house, of which the primary mission is detecting the occurrence of transient luminous events (TLEs) in the upper atmosphere and obtaining corresponding images from a low Earth orbit. An onboard TLE observation system of the VisionCube CubeSat is designed and developed by incorporating a photon-sensitive multi-anode photon-multiplier tube (MaPMT) and an image sensor. Also, a distinctive TLE observation software which enables detection of the TLEs and capture of images in a timely manner is devised. By taking into account the limited resources of a small CubeSat in size and power, the onboard observation system is developed employing a system-on-chip device by which both hardware and software can be integrated seamlessly. The purpose of this study is to investigate the functionality of the hardware and the validity of the software algorithm to show that the onboard system will function properly with no human intervention during the operations in space. To this end, a ground simulation facility is constructed to emulate TLEs occurring in space using a set of ultraviolet light-emitting diodes (UV LEDs) inside a darkbox. Based on the analysis of the spectral and temporal properties of the TLEs, the randomly generated UV LED pulses are chosen for verification scenarios for the TLE observation system. The validation results show that the hardware and the software algorithm of the onboard observation systems can effectively detect the TLEs and obtain the images during the in-orbit operation.

Description: Aerospace, Vol. 5, Pages 99: Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV Aerospace doi: 10.3390/aerospace5040099 Authors: Alejandro del Estal Herrero Mustafa Percin Matej Karasek Bas van Oudheusden Flow visualizations have been performed on a free flying, flapping-wing micro air vehicle (MAV), using a large-scale particle image velocimetry (PIV) approach. The PIV method involves the use of helium-filled soap bubbles (HFSB) as tracer particles. HFSB scatter light with much higher intensity than regular seeding particles, comparable to that reflected off the flexible flapping wings. This enables flow field visualization to be achieved close to the flapping wings, in contrast to previous PIV experiments with regular seeding. Unlike previous tethered wind tunnel measurements, in which the vehicle is fixed relative to the measurement setup, the MAV is now flown through the measurement area. In this way, the experiment captures the flow field of the MAV in free flight, allowing the true nature of the flow representative of actual flight to be appreciated. Measurements were performed for two different orientations of the light sheet with respect to the flight direction. In the first configuration, the light sheet is parallel to the flight direction, and visualizes a streamwise plane that intersects the MAV wings at a specific spanwise position. In the second configuration, the illumination plane is normal to the flight direction, and visualizes the flow as the MAV passes through the light sheet.

Description: Aerospace, Vol. 5, Pages 98: Leading-Edge Roughness Affecting Diamond-Wing Aerodynamic Characteristics Aerospace doi: 10.3390/aerospace5030098 Authors: Andrei Buzica Lisa Debschütz Florian Knoth Christian Breitsamter Diamond wing configurations for low signature vehicles have been studied in recent years. Yet, despite numerous research on highly swept, sharp edged wings, little research on aerodynamics of semi-slender wings with blunt leading-edges exists. This paper reports on the stall characteristics of the AVT-183 diamond wing configuration with variation of leading-edge roughness size and Reynolds number. Wind tunnel testing applying force and surface pressure measurements are conducted and the results presented and analysed. For the investigated Reynolds number range of 2.1 × 10 6 ≤ R e ≤ 2.7 × 10 6 there is no significant influence on the aerodynamic coefficients. However, leading-edge roughness height influences the vortex separation location. Trip dots produced the most downstream located vortex separation onset. Increasing the roughness size shifts the separation onset upstream. Prior to stall, global aerodynamic coefficients are little influenced by leading-edge roughness. In contrast, maximum lift and maximum angle of attack is reduced with increasing disturbance height. Surface pressure fluctuations show dominant broadband frequency peaks, distinctive for moderate sweep vortex breakdown. The experimental work presented here provides insights into the aerodynamic characteristics of diamond wings in a wide parameter space including a relevant angle of attack range up to post-stall.

Description: Aerospace, Vol. 5, Pages 97: Discharge Coefficients of Ports with Stepped Inlets Aerospace doi: 10.3390/aerospace5030097 Authors: Adrian Spencer Components of aeronautical gas turbines are increasingly being constructed from two layers, including a pressure containing skin, which is then protected by a thermal tile. Between them, pedestals and/or other heat transfer enhancing features are often employed. This results in air admission ports through the dual skin having a step feature at the inlet. Experimental data have been captured for stepped ports with a cross flow approach, which show a marked increase of 20% to 25% in discharge coefficient due to inlet step sizes typical of combustion chamber configurations. In this respect, the step behaves in a fashion comparable to ports with inlet chamfering or radiusing; the discharge coefficient is increased as a result of a reduction in the size of the vena contracta brought about by changes to the flow at inlet to the port. Radiused and chamfered ports have been the subject of previous studies, and empirical correlations exist to predict their discharge coefficient as used in many one-dimensional flow network tools. A method to predict the discharge coefficient change due to a step is suggested: converting the effect of the step into an equivalent radius to diameter ratio available in existing correlation approaches. An additional factor of eccentricity between the hole in the two skins is also considered. Eccentricity is shown to reduce discharge coefficient by up to 10% for some configurations, which is more pronounced at higher port mass flow ingestion fraction.

Description: Aerospace, Vol. 5, Pages 96: Aerodynamic Design of a Laval Nozzle for Real Gas Using Hodograph Method Aerospace doi: 10.3390/aerospace5030096 Authors: Aleksandr Chikitkin Mikhail Petrov Roman Dushkov Ernest Shifrin We propose an approach for the design of the subsonic part of plane and axisymmetric Laval nozzles for real gases. The proposed approach is based on the hodograph method and allows one to solve the inverse design problem directly. Real gas effects are taken into consideration using the chemical equilibrium model. We present nozzle contours computed with the proposed method for a stoichiometric methane-air mixture. Results confirm that real gas effects have a strong influence on the nozzle shape. The described method can be used in the design of nozzles for rocket engines and for high-enthalpy wind tunnels.

Description: Aerospace, Vol. 5, Pages 95: Natural Frequencies of Rectangular Laminated Plates—Introduction to Optimal Design in Aeroelastic Problems Aerospace doi: 10.3390/aerospace5030095 Authors: Aleksander Muc Free vibration (or eigenvalue analysis) is a prerequisite for aeroelastic analysis. For divergence analysis, slope influence coefficients (rotation at point i due to unit load at point j) are calculated using free vibration mode shapes and corresponding frequencies. The lowest eigenvalue is of interest and gives the divergence speed. The present paper considers the maximization problem of eigenfrequencies for composite panels. The influence of boundary conditions and constant or variable stiffnesses on optimization results are investigated herein. A new convenient set of design variables is employed in the analysis. The computations are carried out with the use of the Rayleigh–Ritz method and Finite Element analysis (2D quadrilateral and 3D solid elements).

Description: Aerospace, Vol. 5, Pages 94: Fast and Robust Flight Altitude Estimation of Multirotor UAVs in Dynamic Unstructured Environments Using 3D Point Cloud Sensors Aerospace doi: 10.3390/aerospace5030094 Authors: Hriday Bavle Jose Sanchez-Lopez Paloma Puente Alejandro Rodriguez-Ramos Carlos Sampedro Pascual Campoy This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the conventional sensors such as laser altimeters, barometers, or accelerometers, which have several limitations when used individually. Our proposed algorithm includes two stages: in the first stage, a fast clustering of the measured 3D point cloud data is performed, along with the segmentation of the clustered data into horizontal planes. In the second stage, these segmented horizontal planes are mapped based on the vertical distance with respect to the point cloud sensor frame of reference, in order to provide a robust flight altitude estimation even in presence of several static as well as dynamic ground obstacles. We validate our approach using the IROS 2011 Kinect dataset available in the literature, estimating the altitude of the RGB-D camera using the provided 3D point clouds. We further validate our approach using a point cloud sensor on board a UAV, by means of several autonomous real flights, closing its altitude control loop using the flight altitude estimated by our proposed method, in presence of several different static as well as dynamic ground obstacles. In addition, the implementation of our approach has been integrated in our open-source software framework for aerial robotics called Aerostack.

Description: Aerospace, Vol. 5, Pages 93: Effect of Ramie Fabric Chemical Treatments on the Physical Properties of Thermoset Polylactic Acid (PLA) Composites Aerospace doi: 10.3390/aerospace5030093 Authors: Chunhong Wang Zilong Ren Shan Li Xiaosu Yi Ramie fabric-reinforced thermoset polylactic acid (PLA) composites were prepared by using heat pressing technology. Fabrics were treated with alkali, silane, and alkali–silane respectively, expecting an improvement of the interface between the fabric and the matrix. Scanning electron microscopy (SEM) results indicated that after alkali treatment, impurities on the fiber surface were removed and its diameter became finer. After the silane, and alkali–silane treatments, the contact angles of the ramie fibers increased by 14.26%, and 33.12%, respectively. The contact angle of the alkali–silane treated fiber reached 76.41°; this is beneficial for the adhesion between ramie fiber and the PLA. The research revealed that the tensile strength of the fiber increased after the alkali and silane treatments. A slight decrease was noticed on the tensile strength of fibers treated with alkali–silane. After all, three chemical treatments were done, the flexure strength of the ramie fabric-reinforced PLA composites, improved in all cases. Among the three treatments, the alkali–silane treatment demonstrated the best result, as far as the flexure strength and modulus of the fabricated composites were concerned. On the other hand, water absorption of the related composites decreased by 23.70%, which might contribute to the closer contact between the ramie fiber and the matrix. The ramie fabric-reinforced PLA composites, prepared in this study, can meet the standard requirements of aircraft interior structures and have favorable application foreground.

Description: Aerospace, Vol. 5, Pages 92: Unsteady Lifting Line Theory Using the Wagner Function for the Aerodynamic and Aeroelastic Modeling of 3D Wings Aerospace doi: 10.3390/aerospace5030092 Authors: Johan Boutet Grigorios Dimitriadis A method is presented to model the incompressible, attached, unsteady lift and pitching moment acting on a thin three-dimensional wing in the time domain. The model is based on the combination of Wagner theory and lifting line theory through the unsteady Kutta–Joukowski theorem. The results are a set of closed-form linear ordinary differential equations that can be solved analytically or using a Runge–Kutta–Fehlberg algorithm. The method is validated against numerical predictions from an unsteady vortex lattice method for rectangular and tapered wings undergoing step or oscillatory changes in plunge or pitch. Further validation is demonstrated on an aeroelastic test case of a rigid rectangular finite wing with pitch and plunge degrees of freedom.

Description: Aerospace, Vol. 5, Pages 91: Conceptual Advanced Transport Aircraft Design Configuration for Sustained Hypersonic Flight Aerospace doi: 10.3390/aerospace5030091 Authors: Can Alkaya Ashish Alex Sam Apostolos Pesyridis The conceptual aircraft design and its integration with a combined cycle engine for hypersonic cruise at Mach 8 is documented in this paper. The paper describes the process taken to develop a hypersonic aircraft from a conceptual approach. The discussion also includes the design and CFD analysis of the integrated combined cycle engine. A final conceptual hypersonic transport aircraft with an integrated combined cycle engine was achieved through this study. According to the analysis carried out, the aircraft is able to take-off and land at the airports it is intended to be used and will be able to generate enough thrust to sustain hypersonic cruise at an altitude of 30 km.