Coaxial Configuration Research Articles

Experimental Evaluation and Flight Simulation of Coaxial-Rotor Vehicles in Icing Clouds

Coaxial rotor configurations are common in multirotor unmanned aircraft systems (UAV) and are used in some manned helicopters. In the case of small-to-medium-sized unmanned rotorcraft, there is a lack of experimental data on icing and a lack of analysis of vehicle performance and flight characteristics in icing conditions. This paper (a) describes experimental methodology and results of a coaxial rotor system with 0.46-m-diameter rotors operating in hover in an icing cloud, (b) develops an empirical model relating the change in torque and thrust as a function of rotor speed and ice accretion rate based on experimental data, and (c) applies this model to a simulation of UAV in icing conditions. Experimental results showed linear growth in required torque and linear reduction in thrust at a given rotor speed as ice accretes, with the rate of change of torque and thrust dependent on shaft speed and temperature. A significant difference in ice accretion rate was observed between the upper and lower rotors, with the lower rotor showing a lower rate of ice accretion. Simulation of UAV flight in icing conditions showed rapid loss of control and a loss of ability to maintain hover, with loss of sustained flight occurring within 40 s of the onset of icing. Simulation of flight with an ice-shedding event (which results in a step change in thrust and torque) results in a perturbation in pitch and roll, leading to significant lateral acceleration in addition to loss of altitude.

Investigation of the Effects of Plasma Discharges on Methane Decomposition for Combustion Enhancement of a Lean Flame

The present work focuses on the impact of dielectric barrier discharge (DBD) plasma actuators (PAs) on non-premixed lifted flame stabilization in a methane CH4-air Bunsen burner. Two coaxial DBD-PA configurations are considered. They are composed of a copper corona, installed on the outer surface of a quartz tube and powered with a high voltage sinusoidal signal, and a grounded needle installed along the burner axis. The two configurations differ in the standoff distance value, which indicates the positioning of the high frequency/high voltage (HV) electrode’s upper edge with respect to the needle tip. Experimental results highlight that flame reattachment is obtained at a lower dissipated power when using a negative standoff distance (i.e., placing the needle upstream with respect to the corona). At 11 kV peak-to-peak voltage and 20 kHz frequency, plasma actuation allowed for reattaching the flame with a very low dissipated power (of about 0.05 W). Numerical simulations of the electrostatic field confirmed that this negative standoff configuration has a beneficial effect on the momentum sources, which oppose the flow and show that the highest electric field extends into the inner quartz tube, as confirmed by experimental visualization close to the needle tip. The modeling predicted an increase in the gas temperature of about 21.8 °C and a slight modification of the fuel composition at the burner exit. This impacts the flame speed with a 10% increase close to the stoichiometric conditions with respect to the clean configuration.

Lightweight unmanned aerial vehicle for emergency medical service – Synthesis of the layout

The article presents the innovative unmanned aerial vehicle project for emergency medical services. Designed unmanned aerial vehicle combines vertical takeoff and landing characteristics with fast forward flight capability that are vital to perform such an emergency medical mission. The main purpose of the designed unmanned aerial vehicle is to deliver the necessary medical package to the place where access is difficult, and estimated arrival time of conventional ambulance is too long. The cost of the support of such unmanned aerial vehicle could be significantly lower than in case of medical helicopter, which is not necessary in some cases. Designed unmanned aerial vehicle can also be used for fast delivery of essential medical substances (e.g. blood). The selection of configuration was the first and crucial step of the design. After analysis of many different copter configurations, together with selected crash reports analysis, the coaxial quadcopter configuration crossed with conventional airplane was selected. All power units for VTOL capability are electric, and they are doubled for redundancy purposes, with maximum T/W ratio about 2.0. Such configuration allows to sustain a stable flight (vertical phases) in case of one motor failure. Two versions of the vehicle are designed: fully electric (power units for the forward flight and vertical takeoff and landing are electric) and mixed where forward flight unit is a small piston engine. The final layout was the result of conceptual investigation and preliminary research, MDO and trade-off analysis, where as many aspects as possible were considered. The main problem was to meet the vertical takeoff and landing capabilities, relatively long range and endurance, expected payload (3 kg) and the requirement not to exceed 25 kg of maximum take-off weight. Paper presents the design process from initial requirement to the final configuration accepted to be manufactured.

Generation of cold atmospheric plasma jet by a coaxial double dielectric barrier reactor

In this study, the generation of cold atmospheric plasma jet was investigated in a coaxial double dielectric barrier configuration conjugated with a microsecond voltage pulse generator. The advanced reactor comprised two coaxial dielectric tubes of different diameters with two ring-shaped electrodes covering outside the larger tube. The electrodes were immersed in a liquid dielectric (i.e. transformer oil) in order to isolate them from the ambient air, which completely prevented the direct sparks formation between them within the investigated range of the applied voltage. The He discharge gas was fed to the inner tube while either air, N2, or O2 as a shielding gas was introduced into the gap between the two dielectrics. The result revealed that with these shielding gases, the unwanted abnormal discharge in the inter-dielectric gap was extinguished and the plasma discharge occurred only in the He gas in the inner tube. Consequently, the electrical power delivered to the He discharges maintained at a level of around 1 W with a considerable variation in the applied voltage. Meanwhile, the discharge power of the unshielded jet was almost tripled as the applied voltage was increased from 7 to 10 kV. Interestingly, the cold plasma jet generated by the alternative reactor design in this study, which had the electron density up to 2.5 × 1013 cm−3, consumed relatively less He gas with less restriction on the high voltage range applied. The design also enhanced the possibility to control the plasma chemistry and jet temperature by changing the shielding gas. Therefore, the reactor is capable of producing a cold atmospheric plasma jet for the emerging plasma application such as plasma medicine and bio-applications.

Flow-Field and Performance Study of Coaxial Supersonic Nozzles Operating in Hypersonic Environment

The integration of multiple propulsion systems in a coaxial configuration is one of the challenges to realize hypersonic passenger transportation. This study is an attempt to understand the performance of two co-axial jets exiting from the base of slender body, operating in single and dual operation mode in freestream hypersonic flow environment. In addition, the effects on performance by adding a different length common channel to both co-axial jets are studied. In the first part of this study, the experiments have been performed for small slender body kept in hypersonic Mach 7 flow, which consists of two inner high-pressure chambers and two co-axial nozzles at the base: central nozzle (Mach 4) and surrounding nozzle (Mach 2.8) along with extended common region, termed as common channel. Schlieren images have been captured for single and dual operation modes. Axisymmetric numerical simulations have been performed for further understanding of the flow interactions and have been qualitatively validated with experimental images. In the second part, the parametric study has been performed using numerical simulations for resized model with various exit Mach numbers for central and surrounding jets along with effect of no common channel and with common channel for various operation modes. One of the findings of the study is that dual jets should operate and exit at same plane (no common channel) with the same exit area (each nozzle with half of total available exit area) in order to have higher total thrust from both jets than the sum of individual jets operating in single operation mode. For higher central jet Mach numbers, the corresponding surrounding jet Mach number will be lower, and in dual operation mode (without common channel), the total thrust will be the same or lower than the sum of the individual jet operations. Regarding the effect of common channel, it has been found out that the introduction of the extended short or long common channel in dual mode operation does not have significant effect on thrust, while the jet flow field is strongly affected by the common channel presence. In single operation mode, for Mach 2 central-jet, the thrust performance decreases 12.2-14.6 % in presence of short and long (29.5 mm and 59 mm) common channel, while for Mach 2 surrounding jet, the thrust performance increases by 15-17.4 % in presence of common channel.

Numerical modelling of a coaxial Stirling pulse tube cryocooler with an active displacer for space applications

A numerical model for a coaxial Stirling pulse tube cryocooler with an active displacer has been developed. An active displacer, in place of an inertance tube, has already demonstrated good efficiency in an in-line pulse tube, but incorporating this design into a coaxial configuration permits better access to the cold head. A model of the coaxial cold head was developed to include the radial flow and cooling in this region. The sub-assembly models were validated with flow testing of the physical sub-units of the cryocooler. The performance has been predicted for the cryocooler as a function of: fill pressure, operating frequency, and phase angle between the position of the linear compressor and displacer. The projected difference in performance and efficiency of the coaxial configuration was compared to the in-line design. The coaxial cryocooler numerically simulates 6 W of cooling at 80 K with an input power of 85 W, at a fill pressure of 28 bar, an operating frequency of 60 Hz, and a compressor-displacer phase angle of 41°. Overall, the coaxial cryocooler outperforms the in-line design in terms of cooling power, but not in terms of efficiency.

Degradation of Pharmaceutical Contaminant Tetracycline in Aqueous Solution by Coaxial-Type DBD Plasma Reactor

Tetracycline is one of the widely used antibiotic drugs, but it also causes severe water pollution. This research applied a pulsed dielectric barrier discharge (DBD) plasma reactor of coaxial configuration with a screw-type high-voltage electrode to treat tetracycline in an aqueous solution, which was recycled to flow over the surface of the inner electrode. The effects of discharge voltage, initial concentration, and pH value of tetracycline on the degradation efficiency, total organic carbon (TOC) removal rate, kinetic rate constant (k), and energy efficiency were investigated. The results show that 92.3% degradation efficiency and 65.01% TOC removal rate of tetracycline were achieved at the initial concentration of 50 mg/L, corresponding to the energy efficiency of 20.24 g/(kW·h). The tetracycline degradation efficiencies were dependent on the initial concentration from 5 to 75 mg/L, which led to the decrease of the degradation kinetic rate constant from 0.518 to 0.077 min-1. The TOC removal rate of tetracycline was strongly enhanced at higher pH values from 1.5 to 10.5, with the optimum value at 7.5. The intermediate products of tetracycline produced by the plasma treatment were analyzed by liquid chromatography mass spectrometry (LC-MS), which show that the aromatic ring, amino group, and the double bonds were mainly attacked by the hydroxyl radical and other reactive oxygen species. A possible degradation pathway has also been proposed.

FMN riboswitch aptamer symmetry facilitates conformational switching through mutually exclusive coaxial stacking configurations

Knowledge of both apo and holo states of riboswitches aid in elucidating the various mechanisms of ligand-induced conformational “switching” that underpin their gene-regulating capabilities. Previous structural studies on the flavin mononucleotide (FMN)-binding aptamer of the FMN riboswitch, however, have revealed minimal conformational changes associated with ligand binding that do not adequately explain the basis for the switching behavior. We have determined a 2.7-Å resolution crystal structure of the ligand-free FMN riboswitch aptamer that is distinct from previously reported structures, particularly in the conformation and orientation of the P1 and P4 helices. The nearly symmetrical tertiary structure provides a mechanism by which one of two pairs of adjacent helices (P3/P4 or P1/P6) undergo collinear stacking in a mutually exclusive manner, in the absence or presence of ligand, respectively. Comparison of these structures suggests the stem-loop that includes P4 and L4 is important for maintaining a global conformational state that, in the absence of ligand, disfavors formation of the P1 regulatory helix. Together, these results provide further insight to the structural basis for conformational switching of the FMN riboswitch.

Natural Gas Conversion by Pulsed Barrier Discharge at Atmospheric Pressure

We simulated and experimentally studied the process of the interaction of a barrier discharge with natural gas in a plasma-chemical reactor with a coaxial electrode configuration. The obtained dependences of the hydrocarbon concentration on the average specific energy supplied to the discharge are linear. An explanation of the observed results is proposed.

Highly conducting silver nanowire‐polyacrylonitrile hollow fibres for flexible supercapacitors

A new approach for making stable, flexible, and conductive hollow fibres of poly (acrylonitrile) using dry-jet-wet spinning technique is investigated, wherein the inner walls of the poly (acrylonitrile) hollow fibres are deposited with silver nanowires using their dispersion in the bore fluid. The bore fluid plays a crucial role in determining the morphology and flexibility of the hollow fibres and entrapment of long silver nanowires on the inner walls. Fibres with AgNW layer having high conductivity of ~104 Scm−1 are obtained with the use of ~2 wt% of silver nanowires. The conducting fibres are successfully assembled into coaxial configuration to yield highly stable, flexible supercapacitors with capacitance value of 128 Fcm−3. The unique morphology of these conductive hollow fibres opens the possibility of making flexible and stable devices for wearable electronics.

Investigation on “cold” and “hot” characteristics of different configurations of corrugated coaxial slow wave structures

Various configurations of corrugated coaxial Slow-Wave Structures (SWSs) are utilized in O-type Cherenkov oscillators to achieve different goals. This is the reason why a strategy targeting the proper selection of corrugated coaxial SWSs configurations deserves to be further studied. In this paper, high frequency characteristics of different configurations of corrugated coaxial SWSs are calculated and analyzed. The analysis suggests that the coaxial SWSs with corrugations on inner conductor only are characterized by higher coupling impedance and higher growth rate of microwave oscillations, while the coaxial SWSs with corrugations on the outer conductor only are characterized by higher power capacity. Due to the low power capacity, coupling impedance and growth rate, the coaxial SWSs with corrugations on both inner and outer conductors are not suitable for O-type Cherenkov oscillators desired to operate in the quasi-TEM mode. However, if these devices are desired to operate in the TM01 quasi-π mode, the SWSs with both inner and outer conductor corrugations may be a better choice to make it happen.

Effect of Temperature on the Working Parameters of Negative Corona Discharge with Coaxial Electrodes Configuration

The influence of ambient temperature on the various parameters of negative corona discharge in atmospheric dry air with coaxial cylindrical electrodes is investigated. The calculations are achieved using the finite element method by COMSOL Multiphysics software. The investigation aims to notice the effect many of working temperatures on the I-V characteristic curve of negative corona discharge in the air. The calculations of several parameters (electron density, temperature, ...) are presented visually and discussed. The results of the work are compared with theoretical and experimental data and they are in a good agreement.

Influence of Propeller Overlap on Large-Scale Tandem UAV Performance

This paper investigates the interference that arises from overlapping Unmanned Aerial Vehicle (UAV) propellers during hovering flight. The tests have been conducted on [Formula: see text] ultralight carbon fiber propellers using a bespoke mount and the RCBenchmark Series 1780 dynamometer at various degrees of overlap [Formula: see text] and vertical separation [Formula: see text]. A great deal of confusion regarding the losses that are associated with mounting propellers in a co-axial configuration is reported in the literature, with a summary of historical tandem helicopters having been conducted. The results highlight a region of beneficial overlap (0–20%), which has the potential to be advantageous to a wide range of UAVs.

DC-driven atmospheric pressure pulsed discharge with volume-distributed filaments in a coaxial electrode system

A nonthermal atmospheric pressure plasma source based on a dc-driven intermittent spark discharge in a coaxial electrode configuration with volumetrically distributed discharge filaments is presented. Spreading the intermittent spark discharge over the volume of the cylindrical discharge chamber is achieved owing to the mutual action of acoustic and magnetic fields on the discharge. The magnetic field scans discharge filaments over the cross section of the cylindrical electrode, while the acoustic field spreads the discharge along the electrode. Electrical parameters and characteristics of the developed nonthermal atmospheric pressure plasma source with volumetrically distributed plasma microchannels are presented.

The Research of an Equivalent Load Used for Testing an Air-Core Pulsed Alternator

The air-core pulsed alternator has the integrated advantages of high energy density and high power density. It has important applications in new concept kinetic energy weapons such as electromagnetic launching and has become the research focus of many countries at present. However, the air-core machine with a current up to mega-ampere level still lacks testing, it is impractical and unscientific for the machine to drive the railgun directly without any experimental basis, and its huge risk and cost for testing must be taken into consideration. This paper presents an equivalent load instead of the electromagnetic railgun, which is used to accomplish the relevant testing research and theoretical verification. In this text, the design scheme for the equivalent load is proposed according to performance requirements, and it is composed of an inner cylinder and an outer cylinder with a coaxial configuration. Then, the design is carried out by taking parameters of resistance, inductance, maximum temperature rising, stress, and length into consideration. Finally, it is necessary to develop simulations to verify electrical and mechanical performances of the load. The results provide a technical guidance and support for the actual railgun testing. It is helpful to promote the development of the air-core pulsed alternator, directly driving the electromagnetic railgun.

Effects of sloshing gas–liquid interface on dynamics of meandering bubble plumes and mixing in a shallow vessel: PIV and PLIF measurements

Gas–liquid shallow vessels are widely used in steel-making and refining processes in the steel industry. The efficiency of these processes or the quality of steel depends on the extent of gas–induced liquid–phase mixing achieved through top–blowing of oxygen and bottom–blowing of inert gases. In the present work, the effects of combined top and bottom gas injection and sloshing interface on the dynamics of gas–liquid flow, and their role in the liquid–phase mixing in a shallow vessel, that corresponds 1:6 scaled–down model of a ladle used in steel refining, are investigated. The effects of interface sloshing and top blowing on the motion of multiple meandering bubble plumes on the liquid–phase velocity distribution, recirculatory flow structures and turbulent kinetic energy are analyzed using the time–resolved Particle Image Velocimetry (PIV) measurements. Further, the role of the aforementioned parameters on the liquid–phase mixing is analyzed using the Planar Laser Induced Fluorescence (PLIF) measurements. The effects of coaxial and eccentric top blowing configuration on the liquid flow structures and mixing are also investigated. In the case of combined top and bottom gas injection, in which gas was injected very close to the interface, the liquid–phase mixing was found to be significantly faster than that of the other configurations considered in the present work, due to the formation of strong downward flow regions and higher turbulent kinetic energy provided by the top blowing. The present investigations help to understand and to quantify the effects of the different top gas injection configurations on the meandering motion of bubble plumes, liquid flow structures, turbulence and their contributions to liquid–phase mixing.

Hybrid plasma chemical reactors for bio-polymers processing

Design of a hybrid plasma-chemical reactor in which strongly non-equilibrium low-temperature plasma is generated by joint action of a continuous electron beam and RF-gas discharge on gaseous media at moderate pressures (0.1–10 Torr) is described. Several versions of the reactor in a co-axial configuration were tested on the special experimental setup. Main characteristics of the reaction zone were studied as functions of electron beam and gas discharge parameters, plasma-generating media properties and peculiarities of the working process features. Temperature regimes of the materials processing were reliably controlled by the electron beam parameters. The reactor was applied to thin films and dispersed powders of natural polysaccharides (chitosan) and biomaterials (wood) processing to produce valuable low-molecular and bioactive compounds. In hybrid plasma of oxygen, the active particles responsible for the materials modification effects are atomic oxygen, ozone and singlet oxygen. Special software simulating the reactor operation and material treatment processes in plasmas of oxygen was developed and experimentally verified.

Thermal modeling of deep borehole heat exchangers for geothermal applications in densely populated urban areas

Ground coupled heat pumps are known as very energy efficient heating and cooling systems for a variety of building applications. In densely populated areas where new urbanization is intense, deep ground heat exchangers can be a valuable and effective solution for geothermal heat pump applications. In this paper a finite difference numerical model has been developed starting from literature contributions by Holmberg et al. (2016). The in house Fortran90 code has been built and validated to cope with variable longitudinal and radial mesh distribution for simulating coaxial pipe configurations. Different ground properties and geothermal gradients can be applied. Far field boundary conditions, ground pipe meshing and Courant numbers have been varied for enhancing the accuracy in predicting the fluid temperature evolution. The model has been extensively validated against analytical solutions and literature data. The model has been applied for analyzing the behavior of deep heat exchangers in the 500–800 m range and the effects of the pipe diameter ratio have been investigated both in terms of fluid temperature evolution and pressure losses inside inner and annular pipes.

Multi-frequency effect towards High Conductivity Overburden Responses using Horizontal Coplanar (HCP) coil configuration for Landslide Hazard Instrumentation

The instrumentation for the sensing of natural disaster phenomena as like as landslide instrumentation has acquired great importance for the instrumentation community. The novel instrumentation for landslide application has been made and calibrated using Horizontal Coplanar (HCP) coil orientation. The early instrumentation for landslide slopes was gradually equipped with standard and automatic instrumentation consisting of three the piezometric cells, two deep-seated steel wire extensometers, four in clinometric tubes, a rainfall gauge, a snow gauge and an air thermometer. This novel instrumentation works in electromagnetic methods similar with electromagnetic methods in geophysics. HCP coil orientation is a coplanar array where both coils are horizontal. In HCP, the depth of sounding is about 1.5 times of the coils separation which have maximum coupled configuration (HCP, VCP, and Vertical Coaxial configuration). The overburden response had inverted the percent value of maximum negative response then there were three maximum response amplitude peaks. Measurement and data processing were performed using a computer through Delphi program. The diagonal cross sections of the overburden as the centre were the maximum value of inverted response of anomaly positions. In aluminium thin plate overburden, the diagonal cross section point as the overburden centre was the maximum value of inverting value of the highest minimum response amplitude. The measurement graphic in the computer screen with several types of overburdens would be displayed. As the result, that the overburden widths for overburden were determined by subtracted of two turning points positions. The overburden positions were accurate for Type P overburden. The master curve had a high anomaly contrasts with two of positive anomaly peaks. Otherwise, the anomaly positions were between two of the negative anomaly peaks.

Development by robocasting and mechanical characterization of hybrid HA/PCL coaxial scaffolds for biomedical applications

Porous structures consisting of a tetragonal three-dimensional mesh of interpenetrating coaxial tubes were fabricated by robocasting from hydroxyapatite (HA) inks. After sintering the structures, polycaprolactone (PCL) was infiltrated within the tubes core by injection of a polymer solution. The addition of the polymer enhanced the mechanical performance in terms of toughness over dense- and hollow-strut all-ceramic scaffolds, specially under bending stresses. PCL impregnation improved also the compressive strength over hollow-strut scaffolds —although dense-strut structures remained stronger especially in compression. Thus, this coaxial core-shell strut configuration combines the best features of each material: the necessary stiffness and excellent osteoconductivity of the bioceramic, with the high toughness and ductility of the biopolymer; and allows the fabrication of hybrid scaffolds with the interconnected macroporosity necessary for cell ingrowth. Hence, this work successfully provides a proof-of-concept of this novel strategy for the mechanical enhancement of bioceramic-based scaffolds while preserving their osteoconductive properties.