Thrust Efficiency Research Articles

NetherDrone: a tethered and ducted propulsion multirotor drone for complex underground mining stope inspections

Underground stope mapping is crucial to evaluate the quantity of blasted rock and the site integrity. In recent years, lidar-equipped drones have been used to map stopes with higher precision and without blind spots. However, they have limitations, such as large size, challenging lidar positioning on the drone, limited flight time for detailed visual inspections, and unreliable communication underground. This paper discusses the development of a compact tethered drone called the NetherDrone, specifically designed for stope inspections. The NetherDrone uses custom ducted propulsion to increase thrust efficiency by 50%. It reduces the propellers’ diameter and overall frame while maintaining an adequate lifting capability with low power consumption. The drone features an onboard 120 m tether spool for communication and power transmission, as well as a rotating arm to deploy the cable and reduce yaw moments from the tether tension. Flights in a real stope demonstrated that the drone could effectively move at least 50 m deep into a complex stope, complete a detailed lidar scan, visually scan one face of the stope in close proximity during 20 min, travel a total distance of 270 m, and maintain communications with an operator at all times through the tether.

Experimental characterization of thrust production mechanisms in a magnetic nozzle ECR thruster

Direct thrust measurements have been performed on a low-power (30 W) ECR plasma thruster operated with xenon. The total thrust, the force exerted on the walls of the source (thermal thrust), and the force exerted on the permanent magnet (magnetic thrust) have been measured separately for various operating conditions (power and flowrate). The results are compared for two magnetic field topologies (with a different magnetic field gradient and divergence). The magnetic thrust dominates thermal thrust for most operating conditions, and its contribution to total thrust can be as high as 80%. A saturation of magnetic thrust with increasing power has been observed and is correlated with a decrease in thrust efficiency. A high degree of electron anisotropy can be inferred from the thrust measurements.

Model of Multistaged Ducted Thrusters for High-Thrust-Density Electroaerodynamic Propulsion

Electroaerodynamic (EAD) thrusters are a means of producing a propulsive force in air that does not require any moving parts and is nearly silent. In these devices, ions generated from atmospheric air are accelerated by an electric field across two electrodes at different potentials, resulting in an ionic wind and a thrust force. It has been demonstrated that EAD is a feasible form of aircraft propulsion; however, substantial performance improvements are needed for practical applications. Here, multistaged ducted (MSD) EAD thrusters, which have the potential to provide higher thrust density than previously demonstrated, are proposed and modeled. An MSD thruster contains multiple sets of electrode pairs in series, enclosed in a duct and fitted with an inlet and a nozzle. One-dimensional momentum theory is combined with models for two limiting cases for the pressure generated by each stage: ideal one-dimensional EAD stages and wire-to-airfoil corona-discharge stages. The model evaluates how geometric and electrical parameters affect the performance of MSD thrusters under both sets of assumptions. If pressure losses per stage are kept small, the results show that MSD thrusters can provide order-of-magnitude improvements in thrust density and efficiency as compared to single-stage thrusters, potentially broadening the type of missions that can be performed by EAD thrusters.

Modelling of oscillating foil propulsors in waves

This study addresses the possibility of extracting energy from gravity waves for marine propulsion by an oscillating hydrofoil. Moreover, it investigates theoretical and numerical methods to achieve modelling of active oscillating wave thrusters. The first part of this work presents a semi-analytical model based on an extension of classical theory of a 2D unsteady hydrofoil, with large oscillations, in waves, including free-surface effects. The second part investigates the same problem with numerical modelling using a CFD solver. Specifically, a deforming grid method is used for body motion modelling, enabling the simulation of cases with large forced motions. The results of the semi-analytical model for mean thrust and propulsive efficiency are compared with published numerical and experimental data, with fair-to-good agreement. The results of CFD simulations for 2D and 3D test cases are investigated, allowing physical interpretation of flow dynamics and forces. Preliminary comparisons with published numerical and experimental results show a promising good agreement. The overall results suggest that the semi-analytical model may prove its usefulness in preliminary design studies, and the CFD model showed itself to be a tool capable of delivering more accurate results for the most complex cases and providing a comprehensive understanding of the flow dynamics.

Study of a low-power micro coaxial pulsed plasma thruster with axial applied magnetic field

Pulsed plasma thrusters (PPTs) have been widely used in nano/micro-satellites in recent years. However, the efficiency of a low-power (<10 W) PPT is typically lower than 10%. Applied magnetic fields are widely used in electric propulsion to improve performance. However, few attempts have been made to use applied magnetic fields in low-power PPTs because of the high discharge current (kA), short pulse duration (μs), and oscillating current in the discharge process. The results of an experimental study on a low-power micro coaxial PPT with axial applied magnetic field are presented in this paper. The thrust, ablation, and discharge characteristics of the thruster are obtained under different applied magnetic fields. The results show a significant improvement in thruster efficiency. Using magnets that can generate magnetic fields of up to 0.3 T, 0.4 T, and 0.5 T result in efficiencies for the PPT of 15.6%, 24.7%, and 67.8%, respectively, which are 1.91, 3.03, and 8.34 times that in the absence of an applied magnetic field (8.1%). The results also show that the applied magnetic field has little influence on the discharge circuit and slightly affects the discharge characteristics and ablated mass bit (the consumption of propellant per discharge) of the thruster.

Experimental characterization of the electrospray propulsive performance for ionic liquid propellants [EMIm][DCA] and [BMIm][DCA]

A chemical-electrospray dual-mode propulsion system is significant in improving mission capability and flexibility of a spacecraft. Hypergolic ionic liquids are potential propellants of chemical and electrospray propulsion systems. In this work, the electrical propulsive performance of two hypergolic ionic liquids 1-ethyl-3-methylimidazolium dicyanamide ([EMIm][DCA]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIm][DCA]) are experimentally characterized using two array-emitter electrospray thrusters. Compared with a commonly used ionic liquid propellant 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]), the current magnitude and current steadiness of the electrospray thruster with [EMIm][DCA] and [BMIm][DCA] are efficiently improved, especially with [EMIm][DCA] as propellant. The results show that the low viscosity is beneficial for steady and sufficient flow supply and thus favors a long-time steady operation of the thruster. For the propellant [EMIm][DCA], the maximum specific impulse is 1791 s, i.e., 27.8% higher than that of [EMIm][BF4], while the maximum thrust 32.5 μN is 128.9% greater than that of [EMIm][BF4]. For the propellant [BMIm][DCA], the thrust-to-power ratio of the thruster is approximately 82.8% higher than that of [EMIm][BF4] at a similar specific impulse of about 1120 s resulting from a much greater thruster efficiency. These results demonstrate that [EMIm][DCA] has a better performance than [EMIm][BF4] in both maximum thrust and specific impulse, and [BMIm][DCA] performs best in the aspect of thrust-to-power ratios. This work highlights the prospect of hypergolic ionic liquids and is valuable to promote their application in chemical and electrical propulsion communities.

Biomimetic Robotic Sea Lion Foreflippers: Design, Modeling, and Experimentation

Otariidae are excellent swimmers and the only ones among the marine mammals that use foreflippers for propulsion. Taking California sea lion as the bionic prototype, this article proposed and developed a biomimetic robotic sea lion foreflipper device (robotic flipper for short), which is composed of a pair of bionic flippers and a serial mechanism consisting of a wobbling coin mechanism and a RSSR spatial crank-rocker mechanism. The attitude and motion characteristics of the bionic flipper were obtained based on the kinematic analysis of the robotic flipper. Kinematic analysis and tank experiments show that the robotic flipper can effectively imitate the motion characteristics of the sea lion foreflipper. In addition, it can also obtain different flipper tip trajectories by adjusting the length of the connecting rod of the RSSR mechanism, and the generated thrust from the trajectory like sea lion foreflipper is larger than that from other flipper tip trajectories. A higher clapping frequency can generate a higher thrust, and the bionic flexible flipper has higher thrust and thrust efficiency than the rigid one. A larger pitch angle of the robotic flipper can result in a larger peak thrust but not always a larger average thrust. The present robotic flipper shows a better thrust performance at the pitch angle of 15°.

Thrust measurements and mesothermal plasma plume of the Alternative Low Power Hybrid Ion Engine (alphie)

The high specific impulse Alternative Low Power Ion Engine (alphie) is a gridded plasma thruster different from conventional (Kaufman) ion engines. In this disruptive concept, the ionization of the propellant neutral gas and the neutralization of ion outflow is achieved with only one cathode located in front and outside of the thruster. Electrons and ions move under the self-consistent field created by the DC voltage applied to its two planar grids together with the currents of charges flowing through them, unlike to conventional ion engines, where only ions move through its ion optics system. The stationary mesothermal flow of ions and electrons in the plasma plume is characterized with a retarded field energy analyzer in conjunction with Langmuir and emissive probes. The ion velocity distribution functions and the electron energy spectra for different operating conditions of the alphie thruster are discussed. The observed high ion temperatures are explained by the collisional interaction between the fast ionizing electrons and the neutral atoms that increases their average kinetic energy. Finally, the alphie delivers 0.8-3.5 mN throttleable thrusts giving specific impulses in the range of 14000-20000 s with estimated thruster efficiencies between 8% and 40%.

CFD Simulation Model for Optimum Design of B-Series Propeller using Multiple Reference Frame (MRF)

Propulsion system is one of ship systems which require more attention, especially on propeller design. The propeller design greatly affects the ship speed. It is expected to be able to have maximum value of thrust coefficient and efficiency. Hence, the optimum design of propeller can be obtained by multi objective optimization process. In this study, a preliminary optimization is applied to B-series propeller with the Non-dominated Sort Genetic Algorithm-II (NSGA-II). The purpose of this study is to find out the optimum performance of B-series propeller. The thrust coefficient and open water efficiency are maximized in the optimization process which are then subjected to constraint function imposed by required thrust. The optimization is carried out to blade number Z=3 and Z=5. The population of design space is obtained after running the optimization program. The final optimum design parameter is considered using crowding distance value in the population. The result obtained by NSGA-II showed that the optimum design for Z=3 are B3-787, B3-314, B3-560, and Z=5 are B5-416, B5-501, B5-476 respectively. In addition, the Computational Fluid Dynamics analysis (CFD) is employed to investigate the characteristic of each propeller model by using Multi Reference Frame (MRF) approach. The CFD results showed that the highest thrust value of the Z=3 is 172.38 kN generated by the B3-787 whereas the highest thrust value of Z=5 is 168.80 kN generated by the B5-501 model.

Thirty percent conversion efficiency from radiofrequency power to thrust energy in a magnetic nozzle plasma thruster

Innovations for terrestrial transportation technologies, e.g., cars, aircraft, and so on, have driven historical industries so far, and a similar breakthrough is now occurring in space owing to the successful development of electric propulsion devices such as gridded ion and Hall effect thrusters, where solar power is converted into the momentum of the propellant via acceleration of the ionized gases, resulting in a high specific impulse. A magnetic nozzle (MN) radiofrequency (rf) plasma thruster consisting of a low-pressure rf plasma source and a MN is an attractive candidate for a high-power electric propulsion device for spacecraft, as it will provide a long lifetime operation at a high-power level due to the absence of an electrode exposed to the plasma and a high thrust density. The high-density plasma produced in the source is transported along the magnetic field lines toward the open-source exit and the plasma is then spontaneously accelerated in the MN. By ejecting the plasma flow from the system, the reaction forces are exerted to the thruster structure including the source and the MN, and the spacecraft is resultantly propelled. The thruster will open the next door for space technologies, while the performance of the MN rf plasma thruster has been lower than those of the mature electric propulsion devices due to the energy loss to the physical walls. Here the thruster efficiency of about 30%, being the highest to date in this type of thruster, is successfully obtained in the MN rf plasma thruster by locating a cusp magnetic field inside the source, which acts as a virtual magnetic wall isolating the plasma from the source wall. The increase in the thrust by the cusp can be explained by considering the reductions of the loss area and the plasma volume in a thrust analysis combining a global source model and a one-dimensional MN model.

A two-stage μCAT-MPD thruster: toward millinewton thrust

We discuss our efforts aimed at simultaneous improvement of the levels of thrust, thrust-to-power ratio (TPR) and efficiency of the two-stage micro-cathode arc thruster with magneto-plasma-dynamical second stage (μCAT-MPD). Such efforts include planar construction of the first stage (μCAT) with tightly-pressed ring anode and central disc cathode, enhanced hardness and durability of the inter-electrode dielectric gap provided by deposited boron-copper thin film, refractory (Mo) second-stage electrode, higher and stabilized second-stage voltage, and improved thermal isolation of the permanent magnet from the discharge area. Aforementioned features allowed achieve the average thrust of milli-newton range – up to 1.7 ± 0.3 mN, together with high TPR of 37 μN/W and efficiency of 50%, remaining low mass (~ 100 g) and low consuming power (~ 50 W) of the thruster.

Experimental Study on the Working Characteristics of Tri-Electrode Plasma Actuator Utilizing a Combination of Corona and Barrier Discharges

A tri-electrode plasma actuator (TED-PA), which has an additional electrode with a DC voltage, induces jets from two facing electrodes and achieves larger thrust and higher efficiency than a conventional dielectric barrier discharge plasma actuator. However, there are problems such as the large potential difference between the exposed electrodes, which can cause sparks and device destruction. Therefore, it is necessary to clarify the working mechanism of TED-PAs and optimize their configuration and applied voltage. In this study, we obtained the discharge photograph, the thrust, and the flow velocity field and investigated the characteristics of the DC voltage and the frequency of the AC voltage. To isolate the effects of the discharge from the potential variation, a corona discharge plasma actuator and a TED-PA were compared. As a result, increasing the frequency of the AC voltage induced stronger jets from the AC and DC electrodes. This result indicates that the barrier discharge enhances the jet from the DC electrode without changing the potential difference between the electrodes.

Heaving foil propulsion performance under combined base and perturbation signal inputs

The thrust variation, efficiency, and wake evolution of a flapping foil were investigated for a variety of base and perturbation frequencies. The study was inspired by the complex environment in which fish swim. In this numerical study, the waveform of the perturbation signal was adjusted by the waveform parameter k. The results demonstrate that the addition of perturbations increases thrust in the majority of cases, with square wave perturbations having the most substantial effect. However, the addition of a perturbation signal reduces the propulsion efficiency; a square wave perturbation significantly reduces the propulsion efficiency, while a sinusoidal or approximate sawtooth wave perturbation slightly decrease the propulsion efficiency. The change in the wake structure is closely related to the perturbation signal waveform, base frequency magnitude, and perturbation frequency magnitude, according to the wake structure analysis. The present work provides useful findings for optimizing underwater vehicle motion parameters.

Propulsive performance of a two-dimensional elliptic foil undergoing interlinked pitching and heaving

We computationally study the propulsive performance of a two-dimensional elliptic foil undergoing interlinked pitching-heaving motion. This motion is realized by pitching the foil about an axis on its centerline outside the foil and by varying the distance between the pitching point and the leading edge. A distance of 0 and −∞ corresponds to leading edge pitching and pure heaving. An in-house fluid-structure interaction solver based on the sharp interface immersed boundary method is employed to resolve the flow field around the foil. We conducted simulations for different cases of the location of the pitching axis and pitching frequency at a Reynolds number of 100. The thrust generation is explained by the dynamics of leading-edge and trailing-edge vortices. The wake corresponding to thrust is either reverse von Kármán or a deflected reverse von Kármán vortex street. Analysis revealed the existence of an optimal pitching point for maximum thrust or propulsive efficiency at a given reduced pitching frequency. The optimal regions of the thrust and propulsive efficiency are quantified as a function of reduced pitching frequency and the location of the pitching axis. The pitching point for the maximum thrust and efficiency is found to be different. We discuss the fluid-mechanical reasons for the variation of propulsive performance with the location of the pitching point and the pitching frequency and corroborate our reasoning with the wake signatures.

Effects of phase difference on hydrodynamic interactions and wake patterns in high-density fish schools

In this study, we numerically investigate the effects of the tail-beat phase differences between the trailing fish and its neighboring fish on the hydrodynamic performance and wake dynamics in a two-dimensional high-density school. Foils undulating with a wavy-like motion are employed to mimic swimming fish. The phase difference varies from 0° to 360°. A sharp-interface immersed boundary method is used to simulate flows over the fish-like bodies and provide quantitative analysis of the hydrodynamic performance and wakes of the school. It is found that the highest net thrust and swimming efficiency can be reached at the same time in the fish school with a phase difference of 180°. In particular, when the phase difference is 90°, the trailing fish achieves the highest efficiency, 58% enhancement compared with a single fish, while it has the highest thrust production, increased by 108% over a single fish, at a phase difference of 0°. The performance and flow visualization results suggest that the phase of the trailing fish in the dense school can be controlled to improve thrust and propulsive efficiency, and these improvements occur through the hydrodynamic interactions with the vortices shed by the neighboring fish and the channel formed by the side fish. In addition, the investigation of the phase difference effects on the wake dynamics of schools performed in this work represents the first study in which the wake patterns for systems consisting of multiple undulating bodies are categorized. In particular, a reversed Bénard–von Kármán vortex wake is generated by the trailing fish in the school with a phase difference of 90°, while a Bénard–von Kármán vortex wake is produced when the phase difference is 0°. Results have revealed that the wake patterns are critical to predicting the hydrodynamic performance of a fish school and are highly dependent on the phase difference.

Performance Analysis of an Electron Cyclotron Resonance Thruster with Various Propellants

The performance of an electron cyclotron resonance thruster is analyzed for operation with argon, krypton, xenon, and water vapor to understand how mass utilization efficiency and frozen flow losses vary across propellant type. The device was operated from 20 to 220 W for flow rates of 0.06–0.4 mg/s. Thrust performance is measured using an inverted pendulum thrust stand, and plasma characteristics are measured using a retarding potential analyzer, ExB probe, Langmuir probe, and emissive probe. Specific impulse is generally found to decrease as the ratio of mass flow rate over power () increases. Probe measurements indicate that this trend is attributed to a combination of lower propellant mass utilization and decreased electron temperatures. The mass utilization efficiency is found to increase with the ratio of thruster length to ionization mean free path for all propellants; however, the data do not support existing theoretical scaling laws, and a more accurate empirical scaling law is proposed. The decrease in electron temperature with also drives an increase in the relative frozen flow losses, which are found to be about a factor of two higher for water propellant. Multiply charged ions did not constitute a significant fraction of the plume for the atomic species. Mass utilization efficiency and frozen flow losses describe the trends in the thrust efficiency but not the overall magnitude, which suggests that microwave coupling and diffusion to the walls are dominant loss processes.

High-temperature superconductor-based power and propulsion system architectures as enablers for high power missions

The increasing competitiveness of electric propulsion systems (EPS) for primary spacecraft propulsion has paved the way for higher payload mass fractions by offering significantly higher specific impulses than chemical systems. Concurrently, High-Temperature Superconductors (HTS) have reached an unprecedented level of industrial maturity in recent years, and considering their low masses, compactness, and high current densities, they offer the potential to act as a disruptive technology in several spaceflight applications such as power management systems, re-entry and radiation shielding as investigated in the EU-funded MEESST project, as well as EPS. In the latter case, efforts are already ongoing to develop an HTS-enhanced Applied-Field Magnetoplasmadynamic (AF-MPD) thrusters for high power mission applications. The Tsiolkovsky equation infers that the payload mass fraction increases indefinitely with increased Specific Impulse (Isp), however, in the case of electric propulsion, the dependence of thrust on the available power complicates this issue when transfer time is a primary driver. Here, the Tsiolkovsky equation becomes inadequate and considering a non-dimensional version of the Tsiolkovsky equation in terms of the mission ΔV and transfer time, the EPS thrust efficiency, and the specific mass of the power system becomes necessary. This paper first discusses the recent advances in HTS and their suitability for spaceflight, before reviewing The development of power system technologies is reviewed and a conceptual power system architecture incorporating HTS is presented. These technologies are analysed using a non-dimensional Tsiolkovsky approach and their impacts on the overall payload mass fraction are assessed. For high-power missions (>100 kW), the use of HTS is shown to have a highly beneficial impact on the mass of the power system. Correspondingly, this enables higher payload mass fractions achievable at increased specific impulse operation, thus strengthening the case for high-power, high-Isp EPS technologies such as AF-MPDT.

The presence of downstream ramp on fuel mixing of the multi micro jets at supersonic cross flow

Development of the fuel injection system in combustion chamber is greatly important for the overall thrust efficiency of the high-speed vehicles. Current article developed a three-dimensional model to discover the reality of downstream ramp on fuel mixing of the multi-jet at Ma>1. FVM is hired to scrutinize the impact of injector types (3-lobe, circular and rectangular shape) on the mixing productivity of downstream ramp in combustion chamber. Besides, the effects of ramp angle on fuel mixing are also analysed. Fuel mixing mechanisms in the selected models are investigated by comparing the Ma contour and mixing zone. Comparisons of the circulation strength downstream of these models confirm that the 3-lobe nozzles is more efficient than other styles. Our comparison indicates that overall mixing productivity of the circular jet is more than other cases.

A numerical investigation of the effect of blade number on the performance of an INSEAN E779A marine propeller in a cavitating flow using computational fluid dynamics

A propeller's thrust coefficient, efficiency, and torque coefficient are important performance characteristics. They can be harmed by the presence of cavitating flow. Previous numerical studies have shown that cavitating flow can damage a marine propeller as well as reduce its performance. The work presented here investigates the effect of blade number variation on the performance of an INSEAN E779A marine propeller in a cavitating flow. The cavitating flow simulations are performed using computational fluid dynamics with four different rotational and inlet speeds using the fully turbulent standard k-ε model and the Schnerr-Sauer cavitation model. The numerical results of varying the number of blades on propeller performance characteristics are presented here. It is concluded that increasing the number of propeller blades improves propeller performance. In contrast, the cavitation area is reduced, but cavitation is more likely to occur as rotational speed increases.

Design and Analysis of a Novel Tubular High-PM-Utilization Transverse-Flux Linear Machine

Owing to the low permanent magnet (PM) utilization in conventional transverse-flux machines, a novel tubular high-PM-utilization transverse-flux linear machine (HPMU-TFLM) is proposed in this article. The PM utilization ratio of the proposed machine is nearly 100% in theory. Thus, this machine presents a higher power factor and thrust density. First, the basic structure and operation principle of HPMU-TFLM are introduced. The flux-concentrating teeth and multi-unit concentrated winding are designed to improve PM utilization and reduce magnetic flux leakage. Then, the electromagnetic performances of HPMU-TFLM are investigated by the 3-D equivalent magnetic circuit model (EMCM) and the finite element analysis (FEA) method. Finally, its key performances of thrust density, power factor, and efficiency are compared with other typical transverse-flux linear machines (TFLMs). The superiority and feasibility of the proposed machine are verified.