Propulsive Performance Research Articles

Magnetic propulsion performance of a compound spiral micro-robot applied in viscoelastic environment

Magnetic propulsion performance of a compound spiral micro-robot applied in viscoelastic environment

A composite phase change material with large volume change rate for thermal underwater glider

The thermal underwater glider (TUG) is an important device currently used for exploring ocean resources and monitoring ocean temperature. The TUG harvests ocean thermal energy (OTE) through working medium and converts into net buoyancy variation for propulsion. The phase change material (PCM) filled in the thermal engine is the key working fluid for the TUG to harvest OTE. A large volume change rate of PCM at ocean temperature difference is important for improving the TUG's efficiency and performance. Previous studies focus on N-hexadecane for OTE conversion with limited performance. This paper proposes N-hexadecane (C16) based composite PCM for an improved thermal-to-mechanical conversion process. The experimental test results show that the composite PCM (C16:C24 = 9:1 wt%) exhibits a similar phase transition temperature (17.8–18.4℃) with C16 (18.2–18.6℃). As compared to pure C16, the volume shrinkage of this composite PCM was 26.67% higher than that of C16 and the volume expansion rate was 30.74% higher than that of C16, indicating that the composite PCM based TUG could output more net buoyancy variation and propulsion power. Following experimental test, molecular dynamics simulation of the composite PCM is carried out. The reason for this volume expansion/shrinkage improvement was revealed as the larger C–C bond length and H–C–C bond angle variations. The composite materials provided in this paper could potentially improve the propulsion performance of TUG.

Powering performance prediction of a semi-displacement ship retrofitted with Hull Vane

This study predicts the powering performance of a semi-displacement ship, both without and with a Hull Vane (HV). HV is an energy-saving appendage fixed at the transom bottom of the ship's hull. Although the HV is commercially known as a successful resistance-reducing device, there are no studies in the literature examining its effect on propulsion performance in detail. In this study, the effect of the HV on the propulsion performance is investigated and a practical method is proposed as an engineering application to reduce the computation time. Initially, the idealized disc model based on Blade Element Theory (BET) is preferred to create a thrust force instead of using an entire physical propeller. The dynamic motions of the ship are reflected in the computational analysis. Subsequently, the sliding mesh technique, which models the exact propeller geometry, is implemented to calculate the self-propulsion characteristics without and with HV. These computations are achieved by employing a two-phase flow solver available in OpenFOAM. This study provides a significant demonstration to clarify the effect of HV on powering performance. It not only decreases effective power by 11.41% but also increases the propulsive efficiency by 2.1%, which reduces the brake power by 14.61% in total at service speed.

Design and analysis of wire-driven tail fin for bionic underwater glider

A novel bionic underwater glider with a wire-driven flexible tail fin is proposed. The hydrodynamic properties of the wake are analyzed to determine the parameter characteristics associated with the propulsion performance. The structural design and the mathematical model of the bionic wire-driven tail are presented. The motion models of the wire-driven tail are derived. The computational fluid dynamics method is adopted to simulate the changes in the surrounding flow field during the wire-driven tail movement, and the impact of the motion parameters on the hydrodynamics is investigated. Experiments are conducted in a pool, and the results are consistent with those of the simulation. The maximum propulsion force can be achieved by changing the flapping frequency and the amplitude of the tail, which is associated with the reverse Karman vortex streets. The prototype is capable of forward and yaw motions, with a maximum average propulsion speed of 0.67 m/s, which is 34% higher than that (0.5 m/s) of the traditional hybrid-driven underwater glider. The rotation period is around 64 s. Bionic underwater gliders have considerable potential for application in various fields such as ocean science, marine engineering, marine safety, national defence, underwater resource exploration, and environmental protection.

Experimental Investigation on Aluminum-Based Water Ramjet for Propelling High-Speed Underwater Vehicles

Major challenges in developing and realizing a novel aluminum–water reaction-based water ramjet propulsion system for high-speed underwater vehicles and demonstration of a water-breathing jet propulsion test facility are investigated. Two stages of combustion, propellant grain combustion and subsequent water combustion, with primary combustion products are adopted. High-pressure-molded propellant grains up to 45% of micro–nano () aluminum were prepared and combusted in the primary chamber, which exhibits mild ignition delay, and a residue of 4–6% was retained. Once water is injected into the secondary chamber, the net thrust generation is increased more than twice from the exhaust jet and improves the specific impulse by 40%. The lean fuel conditions in the secondary chamber lead to reduction in combustion propensity, which causes drop in efficiency. The ultrafine iron-oxide-catalyzed micro–nano blended propellants marginally improved the propulsive performance than the uncatalyzed compositions. The efficiency of the catalyzed propellants was enhanced up to 38.6%. Aluminum agglomeration in primary combustion considerably occurred; apparently, only a fraction of aluminum particles or agglomerates are completely burnt within the secondary chamber, and the remaining aluminum particles are either partially burnt or go unreacted.

Experimental Investigation on Morphological Characteristics and Propulsion Performance of Typical Metals Ablated with Multipulse Nanosecond Laser

For laser ablation micropropulsion technology with metal as the target to increase the total impulse, the effective utilization and supply of a working medium is a crucial aspect. In this research, the ablation characteristics and propulsion performance of the typical metal targets, copper and aluminum, ablated via nanosecond laser ablation are analyzed. Due to the low melting point of aluminum, the protrusion characteristics in the remelted area are more prominent. Its surface morphology has characteristics for height extremum and roughness that are higher than those of copper. Affected by the anisotropy of the rough surface, the absorbed energy decreases with increasing roughness. The impulse coupling coefficient of the metal decreases and stabilizes at about 6 μN·W−1. The specific pulse of aluminum obtains a minimum value of 603.6 s at 6000 pulses and improves with increasing pulses. The propulsion parameters of copper alters slightly under various working conditions, with a maximum specific impulse of 685 s.

The effect of axisymmetric confinement on propulsion of a three-sphere microswimmer

Swimming at the microscale has recently garnered substantial attention due to the fundamental biological significance of swimming microorganisms and the wide range of biomedical applications for artificial microswimmers. These microswimmers invariably find themselves surrounded by different confining boundaries, which can impact their locomotion in significant and diverse ways. In this work, we employ a widely used three-sphere swimmer model to investigate the effect of confinement on swimming at low Reynolds numbers. We conduct theoretical analysis via the point-particle approximation and numerical simulations based on the finite element method to examine the motion of the swimmer along the centerline in a capillary tube. The axisymmetric configuration reduces the motion to one-dimensional movement, which allows us to quantify how the degree of confinement affects the propulsion speed in a simple manner. Our results show that the confinement does not significantly affect the propulsion speed until the ratio of the radius of the tube to the radius of the sphere is in the range of O(1)−O(10), where the swimmer undergoes substantial reduction in its propulsion speed as the radius of the tube decreases. We provide some physical insights into how reduced hydrodynamic interactions between moving spheres under confinement may hinder the propulsion of the three-sphere swimmer. We also remark that the reduced propulsion performance stands in stark contrast to the enhanced helical propulsion observed in a capillary tube, highlighting how the manifestation of confinement effects can vary qualitatively depending on the propulsion mechanisms employed by the swimmers.

Experimental Study on the Propagation Characteristics of Rotating Detonation Wave with Liquid Hydrocarbon/High-Enthalpy Air Mixture

Rotating detonation engines (RDEs) are a promising propulsion technology featuring high thermal efficiency and a simple structure. To adapt the practical engineering applications of ramjet RDEs, rotating detonation combustion using a liquid hydrocarbon and pure air mixture will be required. This paper presents an experimental study on the propagation characteristics of rotating detonation waves with a liquid hydrocarbon and high-enthalpy air mixture in a hollow cylindrical chamber. The parameters, such as the equivalence ratio and inlet mass flux, are considered in this experiment. The frequency and the propagation velocity of rotating detonation combustion are analyzed under typical operations. The experimental results show that the peak pressure and propagation velocity of the rotating detonation wave are close to the C-J theoretical values under the inlet mass flux of 400 kg/(m2s). Both the propagation velocity and peak pressure of the rotating detonation wave decrease as the mass flux and equivalence ratio are reduced while the number of detonation wavefronts increases. Detonation wave instability tends to occur when the inlet mass flux decreases. There is a transition progress from thermo-acoustic combustion to rotating detonation combustion in the experiment under the condition of mass flux 350 kg/(m2s) and the equivalent ratio 0.8. The static pressure in the chamber is higher during detonation combustion than during thermo-acoustic combustion. These experimental results provide evidence that rotating detonation waves have the potential to significantly improve propulsion performance. The findings can serve as a valuable reference for the practical engineering application of rotating detonation engines.

On the selection of propellants for cold/warm gas propulsion systems

Cold/warm gas spacecraft propulsion systems generate thrust by accelerating a cold or moderately heated gas through a nozzle. Despite their simplicity compared with typical chemical or electric propulsion systems, the choice of propellant nonetheless represents an important consideration that affects the design, operation, and performance of such thrusters. Here we review different propellants that have been used or proposed for cold/warm gas propulsion systems, and we perform a study investigating almost 5000 other possible alternatives. Propellants include organic and inorganic substances that can be stored in solid, liquid, gaseous, and multi-phase states at ambient conditions, and which undergo a phase change to a pure gaseous state (where needed) by heating before being ejected from the thruster. The different propellants are assessed by considering important evaluation factors, such as propulsive performance, storage requirements and storage density, mission suitability, safety, and cost. While conventional thruster performance metrics like the specific impulse are low for some propellants, the design and operational advantages they offer, together with a higher total impulse mass density (i.e. the impulse per propulsion system wet mass), make them superior choices for many missions.

Propulsive performance of a rigid wingsail with crescent-shaped profiles

Wind-assisted ship propulsion is considered an effective method for reducing greenhouse gas emissions. This paper presents numerical analyses of the aerodynamics of a single rigid wingsail conducted using the unsteady Reynolds-averaged Navier–Stokes (uRANS) equations. The wingsail is designed with a new sectional profile: a crescent-shaped foil. This new profile and the classical NACA 0015 profile were compared. Simulations were performed in two and three dimensions, with a focus on key physical quantities such as the external loads on the wingsail, the flow field, and the propulsive performance. It is concluded that the wingsail with the crescent-shaped section has higher propulsion efficiency than the NACA 0015. However, stronger flow separation was detected for the crescent-shaped section. As the separation deteriorates, the flow unsteadiness, challenges the strength and stability of the wingsail structure. The three-dimensional simulations of both profiles, particularly NACA 0015, show that the tip vortices induced from the side edge of the wingsail account for substantial negative effects on the propulsion performance. A case study revealed that installing a wingsail with a crescent-shaped profile reduced fuel consumption by 9% compared with no wingsail.

Experimental study on tesla valve and bypass manifold to suppress feedback of rotating detonation engine fuel by kerosene

In this paper, the effects of the Tesla valve intake structure with or without bypass manifold on suppressing pressure feedback and combustion product backflow in rotating detonation engine fueled by kerosene and enriched air with 29% oxygen content are investigated, with the configuration of convergent–divergent intake without bypass manifold being used for comparison. The working range, detonation wave propagation characteristics, and propulsion performance for the three configurations are evaluated. It is found that the Tesla valve intake structure can effectively improve the suppression of pressure feedback and combustion product backflow through the diversion function of the Tesla valve bypass channel and that the addition of the bypass manifold further improves the suppression of pressure feedback. The Tesla valve intake with bypass manifold configuration has the best ability to suppress pressure feedback, with a minimum value of pressure feedback percentage of about 6.5% and a minimum value of air plenum pressure fluctuation percentage of about 6.7%. By comparison, the minimum value of pressure feedback percentage of the convergent–divergent intake without bypass manifold configuration is about 29.8%, and its minimum value of pressure feedback percentage is about 7.8%. The Tesla valve intake without bypass manifold configuration is most effective in suppressing combustion product backflow, with the effective inlet area ratio of about 95.7%. Under the same conditions, the minimum effective inlet area ratio of the convergent–divergent intake without bypass manifold configuration is about 90.2%. Ultimately, optimizing the engine structure leads to a broader working range and higher propulsion performance. The Tesla valve intake structure broadens the working range by suppressing the generation of the longitudinal pulsed detonation mode. When the bypass manifold is incorporated, some combustible reactants directly enter the rear of the combustion chamber from the head of the chamber, and the working range is reduced. Compared with the convergent–divergent intake without bypass manifold configuration, the working range of the Tesla valve intake with bypass manifold configuration is widened by 383.3%, and that of the without bypass manifold configuration by 700%. Both the Tesla valve intake and bypass manifold increase the strength of detonation waves and improve propulsion performance. The Tesla valve intake with bypass manifold configuration has the highest specific thrust, at about 90.1 N s3/(kg·m). This is increased by an average of 10% compared with the Tesla valve intake without bypass manifold configuration, and by an average of 30.1% compared with the convergent–divergent intake configuration.

A comparative study on the different energy supply modes for a micro-cathodic arc thruster

The energy supply mode of a micro-cathodic arc thruster (μ-CAT) was adjusted based on the charge and discharge characteristics of the energy storage element, and the cathode discharge characteristics of μ-CAT were studied under different energy supply modes. We applied an electrical method to measure the discharge characteristics of μ-CAT, with an enhanced intensified charge coupled device spectrum detector to measure the plasma parameters of μ-CAT, allowing analysis of the internal logic among thruster plasma parameters, arc discharge characteristics, and thruster energy supply mode. The mechanisms of μ-CAT were analyzed and characteristics of accumulated discharge, energy distribution, and ion velocity distribution of thruster were compared under different energy supply modes to obtain the effect of the energy supply mode on the discharge characteristics of the interelectrode of μ-CAT. The results show that the energy supply mode of μ-CAT affected the ionization characteristics and ionization stability of the micro-cathodic arc thruster, causing a multistage ionization difference in the cathode metal target. This would not only affect the propulsion performance of the thruster, but also affect the change of the number of particles in the cathode region in a single discharge cycle.

Propulsion characteristics of self-pitching flapping foil

As a promising form of oscillating hydrofoil propulsion, self-pitching flapping foil (SPFF) has been widely used in ocean engineering applications such as ships, underwater vehicles and ocean energy devices. Due to the complexity of its mass spring system, it is still a lack of comprehensive parametric analysis to conclude the theoretical maximum efficiency of SPFF up to now. Particular interest of this work is centered on the influence of frequency ratio (r), spring stiffness ratio (K′), advance coefficient (J) and pitch axis (c0/c) on the propulsive performance of self-pitching flapping foil (SPFF), including induced propulsion force, propulsive efficiency and related wake structure. The analysis covers the range of full advance coefficient, which starts around 0 and ends at a thrust drop of 0. The influence of stiffness ratio (K’) on the SPFF performance was discussed in the large range of 0.1–100. Special attention is also paid to the impact of system resonance on performance. By employing an appropriate combination of various parameters, the highest efficiency of SPFF could reach 87.6%, which shows it could perform a satisfactory propulsion performance as a marine propulsion. This study is expected to provide guidance on both academics and industries in relevant fields.

Impact of jet velocity profile on the propulsive performance and vortex ring formation of pulsed jet propulsion

A squid-inspired jet propulsion system that indudes a deformable body and a nozzle exit attached to it is numerically studied. By prescribing the body deformation during a single discharge, we examine the impact of jet speed profiles on the vortex ring formation and propulsion performance of the system. Our results show that a secondary vortex ring following the leading vortex ring can be produced by the reverse cosine jet speed pattern at a given maximum stroke ratio, and for the other profiles (i.e., constant, cosine, reverse cosine, half cosine and rever half cosine styles) only distributed vortices are seen behind the leading vortex ring. The constant jet speed produces the largest time-averaged thrust due to jet momentum flux related thrust associated with its large jet speed. Except for the constant speed style, the largest mean thrust production and propulsion factor are obtained by the reverse cosine profile among the other four styles attributed to the formation of the secondary vortex ring. Nevertheless, this secondary vortex ring would not be produced at a small maximum stroke ratio for the reverse cosine speed fashion. We also find that the mean thrust production can reach a maximum under a specific maximum stroke ratio (Γm = 7.60) when two vortex rings are produced. This work may provide insight into the mechanical and control design of jet-based biomimetic propellers and robots.

Performance improvement of flapping propulsions from spanwise bending on a low-aspect-ratio foil

Inspired from deformable caudal fins, continuous bending motion is utilized to improve the propulsive performance of flapping foils for underwater vehicles. The propulsive performance of a flapping foil with spanwise bending motion is studied numerically using the immersed boundary-lattice Boltzmann method. Simulations are conducted by varying the bending parameters and phases of motion at Re = 200 in uniform flow. It is found that the spanwise bending significantly affects vortex evolution and wake structures, which results in the variation of the flapping propulsion. For the present model with an aspect ratio of two, the most powerful (highest thrust) bending is achieved when fixing the phase lag between bending and flapping at 150°, while the most efficient (highest propulsive efficiency) bending is reached at a phase lag of 270°. With proper phase lags, the propulsive performance could be improved into 137% in thrust and 111% in efficiency from the rigid one. Under the most efficient phase lag, the efficiency could be furtherly improved into 112% through adjusting the bending amplitude due to the weak vortex tangle. The propulsive performance is also sensitive to the bending shape. This study presents a numerical guide for the high-performance flapping foil design with spanwise bending movement.

Design and Synthesis of High-Performance Planar Explosives and Solid Propellants with Tetrazole Moieties.

A straightforward synthetic strategy for newly designed nitrogen-rich planar explosives and solid propellants is reported. These materials exhibit high densities (1.69-1.95 g cm-3), high positive enthalpies of formation (approaching 1149.21 kJ mol-1), promising energetic properties (P = 26.36-33.78 GPa, D = 8258-9518 m s-1), acceptable thermal stabilities (Td = 132-277 °C), good sensitivities (IS = 4-40 J, FS = 60-360 N) and excellent propulsive performance (Isp = 176.80-253.06 s).

A Torque Control Strategy for a Robotic Dolphin Platform Based on Angle of Attack Feedback.

Biological fish can always sense the state of water flow and regulate the angle of attack in time, so as to maintain the highest movement efficiency during periodic flapping. The biological adjustment of the caudal fin's angle of attack (AoA) depends on the contraction/relaxation of the tail muscles, accompanying the variation in tail stiffness. During an interaction with external fluid, it helps to maintain the optimal angle of attack during movement, to improve the propulsion performance. Inspired by this, this paper proposes a tail joint motion control scheme based on AoA feedback for the high-speed swimming of bionic dolphins. Firstly, the kinematic characteristics of the designed robot dolphin are analyzed, and the hardware basis is clarified. Second, aiming at the deficiency of the tail motor, which cannot effectively cooperate with the waist joint motor during high-frequency movement, a compensation model for the friction force and latex skin-restoring force is designed, and a joint angle control algorithm based on fuzzy inference is proposed to realize the tracking of the desired joint angle for the tail joint in torque mode. In addition, a tail joint closed-loop control scheme based on angle of attack feedback is proposed to improve the motion performance. Finally, experiments verify the effectiveness of the proposed motion control scheme.

Comparative Analysis of Hybrid-Electric Regional Aircraft with Tube-and-Wing and Box-Wing Airframes: A Performance Study

The continuously expanding transport aviation sector has a significant impact on climate change, and measures must be taken to limit its environmental impact. The study of advanced airframes, which may increase the lift-to-drag ratio and structural efficiency, and the development of innovative high-efficient powertrains, could be a way to achieve air transport decarbonization. This paper explores this broad topic by proposing a classical performance comparison between an aircraft with a traditional tube-and-wing (TW) airframe and a corresponding one with an advanced box-wing (BW) lifting architecture, both equipped with a parallel hybrid-electric powertrain. In fact, the propulsion technologies selected for this comparative study are consistent with the 2035 forecast, and both aircraft concepts are designed to belong to the regional transport category. The comparison between TW and BW is conducted on a conceptual and multi-disciplinary level, offering an analysis of the competitive benefits and limitations in terms of the aerodynamic, structural, and propulsive performance of the two configurations. The metrics selected to make the comparison are related to aircraft performance, such as the structural weight, the block fuel, or the energy required to accomplish the assigned mission. The outcomes obtained highlight the potential of BW airframes coupled with hybrid-electric powertrains to reduce fuel consumption, and hence the related greenhouse gas emissions, because of improvements introduced by this advanced architecture in both the aircraft’s empty weight and energy efficiency.

Influence of a Deflectable Leading-Edge on a Flapping Airfoil

Flapping wing dynamics are of great interest in many research areas, such as bioinspired systems and aircraft aeroelasticity. The findings of the present study provide significant insight into the importance of the leading-edge dynamic incidence on the propulsive performance of flapping airfoils. The main objective is to improve the propulsive characteristics by adding a pitching leading-edge to a conventional NACA0012 airfoil at the lower spectrum of the Reynolds number. The problem is solved numerically at a Reynolds number of 104 under various flapping conditions. The results show that the leading-edge pitching amplitude has a great impact on the propulsive power and efficiency, providing meaningful improvements. The required power coefficient is reduced overall, although not as significantly as the propulsive power. The influence of the movable leading-edge on the pressure distribution is analyzed, showing that the enlargement of the frontal area is the root cause of propulsive augmentation. The proposed geometry provides an innovative way of flapping an airfoil with propulsive purposes, offering remarkable improvements that can defy conventional flapping.

Effects of body stiffness on propulsion during fish self-propelled swimming

Many fish propel themselves using wave-like lateral flexion of their body and tail in the water. The undulatory body is driven by the distributed muscles, and locomotion is achieved by internal muscular stimulation and the external action of the fluid. As one of the material properties, the stiffness of the body being propelled plays an important role in the deformation process, especially for the muscle power input and phase lag. In this paper, a three-dimensional self-propelled elongated body model is employed to numerically investigate the effects of stiffness on the propulsion performance, including the forward speed, energy consumption, and energy-utilization ratio. According to various deformation characteristics and energy-utilization ratios, three deformation modes corresponding to high, medium, and low stiffness are identified. Our results indicate that a deforming body with medium stiffness has the highest efficiency, and its corresponding deformation is closest to that of fish in nature. When the stiffness of the fish body is higher than the normal level, more muscle energy is needed to sustain the tail beating of the same amplitude. A lower level of stiffness produces a more obvious phase lag in the fish body, which might lead to slow control responses. We also show that the stiffness of the fish body affects the scaling relationship between the swimming speed and the tail beating velocity. The upper and lower limits of the scaling exponent correspond to high and low levels of stiffness, respectively, and are also affected by the wavelength of the muscle contraction.