Propulsion Characteristics Research Articles

Numerical investigation of yaw angle effects on propulsive characteristics of podded propulsors

The present paper deals with the problems of yaw angle effects on podded propulsor performance. The study aims at providing insights on characteristics of podded propulsors in azimuthing condition. In this regard, a wide numerical simulation that concerned yaw angle effect measurement on podded propeller performance was performed. The Reynolds-Averaged Navier Stokes (RANS) based solver is used in order to study the variations of hydrodynamic characteristics of podded propulsor at various angles. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. Structured and unstructured mesh techniques are used for single propeller and podded propulsor. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The characteristic parameters including the torque and thrust of the propeller, the axial force and side force of unit are presented as function of velocity advance ratio and yaw angle. The results shows that the propeller thrust, torque and podded unit forces in azimuthing condition depend on velocity advance ratio and yaw angle.

Numerical investigation of yaw angle effects on propulsive characteristics of podded propulsors

The present paper deals with the problems of yaw angle effects on podded propulsor performance. The study aims at providing insights on characteristics of podded propulsors in azimuthing condition. In this regard, a wide numerical simulation that concerned yaw angle effect measurement on podded propeller performance was performed. The Reynolds-Averaged Navier Stokes (RANS) based solver is used in order to study the variations of hydrodynamic characteristics of podded propulsor at various angles. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. Structured and unstructured mesh techniques are used for single propeller and podded propulsor. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The characteristic parameters including the torque and thrust of the propeller, the axial force and side force of unit are presented as function of velocity advance ratio and yaw angle. The results shows that the propeller thrust, torque and podded unit forces in azimuthing condition depend on velocity advance ratio and yaw angle.

Wake structure and aerodynamic characteristics of an auto-propelled pitching airfoil

In the present study, we investigate the wake configuration as well as the flow aerodynamic and propulsive characteristics of a system equipped with a nature-inspired propulsion system. The study focuses on the effect of a set of pitching frequency and amplitude values on the flow behavior for a symmetric foil performing pitching sinusoidal rolling oscillations. The viscous, non-stationary flow around the pitching foil is simulated using ANSYS FLUENT 13. The foil movement is reproduced using the dynamic mesh technique and an in-house developed UDF (User Define Function). Our results show the influence of the pitching frequency and the amplitude on the wake. We provide the mechanisms relating the system behavior to the applied forces. The frequency varies from 1 to 400Hz and the considered amplitudes are 18%, 24%, 30%, 37%, 53%, 82% and 114% of the foil chord.

Dynamic modeling of a CPG-governed multijoint robotic fish

This paper is devoted to the formulation of a dynamic model of a serially connected multijoint robotic fish with a pair of wing-like pectoral fins, in which the whole robot is treated as a moving multilink rigid body in fluids. Considering that the thrust of fish mainly results from the force of trailing vortex, added lateral pressure, and leading edge suction force, the dynamic equations of the swimming fish have been derived by summing up the longitudinal force, lateral force, and yaw moment on each propulsive component in the context of Lagrangian mechanics. Along with the bio-inspired central pattern generators (CPGs) as the locomotor controller, the overall dynamic propulsive characteristics of the swimming robot are then estimated in a mathematical environment (i.e. Mathematica). Finally, simulations and experiments are carried out to validate the effectiveness of the built dynamic model. Results demonstrate that the CPG-coupled dynamic model provides a fairly good guide to seeking pragmatic backward swimming patterns for a carangiform robotic fish.

Plasma microthruster based on spark discharge with a liquid metal cathode

The parameters of low-inductance vacuum spark discharge with an In-Ga liquid metal eutectic cathode have been experimentally studied. The application of a constant magnetic field of a permanent magnet significantly modifies the character of plasma flow in discharge, which ensures a significant (1.5- to 2-fold) increase in the cathodic jet impulse. The proposed discharge provides high propulsion characteristics: jet impulse per unit energy stored amounts up to about 10 (μN s)/J, which is close to the best-known values for analogous ion sources with solid metal cathodes.

Diagnosing Propulsion Systems of a Vessels in Varying Marine Conditions

The paper presents some problems of carrying out measurements of energetic characteristics and vessels performance in the conditions of sea examinations. We present the influence of external conditions in the change of vessels hull resistance and propeller characteristics as well as the influence of weather conditions in the results of examinations and characteristics of gas turbine engine. We also discuss the manner of reducing the results of measurements to the standard conditions. We present the way of preparing propulsion characteristics and the analysis of examination uncertainty for the measurement of torque.

Charge emissions from electrosprays in vacuum: Mixtures of formamide with methylammonium formate

The charge/mass distribution f(q/m) of nanodrops and ions electrosprayed in vacuum from mixtures of formamide (FM) and methylammonium formate (MAF) is studied by time of flight mass spectrometry at MAF/FM volumetric concentrations of 5%, 10%, 25%, and 50%. Positive and negative polarities yield comparable f(q/m) curves, though the negative mode yields ∼30% larger currents. On shifting from the highest to the lowest liquid flow rates at which a cone-jet is stable, the more conductive solutions evolve from mostly drop to primarily ion emission. A purely ionic regime is not reached under any condition, but the drops achieve unusually high q/m. As a result, these sprays have excellent electrical propulsion characteristics, some being able to cover a 25-fold range of average q/m with a polydispersive efficiency typically in the range of 80%. Results of formamide electrolytes with formates and nitrates of several other amines are more briefly reported.

Simple method for performance evaluation of multistage rockets

Multistage rockets are commonly employed to place spacecraft and satellites in their operational orbits. Performance evaluation of multistage rockets is aimed at defining the maximum payload mass at orbit injection, for specified structural, propulsive, and aerodynamic data of the launch vehicle. This work proposes a simple method for a fast performance evaluation of multistage rockets. The technique at hand is based on three steps: (i) the flight-path angle at each stage separation is guessed, (ii) the spacecraft velocity is maximized at the first and second stage separation, and (iii) for the last stage the thrust direction is obtained through the particle swarm optimization technique, in conjunction with the use of the Euler–Lagrange equations and the Pontryagin minimum principle. The coast duration at the second stage separation is optimized as well. The method at hand is extremely simple and easy-to-implement, but nevertheless it proves to be capable of yielding near-optimal ascending trajectories for a multistage launch vehicle with realistic structural, propulsive, and aerodynamic characteristics. The solutions found with the technique under consideration can be employed either for a rapid evaluation of the multistage rocket performance or as guesses for more refined optimization algorithms.

1A2-A14 弾性平板のねじりによる可変剛性フィンを用いた生物規範型流体内推進機構 : 一様流中における推進特性(バイオミメティクス・バイオメカトロニクス(2))

1A2-A14 弾性平板のねじりによる可変剛性フィンを用いた生物規範型流体内推進機構 : 一様流中における推進特性(バイオミメティクス・バイオメカトロニクス(2))

J027023 可変剛性フィンを用いた生物規範型流体内推進機構を備えた模型船の推進特性([J027-02]生物規範メカニクス・システム:生物の運動,力学及びミメティクス(2))

J027023 可変剛性フィンを用いた生物規範型流体内推進機構を備えた模型船の推進特性([J027-02]生物規範メカニクス・システム:生物の運動,力学及びミメティクス(2))

1A2-B01 可変剛性フィンを用いた生物規範型流体内推進機構を備えた模型船の開発(バイオミメティクス・バイオメカトロニクス(2))

Recently, the use of a bio-inspired oscillating elastic fin has been proposed as an alternative propulsion mechanism in water. It is thought that the new mechanism will improve efficiency and safety, relative to the screw propeller. The optimum elasticity of the fin is not constant and changes based on swimming speed and task. However, it is very difficult to exchange fins of different stiffness while moving. We have developed a propulsion mechanism using a variable stiffness fin with torsional rectangular elastic plates. In this study, we developed a model boat with the variable stiffness fin and evaluated the effectiveness of variable stiffness to provide basic data for the development of boats and autonomous underwater vehicles. As a first step of this study, we designed and built a model boat, and drove it on water pool. We discussed propulsion characteristics of the model boat.

2A2-O02 羽ばたき弾性フィンによる流体内推進機構(水中ロボット・メカトロニクス)

In this study, the authors focus on Manta ray since it can effectively swim by swinging own fins with low frequency in under water. In this paper, therefore, a swinging mechanism that can reproduce the motion of Manta ray is developed. Furthermore, some flexible fins are developed by combining rigid material and elastic material and are imitated the fin of Manta ray. This paper conducts comparison experiment, and propulsion characteristics of a rigid fin and each flexible fin are compared. These characteristics are measured with the use of three markers attached to each fin. As a result, it is shown that the flexible fins yield better propulsive velocity more than that of the rigid fin.

Study of Side Thrust of Diesel Piston Based on Time-Domain Finite Element Method

Grasping the transmission of side thrust of piston is one of the effective methods to control engine vibration and noise. The paper uses time-domain FEM to study engine vibration. Firstly the finite element model is established after simplifications and modal analysis is conducted. Then the side thrust of piston is calculated and applied to cylinder liner using equivalent nodal load. The surface vibration is gained, from which it can be concluded that the displacements of upper block and top cylinder head reflect changes in cylinder pressure, while the vibration of observation window is complex. Finally, the vibration in a variety of engine working conditions is analyzed. Under load characteristics, the amplitude of engine surface vibration changes with loading; under propulsion characteristics, the surface vibration is essentially the same.

Micropropulsion and microrheology in complex fluids via symmetry breaking

Many biological fluids have polymeric microstructures and display non-Newtonian rheology. We take advantage of such nonlinear fluid behavior and combine it with geometrical symmetry-breaking to design a novel small-scale propeller able to move only in complex fluids. Its propulsion characteristics are explored numerically in an Oldroyd-B fluid for finite Deborah numbers while the small Deborah number limit is investigated analytically using a second-order fluid model. We then derive expressions relating the propulsion speed to the rheological properties of the complex fluid, allowing thus to infer the normal stress coefficients in the fluid from the locomotion of the propeller. Our simple mechanism can therefore be used either as a non-Newtonian micro-propeller or as a micro-rheometer.

500 N급 과산화수소/케로신 로켓엔진의 추진제 액적 분무와 증발을 고려한 연소 수치해석

96% 과산화수소와 케로신을 추진제로 사용하는 500 N 급 로켓엔진에 대하여 추진제의 분무, 기화, 혼합, 연소를 포함하는 수치해석을 수행하였다. 1/6 조각의 연소실을 격자로 생성하였으며, 세 가지 종류의 액체상 추진제(케로신, 과산화수소, 물)가 속이 빈 콘 형태로 공급되는 분무를 모사하였고, Rosin-Rammler 함수에 따른 액적크기 분포를 가정하였으며, 연소 해석에는 와류소산모델을 사용하였다. 본 계산에서는 작은 연소실 크기, 그리고 과산화수소 및 물의 큰 잠열 및 비열로 인하여 평균 액적 크기 변화에 따라 큰 성능의 차이를 나타냈으며, 평균 액적 크기가 30 micron인 경우 가장 좋은 추진성능을 보여주었다. The numerical simulations on 500-N class rocket engine using 96% hydrogen peroxide and kerosene have been conducted, considering atomization, evaporation, mixing and combustion of its propellants. The grid containing 1/6 part of combustion chamber has been generated and it is assumed that 3 kinds of liquid-phase propellants (kerosene, hydrogen peroxide and water) were injected as hollow cone spray pattern, using Rosin-Rammler function for distribution of droplet diameter. For the calculation of combustion the eddy-dissipation model was applied. Owing to small size of combustion chamber and large specific heat / latent heat of hydrogen peroxide and water the propulsion characteristics were highly influenced by the size of droplet particles, and in this analysis the engine with droplet particles of 30 micron in average has shown the best propulsion performance.

Nonlinear Adaptive Velocity Controller Design for an Air-breathing Supersonic Engine

This paper presents an approach on the design of a nonlinear controller to track a reference velocity for an air-breathing supersonic vehicle. The nonlinear control scheme involves an adaptation of propulsive and aerodynamic characteristics in the equations of motion. In this paper, the coefficients of given thrust and drag functions are estimated and they are used to approximate the equations of motion under varying flight conditions. The form of the function of propulsive thrust is extracted from a thrust database which is given by preliminary engine input/output performance analysis. The aerodynamic drag is approximated as a function of angle of attack and fin deflection. The nonlinear controller, designed by using the approximated nonlinear control model equations, provides engine fuel supply command to follow the desired velocity varying with time. On the other hand, the stabilization of altitude, separated from the velocity control scheme, is done by a classical altitude hold autopilot design. Finally, several simulations are performed in order to demonstrate the relevance of the controller design regarding the vehicle.

Propulsive characteristics of metal fuel-rich pyrotechnics in hydro-reactive motors

In this paper, the propulsive characteristics of metal fuels in a hydro-combustion chamber are investigated in a thermodynamic approach. Using chemical equilibrium calculations, the thermo-chemistry of common metal fuels and water is studied and focused on magnesium. Next, the combustion temperatures and characteristic velocities of mixtures of magnesium and some important solid oxidizers are investigated. For the purpose of hydro-reactive propulsion, where it is necessary to use the water as the main oxidizer, the hydro-reaction of some fuel-rich mixtures of magnesium and sodium nitrate is studied. For such compounds, the maximum combustion temperature is estimated to be about 3100 K at different mass fractions of water. More fuel-rich mixtures offer higher characteristic velocity. It reaches about 1700 m/s for the compound with maximum magnesium value content. The characteristic velocity and combustion temperature decrease for high values of water mass fraction, while the specific impulse increases with water monotonically beyond 500 s. The analysis of hydro-reaction products shows that magnesium oxide, hydrogen, and steam are the main species formed. The magnesium oxide presents in its condensed forms. However, for a high amount of water, the main product is steam.

Evaluation of flapping wing propulsion based on a new experimentally validated aeroelastic model

To evaluate the propulsion system capabilities of a Flapping Micro Air Vehicle (FMAV), a new aeroelastic model of a typical flexible FMAV is developed, utilizing the Euler–Bernoulli torsion beam and quasi steady aerodynamic model. The new model accounts for all existing complex interactions between the mass, inertia, elastic properties, aerodynamic loading, flapping amplitude and frequency of the FMAV, as well as the effects of several geometric and design parameters. To validate the proposed theoretical model, a typical FMAV, as well as an instrumented test stand for the online measurement of forces, flapping angle and power consumption, has been constructed. The experimental results are initially utilized to validate the flight dynamic model, and several appropriate conclusions are drawn. The model is subsequently used to demonstrate the flapping propulsion characteristics of the FMAV via simulation. Using dimensionless parameters, a set of new aeroelastic coordinates are introduced. In this reduced design space, new generalized performance curves have been deduced. The results indicate that by proper adjustment of the wing stiffness parameter, as a function of reduced frequency, the FMAV will attain its optimum propulsive efficiency. This fact raises additional ideas of utilizing intelligent variable stiffness materials and/or an active morphing technology for the sustained flight of FMAVs.

Influence of grid type and turbulence model on the numerical prediction of the flow around marine propellers working in uniform inflow

In this work we analyze the influence of grid type and turbulence model on the numerical prediction of the flow around marine propellers, working in uniform inflow. The study is carried out comparing hexa-structured meshes with hybrid-unstructured meshes using the SST (Shear Stress Transport) turbulence model and the BSL-RSM (Baseline-Reynolds Stress Model) turbulence model. The simulations are carried out with a commercial CFD solver. The numerical results are compared with the available experimental data of two propellers in model scale. The comparison is carried out evaluating the global field values, represented by the thrust and torque coefficients, and also considering some local field values measured in the propeller wake. The computational results suggest that, for the numerical predictions of the propeller open water propulsion characteristics, the hexa-structured and hybrid-unstructured meshes can guarantee similar levels of accuracy. Nevertheless hybrid-unstructured meshes seem to exhibit a more diffusive character than hexa-structured meshes, and thus they are less suited for detailed investigations of the flow field. Finally, the two different turbulence models behave similarly on both types of meshes, with the BSL-RSM turbulence model providing only slightly better predictions than the computationally more economical SST turbulence model.

船外機付き高速滑走艇の推進性能評価法の構築

The purpose of this study is to propose the propulsive performance estimation method for high-speed planing craft with outboard engine. In order to understand the characteristics of propulsion, a fully captive model test with propulsion is carried out. Based on the results, an estimation method taking the self-propulsion factors, which are the changes of hydrodynamic forces acting on hull with lower-hull of outboard engine caused by propeller action, the effective wake fraction and the relative rotative efficiency, is proposed. Using the proposed method, running attitude, thrust (or THP), crank shaft torque (or BHP), maximum forward speed and fuel consumption of a real craft are estimated. As the results, it is found that the effective wake fraction and the relative rotative efficiency of the self-propulsion factors are significant to estimate maximum forward speed of the craft.