Propulsion and Power Research最新文献

Magnetic nozzle appears to be a practical solution for prolonged space missions. For efficient handling of the spaceship, an in-flight solution to customize the thrust from the magnetic nozzle is essential. Here a new concept of three-thick coils system is proposed for tailoring the magnetic field in-flight in accordance with electron pressure distribution. The role of peak position of the pressure and its axial gradient is also uncovered for realizing higher thrust. About three-fold increase in thrust is observed when the electron temperature is raised to ∼2.5 times of its original value at the exit plane. The set-up is optimized for its best performance and efficient use in the electric space propulsion sector with thrust approaching 5 mN. In particular, this can contribute to the attitude control or the precision pointing of the spacecraft, the technology for removal of space debris and manipulating the ion momentum flux lost to a wall or unsteady laser produced plasma flow in a magnetic nozzle.

The chemical kinetics of hydrogen atom (H-atom) abstraction reactions from norbornadiene (NBD) by five radicals (H, O(³P), OH, CH₃, and HO₂), and the unimolecular reactions of three NBD derived radicals, were studied through high-level ab-initio calculations. The geometries optimization and vibrational frequencies calculation for all the reactants, transition states, and products were obtained at the M06-2X/6-311++G(d,p) level of theory. The zero-point energy (ZPE) corrected potential energy surfaces (PESs) were determined at the QCISD(T)/cc-pVDZ, TZ level of theory with basis set corrections from MP2/cc-pVDZ, TZ, QZ methods for single point energy calculations. Conventional transition state theory (TST) was used for the rate constants calculations of H-atom abstraction reactions by five radicals (H, O(³P), OH, CH₃, and HO₂) at temperatures from 298.15 to 2000 K, while the α-site H-atom abstraction reaction rate constant of NBD by OH radical has been obtained through variational transition state theory (VTST). The results show that the H-atom abstraction reactions from the α-carbon atom of NBD are the most critical channels at low temperatures. Total rate constants for H-atom abstraction reactions by OH radical are also the fastest among all of the reaction channels investigated at the temperature range from 298.15 to 2000 K. Rice-Ramsperger-Kassel-Marcus/Master Equation (RRKM/ME) has been used to calculate the pressure- and temperature-dependent rate constants for the unimolecular reactions of three related C₇H₇ product radicals which generated from H-atom abstraction reaction within temperature ranges of 300–2000 K and pressures of 0.01–100 atm. A combination of composite methods has been used to calculate the temperature-dependent thermochemical properties of NBD and related radicals. All the calculated kinetics and thermochemistry data can be utilized in the model development for NBD oxidation.

Optimizing flying objects' wing performance has attracted a significant attention in the last few decades. In this article, some of the main mechanisms for changing the geometry of the wing were investigated and a new mechanism is proposed to improve the aerodynamic performance of the airplane wing. The designs have been simulated and analyzed from both aerodynamic and control points of view. In aerodynamic simulations using CFD methods, two airfoils of NACA series 6 with specifications 65-212 and 65-2012 were modeled. The results indicated that both airfoils used have a better performance compared to others in a certain range of the angle of attack. Subsequently, a new mechanism is proposed to change the wing geometry to optimize its structure. In the proposed mechanism, the structures of airfoils and wings consist of two fixed and moving parts, which can change their geometry with the help of a control circuit. The fixed part has a grooved track, and as the moving part moves in the direction of the grooves, the curvature of the upper and lower parts of the wing changes. The design control circuit includes an angle sensor, a micro controller, and a servomotor. The CFD results are entered into the micro controller as code. At any moment, the micro controller receives the angle data from the angle sensor and by comparing them with the CFD data, and issuing a command to the servomotor, it situates the wing curvature in the optimal state at all times. The built mechanism was tested at an attack angle of 0° and 25°. The results showed that the different parts of the mechanism work with very high precision and put the geometric shape of the wing in an optimal state in a completely intelligent way. It should be noted that the average error in test for t/c and Xt/c was 15.3% and 9%, respectively.

Owing to their precedent characteristics, micro gas turbines (MGTs) have been favored as popular power machinery in plenty of energy systems such as distributed energy systems, range extenders, solar power generations, fuel cell systems and individual power supplies. Their specific features essentially include but are not limited to strong fuel adaptability, low emissions, flexible structure, and easy maintenance. Over the past 20 years, various types of MGTs have been developed. Classical and forward-looking technologies have been employed in the design and production of MGTs and their components. Among them, fully radial flow structures, gas lubricated bearings and efficient recuperators are typical approaches to enhance the overall performance and compactness, however, the exploitation of ceramic based materials and intelligent algorithms in component design can also assist in improving the performance. The applications of MGTs have been expanded to many fields, and the research on related components has also made new progress. Due to the time frame, there is no systematic summary of the latest relevant research, so it is essential to have a comprehensive understanding of the applications of MGTs and their pertinent components. This paper aims to present a comprehensive review on MGTs, covering the development status, applications, factors of performance and representative explorations of their components. Some investigations regarding the characteristics of commercial MGTs are also conducted. Applications in distributed energy, range extenders, solar generations, and fuel cell systems are distinctly introduced. Recent research work on compressors, turbines, combustors, recuperators, and rotor systems are reviewed and analyzed. The technologies and methods associated with materials, manufacturing, and cycles beneficial to the future development of MGTs are also explained and discussed in some detail.

Ion-driven magnetic nozzles (T_i > T_e) are designed as intrinsic parts of cutting-edge propulsive technologies such as variable specific impulse magnetoplasma rockets (VASIMRs) and applied-field magnetoplasmadynamic thrusters. Employing a two-dimensional axisymmetric particle-in-cell (PIC) code, in the ion-driven magnetic nozzle, the compositions and distributions of azimuthal currents in different axial regions are investigated under various inlet ion temperatures T_i0 and found to differ dramatically from that in the electron-driven magnetic nozzles. Previously reported to be all paramagnetic and vanishing under a high magnetic field, the azimuthal currents resulting from the E × B drift are shown to turn diamagnetic and sustain a considerable magnitude when T_i0 is considered. The previously reported profile of diamagnetic drift current is altered by the introduction of inlet ion temperature, and the paramagnetic part is significantly suppressed. Moreover, a wide range of paramagnetic currents appear downstream due to the inward detachment of ions, which can also be reduced by increasing inlet ion temperature. Albeit considered in this paper, the azimuthal currents resulting from grad-B and curvature drift are still negligible in all cases of interest. The magnitude of diamagnetic azimuthal currents increases with amplifying T_i0, indicating a clear physical image of energy transformation from ion thermal energy to the directed kinetic energy through electromagnetic processes in the magnetic nozzle. Additionally, the magnetic inductive strength also has noticeable impacts on the azimuthal currents, the current magnitude tends to decrease as the magnetic field increases, and over-increment of it may result in larger divergence angles and lower nozzle efficiency.

The main interest in the current study focuses on the possibility of overspeeding for the gas-generator cycle air turbo ramjet (GG-ATR) engine. The authors developed the air turbo ramjet engine and investigated its compressor performance. Based on those data, the authors developed the analytical code for the air turbo ramjet engine, which calculates the performances of turbomachinery, gas-generator, and ram combustor. The previous study described that the rotor overspeeding would not occur in the air turbo rocket engine. However, the current results show that degraded ram combustion can decrease the compressor pressure ratio and the compressor power. This reduced compressor power can cause overspeeding for the air turbo ramjet engine. The experimental results of compressor power and turbine inlet pressure support those analytical results.

In thermofluid systems, the lid-driven square chamber plays an imperative role in analyzing thermodynamics’ first and second laws in limited volume cases executed by sheer effects with a prominent role in many industrial applications including electronic cooling, heat exchangers, microfluidic components, solar collectors, and renewable energies. Furthermore, nanofluids as working fluids have demonstrated potential for heat transfer enhancement systems, however there are some concerns about irreversibility problems in the systems. Due to this problem and in line with the applications of partial slip on fluid flow modification and irreversibilities, the present study considers laminar mixed convection and entropy generation analysis of aluminum oxide nanofluid inside a lid-driven wavy cavity having an internal conductive solid body in the presence of a partial slip on the upper surface, which to the best of our knowledge, has not been investigated so far. The fundamental equations of the current work with the appropriate boundary conditions are first made dimensionless and then solved numerically using the Galerkin weighted residual FEM. The main parameters of the flow and heat transfer, entropy generation, and Bejan number are presented and explained in details. The outcomes indicate that the partial slip is more effective when friction irreversibilities govern the cavity. In the presence of slip condition, the flow circulation changes the trend in the middle of the cavity around the solid block leading to a decrease in the isentropic lines at the dense sections with almost 30% less than the case of no-slip condition. It is concluded that partial slip shows different trends on the local Nusselt number interface along the wavy wall improving the average Nusselt number where high friction irreversibilities dominate.

The present paper explains the temperature attribute of a convective-radiative rectangular profiled annular fin with the impact of magnetic field. The effect of thermal radiation, convection, and magnetic field on thermal stress distribution is also studied in this investigation. The governing energy equation representing the steady-state heat conduction, convection, and radiation process is transformed into its dimensionless nonlinear ordinary differential equation (ODE) with corresponding boundary conditions using non-dimensional terms. The obtained ODE is then solved analytically by employing the Pade approximant-differential transform method (DTM) and modified residual power series method (MRPSM). Moreover, the important characteristics of the temperature field, the thermal stress, and the impact of some non-dimensional parameters are inspected graphically, and a physical explanation is provided to aid in comprehension. The significant findings of the investigation reveal that temperature distribution enhances with an increase in the magnitude of the heat generation parameter and thermal conductivity parameter, but it gradually decreases with an increment of convective-conductive parameter, Hartmann number, and radiative-conductive parameter. The thermal stress distribution of the fin varies considerably in the applied magnetic field effect.

In this study, a turbulent non-premixed (diffusion) methane-air flame has been investigated computationally to analyze the influences of pressure and gravity on flame structure and sooting characteristics between 1 and 10 atm. The simulation has been conducted in a 2-D axisymmetric computational domain using the finite volume-based computational fluid dynamics (CFD) code. The interaction of turbulence and chemistry is modeled by considering the steady laminar flamelet model (SLFM) and the GRI Mech 3.0 chemical mechanism. The radiative heat transfer calculation is carried out by considering the discrete ordinate (DO) method and the weighted sum grey gas model (WSGGM). The semi-empirical Moss-Brookes model is considered to calculate soot. The impact of gravity on flame and sooting characteristics are evaluated by comparing the normal-gravity flames with the zero-gravity flames. The effect of soot and radiation on flame temperature is also examined. The results show a close agreement with the measurement when both soot and radiation are included in the numerical modeling. The rates of soot formation, surface growth, and oxidation increase with increased operating pressure, regardless of gravity. Zero-gravity flames have a higher soot volume fraction, a wider soot-containing zone, a higher CO mass fraction, and a lower flame temperature than normal-gravity flames while maintaining constant pressure. In normal-gravity flames, the CO mass fraction decreases with pressure, whereas it increases with pressure rise in flames of zero gravity. Flames of zero gravity appear taller and broader compared to the flames of normal-gravity for a fixed pressure. An increase in pressure significantly reduces the flame length and width in normal-gravity flames. However, the pressure elevation has little effect on the shape of a zero-gravity flame. The outcomes of the present study will assist in fully understanding the combustion and sooting characteristics of turbulent diffusion flames that will help design and develop high-efficiency, pollutant-free combustion devices and fire suppression systems for space application.

In pursuit of improved thermal transportation, the slip flow of Casson nanofluid is considered in the existence of an inclined magnetic field and radiative heat flux flow over a non-linear stretching sheet. The viscosity of the fluid is considered as a function of temperature along with the convective thermal boundary condition. Numerical solutions are obtained via Runge-Kutta along with the shooting technique method for the chosen boundary values problem. To see the physical insights of the problem, some graphs are plotted for various flow and embedded parameters on temperature function, micro-organism distribution, velocity, and volume fraction of nanoparticles. A decline is observed in the velocity and the temperature for Casson fluid. Thermophoresis and Brownian motion incremented the temperature profile. It is also found that thermal transportation can be enhanced in the presence of nanoparticles and the bioconvection of microorganisms. Present results are useful in the various sectors of engineering and for heat exchangers working in various technological processors. The main findings of the problem are validated and compared with those in the existing literature as a limiting case.