The ion energy angle distribution and its relationship to plasma parameters for spot and plume modes are elucidated for a LaB6 hollow cathode with a radiative heater. Measurements were conducted using a retarding potential analyzer (RPA) and a single Langmuir probe. The ion energy distribution function (IEDF) characteristics showed different tendencies in the current density and mass flow-rate dependence under different plasma modes. The IEDF peak potential for the spot mode varied from 16 to 23 V with increasing current density, and the IEDF peak potential for the plume mode varied from 16 to 32 V with decreasing mass flow rate. Considering angle dependency of ion energy, when the observation angle was changed from the radial direction to the axial direction, the IEDF peak potential increased from 29 to 40 V for the plume mode (10 A, 10 sccm) and increased slightly from 16 to 18 V for the spot mode (20 A, 30 sccm). The probe measurement analysis revealed that the IEDF peak energies are the same as, or exceed, the plasma potential and have a qualitative correlation with the electron temperature spatial distribution.
There have been several advanced space missions using large gossamer space structures proposed recently, such as a spinning solar sail. However, only certain missions have been implemented, primarily because the on-orbit dynamic behavior of such structures cannot be precisely predicted through ground tests. To address this limitation, a scale law between a small- and a full-scale model of large membrane structures is proposed herein. In addition, small or reduced-order models for numerical simulations are proposed to reduce computation costs. However, the development of a small model, which has to be completely identical (geometrically) to the full-scale model, is challenging. Thus, a scale law between the small- and full-scale models of a large gossamer space structure, which is geometrically non-similar to the full-scale model, is also proposed. The scale law is also applied to the spin deployment motion of thin membrane and verified using numerical simulations.
The image vortex model is widely used in lifting line method to predict the flow induced by the shroud and hub surface in ducted fan, but it does not perform well in lift fan design due to the zero far field inflow. In this paper the theoretical defects and numerical error propagation characteristic of the image vortex model in simulating duct surface are studied. Then the vortex rings correction based on image vortex model is verified and applied in lifting line method. In order to test the improved method, a 150 mm diameter lift fan is designed by the modified lifting line method, after that, analyzed by the modified lifting line itself and RANS solver respectively. The results show that the contribution of the vortex rings at the rotor accounts for 50% of the total induced velocity, and it accounts for 35% at the stator, which verifies the necessity of the vortex rings correction. The performance of the rotor and stator geometry is consistent with the design expectation, the efficiency is up to 90.97% by numerical simulation and 88.32% by experimental measurement, which confirms the reliability of the modified lifting line method developed in this paper especially on lift fan design.
In scramjet engines, ignition must take place within a residence time on the order of milliseconds. In this study, secure ignition conditions for specified n-octane pyrolysis fuel components used in autoignition or forced-ignition by plasma jet torch in a high-speed flow were numerically investigated. First, the ignition delay time within the combustor and cavity flame-holder was estimated using chemical reaction analysis. Three fuel components (n-C8H18, all pyrolysis fuel (15 components, decomposition rate under 11%)), and pyrolysis gas fuel (eight gas fuel components, decomposition rate under 11%) could not self-ignite within the combustor and cavity residence time. Secondly, ignition using a plasma jet torch in the cavity was numerically investigated. In the case of forced-ignition by plasma jet torch, all pyrolysis fuel (No. 3) and n-C8H18 could ignite within the cavity residence time with less input energy than pyrolysis gas fuel (No. 3) under three kinds of Mach number flight conditions (M0 = 4, 6, and 8). Moreover, the effect of shortening the ignition delay time by raising the plasma jet torch gas temperature and O radical rate within the cavity was investigated. Ignition of the three kinds of mixture fuel was more greatly affected by the torch injection temperature than the O radical rate in the cavity under all Mach number flight conditions.