A grid lifetime model is proposed for the lifetime estimation of a 3-grid ion engine system. Grid life is assumed to be determined by electron backstreaming caused by the decreased negative voltage due to the enlargement of accel grid hole radius by charge exchange ion erosion. The model is based on the following grid life scenario: 1) the charge exchange ion erosion enlarges the accel grid hole radius, 2) the enlarged accel grid hole radius decreases the extended effective acceleration length between the screen and accel grids, and 3) the decreased extended effective acceleration length decreases the negative voltage to satisfy the space-charge limited current density law. The characteristic of the model is that lifetime exhibits very strong dependence on beam current and accel grid voltage. A computer program was used to validate the model and it was shown that the model agrees fairly well with the simulations in high NP/H conditions.
Static normal force and rolling moment measurements for 60° and 70° delta wings with vortex flaps have been done for different roll angles at a Reynolds number based on a centerline chord of 1.3×105. Smoke visualization tests have also been done. Results show that the 60° delta wing is statically unstable in roll at the angle of attack of 35° when vortex flaps were deflected 30° downward. This is because the chordwise position where the vortex breakdown occurs is different for the left and right wings when in roll. The 70° delta wing with vortex flaps possesses static roll stability. Static rolling moment hysteresis has been observed for the 60° delta wing with a flap deflection angle of 30° at an angle of attack of 45°.
Seven shaped-charge hypervelocity impact tests were conducted to evaluate the Japanese Experiment Module (JEM) space debris protection stuffed Whipple shield at an approximate velocity of 11 km/s. The shape and the characteristics of the shaped-charge jet differ from those of the light gas gun because of the jet generation mechanism. It is therefore necessary to evaluate and compensate the results for a solid aluminum sphere, which is the design requirement. Comparative two-dinensional hydrocode simulations were conducted to assess the shape effects on the impact damage. The shapes assessed are arrowheads that simulate the shaped-charge jet, hollow cylinders, and solid spheres. By assessing the projectile kinetic energy, the authors concluded that the shaped-charge jet produces three to five times more severe damage to the pressure wall than the solid sphere, even if both have the same mass. The authors also confirmed that the shaped-charge testing and hydrocode simulation correlate well for the pressure wall damage.
Improvements of the take-off and climb performance of the next generation supersonic transport (SST) are one of the key features for the SST development. Estimations of take-off and climb performance have been done to investigate the effect of leading-edge vortex flaps that can improve the low-speed aerodynamic characteristics of the SST main wing. Results show that the climb gradient of the SST is improved when the vortex flaps are deflected downward after lifting-off. The thrust required for the constant climb gradient can be reduced by the benefit of the vortex flaps.
The unsteady flowfields of the sonic jet impinging on a flat plate are numerically investigated using the two-dimensional axisymmetric Euler equations. The characteristics of the jet oscillations qualitatively agree with the experimental results, and the mechanism of jet oscillation and the physical model of sound wave generation are discussed. The jet oscillations have the same period as the sound waves, because passing of sound waves around the nozzle exit causes oscillations of the jet itself. The mechanism of jet oscillations consists of sound waves passing and the vortex convection. In the mechanism, the time delay between the sound wave passing and the vortex occurrence at the nozzle lip is newly pointed out and corresponds to half wave length of the sound wave. A physical model including the time delay is newly suggested and well agrees with both computational and experimental results.
The Taylor vortices were reproduced in a spreadsheet. Spreadsheets are used extensively in scientific and engineering calculations these days. The cells in a spreadsheet can be regarded as the grids in Computational Fluid Dynamics (CFD). Furthermore, the cells have the iteration function, and are able to represent the physical characters of the flow field for example. The axi-symmetric laminar incompressible Navier-Stokes equations were solved to investigate the Taylor-Couette flow. The calculation procedures were briefly introduced and the computational results were in reasonable agreement with the experimental ones.