Computational fluid dynamics (CFD) analysis coupled with pitching motion of a reentry capsule is performed, and a model equation for the aerodynamic force coincident with the CFD result is proposed. The self-excitation of pitching oscillation and the subsequent limit-cycle oscillation are reproduced in a fine-grid CFD simulation. The axis of the vortex ring in the wake extracted by the phase average is displaced to the lower side of the capsule base when the pitch angle α = 0 and > 0. Such a displacement induced the dynamic component of pitching moment around α = 0. Subsequently, the pitching moment coefficient is decomposed into a Fourier series, where the amplitude of the third harmonics is larger than the dynamic component of the fundamental frequency. The proposed model equation for the pitching moment, which fully includes the third harmonics, reproduces the same amplitude and the same frequency of the CFD result in the case of limit-cycle oscillation. Compared to conventional models, the present model was found to give a better approximation of the dynamic component CMdy of the unsteady aerodynamic work per unit time.
When simulating airflow we assume an ideal situation, however, flight test data includes measurement noise when actually conducted. Therefore, it is difficult to compare simulation data with flight test data without considering uncertainty. First, we applied the Noisy Input Gaussian Process (NIGP), which can utilize uncertain inputs to estimate aerodynamic coefficients with confidence intervals to an aircraft's simulation data. This enabled us to verify the effectiveness of NIGP. We then applied NIGP to the aircraft's real flight data and compared them with aerodynamic tables based on wind tunnel testing and CFD. We found that the lift coefficient estimated using the flight test data did not contradict that obtained using simulation data, while the drag coefficient estimated using the flight test data was smaller than that obtained using the simulation data.
DELPHINUS is a camera system mounted on EQUULEUS, which is planned to be launched using NASA’s Space Launch System EM-1 in 2021. DELPHINUS aims to investigate size distribution, influx ratio, and daily variation of meteoroids in the cislunar space through observations of lunar impact flashes (LIFs) from the far side of the moon. DELPHINUS will observe the moon's surface with the 60-fps camera modules to capture the flashes that are short duration phenomena. All image data cannot be downlinked due to constraints in memory size and communication capability. Therefore, an on-board image processing algorithm was developed to reduce downlinked data size by extracting only necessary pixel data including LIFs. Three experiments using three simulators were demonstrated to verify the real-time processing performance and detection capability. This paper reports the details of the proposed algorithm and the verification results.
A quasi-one-dimensional model is proposed to predict a thermal choked flow-field with a pseudo-shock wave system (ramjet-mode operation) in diverging dual-mode combustors. To predict pressure-rise upstream of the injector through the pseudo-shock wave system, the model used an empirical correlation between the penetration length of the pseudo-shock wave system and the rise in pressure. In addition, to predict the thermal choking location in diverging combustors, the model used the combustion efficiency distribution against a streamwise location, which was deduced from the combustion test results reported in the present study. Results indicate that the model simulates ramjet-mode operation with a reasonable degree of accuracy by correlating of the pseudo-shock wave system and combustion efficiency distribution.
To investigate the neutral xenon density distribution of electric thrusters such as ion and Hall thrusters, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy was applied to a microwave cathode. First, the background pressure of the vacuum chamber was measured by TALIF. In the present measurements, the ground state was excited by a 224.29 nm laser, and 834.68 nm fluorescence was detected. The first measurement confirmed that the fluorescence intensity linearly increases with respect to the ground state number density. Based on this result, the density of neutral ground-state xenon was measured at the exit of the nozzle of the microwave cathode. The variation in the density with the microwave power was successfully measured at xenon flow rates of 0.029 and 0.098 mg/s. The measured densities varied from 2.3 × 1019 to 8.4 × 1019 m3 with a maximum error of ±20% due to the plasma fluorescence.