R.J. Hung

Similarity rules in gravity jitter-related spacecraft liquid propellant slosh waves excitation

Abstract The dynamical behavior of fluids, in particular the effect of surface tension on partially filled rotating fluids (cryogenic liquid helium and helium vapor) in a full-scale prototype Gravity Probe-B Spacecraft propellant tank and various 10% subscale containers with identical values of similarity parameters such as Bond number, dynamical capillary number, rotational Reynolds number, and Weber number, as well as imposed gravity jitters have been investigated. It is shown that the Bond number can be used to simulate the wave characteristics of slosh wave excitation, whereas the Weber number can be used to simulate the wave amplitude of slosh-mode excitation. This is because the slosh-wave excitation is mainly governed by the interaction of gravity (gravity jitters) and surface tension (interface between liquid and vapor fluids) forces, which is characterized by the Bond number; whereas the amplitude of slosh-wave excitation is dominated by the interaction between dynamical (centrifugal) and surface tension forces, which is characterized by the Weber number. In this study, perturbation of fluid stress distribution on the outer walls of the rotating container, caused by the excitation of slosh waves and their associated large amplitude disturbances on the liquid-vapor interface, have also been investigated. It is shown that a dynamical capillary number can be used to simulate the induced perturbation of the fluid stress distribution exerted on the wall. This distribution is governed by the interaction between surface tension (slosh-wave excitation along the liquid-vapor interface) and viscous (fluid stress exerted on the wall) forces.

Slosh wave excitation in a partially filled rotating tank due to gravity jitters in a microgravity environment

The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids (cryogenic liquid helium and helium vapor), in a full-scale Gravity Probe-B Spacecraft propellant tank without probe imposed by various frequencies of gravity jitters have been investigated. Twelve case studies of slosh wave excitation due to various frequencies of gravity jitters under different rotating speeds of propellant tank and different levels of background gravity environment have been numerically simulated. Results disclose the conditions for the excitation of large amplitude slosh waves which shall be avoided in the design of cryogenic liquid propellant system.

Excitation of slosh waves associated with low frequency impulsive reverse gravity acceleration of geyser initiation

Abstract The objective of the cryogenic fluid management of the spacecraft propulsion system is to develop the technology necessary for acquisition or positioning of liquid and vapor within a tank in reduced gravity to enable liquid outflow or vapor venting. The requirement to settle or to position liquid fuel over the outlet end of the spacecraft propellant tank prior to main engine restart poses a microgravity fluid behavior problem. The purpose of the present study is to investigate the stability of the most efficient technique for propellant resettling through the minimization of propellant usage and weight penalties. In this study slosh wave excitation induced by the resettling flow field activated by 0.1 Hz low frequency, impulsive reverse gravity acceleration, during reorientation with the initiation of geyser for liquid fill levels of 30, 50, 65, 70 and 80%, have been studied. Characteristics of slosh waves with various frequencies excited are discussed. Slosh wave excitations shift the fluid mass distribution in the container which impose time dependent variations in spacecraft moment of inertia. This information is important for the spacecraft control during the course of liquid reorientation.

Remote sensing of mesospheric and thermospheric density perturbations induced by subtropical heavy rainfalls for spacecraft environment study

Abstract The VHF radar and HF Doppler sounder located at the subtropical and low latitude observing site of Taiwan has been used to make a simultaneous observation for atmospheric parameters from the troposphere to the middle atmosphere, and then to the thermosphere, induced by the convective motions associated with subtropical heavy rainfall during the period of rainy season in late spring and early summer time. For observations at mesospheric heights, time dependent wind velocities with three-dimensional profiles are detected in the backscattered power, radial velocities and Doppler spectral width. For observations at thermospheric heights, time-dependent phase path change of high frequency radio wave reflected from ionospheric heights is used to measure Doppler frequency variation of gravity wave parameters. The density perturbations caused by the propagation of the gravity waves due to the convective motions associated with subtropical heavy rainfall in rainy season were calculated from the VHF radar and HF Doppler sounder observations simultaneously. These results are then subsequently compared with that of density perturbations caused by typhoons, tropical storms, winter time drizzles associated convection motions. These short-term, middle atmospheric and thermospheric density changes are a key element needed for space vehicle design together with stability and attitude control.

Remote sensing of tornadic storms from geosynchronous satellite infrared digital data

Abstract Two cases of GOES digital infrared data were analysed during the three-hour period immediately prior to the tornado touchdown times. Clouds associated with tornadoes were compared to those without tornadoes using a combination of satellite infrared and rawinsonde data. On the basis of this limited data sample, it appears as if the altitude to which the overshooting cloud top penetrated above the tropopause is the factor which determines whether or not a tornado is formed. In these cases, the over-shooting cloud top collapsed about 15 to 30 min before the tornado touchdown.

VHF radar remote sensing of atmospheric parameters over Taiwan during the time period of Typhoon Wayne

Abstract The VHF radar located at the subtropical and low latitude observing site of Taiwan has been used to observe atmospheric parameters from the troposphere to the middle atmosphere during the time passage of Typhoon Wayne in August 1986. Time-dependent wind velocities with three-dimensional profiles have been plotted by processing the recorded data of the backscattered echo power and the Doppler spectral width of the signal returns from the VHF radar. Propagation characteristics of the gravity waves excited by the enhanced convective motions of Typhoon Wayne have been detected from the Fourier power spectrum analysts of the three-dimensional wind velocities from multiple beams of the VHF radar and their cross-correlation analysis. The density perturbations caused by the propagation of the gravity waves can be calculated from the VHF radar observations. The VHF radar can also be used to detect time-dependent vertical profiles of the liquid water content. The present study shows that the equivalent rai...

Gravity jitter effected slosh waves and the stability of a rotating bubble under microgravity

The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh wave with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.

Gravity jitter response slosh wave excitation on the fluid in a rotating dewar

Abstract The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled fluids in a rotating dewar in a microgravity environment has been investigated. Results show that there is a group of wave trains, both in longitudinal and transverse modes, with various frequencies and wavelengths of slosh waves generated by the restoring force field of gravity jitters and centrifugal forces in this study. The longest wave periods of slosh waves, either the longitudinal or transverse modes, are responsible for the production of wave modes with the highest ratio of maximum wave amplitude to wavelength. Also, the lower frequency slosh waves are the wave modes with higher wave energy than that of the higher frequency slosh waves.

Remote sensing of Arkansas tornadoes on 11 April 1976 from a satellite, a balloon and an ionospheric sounder array

Abstract The Arkansas tornadoes on 11 April 1976 were investigated using regular 30 min interval GOES digital infrared data, rawinsonde observations, Doppler sounder records and radar summaries covering the 3 hour time period immediately preceding the touchdown of the tornadoes. Clouds associated with the tornado were compared to other clouds that were not associated with tornadoes. It appears as if the altitude to which the overshooting cloud top penetrates above the tropopause is the major factor that controls tornado formation. Gravity waves were first observed at ionospheric heights when the overshooting cloud top began to penetrate the tropopause. Rawinsonde and radar observations were used to establish the background meterological conditions.

Cryogenic hydrogen reorientation and geyser initiation at various liquid-filled levels in microgravity

Abstract Resettlement or reorientation of liquid propellant can be accomplished by providing optimal acceleration to the spacecraft such that the propellant is reoriented over the tank outlet without any vapor entrainment, any excessive geysering, or any other undesirable fluid motion for the space fluid management under microgravity environment. Based on the computer simulation of flow fields during the course of fluid reorientation, six dimensionless parameters are resulted in this study.