Experimental Investigation and CFD Simulation of Active Damping Mechanisms for Propellant Slosh in Spacecraft and Launch Vehicles Dhawal Leuva Graduate Student, Aerospace Engineering, Embry Riddle Aeronautical University Daytona Beach, Florida 32114 Priya Sathyanarayan Student Research Assistant, Mechanical Engineering, Embry Riddle Aeronautical University International Baccalaureate Program, Spruce Creek High School, Daytona Beach, Florida 32114 Deepak Sathyanarayan Student Research Assistant, Bio-Medical Engineering, Duke University Durham, North Carolina 27708 and Sathya Gangadharan Professor, Mechanical Engineering, Embry Riddle Aeronautical University Daytona Beach, Florida 32114 ABSTRACT Violent motion of propellant in the tank due to inertial forces transferred from actions like stage separation and trajectory correction is termed as propellant slosh. If unchecked, propellant slosh can reach resonance and lead to complete loss of the stability of spacecraft, change the trajectory or increase consumption of propellant from the calculated requirements, thereby causing starvation of the latter stages. A spherical tank modeled for CFD simulation in ANSYS CFX software package considers free surface of the propellant exposed to atmospheric pressure. The propellant is hydrazine. Hydrazine being toxic and its properties being close to that of water, water is used as propellant for experimental study. For close comparison of the data, water is chosen as propellant in CFD simulation. The research is done in three phases. First phase is modeling of CFD simulation and validation of model by comparison to previous experimental results. Second phase is developing a damping mechanism and simulating the behavior by FSI model. Third phase is experimental development of damping mechanism and comparing the FSI simulation and experimental results. Various passive damping devices (diaphragm and baffles) and active damping device (frequency control) are compared in terms of their effectiveness in damping of fuel slosh. I. INTRODUCTION For spin stabilized spacecraft, unwanted vibrations lead to propellant slosh [1]. Energy dissipation of this propellant slosh is difficult. This energy causes nutation of spacecraft about its spin axis [2, 3]. For non-spinning spacecraft, actions like trajectory control and stage separation induced propellant slosh. Sloshing is of two types. First type is small amplitude sloshing caused by transient excitation so the amplitude is small with well-defined oscillation frequency. It is the function of gravity, tank shape and propellant fill level in the tank [4]. Second type of sloshing is large amplitude sloshing caused during main engine ignition and burnout, the waves begin to break and oscillations become erratic in large amplitude sloshing. When slosh waves are allowed to freely oscillate, they have a tendency to reach resonance. At resonance, slosh waves have maximum amplitude. The forces of sloshing propellant cause the spacecraft to nutate about its spin axis. Traditional vector correction methods are used to correct the nutation, but high frequency of direction change and high magnitude of sloshing propellant forces quickly overpower the corrections being made and sometimes results in more nutation and complete loss of spacecraft. To prevent sloshing, presently many passive damping devices are being used. These passive damping devices (diaphragms and baffles) provide excellent propellant slosh damping for a small range of frequency and small amplitude of sloshing, but they are not effective when propellant fill level changes and sloshing frequency is outside their design range. These devices are bulky, consume space, add significant weight, have small operation range and requires extensive testing [5]. Active damping devices are developed to overcome the disadvantages of passive damping devices. Active damping devices work for a wide range of amplitude and frequencies and for all the propellant fill level in the tanks. An active damping device consist a device that can generate high frequency small amplitude waves with opposite phase to that of sloshing waves. The ultimate goal for active damping device development research is to make an automated device with a feedback loop that can measure tank fill level, amplitude and frequency of propellant slosh in real time and apply required input of amplitude and frequency of damping waves to quickly stop propellant sloshing [6].
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Experimental Investigation and CFD Simulation of Active Damping Mechanisms
for Propellant Slosh in Spacecraft and Launch Vehicles
Dhawal Leuva
Graduate Student, Aerospace Engineering, Embry Riddle Aeronautical University
Daytona Beach, Florida 32114
Priya Sathyanarayan
Student Research Assistant, Mechanical Engineering, Embry Riddle Aeronautical University
International Baccalaureate Program, Spruce Creek High School, Daytona Beach, Florida 32114
Deepak Sathyanarayan
Student Research Assistant, Bio-Medical Engineering, Duke University
Durham, North Carolina 27708
and
Sathya Gangadharan
Professor, Mechanical Engineering, Embry Riddle Aeronautical University
Daytona Beach, Florida 32114
ABSTRACT
Violent motion of propellant in the tank due to inertial forces
transferred from actions like stage separation and trajectory
correction is termed as propellant slosh. If unchecked,
propellant slosh can reach resonance and lead to complete loss
of the stability of spacecraft, change the trajectory or increase
consumption of propellant from the calculated requirements,
thereby causing starvation of the latter stages. A spherical tank
modeled for CFD simulation in ANSYS CFX software package
considers free surface of the propellant exposed to atmospheric
pressure. The propellant is hydrazine. Hydrazine being toxic
and its properties being close to that of water, water is used as
propellant for experimental study. For close comparison of the
data, water is chosen as propellant in CFD simulation. The
research is done in three phases. First phase is modeling of CFD
simulation and validation of model by comparison to previous
experimental results. Second phase is developing a damping
mechanism and simulating the behavior by FSI model. Third
phase is experimental development of damping mechanism and
comparing the FSI simulation and experimental results. Various
passive damping devices (diaphragm and baffles) and active
damping device (frequency control) are compared in terms of
their effectiveness in damping of fuel slosh.
I. INTRODUCTION
For spin stabilized spacecraft, unwanted vibrations lead to
propellant slosh [1]. Energy dissipation of this propellant slosh
is difficult. This energy causes nutation of spacecraft about its
spin axis [2, 3]. For non-spinning spacecraft, actions like
trajectory control and stage separation induced propellant slosh.
Sloshing is of two types. First type is small amplitude sloshing
caused by transient excitation so the amplitude is small with
well-defined oscillation frequency. It is the function of gravity,
tank shape and propellant fill level in the tank [4]. Second type
of sloshing is large amplitude sloshing caused during main
engine ignition and burnout, the waves begin to break and
oscillations become erratic in large amplitude sloshing.
When slosh waves are allowed to freely oscillate, they have a
tendency to reach resonance. At resonance, slosh waves have
maximum amplitude. The forces of sloshing propellant cause
the spacecraft to nutate about its spin axis. Traditional vector
correction methods are used to correct the nutation, but high
frequency of direction change and high magnitude of sloshing
propellant forces quickly overpower the corrections being made
and sometimes results in more nutation and complete loss of
spacecraft.
To prevent sloshing, presently many passive damping devices
are being used. These passive damping devices (diaphragms and
baffles) provide excellent propellant slosh damping for a small
range of frequency and small amplitude of sloshing, but they are
not effective when propellant fill level changes and sloshing
frequency is outside their design range. These devices are
bulky, consume space, add significant weight, have small
operation range and requires extensive testing [5]. Active
damping devices are developed to overcome the disadvantages
of passive damping devices. Active damping devices work for a
wide range of amplitude and frequencies and for all the
propellant fill level in the tanks.
An active damping device consist a device that can generate
high frequency small amplitude waves with opposite phase to
that of sloshing waves. The ultimate goal for active damping
device development research is to make an automated device
with a feedback loop that can measure tank fill level, amplitude
and frequency of propellant slosh in real time and apply
required input of amplitude and frequency of damping waves to
quickly stop propellant sloshing [6].
II. APPROACH
CFD Theory
Computational Fluid Dynamics (CFD) is used to model the
propellant slosh behavior. The CFD method solves Navier
Stokes equations at required points in the fluid domain to get
the properties of the fluid flow at those points. Simple CFD
problems were solved analytically, but with increase in fluid