NASA Technical Reports Server (NTRS) 20030002240: Computational Analysis of Towed Ballute Interactions

18 Pages·2.2 MB·English

by  NASA Technical Reports Server (NTRS)

AIAA Paper 2002-2997
Computational Analysis of Towed Ballute
Interactions
Peter A. Gnoffo
NASA Langley Research Center
Hampton, Virginia 23681-0001
Brian P. Anderson
George Washington University- JIAFS
Hampton VA, 23681-0001
AIAA/ASME Joint Thermophysics and Heat
8 th
Transfer Conference
St. Louis, MO
24-26 June 2002
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AIAA 2002-2997
COMPUTATIONAL ANALYSIS OF TOWED BALLUTE INTERACTIONS
Peter A. Gnoffo * Brian P. Anderson;
p.a.gnoffo @larc.nasa, gov b.p.anderson @larc.nasa.gov
NASA Langley Research Center GWU- JIAFS
Hampton, VA 23681-0001
Abstract
A ballute (balloon-parachute) is an inflatable, aerodynamic drag device for application to
planetary entry vehicles. Ballutes may be directly attached to a vehicle, increasing its cross-
sectional area upon inflation, or towed behind the vehicle as a semi-independent device that can
be quickly cut free when the requisite change in velocity is achieved. The aerothermodynamics
of spherical and toroidal towed ballutes are considered in the present study. A limiting case of
zero towline length (clamped system) is also considered. A toroidal system can be designed
(ignoring influence of the tethers) such that all flow processed by the bow shock of the towing
spacecraft passes through the hole in the toroid. For a spherical ballute, towline length is a
critical parameter that affects aeroheating on the ballute being towed through the spacecraft
wake. In both cases, complex and often unsteady interactions ensue in which the spacecraft and
its wake resemble an aero spike situated in front of the ballute. The strength of the interactions
depends upon system geometry and Reynolds number. We show how interactions may envelope
the base of the towing spacecraft or impinge on the ballute surface with adverse consequences to
its thermal protection system. Geometric constraints to minimize or eliminate such adverse
interactions are discussed. The towed, toroidal system and the clamped, spherical system show
greatest potential for a baseline design approach.
Nomenclature
T temperature, K
,,
V velocity, km/s
D diameter, m x, y, z Cartesian coordinates
L separation distance, m )(3 mole fraction of species i
M Mach number
P density, kg/m 3
,11 molecular weight, kg/kmole
qw wall heat transfer rate, W/cm 2 Subscripts
r radial distance, m
i species index
Rc toroid cross-section radius, m w wall surface conditions
RI toroid inner (hole) radius, m oo freestream conditions
Re P=VooL/ g=, Reynolds number
t Senior Research Engineer, Aerothermodynamics Branch, Associate Fellow AIAA
$Graduate Student, Student Member AIAA
Copyright © 2002 bythe American Institute ofAeronautics and Astronautics, Inc. No copyright isasserted inthe
United States under Title 17,U.S. Code. The U.S. Government has a royalty-free license to exercise allrights under
the copyright claimed herein for Governmental Purposes. All other rights are reserved bythe copyright owner.
1
American Institute of Aeronautics and Astronautics
Introduction fixed towline length are studied to scope
interaction effects on aeroheating on both
Large, inflatable ballutes (balloon- the ballute and base of the towing
parachutes) have been proposed 1'2as spacecraft. Important considerations of
hypersonic decelerators for planetary interactions associated with angle of attack
aerocapture applications. Ballutes may be have not yet been addressed for such a
attached to a vehicle, increasing its cross- system. Limited results for angle of attack
sectional area upon inflation, or towed on the toroidal system without interactions
behind the vehicle as a semi-independent from the spacecraft are introduced.
device that can be quickly cut free when the The second system considered is a
requisite change in velocity is achieved. spacecraft- spherical ballute at identical
Aeroheating on spherical and toroidal freestream conditions to the toroidal system.
ballutes has been documented for the
Here, aeroheating on the spherical ballute is
limiting, most benign case that ignores strongly influenced by separation distance.
interactions from the wake of the towing These environments are studied as a
spacecraft 3. This paper presents a status of
function of separation distance for a single
towed-ballute system simulations including trajectory point. Effects of varying Reynolds
axisymmetric interactions based on number for a single separation length are
continuum analyses. Future work will move also studied. Finally, a special case of zero
beyond axisymmetric and continuum separation is presented (the base of the
limitations, focusing on the most promising spacecraft is contained within the spherical
systems identified in this initial scoping ballute) that shows a relatively benign
effort. Effects of interactions between the interaction environment.
towlines and the spacecraft-ballute system
are also deferred for a subsequent study. Configurations
Numerical simulations are conducted
with the Langley Aerothermodynamic The towed, spherical ballute system
Upwind Relaxation Algorithm (LAURA4). is shown in Fig. 1 and the towed, toroidal
Physical models in LAURA have been
ballute system is shown in Fig. 2. A Viking
updated 3to include chemical species shaped towing spacecraft six meters in
expected in the shock layer of ballutes diameter is utilized in all simulations of
entering the atmospheres of Venus, Saturn, interacting flows presented herein. System
Titan, and Neptune- in addition to the geometric parameters are indicated on each
models for Mars and Earth already present. figure. The spherical system in Fig. 1 has a
However, most of the simulations presented towline length, L, equal to 100 m and ballute
here utilize a perfect-gas approximation to diameter, D, equal to 70m. The toroidal
quickly scope relative effects of spacecraft- system in Fig. 2 has a towline length, L,
ballute separation distance.
equal to 28.46 m, toroid diameter, D, equal
The first system considered is a to 52 m, cross-sectional radius, Rc, equal to
spacecraft- toroidal ballute for the Titan
6.5 m, and inner (hole) radius, RI, equal to
Organics Explorer mission. In this case, 19.5 m. (Note that RI = D/2 - Rc). Pressure
separation distance is constrained by a contour lines are included to qualitatively
requirement that the wake of the spacecraft define the nature and extent of the
pass through the toroid with minimal interaction of the spacecraft wake with the
interaction to the ballute surface. Given this
shock layer surrounding the ballute. These
constraint, effects of Reynolds number for a interactions will be discussed in later
2
American Institute of Aeronautics and Astronautics
AIAA 2002-2997
COMPUTATIONAL ANALYSIS OF TOWED BALLUTE INTERACTIONS
Peter A. Gnoffo * Brian P. Anderson;
p.a.gnoffo @larc.nasa.gov b.p.anderson @larc.nasa.gov
NASA Langley Research Center GWU- JIAFS
Hampton, VA 23681-0001
Abstract
A ballute (balloon-parachute) is an inflatable, aerodynamic drag device for application to
planetary entry vehicles. Ballutes may be directly attached to a vehicle, increasing its cross-
sectional area upon inflation, or towed behind the vehicle as a semi-independent device that can
be quickly cut free when the requisite change in velocity is achieved. The aerothermodynamics
of spherical and toroidal towed ballutes are considered in the present study. A limiting case of
zero towline length (clamped system) is also considered. A toroidal system can be designed
(ignoring influence of the tethers) such that all flow processed by the bow shock of the towing
spacecraft passes through the hole in the toroid. For a spherical ballute, towline length is a
critical parameter that affects aeroheating on the ballute being towed through the spacecraft
wake. In both cases, complex and often unsteady interactions ensue in which the spacecraft and
its wake resemble an aero spike situated in front of the ballute. The strength of the interactions
depends upon system geometry and Reynolds number. We show how interactions may envelope
the base of the towing spacecraft or impinge on the ballute surface with adverse consequences to
its thermal protection system. Geometric constraints to minimize or eliminate such adverse
interactions are discussed. The towed, toroidal system and the clamped, spherical system show
greatest potential for a baseline design approach.
Nomenclature T temperature, K
V velocity, km/s
D diameter, m x, y, z Cartesian coordinates
L separation distance, m )(;i mole fraction of species i
M Mach number
9 density, kg/m 3
all molecular weight, kg/kmole
qw wall heat transfer rate, W/cm 2 Subscripts
r radial distance, m
i species index
Rc toroid cross-section radius, m w wall surface conditions
RI toroid inner (hole) radius, m oo freestream conditions
Re P_oVooL/ goo, Reynolds number
_"Senior Research Engineer, Aerothermodynamics Branch, Associate Fellow AIAA
:_Graduate Student, Student Member AIAA
Copyright © 2002 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the
United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under
the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner.
1
American Institute of Aeronautics and Astronautics
Introduction
fixed towline length are studied to scope
interaction effects on aeroheating on both
Large, inflatable ballutes (balloon- the ballute and base of the towing
parachutes) have been proposed 1'2as spacecraft. Important considerations of
hypersonic decelerators for planetary interactions associated with angle of attack
aerocapture applications. Ballutes may be have not yet been addressed for such a
attached to a vehicle, increasing its cross- system. Limited results for angle of attack
sectional area upon inflation, or towed on the toroidal system without interactions
behind the vehicle as a semi-independent from the spacecraft are introduced.
device that can be quickly cut free when the The second system considered is a
requisite change in velocity is achieved. spacecraft- spherical ballute at identical
Aeroheating on spherical and toroidal freestream conditions to the toroidal system.
ballutes has been documented for the
Here, aeroheating on the spherical ballute is
limiting, most benign case that ignores strongly influenced by separation distance.
interactions from the wake of the towing These environments are studied as a
spacecraft 3. This paper presents a status of function of separation distance for a single
towed-ballute system simulations including trajectory point. Effects of varying Reynolds
axisymmetric interactions based on
number for a single separation length are
continuum analyses. Future work will move also studied. Finally, a special case of zero
beyond axisymmetric and continuum separation is presented (the base of the
limitations, focusing on the most promising spacecraft is contained within the spherical
systems identified in this initial scoping ballute) that shows a relatively benign
effort. Effects of interactions between the interaction environment.
towlines and the spacecraft-ballute system
are also deferred for a subsequent study. ,Configurations
Numerical simulations are conducted
with the Langley Aerothermodynamic The towed, spherical ballute system
Upwind Relaxation Algorithm (LAURA4). is shown in Fig. 1 and the towed, toroidal
Physical models in LAURA have been
ballute system is shown in Fig. 2. A Viking
updated 3to include chemical species shaped towing spacecraft six meters in
expected in the shock layer of ballutes diameter is utilized in all simulations of
entering the atmospheres of Venus, Saturn, interacting flows presented herein. System
Titan, and Neptune- in addition to the geometric parameters are indicated on each
models for Mars and Earth already present. figure. The spherical system in Fig. 1 has a
However, most of the simulations presented towline length, L, equal to 100 m and ballute
here utilize a perfect-gas approximation to diameter, D, equal to 70m. The toroidal
quickly scope relative effects of spacecraft- system in Fig. 2 has a towline length, L,
ballute separation distance.
equal to 28.46 m, toroid diameter, D, equal
The first system considered is a to 52 m, cross-sectional radius, Rc, equal to
spacecraft- toroidal ballute for the Titan 6.5 m, and inner (hole) radius, RI, equal to
Organics Explorer mission. In this case, 19.5 m. (Note that R_= D/2- Rc). Pressure
separation distance is constrained by a contour lines are included to qualitatively
requirement that the wake of the spacecraft define the nature and extent of the
pass through the toroid with minimal interaction of the spacecraft wake with the
interaction to the ballute surface. Given this
shock layer surrounding the ballute. These
constraint, effects of Reynolds number for a interactions will be discussed in later
2
American Institute of Aeronautics and Astronautics
64cellsnormaltothebody,with cell reduced dynamic pressure flow (less than
Reynolds number of order 1 at the body. 10% of freestream dynamic pressure at z =
The spacecraft domain has the same grid 10.0). A reverse flow sets up from the
metrics. Grid quality in the near vicinity of original location of the Mach disk towards
the toroid and spacecraft is considered the base of the spacecraft. At these
adequate for good resolution of heat conditions, a steady condition is achieved
transfer, based on experience with related where the leading edge of the interaction
simulations. Grid quality along the stabilizes at a position 16 m behind the base
spacecraft wake is relatively coarse and the of the spacecraft.
solution of the wake interaction region is
probably not grid converged. Of greater
I Temperature Contours
concern is that Knudsen numbers in the 60
Coupled, Steady, Perfect Gas
wake feeding the interaction region are of y= 1.2 Mol. Wt. =18.86
order I or higher based on local densities 50 Sutherland's Law (Air)
and wake-core diameter. Ongoing work will V =8550 m/s, p_= 1.9 10_ kg/m3
=26.3 Re =1.225 103/m
address these deficiencies; for now the 40
interaction trends that follow should be
considered qualitative. x 30
20
[ Temperature Contours
60
Coupled, Steady, Perfect Gas
y= 1.2 Mol. Wt. =18.86
Suthedand's Law (Air)
V®= 8550 m/s, p®=1.9 10"_kg/m3
=26.3 Re =1.225 10=/m °-30 -20 -10 0 10 20 30
40 Z
x 30
Figure 10: Temperature distribution in plane
of symmetry using factor 10 increase in free
20
stream density to 1.9 10.6kg/m 3.
10 Recent numerical results by
Hornung 5for inviscid interacting flow
between a spacecraft and ballute indicate
0 10 20 30
Z strong unsteady interactions with waves that
completely envelope the spacecraft. A
Figure 9: Temperature distribution in plane steady interaction was never achieved in the
of synunetry for interacting spacecraft- inviscid model. In the present simulation
ballute system with perfect-gas model using (Fig. 10), an increase in the Reynolds
effective 7=1.2 for Titan Organics Explorer. number (through increase in freestream
density) produces a much stronger
The interacting flow simulation in
interaction, enveloping the base of the
Fig. 9 uses inter-block boundary communi-
spacecraft as in Hornung's inviscid
cation between the spacecraft grid domain
simulations. However, the flow appeared to
and the ballute grid domain. In this case, the
be nearly steady in the present viscous
flow passing into the Mach disk along the
simulation; some weak, time-like
axis has already been processed through the
oscillations were evident in the base of the
spacecraft bow shock and wake, resulting in
7
American Institute ofAeronautics and Astronautics
towingspacecraftthoughthesimulationwas
backwash. Ideally, the towline should be
nottime-accurate.
long enough to avoid the backwash heating
Hotgasesforcedupstreaminthe
on the base but short enough to allow the
interactionswill haveadverseimpactonthe
wake to pass through the core of the toroid
aeroheatingtothebaseofthespacecrafta,s
without choking. Still, these results add
demonstratedin Fig.11.Changestoheating
credibility to the design concept that a toroid
associatedwithchangesindensityare
ballute system can avoid interaction-heating
substantiallymaskedwiththenon-
effects on the flexible ballute surface itself.
dimensionalizationt,hushighlightingthe Future work will focus on 3D interaction
effectoftheinteraction.Thefight sideof
effects and the possibility of using an
Fig.11showstheheatingdistribution
elliptical toroid to generate lift in addition to
aroundthecylindricalcrosssectionofthe
drag.
ballute.Thespacecraft-ballutienteraction
hasnoeffectontheballuteportionofthe
Spacecraft- Sphere Interactions
system.TheleftsideofFig.11showsthe
heatingdistributionaroundtheViking
Separation 30 rn < L < 200 m:
shapedspacecraftT. hestrongerinteraction
Spacecraft- sphere interactions are
atthehigherdensitycausesthedimension-
expected to be stronger than spacecraft -
lessheatingpatterntoincreasebyafactorof
toroid interactions because there is no flow-
approximatelythree(fromvalueslessthan
through path behind the interaction region.
0.1tovaluesgreaterthan0.3).
Consequently, a longer separation distance
(longer towline) will be required. A
sufficiently long separation distance, L, will
1_
1.4 Scaled Heating Rate avoid bow shock and wake recompression
1.3- shock impingement onto the inflatable
Poo
1.2 ballute surface material. Results in this
1.9 10.7kg/m 3
1.1
section will explore aeroheating as a
1.9 10.6kg/m 3
1
function of towline length in an attempt to
0.9
answer how long is "sufficiently" long.
0.8
o._ Titan Organics Explorer cases were
% 0.6
simulated for separation distances of 30, 40,
_ 0.5
50, 100 and 200 m. Freestream conditions
O.4
O3 and gas models are identical to the space-
02 craft- toroid interaction cases discussed in
0.1 the previous section. A spherical ballute
0 i i i I i i i i
0 10 2o 30 radius of 35 m was specified.
X, Ill
A representative grid is presented in
Fig. 12 for the 40 m separation. The towing
Figure 11" Heating distribution around
spacecraft is resolved with 125 circumfer-
spacecraft (left) and ballute (fight) for
ential cells and 64 cells from the body to the
nominal density (1.9 10-7kg/m 3)
outer boundary. The spherical ballute
Additional thermal protection to the domain is resolved with 56 circumferential
base of the towing spacecraft may be cells and 44 cells from the body to the
required for some combinations of towline inflow boundary. The domain spanning the
length and Reynolds number in the toroid distance between the spacecraft outflow and
ballute system as a consequence of this the ballute inflow is resolved with 58 span-
8
American Institute of Aeronautics and Astronautics
wise cells and 56 cells from the axis to the
ment changes the result only slightly. No
farfield boundary. The number of spanwise recirculation is present for a separation
cells will vary with separation distance to distance of 200 meters.
maintain approximately constant cell size.
Cell Reynolds numbers at the surface are of
order 1. Solutions are grid converged except 70
in the vicinity of shock impingement on the
spherical ballute, as will be described 6O
subsequently.
5O
40
X
30
2O
5O
40
30
-70 -I_O -50 -40 -30 -20 -10 O'
Z
20
Figure 13" Temperature distribution in plane
of symmetry for interacting system with
L=40 m.
_,, I.=30
2_- [] L=40
Figure 12: Mesh over spacecraft - spherical 1e_,. ' q, 1.,,50
" j: . n I.=100
ballute system with L=40 m.
1.8_" / _ - _i_ Lz200
1.4_ _ /_ © Sphere Only
Temperature contours for a
1.2 /' -
separation distance of 40 meters are featured
in Fig. 13 as an example of the results
acquired for different towing distances. For
0.8 ,
each tow distance, excluding the 200-meter °I. /p/
case, reverse flow extends from the front of
0.4 ,
the sphere toward the base of the spacecraft.
This recirculation is caused by interaction
between low dynamic pressure flow in the
10 20 30
wake of the towing spacecraft and the high
r,m
dynamic pressure region ahead of the
spacecraft bow shock. Fig. 13 shows that
Figure 14: The effects of varying separation
the recirculation leading edge is located 8 distances on wall heat transfer rate.
meters from the front of the sphere.
Examination of the results for the other
Fig. 14 shows the effect of varying
separation distances studied shows that this
separation distance on ballute wall heat
result is independent of tow length for
transfer rate. Trends in the results for
lengths less than 200 meters. Grid refine-
ballute surface pressure and surface
9
American Institute of Aeronautics and Astronautics
temperatureasafunctionofseparation
simple extrapolation to longer towline
distancearesimilartothoseforwall heat
distances indicates that drag effectiveness
transfer rate. To facilitate comparison, the will decrease further before recovering the
non-interacting result for a 70-meter non-interacting sphere limit in Table 1. A
diameter sphere with the same free stream simulation of longer towline distances
conditions is included in the figure. A large (possibly using a space-marching approach
heating spike due to impingement of the to define wake growth) will be deferred
spacecraft bow shock on the ballute is pending further system option studies.
evident. (This behavior is further explored in
subsequent grid convergence study.) As the
1
separation distance is increased, the
magnitude of the heating spike is decreased.
Also, for 30 < L < 100, surface heating 0.95
approaches zero at the ballute geometric
stagnation point. This behavior is thought to
be a consequence of the strong expansion
,0.9
and relatively high energy-flux into the o
surface originating from the shock
0.85
impingement zone.
Vacuum like pressures and densities
are computed in the near wake of the towing 0.8
spacecraft. Pressure levels are on the order
of 10-20N/m 2, while densities are as low as
0.75 0 .... 50I , , , ,1OI0, , , ,15I0, , , i20I0 j _ _ _25I0
1018 kg/m 3. These low values for density
are outside the limits of the continuum L,m
approximation. DSMC simulations are Figure 15" Effects of varying separation
required to better quantify interaction effects distance on ballute drag coefficient.
initiated behind this near wake core.
Fig. 15 shows how the ballute drag 3 A 28 x 44
z 56 x 58
coefficient changes with varying separation
112 x 58
distance. Only contributions from the
2.5 0 Sphere, 56 x44
spherical ballute are included. The drag
reaches a maximum at a tow length of 50 m. 2 <
As the distance is increased, the ballute is
almost completely enveloped in the low _1.5
dynamic pressure flow of the spacecraft 0
wake, resulting in reduced drag.
Results of Figs. 14 and 15 make a
strong case that 200 m (33.3 spacecraft 0.5
diameters, 2.86 ballute diameters) is not a
"sufficiently" long towline. A shock
10 20 30
impingement spike still exists on the flexible
r,m
ballute surface and the drag effectiveness of
Figure 16: Results of grid convergence
the spherical ballute is substantially reduced
study on heating for a separation distance of
because it is immersed in the low dynamic
40 meters.
pressure of the spacecraft wake core. A
10
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