In an attempt to explain the high loss of panels from the south face of the Vehicle Assembly Building (VAB) during Hurricane Frances, a three-dimensional computational fluid dynamics (3-D CFD) model was developed to simulate local velocity and pressure distributions resulting from such a storm. A preconditioned compressible Navier-Stokes flow solver 1 was used to compute the flow field around the VAB complex, including the Launch Control Center, the Low and High Bays of the VAB, and several outbuildings in the immediate LC-39 area. The mapping of the forces and velocities on and along the affected faces of the VAB correlated surprisingly well with the extensive damage areas realized on both on the south face and on the southeast section of the roof. The model results were also consistent with the minimal damage seen on the east, north, and west faces of the structure

Vu, B. T.

Zysko, J. A.

NASA Technical Reports Server

Proceedings of ASME. 
Fluids Engineering Summer Conference

June 19-23, 2005, Houston, Texas 
DRAFT: FEDSM2005-77052 
A CFD ANALYSIS OF EASTERLY WIND FLOW IMPACTING THE VEHICLE ASSEMBLY
BUILDING 
B. T. Vu	 J. A. Zysko 
NASA Kennedy Space Center 	 NASA Kennedy Space Center 
Spaceport Engineering and Technology 	 Spaceport Engineering and Technology 
KSC, FL 32899
	 KSC, FL 32899 
ABSTRACT 
In an attempt to explain the high loss of panels from the 
south face of the Vehicle Assembly Building (VAB) during 
Hurricane Frances, a three-dimensional computational fluid 
dynamics (3-D CFD) model was developed to simulate local 
velocity and pressure distributions resulting from such a storm. 
A preconditioned compressible Navier-Stokes flow solver 1 was 
used to compute the flow field around the VAB complex, 
including the Launch Control Center, the Low and High Bays 
of the VAB, and several outbuildings in the immediate LC-39 
area. The mapping of the forces and velocities on and along the 
affected faces of the VAB correlated surprisingly well with the 
extensive damage areas realized on both on the south face and 
on the southeast section of the roof. The model results were 
also consistent with the minimal damage seen on the east. 
north, and west faces of the structure. 
INTRODUCTION 
The local wind environment resulting from Hurricane 
Frances varied in speed and direction throughout the course of 
the storm's track through the Bahamas, making landfall near 
Stuart, Florida (84 rim [97 statute miles] to the southeast), along 
its trek across Florida, and ultimately out of our area via 
Florida's western panhandle. Figure 2 shows the approach, 
landfall, and departure track of Frances. 
Unfortunately, because of a loss of power at the Cape 
Canaveral Air Force Station X-Y building, all KSC wind 
information was lost at 1220Z on September 5, presumably 
very close to the occurrence of maximum winds as evidenced 
by other sources. A National Weather Service automatic water 
level station, located at the Trident Pier at Port Canaveral 
approximately 16 miles to the south-southeast, indicated 
maximum surface winds occurred between 1 224Z and 1 300Z. 
The winds at the port during this period were sustained at 41 kt, 
gusting to 57 kt and shifting (veering) rather quickly from 700 
(true) to a more easterly direction. Over the next several hours, 
the wind direction eventually shifted to be from the east-
southeast. The average wind speed continued to drop, but even 
12 hours after the occurrence of maximum winds, they were 
still close to 30 kt steady-state and gusting to nearly 50 kt. 
Figure D-3 shows a 3-day time history plot of signicant winds 
as measured at the Trident Pier from 0000Z on September 4 to 
0000Z on September 7 resulting from Hurricane Frances.
I 
Figure 1 Panel loss from Hurricane Frances on the .routhfce

of the VAB 
The Trident Pier wind data allows us to use the KSC wind 
tower data with some degree of con. dence that the worst part 
of the storm winds were captured prior to the loss of data at the 
Center. The 500-ft meteorological tower (Tower 313) provides 
a reasonable estimate of the vertical structure of the wind 
impacting the VAB because it is located 2.7 miles north-
northwest of the VAB and has wind sensors at multiple levels. 
Sensors are installed at the 12-fl, 54-ft, 162-ft, 204-ft, 295-fl, 
394-fl, and 492-ft levels and are located on both the northeast 
and southwest corners of the tower structure for "best" free-
stream exposure.
Copyright © 2005 by ASME
https://ntrs.nasa.gov/search.jsp?R=20120003222 2019-08-30T19:20:47+00:00Z
Since it is not known exactly when any of the panels 
departed the building, we opted for three most likely wind flow 
scenarios for the CFD analysis. The first starting point was to 
select a wind speed and corresponding direction based on the 
maximum sustained velocity seen at Tower 313. We would 
then bias the direction ±100 about that direction. 
Between 0930Z and 1200Z on September 5, the maximum 
sustained wind at the 492-ft level was about 70 kt, with a peak 
gust of 89 kt (see Figure D-4). The direction was between 062° 
and 077° and was rapidly veering (turning clockwise with 
time). At the 295-ft level, the maximum sustained wind was 
about 61 kt from a general direction of 640 to 78°, with a 
maximum gust of 78 
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Figure 3. Hurricane Frances wind data from Trident Pier at 
Port Canaveral 
Considering the variability of the measurements, terrain, 
and other uncertainties, we selected a working wind speed 
consistent with a minimal Category I hurricane (64 kt) and a 
general first-guess wind direction of 080°. With the VAB sited 
on a line biased 13.5° counterclockwise from true north, the 
initial CFD wind direction of 080° would be hitting the east 
face of the building nearly dead on—or at least within 3.5°. For
simplicity, the CFD wind direction was selected to impact the 
east face directly and then varied ±10°. 
All of the CFD model runs to date have been with a 
uniform vertical distribution, though in reality we know the 
wind speed in the planetary boundary layer increases 
nonlinearly with height. Even so, the analysis results show 
good agreement with what was seen in actuality in terms of 
location, area, and extent of damage on the VAB. 
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Figure 4. Hurricane Frances wind data from Tower 313 at 492 
ANALYSIS 
Similar CFD analysis has been conducted for the wind 
flow simulation around the VAB 2 In the present simulation, a 
viscous, Reynolds-averaged Navier-Stokes (RANS) with ke 
turbulence model was selected. The flow is assumed to be 
uniform, with wind speed and direction prescribed as the 
freestream boundary conditions. Due to the complexity of the 
building geometry and surrounding structures, an unstructured 
grid system was used. A grid-independence study was 
performed with two grid levels: coarse mesh with 501,025 
cells, and fine mesh with 884,382 cells. To speed up the 
convergence, a multigrid scheme was also used. The 
computations were made on the Beowulf cluster using parallel 
processors at KSC's Launch Systems Testbed. Several case 
studies were made for different wind speeds and flow 
directions. Figure 5 shows the computational domain 
considered for the simulations. A parametric study was 
performed with different wind magnitudes and directions. 
DISCUSSION OF RESULTS 
Though the low-level surface winds at KSC never reached 
hurricane strength (74 mph) during Hurricane Frances, 
extensive panel failure occurred at wind speeds far below the 
118- to 125-mph wind load limit reported in the literature. The 
maximum sustained winds measured at a nearby wind tower 
were 53 mph at a height of 54 ft and 80 mph at 492 ft. with 
such low-velocity winds actually seen along the similar 525-ft 
vertical extent of the VAB, we need to turn to the results of the 
CFD analysis to help explain the inordinate loss of panels from 
the south face. The final panel loss count was approximately 
825 panels, or 20 percent of the total VAB side-surface area, 
with the majority of the damage occurring on the south face, 
above and toward the right of the low bay. 
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2	 Copyright © 2005 by ASME 
CFD model runs showed the only wind flow cases that 
would exceed an allowable pressure difference on the panels of 
115 psf (190 psf less an allowable margin of safety) are those 
from Category 4 storms and higher (greater than 131 mph). We 
suspect something else at play here. A range of wind cases 
(wind speed and direction) was generated for a variety of 
additional, arbitrarily defined pressure differentials that would 
yield surface area disturbances near 20 percent or greater. Table 
1 shows a range of wind conditions and calculated pressure 
differentials for a quick-look assessment. The threshold areas 
are integrated over the south face of the VAB, which has a total 
surface area of 220,014 sq ft. 
Table 1. Surface area affected at prescri bed pressure
differential (Max M')
Wind Wind Max Potential Percent Hurricane Speed Directi 1 Damage of Total Category (mph) on (psf) Area Area (sq ft) Damage 
74 90° 23 42,518 19.3 
2 96 90° 38 65,829 29.9 
3 120 90° 60 73,777 33.5 
3 120 80° 60 48,771 22.2 
3 120 100° 60 157,250 71.5 
3 120 100° 67 69,077 31.4 
4 155 90° 118 64,608 29.4 
5 200 90° 180 64,354 29.3
This analysis shows the potential damage area on the south 
face is sensitive not only to wind speed, but to relatively small 
changes in direction. The table shows four simulation that were 
made for a Category 3 hurricane: a wind directly impacting the 
east face, plus three of the same speed that were biased ±10° off 
the east face. The maximum pressure difference is encountered 
when the wind direction is 10° south of the building's east-west 
axis. This direction nicely corresponds to the period of the 
storm when the wind was at its maximum. 
Figures 6 through 12 graphically show the CFD pressure 
distributions on the VAB for various wind intensities from the 
east. Figures 9 and 10 show the results when the wind is biased 
±10° about the East face. The predicted streamlines in Figure 
13 indicate strong vortices in the region between the low and 
high bays of the VAB. This indication is consistent with the 
fact that the most damage was confined to the south face. In 
addition, photographs taken after Hurricane Frances indicate 
that the panels in this region were peeled off the wall in two 
directions (i.e., either toward the upper left corner of the south 
face or toward the upper right corner). This two-directional 
flow phenomenon (Figure 14) is also predicted by the velocity 
vectors of the computational simulation (Figure 15), indicating 
a strong recirculation zone near the region where the panels 
were stripped off the surface. The CFD analysis also predicted 
flow separation around the top of the building, which again is 
consistent with the actual damage seen on the roof (Figure 16). 
The north side of the building only suffered minimal damage, 
as shown in Figure 17. 
6. Coarse grids (high-wind 
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Figure 7. Coarse grids (high-wind case) 
3	 Copyright © 2005 by ASME 
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Figure 14. Peels from two directions 
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Figure 8. Coarse grids (high-wind case) 	 Figure 12. Coarse grids (high -wind case) 
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Figure 13 High i'inds (V=59. 
4	 Copyright © 2005 by ASME 
Figure 15. Flow separation around VAB (V10 knots) 
7
Figure 16. Roof damage (Category], 74mph East wind) 
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Fire 17. Comparison of damage on the north side of VAB 
CONCLUSIONS 
The CFD analysis explained the flow phenomena around 
the VAB. The results agree well with actual damage seen after 
the hurricanes. The south wall of the VAB sustained the most 
damage because of pressure interactions among surrounding 
buildings in the LC-39 area. Flow visualizations also help 
explain what actually happened during the hurricane; 
streamlines and velocity vectors reveal strong vortices near the 
south face of the VAB. The flow reversals, as seen in the 
velocity vectors, explain why the panels were stripped off the 
surface in vo different directions. Finally, the area of the 
pressure gradients on the south face are consistent with the 
location and size of the area of failed panels, even though the 
magnitude of the wind was much lower than what was 
anticipated for failure. The cmbination of the pressure and 
velocity distributions suggests that the panel failures were 
caused by shear, peeling, and tension rather than compression.
Inspection of the panels corroborated the failure modes, and 
corrosion of the panels and fasteners suggests material 
degradation may have played an important role in the panels' 
failing in winds far weaker than hurricane force. CFD analysis 
is an important tool to understanding potential or actual failure 
mechanisms because it can help facilities engineers plan their 
repair and reinforcement strategy in order to mitigate future 
damage to complex structures. 
ACKNOWLEDGMENTS 
The authors would like to express their appreciation to 
KSC management for their mcouragement and interest in these 
analysis efforts. 
REFERENCES 
1.0. Peroomian, S. Chakravarthy, S. Palaniswamy, and U. 
Goldberg. "Convergence Acceleration for Unified-Grid 
Formulation Using Preconditioned Implicit Relaxation," AIAA 
Paper No. 98-0116, Reno, Nevada, 1998. 
2. Vu, B. and Verdier, M.., "Wind Flow Simulation around 
NASA KSC Vehicle Assembly Building," ASME Heat 
Transfer/Fluids Engineering Summer Confemnce, Charlotte, 
North Carolina, July 11-15, 2004
Copyright © 2005 by ASME


A CFD Analysis of Easterly Wind Flow Impacting the Vehicle Assembly Building

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