The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
LARGE-EDDY SIMULATION OF THE WIND FLOW ACROSS
A TERMINAL BUILDING ON THE AIRFIELD
James O.P. Cheung*, P.W. Chan**, and Dennis Y.C. Leung *
*The University of Hong Kong, Hong Kong, China; **Hong Kong Observatory, Hong Kong, China
Abstract
Airflow disturbances associated with buildings on the airfield may affect the operation of aircraft. This project,
employing computational fluid dynamics (CFD) model, aims to study the turbulent wake after the wind flows over
a hypothetical airport terminal and its potential impact on the low-level winds along the runway in the downwind
region. Large-eddy simulation (LES) is used to calculate both the mean and fluctuating winds along the glide path.
Three prevalent wind directions, which are at different incident angles to the airport terminal, are examined to
illustrate how the building induces wind deficits over the runway. The LES results show that there are rather
abrupt losses in headwind, hence lift force to the aircraft, along the glide path under certain condition. The
maximum drop in mean wind speed can be as large as 10 m/s, greater than three times of the standard deviation
of wind speed, and thus considered to be due to artificial effects and not natural wind fluctuations. This amount of
wind deficit also exceeds the 7-knot (3.6 m/s) criterion proposed by Krüs et al. (2003) in their study of buildings at
the Amsterdam Airport Schiphol. Under this circumstance, the landing aircraft may experience abrupt wind
changes while flying through the building wake region. Even though the LES might have over-estimated the wind
deficit, this study provides insights into possible effects of building wake over an airfield and could serve as a
useful reference for real case studies for the assurance of aviation safety.
Key words: Computational fluid dynamics (CFD); large-eddy simulation (LES); wake turbulence; building wake;
aircraft safety
1. INTRODUCTION
Airflow disturbances may adversely affect the operation of aircraft. For instance, in severe turbulence, the aircraft
may change altitude and attitude and the pilot may lose the control of the aircraft temporarily. Such disturbances
in the airflow could occur in various conditions. If the airport is situated in an area of complex terrain, the winds
climbing over the mountains and valleys near the airport may be disturbed, resulting in the generation of mountain
waves, mountain wake flow, hydraulic jumps, etc. Buildings inside and around the airport could be another
source of airflow disturbances. Apart from the terminal buildings and the hangars, there could be quite a lot of
commercial and even residential developments around the airport. Airflow disruptions arising from the buildings,
such as building wakes and corner jets, may have significant impact on the operation of aircraft.
In the study of buildings at Amsterdam Airport Schiphol, Krüs et al. (2003) established some criteria about the
impact of buildings on the airflow that may affect the aircraft. With a background crosswind of about 25 knots, a
wind deficit of 7-knot or more downstream of the building is considered to have significant impact on aircraft
operation. Such a criterion is further established in a more recent and comprehensive study based on flight
simulation (Nieuwpoort et al., 2006). Moreover, if the wind change associated with the building exceeds three
times the standard deviation of the disturbed airflow, it is considered to be more significant than natural wind
fluctuations and the pilot may need to pay due attention in controlling the aircraft under such condition.
In this study, a LES model available in a commercial code (FLUENT) is used to study the wind disturbances
arising from a hypothetical Y-shaped building, noting that this shape is becoming popular in modern airport
terminal building design, e.g. in Beijing, China and St. Louis, U.S.A., and examine the impact of such
disturbances on aircraft operation. Since LES calculation is computationally very expensive, only a limited
number of incident angles of the wind relative to the building’s orientation have been considered. The impact on
aircraft operation would be discussed by considering the 7-knot criterion and 3-times-standard-deviation wind
fluctuation condition as described above. The limitations of the methodology, rendering this study a preliminary
one, would also be discussed.
2. LES MODEL
The LES model used in this study was the new dynamic subgrid-scale (SGS) parameterizations, which has been
successfully implemented in the framework of unstructured, mesh-based finite-volume method. The dynamic
turbulent kinetic energy transport model (DTKEM, Kim & Menon 1997) was employed by using the commercial
CFD code FLUENT (FLUENT 2009). The model constants were determined dynamically during the computation.
The LES model is detailed elsewhere (Kim & Menon 1991, Fluent 2009).
The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
3. BACKGROUND WIND PROFILE AND Y-SHAPED BUILDING
A power-law is adopted for the background wind profile. A reference height of 200 m is chosen with a free stream
velocity of 22 m/s and an exponent of 0.27:
.
(1)
The hypothetical Y-shaped building (Figure 1) has a height which varies between 20 and 40 m. A 1:1000 model
of the building has been developed and implemented in FLUENT using the software GAMBIT. The simulation
domain has a total grid number of about 2,000,000.
4. RESULTS OF THE VARIOUS INCIDENT ANGLES OF WIND
Three incident angles of the background wind direction have been considered. They are taken to be relative to
the minor axis of the building (Figure 1). Negative angles mean anti-clockwise relative to the axis.
4.1. -22 DEGREES
The streamwise velocity plot at a height of 10 m is given in Figure 1. It could be seen that the building leads to
two areas of V-shaped wind deficit (coloured green and blue in Figure 1). At the same time, nearby the areas of
wind deficit, there are also two areas of stronger flow downstream of the building (coloured yellow and orange in
Figure 1). To find out the impact of such areas of wind deficit and wind gain on the operation of the aircraft, the
perturbed wind along the glide path (i.e. simulated wind along the glide path minus the unperturbed wind in the
absence of the building) is calculated. Glide path refers to the line at 10 m above ground along the runway up to
the runway threshold and a straight line of 3 degrees above the horizon beyond the runway threshold. The
perturbed wind (coloured green in Figure 2) is compared with 7-knot threshold and 3 times of standard deviation
of the wind. It could be seen that, at a height of about 60 m, the wind deficit is large so that both criteria are met.
There is also another wind deficit near the touchdown location that is close to meeting both criteria.
In order to examine the first wind deficit area in more detail, the resultant wind velocity at 60 m is plotted in Figure
3, with the 60 m location along the glide path indicated by a circle. It could be seen that the wind deficit is
associated with the wake of upper end of the building (i.e. base of Y-shape). From vertical cross-secton along the
glide path (Figure 4), the wake extends to a height of about 120 m, which is about 3 times of the building’s height.
The vertical velocity along the glide path is shown in Figure 5. There is a peak of upward motion of the air at the
60-m location. The maximum vertical velocity is about 1.2 m/s. This upward motion is studied in more detail by
examining the spanwise velocity component at a height of 25 m in Figure 6. It looks like the upper end of the
building causes the airflow to converge in the spanwise direction at the glide path, resulting in upward motion.
glide path
minor
axis of
the
Y-shaped building
building
incident
wind
direction
Figure 1 Streamwise velocity plot a height of 10 m for
wind direction = -22 degrees. X and Y axes in km.
4.2. -35 DEGREES
Figure 2 Perturbed wind, 7-knot criterion and 3 times
standard deviation of the wind at the glide path in
Figure 1. The lowest height is 10 m (over the runway).
From the streamwise velocity plot at 10 m high (Figure 7), similar to the previous case, there are two areas of
wind deficit and two areas of wind gain downstream of the building. Due to the wind deficit areas associated with
the building, the perturbed wind (Figure 8) also shows two wind drops, one occurring at a height of about 60-70 m
and another at about 10-20 m. For the former one which is related to the upper end of the building, the wind drop
The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
is smaller than the corresponding result in Section 3.1, and there is a region over which both the 7-knot criterion
and the 3-times-standard-devation criterion are marginally met. The maximum upward motion at that location is
about 0.6 m/s (not shown).
Height in km
B
A
A
Figure 3 Resultant wind velocity at a height of 60 m.
Figure 5 Vertical velocity along the glide path.
B
Figure 4 Resultant wind velocity along the vertical
cross section of AB in Figure 3.
Figure 6 Spanwise velocity at a height of 25 m.
incident
wind
direction
Figure 7 Steamwise velocity at 10 m for -35 degrees. Figure 8 Same as Figure 2, but for -35 degrees.
4.3. -10 DEGREES
The resultant velocity plot at 10 m high (Figure 9) shows that there is wind gain at the touchdown point. The
perturbed wind exceeds 7 knots, and is close to 3 times the standard deviation of the wind (Figure 10). The wind
deficit associated with the upper end of the building occurs at a height of about 50 m of the aircraft, and fulfills
both criteria (Figure 10). The maximum upward motion at 50-m high is about 0.7 m/s (not shown).
The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan
incident
wind
direction
10-m touchdown point
Figure 9 Streamwise velocity at 10 m for -10 degrees.
Figure 10 Same as Figure 2, but for -10 degrees.
5. CONCLUSIONS
From LES simulations, it could be seen that a Y-shaped building could give rise to two areas of wind deficit and
two areas of wind gain downstream. Such perturbed wind areas may affect the aircraft along the glide path. For
the various wind directions considered in this study, the more prominent wind deficit area (in terms of the resulting
wind drop along the glide path) occurs at an aircraft height of about 50-70 m. It fulfills both the 7-knot and 3times-standard-deviation criteria. There is another perturbed wind area near the touchdown location of the
aircraft at the runway. Depending on the incident wind direction, the perturbed wind could be wind gain or loss.
However, it is known that LES simulations may over-estimate the magnitude and size of the building wake (e.g. in
comparison with RANS simulations), and the preliminary results in this paper should be viewed with this
perspective.
There are several limitations of the present study rendering the results preliminary: (a) the validity of the LES
model is not fully established, e.g. by comparison with wind tunnel measurements; and (b) the simulation time is
limited due to the computationally expensive LES code – it is in the order of several minutes only. Moreover, in
order to resolve the highly fluctuating winds and turbulent kinetic energy production, a denser mesh may be
necessary. The simulation results could also be sensitive to the exact shape and design of the building (e.g.
curved roof, presence of sharp edges, etc). All these issues would be considered in future studies.
Acknowledgement
The authors would like to thank Dr. C.H. Liu of the University of Hong Kong in setting up the LES model and
providing useful advice for the study.
References
FLUENT, 2009. http://www.fluent.com/
Kim, W.W. and Menon, S., 1997. Application of the localized dynamic subgrid-scale model to turbulent wallbounded flows. Technical Report AIAA-97-0210, American Institute of Aeronautics and Astronautics, 35th
Aerospace Sciences Meeting, Reno, NV, January 1997.
Krüs, H.W., Haanstra, J.O., van der Ham, R. and Schreur, B.W., 2003. Numerical simulations of wind
measurements at Amsterdam Airport Schiphol, Journal of Wind Engineering & Industrial Aerodynamics, 91, 12151223.
Nieuwpoort, A.M.H., Gooden, J.H.M. and de Prins, J.L., 2006. Wind criteria due to obstacles at and around
airports, NLR-CR-2006-261, National Aerospace Laboratory, 200 pp.