Aeronautical applications of simulation technology at Ames Research Center are described. The largest wind tunnel in the world is used to determine the flow field and aerodynamic characteristics of various aircraft, helicopter, and missile configurations. Large computers are used to obtain similar results through numerical solutions of the governing equations. Capabilities are illustrated by computer simulations of turbulence, aileron buzz, and an exhaust jet. Flight simulators are used to assess the handling qualities of advanced aircraft, particularly during takeoff and landing

Inouye, M.

English

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NASA Technical Memorandum 85846
NASA_TM-8584619840011294
Simulation Applications at NASA
Ames Research Center
Mamoru Inouye
March 1984
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NASA Technical Memorandum 85846
Simulation Applications at NASA
Ames Research Center
Mamoru Inouye, Ames Research Center, Moffett Field, California
NI\S/\
National Aeronautics and
Space Administration
Ames Research Center
Moffett Field, California 94035
SIMULATION APPLICATIONS AT NASA AMES RESEARCH CENTER
Mamoru, Inouye*
1. Introduction
The National Aeronautics and Space Administration (NASA) is a
civilian agency of the United States government responsible for planning,
directing, and conducting aeronautical and space activities. Ames
Research Center is one of ten major NASA field installations and was
originally established in 1940 as a laboratory of the National Advisory
Corntnittee for Aeronautics (NACA). The Center is located 60-km southeast
, "
of San Francisco and occupies 168 hectares adjacent to San Francisco Bay
as shown in Fig. 1. A staff of 1,800 Ciyil Service employees and over
1,000 contract workers a.nd students are involved with research and tech-
nology programs in aeronautics, space science, life science, and space-
craft missions.
One of Ames Research Center's prime goals is to conduct aeronautical
research that will be required to develop future aircraft and other flight
vehicles. Specific research areas include aerodynamics, computational
fluid dynamics, and flight simulation applicable to subsonic and tran-
sonic aircraft, including STOL and rotorcraft technology. The objective
of this paper is to describe applications of simulation technology in
aerone:tut:ics, including wind tunnels for investigating aerodynamics, com-
paters for solving fluid dynamics problems, and flight simulators for
studying aircraft handling qualities.
*Assistant Chief, Computational Fluid Dynamics Branch, NASA Ames
Research'Center, Moffett Field, California 94035, U.S.A.
1
2. Wind Tunnel Simulation
The testing of small-scale models in a wind tunnel dates back many
years. In the early 1900's, the Wright brothers constructed a wind tunnel
and tested various airfoil shapes before their first successful manned
flight in 1903. Today, Ames Research Center has a collection of more
than a dozen wind tunnels that operate at subsonic to hypersonic speeds.
These facilities ,are used to determine the flow-field and aerodynamic char-
acteristics for various aircraft, helicopter, and missile configurations.
The largest wind tunnel at Ames Research Center and in the world
has two test sections, the older measuring 12- by 24-m and the newer,
24- by 36-m. The newer test section with its inlet may be seen attached
to the original closed-circuit tunnel in the upper left-hand corner of
Fig. 1. Both test sections are driven by the same set of six variable-
pitch, IS-bladed fans, each powered by 18,000-hp electric motors. The
maximum air speed is S55 km/hr in the 12- by 24-m test section and
185 km/hr in the 24- by 36-m test section. The large size permits test-
ing of full size aircraft or very large models such as the one~third
scale model of the Space Shuttle shown in the 12- by 24-m test section
in Fig. 2. Although operable only at subsonic speeds, tests in this
tunnel are required because supersonic aircraft must land and take off
at subsonic speeds.
Wind-tunnel simulations have limitations because the model support
and wind-tunnel walls interfere with the air flow around the model. In
addition, the flight conditions may not be completely reproducible.
Cost is also a factor. As ·aircraft become more complicated, the amount
of wind-tunnel testing required has increased markedly as shown in Fig.3.
2
Combined with the rising cost of energy, labor" and materials, extensive
wind-tunnel tests become prohibitive. As a result, computer simulations
are becoming increasingly attractiv~ for preliminary design studies with
wind-tunnel tests providing final verification of a design prior to a
flight prototype.
3. Computer Simulation of Aerodynamics
During the past decade, advances in computer technology have made it
practical to solve problems that were previously considered impossible.
As shown in Fig. 4, the cost of performing the same calculations has
dropped markedly as each new generation of computers offers considerably
more speed and capacity without a proportionate increase in cost. Con-
current advances in numerical methods have produced algorithms that make
the most effective use of the available computer hardware. As a result,
computational fluid dynamics has become an important tool in the study
of basic fluid flow phenomena and the solution of practical aerodynamics
problems. NASA's goal is to predict the flow field around aircraft con-
figurations and to design airplanes better, faster, and at lower cost.
The steps in a computer simulation of a fluid dynamics problem are
the following:
1) The governing partial differential equations are formulated. In
the most general form, the unsteady Navier-Stokes equations are used.
With turbulent flow, the turbulence terms are usually time-averaged to
yield the Reynolds-averaged Navier-Stokes equations. When the viscous
effects can be neglected or accounted for separately, the equations reduce
to the Euler equations.
3
2) A grid including the body geometry and exterior boundary is
created. The mesh must be orderly, and the points must be clustered
where large gradients of flow properties occur.
3) A solution method, usually of finite-difference form, is selected.
The method must be accurate, stable, and fast.
4)A computer program is written to obtain numerical solutions on a
large computer. For large programs the specific computer architecture
must be considered to take maximum advantage of the speed and storage
capacity.
5) The results are processed to obtain graphical displays of the
output for analysis. The accuracy of the computer simulations must be
verified by comparisons with analytical solutions or experimental data.
Current computer simulation capabilities will be illustrated by the
following three examples: large eddy simulation of turbulence, aileron
buzz, and exhaust jet.
Turbulent flow is present in practically all aerodynamics problems.
The calculation of the details of turbulence, however, is not possible
even with the supercomputers expected to be available in the near future.
Consequently, turbulence modeling based mainly on experimental data is
required. For simple geometries, however, turbulence calculations are
possible. Moin and Kim (Ref. 1) have performed computer simulations of
incompressible turbulent flow between two parallel plates using the large
eddy simulation method. In this approach, the subgrid scale eddies are
modeled and the large eddies are solved using the unsteady, three-
dimensional Navier-Stokes equations. Typical results are the contours
of streamwise velocity fluctuations shown in Fig. 5 for a plane parallel
4
to the two walls. Over half a million grid points were used in .these
calculations, and the small rectangle in the lower right-hand corner
depicts a grid cell. Th~ computer simulations reveal minute details of
the flow that are difficult or impossible to obtain experimentally and
they provide information for ,turbulence models required in solving the
Reynolds-averaged Navier-Stokes equations. The large eddy simulation
method has also been used to show the effects of blowing or suction,
compliant walls, and rotation on the viscous drag at the wall.
At transonic speeds the movement of the shock wave over a wing can
cause an osciliation of the aileron known as aileron buzz. This phenom-
enon was observed initially toward the end of World War II, and experi-
ments were conducted at that time in the Ames 16-foot Wind Tunnel as
shown in ,Fig. 6. Steger and Bailey (Ref. 2) have recently reproduced
this phenom~non by solving the unsteady, two-:-dimensional, Reynolds-averaged
Navier-Stokes equations. The computer simulations show good agreement with
the old experimental data for the buzz boundary as a function of the free-
stream Mach number and angle of attack. A typical solution for aileron
buzz is shown in Fig. 7, where the aileron deflection angle is plotted
against time for a free-stream Mach number ,of 0.82. Both the' amplitude
and frequency of the oscillations agree with the experimental data.
Three-dimensional solutions of the Reynolds-averaged Navier-Stokes
equations are possible using the supercomputers available today. Deiwert
,and Rothmund (Ref. J) have used ,a CDC CYBER 205 computer to calculate the
flow over a conical afterbody with an exhaust jet. The resolution of
flow details near the surface and j~t required over 200,000 grid points
and a data base of 5-million words. The surface streamlines on the
5
afterbody are shown in Fig. 8, together with the density contours in the
symmetry plane for a free-stream Mach number of 2, angle of attack of
6 degrees, and jet pressure three times the free-stream value. The
expansion of the jet has caused the flow to separate on the conical
afterbody.
To develop the capability to solve more complex problems, Ames
Research Center is acquiring advanced computer hardware and supporting
research on new numerical methods and computer codes. A long-range goal
is to develop a Numerical Aerodynamic Simulator with the capability to
calculate the viscous flow over an aircraft configuration in a matter of
minutes. The computer requirements include a sustained processing speed
of one-billion floating-point operations per second, main memory with
32-million words, and secondary memory with 256-million words. The
planned operational date is 1987.
4. Flight Simulation
Aircraft operation involves the interaction between an airplane and
its pilot. Flight simulators provide this experience without leaving the
ground. Ames Research Center has more than eight flight simulators in
operation, the largest of which are the Flight Simulator for Advanced
Aircraft and the Vertical Motion Simulator. Different aircraft can be
"flown" safely by a pilot in a flight simulator to assess their handling
qualities, particularly during takeoff 'and landing. Existing designs
can be tested to establish emergency procedures in the event of engine
failure or other malfunction, and to recreate accidents and determine
their cause. New designs can be studied to evaluate their performance
and correct any deficiencies.
6
The most advanced flight simulators have six degrees of motion and
they are provided with all the aircraft instruments and controls, the
visual display of the terrain on the windshield, and the audio output of
engine or the rotor blade noise and landing gear rumble. A high-speed
digital computer provide~ the flight dynamics from aerodynamic data
obtained from wind-tunnel tests or computer simulations and. controls the
various subsystems. Th~ scene displayed on the windshield is produced
by a closed-circuit television system with the camera mounted on a carriage
that traverses a miniature landscape.
The Flight Simulator for Advanced Aircraft, shown in Fig. 9, was
completed in 1969 for research on large aircraft. Lateral motion is
emphasized - the cockpit can be moved 24-meters laterally and can be
reconfigured for different aircraft with all the flight controls and
instruments. The Concorde and the Space Shuttle operations have been
some of the aircraft simulations which have been conducted.
The Vertical Motion Simulator was completed in 1979 for research on
STOL and VTOL aircraft, including helicopters. The cockpit can be moved
18 meters vertically and 12 meters laterally. The large vertical motion
permits simulation of maneuvers such as helicopter autorotations.
7
References
1) Moin, P., and Kim, J.: Numerical Investigation of Turbulent Channel
Flow, Journal of Fluid Mechanics, Vol. 18, 1982, pp. 341-377.
20 Steger, J. L., and Bailey, H. E.: Calculation of Transonic Aileron
Buzz, AIAA Journal, Vol. 18, No.3, March 1980, pp. 249-255.
3) Deiwert, G. S. and Rothmund, H.: Three-Dimensional Flow over a
Conical Afterbody Containing a Centered Propulsive Jet: A Numerical
Simulation: AIAA 16th Fluid and Plasma Dynamics Conference Paper
No. 83-1709, Danvers, Massachusetts, July 12-14, 1983.
8
Fl (;U1m T1TI ,J·:S
Fig. 1 Aerial view of Ames Research Center.
Fig. 2 One-third scale model of Space Shuttle in 12- by 24-m wind tunnel.
Fig. 3 Wind-tunnel testing time for commercial aircraft.
Fig. 4 Computing costs for new computers relative to IBM 360/67.
Fig. 5 Contours of streamwise velocity fluctuations in plane parallel
to walls for incompressible turbulent flow between two parallel
plates.
Fig. 6 Aileron buzz test in old Ames 16-foot wind tunnel.
Fig. 7 Variation of aileron deflection angle with time for aileron buzz
conditions.
Fig. 8 Surface streamlines on conical afterbody and density contours in
symmetry plane of jet exhaust.
Fig. 9 Flight Simulator for Advanced Aircraft.
9
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1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
NASA TM 85846
4. Title and Subtitle 5. Report Date
SIMULATION APPLICATIONS AT NASA AMES RESEARCH March 1984
CENTER
6. Performing Organization Code
7. Author(sl 8. Performing Organization Report No.
Mamoru Inouye A-9503
10. Work Unit No.
9. Performing Organization Name and Address T-6465
Ames Research Center 11. Contract or Grant No.
Moffett Field, CA 94035
13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address Technical Memorandum
National Aeronautics and Space Administration 14. Sponsoring Agency Code
Washington, DC 20546 505-31-01
15..Su pplementary Notes
Point of Contact: M. Inouye, MS 202A-1, Ames Research Center, Moffett Field,
CA 94035, (415)965-5126 or FTS 448-5126
16. Abstract
The paper describes aeronautical applications of simulation technol-
ogy at Ames Research Center, which is one of ten major field installations
of the National Aeronautics and Space Administration, the civilian agency
of the United States government responsible for planning, directing, and
conducting aeronautical and space activities. The largest wind tunnel in
the world is used to determine the flow field and aerodynamic characteris-
tics of various aircraft, helicopter, and missile configurations. Large
computers are used to obtain similar results· through numerical solutions
of the governing equations. Capabilities are illustrated by computer simu-,
lations of turbulence, aileron buzz, and an exhaust jet. Flight simulators
are used to assess the handling qualities of advanced aircraft, particularly
during takeoff and landing.
17. Key Words (Suggested by Author(s)) 18. Distribution Statement
Wind tunnels Unlimited
Computational fluid dynamics
Flight simulation
Subject Category - 01
19. Security Ctassif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price"
Unclassified Unclassified 22 A02
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