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American Institute of Aeronautics and Astronautics

Wind Tunnel Testings Future: A Vision of the Next

Generation of Wind Tunnel Test Requirements and Facilities

Mark R. Melanson1

Lockheed Martin Aeronautics, Fort Worth, TX 76101, USA

Ming Chang2

Lockheed Martin Aeronautics, Palmdale, CA, 93599, USA

and

Wendell M. Baker, II3

Lockheed Martin Aeronautics, Fort Worth, TX 76101, USA

Future wind tunnel test requirements are very difficult to forecast due to the

uncertainties of anticipating future direction of national needs, budgetary pressures,

military requirements, and evolving technology. Wind tunnel testing is anticipated to

continue to provide a very significant percentage of development and validation data needed

in pursuit of new technologies and systems of aerospace vehicles. While aerodynamics,

propulsion, and loads development are considered mature disciplines, growing technical

complexities of future air vehicle systems will stress existing wind tunnel and computational

tools that currently provide the bulk of developmental data. As a result, more efficient and

effective wind tunnel test facilities that provide the user with more extensive data and test

capabilities will be required. The authors propose a vision of the future of testing

requirements and possible next-generation wind tunnel test facilities capabilities.

Nomenclature

AFRL = Air Force Research Laboratory

AIAA = American Institute of Aeronautics and Astronautics

AoA = Analysis of Alternatives

ARL = Applied Research Lab

ATD = Advanced Technology Development

CAD = Computer Aided Design

CFD = Computational Fluid Dynamics

CTD = Concept Technology Development

ERA = Environmentally Responsible Aviation

DMM = Direct Metal Manufacturing

FDM = Fuse Deposition Modeling

HPC = High Performance Computing

IDA = Institute for Defense Analysis

ISIS = Integrated Sensor is Structure

ISR = Intelligence, Surveillance and Reconnaissance

MDOE = Modern Design of Experiments

NPAT = National Partnership for Aeronautical Testing

1 Manager, Engineering Laboratories, P.O. Box 748, Mail Zone 6449, Fort Worth, TX, 76101, Associate Fellow.

2 LM Fellow, Air Vehicle Sciences & Systems, 1011 Lockheed Way, Mail Zone 1100, Palmdale, CA, 93599, Senior

Member. 3 Research Engineer Senior Staff, Engineering Laboratories, P.O. Box 748, Mail Zone 6449, Fort Worth, TX, 76101,

Senior Member.

48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition4 - 7 January 2010, Orlando, Florida

AIAA 2010-142

Copyright 2010 by Lockheed Martin Corporation. All Rights Reserved. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

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NC = Numerical Control

Rn = Reynolds Number

RP = Rapid Prototyping

SLA = Stereolithography Apparatus

SLS = Selective Laser Sintering

UAV = Unmanned Aerial Vehicle

UCAV = Unmanned Combat Aerial Vehicle

WT = Wind Tunnel

I. Introduction

OR the past decade and a half the aerospace industry has seen a decline in the overall usage of wind tunnel

testing to acquire aerodynamic and propulsion data for many of the research and development programs. This

decline can be largely attributed to the shrinking number of air vehicle development programs coupled with

improvements in both the speed and accuracy of numerical flow field simulations for complex configurations.

Computational fluid dynamic (CFD) analysis has benefited from the growth in computing power (spurred on by the

computer video game industry), increasing the ability to conduct improved modeling and simulations of complex

problems that give insight to flow phenomenon. These improvements in computational speed and accuracy, coupled

with low developmental budgets on most contemporary programs, have helped grow the increasing reliance on

computational tools during conceptual and preliminary design phases on many programs. Trade studies are often

conducted, isolating likely configurations, based largely on computational solutions. Smaller amounts of validation

wind tunnel testing typically provide the anchor points for these studies.

As a result of these changes in preliminary design processes, wind tunnel testing that follows preliminary design

efforts are typically very focused, targeting validation of the CFD solutions and then expanding to provide the broad

operating envelope data that are well beyond the current speed, accuracy, cost, and throughput for computational

solutions. Wind tunnels remain the only viable source for the volumes of data needed to fully develop and validate

air vehicle systems.

Overall, these factors have reduced the number of wind tunnel entries, impacting the ability to maintain the wind

tunnel infrastructure (which includes not only the test facilities, but also items like wind tunnel model design and

fabrication capabilities, wind tunnel balance providers, instrumentation sources, etc.). Fallout from this reduction in

testing has included the closure of many wind tunnel facilities that have low utilization or high up-keep costs.

Closures of these national assets are setting off concerns within the aerospace community about maintaining

adequate wind tunnel test capability /capacity and skill levels to successfully support future programs. As wind

tunnel facilities and capabilities decrease and test costs almost certainly increase, programs become forced to choose

between accepting increased vehicle development risk through limited testing, utilizing foreign test assets, or

forgoing testing altogether and committing to full dependency on computational modeling. These alternate scenarios

present potential risks of significant design issues and flight failures that can be costly and time consuming to

rectify. Given the present state of the nations wind tunnel test assets and the budgetary constraints, it would be

prudent to understand the industrys future direction and program needs in order to identify our next generational

wind tunnel test requirements and facility needs.

II. Vision of Future Aerospace

If we had a crystal ball providing an accurate projection of the future, there is little doubt that our national focus

would commit the necessary funding to maintain appropriate wind tunnel infrastructure. Since we do not, we are left

with examining the past, reviewing our present program status and health, and projecting our future needs to define

the next generation wind tunnel test capabilities required. Table I lists advanced vehicle concepts being considered

and the time frame for potential development. The table shows a repertoire of vehicle types under study that span

vast speed ranges. As time goes by, the requirements illustrated in Table I will evolve with changing political,

economic, and military environments. Concepts will come, go, manifest into unique needs, or merge to become part

of a bigger program. As a result, the continuing decline in aircraft reaching first flight is shown in Fig. 1.

Several factors appear to be major contributors to this decline. First, as technology has increased, the cost to

develop and field air vehicles has grown exponentially. Norm Augustine, former chairman of Lockheed Martin,

summed it up very eloquently in his book, Augustines Laws: Law Number XVI: In the year 2054, the entire

defense budget will purchase just one aircraft. This aircraft will have to be shared by the Air Force and Navy 3 1/2

days each per week except for leap year, when it will be made available to the Marines for the extra day.1 The

F

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Airbus A380 and Boeing 787 illustrate the commercial equivalent of the major investment and financial exposure

that a single aircraft program represents to developers today.

Table I. Aerospace Vehicle Concepts through 20202.

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Contemporary technology gives air vehicle designers flexibility not available 15 to 20 years ago. Todays

onboard computers and active flight controls, advanced light-weight materials and higher performing electronics

enable expansion of many platforms utility, making it possible to design multi-purpose vehicles rather than the

single-purpose vehicles more typical in past decades. Additionally, these technologies have extended the useful life

span of existing platforms such as B-52, C-130, P-3, MD-80/DC-9, eliminating the need to start new programs.

Rough Estimated Number of Aircrafts Designs Reaching First Flight

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Finally, the historical tradition of wind tunnel testing to gather all necessary data was mainly due to the lack of

alternatives, such as reliable numerical simulation capability. Todays high performance computers coupled with

more reliable CFD modeling has opened avenues to conduct multi-point optimizations driving multi-dimensional

Table I. Aerospace Vehicle Concepts through 20202 (contd).

Figure 1. Estimated number of aircraft designs reaching first flight2.

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parameters into an optimal solutions. Faced with ever tightening budget constraints, todays conceptual design teams

typically conduct limited wind tunnel test programs for CFD validation and focus data for baseline analysis.

Wind tunnel testing today also focuses on more diverse data for a baseline concept that can include force and

moment data, pressure data, hinge moments, on- and off-body flow field surveys, and noise surveys for source

detection. The objective is to gather the repertoire of data that will enable engineering analysis and trade studies to

be conducted, narrowing the field to a baseline for full-scale development and deployment. Development that took

five or more rounds of wind tunnel testing in years past now require only one to three rounds of testing before going

to first flight. Therefore, wind tunnel testing has evolved away from extensive concept development to become the

critical process validating vehicle performance prior to first flight. In 2003, Douglas Ball of Boeing reported3 a

decrease in the typical number of developmental wind tunnel tested wing configurations from seventy-seven to

approximately five between 1980 and 2003 due to the use of CFD modeling.

Despite the change in emphasis and purpose, wind tunnel testing remains the largest and most extensive source

of data for major programs. The continued heavy reliance on wind tunnel testing can be seen in Fig. 2. The increased

complexity and scope of air vehicle designs, coupled with the need to avoid risky and costly problem identification

during flight testing, have actually driven continued increases in wind tunnel testing (on a per-program basis).

It is expected that future programs will rely on highly integrated computational simulation and physical

modeling in the wind tunnel. The most ideal future scenario will include highly integrated computational and

physical simulation capable of rapid evaluation of concepts and configurations. Robust and reliable CFD modeling

simulation will be used to evaluate and narrow the design options to a chosen few. Rapid wind tunnel model design

and fabrication would begin taking advantage of light-weight, easily workable, and high-strength materials to

manufacture modularized model parts for testing. Wind tunnels would be readily available with capabilities

spanning a large speed range and flow visualization at any speed, efficient data gathering process (hardware and

software), automation that reduces model changes, and adaptable to various types of testing, i.e., aero, propulsion,

loads, and noise. Entries in the tunnel will be shorter and more rapid, providing focused physical validation of

analytic estimates and, where appropriate, volumes of data required for extensive control law and flight envelope

expansion.

0

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20,000

30,000

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1950 1960 1970 1980 1990 2000

Year

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B-707

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at CDR

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B-757 @ FF

B-767 @ FF

F-35 thru SDD

(All 3 Variants)

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B-777-200

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F-111 All

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Te

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F-14

DC-6

Figure 2. History of Wind Tunnel Testing on Major Aircraft Programs4.

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Achieving this ideal scenario requires significant progress across many fronts:

Improvements in speed and accuracy of computational simulation

Highly integrated simulation and wind tunnel testing

Rapid development of wind tunnel model hardware

Wind tunnel facilities capable of rapid evaluation of on- and of-body flow physics for identified configurations for a broad range of test types and speed ranges.

Each of these topics is discussed in additional detail below.

A. Future Improvements in Speed and Accuracy of Computational Simulation Over the last few decades, CFD has progressed in leaps and bounds in capability, both in the hardware and

software arena. Twenty years ago developing and running lower order methods were the norm. The focus at that

time was on de-coupling of the inviscid portion of flow from the viscous portion using combinations of Eulers

equation with the boundary layer equations to describe the viscous/inviscid coupling. This was done primarily due to

the limitations in computational speed and memory, forcing trade-offs between the two at a cost to accuracy and

reliability. From an aerodynamic perspective, CFD was of marginal engineering value, with aerodynamic design

determined by extensive wind tunnel studies. CFD, at best, was used as a preliminary design tool and to validate the

results of wind tunnel studies.

Today, supercomputers in a networked ensemble run Navier-Stoke solvers with adjoint methods on overset

grids. This massively parallel supercomputing capability offers trillions of floating point operations and terabytes of

memory to produce high-fidelity, grid-refined CFD simulations in a reasonable amount of time. Again, the cost of

acquiring computers has been reduced by orders of magnitude, enabling low-cost supercomputing to reach a broader

base of CFD researchers in academic and government labs, while also making the technology more affordable for

industry. The application of massively parallel computers enabled 3-D steady and unsteady CFD models to be

applied with increasing confidence in the numerical solution. Today, it is not uncommon to find aerodynamic

models with computational grids up to 100 million cells providing reliable solutions to complex problems. High

performance computing (HPC) has come of age to become a tool that provides programs with predictions, analysis,

and sanity checks of complex designs at cost savings that meet todays budgetary constraints.

Future CFD applications (shown in Fig. 3) will evolve towards multidisciplinary studies for system design and

optimization. Moving control surfaces, computational maneuverability, and vehicle systems with integrated

propulsion are all prime application areas of interest. The net effect of this new generation of applications will be an

increasing reliance on CFD modeling for aerodynamic design and systems optimization where wind tunnel

modeling cannot be so easily or cost-effectively applied.

CFD Application Trends

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Figure 3. CFD Application Trends.

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B. Highly Integrated Simulation and Testing A key challenge has been integrating computational simulation and experimental efforts. Because of the highly

specialized nature of each approach, practitioners have usually either been experimentalists or computationalists.

The well-meaning questions posed in a 1980s article, Will computers replace the wind tunnel? probably did more

to polarize and set back efforts to truly integrate the tools.

The growing speed and improved utility of most computational tools have moved their use from the doctoral

engineer on a supercomputer to an aircraft designer on a PC as a port to networked computing ensemble. Those that

participate in wind tunnel testing now also are often the same personnel that participate in computational simulation.

This expansion has opened the door for highly integrated and streamlined use of both tools in the aircraft

development process.

Simply replacing or supplementing one tool with another does not optimize design efficiency. Use of approaches

like Modern Design of Experiments (MDOE) is required to truly increase the effectiveness of the process.

Integration also requires careful alignment of processes used. As an example, it is not unusual to discover (usually

afterwards) that CFD models do not match the wind tunnel model, thus throwing into question the validity of

computational solutions. Test conditions in the tunnel are often run without regards to the computational simulations

performed beforehand. These seemingly simple process issues often detract from the entire process efficiency.

Both tools, wind tunnels or computational fluid dynamics, are perfectly capable of producing garbage if not

properly used. Expertise and experience are still overriding factors in producing results that are meaningful.

Therefore, it is the integration of these tools, in the hands of knowledgeable experts that ultimately will produce the

improvements required.

C. Rapid Development of Wind Tunnel Model Hardware Traditional wind tunnel models are constructed of metal for high-speed testing, with fiberglass, foam, or wood

added to the mix of materials for low-speed testing. These construction methods are frequently time consuming and

costly requiring long lead times in order to execute model fabrication for a test program.

To better respond to future aircraft design processes, current methods of wind tunnel model fabrication must be

improved to enable a test program to be executed more rapidly. With todays CAD and CFD capabilities, aircraft

design concepts are being evaluated and discarded in one-third of the time that it takes to construct a typical model.

This puts wind tunnel testing in a lagging position, solely to validate predictions.

Tools such as rapid prototyping and high-speed machining are being used to significantly reduce both the cost

and time required for model fabrication. Rapid prototyping is a class of technologies that automates the physical

construction directly from a CAD database. These three-dimensional printers quickly create tangible parts for

purposes from display to test articles. The aerospace industry has adapted a number of these technologies such as

stereolithography (SLA), selective laser sintering (SLS), and fused deposition modeling (FDM) to construct

inexpensive models for primarily low-speed testing or, in more limited cases, in the high-speed test environment.

The RP manufacturing process is an additive process which combines layers of paper, wax, plastic, or resin to

create a solid object. This is in contrast to most machining processes of subtractive, such as milling, drilling,

grinding, etc. that removes material from a solid block to form an object. This allows the creation of complicated

objects with internal features that cannot be manufactured by other means at low cost, making it an ideal process for

aerospace applications (and models in particular).

Direct metal manufacturing (DMM) is a growing subset of the RP world, offering strong potential for high-

strength parts produced directly from RP equipment. After years of development, small volume systems are now

available that can produce metal parts (stainless steel, aluminum, titanium, etc). If the growth trend (see Fig. 4) for

part volume follows similar trends shown in SLS, FDM, and SLA machines, DMM may provide a portion of the

answer for rapid, high-strength models required in the future.

High-speed machining coupled with ever improving CAD design capabilities will be another important

contributor to future reductions in model span time and cost. NC machining currently is generally considered the

critical path process for most metal models. Increases in cutting speeds and improvements in cutters are creating the

capability to produce metal parts quite rapidly with very little hand finishing. Coupled with associative and

parametric CAD design tools that can be employed to rapidly produce designs and machine instructions, machining

cycle times will continue to decrease.

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D. Future of Rapid Prototyping Development Rapid prototyping is beginning to change the way companies design and build products. On the horizon are

several developments that will help to revolutionize manufacturing as we know it. One such improvement is

increased speed. "Rapid" prototyping machines are still relatively slow. By using faster computers, more complex

control systems, and improved materials, RP manufacturers are working to dramatically reduce build time.

Continued reductions in build time will make rapid manufacturing economical for a wider variety of products.

Another future development is improved accuracy and surface finish. Todays commercially available machines

are accurate to approximately 0.003-inch in the x-y plane, but less in the z (vertical) direction. Improvements in laser

optics and motor control should increase accuracy in all three directions. In addition, RP companies are developing

new polymers that will be less prone to curing and temperature-induced warpage.

The introduction of non-polymeric materials, including metals, ceramics, and composites, represents another

highly anticipated development. These materials would allow RP users to produce higher strength functional parts.

Todays plastic prototypes work well for visualization and fit tests, but they are often too weak for functional

testing. More rugged materials would yield parts that could be subjected to actual service conditions. In addition,

metal and composite materials will expand the range of products that can be made by rapid manufacturing. For

example, the University of Dayton is working with Helisys to produce ceramic matrix composites by laminated

object manufacturing.6 An Advanced Research Projects Agency / Office of Naval Research sponsored project is

investigating ways to make ceramics using fused deposition modeling.7,8

Sandia National Labs and Stanford

University are developing laser based systems that can create solid metal parts. These three groups are just a few of

those working on new RP materials.

Another important development is increased size capacity. Even with the growth of rapid prototyping build

volumes illustrated in Fig. 4, part sizes are still relatively small. To remedy this situation, several "large prototype"

techniques are in the works. The most fully developed is Topographic Shell Fabrication from Formus in San Jose,

CA. In this process, a temporary mold is built from layers of silica powder (high-quality sand) bound together with

paraffin wax. The mold is then used to produce fiberglass, epoxy, foam, or concrete models up to 10.8 ft. x 6.6 ft. x

3.9 ft. in size.7 At the University of Utah, research is continuing to develop systems to cut intricate shapes into 3.9 ft.

x 7.9 ft. sections of foam or paper. Researchers at Penn States Applied Research Lab (ARL) are aiming even

higher: to directly build large metal parts such as tank turrets using robotically guided lasers.

Figure 4. Trends in build volumes for RP5.

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III. National Wind Tunnel Infrastructure, Now and in the Future

As stated earlier, the declining government defense and NASA Aeronautics budgets, coupled with industrial

consolidations, have driven the closures of many U.S. wind tunnel facilities. This deterioration of the wind tunnel

test infrastructure can impact our nations ability to develop and field complex aerospace systems, forcing the use of

foreign facilities that may not afford the protection from unauthorized access to technologies being tested. Fig. 5

shows that the number of major U.S. test facilities has been reduced by nearly 50 percent within a 24-year period

(1985 to 2009).

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Compounding the problem, existing tunnels are experiencing a steady decline in overall usage, forcing cutbacks

that impact facility up-keep and improvements. At present, the repertoire of tunnels still open is adequate to support

existing research and development programs. However, many of these tunnels are in need of maintenance and

upgrade to meet the needs of future programs. With average facility ages nearing fifty years (illustrated in Fig. 6),

maintenance and upgrades are an ever increasing and largely unfunded issue with the current tunnel suite.

In the near future, many existing programs will have progressed past their ground test phase and will be in flight

test or are in final certification. As previously discussed, programs currently in the conceptual phase are not utilizing

the tunnels to a high degree, which results in putting many of the test facilities in a low-use state. Therefore, for

those tunnel facilities that are seen to have low utilization will be in danger of closure, further degrading the nations

capability to maintain our global leadership in aerospace.

The challenges of maintaining this infrastructure center on required costs and perceived value. The cost of

owning and operating these facilities is substantial, and the burden is heavier when the facility is not fully used.

Their value, at the national level, is our ability to effectively develop and field leading-edge technologies both for

commercial and military aeronautical systems. This value, in our current wind tunnel business model, is not

reflected in the operating budgets that sustain our existing capabilities. This is analogous to the national highway

system which does not generate income directly but without which we would not have a viable economy. The

continued decline in our wind tunnel infrastructure is similar to closing several national interstate highways each

year; soon there will be no way to effectively move our industry forward. The aerospace industry (both government

and private sector) must adapt to a strategy of maintaining and operating key and critical wind tunnels as essential

assets which insures the nations leadership in the aerospace field.

Figure 5. Reduction in number of major U.S. wind tunnel test facilities in operation from 1985 to 2009.

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LARC 8' High Temperature Tunnel

LARC Aerothermaldynamics Lab

GRC Propulsion Systems Lab

ARC 9x7 Supersonic Wind Tunnel

GRC 10x10 Supersonic Wind Tunnel

LARC 4' Supersonic UPWT

ARC 11' Transonic

LARC National Transonic Facility

LARC 14x22 Supsonic Wind Tunnel

GRC 8x6 Supersonic Propulsion WT

GRC 9x15 low speed Propulsion WT

LARC Transonic Dynamics Tunnel

GRC Icing Research Tunnel

LARC Vertical Spin Tunnel

Dryden Flight Loads Laboratory

Average

Various government agencies and private industry have begun to engage in strategies to revitalize the wind

tunnel test infrastructure. A good example of strategic collaboration is the National Partnership for Aeronautical

Testing (NPAT), which brings together key Department of Defense and NASA test infrastructure leaders. This

partnership reviews laboratory facilities and capabilities and coordinates issues (including planned closures and

investments) between the two primary owners of most U.S. government wind tunnels.

Throughout, most national infrastructure forums have made a number of key recommendations for the future of

wind tunnel testing. Highly representative of those recommendations, the AIAA Ground Test Technical Committee

(GTTC) made the following recommendations9:

1) Development of a knowledgeable test workforce is critical for the national infrastructure. 2) Improved test technology is crucial to enabling future system development. 3) Maintenance and improvement of key test assets is a vital component of enabling future test capabilities. 4) Divestment of redundant and nonessential test infrastructure is required to focus limited resources on

critical capabilities and new infrastructure requirements.

5) New high-speed test infrastructure is required to meet anticipated requirements for future systems.

Currently, no champion has stepped up to accept these challenges. Until one does, the nations wind tunnel

testing capability will continue to decline.

IV. Future Aircraft Design Process Evolution

In the past, wind tunnel testing has been the pacing item on aircraft development programs. The critical path for

most wind tunnel tests typically involves design and fabrication of the model (i.e., the long pole). As modeling and

simulation techniques have become more reliable, faster, and cost-effective to use, program managers are more

willing to rely on CFD to provide first-order answers to conduct conceptual and preliminary design studies prior to

committing to a wind tunnel test effort. Wind tunnel testings purpose is then to provide an anchor point with which

to validate predictions or to provide incremental corrections to existing designs instead of helping to drive the

design. This practice can be acceptable for a one-of-a-kind design with limited operability for demonstration

purposes, but is not acceptable for production programs.

More and more, test programs will consist of CFD simulations, coupled with wind tunnel testing in an integrated

fashion, to help reduce cost and shorten schedules. Technologies that are used to provide HPC are being adapted to

the model design and fabrication process in a rapid prototyping fashion for faster and lower-cost models. The faster

computing power and the larger storage capacities are providing throughput for automation in the test environment,

making test operations more efficient in data gathering and flow visualization. Current and future wind tunnel test

Figure 6. Ages of a variety of NASA wind tunnel facilities.

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programs will be an integrated process looping through CFD modeling, rapid prototyping, and efficient automated

testing for concept development.

Within the aerospace community, wind tunnel testing will continue to be utilized to validate predictions,

populate databases, and provide an anchor point for baseline concepts. Figure 7 shows the anticipated impact of

CFD on overall major-program wind tunnel testing requirements. CFD will increasingly complement wind tunnel

data acquisition requirements. It should be noted that wind tunnel testing will be a fundamental aspect of vehicle

development and will continue to be so for the foreseeable future. As stated in the 2005 Institute for Defense

Analysis (IDA) Science & Technology Policy Institute, Review of CFD Capabilities,10

Assuming computing

power follows historical trend lines, complete aircraft design database generation using CFD is still 40+ years off.

The emerging programs identified in Table I set the stage for future wind tunnel testing requirements.

Additionally, both the U.S. Air Force and NASA have defined technology and capability requirements (listed in

Table II and Table III) to advance the state of the art of future aerospace in both analysis and test and validation

areas.

Micro Air Vehicles- Puts stealthy eyes and ears in dense or anti-access area- Build competency in low-speed aero, controls and advanced structural concepts

Cooperative and Intelligent Control- Help UAVs work together, act and react like manned assets- Build competency in cooperative control and adaptive control- Condition-Based Maintenance + Structural Integrity- Increase affordability and availability of the Air Force fleet- Build competency in structural health monitoring and structural integrity

Hypersonics- Enables survivable long-range strike and ISR missions- Build competency in high-speed flows, controls thermal structures and management

Figure 7. Anticipated impact of CFD on overall major program wind tunnel testing.

Table II. Air Force Research Laboratory Air Vehicles Directorate Growth Areas11

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Vision- Expands viable and well informed trade space for vehicle design decisions, enabling

simultaneous realization of national noise, emission, and performance goals- Enables continued aviation growth while reducing or eliminating adverse effects

on the environment Mission- Performs research to explore/assess feasibility, benefits, interdependencies, and

risks of vehicle concepts and enabling technologies identified as having potential to mitigate the impact of aviation on the environment

- Transfers knowledge outward to the aeronautics community and inward to NASA fundamental aeronautics projects

Scope- N+2 vehicle concepts and enabling technologies- System/subsystem research in relevant environments

V. Next Generation Wind Tunnel Requirements

Many factors such as budgets, technology maturity, and availability will affect future programs and anticipated

wind tunnel requirements. Figure 8 illustrates the anticipated wind tunnel requirements based on this challenge.

JFTL, Micro/Nano UAV, FA/XX,

Hybrid Airship, Hypersonic

2025 WT

Capability

Stratospheric

Low Rn, ultra low

turbulence

High Rn low turbulence

Unconventional flight

Ultra low Rn, ultra

low turbulence

Unsteady flow

Urban flow, large turbulence

Aero

Propulsion

Database

ISIS, Orion, Motr, UAV

Programs

Present 2015

Based on our customers needs (as described in Tables I to III), Lockheed Martin finds several areas of emerging

technology and development challenge that will require improved test and evaluation assets. These are:

Table III. NASA Environmentally Responsible Aviation (ERA) Project Framework for Commercial

Transports.

Figure 8. Emerging Aerospace needs and anticipated 2025 wind tunnel capabilities.

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High-speed testing for transonic transports to hypersonic vehicles: Facilities to test transports, high-altitude ISR, and time-critical-to-target platforms are reaching critical mass; and they are in need of major

upgrades or maintenance to continue operation. In addition, to answer the governments challenge of

advancing our technology to reduce energy consumption, reduce noise impact, and improve vehicle

performance, these major tunnel facilities will need to support non-traditional concept entries requiring

unique or innovative test methodology.

Low Reynolds number (Rn) micro UAV flight (ultra low turbulence) simulation: Adequate tunnel facilities are still available to address normal low-speed testing. The Air Force Research Laboratorys challenge

growth initiative11

may be the venue to address wind tunnel test needs for nano and micro UAVs.

Unsteady aerodynamic testing for flapping wing.

Urban flow, large-turbulence testing for micro vehicles and hybrid airships.

Stratospheric test capability ranging in Mach numbers from 0.5 to 2.5, Rn/ft up to 5 million, dynamic pressures up to 1500 psf and simulating altitudes up to 80,000 ft are required.

Low Rn, ultra-low-turbulence flow for ISR platform testing.

High Rn low-turbulence flow for high-speed platforms.

VI. Recommendations for Future Capabilities

Recommendations to draw down the existing infrastructure in favor of critical capabilities and investment in new

capabilities (based on future needs) point to consideration of potential new wind tunnels. With a vision of the future

in mind, key capabilities and characteristics for a new (or upgraded) capability should include:

Multi-mission capability. Any new test facility must be capable of a broad range of test types and speed ranges. Speeds from M=0 to M=5.0, altitude simulations up to 80,000 ft (stratospheric testing), Reynolds

numbers up to 5 million/ft should be capability goals.

Moderate Test sections size. Approximate 60 to 100 sq. ft. test section size is a reasonable compromise between high-cost large-volume test section sizes for large models and efficient, low-operational-cost

smaller facilities. This nominal test section size facilitates models of reasonable size to obtain reliable data

and without flow issues such as blockage, flow breakdown, and shock reflections.

Advanced data mining capability. Real-time quantitative and visualization data of on- and off-body flow fields will be required to integrate and validate computational simulations.

Excellent test section optical access for application of developing on- and off-body flow visualization and measurements. Future data mining requirements (above) will drive significant optical access requirements.

Ease of access and installation. With the anticipation that future windows will require rapid access, new capabilities must have extremely rapid access. The ability to install and test a model within a single

operational shift is essential.

Highly automated testing. Efficient and highly productive operations will drive crew sizes down in favor of automation. Tunnel and model automation capability are a must for any future capability.

Highly connected facility. Full remote access, including data streaming, audio and video feeds (to facilitate virtual presence), will enable test teams to be spread across the nation without the requirement to

physically attend testing. Fully integrated computational access to existing design simulation or test

databases is essential.

Ability to create model configurations on-site. Rapid model creation capability (as discussed in previous sections) will become essential to a rapid test mindset.

Energy efficiency. Any new facility must be extremely energy efficient. Evaluation of non-traditional designs such as oval circuits, multi-cycle test environments, extremely low-friction circuit design, and

variable test section sizes should be important considerations.

Expert staff. Test success is more often influenced by the expertise and behavior of the staff than by equipment or underlying infrastructure. To enable rapid, efficient, and successful testing, a well rounded

staff of experts (in both facility operation and aircraft development) is needed. The ability to perform

testing without extensive customer presence absolutely revolves around a facility having expertise and

efficient processes.

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VII. Conclusions

Wind tunnel testing will remain a cornerstone activity for aircraft development, but the application and role for

testing will continue to evolve. Investment must be maintained for our wind tunnel infrastructure for those facilities

that are uniquely required to maintain the national capability to develop future aerospace products. Vital to this

investment is bringing together the key stakeholders (NASA, Department of Defense, and industry) to develop a

national consensus on what facilities are critical. Divestiture of non-critical assets should be considered in order to

facilitate development of new test capabilities that will be required to fill the anticipated gaps in future testing

capabilities.

Evolution of the aircraft design process will require a more integrated and streamlined design/analysis/test

process that requires careful and deliberate integration of computational tools with wind tunnel testing. Developing

skilled practitioners capable of using both tools effectively is a key. Recommendations were presented for desired

capabilities and characteristics of new or upgraded facilities that will likely be required.

References 1Augustine, Norman R., Augustines Laws, 6th ed., AIAA, New York, 1997. 2Antn, Philip S., Gritton, Eugene C., Mesic, Richard, Steinberg, Paul, et al, Wind Tunnel and Propulsion Test Facilities

An Assessment of NASAs Capabilities to Serve National Needs, RAND Report, Santa Monica, California, Prepared for

NASA, 2004; reprinted with permission. 3Ball, Douglas N., Aviation Week & Space Technology, 8 December 2003; URL:

http://www.nitrd.gov/subcommittee/hec/hecrtf-outreach/sc03/sc03_hecrtf_dball.pdf. 4Melanson, Mark R., An Assessment of the Increase in Wind Tunnel Testing Requirements for Air Vehicle Development

Over the Last Fifty Years, AIAA 2008-830, 46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, 7-10 January

2008. 5Melanson, Mark R., Model Design and Manufacturing, Presentation at the Global Wind Tunnel Symposium, Fort Worth,

Texas, November 2008. 6Freeform Fabrication of Structural Ceramics and Ceramic Matrix Composites by Laminated Object Manufacturing

(LOM), Dayton University Rapid Prototyping, 1998. URL: www.udri.udayton.edu/rpdl/sff2.htm (Accessed 21 April 1998). 7Palm, William, Rapid Prototyping Primer, Learning Factory Rapid Prototyping Home Page. Penn State University,

revised 30 July 2002. 8Laboratory of Freeform Fabrication of Advanced Ceramics at Rutgers University, 1998. URL: www.caip.rutgers.edu/sff

(Accessed 21 April 1998). 9Position Statement Prepared by the American Institute of Aeronautics and Astronautics Ground Test Technical Committee,

11 January 2008, Chairman, Mark R. Melanson, and Vice-Chair, Sheri Smith-Brito, Infrastructure Recommendations for

Implementation of Executive Order 13419 National Aeronautics Research and Development Policy, AIAA URL:

http://pdf.aiaa.org/downloads/publicpolicypositionpapers//windtunnelinfrastucpaperbodapproved011108.pdf (Accessed 10

September 2009). 10Garretson, Dan; Mair, Hans; Martin, Christopher; Sullivan, Kay; and Teichman, Jeremy; Review of CFD Capabilities,

Institute for Defense Analyses Science & Technology Policy Institute Report D-3145, prepared for the Office of Science &

Technology Policy, Executive Office of the President, September 2005. 11Wissler, John B. (Col), Air Vehicles Vision 2009, Air Force Report, Distribution Approved for Public Release 88ABW-

2009-1106; reprinted with permission.

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