Virtual Diagnostic Interface: Aerospace Experimentation InThe Synthetic Environment

Richard J. Schwartz, Senior Research Engineer; Andrew C. McCrea, Research EngineerATK Space, supporting the Advanced Sensing and Optical Measurement Branch

NASA Langley Research Center, Hampton, VA 23681 USARichard.J.Schwartz(aD-NASA.gov, Andrew.C.McCrea(aD-NASA.gov

Abstract. The Virtual Diagnostics Interface (ViDI) methodology combines two-dimensional imageprocessing and three-dimensional computer modeling to provide comprehensive in-situ visualizationscommonly utilized for in-depth planning of wind tunnel and flight testing, real time data visualization ofexperimental data, and unique merging of experimental and computational data sets in both real-timeand post-test analysis. The preparation of such visualizations encompasses the realm of interactivethree-dimensional environments, traditional and state of the art image processing techniques, databasemanagement and development of toolsets with user friendly graphical user interfaces. ViDI has beenunder development at the NASA Langley Research Center for over 15 years, and has a long trackrecord of providing unique and insightful solutions to a wide variety of experimental testing techniquesand validation of computational simulations. This report will address the various aspects of ViDI andhow it has been applied to test programs as varied as NASCAR race car testing in NASA wind tunnels toreal-time operations concerning Space Shuttle aerodynamic flight testing. In addition, future trends andapplications will be outlined in the paper.

INTRODUCTIONThe advent of affordable very high powereddesktop computer processing has provided alevel of access to advanced three-dimensionalcomputer graphics that have never before beenavailable outside of a limited, computer scienceorientated environment. Today’s personalcomputer (PC) based systems with workstationclass graphics cards are capable of displayingand manipulating highly complex three-dimensional geometries with detailed texturemaps under stunning simulated lightingconditions. The origins of these capabilitiesbegan to emerge in the early 1990’s, and wereimmediately put to use in support of advancedwind tunnel and flight test instrumentationsystems being developed at the NASA LangleyResearch Center (LaRC). This paper will reviewthe applications of three-dimensional modelingand simulation work developed in the AdvancedSensing and Optical Measurement Branch(ASOMB) over the last seventeen years,concentrating on the current suite of applicationsand our plans for future development.

What is ViDI?The Virtual Diagnostics Interface, or ViDI, is amethodology of applying two-dimensional imageprocessing, three-dimensional computergraphics, physics-based modeling, and thehandling of large data sets to use in solvingcomplex aerospace testing and data visualizationproblems. To date, most of the two-dimensionalimage processing has been developed withinNASA, while the three-dimensional visualizationcapabilities have been derived from Commercial-Off-the-Shelf (COTS) software packages.However, these COTS programs were chosen for

their ability to be programmed and workseamlessly with custom user interfaces andlibraries of physics based simulation software.There are three main areas in which ViDI isutilized: (a) pre-test planning, which involved thesimulation of an experiment and the plannedinstrumentation system in a three-dimensionalvirtual world as shown in Figure 1, (b) real-timedata visualization in an interactive virtualenvironment, and (c) post-test data unification,where disparate forms of data are broughttogether in-situ in the virtual environment to helpobtain a more global perspective on the causesand relationships of experimental parameters andthe resulting physical phenomena reported by the

Figure 1: ViDI Visualization of laser light sheetfor aerodynamic flow investigation on Space

Shuttle wind tunnel model

History of ViDIIn 1990 NASA embarked upon the developmentof an instrumentation system to be placed aboarda flight test aircraft which would use lasers and

https://ntrs.nasa.gov/search.jsp?R=20090037086 2018-07-12T18:27:58+00:00Z

cameras to obtain quantitative images of thevelocity of the airflow of the aircraft. Thisinstrumentation would record megabytes of datain a few seconds of operation, which at the timewas problematic on several fronts. One of thefirst issues was how to display the time variantdata images in a meaningful way. Fortuitously,the first three-dimensional computer visualizationsystems were coming on the market, and a DOSbased commercial program, running on an Intel486 class computer was utilized to experimentwith mapping the data images into the virtual

Figure 2: First data mapping of windtunnel data representing airflow velocity

over F/A-18 aircraft in preparation for flighttests of this configuration.

Almost immediately it became apparent that thecamera simulation capabilities of the virtualenvironment would be ideal for use simulating theexperiment as a whole for planning purposes.Ultimately, the instrumentation flight test serieswas cancelled by NASA due to funding issues,and the continued instrument development wasfocused on wind tunnel applications. Thevisualization work, then called Virtual Facilities,continued to grow, supporting a wide variety ofground based aerospace testing techniques, aswell as flight test applications. Reincarnated asthe Virtual Diagnostics Interface (ViDI) in the late1990’s, the scope of applications has expandedto include real-time data visualization andcomparison in virtual environments, new ways ofmerging experimental and computational data,and support for hypersonic aerodynamic flighttesting on the Space Shuttle.

CURRENT APPLICATIONS

Pre-test PlanningThe cost of experimental aerospace testing is akey driver determining the design cycle of a newconfiguration. Modern computational techniques

have relieved some of the requirements forexperimental testing, but there is still a strongneed to validate computational results and runtests on conditions where computational methodsare not yet fully developed. ViDI has played a keyrole in optimizing the design of wind tunnel teststo minimize the test set-up time and ensure the

Figure 3. Screen capture of a typical wind tunneltest setup, shown here for PSP. Yellow cones

represent lights; the upper left image is thesimulated camera image.

ViDI utilizes the virtual world as a stage uponwhich an experiment can be designed. At thecore of the visualization is a carefully scaledmodel of the test facility, usually a wind tunnel inthis case (Figure 3). The model is crafted torepresent both the inside and the exterior of thefacility. Sufficient detail is required to provide theresearcher with enough information to determinewhere to place items such as sensors or camerasand lights. Additionally, the researcher has tohave an accurate three-dimensional computermodel of the article being tested, such as anaircraft or rocket. Most often, these geometryfiles are provided by the company that createsthe actual wind tunnel model, and are received incommon Computer Aided Design (CAD) fileformats. If necessary, these files can betranslated into formats readable by thevisualization software using commercial softwareproducts. The test configuration model files aremerged with and scaled to the geometry of theexperimental facility. Lastly, the mounting device,known as a sting, is added. This unites the testconfiguration to the facility model, and oftenrequires dynamic modeling to provide the propermotion of the test configuration as it is pitched,rolled, yawed and translated through the testsection.Given a virtual scene that realistically mimics aplanned test; the research may concentrate onhow the test will be instrumented. Manyadvanced wind tunnel techniques utilize cameras

as their sensors. Examples include Pressure andTemperature Sensitive Paints (PSP and TSP),which require specific camera views and lightingconditions on the test configuration. Additionally,Particle Image Velocimetry (PIV) measures airflow velocities using high resolution images ofsmoke particles in a flow, and Projection MoiréInterferometry (PMI) uses cameras and speciallighting techniques to measure surfacedeflections. The common element is the use ofcameras and lighting as integral components ofthe instrumentation. Using the virtualenvironment the researcher may experiment withcamera placement, required field of view anddepth of field. Multiple lighting conditions can beanalyzed to eliminate unwanted shadowing, andmost importantly the optical access to key regionsof the flowfield can be assessed under allpossible model positions and orientations. Thisin-situ investigation of experimental setups hasproven to save significant time in both the testsetup and the running of the experiment byeliminating surprises and providing a clear line ofcommunications to the test team.The examples below depict test setups forapplications as varied as PSP testing in theLangley 30 x 60 Foot Full Scale tunnel on anactual NASCAR racing car to a Laser Velocimetryexperiment on the Space Shuttle in the USAFArnold Engineering Design Center (AEDC) to aNASA Ares rocket in the NASA LaRC Unitary

Figure 4. Test setup visualizations used forNASCAR testing, Space Shuttle flow visualization

and Ares rocket stage separation testing.Real Time Data VisualizationThe virtual environment developed in the pre-testphase described above can also be used as thefoundation for displaying data in real time in aninteractive three-dimensional visualization. Todate, three forms of data have been incorporatedinto the visualization; two dimensional imagery,vector forces, and scalar point information, suchas pressure and temperature [2].At the heart of the real-time data visualization is acustom program developed to feed informationinto the virtual environment. The first version ofthis software was designed to interface withcameras to provide real-time streaming video thatwas embedded into the virtual environment. Thiswas especially useful for techniques such aslaser light sheet flow visualization (Figure 5) orSchlieren, which provided a view of the flow thatcould be rapidly mapped to a plane in the virtualenvironment.Following the successful deployment of the realtime imagery in the wind tunnel, the system wasexpanded to interact with the wind tunnel DataAcquisition System (DAS). The DAS is acomputer that can process hundreds of scalarparameters defining the wind tunnel environmentand test conditions at a given moment in time.This provided a source of information for thethree-dimensional virtual environment forpressure, temperature, tunnel velocity, forces andmore. Using this information, a comprehensivevisualization depicting the actual state of theexperimental test article in real time wasdeveloped. Pressures and temperatures wereshown as bars located at the points where the

Figure 5. Flow Visualization experiment first usedfor real-time data visualization in the virtual

environment.

sensors were located, arrows of changingmagnitude represented forces and moments(Figure 6), and state information such as velocity,angle of attack, or flow temperature was affixed tothe display.

Figure 6. Sample real-time visualization – smallbars on model represent measured pressures,

arrows show measured forces.An addition and very important portion of the real-time data visualization capability was theinclusion of pre-computed results from predictivemethods such as Computational Fluid Dynamics(CFD). A database of computational results wasstored on the ViDI computer in a manner thatallows the information to be retrieved based onkey test parameters, such as model attitude (roll,pitch and yaw), flow velocity or Mach number,and other pertinent parameters. Then, as theViDI computer received data from the DAS itautomatically retrieved the correct computationalsolution and displayed it in real time along withthe experimental data. It also did a real-timedifferencing, which rapidly showed the level ofagreement between experimental values andprediction (Figure 7). This system was runautomatically for hours on end during tests, whichallowed the user to concentrate on the datavisualization and not the care and feeding of thesoftware.The real-time software has been developed withwind tunnel testing as the primary application.However, the technology is clearly not limited tojust wind tunnel experiments and validation ofCFD predictions. This capability can easily beexpanded to include computational predictions forany form of analysis – structural, thermal, orother, and the experimental data source mayoriginate from any form of experimentalapparatus. The ViDI capability is designed torapidly allow the user to investigate the fidelity ofboth the computational and experimental results,and provide a validation capability in real-timethat will allow the user to identify issues during atest, while there is still time to affect the way theexperiment is being conducted.

Figure 7. Display from real time test – black barsare experimental pressures, red bars are CFDpressures, surface coloration is CFD pressuredistribution, yellow bars show difference from

experiment and CFD. X-Y plot is also created inreal time to augment visualizations.

Post–test Data UnificationOver the many decades of wind tunnel testing,data visualization has usually been confined totwo-dimensional data plots. With the emergenceof CFD data visualization, visualizing data sets offlow features and the physical conditions on anaerodynamic surface (pressure, temperature,shear stress, etc) became integrated with thethree-dimensional representations of the testgeometries. ViDI has expanded upon this toinclude disparate forms of experimental dataunified into a single visualization, often combinedwith computational predictions as well. Thisprovides two very important capabilities; theability to compare very large quantities ofexperimental and computational results quicklyand intuitively, and the ability to obtain a globalawareness of the cause and effect relationshipsbetween the physical features and trendsoccurring in the datasets. This level of integrationhas led to better understanding of thefundamental physics, as well as the oftenoverlooked limitations of either experimental orcomputational methods. Ultimately, it allows theresearcher to have a far superior situationalawareness of the experiment that has beenconducted than is possible only with a series oftraditional X-Y plots (Figure 8).

Figure 8. Combination of experiential Schlierenphotograph with computational prediction of flow

density as well as surface pressure distribution onAres rocket.

Finally, ViDI has been used as a forensic tool. Ininstances where experimental results orcomputational data seem inconsistent, ViDI hasallowed researchers to re-create plausiblescenarios and experiment with differenthypothesis to see if a scenario is physicallypossible and if the discrete data sources supportthe hypothesis.

HYTHIRMOne expansion of ViDI applications to flighttesting involves the HYTHIRM (HypersonicThermodynamic Infrared Measurements) project.The HYTHIRM project is tasked with obtaininghigh resolution infrared imagery of hypersonicvehicles (flying greater than Mach 5) in flight todetermine the heating on the vehicle. This isespecially critical for reentry spacecraft, whoseproperly designed heat shields are essential toensure adequate vehicle performance whileensuring the craft will not burn up due toinadequate protection. To date, the largest andmost complex hypersonic vehicle is the SpaceShuttle. After more than twenty years and one-hundred twenty flights there are still a number ofimportant engineering questions concerning thefundamental flow physics involved in theaerodynamic behavior of the Space Shuttleduring reentry [3].The HYTHIRM project relies upon aircraft andground based systems to locate the SpaceShuttle during reentry. The vehicle is flying atvelocities over Mach 18 (roughly 14,000 miles perhour) many hundreds of miles away. Theseimaging assets have to track the vehicle opticallyfrom close to horizon break to beyond the point ofclosest approach, which is typically about 30nautical miles from the deployed infrared camera.For such a mission pre-planning is critical.Reentry trajectories are obtained from the FlightDynamics Office (FDO) at the Johnson SpaceCenter (JSC). These trajectories are placed in acustom ViDI program tied in with the COTSgraphical software to plot the trajectory on a

virtual three-dimensional Earth (Figure 9). Inaddition, a Space Shuttle model is animatedalong the trajectory, and the program allows theuser to specify an imaging assets (such as aparticular telescope mount on an aircraft) andquickly determine the view of the shuttle from thetelescope, based on the aircraft position and thepoint on the Shuttle trajectory being observed

Figure 9. Typical trajectory plot for Space Shuttlereentry, shown here for the STS-125 mission.

The Space Shuttle reentry trajectories have amultitude of variables that can allow the vehicle toapproach the Kennedy Space Center (KSC) byflying approaches ranging from the east of Cubato the center of Mexico. An advancedunderstanding of how to position the imagingassets is a complex and essential task to ensuremission success. Additionally, it may be onlyhours before reentry that the actual path isknown, and less than an hour before touchdownbefore a highly accurate track is computed. Realtime updates are processed using the ViDI toolsin the Mission Control Center in Houston andradioed up to the flight crews or land basedtelescope operators. To date, ViDI support hasbeen provided to the two HYTIRM missions, STS-119 and STS-125, both of which had completesuccess in acquiring and tracking the SpaceShuttle from an airborne platform, and obtaininghigh resolution thermal imagery of the criticalunderside heat shield of the Space Shuttle during

Figure 10. Comparison of flight data image fromSTS-119 (left) and ViDI virtual prediction prior toreentry (left).

Figure 11. Unprocessed infrared images of STS-119 (left) and STS-125 (right).

Following the data capture, ViDI has been usedfor mapping the two-dimensional thermal imagesof the surface of the vehicle back to a three-dimensional geometry. This texture mappingtechnique relies on a unique application ofspatially calibrating the data using a virtualreference. In order to properly texture map thedata with scientific rigor, the data must be ‘de-warped” to remove optical aberrations,perspective distortion, and foreshortening of thedata on the vehicle due to the angle the vehiclemakes with the camera. Traditionally,photogrammetric techniques are used thatrequired knowledge of the exact position andorientation of the camera relative to the targetobject, or the Space Shuttle, in this instance.However, with this virtual calibration technique,this knowledge is not required. A referencepattern of equi-spaced dots is applied to thethree-dimensional geometry of the Orbiter, andthen a rendering of the Orbiter is made thatmatched to orientation of the actual Orbiter in thedata image as closely as possible (most easilydone by making the three-dimensional orbitertransparent and overlaying it on the actual dataimage, Figure 12.) This virtual calibrationrendering is then processed by an image de-warping program (custom written at LaRC) toremap the two-dimensional data to remove alldistortions and create a transformed image thatappears as if it was taken from a camera directlyperpendicular to the underside of the vehicle, withno perspective distortion. This image can then bemapped to the three-dimensional virtual model fordata visualization.

FUTURE DEVELOPMENTSWith new measurement and visualizationtechnologies emerging and maturing, ViDI willgrow and adapt to interface with the newtechnologies. Despite using commerciallyavailable software, the current cost is still highenough to make the sharing and distribution ofViDI results challenging. The solution lies inplatform-independent stand-alone applicationsthat the user can open and run without additionalsoftware. These applications would use existingmethods utilized by three dimensional gamerendering engines or web browsers to createapplications that allow the user to view and

manipulate the virtual environment. The nextmilestone for ViDI is three dimensional displays.With three dimensional presentation methodsrapidly growing in use, the future of ViDI lies inthree dimensional presentations. The ability toview and move through a virtual environment withthe use of active or passive three dimensionaltechniques would only heighten the informationand understanding gained by the user.

De-warped Images

Infrared data Image

WK 1

Visual ImageRendering of shuttle

IR Data1aligned to match +

^- flight data with virtual* fiduciary marks ^

applied. f^•_^

^r.aa^ T';

Visual Data

Figure 12. Data de-warping method for texturemapping thermal imagery data to Space Shuttle

three-dimensional computer model.

CONCLUSIONThe Virtual Diagnostic Interface software hasbecome a powerful tool for a wide range ofaerospace testing applications. The ability torapidly combine experimental and computationaldata sets with three-dimensional geometry intoone interactive environment gives the user agreater situational understanding throughout atest. ViDI will continue to grow its visualizationcapabilities in support of ground and flight testapplications. As personal computing powercontinues to expand these techniques can still beimproved upon and increased in scope. Everynew project presents its own unique set ofchallenges to overcome and expands thecapabilities of the ViDI software.

REFERENCES1. Schwartz, R.J., "ViDI: Virtual Diagnostics Interface Volume 1-The

Future of Wind Tunnel Testing" Contractor Report NASA/CR-2003-212667, December 2003

2. Schwartz, R.J., Fleming, G.A.,”LiveView3D: Real Time DataVisualization for the Aerospace Testing Environment”, AIAA-2006-1388, 44th AIAA Aerospace Sciences Meeting and Exhibit, Reno,Nevada, Jan. 9-12, 2006.

3. Berry, S., Horvath, T., Schwartz, R., Ross, M., Campbell, C.,Anderson, B., “IR Imaging of Boundary Layer Transition FlightExperiments,” AIAA-2008-4026, June 2008.