Fcus Sessin n Simulatin at Aernautics Test Facilities Octber 15, 2014
Overview f Presentatin Questins t be addressed during presentatin Hw has the ability t d increasingly accurate mdeling and simulatin (M&S) changed the way aernautics test and evaluatin (T&E) facilities are used? Hw has it changed the way we d flight test? Frm a T&E standpint, are U.S. M&S capabilities sufficiently mature and reliable? Hw well are NASA facilities meeting the needs f industry regarding advanced M&S capabilities fr aernautics T&E? Hw well is NASA wrking with ther gvernment entities and academia t enhance M&S capabilities fr aernautics T&E? Backgrund fr presentatin This presentatin will treat M&S as synnymus with CFD and T&E as synnymus with grund test facilities, specifically wind tunnels 2
Effects f Increasingly Accurate M&S Capabilities Utilizatin f CFD has becme prevalent n prgrams primarily because f imprved accuracy and efficiency Algrithm imprvements Turbulence mdel imprvements Availability f increased cmputatinal pwer is a key enabler Enables faster turn-arund Enables higher-fidelity mdeling via discretizatin refinement Enables database develpment, i.e. ppulatin f large run matrices Example fr a similar launch vehicle cnfiguratin: 1991 0.5M grid pint mdel, 30 days/case, 1 case at a time, UCLA supercmputer 2014 10M grid pint mdel, 45 minutes/case, 25 cases at a time, inhuse Linux cluster Imprved accuracy based n grid reslutin enhancement f 20x, plus imprved accuracy due t algrithm and turbulence mdel imprvements Imprved efficiency f 480000x per grid pint, r 24000x per slutin Accuracy Efficiency 3
Effects f Increasingly Accurate M&S Capabilities (cnt d) Trend is t intrduce high-fidelity CFD methds in early design cycles alng with a crrespnding reductin in wind tunnel testingti Gemetry is ften in a state f flux which makes cmputatinal apprach mre appealing Fabricatin f wind tunnel mdels and availability f test facilities are ften pacing items during early, shrt-duratin design cycles Access t rapid and accurate CFD methds enables reductin in design cycle duratin and reduced reliance n third-party schedules (WT mdel vendrs, WT test facilities, etc) Heavy reliance n wind tunnel testing ti (alng with CFD) fr final design and verificatin activities Desire is t reduce reliance n wind tunnel testing further, but is this feasible in the near term? Being X-37B Airbrne Launch Assist Space Access 4
M&S Maturity and Reliability Fr sme cnfiguratins, M&S capabilities are sufficiently mature and reliable t reduce reliance n wind tunnel testing Hwever, this is nt true fr every cnfiguratin, as indicated n the next slide M&S capabilities ften fall shrt when flw separatin, bundary layer transitin, turbulent mixing, etc., are 1 st -rder cntributrs t the parameters f interest Users f data must understand d limitatins it ti f M&S methds Imprper reliance n pr quality M&S data can have severe adverse impacts t a prgram Design issues nt identified until late in the design r verificatin cycles cause significant cst and schedule issues Grund test facilities (wind tunnels) are required t develp the truth data needed t gage adequacy f M&S methds Users must als understand limitatins f grund test data Delta IV 5
M&S Maturity and Reliability (cnt d) Space Access Cnfiguratin #1 Space Access Cnfiguratin #2 6
Challenge Prblems CFD methds are relatively immature fr tackling the mst difficult prblems ften encuntered One example massive flw separatin leading t aerdynamics, aeracustics, and/r buffet issues The #1 prgram risk n several recent high-prfile develpment prgrams Steady and unsteady RANS mdeling is inapprpriate and insufficiently accurate fr these simulatins Hybrid mdels, such as DDES, ffer an imprvement ver URANS, but accuracy remains marginal Unsteady CFD simulatins n full-scale vehicle platfrms with sufficient grid reslutin t capture the flw physics remain grand challenge prblems These simulatins are perfrmed rutinely with less-than-desired grid reslutin Cnsume tremendus cmputatinal resurces and calendar time Data accuracy is typically gd enugh fr trends, insufficiently accurate fr design Des nt even scratch the surface in terms f database cverage (Mach / alpha / beta) In spite f these deficiencies, CFD can be used t help reslve these types f issues Aer shape ptimizatin i t eliminate i massive flw separatin Develpment f aerdynamic devices fr flw cntrl Other challenge examples bundary layer transitin, turbulent mixing and chemical kinetics, etc. Reliance n test facilities will be required fr the freseeable future t address these challenge prblems Prvide final design and verificatin datasets prir t flight Prvide high-quality validatin datasets t supprt develpment f imprved cmputatinal mdels 7
NASA Cllabratin with Gvernment and Academia Branches f the DD are cllabrating in the develpment f the next generatin f cmputatinal tls fr aerspace applicatin CREATE-AV Prject Full crdinatin acrss DD t prduce next generatin f physics-based cmputatinal methds fr DD acquisitin engineering Significant investment cmmitments by DD fr a lng-duratin cmputatinal sciences develpment effrt Cmputatinal ti science develpment effrts within NASA appear t be less crdinated acrss the agency Per recmmendatins f the recent NASA-funded Visin 2030 CFD study reprt prepared p by Being-led team f CFD experts, a lng-term base research and develpment effrt crdinated acrss the agency must be initiated t address CFD technlgy gaps and enhance CFD capabilities Increased cllabratin between NASA and DD wuld als be beneficial * CREATE-AV images btained frm publicly released CREATE-AV presentatin 8
Clsing Cmments Sustained and crdinated investments in the cmputatinal sciences will cntinue t pay huge dividends Efficiency and accuracy imprvements cntinue t be realized Autmated slutin adaptive gridding Imprved algrithms and turbulence / transitin mdeling Imprved aer shape ptimizatin and MDAO methds Reductin in reliance n CFD expert t ensure quality enhancing the availability f reliable and accurate cmputatinal methds Wind tunnel facility advancements shuld remain high pririty A cuple f examples frm recent aeracustics test experiences Fast Pressure Sensitive Paint (Fast PSP) capability prmises t enable characterizatin f high-frequency fluctuating pressures (aeracustics) ver the surface with greatly imprved reslutin relative t mdels instrumented with pressure transducers nly Imprved data acquisitin systems allw fr cllectin f large vlumes f higher-frequency data required t characterize these envirnments The few remaining wind tunnel test facilities are natinal assets, and cntinued advancement f WT test technlgies is critical fr the cntinued success f the US aerspace industry NASA SLS 9