Abrupt Wing Stall W.H. Mason Kevin Waclawicz, Michael Henry Virginia Tech , 11 July 2002

air code 2 Aerodynamics of Abrupt Wing Stall General Description We tackled two different tasks: - a 2-D model problem - detailed examination of NAVAIR computed porous door solutions The goal: to discover physical basis for abrupt wing stall phenomena We obtained improved understanding of an extremely complex flowfield Task 2: Kevin Waclawicz –Post-processing of porous door configuration CFD files. –Comparison of the porous door and baseline configuration Task 1: Mike Henry –Investigation of “F/A18-E/F like” foil (NACA 65A series, 5.7%) –Comparison with “F/A18-C/D-like” airfoil (NACA 65A series, 3.5%) Oblique Shock 6 deg Normal Shock Crossflow Pattern?

air code 3 Approach : 2-D Model Problem Question: Can a 2-D calculation show the sudden forward movement in the shock observed in 3-D? Use FLOMG from NASA Langley to compute flowfields - both Johnson-King and Baldwin Lomax Turbulence models used Compare E/F and C/D airfoils at critical span station

air code 4 Shock Movement with increasing lift 2D movement is aft, essentially attaches to hinge line E/F and C/D are similar, but E/F happens “sooner” because it’s thicker 2D shows no hint of forward shock movement, trends the same for each turbulence model 2D airfoil 3D wing

air code 5 Approach: Computational Flo Viz Classify off-the-surface and crossflow velocity singular points as well as examine mathematical predictions made in singular point mathematics using CFD. Navy provided CFD Solutions –6, 7, 8 & 10 degree AOA grid and solution files Wind-Up-Turn Mach 0.80, 15K feet File sizes, each solution is: – ~6 million grid points into 46 zones –Grid: 117 MB –Solution: 195 MB –Tecplot files are an additional 1.2 GB for each solution

air code 6 Survey all aspects of flowfield Emphasize cross-flow topology Location of Crossflow Stations 7 deg AOA, M = 0.8 Topology nomenclature Nodal Point Focus Saddle Point

air code 7 Significant Accomplishments Two MS Theses provide details of the two tasks: Kevin Waclawicz, July 2001, MS, “The Investigation of Crossflow Velocity and Off-the-Surface Streamtrace Topology for a Moderately Swept Wing at Transonic Mach Numbers,” Michael Henry, August 2001, MS, “Two-Dimensional Shock Sensitivity Analysis for Transonic Airfoils with Leading-Edge and Trailing-Edge Device Deflections, ” These theses and final presentations are available on the web, after being held for one year

air code 8 Cross Flow Velocity Traces M = 0.8, AOA = 10 o, Wind-Up-Turn, Altitude 15k feet Chine and snag locations dominate crossflow topology, No sudden breaks occur with examination of all the CFD solutions provided

air code 9 Off-the-Surface Velocity Traces M = 0.8, AOA = 10 o, Wind-Up-Turn, Altitude 15k feet Approximately on the surface

air code 10 Off-the-Surface Velocity Traces M = 0.8, AOA = 10 o, Wind-Up-Turn, Altitude 15k feet Approximately 0.25 feet off the surface

air code 11 Off-the-Surface Velocity Traces M = 0.8, AOA = 10 o, Wind-Up-Turn, Altitude 15k feet Approximately 0.5 feet off the surface

air code 12 Off-the-Surface Velocity Traces M = 0.8, AOA = 10 o, Wind-Up-Turn, Altitude 15k feet Approximately 0.75 feet off the surface Note that spiral moves aft and behind the surface as you move further above the wing

air code 13 Conclusions from Task 1 Two-dimensional shock moves in the opposite direction as that of the Three-dimensional wing –Separation phenomenon which pushes the shock forward on the 3-D wing is not present on the 2-D airfoil Without 3-D effects the separation bubble is confined to the region aft of the hinge line at low AOA’s The NACA 65A005.7 airfoil does not exhibit any tendency to abrupt shock movement, forward or rearward In the 2-D case a deflected trailing edge minimizes the adverse effect of the separation region on the inviscid flow, thus preventing the shock from being pushed forward

air code 14 Conclusions from Task 2 Verified that a line of separation in the crossflow is an indication that separation may be present on the surface of the wing Flow topology for this wing is more sensitive to shock location as opposed to angle of attack Increasing the angle of attack increases the area of separation and distance in which it occurs off the wing Verified that a line of separation present in the off-the-surface planes is an indication of separation Showed that the lines of separation may also indicate the location of the separated region

air code 15 Summary CFD analysis and computational flow visualization has provided insight in a 2D model and the actual computed flowfields 2D model problem showed the problem to be fundamentally 3D The separated flow topology of the full 3D problem requires extension of the usual flow topology concepts Two theses are available with complete documentation