Abrupt Wing Stall

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Abrupt Wing Stall

• W.H. Mason
• Kevin Waclawicz, Michael Henry
• Virginia Tech
• 540-231-6740, whmason_at_vt.edu
• 11 July 2002

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Aerodynamics of Abrupt Wing Stall General
Description
Normal Shock
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
Crossflow Pattern?
Oblique Shock
6 deg

• 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)

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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
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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 its thicker 2D shows
no hint of forward shock movement, trends the
same for each turbulence model
2D airfoil
3D wing
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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

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Survey all aspects of flowfieldEmphasize
cross-flow topology
Location of Crossflow Stations
Topology nomenclature
Nodal Point
Focus
Saddle Point
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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 http//www.aoe.vt.edu/aoe/faculty/Mason_f/MRt
hesis.html
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Cross Flow Velocity Traces M 0.8, AOA 10o,
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
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Off-the-Surface Velocity Traces M 0.8, AOA
10o, Wind-Up-Turn, Altitude 15k feet
Approximately on the surface
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Off-the-Surface Velocity Traces M 0.8, AOA
10o, Wind-Up-Turn, Altitude 15k feet
Approximately 0.25 feet off the surface
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Off-the-Surface Velocity Traces M 0.8, AOA
10o, Wind-Up-Turn, Altitude 15k feet
Approximately 0.5 feet off the surface
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Off-the-Surface Velocity Traces M 0.8, AOA
10o, 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
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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 AOAs
• 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

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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

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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