C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Aeroelastic Interactions in the Presence
of Reflecting Oblique Shockwaves
CCAS Review – May 2015
Nathan Boyer and Jack McNamara
AFRL Contacts: Dr. M.Visbal
Acknowledgements
Sponsors: CCAS
CPU: DoD HPCMP and OSC
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Introduction
•  In second year of graduate school under Dr. McNamara
•  Finished coursework this past semester
•  Beginning full-time research now
•  2nd internship at AFRL/RQ this summer under Dr. Miguel
Visbal
2
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Motivation
Reflecting oblique shockwaves …
•  are common.
•  cause severe loading conditions.
•  can incite aeroelastic instabilities. (Visbal 2012, 2014)
High Performance
High Efficiency
Lightweight Structures
Flexible Surfaces
Aeroelastic Coupling
3
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Visbal 2012
4
Scope
Parameters of Interest
•  Mach Number
•  Reynolds Number
•  Shock Strength (Angle)
•  Shock Impingement
Location
•  Panel Dimensions
•  Panel Material Properties
•  Panel Preload
•  Boundary Conditions
•  Cavity Pressure
•  Turbulence
•  Three-Dimensionality
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Previous Work on the Topic
•  Relatively little work has been done to date
•  OSU and AFRL have pioneered work in this field
–  S. M. Spottswood, T. Eason, T. Beberniss (AFRL/RQHF)
–  Gogulapati, Deshmukh, Crowell, McNamara et al. (OSU)
–  M.Visbal (AFRL/RQVA)
5
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
l
el
Previous Work – Spottswood, Eason, Beberniss
•  Goal: Improve fundamental understanding of structural response to SBLI-induced
loads
•  Carried out wind tunnel experiments at AFRL/RQ RC-19 tunnel at WPAFB (Mach
2.0)
•  Structural response is sensitive to shock impingement location
•  Need for continuing experiments and modeling capabilities to understand behavior.
•  Experiments on-going
6
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Previous Work – Gogulapati, McNamara et al.
•  Computational study using Spottswood, Eason, and Beberniss
experiments for validation
•  Goal: Assess model reduction approaches for prediction of structural
response to SBLI
Approach:
•  Mean flow modeled using CFD (RANS) surrogate
•  TBL load modeled using semi-empirical approach
•  Structure modeled using nonlinear full and reduced order FEM
7
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Previous Work – Visbal
•  Goal: Expand understanding of impinging-shock fluid-structure
interactions
•  Invicid and viscous (laminar) flow using a high-order flow solver at Mach
2 and 2.5
•  2D flexible panel modeled using a non-linear von Karman plate model
•  Investigated: shock strength, shock impingement location, cavity
pressure, dynamic pressure, laminar SBLI
8
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Previous Work – Visbal
•  Discovered new aeroelastic instability induced by reflecting shockwaves.
•  Weak shocks “stiffen” panel and can prevent fluttering.
•  Strong shocks excite higher-frequency, higher-amplitude flutter at lower
dynamic pressures.
𝜆=​𝜌↓∞ ​𝑢↓∞↑2 ​𝑎↑3 /𝐷 𝐷=​𝐸↓𝑠 ​ℎ↑3 /12(1−​𝜈↑2 )
​𝐸↓𝑠 ≡𝑌𝑜𝑢𝑛​𝑔↑′ 𝑠 𝑚𝑜𝑑𝑢𝑙𝑢𝑠
𝑎≡𝑝𝑎𝑛𝑒𝑙 𝑙𝑒𝑛𝑔𝑡ℎ
h≡𝑝𝑎𝑛𝑒𝑙 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
𝛿𝑤≡█■𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙@𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒
9
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Current Work – Fluid (No-Shock Case)
𝑅𝑒=120,000 𝑀=2 𝜆=875
•  Shockwave is from leading-edge no-slip condition
•  High-frequency fluctuations are from disturbances in the boundary layer
interacting with the flexible panel
•  Fluid eventually stabilizes
10
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Current Work – Panel (No-Shock Case)
𝑆𝑡≈0.4
𝑓≈250𝐻𝑧 for typical values
•  Unsteadiness decays to steady-state deflection over time
•  Coupling between panel and fluid is evident.
11
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Current Work – Coupling (No-Shock Case)
•  The panel and fluid evolve towards stability together
•  One cannot be stable while the other is unstable
Overall, the observed response is not a significant cause for concern.
12
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Current Work – Fluid (Shock Case)
𝑅𝑒=120,000 ​𝑝3/𝑝1 =1.8 𝑀=2 𝜆=875 ​𝑥↓𝑖 =0.5
•  The presence of a reflecting shockwave over the panel greatly changes
the flow physics
•  Fluid response is highly unsteady and nonlinear
13
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Current Work – Panel (Shock Case)
•  The presence of a reflecting shockwave causes the panel to behave wildly
•  High frequency, high amplitude oscillations are a big problem for fatigue
14
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
e
r o f E xc
ll
Current Work – Coupling (Shock Case)
•  Irregular response does not decay to steady state
•  Rather, limit cycle oscillations develop and persist
Reflecting shocks could pose serious problems for both structural
integrity and flow unsteadiness.
15
C
en
te
en
ce
Comp
u
es
nc
nal Sc
tio
ie
ta
r o f E xc
el
l
Research Goals
•  Understand complex aeroelastic response in the presence
of reflecting shockwaves
•  Explore vast parameter space
–  Determine parameter impact and influence
–  Discover (un)desirable configurations
Current Path:
•  Replace finite difference structural solver in FDL2D with
finite element structural solver.
•  Migrate to FDL3D
•  Couple finite element structural solver into FDL3D
•  Explore effect of 3-D and turbulence
16