Three-Dimensional Flow Separation Induced by a Model Vocal Fold Polyp
Kelley C. Stewart, Ph.D., Byron D. Erath, Ph.D*, and Michael W. Plesniak, Ph.D.
Department Mechanical and Aerospace Engineering
* Currently at Clarkson University
Motivation
Experimental Setup
Steady Flow
Chodara et al., 2012
o Reynolds number (Re) is a nondimensional ratio of inertial
𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 ×𝑐ℎ𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑖𝑠𝑡𝑖𝑐 𝑙𝑒𝑛𝑔𝑡ℎ
forces to viscous forces,
.
𝑘𝑖𝑛𝑒𝑚𝑎𝑡𝑖𝑐 𝑣𝑖𝑠𝑐𝑜𝑠𝑖𝑡𝑦
Normal
Unilateral
Polyp
Bilateral
Nodules
Asymmetry between folds and
spatio-temporal irregularities in
vocal fold vibrations have been
observed in vocal folds with a
polypoid mass.
(Zhang and Jiang, 2008)
Y. Zhang and J. J. Jiang , 2008
 Downstream unsteadiness generators create pulsatile
flow fields.
4
o Strouhal number (St) is a nondimensional number describing
𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 ×𝑐ℎ𝑎𝑟𝑎𝑐𝑡𝑒𝑟𝑖𝑠𝑡𝑖𝑐 𝑙𝑒𝑛𝑔𝑡ℎ
oscillating flow mechanisms,
.
Unsteady pressure
measurements are
acquired downstream
of a surface mounted
2:1 aspect ratio
prolate hemispheroid
using a Scanivalve DSA
3217.
Inlet
Martinuzzi and Tropea, 1993
The flow structures produced by three-dimensional flow
separation from a polyp in pulsatile flow are poorly
understood.
Prior Work: Driven Model
Previous work utilized a 7.5 times scaled-up driven model to investigate
the intraglottal flow field.
 The model polyp disrupts the normal flow behavior of the
glottal jet throughout the phonatory cycle.
 During the divergent portions of the cycle, the flow is
characterized by the formation of downstream hairpin vortices.
Oil-film techniques enable the visualization
of skin friction lines, high and low velocity
regions, and separation and attachment
points within a surface flow.
Hemispheroid
Separation Line
Skin friction line pattern showing the
location of the singularity points,
attachment and separation nodal
points (N) and the saddle points (S) .
Vorticity
concentration
Nodes
Attachment
Node
 Two saddle points exist symmetrically around the
attachment node downstream of the polyp .
Scaled-up vocal fold model
geometry and orientation relative
to the coordinate system.
(Erath and Plesniak, 2012)
Streamwise velocity fields in the x-y plane
at z = 0.0 mm plotted as velocity
magnitude contour plots with overlaid
streamlines. (Erath and Plesniak, 2012)
-2
-6
1
2
3
4
 The dark lines extending from the sides of the polyp
(representing the outer limits of the wake) converge
until the attachment point, due to the recirculation
vortex behind the object.
5
6
Position
Unsteady Flow
Conclusions
Primary Upstream
Separation Line
Primary
Horseshoe
Vortex
0
-4
𝑣𝑒𝑙𝑐𝑜𝑖𝑡𝑦
Skin Friction Line Visualization
.
x 10
Pressure minima occur
in the wake of the polyp
at the vorticity
concentration nodes.
-3
2
Model polyp
Acarlar and Smith, 1987
(𝑃 − 𝑃∞ )
𝐶𝑝 =
1 𝜌𝑈 2
2 ∞
Re = 9,000
Cp
Geometric abnormalities associated
with polyps and nodules disrupt the
dynamics of the vocal folds, and can
have devastating consequences on
the patient’s ability to communicate
(Petrović-Lazić et al., 2011).
The current experimental work is conducted in a suction
wind tunnel with a 5:1 contraction ratio.
 Reynolds numbers (Re) of 6,000-11,000.
Re = 6,300 St = 1.2 x 10-3
 Understanding the formation and propagation of vortical structures
from a surface protuberance, and their subsequent impact on the
aerodynamic loadings that drive vocal fold dynamics, will provide
critical information for advancing the treatment of this pathological
condition.
 Variations in aerodynamic loadings caused by the model polyp are
expected to be contributing mechanisms for producing irregular vocal
fold dynamics observed in patients with polyps.
Acknowledgements
Supported by the National Science Foundation, Grant No. CBET-1236351 and GW Center for
Biomimetics and Bioinspired Engineering (COBRE).
References
 Acarlar, M.S. ,and Smith, C.R., A study of hairpin vortices in a laminar boundary layer . Part 1
. Hairpin vortices generated by a hemisphere protuberance. Journal of Fluid Mechanics, 175,
1-41 (1987).
 Chodara, A. M., Krausert, C. R., & Jiang, J. J., Kymographic characterization of vibration in
human vocal folds with nodules and polyps. The Laryngoscope, 122(1), 58–65, (2012).
 Erath, B. D., and Plesniak, M. W., Three-dimensional laryngeal flow fields induced by a model
vocal fold polyp, International Journal of Heat and Fluid Flow, 35, 93-101, (2012).
 Martinuzzi, R., & Tropea, C., The flow around surface-mounted , prismatic obstacles placed
in a fully developed channel flow. Journal of Fluids Engineering, 115, 85–92, (1993).
 Petrović-Lazić, M., & Kosanović, R., Acoustic analysis findings in patients with vocal fold
polyp. Acta Medica Saliniana, 38(2), 63–66, (2009).
 Zhang, Y., & Jiang, J. J., Asymmetric spatiotemporal chaos induced by a polypoid mass in the
excised larynx. Chaos, 18, 043102 (1–4), (2008).