PIV Analysis of Wake Induced by a Real Seal WhiskerJodi Turk1, Joseph Bunjevac1, Aidan Rinehart1, Vikram Shyam2, Wei Zhang1

• Highly structured flow pattern in the wake of Elephant Seal whiskers, which is well correlated with

the peaks and troughs.

• Undulating whisker suppresses the wake area as the major axis is aligned with the inflow

direction, compared with the smooth whisker.

• Angle of attack significantly changes the wake structure, indicated by the instantaneous

streamwise velocity and spanwise vorticity.

• Vortex shedding behavior will be further studied using the high-speed PIV data.

Test Conditions:

• Water channel test section: 5.5 in (W) x 8 inch

(H) x 24 in (L)

• U0 = 0.12 m/s and 0.45 m/s

• Turbulence intensity of ~ 4%

• Re = 120 and 450 based on the whisker diameter

and the free-stream flow speed

Motivation

PIV Experiments

Seal Whisker Morphology

Instantaneous Flow Field: Effects of AOA

Summary

PIV Systems:

• 2D2C PIV (Lavision): up to 14.7 Hz

• High-speed PIV system: up to 2000 Hz

• 1200-1500 instantaneous velocity fields

• Measurement planes: vertical central plane and horizontal

planes at peaks and troughs

• Data processing: Davis 8.4, interogation window of 16 pixel by

16 pixel with 50% overlap

Flow Statistics of Wake: AOA = 0˚

Figure 1. Particle Image Velocimetry (PIV)

setup for measuring flow in horizontal planes.

Figure 2. Locations of the laser light sheet for PIV

measurements in the horizontal planes.

1. Mechanical Engineering Department, Cleveland State University, Cleveland, OH, 441152. NASA Glenn Research Center, Cleveland, OH, 44335

Figure 7. Instantaneous streamwise velocity of the wake induced by an undulating whisker and a smooth

whisker at Re = 450.

Figure 8. Instantaneous velocity and vorticity of the wake induced by an undulating whisker and a smooth

whisker at Re = 450.

Figure 5. The mean streamwise velocity, vorticity and the stremawise turbulence intensity of the wake behind the

elephant seal whisker A at Re = 120.

Acknowledgments

The Authors would like to acknowledge the Civil Engineering Department for the access of the water channel,

technician Mr. David Epperly for assistance in making the test setup, and Prof. Sang Joon Lee and graduate

students in BBRC at POSTECH for providing the facility and help for Jodi Turk’s high-speed PIV experiments. NSF

EAPSI program is greatly appreciated.

Figure 6. Mean streamwise velocity, vorticity, and streamwise turbulence intensity at peaks and troughs of the elephant seal

whisker A at Re = 120.

Figure 3. Computer Tomography (CT) Scanning of whisker morphology based on the framework established in [1].

References

[1] Hanke, W. 2010. Harbor Seal Vibrissa Morphology Suppresses Vortex-Induced Vibrations. Journal of Experimental

Biology 213, 2665-2672.

[2] Rinehart, A; Shyam, V., Zhang, W. 2017. Characterization of seal whisker morphology: impliations for whisker-inspired

flow control applications. Bio-inspriration and Biomimetics.

- Seals with beaded (or undulating) whiskers can accurately trace even minute

disturbance in the ambient flow using only their whiskers.

- Suppression of VIV and drag reduction by seal whiskers is promising to a wide

range of aero-propulsion and flow control applications.

- Limited understanding of the wake structure and vortex shedding induced by

real seal whiskers, in contrast to idealized whisker-like models.

Smooth Peak Trough

AOA = 0˚

AOA = 90˚

AOA = 0˚

AOA = 90˚

Seal Lion Whisker

(Smooth morphology)

Elephant Seal Whisker

(Undulating morphology)

Inflow Direction

Inflow Direction

Mean streamwise velocity Spanwise vorticity Streamwise turbulence intensity

Smooth Peak Trough

Objectives

Table 1. Statistics of Parameters of Whisker morphology [2]

Figure 4. Distribution of angle of incidence at peaks/troughs for Harbor seal whiskers and Elephant seal whiskers [2]

Harbor seal whiskers Elephant seal whiskers

- Characterize the parameters of whisker morphology by high-res. CT scanning.

- Quantify the wake structure and examine the angle of attack effects using PIV

measurements in a laboratory water channel.

Harbor seal α (Deg) a (mm) b (mm) M (mm)

Mean 0.299 0.525 0.178 1.724 0.924 0.836

Std Dev 5.266 0.118 0.067 0.364 0.115 0.121

β (Deg) k (mm) l (mm) (mm) λ/

Mean 1.218 0.416 0.219 0.664 5.257

Std Dev 5.838 0.094 0.083 0.083 0.918

Elephant seal α (Deg) a (mm) b (mm) M (mm)

Mean -5.092 0.599 0.282 1.931 0.856 0.751

Std Dev 17.359 0.186 0.104 0.432 0.12 0.165

β (Deg) k (mm) l (mm) (mm) λ/

Mean -9.604 0.56 0.33 0.886 4.57

Std Dev 21.049 0.224 0.132 0.275 1.115

Trough TroughTrough

Peak PeakPeak