1. Cavitation and Hydrodynamic Evaluation of a Uniquely Designed Hydrofoil for Application on Marine Hydrokinetic Turbines
R. Phillips, W. Straka, A. Fontaine (Penn State/ARL)
M. Barone, E. Johnson (Sandia National Laboratory)
C.P. van Dam, H. Shiu (Univ. California, Davis)
8th International Symposium on Cavitation
August 14-16, 2012

2. Motivation of Study
Increased interest in marine renewable energy in US and around the world
Leveraging wind turbine technology
Desire to maximize power output
Underwater environment has unique issue
Maintenance and lifecyle
Bio-fouling
Cavitation and erosion
Environmental/noise concerns
(Kermeen 1956)
MHK turbine concept
Wang [2007] – Turbine cavitation

3. Model of 3-bladed MHK turbine blade
Focus of Present Study
Performance evaluation of hydrofoil designed specifically for marine hydrokinetic (MHK) turbine application
Foil designed by Univ. California-Davis [Shiu, et al (2012)]
Foil design objectives:
High L/D (power output and efficiency)
Designed with extended region of laminar flow
Low roughness sensitivity (bio-fouling resistance)
Well defined stall point (stall controlled turbine)
Resistance to surface cavitation (erosion)
Anti-singing TE (environmental)
(Kermeen 1956)
Model of 3-bladed MHK turbine blade
MHKF1-180s
Tip Section Foil
Wang [2007] – Turbine cavitation

4. Three part fin design to minimize end wall effects
Experimental Setup
Penn State 12-inch diameter water tunnel (2-dimensional test section)
Two foils tested (clean / fouled)
NACA 4412 – baseline/validate test process
One & three-part foils model tested
MHKF1-180s
Three-part foil
Measurements:
Lift/drag/moments – 6-DOF load cell
Wake profiles and trailing shedding - LDV
Cavitation inception performance
Cavitation breakdown performance
203.2mm chord , Re = 1.3M
Three part fin design to minimize end wall effects
508x114mm Rectangular Test Section

5. Test Results: NACA 4412 - Force data
NACA 4412 – baseline foil used to validate setup / reduction procedure
Clean foil
Force data correction applied
Gap corrections [Kermeen (1956)]
Solid and Wake Blockage [Barlow, Rae and Pope (1999)]
No horizontal buoyancy correction needed
Good agreement with historical data
Lift
Drag

6. Test Results: NACA 4412 - Clean Cavitation
NACA 4412 – baseline/validation test
Clean foil
Cavitation inception performance
Desinent cavitation calls
4.0 ppm air content
Good Agreement with historical data
Minimal hysteresis found (incepient vs. desinent)
NACA 4412 one-part Fin
Developed Cavitation
Bubble
Sheet
Gap
Cavitation Inception Performance
σ=2.0, =10
σi=2.18
NACA 4412 one-part Fin
(near inception)

7. Test Results: MHKF1-180 - Force Data
MHKF1-180 – Clean
Slightly higher lift before stall
Well defined stall
MHKF Fouled
60 grit elements (0-7% Chord)
Trip wire (.4mm) at 7% chord
Foil sensitive to fouling
Effectively de-cambers foil
Decrease both max lift and lift curve slope
Significant drag increase over clean foil
Premature transition
Lift performance (clean vs fouled foil) 7%
60 grit carborundum roughness applied
Drag performance (clean vs fouled foil)

8. Test Results: MHKF1-180 - Cavitation visualization
MHKF1-180 – Clean foil
Sigma = 1.1, alpha = 8 deg.
Sigma = 3.9, alpha = 14 deg.
Developed Cavitation
Near Inception (bubble/patch)

9. Test Results: MHKF1-180 - Cavitation Performance
MHKF1-180 – Clean foil
Minimal hysteresis found
Improved inception performance compared to 4412 at higher angles of attack
Improvement due to thickness effect
Cavitation performance
(MHK vs NACA 4412)
Incipient vs Desinent Performance

10. Test Results: Fouled Cavitation Performance
Cavitation performance sensitivity to roughness
Three “fouled” conditions
Distributed: grit [250μm] - 50% coverage over 7% chord
Isolated: 46 grit [350μm]
16 grit [1092μm]
Applied to both NACA 4412 and MHKF1-180
36%
33%
26%
19%
12% 6%
1 to 2.5%
Isolated roughness elements
Gap Cavitation
MHKF1-180
σ=1.15, =4
Localized
Patch Cavitation
σi=1.07 7%
Distributed leading edge roughness

11. Test Results: Fouled Cavitation Performance
Distributed Roughness
NACA minimal effect on cavitation inception
MHKF small degradation
Thickness and turbulent transition effects
Lift curve reduced with roughness
Neither show hysteresis
Isolated Roughness
NACA 4412 Large effect on cavitation performance / size had minimal effect
MHKF1-180 Decreased performance with increase element size
Sensitive region located aft along chord
- NACA 4412 showed significant hysteresis at higher angles of attack and larger elements
NACA 4412
MHKF1-180

12. Conclusions
Performance evaluations were completed for a new MHKF1-180 tip hydrofoil
Improved clean performance compared to NACA 4412
Not quite fair comparison (t/c)
MHKF1-180 sensitivity to fouling
Lift/drag performance shows significant changes
Likely due to early transition
Cavitation performance minimally degraded with distributed roughness
Cavitation performance degraded with isolated roughness
MHK applications will require tradeoff between max power and longevity

13. Questions?