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

ARLPenn State 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)

Wang [2007] – Turbine cavitation

MHK turbine concepthttp://www.verdantpower.com/

http://www.seageneration.co.uk

ARLPenn State 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

Wang [2007] – Turbine cavitation

MHKF1-180s Tip Section Foil

ARLPenn State 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

508x114mm Rectangular Test Section Three part fin design to minimize end wall effects

203.2mm chord , Re = 1.3M

ARLPenn State

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

ARLPenn State

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)

Bubble

Sheet

Gap

NACA 4412 one-part Fin Developed Cavitation

σ=2.0, =10

σi=2.18

NACA 4412 one-part Fin (near inception)

Cavitation Inception

Performance

ARLPenn State

Test Results: MHKF1-180 - Force Data

• MHKF1-180 – Clean – Slightly higher lift before stall– Well defined stall

• MHKF1-180 - 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

Drag performance (clean vs fouled foil)60 grit carborundum roughness applied

Lift performance (clean vs fouled foil)

7%

ARLPenn State

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)

ARLPenn State

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

ARLPenn State

Test Results: Fouled Cavitation Performance

• Cavitation performance sensitivity to roughness• Three “fouled” conditions

– Distributed: 60 grit [250μm] - 50% coverage over 7% chord– Isolated: 46 grit [350μm]

16 grit [1092μm]

• Applied to both NACA 4412 and MHKF1-180

Distributed leading edge roughness

36%

33%

26%

19%

12%

6%

1 to 2.5%Isolated roughness elements

7%

Gap Cavitation

LocalizedPatch Cavitation

MHKF1-180σ=1.15, =4

σi=1.07

ARLPenn State

Test Results: Fouled Cavitation Performance

• Distributed Roughness– NACA 4412 minimal effect on cavitation inception

– MHKF1-180 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

ARLPenn State 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

ARLPenn State

Questions?