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

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 http://www.seageneration.co.uk http://www.verdantpower.com/ Wang [2007] – Turbine cavitation

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

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

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

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)

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 Lift performance (clean vs fouled foil) 7% 60 grit carborundum roughness applied Drag performance (clean vs fouled foil)

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)

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

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 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

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

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

Questions?