Downwind Aero Moments & Forces

Transcription

1 Downwind Aero Moments & Forces Fluid-Structure-Interaction (FSI) modeling of Downwind Sails Phase 2 Prepared for: SYRF November 2016! 1

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3 Contents List of Terms... 4 Executive Summary Project Description Introduction Methodology Rig and Sail Inventory Description Phase 2A Phase 2B Setup & Process Phase 2A Setup Results Result Files Phase 2A Results Phase 2B Results Discussion Proposal for Future Contribution/Collaboration: Observations Conclusion List of Figures Figure 1. Total Pressure Isosurface... 7 Figure 2. Sail and Rig Combinations... 8 Figure 3. Swan 42 and M&R48 Mainsail...11 Figure 4.Swan 42 A Figure 5. M&R48 42 S Figure 6. M&48 Origin Figure 7. TP52 and Swan 42 Origin Figure 8. Luff Curve Pressure Figure 9. Wind Model Frame of Reference Figure 10. CFD Mesh Domain Figure 11.Results Spreadsheet Header Columns A-T" Figure 12. Results Spreadsheet Header Columns W-BX" Figure 13. Results Spreadsheet Header Columns CB-CV Figure 14. Lift coefficient and drag coefficient plots for Swan 42 Phase 1 & Figure 15. Lift coefficient and drag coefficient plots for TP52 Phase 1 & Figure 16. Total Sailplan Surge and Sway Force for Swan Figure 17. Total Sailplan Surge and Sway Force for TP Figure 18. Force and moment origin Figure 19.TP52 AWA65 Flow Separation Figure 20. TP52 AWA 65 Flow Separation Figure 21. TP52 AWA 65 Flow Separation - 10 Meter Section Slice... 27!3

4 List of Tables Table 1. Sail Dimensions (meters)... 9 Table 2. Phase 2B Sail Sizes Table 3. Basic Test Matrix for Phase 2A Table 4a. Swan 42 Sailing Conditions Table 4b. TP52 Sailing Conditions Table 5a. M&R48 Run Matrix Table 5b. Swan 42 Run Matrix List of Terms Apparent Wind Angle (AWA) Apparent Wind Speed (AWS) Autocad Plotter Document (PLT) Center of Effort (CoE) Computational Fluid Dynamics (CFD) Drag Coefficient (Cd) Finite-Element Analysis (FEA) Fluid-Structure Interactions (FSI) Lift Coefficient (Cl) Reynolds-Averaged Navier-Stokes (RANS) Pressure Coefficient (Cp) True Wind Direction (TWD) True Wind Speed (TWS) Velocity Prediction Program (VPP)!4

5 Executive Summary Objectives The Downwind Aero Moments and Forces project was designed and carried out to improve the understanding of downwind aerodynamic performance. With Phase 1 (February 2016) providing the moments and forces for a range of downwind sails from AWA 45 to AWA 170, Phase 2A was designed to expand the initial dataset to include tighter AWA data with simulated custom tight angle sails, compared to the Phase 1 sails which were based on produced sail designs. Phase 2B sought to quantify the effect of increasing and decreasing the girths of the mainsail and gennaker; using the sail designs from Phase 1 as a base, Phase 2B separately morphed the girth of the mainsail and gennaker, re-running the AWA and TWS sweep from Phase 1 to capture geometric effect of such changes. Methods Using fluid-structure interaction (FSI) modeling, the project simulated three yachts that represent a range of performance for typical modern racing yachts. A modified TP52, Swan42, and McCurdy and Rhodes 48 (M&R48) were simulated with A2 and A3 sail plans and configurations, with an S2 configuration also being simulated for the latter. Sail designs were created using North Sails Global DesMan Design Base and were then used by North s design suite to create the 3D finite element analysis (FEA) models. Using North s FEA tool MemBrain, these models were coupled with OpenFOAM to get a converged solution, with sail trim adjusted between each iteration to achieve neutral luff pressure. Simulations were meshed to identify the differences in sail forces and moments through a range of sail designs and boat performance. Sailing conditions were taken from the current performance targets provided for each boat, with leeway set to zero in all cases, and simulations onset flow defined at 10 meter elevation at true wind speeds (TWS) of 8, 12, and 16 knots. Additionally, a heel sweep and traveler sweep were done in TWS 12 without changes to the sail trim, other than rotating the mainsail s foot angle +/- 5 degrees throughout the traveler sweep. Results The results spreadsheets 1 include lift (Cl) and drag coefficients (Cd) for the total sail plan, as well as the mainsail and gennaker separately. Additionally, individual forces, moments, and center of effort locations are also listed for combined and individual components (mainsail, gennaker, hull and mast). The coordinate system is taken from a user-defined origin. Forces are reported in Newton s, moments in Newton-meters, and dimensions in meters. Discussion The approach of Phase 2 proved valuable in developing a comprehensive collection of the total forces and moments on each sail as well as total sail plan. Supplementing the wider AWA range dataset produced by Phase 1 with Phase 2A s tighter AWA Code 0 type sail data helps better define the relationships and crossovers between Code 0, A2, and A3 sails through a range of wind angles and speeds. In particular, Phase 2A demonstrates how the crossovers change as the girth of a Code 0 is modified. 1 Results are available for download via the SYRF Website!5

6 Combining the results of Phase 1 and Phase 2A yields a more complete dataset that covers a full range of off the wind sailing angles. Phase 1 provided data across a range of AWA from 45 to 150 for three types of gennakers across a TWS of 8, 12, and 16 knots. Phase 2A provided data for two types of Code 0 sails (a Code 0 without girth restriction and a Code 0-75% conforming to a 75% girth rule) across a range of tighter AWA.!6

7 1. Project Description 1.1.Introduction It is the goal of the Downwind Aero Moments and Forces project to improve the accuracy of modern handicapping rules in understanding downwind aerodynamic performance. By using FSI modeling, phase two produces a set of results comprised of all aerodynamic moments and forces for a range of boats with downwind sails at specific onset flow angles, and wind speeds utilizing a coupled RANS - finite element analysis. These results should serve as a validation source for the improvement of VPP s downwind performance predictions. Figure 1. Total Pressure Isosurface, hull, mast Code 0 & Mainsail!7

8 2. Methodology 2.1 Rig and Sail Inventory Description Figure 2 represents the sail and rig combinations tested. Three yachts were simulated that represent a range of performance for typical racing yachts today: Modified TP52 Spookie Swan 42 McCurdy & Rhodes 48 (M&R48) Carina The TP 52 and Swan 42 were simulated with 2 sail types for Phase 2A and one gennaker for Phase 2B: Phase 2A Code 0-75% Reaching gennaker with a ~ 2.5% 2-D miter depth. Code 0 65% Reaching gennaker with a ~ 2.5% 2-D miter depth. Phase 2B AP running gennaker A2 with ~ 7% 2-D miter depth. AP Symmetrical spinnaker S2 with 10.5% 2-D miter depth Figure 2. Sail and Rig Combinations A2 Code 0 s Swan42 Code 0 75% mid girth Code 0! 8

9 Table 1. Sail Dimensions (meters) Mainsails TP52 Swan 42 Luff Leech (straight-line) Foot Head IMS Area, m Downwind sails A2 Swan 42 Spinnaker Tack Length (STL) 7.35 Luff Leech Foot SMG IMS Area, m Reaching sails Code 0 75% Code 0 TP52 Swan 42 TP52 Swan 42 Spinnaker Tack Length Luff Leech Foot SMG IMS Area, m !9

10 2.2 Phase 2A Phase 2A adds additional tighter AWA s data points to the Phase 1 dataset, overlapping with AWAs from the Phase 1 data. Two additional sails were designed for a TP52 and Swan42 labeled Code 0 & Code 0-75%. The Code 0 was designed without girth restrictions defined by rules; the Code 0-75% is a similar sail but designed to conform to the 75% mid girth imposed by several rules, classifying the sail as a gennaker or (spinnaker). These two Code 0 sails were run at AWA of 35, 45 and 65 degrees across TWS 8, 12, and 16 knots. The runs across AWA 45 and 65 overlap with the A3 runs in Phase 1 and therefore provide insight into the crossover between Code 0 and A3 sails. 2.2 Phase 2B Phase 2B investigates the effect of sailplan variations on the aerodynamic forces. New mainsail and gennaker moulds were created, with areas of plus and minus 10% versus the baseline geometries from the Phase 1 study. The combinations run through OpenFoam were: Base mainsail, A2 plus 10% area Base mainsail, A2 minus 10% area Base A2, mainsail plus 10% area Base A2, mainsail minus 10% area Mainsail re-sizing method The roach profile (fanned leech shape) was held constant in all cases. The clew height relative to the tack was held constant in all cases. The head width as percent of the foot length was held constant at 3%. The foot length was adjusted to achieve plus or minus 10% of the area of the baseline sail. The mainsails were then trimmed to the same mid twist and the same boom angle off centerline as the baseline run. Swan 42 A2 re-sizing method There are many options for varying the gennaker area, depending on what parameters you choose to change. The approach used here was to try to maintain a similar amount overlap of the gennaker foot with the mast, therefore adjusting the sprit length along with the foot length to increase or decrease the area. The mould parameters were held constant in all cases, while varying the edge lengths. The sprit length, foot length, and leech length were varied to achieve plus or minus 10% of the area of the baseline sail. The luff length was varied as the sprit length changed, to maintain the same tack height above the waterline. The gennakers were trimmed to the same mid twist and foot camber as the baseline run. Several iterations in Membrain were required to get the sizing dialed in by adjusting the luff, leech, foot, and sprit lengths.!10

11 Carina S2 size morphing method The ratio of maximum width to pole length (SMW/SPL) was held constant at 1.90 The ratio of foot length to pole length (SF/SPL) was held constant at 1.8 The luff and leech length were calculated by the formula SLU= 0.973* SQRT(ISP^2 +SPL^2). The ratio of the 2D mitre depth to the midgirth (2D/SMG) was held constant at The pole length was varied while maintaining the above parameters to achieve plus or minus 10% of the area of the baseline sail. Figure 3. Swan 42 (left) and M&R48 (right) Mainsail.!11

12 Figure 4. Swan 42 A2. Figure 5. Carina S2.!12

13 Table 2. Phase 2B Sail Sizes. Phase 2B: Swan 42 mainsail size variations Luff clew to head point Foot Head Surface Area IMSArea MGL MGM MGU MGT minus 10% area baseline plus 10% area Phase 2B: Swan 42 A2 size variations SLU SLE SF SMG SMG as % SF Surface Area GKArea sprit length SF as % SPL SF minus sprit length minus 10% area baseline plus 10% area Setup & Process A generic hull surface for each yacht (solid one surface deck) and mast surfaces were included in the OpenFOAM simulation, primarily to capture the effect of the hull and mast on the sails. The origin for the TP52 and Swan42 were set at the waterline below the forward face of the mast. For the M&R48, the origin was set at the bow s projection to the waterline; the different origin position for the M&R48 s was not intentional but rather a result of an existing DesMan model. Figure 6. M&R48 Origin!13

14 Figure 7. TP52 and Swan 42 Origin (Hull not shown to allow display of origin) North Sails Global DesMan Design Base was used to create the designs which were then used in North s design suite to create the 3D FEA models. This ensured consistency in the sail designs that were designed and sized to fit each yacht. Light Polyester cloth was used for the structure of the gennakers, with a modulus of 70 grams/denier. Nylon was used for the structure of the spinnaker, with a modulus of 35 grams/denier. Light Dyneema cloth was used for the simulations of the Code 0 s, with a modulus of 1050 grams/denier. North s FEA tool MemBrain was coupled with OpenFOAM to get a converged solution, typically requiring several iterations to converge. In Phase 2A, the trim of each sail was adjusted between each iteration, with the target of achieving neutral pressure on the luff. In Phase 2B, the sails were morphed and inflated with the baseline pressure files. Figure 8. Luff Curve Pressure. Sail trim was adjusted between iterations to achieve neutral pressure on the luff as indicated by white color.!14

15 The sailing conditions used in the OpenFOAM runs were taken from the current performance targets provided for each boat. The simulations onset flow was defined at 10 meter elevation and TWS of 8, 12, and 16 knots. The leeway was set to zero in all cases. The input file to OpenFOAM that defines the onset flow included the following parameters: TWS TWA Boatspeed Heel Leeway (set to zero in all cases) Air Density = kg/m 3 Viscosity= E-5 m/s 2 Reference height for TWS, AWA = 10 m Wind Gradient used the exponent power law = 0.10 In addition to these runs, a heel sweep and traveller sweep were done in TWS 12. The heel & traveller runs could be a basis for deriving a depowering function in a VPP aero data set. 2.3 Phase 2A Setup Heel Sweep: For each code 0, heel sweeps were performed at 0, 10, 15, 25 degrees of heel in TWS 12 at AWA 45: TP52 at TWS 12: Code 0-75%: AWA 45 Code 0: AWA 45 Swan 42 at TWS 12: Code 0-75%: AWA 45 Code 0: AWA 45 The sail trim was not changed during the heel sweep; converged sail shapes from the baseline run were maintained through the heel sweep. Traveller Sweep: For each boat, mainsail traveller sweeps of +/- 5 degrees were performed at AWA 45 in TWS 12. As above, the converged sail shapes from the baseline run were maintained through the traveller sweep, other than rotating the main s foot angle +/- 5 degrees. In addition to these runs, a heel sweep and traveller sweep were done in TWS 12. The heel & traveller runs could be a basis for deriving a depowering function in a VPP aero data set.!15

16 Table 3. Basic Test Matrix for Phase 2A. AWA Code 0-75% x x x Code 0 x x x Table 4a. Swan 42 Sailing conditions used in OpenFOAM runs for Phase 2A Swan 42 MN + Zero75 Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero75 Full Zero75 Full Zero75 Full Swan 42 MN + Zero Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero Full Zero Full Zero Full Swan 42 MN + Zero75 Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero75 Full Zero75 Full Zero75 Full Zero75 Full Swan 42 MN + Zero Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero Full Zero Full Zero Full Zero Full Swan 42 MN + Zero75 Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero75 Full Zero75 Full Zero75 Full Zero75 Full Swan 42 MN + Zero Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero Full Zero Full Zero Full Zero Full!16

17 Table 4b. TP52 Sailing conditions used in OpenFOAM runs for Phase 2A TP52 MN + Zero75 Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero75 Full Zero75 Full Zero75 Full TP52 MN + Zero Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero Full Zero Full Zero Full TP52 MN + Zero75 Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero75 Full Zero75 Full Zero75 Full TP52 MN + Zero Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero Full Zero Full Zero Full TP52 MN + Zero75 Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero75 Full Zero75 Full Zero75 Full TP52 MN + Zero Headsail Main Hoist TWS TWA AWS AWA Vs Heel Leeway Roll MomeDynHead Main Area Kite Area [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Zero Full Zero Full Zero Full !17

18 2.4 Phase 2B Setup The morphed sails were inflated and converged in Membrain using the pressure files from the baseline runs in Phase 1. That geometry was then sent to OpenFoam, which returned the final pressure file specific to that geometry. The combinations run through OpenFoam were: Base mainsail, A2 or S2 plus 10% area Base mainsail, A2 or S2 minus 10% area Base A2 or S2, mainsail plus 10% area Base A2 or S2, mainsail minus 10% area In all cases the mainsails were trimmed to the same mid twist and boom angle off centerline as the baseline run. The Swan 42 A2s were trimmed to the same mid twist and foot camber as the baseline run. This required several iterations through the sizing process and back through Membrain, adjusting the leech and foot length until a match in both mid twist and foot camber was achieved. The Carina S2s were trimmed to the same mid twist as the baseline run. Because these are symmetrical sails, we did not have the option of varying the leech length to achieve a match in both mid twist and foot camber the way we did with the Swan 42 A2s. The Swan 42 runs were done in TWS of 8, 12, and 16 knots at AWA of 65, 85, 105, and 150. The Carina runs were done in TWS 12 knots at an AWA of 105. Figure 9 describes the wind triangle, the origin of the model, and their relationships. In the wind model frame of reference, the boat is on starboard tack, with TWA defined to the centerline of the boat instead of the track through the water. Table 5a. M&R48 Run Matrix!18

19 Table 5b. Swan 42 Run Matrix. Headsail Main TWS TWA AWS AWA Vs Heel Leeway Roll Moment DynHead Main Area Kite Area configuration Hoist [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Headsail Main TWS TWA AWS AWA Vs Heel Leeway Roll Moment DynHead Main Area Kite Area configuration Hoist [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Headsail Main TWS TWA AWS AWA Vs Heel Leeway Roll Moment DynHead Main Area Kite Area configuration Hoist [knots] [deg] [knots] [deg] [knots] [deg] [deg] [kn-m] [Pa] [m^2] [m^2] Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full Baseline, first study A2 Full Baseline re-run Aug 2016 A2 Full MN plus 10% area A2 Full MN minus 10% area A2 Full A2 plus 10% area A2 Full A2 minus 10% area A2 Full !19

20 OpenFOAM All runs were completed with North Sails 'dropbox' style CFD process, which has been a collaboration between North Sails and the Wolfson Unit since 2010, initially as a tool for high-end projects (America s Cup, Volvo Ocean Race, etc.). It is used today for a variety of projects with different goals including: performance prediction, sail pressure distribution, windage calculations, and flow visualization. The system uses the University of Southampton's supercomputer Iridis4, running a RANS solver of the OpenFOAM software, controlled via an automated process. Mesh Generation Critical part of solve process as it has a strong influence on accuracy and efficiency of runs Open-source meshing provided by blockmesh and snappyhexmesh utilities, supplied as part of OpenFOAM Procedure: 1. Create STL file from CAD file 2. Run blockmesh to create initial grid 3. Run snappyhexmesh to create final grid Simulations were meshed to identify the differences in sail forces and moments through a range of sail designs and boat performance, and not a detailed evaluation of the hull and rig. Each CFD simulation has an APPROXIMATE NUMBER OF CELLS = 10,082,580 with mesh refinements around the sails, mast & hull. Figure 7 displays the analysis domain and results output domain in green with relative size of the yacht. Figure 9. Wind Model Frame of Reference. Figure 10. CFD Mesh Domain.!20

21 3. Results The same spreadsheet formats from Phase 1 were used to present the data for Phase 2. Three summary spreadsheets with tabs corresponding to the TWS simulated are provided, one spreadsheet for each yacht. The TWS12 tab list the heel and traveler sweeps where specified. The first block, columns A T list the onset flow used in the simulation and the combined as well as individual Cl and Cd values. The baseline or center points highlighted in grey with the sweep s on either side. Figure 11. Results Spreadsheet Headers Columns A-T. Columns W BX list the individual force, moments and Ce locations, listed for combined and individual components. Figure 12. Results Spreadsheet Headers Columns "W-BX." Blocks of data corresponding to: All: is all the geometry combined. Sails: are just the sails, Main & Gennaker/Spinnaker. Hull: Hull Mast: Mast Main: Main Gennaker: Gennaker or Spinnaker Column CB onwards was used for North s PreVPP fitting method. Figure 13. Results Spreadsheet Headers Columns "CB-CV."!21

22 3.1 Result Files The result files are available for download via the SYRF Website and at the following links. Phase1&2Summary-OpenFoam-Results-TP52-Zero-A2&3-Revised xlsm Phase1&2Summary-OpenFoam-Results-Swan42-Zero-A2&3-Revised xlsm Summary-OpenFoam-Results-Swan42-A2 phase 2, xlsm Summary-OpenFoam-Results-Carina-S2 phase 2, xlsm 3.2 Phase 2A Results A general trend of Cl s increasing to ~ AWA 65 and then a slow decrease. Phase 2A data added to Phase 1 data displays this trend, the plots are for all points tested and center points only. For Phase 2A, Code 0 sails trimmed at TWS 16, AWA 45 and 35 the sails were overpowering and both main and Code 0 s needed to be eased to keep the RM under control. The Cl ad Cd reflect the trimming to keep the RM within reason in TWS 16. Figure 14. Lift coefficient and drag coefficient plots for Swan 42 Phase 1 & 2 combined.!22

23 Figure 15. Lift coefficient and drag coefficient plots for TP52 Phase 1 & 2 combined. Summary Cl and Cd plots are listed for all TWS, AWA and sweeps on the Cl Cd Plot tab in all the sheets. 3.3 Phase 2B Results Morphing main and gennaker size % did not result in large variations in the associated coefficient values as one would expect. However, there were consistent changes in the force and moments associated with the change in sail areas. Each data spreadsheet, displayed on the sail force ratio tab, plots the global forces normalized to the base line run from Phase 1. Some variation in these results could creep into the data due to the technique used to change the size and position of the sails during the morphing. Changing the sails size created a need to bring the sail back to a constant to try and just capture the change in area. To achieve this, the re-sized sails were designed and trimmed to the same foot camber and mid leech twist as the base line run.!23

24 Figure 16. Total Sailplan Surge and Sway Force for Swan 42. Figure 17. Total Sailplan Surge and Sway Force for M&R48.!24

25 The directions of the coordinate system are taken from the user-defined origin.the following descriptions are the reported results for each simulation which are compiled in the result files; forces in Newtons, moments in Newton-meters and dimensions in meters. The North Design Suite is a right hand coordinate system, which also defines the sign of moments. 1. Fsurge[N], horizontal, along the center line, CL, of the yacht, positive aft (downstream). Surge Force 2. Fheave[N], vertical, positive upwards. Heave Force 3. Fsway[N], sideways horizontal, orthogonal to 1 and 2, positive downwind, which is also Sway Force For the moments this gives: 1. Roll Moment, positive to leeward. 2. Yaw Moment, positive turning "head-from-wind". 3. Pitch Moment, positive "bow-down". The Centre of Effort numbers are given as a distance from where the origin is situated in global coordinates with respect to heeled center plane of the yacht. The CoE_long[m] - CoE_trans[m] numbers refer to longitudinal and transverse (along the CL ) directions, while the CoE_vert[m] numbers references are vertical in world coordinates for all heel angles and along the path travelled by the yacht (leeway direction in our case = 0 degrees). Figure 18. Force and moment origin.!25

26 4. Discussion 4.1 Proposal for Future Contribution/Collaboration: Create a dll that utilizes this data as a foundation to generate similar data for various boats. Examine effect of gennaker aspect ratio, some sport boats have lower aspect sails. Investigate odd points identified in discussion section. Potentially different methods or trim could be used for FSI, which would result in different flying sail shapes and thus different coefficients. 4.2 Observations In Phase 2A, it is surprising to see the Cls drop off at AWA 65 for the TP52 Code 0. To confirm this observation, a few trims were re-run without much effect (main and gennaker twist trim variations plus and minus); this delta might be partially due to the fact that the TP52 sails at a lower AWS in this setting. Still, more time could be spent on this area as there might be more efficiency. This delta is illustrated in Figure 13a and Figure 13b, in which the luffs of both the TP52 and Swan 42 Code 0s are starting to luff, with the TP52 showing slightly more ease while also exhibiting signs of more separation in the upper section. Figure 19. TP52 AWA65 Flow Separation! 26

27 Figure 20. TP52 AWA65 Flow Separation Figure 14 shows a 10 meter section slice of the TP52 on the left and Swan 42 right. In this figure, the upper portion of the TP52 Code 0 is stalling, illustrated by the large area where the velocity is close to zero (indicated by the color blue), while the Swan 42 has significantly less separation. Figure 21. TP52 AWA65 Flow Separation In TWS 16 at AWA 35 the Code 0s for both the TP52 and Swan 42 needed to be depowered and substantial parts of the sails were luffing, thus resulting in a significant drop in the Cls; this looks to be real as the RM was well exceeded unless the sails were depowered. This luffing is illustrated in Figure 22, in which white areas indicate back pressure and the resulting luffing of the sails seen in the luff of the Code 0 and upper quarter of the mainsail. This back pressure results is a significant drop in the Cls and global sail efficiency.!27

28 Figure 22.. Backpressure Observed on TP52 at TWS16 at AWA Conclusion The addition of the Phase 2A data to the original results from Phase 1 provides a comprehensive set of data for forces and moments at apparent wind angles of 35 through 150 degrees. The use of FSI modeling coupled with Membrain provides information on the overall global forces and also the breakdown of forces between the various components, something that cannot be derived from wind tunnel tests. The Phase 2B results show that, while the actual forces and moments vary significantly with the sailplan configuration, the force coefficients are quite consistent assuming the trim is consistent. This does not take into account the effect of any depowering of the sails that might be required for a specific boat. The Downwind Aero Moment and Forces project is intended to provide a foundational dataset with which to improve the aero models currently used by handicap rules, designers, and researchers. Putting such a complete dataset in the public domain is unique as such information is often linked to proprietary and boat-specific efforts. Both SYRF and the North Sails team that carried out this effort welcome all feedback on the utility of the dataset and this project.!28