brian eiland
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Wind tunnel and CFD investigation of unconventional aftmast rigs
INTERESTING RESULTS
ABSTRACT
This paper presents research activities carried out by the authors to investigate aerodynamic behavior of several unconventional sailplans,... in comparison to the sloop traditional solution. In particular an 'A-shaped' mast placed in the stern area of the yacht has been considered in single-jib and double-jib configurations. Wind Tunnel tests and performance prediction analyses have been performed in order to compare different configurations.
...a most interesting solution, including major potential development, appears to be the one configured on an “A” shaped mast, placed in the stern area of the yacht. In this way, what was the mainsail is now transformed into another jib (in the double jibs configuration) or even completely removed (single jib configuration).
....Many attempts to reduce drawbacks of aerodynamic interference of the mast on sails, both in sloops and in multiple mast sailplans, have been made in the past. On the experimental yacht Amoco Procyon by O. Harken
.....
(BE note: They were apparently quite knowledgeable about the Procyon rig, and several others, but made no mention of my numerous postings on the subject of aftmast?)
So far the purpose of this research, conducted by a cooperation between Mechanics Department of Politecnico di Milano and IDEA Department of Facoltà di Architettura di Pescara, was to compare through wind-tunnel tests, a traditional sloop sail plan with a (similarly sized) “A” shaped stern mast sail plan, both in the single-jib and the double-jib configuration.
Two complete scaled models for both single rigged yacht and traditional sloop yacht have been built and tested in the Politecnico di Milano Twisted Flow Wind Tunnel.
The yacht model, consisting of yacht hull body (above the waterline) with deck, mast, rigging and sails, is mounted on a six component balance, which is fitted on the turntable of the wind tunnel. The turntable is automatically operated from the control room enabling a 360° range of headings. In order to correlate force measurement readings and the sail shape and in order to provide input data for CFD calculations, an in-house photogrammetric measuring system has been developed to recover flying shapes during tests.
The traditional sloop yacht rig used as a reference is a Comet 51’a Vallicelli Yacht Design & Co 51 feet IMS cruiser-racer sailing yacht, winner of 2007 IMS Italian Championship.
Wind tunnel tests were performed using a 1:10 scaled model of this yacht where a mainsail with the maximum IMS rule allowed roach and 100% non overlapping jib have been used.
Apparent wind angles were chosen to be 22°, 27°, 32° and 42° which cover the upwind range. Tests were conducted in upright condition. For each apparent wind angle tested the first task was to determine the maximum driving force potentially achievable At the same time the influence of the sails trimming changes was observed using the data acquisition program that visualizes the forces acting on yacht model in real time.
At the end, some runs were performed on the bare hull and rigging (without sails) for both yacht models at different apparent wind angles and in different heeling conditions in order to measure windage. These values are subtracted from each of the measured data points in order to produce the sail force coefficients.
From a pure aerodynamic point of view the relative performance of different rigs can be compared by comparing the driving force at similar apparent wind
angles and heeling moment. From these figures unconventional rigs seem to perform better than the standard sloop configuration.
As can be seen at closer AWA unconventional solutions are better than the standard sloop and in particular the two jib configuration with overlap seems to be able to produce higher driving force (at dynamic pressure =1) at the same heeling moment.
As can be seen unconventional configurations have aerodynamic centre of effort which are lower than the standard sloop and in particular the two jibs without overlap sailplan has the lowest values.
In order to gain further understanding of the sailplans aerodynamic behavior numerical simulations have been carried out using RANS method.
For each design scenario performance prediction have been carried out in 4-20 Knots true wind speed. Figure 24 shows a comparison in terms of optimal VMG in close hauled condition between standard sloop and
unconventional rig with reference to both single and double jib configurations. In particular figure 24 refers to full scale case with the same sails tested in the scaled model.
The results obtained confirm that the double jib configuration performance is better than the standard sloop up to 10 knots TWS, while the single jib
performance is pretty similar to sloop configuration. In windier conditions all the unconventional rig solution are faster and in particular the double jib with overlap gives the best performance.
CONCLUSIONS
In the present paper an unconventional rig has been investigated in comparison with a standard sloop rig by means of wind tunnel tests. The traditional sloop yacht rig used as a reference is a Comet 51’a Vallicelli Yacht Design & Co 51 feet IMS cruiser-racer. Several unconventional configurations have been tested, all characterised by an “A” shaped stern mast without mainsail in single-jib and double-jib configurations. Aerodynamic data available from experiments have been used to perform some performance prediction at full scale by means of a VPP code.
Both experimental tests and VPP calculation show that the double jib
configuration with overlap gives the best performance and also the same configuration without overlap gives better results in comparison with the standard sloop solution.
Numerical investigation have been carried out using RANS simulation in order to better understand the aerodynamic differences resulting from the experimental tests. Simulation results put in evidence a slat effect in the overlapping jibs configuration leading to more attached flow on the aft jib allowing for an higher pressure drop on the sailplan.
INTERESTING RESULTS
I'm going to summarize some of this paper here in case it should be taken down, or disappear from the web, as many things tend to do nowadays.
ABSTRACT
This paper presents research activities carried out by the authors to investigate aerodynamic behavior of several unconventional sailplans,... in comparison to the sloop traditional solution. In particular an 'A-shaped' mast placed in the stern area of the yacht has been considered in single-jib and double-jib configurations. Wind Tunnel tests and performance prediction analyses have been performed in order to compare different configurations.
...a most interesting solution, including major potential development, appears to be the one configured on an “A” shaped mast, placed in the stern area of the yacht. In this way, what was the mainsail is now transformed into another jib (in the double jibs configuration) or even completely removed (single jib configuration).
....Many attempts to reduce drawbacks of aerodynamic interference of the mast on sails, both in sloops and in multiple mast sailplans, have been made in the past. On the experimental yacht Amoco Procyon by O. Harken
.....
(BE note: They were apparently quite knowledgeable about the Procyon rig, and several others, but made no mention of my numerous postings on the subject of aftmast?)
So far the purpose of this research, conducted by a cooperation between Mechanics Department of Politecnico di Milano and IDEA Department of Facoltà di Architettura di Pescara, was to compare through wind-tunnel tests, a traditional sloop sail plan with a (similarly sized) “A” shaped stern mast sail plan, both in the single-jib and the double-jib configuration.
Two complete scaled models for both single rigged yacht and traditional sloop yacht have been built and tested in the Politecnico di Milano Twisted Flow Wind Tunnel.
The yacht model, consisting of yacht hull body (above the waterline) with deck, mast, rigging and sails, is mounted on a six component balance, which is fitted on the turntable of the wind tunnel. The turntable is automatically operated from the control room enabling a 360° range of headings. In order to correlate force measurement readings and the sail shape and in order to provide input data for CFD calculations, an in-house photogrammetric measuring system has been developed to recover flying shapes during tests.
The traditional sloop yacht rig used as a reference is a Comet 51’a Vallicelli Yacht Design & Co 51 feet IMS cruiser-racer sailing yacht, winner of 2007 IMS Italian Championship.
Wind tunnel tests were performed using a 1:10 scaled model of this yacht where a mainsail with the maximum IMS rule allowed roach and 100% non overlapping jib have been used.
Apparent wind angles were chosen to be 22°, 27°, 32° and 42° which cover the upwind range. Tests were conducted in upright condition. For each apparent wind angle tested the first task was to determine the maximum driving force potentially achievable At the same time the influence of the sails trimming changes was observed using the data acquisition program that visualizes the forces acting on yacht model in real time.
At the end, some runs were performed on the bare hull and rigging (without sails) for both yacht models at different apparent wind angles and in different heeling conditions in order to measure windage. These values are subtracted from each of the measured data points in order to produce the sail force coefficients.
From a pure aerodynamic point of view the relative performance of different rigs can be compared by comparing the driving force at similar apparent wind
angles and heeling moment. From these figures unconventional rigs seem to perform better than the standard sloop configuration.
As can be seen at closer AWA unconventional solutions are better than the standard sloop and in particular the two jib configuration with overlap seems to be able to produce higher driving force (at dynamic pressure =1) at the same heeling moment.
As can be seen unconventional configurations have aerodynamic centre of effort which are lower than the standard sloop and in particular the two jibs without overlap sailplan has the lowest values.
In order to gain further understanding of the sailplans aerodynamic behavior numerical simulations have been carried out using RANS method.
For each design scenario performance prediction have been carried out in 4-20 Knots true wind speed. Figure 24 shows a comparison in terms of optimal VMG in close hauled condition between standard sloop and
unconventional rig with reference to both single and double jib configurations. In particular figure 24 refers to full scale case with the same sails tested in the scaled model.
The results obtained confirm that the double jib configuration performance is better than the standard sloop up to 10 knots TWS, while the single jib
performance is pretty similar to sloop configuration. In windier conditions all the unconventional rig solution are faster and in particular the double jib with overlap gives the best performance.
CONCLUSIONS
In the present paper an unconventional rig has been investigated in comparison with a standard sloop rig by means of wind tunnel tests. The traditional sloop yacht rig used as a reference is a Comet 51’a Vallicelli Yacht Design & Co 51 feet IMS cruiser-racer. Several unconventional configurations have been tested, all characterised by an “A” shaped stern mast without mainsail in single-jib and double-jib configurations. Aerodynamic data available from experiments have been used to perform some performance prediction at full scale by means of a VPP code.
Both experimental tests and VPP calculation show that the double jib
configuration with overlap gives the best performance and also the same configuration without overlap gives better results in comparison with the standard sloop solution.
Numerical investigation have been carried out using RANS simulation in order to better understand the aerodynamic differences resulting from the experimental tests. Simulation results put in evidence a slat effect in the overlapping jibs configuration leading to more attached flow on the aft jib allowing for an higher pressure drop on the sailplan.
