Advanced Search provides additional search options providing the ability to narrow your search by combining multiple search variables.
Note that by default, the Date Range set to 2017 will return all results from a text search. You can select both Date Range settings to narrow the returned results.
Location : Naval Academy Research Institute, France
Results 1 - 5 of 10
To Curl or Not to Curl: Wind Tunnel Investigations of Spinnaker Performance
This work presents a wind tunnel experimental study of the effect of curling on the spinnaker aerodynamic performance. Four spinnakers combining two different panellings and sail materials are tested at different wind speeds and wind angles in the Twisted Flow Wind Tunnel of the University of Auckland. Results show that the curling has a significant benefit on the propulsive force at an AWA ≥ 100◦ when this conclusion cannot be made at lower AWA where the best propulsive force is reached on the verge of curl- ing or before. Sail material and panelling have an effect on the sheet length where curling appears, stiffer material and cross cut panelling being the latest to curl. Finally, it is shown that the curling frequency increased linearly with the flow speed at AWA = 120◦.
Aerodynamics of a Highly Cambered Circular Arc Aerofoil: Experimental Investigations
While the aerodynamics of upwind sails are relatively well understood, flows past downwind sails are still very challenging. Indeed, downwind sails which can be considered as highly cambered thin wing profiles, are well known for their massive separations and complex wake flows. Therefore the aim of this study was to examine a very simple highly curved thin wing profile in order to elucidate features of real flow behaviours past such sails. Therefore, a two-dimensional thin circular arc has been investigated. The studied model had a camber of 21 - 22% comparable to downwind sails. The wind tunnel pressure measurements have enabled us to understand why the sudden transition in the lift force exists at low incidences but not at higher incidences. At low incidences the flow stagnates on the top face and a laminar boundary layer develops first. If the Reynolds number is too low, the laminar boundary layer is not able to transition to turbulent. This laminar boundary layer separates very early leading to low lift and high drag. However, when the Reynolds number is high enough, the boundary layer transitions to turbulent creating a laminar separation bubble. This more robust boundary layer can withstand the adverse pressure gradient and stay attached much longer, creating a sudden significant increase in lift and a drop in drag. At high incidences, a leading edge bubble forces the flow to transition to turbulent. Therefore, the boundary layer is fully turbulent irrespective of the Reynolds number and a unique flow regime exists at these high incidences.
Aerodynamics of a Highly Cambered Circular Arc Aerofoil: Experimental Investigations
While the aerodynamics of upwind sails are relatively well understood, flows past downwind sails are still very challenging. Indeed, downwind sails which can be considered as highly cambered thin wing profiles, are well known for their massive separations and complex wake flows. Therefore the aim of this study was to examine a very simple highly curved thin wing profile in order to elucidate features of real flow behaviours past such sails. Therefore, a two-dimensional thin circular arc has been investigated. The studied model had a camber of 21 - 22% comparable to downwind sails. The wind tunnel pressure measurements have enabled us to understand why the sudden transition in the lift force exists at low incidences but not at higher incidences. At low incidences the flow stagnates on the top face and a laminar boundary layer develops first. If the Reynolds number is too low, the laminar boundary layer is not able to transition to turbulent. This laminar boundary layer separates very early leading to low lift and high drag. However, when the Reynolds number is high enough, the boundary layer transitions to turbulent creating a laminar separation bubble. This more robust boundary layer can withstand the adverse pressure gradient and stay attached much longer, creating a sudden significant increase in lift and a drop in drag. At high incidences, a leading edge bubble forces the flow to transition to turbulent. Therefore, the boundary layer is fully turbulent irrespective of the Reynolds number and a unique flow regime exists at these high incidences.
Flexible Hydrofoil Optimization for the 35th America's Cup with Constrained Ego Method
We compare the optimized flexible hydrofoil with a rigid foil geometrically optimized for the same sailing conditions. This comparison highlights the hydrodynamical advantages brought by the flexibility: a reduction of the drag over a large range of boat speeds, less susceptibility to cavitation and a smaller angle of attack tuning range.
Experimental and numerical trimming optimizations for a mainsail in upwind conditions
This paper investigates the use of meta-models for optimizing sails trimming. A Gaussian process is used to robustly approximate the dependence of the performance with the trimming parameters to be optimized. The Gaussian process construction uses a limited number of performance observations at carefully selected trimming points, potentially enabling the optimization of complex sail systems with multiple trimming parameters. We test the optimization procedure on the (two parameters) trimming of a scaled IMOCA mainsail in upwind conditions. To assess the robustness of the Gaussian process approach, in particular its sensitivity to error and noise in the performance estimation, we contrast the direct optimization of the physical system with the optimization of its numerical model. For the physical system, the optimization procedure was fed with wind tunnel measurements, while the numerical modeling relied on a fully non-linear Fluid-Structure Interaction solver. The results show a correct agreement of the optimized trimming parameters for the physical and numerical models, despite the inherent errors in the numerical model and the measurement uncertainties. In addition, the number of performance estimations was found to be affordable and comparable in the two cases, demonstrating the effectiveness of the approach.