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Author : J.B. Braun
Results 1 - 3 of 3
High Fidelity CFD Simulations in Racing Yacht Aerodynamic Analysis
Advances in hybrid approaches comprising advanced mesh generation techniques, Navier-Stokes solver technology, and structural dynamic modeling of membranes, have enabled sail designers and research aerodynamicists to implement high fidelity aerodynamic and fluid-structure interaction (FSI) simulation models of yacht and sail aerodynamics. This paper will describe recent trends in aerodynamic CFD analysis of racing yachts where the simulations are extended to include other geometry interacting with the sail such as the hull, mast and boom for example. The aerodynamic interaction effects between the various components will be presented and discussed through relevant examples.
Measurement and Simulation of Pressure Distribution on Full Size Sails
Technological advances in wireless networking equipment and atmospheric pressure sensors have enabled the measurement of the pressure distribution across full size sails in normal operation. The pressure measurements may be generated separately on the windward and leeward sides, and on other parts of the rig. Pressure maps of the entire sail can be produced in real-time to provide a detailed time-dependent picture of the pressure distribution, showing the fluctuations and deviations from nominal values due to any changes of the rig, boat motion, or wind. This information is useful in the design process, where sail designers and research aerodynamicists can quantify real-world, full-scale measured differences against computer simulations or alternative sail shapes. It also can be used by sail trimmers to set the best sail shape rapidly and in changing conditions. The pressure sensors are small and lightweight, allowing them to be applied in high density across the entire sail. Laptop software collects and analyses the data, displaying the pressure values and logging the data for post-analysis. This paper provides a descr. of the technologies used to implement the wireless pressure measurement system, presents examples of the data obtained, and compares the measured results with CFD simulations.
In recent years computational fluid dynamics (CFD) has demonstrated the ability to predict sail and appendage forces under upwind conditions or at angles of attack conducive to attached flow. Few sail or yacht designers would be without this tool, at least to check or confirm performance estimates made with other methods. More advanced codes (RANS) solve the full Navier-Stokes equations, thus including viscous effects and placing relatively less importance to fully attached flow. Due to the large proportion of downwind sailing, where the sails might operate in separated airflow, it is useful to evaluate the performance of sails as used off wind despite the added uncertainty resulting from the elasticity of the light material that must be used to allow the sails to fill properly at the low relative wind speeds. While downwind sail forces have been often tested in wind tunnels, CFD codes are now sufficiently advanced to predict such forces with confidence similar to that achieved in prediction of upwind forces. This paper presents a new method of linking a CPD code with a Finite Element Analysis (PEA) computer program, for evaluating the sail shapes and proper trim for known sail materials and fiber orientation. A VPP (Velocity Prediction Program) is used to predict leeway, heel, and boat speed for a given true wind angle and wind speed. Then the CPD code computes the airflow around the sails for the given onset flow conditions and provides the pressure distribution on the sails as needed for the PEA program. This is done in full scale considering the boundary layer above the water. This process of updating the pressure for the PEA program from the CPD code is repeated several times until optimal trim and sail shapes can be obtained for best sailing performance, e.g., the maximum driving force. Thus, this method can be considered a "Virtual Wind Tunnel" (VWT).
