where CL is the fin lift coefficient, CD is the fin drag coefficient, AR is the fin planform area, and ve is the effective fin velocity. The values of lift coefficient CL and drag coefficient CD are related with effective fin angle of attack a .
We can adopt experiment, theroy computation, or empirical fomular to get CL and CD . Experiment and empirical fomular method will be introduced below.
A series of data of angles of attack a vs. lift coefficient CL and drag coefficient CD can be obtained from hydrodynamic experiment, and then fitted curves of CL and CD can be generated through least squares fit. For example, the fitted currves of a fin is shown in Fig.3. When we know the current angle of attack of fin on the AUV, the values of CL and CD under this angle can be obtained by curves interpolation.
2. Method of empirical equation
The empirical equations to calculate CL and CD are given by
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