On the form factor scale effect

Four geosim families, with fully available resistance test results, have been re-analyzed to check the possible scale effect on the form factor. The form factor determined by Prohaska's method, with exponent n = 4 and ITTC'57 correlation line, increases with the model size in all four cases analyzed. Because of its high correlation coefficient, a linear variation of the form factor with the scale is assumed. It is possible to have a first estimation of the ship's form factor extrapolating for lambda = 1 in the regression line. Form factor Reynolds number dependency will always be associated with a friction line. Using the ITTC'57 correlation line, the following equation K-S - K-M = 1.91 . (lambda - 1) . 10(-3) can be used to estimate the scale effect on the form factor. Calculations carried out, for axisymetric bodies, with some CFD codes are in good agreement with the experimental findings. (C) 1999 Elsevier Science Ltd. All rights reserved.