A scaling procedure for modern propeller designs

The extrapolation procedures currently used to scale propeller characteristics tested at model scale to their full scale performances are commonly either based on a statistical, the Lerbs–Meyne or the recently developed strip method.With the emergence of so-called unconventional propellers and different design strategies associated with them, it has been questioned whether the assumptions used in these scaling methods are still universally valid. E.g. with tip and root unloading employed, the circulation distribution deviates from the optimum, which is assumed by the Lerbs–Meyne method; more modern profiles show a different camber distribution and hence the drag coefficient must be aligned with the hydrodynamic inflow angle and not with the geometric pitch as assumed by the strip method (and implicitly by the ITTC 1978 method).The work presented uses the assumption of the equivalent profile and will explain a modified scaling procedure showing how to calculate the hydrodynamic inflow angle solely from one open-water test conducted at a constant Reynolds number. Finally worked examples comparing a propeller of conventional type with a recent propeller design will also be shown.