A scaling procedure for modern propeller designs

Abstract

The extrapolation procedures currently used to scale propeller characteristics tested at model scale to their full scale performances are either based on a statistical [1], the Lerbs- Meyne [2] or the recently developed strip method [3].

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 pitch to diameter ratio as assumed by the strip method (and implicitly by the ITTC 1978 method [4]).

The work presented still uses the assumption of the equivalent profile and will explain a modified scaling procedure showing a way to calculate the hydrodynamic inflow angle solely from one open-water test conducted at a constant Reynolds number. Finally exemplary results comparing a propeller of conventional type with a recent propeller designs will also be shown.

The new proposed method shows a superior performance when compared to other scaling

methods.