PhD ThesisThe main objective of the project is to investigate the influence of
surface roughness of marine propeller blades on propulsive power. The
work has involved studies in the concept and practice of surface
roughness measurement and characterisation as well as application of
boundary layer theory for the analysis
propeller-ship hull flow interaction
of propeller flow and propellar-ship hull flow interaction. From extensive measurements of the surface topography of in-service
propellers, a standard measurement procedure using different commercially
available propeller-surveying instruments is described.
A development of turbulent boundary layer procedures has been made to
determine sufficiently accurately the increment of drag coefficient of
propeller blade sections due to propeller blade surface roughness. The
roughness function used for this integral boundary layer analysis is
derived using, principally, Musker's experimental data.
In addition, an experimental determination of the roughness function
of a replicated propeller surface using a rotor apparatus has been
carried out and described in detail.
The turbulent boundary layer procedures require a knowledge of the
surface variation of pressure over the propeller blade. For this purpose
a program based on Riegels method has been used to give the velocity
distribution for a given propeller section geometry. This is used with
the boundary layer procedures for developing a complete program
"PROFNESS" to calculate the increment of drag coefficient of the blade
section. Results from different propellers analysed indicate that the
power penalty is proportional to the relative blade roughness to the 1/3
power.
An investigation has been made to compare the increment of frictional
coefficient for a flat plate and propeller section profiles. It is shown
that a "rough" flat plane calculation is quite adequate for such work.'
The use of a flat plate analogue as a reference to calculate the skin
friction resistance of both propeller and hull surfaces is considered.
It is shown that the proposed solution of flat plate momentum integral
equations provides a valid, simple and practical solution to the problem
of predicting the hull and propeller roughness drag penalties. It also
provides, particularly for ship hull resistance, a strong support for the
ITTC Correlation Line, not only, and importantly, in regard to its slope,
but also its level.
For shipowners and operators who may not wish to access advanced
computer programs, a simplified method has been proposed to calculate the
propeller roughness penalties. There is a good agreement between the two
simplified and detailed propeller analysis methods.
The propeller roughness penalties, which can be obtained from either
the simplified or the more rigorous method, can be related to the Rubert
Propeller Comparator Gauges in order to quantify the benefits and justify
the cost of the blade surface roughness.
Analytical procedures have been included which can be used to
calculate the combined effects on ship performance of propeller blade and
ship hull surface roughnesses.Egyptian Government:
1983/84 & 1984/85 ORS Awards from the Vice-Chancellors and Principals of
the Universities of the United Kingdom