Avia Propeller (Czechia)

When considering the propulsion performance of a ship, one of the most important factors is the propeller design. Generally, it has been known that propulsion efficiency is greater if a propeller has a larger diameter and low propeller shaft speed. However, it is equally important to maintain sufficient distance between the hull and the propeller, known as ‘propeller clearance’, to mitigate fluctuation pressure and the potential for inducing severe hull vibrations. Therefore, propeller designers must consider the propeller clearance while sizing a propeller. KITANIHON SHIPBUILDING CO., LTD is producing 27 chemical tankers of 19,950DWT, using three kinds of propellers with different propeller diameters. Each kind of propeller is similar in geometry except for the diameter. The sea trial results will demonstrate how the propeller diameter affects the ship’s performance. The wave conditions were not ideal during the sea trials, hence the investigation on the performance of propellers requires highly accurate hydrographic data. The authors have analyzed the sea trial data using values from ‘wave hindcast database’ which is reanalyzed historical database from the Japan Weather Association (referred to as JWA) and the authors examined the influence of propeller diameters on performance.

The influences of film thickness of vinyl and silicone resin coatings on cavitation erosion were examined quantitatively in seawater using a vibratory apparatus. The maximum instantaneous volume loss rate indicates the increase, decrease, or constant with a decreased top coat thickness less than the critical thickness, depending on the combination of the top coat and primer of the acoustic impedance. The critical thickness can be calculated approximately from the duration of impulsive force and propagation velocity of a longitudinal wave created by the collapse of a cavitation bubble, when covered with a resin coating material.

Knowledge of propeller or rotor blade behaviour under real operating conditions is crucial for optimizing the performance of a propeller or rotor system. A team of researchers, technicians and engineers from Avia Propeller, DLR, EVEKTOR and HARDsoft developed a rotating stereo camera system dedicated to in-flight blade deformation measurements. The whole system, co-rotating with the propeller at its full speed and hence exposed to high centrifugal forces and strong vibration, had been successfully tested on an EVEKTOR VUT 100 COBRA aeroplane in Kunovice (CZ) within the project AIM2—advanced in-flight measurement techniques funded by the European Commission (contract no. 266107). This paper will describe the work, starting from drawing the first sketch of the system up to performing the successful flight test. Apart from a description of the measurement hardware and the applied IPCT method, the paper will give some impressions of the flight test activities and discuss the results obtained from the measurements.

In this study, the authors conducted mechanical property tests and the vibration characteristic tests of CFRP (carbon fiber reinforced plastics) specimens that can be adopted as new marine propeller materials. CFRP materials exhibited higher strength than NAB (nickel aluminum bronze casting) which is conventionally used as material for marine propellers. The damping ratio of CFRP materials was four times larger or more than that of NAB. In field tests using a small fishing boat, two types of CFRP propellers were manufactured by using CF-prepreg. One propeller was laminated with CF-Fabric and another with CF-UD, to obtain a quasi-isotropic composite. These are the so-called "built-up type" as three CFRP blades were assembled in an NAB boss. An NAB propeller of the so-called "mono-block type" was also manufactured to facilitate comparison with CFRP propellers. Analyses of field test results are ongoing. In vibration tests, the damping ratios of the both types of CFRP propellers were about ten times larger than that of the NAB propeller. Cavitation which can cause erosion on the surface is a severe problem for FRP propellers. Therefore, we cavitation erosion resistances for eight kinds of FRP and an NAB were evaluated in cavitation tests using a magnetostriction ultrasonic transducer. The cavitation erosion resistance of the NAB was much superior to that of FRP materials. However, it was found that aramid fibers on the surface of FRP can improve the erosion resistance. In order to improve the erosion resistance of FRP materials to the same level as that of NAB, the further research is necessary.

A new surface modification for bio-titanium alloy products by electron beam (EB) polishing is proposed. In this EB polishing method, high energy density EB can be irradiated without concentrating the beam. Therefore, large-area EB with a maximum diameter of 60mm can be used for instantaneously melting or evaporating metal surface. Experimental results made it clear that surface characteristics, such as repellency, corrosion resistance and coefficient of friction could be improved simultaneously with the surface smoothing in a few minutes under a proper condition. Therefore, EB polishing method has a possibility of high efficient surface smoothing and surface modification process for bio-titanium alloy.

Apatite-polymer hybrids are expected as novel bone substitutes exhibiting bone-bonding ability and mechanical performances analogous to those of natural bone. In this study, we attempted preparation of organic-inorganic hybrids from different pectins such as pectic acid, apple-derived pectin and citrus-derived pectin through apatite deposition in simulated body fluid (SBF). Pectin gels were prepared by CaCl2 treatment of aqueous solutions of pectin. Apatite-forming ability of the gels was examined in SBF. The citrus-derived pectin showed tendency to form the largest amount of the apatite in SBF.

A new surface modification for bio-titanium alloy products by EB polishing is proposed. In this EB polishing method, high energy density EB can be irradiated without concentrating the beam. Therefore, large-area EB with a maximum diameter of 60mm can be used for instantaneous melting or evaporating metal surface. Experimental results made it clear that surface characteristics, such as repellency, corrosion resistance and coefficient of friction could be improved simultaneously with the surface smoothing in a few minutes under a proper condition. Therefore, EB polishing method has a possibility of high efficient surface smoothing and surface modification process for bio-titanium alloy.

Generally, the propeller is applied with an anti-singing trailing edge for the prevention of irregular noise resulted from Karman vortices generated from the trailing edge of the propeller. It is well known that the anti-singing trailing edge exercises a greater effect on propeller open characteristics (POC in short) and propeller shaft speed, the effect of which is to be taken into account when propeller pitch is decided accordingly. On the other hand, in the propeller open test (POT in short), the finished accuracy of the trailing and leading edges greatly influences test results; however, it is difficult to attain higher accuracy on the very thin trailing edges of the propeller model. As a result, the effect of the anti-singing trailing edge is studied experientially in spite of a greater effect of the anti-singing trailing edge upon the POC. With this research based on the POT using 400 mm diameter model propellers in the two different conditions, without (case-A) and with (case-BJ the application of anti-singing trailing edge, the POC prediction was made through several calculations by means of potential flow theory (lifting surface, source and quasi-continuous vortex lattice method (SQCM in short), surface panel method) and generally applicable CFD. Although the calculation results by the potential flow theory overestimated the values of differences of thrust and torque between case-A and case-B respectively, the CFD calculation result showed a closer agreement with the POT results. Finally, a reasonable agreement was verified between the CFD calculation result and the sea trial results with the full-scale vessel.