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Effect of Conduits on Performance of Duct Propeller

Dec 26, 2023 | Technical Literature | 0 comments

1.Introduction

Since its introduction, the catheter thruster has been widely promotion and application.The most important feature of propellers is their high efficiency under heavy load, so they are especially suitable for trawlers in fishery production.At present, guided propellers are becoming more and more popular on trawlers in China.
Compared with ordinary propellers, it can increase the towing force by about 30% under trawling condition, and the speed is the same as that of ordinary propellers under free sailing condition. This makes this special propeller is more and more popular among fishermen.
Effect of Conduits on Performance of Duct Propeller
In the design of conduit paddles, Two types of conduits are used in the design of conduit propellers: the No.19A conduit representing the wing type profile and the JD 7744 conduit of Shanghai Jiao tong University, which represents the folded angle type.
Practice has proved that, as long as the main parameters of the conduit (such as conduit length to diameter ratio, shrinkage coefficient, diffusion coefficient, etc.) to choose the right, the shape of the profile on the efficiency of the conduit is very small.
Shandong Yantai area 136 kW steel trawler as an example, respectively, the use of these two catheter paddle, in different diameters, different design conditions, the efficiency is almost equal (see table l).
It can be seen that for the promotion of conduit paddle for the majority of medium and small trawlers, the simple conduit of folded angle type with simple processing and low cost has a broad future.However, with the change of production fishing ground, the requirement of gearsThe requirement of towing speed is getting higher and higher. This makes the main engine of the fishing vessel power, the power coefficient value of the propeller has a wide range of variations.The range of power coefficients for propellers is quite large, from BP = 30 to 160, and even larger in some cases.
Generally speaking, when the ship power coefficient B P value is greater than 25, catheter propellers begin to show its superiority, the higher the load, the greater the efficiency gains. However, it can not be expected that the type of conduit propeller can adapt to this large range of B P value.
Therefore, in order to give full play to the potential of conduit propellers and make them suitable for different trawlers, in the design of conduit propellers, it is important to choose certain types of conduit propellers carefully.
In this paper, the JD7704 catheter’s length-to-diameter ratio and shrinkage coefficient over a range of Expanded series of catheter modelling test results analysis , and It is proposed that The main parameter of conduit L/D ratio on the propeller performance of conduit performance of conduit propellers with the main parameter of conduit length-diameter ratio for designers’ The results were analysed and presented.
Effect of Conduits on Performance of Duct Propeller

2.Introduction of catheter parameters

The main parameters of the catheter, as an example, are shown in Fig. 1.The geometrical characteristics of the catheter can be expressed by the following parameters:
a. Working area of the catheter

D is the propeller diameter
Δ is the gap between the tip of the blade and the inner wall of the duct.

b. Axial length of conduit L = Le+ La
where Le is the length of the inlet section and La is the length of the outlet section.

c. Shrinkage coefficient of the conduit

Fe is the cross-sectional area at the inlet of the conduit.

d. Diffusion coefficient of the catheter

Fa is the cross-sectional area of the conduit outlet
e. Length-to-diameter ratio of the conduit
                                    

Table 2 lists a group of conduits with altered L/D ratios using JD7704 conduit as the parent model. Based on the results of open water tests of these conduits and Ka4-70 series propeller open water test results and data can be collated to understand the effect of changes in the parameters of the conduit L/D ratio on the performance of the conduit.

3.Influence of length-to-diameter ratio on conduit paddle performance

JD7801, JD7704 and JD7805 are a group of ducts with identical profile shapes and L/D ratios of 0.5, 0.655 and 0.8, respectively. Figure 2 shows their best-case efficiency comparison curves.
As can be seen from the graph, except for the light load case of, it is the longer conduit that appears to have the efficiency advantage.
On average, the JD7805 is about 2% more efficient than the JD7704, and the JD7704 is about 2% more efficient than the JD7801, but for light loads, the shorter conduits are more efficient. In terms of mooring performance. Longer conduits are also slightly better than shorter ones.
If the mooring efficiency coefficient is used as a basis for comparison:
where KT is the thrust coefficient. KQ is the torque coefficient. The physical concept is to express the thrust per unit of horsepower for a disc load.
Figure 3 shows that both forward and reverse. The coefficient of mooring efficiency increases with the increase of the length-to-diameter ratio of the conduit.
increases with an increase in the length-to-diameter ratio of the conduit. Take the paddle with pitch ratio P/D = 1.0 as an example. When the L/D ratio is increased from 0.5 to 0.8, the  increases by about 6%.

Effect of Conduits on Performance of Duct Propeller
Effect of Conduits on Performance of Duct Propeller
Effect of Conduits on Performance of Duct Propeller

Theoretically, the improvement of the efficiency of the catheter propeller is to make the catheter share as much as possible in the total thrust. This means that part of the propeller’s wake vortex becomes the duct’s attached vortex, thus reducing the energy loss in the propeller wake. There are two ways to do this, one is to increase the arch and diffusion coefficient of the duct profile; the other is to increase the length of the duct. But because the diffusion coefficient increases too much will cause the trailing edge of the flow separation. And increase the length-to-diameter ratio does not have this problem. Therefore, only by increasing the length of the conduit to obtain a larger conduit thrust.
However, things are always two sides of the same coin, because the resistance of the conduit itself is increased with the increase of scale, therefore, long conduit is only desirable at low speed and heavy load. When the speed increases, the resistance of the conduit increases rapidly, which is not worth while.In this case, the shorter conduit should be taken.

The following is an example of a steel trawler in southern Fujian Province.The main engine is a Cummins KTA-1 150 1M. The main engine is a Cummins KTA-1150-M. Continuous power 507 Horsepower . Main engine speed 180 rpm. Gearbox speed double i = 7.5 4: 1 , conduit paddles with limited diameter D =2m , and Designed as a compromise

Effect of Conduits on Performance of Duct Propeller

4.Some conclusions

     4.1
Catheter propeller is a kind of propulsion device for trawler with excellent performance.
For general shipyards, in order to facilitate the manufacture and maintenance, it is possible to choose the folding line type simple conduit.

     4.2
The main parameters of the conduit have a great influence on the performance of the conduit paddle. In general, preference is given to paddles with small L/D ratio for light loads and large L/D ratio for heavy loads. If the power coefficient Bp indicates.

Effect of Conduits on Performance of Duct Propeller
     4.3
As a trawler is a multitasking vessel, it requires both high free speed and high trawl drag. This contradiction is obviously difficult for a certain length-to-diameter ratio of the conduit propeller to be the best of both worlds. This is to judge the trawler’s specific type of operation, time and operation of the fishing ground and the conditions of the vessel itself to determine the parameters of the conduit carefully. Reasonable selection of the form of conduit propeller will certainly get satisfactory results.

5.something you may need

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