Numerical investigation on the performance of ducted propeller

As a part of the important thing in ship design is propeller design. Propeller its self has many kinds of the design. This study investigates the effect on the performance of ducted propeller. The investigation was carried out by solving the Navier-Stokes equations with the Computational Fluid Dynamics (CFD) method. These simulations were compared in accordance SHUSKIN nozzle that has 3 types of design. Each type of thruster model indicates different force and torque. Thus, for the analysis will be generated by each model and it can be discovered that which model has the most optimal for the thrust. The analysis by using CFD indicates the change of fluid flow around the ducted propeller. The results showed that the nozzle on the propeller will give the extra of thrust for the performance of propeller.


Introduction
Many remote operated vehicle (ROV) have been developed for the maintenance and inspection of ocean structures. Most of them in practical use are self-propulsive with umbilical cable. To avoid the effects of noise force from the cable a free swim power would be ideal, but most are tethered, then the electrical power can be supplied and control signals and data obtained can be transmitted. A self-propulsive ROV can be guided to target more accurately than towed one. Consequently, a tethered self-propulsive which is usually used to inspect and maintain ocean structures [1]. In ship hydrodynamics, fixed propellers, also named screw propellers, have an important place among the propulsion systems to propel a ship. Propeller design is to obtain the optimum propeller which applies to minimum power requirements and against maximum efficiency conditions at an adequate revolution number. Usually two methods are used in the propeller design. The first is use diagrams obtained from the open water propeller experiments for systematic propeller series. The second is to use mathematical method (lifting line, lifting surface, vortex-lattice, boundary element method) based on circulation theory [2]. The characteristics of flow around propeller ducted with decelerating nozzle have been analysed [3]. Form from the previous research, the nozzle produces a decrease in the propulsive efficiency. Thus, the nozzle is important to use in propeller as ROV thruster.

ROV design
In this research, ROV project in Fig.1 has been designed [4] and the dimension is presented in Table 1.

Propeller design
The propeller dimension and geometry design are listed in Table 2.  Fig.2.

Nozzle design
For the calculation of nozzle, there are three types of nozzle as shown in the Fig.3 and the dimension is listed in the Table 3.

Outlet pressure Propeller
In this research to validate the result of the test model, used the software test result that already existed and was conducted [6]. Validation of underwater thruster is used to determine the exact boundary condition. ROV thruster using CFD-based software. Reference is taken from the validated model for the testing thruster. Used propeller type of Ka5-75 series and based on the theory of Wageningen [7]. The open water propeller characteristics conventionally were presented in form of the thrust and torque coefficient KT and KQ in term of the advanced coefficient J which is given as Eq.3, 4 and 5.

Meshing process
For this process, there were the same input of parameters and produced different results for the mesh size. Fig.5 is represented as sample of meshing of the models. All of the nozzle's meshing size as shown in the Table 4. 6 Result and discussion 6

.1 Streamline simulation
For the simulation of streamline, the input for all types were same. The rotational speed is 300 rpm. The results of streamline is presented in Fig.6.   Fig. 6. Streamline of model.

Pressure Contour simulation
This process was indicating the pressure distribution on the blade area. The results of pressure contour as shown in Fig.7.   Fig. 7. Pressure contour of model.

Discussion
From the analysis of CFD method, it can be seen on the Table 5. For the B-series and  Table 6. For Kaplan series. The changes of the force as clearly shown in Fig.8 and the change of the torque shown in Fig.9.   In this paper, we have described the specification and the design concepts of ducted propeller as the thruster of ROV. From 6 models, B-series (B5-75) and Kaplan-series (Ka5-75) with nozzle type A, B, and C. Based on the simulations which were conducted, can be concluded that the highest of force (T) was model Kaplan-series (Ka5-75) with type C of nozzle. The model could produce 2.53 N or 25.24% of extra thrust. The lowest of torque (Q) was model of B-series (B5-75) with type A of nozzle. Thus, the best model will be used for ROV thruster is model of Kaplan-series (Ka5-75) with type C of nozzle.

Conclusions
The present work described that the numerical investigation by CFD method has been demonstrated to be more effective as the problem solver for determining the ducted propeller performances. Nozzle can produce the extra thrust for the propeller and Kaplan series with type C nozzle is the best model for ROV thruster.