• International Journal of Aeronautical and Space Sciences
• /
• v.16 no.4
• /
• pp.485-492
• /
• 2015

Small advance ratio and low Reynolds number of stratospheric propulsion system bring lots of challenges to the design of propellers. Contra-rotating propeller configuration is proposed to improve the propulsion efficiency. In this paper, the feasibility of contra-rotating propeller for stratospheric airship has been assessed and its performance has been investigated by wind tunnel tests. The experimental results indicate, at relatively low Reynolds number, although the advance ratio is fixed, the performance of propellers is different with variation of Reynolds number. Moreover, at the same Reynolds number, the efficiency of contra-rotating propeller achieved appears to be a few percent greater than that for a standard conventional propulsion system. It can be concluded that contra-rotating propellers would be an efficient means to improve the performance of stratospheric airship propulsion system.

• Journal of Ocean Engineering and Technology
• /
• v.14 no.2
• /
• pp.36-43
• /
• 2000

In this paper a Vortex Lattice Method is used to predict the performances of a contra-Rotating Propeller. Greeley and Kerwin's(1982) wake model is adopted instead of the exact trailing vortex geometry. The interaction of the two propellers is treated by the sense that the induction of one propeller upon the other propeller is averaged in the circumferential direction . Two single propellers (DTRC 4119 & DTRC 4842) are chosen and compared with the experimental and other numerical results published. Then the computational results for three CRP's (4-0-4 CRP(DTRC 3686+DTRC 3687A) 4-0-5 CRP(DTRC 3686+DTRC 3849) & DTRC CRT(DTRC 5067+DTRC 5068) are compared with the experimental and numerical results published. The interaction of both propellers by the change of inflow velocity and circulation of each propeller is investigated.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.1 no.1
• /
• pp.29-38
• /
• 2009

A ship's screw-propeller produces thrust by rotation and, at the same time, generates rotational flow behind the propeller. This rotational flow has no contribution to the generation of thrust, but instead produces energy loss. By recovering part of the lost energy in the rotational flow, therefore, it is possible to improve the propulsion efficiency. The contra-rotating propeller (CRP) system is the representing example of such devices. Unfortunately, however, neither a design method nor a full-scale performance prediction procedure for the CRP system has been well established yet. The authors have long performed studies on the CRP system, and some of the results from the authors' studies shall be presented and discussed.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.3
• /
• pp.595-609
• /
• 2015

The wake characteristics of Contra-Rotating Propeller (CRP) were investigated using numerical simulation and flow measurement. The numerical simulation was carried out with a commercial CFD code based on a Reynolds Averaged Navier-Stokes (RANS) equations solver, and the flow measurement was performed with Stereoscopic Particle Image Velocimetry (SPIV) system. The simulation results were validated through the comparison with the experiment results measured around the leading edge of rudder to investigate the effect of propeller operation under the conditions without propeller, with forward propeller alone, and with both forward and aft propellers. The evolution of CRP wake was analyzed through velocity and vorticity contours on three transverse planes and one longitudinal plane based on CFD results. The trajectories of propeller tip vortex core in the cases with and without aft propeller were also compared, and larger wake contraction with CRP was confirmed.

• Ocean Systems Engineering
• /
• v.7 no.4
• /
• pp.329-344
• /
• 2017

This paper introduces a BEM/RANS interactive scheme to predict the contra-rotating propeller (CRP) performance. In this scheme, the forward propeller and the aft propeller are handled by two separate BEM models while the interactions between them are achieved by coupling them with a RANS solver. By using the body force field and mass source field to represent the propeller in the RANS model, the number of RANS cells and the number of required RANS iterations reduce significantly. The method provides an efficient way to predict the effective wake, the steady/unsteady propeller forces, etc. The BEM/RANS interactive scheme is first applied to a CRP in both an axisymmetric manner and a non-axisymmetric manner. Results are shown in good agreement with the experimental data in moderate to high advance ratios. It is proved that the difference between the axisymmetric scheme and the non-axisymmetric scheme mainly comes from the non-axisymmetric bodies. It is also found that the error is larger at lower advance ratios. Possible explanations are given. Finally, some additional cases are tested which justifies that the non-axisymmetric BEM/RANS scheme is able to handle a podded CRP working at given inclination angles.

• Journal of the Society of Naval Architects of Korea
• /
• v.50 no.5
• /
• pp.282-290
• /
• 2013

The effects of the combination of blade number for forward and after propeller on the propeller shaft forces of a contra-rotating propeller (CRP) system are presented in the paper. The research is performed through the numerical simulations based on the Reynolds-Averaged Navier-Stokes equations (RANS). The simulation results of the present method in open water condition are validated comparing with the experimental data as well as the other numerical simulation results based on the potential method for 4-0-4 CRP (3686+3687A) and 4-0-5 CRP (3686+3849) of DTNSRDC. Two sets of CRP are designed and simulated to study the effect of the combination of blade number in behind-hull condition. One set consists of 3-blade and 4-blade, while the other is 4-blade and 4-blade. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. From the simulation results, the fluctuations of axial force and moment are dominant in the case of same blade numbers for forward and after propellers, whereas the fluctuations of horizontal and vertical forces and moments are very large in the case of different blade numbers.

• International Journal of Aeronautical and Space Sciences
• /
• v.16 no.4
• /
• pp.500-509
• /
• 2015

The numerical simulation of two-dimensional moving blade row interactions is conducted by CFD means to investigate the interactions between the front and rear propeller in a stratospheric airship contra-rotating open propeller configuration caused by different rotational speeds. The rotational speed is a main factor to affect the propeller Reynolds number which impact the aerodynamic performance of blade rows significantly. This effect works until the Reynolds number reaches a high enough value beyond which the coefficients become independent. Additionally, the interference on the blade row has been revealed by the investigation. The front blade row moves in the induced-velocity field generated by the rear blade row and the aerodynamic coefficients are influenced when the rear blade row has fast RPMs. The rear blade row moving behind the front one is affected directly by the wake and eddies generated by the front blade row. The aerodynamic coefficients reduce when the front blade row has slow RPMs while increase when the front blade row moves faster than itself. But overall, the interference on the front blade row due to the rear blade row is slight and the interference on the rear blade row due to the front blade row is much more significant.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.16 no.4
• /
• pp.248-254
• /
• 2013

Recently, contra-rotating propellers (CRP) having higher efficiency draw much attention since the EEDI regulation of IMO has been enforced. In this paper a numerical method based on the vortex lattice potential theory with a wake model and an experimental procedure with a newly built measuring device, specifically focusing on CRPs, are introduced. And they are applied to a series of CRP known to be designed for the purpose of improving EEDI. The numerical and experimental results showed good agreement explaining the characteristics of the CRP properly. The proposed method is believed to be effectively used for various CRP related studies.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.7
• /
• pp.391-398
• /
• 2020

If the lost energy produced by a propeller can be partially recovered, the propulsive efficiency can be increased, and the fuel consumption reduced. The devices installed for this purpose are called Energy Saving Devices, of which the Contra-Rotating Propeller system is one of the most effective devices. The first problem to be solved to install the Contra-Rotating Propeller system on a large ship is that the mean pressure generated in the journal bearing needs to meet the design criteria of the classifications. In Korea, however, the practical use is being delayed because it cannot overcome this step. The next step is to lower local pressure to increase the reliability. In this study, to solve the mean pressure problem as the first step of practical use, a product carrier with a short stern shape was selected to reduce the weight of the shafting system, and a suitable shafting-system design plan was proposed. Shaft analysis confirmed that the mean pressure of 0.8 MPa (8 bar), which is a design criterion of the classifications for a journal bearing lining material (white metal), was satisfied. In addition, the necessity of reducing the local pressure was also confirmed.

• Journal of the Society of Naval Architects of Korea
• /
• v.50 no.3
• /
• pp.153-159
• /
• 2013

The power transmission system has always been considered critical for a human powered boat(or water bike) since it first showed up at Human Powered Vessel Festival. Mechanical problems, such as abrasions and other damages of the gear system for the power transmission, lead to poor durability and low efficiency of a boat. This paper described mechanical problems and a design process of power transmission system and then suggested the method to solve the problems. It is selected a module and a type of gears that are structurally stable thus can transmit the power durable. Especially the lower gear box is applied to CRP(contra rotating propeller) system for improving the structural stability and the propeller efficiency as well. As the results, the upper and lower gear box are designed and manufactured. And from the trial test, it is confirmed that the power transmission system is reliable.