Numerical and experimental investigation of submarine tail form

The paramount of scientific investigations on submarine hydrodynamics focus on the acoustics and efficiency of the propulsion systems. In order to determine the propulsion characteristics of a ship, it is very important to use both numerical and experimental methods collectively. Lack of experimental data on submarine hydrodynamics, lead DARPA (Defence Advanced Research Projects Agency) to start Suboff Project. Which enables researchers to validate their numerical and experimental studies on a generic submarine form. A number of different properties of DARPA Suboff form; including resistance, wake and maneuvering have been studied as a part of the Project. However propulsion characteristics of DARPA Suboff propelled by a generic submarine propeller model E1619, designed by INSEAN (Italian Ship Model Basin) has only been studied numerically and these studies seek experimental validation. One of the major factors which effect the propulsion characteristics of a submarine is the half tail cone angle at the stern part. There are limited references concerning the influence of the tail cone angle. In these references, thrust deduction and Taylor wake fraction and hull efficiency terms relate to submarine's tail cone angle and length to beam ratio. However, comparison between these references shows diversity especially on prediction of the hull efficiency. Within the scope of these differences and their contradiction, in this thesis it is decided to perform both experimental and numerical studies on DARPA Suboff generic submarine model's propulsion characteristics while she is propelled by E1619 propeller. Studies cover the validation of resistance and self propulsion results and numerical investigation of the effect of the tail cone angle and length to beam ratio. In order to experimentally investigate the submarine form, Turkey's first submarine self propulsion experimental setup is designed and manufactured. Moreover a precisely 5 axis manufactured model of E1619 propeller milled out of an aluminum block for the first time in Turkey. By using the designed experimental setup, resistance and self propulsion tests of DARPA Suboff and INSEAN E1619 were conducted in İTÜ Ata Nutku Ship Model Experimental Laboratory. Resistance tests were done for three different speeds and results show good agreement with the published experimental results. Propulsion tests were conducted by load varying self propulsion for constant speed and seven different propeller rotation rates. Rotational speed, thrust force and torque rates at self propulsion point were investigated. Self propulsion test results organized by thrust identity approach and Taylor wake, thrust deduction fraction and hull efficiency terms are obtained. Commercial CFD code, ANSYS Fluent 14.5 was used for the numerical computations. Steady computations have been made. The E1619 propeller has been placed in a Chimera block and the rotation of the propeller has been provided with the moving reference frame (MRF) option. The SST k-w turbulence model which is widely used in propeller analysis has been selected for the computations. A mesh independence study has been conducted for different mesh densities. Propeller open water characteristics and non-dimensional velocities behind the propeller have been obtained. The results have been compared with those from INSEAN and it is seen that a good accordance is obtained. The propeller open water characteristics and non-dimensional velocities behind the propeller have also been obtained for the scaled propeller geometry behind the submarine. The resistance characteristics for the fully appended AFF-8 configuration of the DARPA Suboff submarine model have been obtained by CFD for different speeds. The results have been compared with experimental results from open literature and results obtained from own experiments. It is seen that a good accordance is obtained for numerical results. To numerically obtain the self-propulsion point of the DARPA Suboff submarine model propelled with INSEAN E1619 propeller, analysis have been carried out for two different propeller loading, above and below the predicted self-propulsion point, in accordance with the load varying self propulsion test method. The intersection generated by the drawing of the thrust force and resistance values in accordance the propeller rate of revolution gave the self propulsion point of the submarine. Another analysis for the obtained rate of revolution was carried out and the propulsion characteristics such as the thrust deduction fraction, Taylor wake fraction and hull efficiency have been obtained by the thrust identity method. The numerical results obtained have been compared with the results obtained from the experiment and it is seen that especially the propeller rate of revolution and thrust force is predicted with very good agreement. After that the self-propulsion point has been obtained with good accordance, the generated geometries of the DARPA Suboff submarine model for different tail cone angles and length to beam ratios have been analysed and the propulsion characteristics have been calculated. In order to derive geometries with different tail cone angles the submarine tail form's mathematical formulation has been used. The coefficients in this formulation have been varied systematically in order to obtain different tail shapes for constant displacement. Within these generated geometries four meaningful forms were selected and the resistance and self propulsion characteristics were obtained numerically. The obtained thrust deduction coefficient, Taylor wake fraction and hull efficiency expressions were compared with results from open literature. Submarine geometries derived for different length to beam ratios were obtained by scaling the tail form of the submarine with a scale ratio and by adjusting the parallel midbody so as to keep the constant displacement condition. The resistance and self propulsion analysis have been made for the geometries derived for the original tail cone angle for different length to beam ratios. The self propulsion points have been obtained and the propulsion characteristics have been calculated and compared with those given in open literature. As a result in this study the self-propulsion experiments for the DARPA Suboff submarine model propelled with INSEAN E1619 propeller have been made, the self propulsion point and propulsion characteristics have been calculated and presented to the open literature. The effects of the tail cone angle on the propulsion characteristics have been investigated. And finally a guide for experimental and numerical submarine propulsion studies for the national submarine projects in Turkey is provided.