A numerical investigation into the effect of the vertical tapered winglets on fully-submerged hydofoils

In this study, the effects of variations of the basic parameters of winglets, which have similar characteristics in each wing, on the efficiency of a wing underwater are examined. Computational Fluid Dynamics (CFD) was used to obtain the result. The executive equations of the CFD analyzes were used with the SIMPLE algorithm, which is a decompression method that gives a pressure rate-dependence for the continuous flow of a Reynolds-averaged Navier Stokes (RANS) based numerical study, and the SST k-ω turbulence model chosen for boundary layer flow analysis. In the study, a rectangular wing with a cross section of NACA0012, a section length of 1 meter and a side ratio of 6 was used. During the entire study, the attack angle of the main wing was kept constant at 5o and the Reynolds number at 6x106. The solution volumes created for the analyzes were created around the half-wing opening using the mirror principle. The performance of the new wing structures formed by attaching the selected blades NACA0006 onto the tip of the bare wing were compared with each other and with the bare wing for each parameter examined. The wings are generally regarded as simple wedges with a taper ratio of 0.3 as a simple basic geometry. A validation study has been conducted with the aim of checking the consistency and reliability of the CFD solution mesh and method used. The independence studies of the grids were carried out together with the validation studies and the final solution grid parameters selected for the 3D wing were preserved while the solution meshes of the wingleted wings were constructed. The winglet geometry parameters examined in this study are the ratio of the winglet root section length to the base wing section length, the ratio of the winglet span to the base wing section length, the direction of the winglet, and the angle of the winglet trailing edge. These parameters are symbolized as CCR, SCR, DW and β, respectively. Parameters such as the radius of junction and the cant angle are not investigated since the optimal values may vary in different basic wings and in different flow conditions. It was predicted that the effect of the examined winglets only on the induced speeds should not be attributed to the lift force of the whole wing itself and therefore the slope of the bladder was fixed at 0 °. Firstly, the CCR ratio was fixed upwards at a direction of 0.5 and at β 0o. The flapping wings examined are labeled W1, W2 and W3 respectively. As a result of analysis, the most efficient wing was determined as W1 with 6.19% CL / CD increase. The W1 wing also provided the highest value of 10.03 per cent as a CL increase between 3 wings. No decline was observed in CD values, but W3 was observed with a minimum increase of 2.41%. This shows that the winglets are not effective enough in reducing the induced drag force than the contributions to the profile drag force. W3 has the least surface area and gives the least value in CD increase. However, it has been found that the tip has the lowest value in yield increase since it is the most unsuccessful wing in terms of damping or deformation. Secondarily, the SCR parameter was examined at three different values of 0.5, 0.75, 1 and the other parameters were kept constant at the same value as the parameters of W1. Therefore, two new wingleted wing analyzes were performed and these wings were coded as W4 and W5, respectively, with SCR values 0.75 and 1, respectively. As a result of analysis, the most efficient wing was determined as W4 with 6.44% CL / CD increase. W4 wing increased 12.22% in CL and 5.42% in CD compared to wingless wing. The W5 wing achieved the highest CL increase by 13%, but at the same time it had the highest value of 7.23% in the CD increase, and performed a more unsuccessful performance than the W4 with a CL / CD value of 5.38%. In view of the results obtained, it has been observed that the liquefaction effect of the SCR ratio has a parabolic structure. Although the optimal SCR rate for this study was found to be 0.75, this value may vary in different wings and in different flow parameters. The next parameter, the direction of the fin direction, has been investigated in three different ways, up, down and on both sides in total. The other parameters are the same as W4 wing and the wingleted wings directed downwards and oriented to both sides are coded and analyzed and coded as W6 and W7 respectively. As a result of the analysis, the W6 was the wing which provided the least efficiency (CL / CD) increase among all wingleted wings examined. However, it has an important feature that it does not cause CD increase compared to the bare wing. This feature can be applied directly on the existing wing on a hydrofoil boat. In other cases, the other winglets will cause the wing to increase the overall resistance and slow down the vessel by producing extra drift while traveling at maximum speed where the vessel does not need more lifting force. W6 is predicted not to cause a loss in the course of maximum speed but also to decrease the speed of the vessel to go from the hullborne to the foilborne cruise because it will increase the wing efficiency, that is to say, it will produce more lifting force than the same drag force. In order to use the W4 advantage, a wing that is smaller in size and smaller in attack angle should be used, by removing the existing wing, producing the same drift value as the existing wing but producing more lift because the efficiency is higher. In this case, it is predicted that the speed needed to switch from hullborne to foilborne will decrease more than that of the W6. With a different wing design, it is predicted that by replacing the wing with a wing that has a winglet, it is possible to keep the coefficient of lift force constant and to increase the maximum speed of the craft by reducing the resistance. In other words, the advantage of W6 is the ability to increase boat efficiency with a lower investment cost, although it is less efficient than other winglets. The W7 wing provides greater lift than the W4 wing with a CL increase of 13.55% compared to the base wing. However, the CD also caused a further increase of 7.83% from the W4 wing. As a result of these values, it was observed that CL / CD ratio could be increased by 5.28% behind W4. Similar to the comparison of the W4 wing with the W5 wing, this results in a high profile drift force, which is caused by the large surface area, negatively affects the CL / CD ratio, although the W7 wing also damps the induced velocities more effectively. As a final parameter, the sweep angle β, 0o and 15o of the trailing edge are examined. In comparison with W4, the analysis of the winglet which has β = 15o coded as W8 and the same as the other parameters W4 has been carried out. As a result of the analysis, the increase of 11.93% CL, which the W8 wing provided in accordance with the bare wing, lagged behind the W4 wing. However, the exhibited 6.78% CL / CD increase is only 0.03% higher than the W4. When the distributions of the wake of these two wings and the distribution of pressure coefficients are examined, it is left open to debate whether the W8 wing has the advantage of having a lower risk of cavitation, but with a more distorted wake distribution and a more complex structure in terms of production.