Experimental investigation of flow structures around a torpedo-like geometry placed in a boundary layer flow

Defense applications for both under oceans and seas, particularly underwater vehicles have been considered in this research. With this aim, flow characteristics around a torpedo-like geometry under the effect of the boundary layer flow over a smooth flat plate have been experimentally examined by using PIV technique. All of the experiments have been done for Re = 20000 and Re = 40000 based on the length (L) of the geometry as a characteristic length. As a result, time-averaged streamwise velocity components < u* >, velocity vectors < v >, streamline topologies < ψ > and Reynolds stress correlations < u'v'/U_∞² > in the wake region of the torpedo-like geometry have been acquired in the range of 0 ≤ G/D ≤ 1.5. Here, G is the space between the bottom point of the geometry and flat plate surface; D stands for the diameter of the geometry. It is found that at the smallest value of G/D = 0.25, jet-like flow occurs between the plate and the model which causes a powerful scouring. As the gap ratio is increased to G/D = 0.5 and G/D = 1.0, the jet-like flow diminishes slightly and then the flow structure in the wake region becomes similar to the uniform incoming flow condition for G/D = 1.50. Due to the effect of the jet-like flow and boundary layer flow, time-averaged flow patterns present asymmetrical distributions which are clearly shown a bigger size focus close to the plate in streamline topology. Reynolds stress patterns form more powerful viscous forces in the boundary layer flow due to the occurrence of eddy vortices and viscosity effect. It is observed from the aforementioned flow patterns that interaction between the flow structure, the model and boundary layer flow yields very complex structure. In order to decrease the energetic flow in this condition, passive or active flow control method can be integrated on the torpedo-like geometry.