Experimental investigation of free-surface effects on flow characteristics of a torpedo-like geometry having a cambered nose

In this study, the free-surface effect in the wake region of a torpedo-like geometry having a cambered nose was investigated experimentally via Particle Image Velocimetry (PIV) and dye flow visualization methods. The Reynolds number was taken as Re = 2 × 104 and 4 × 104 while keeping the angle of attack (α =0°). The torpedo-like geometry is submerged at various positions from the free-surface in the range of 0.50 ≤ h/D ≤3.50 in which (h) is the distance from the water free-surface to the central plane of the geometry, and D is the diameter of the midsection of the torpedo-like geometry. The effect of the free-surface of water on the flow properties is also measured and presented comparatively in terms of normalized contours of instantaneous vorticity, time-averaged streamwise velocity, vorticity contours, Reynolds stress correlation, turbulent kinetic energy, velocity fluctuations in streamwise and cross-streamwise, vortex shedding frequency, spectral density distribution as well as pointwise variation. It is observed that the flow structures become asymmetric when the body is located near the free-surface for the submersion ratio of h/D ≤1.0. With the largest submersion ratio of h/D = 3.50, the flow characteristics are almost identical and symmetrical on both sides of the geometry. •A cambered nose of a torpedo-like geometry affects the flow separation and reattachment intensively.•Depending on the immersion ratio, the free-surface has a significant impact on the vortex shedding frequency due to surface wave deformation.•Spectral analysis of flow field using PIV data for free-surface flow condition was performed.•Asymmetrical chaotic flow structures occur in the wake due to the free-surface effect.•Asymmetrical wake distributions diminish when the submersion ratio increases beyond h/D ≥ 1.5.