Experimental investigation of flow characteristics over a surface-modified structured torpedo model

Abstract

The present work aims to improve the aerodynamic performance of navigating objects using bio-inspired surface modification. Inspired by the denticles present over sharkskin, this work investigates the study of a surface-modified structured torpedo model. Different modified surface structures (riblets) are used to study their effect on the drag and flow characteristics. The modified structure placed in the shear layer modifies the flow above as well as behind the torpedo. A detailed flow field is studied using PIV (Particle Image Velocimetry) and CTA (Constant Temperature Anemometry) over the torpedo model. The experiments are performed in a subsonic wind tunnel for the Reynolds numbers (Re) range of 1.02–5.08 × 105, thus covering the laminar-turbulent transition range. The study reveals that riblets structure enhances the momentum flux, thus enabling the surface to reduce drag by suppressing the vorticity generation and reducing the turbulent dissipation. Different turbulent and wake characteristics are measured in the work. The velocity and fluctuation analysis shows the variation in wake width and wake velocity for different cases. The result showed that riblet effectively reduces drag coefficient by 11.7% using an optimal structure. The maximum reduction in formation length of 4.76% is observed at Re 3.05 × 105. The decrease in the formation length reduces the adverse pressure gradient zone and decreases the power requirement. The wake half-width at the 2D downstream location in the streamwise direction shows a reduction of 9% for the drag-reducing case at Re 3.05 × 105. The vorticity reduction is observed in the wake zone of drag-reducing riblets and suggests less dissipation of the eddy. The results show the perspective to improve the current research status by using riblet surface for marine application. The study could effectively reduce drag, thus improving the operating performance by reducing the energy consumption and increasing the speed of the navigating vessel.